CN113003845B

CN113003845B - Zero-emission treatment process and system for sewage with high sulfate content and high COD (chemical oxygen demand)

Info

Publication number: CN113003845B
Application number: CN201911319842.2A
Authority: CN
Inventors: 李家亮; 边立军; 庄鲁维; 王星; 李�瑞
Original assignee: Shandong Xiangshuo Chemical Co ltd; Shandong University of Technology
Current assignee: Shandong Ruixiangyuan Environmental Technology Co ltd
Priority date: 2019-12-19
Filing date: 2019-12-19
Publication date: 2022-12-20
Anticipated expiration: 2039-12-19
Also published as: CN113003845A

Abstract

Discloses a zero discharge treatment method and a system for sewage with high sulfate content and high COD value. The method comprises (1) biological desulfurization: performing biological desulfurization on raw sewage through biological reduction reaction under anaerobic conditions by using sulfate reducing bacteria in a biological desulfurization tank, and (B) performing biochemical treatment on the sewage; (C) separating to obtain purified sewage; and (D) electrochemical impurity removal: the purified sewage is electrochemically treated in an electrochemical treatment tank by applying a direct current voltage between a combined anode comprising a sacrificial anode and an inert anode and a cathode to remove ammonia nitrogen impurities, inorganic salts and COD, thereby further purifying the purified sewage. The method further comprises the following steps: (E) Chemical softening, (F) filtration and separation, (G) reverse osmosis, and (H) nanofiltration of salts. The above method enables economical removal of sulfate and sufficient removal of fluorine and silicon in sewage.

Description

Zero-emission treatment process and system for sewage with high sulfate content and high COD (chemical oxygen demand)

Technical Field

The invention relates to a zero-emission treatment process and a zero-emission treatment system for sewage containing fluorine and silicon and having high sulfate content and high COD value in the fields of coal chemical industry, mining and mineral separation, fluorine chemical industry, metallurgy, pharmacy, petrochemical industry and the like.

Background

The sewage with high salt content and high COD value in the fields of coal chemical industry, mining and mineral processing, fluorine chemical industry, metallurgy, pharmacy, petrochemical industry and the like is very difficult to treat. In particular, high salt content, high COD value sewage in the coal chemical industry, mining and beneficiation, and fluorine chemical industry fields is more difficult to treat because of the complex pollutant components (metal ions, heavy metals, and refractory organics) because such sewage contains fluorine, silicon, heavy metals, and refractory organics.

CN108545892A discloses a treatment system and a treatment method for wastewater from coal-to-ethylene glycol production, and CN108726807A discloses a system integration technology for treating wastewater from high concentration sodium nitrate in coal-to-ethylene glycol production. However, the sewage treatment techniques disclosed in both of these patent applications ignore fluorine, silicon, heavy metals contained in coal carbonization industrial sewage; meanwhile, it has not been noticed that when the sewage purified by the previous process contains calcium and magnesium ions at high concentrations, the subsequent treatment effect is also seriously affected.

CN105036476A discloses a method for treating electroplating sewage, which comprises electrochemical treatment and microbial treatment, wherein the electrochemical treatment uses waste iron as an anode and sodium chloride solution as an electrolyte.

CN102910708A discloses an electrochemical combined anode treatment method for industrial wastewater, wherein an iron plate cathode is adopted, and a combined anode consisting of a soluble iron plate anode and an insoluble titanium plate anode is adopted. Proper amount of NaCl is respectively added into the wastewater medium in the electrochemical treatment tank to serve as electrolyte to improve the conductivity and keep the conductivity of the wastewater medium to be more than or equal to 800 mu s/cm. The method uses an electrochemical method to generate strong oxidizing free radicals (. OH) and does not use a biochemical treatment method to treat wastewater.

Chinese utility model CN208829463U (application No. CN 201821161544.6) discloses a high oil content organic wastewater treatment device, in which only a small amount of sodium chloride and activated carbon powder need to be added into the micro-electrolysis system to improve the conductivity during the system operation, thus saving electricity and greatly reducing the cost of the medicament.

CN106007176A discloses a high-temperature, high-hardness, high-COD, ammonia-nitrogen sewage treatment system and process, the system includes a hardness-removing device, an air flotation tank, a water cooling tower, a secondary sedimentation tank, etc.

CN106517634A 20170322 is a method for treating wastewater with high salt content, high COD content and high solvent content, which comprises the following steps: 1) Carrying out organic solvent extraction on the wastewater with high salt content, high COD content and high organic solvent content; 2) Carrying out micro-electrolysis reaction on the water body obtained in the step 1; 3) Performing flocculation precipitation on the water body obtained in the step 2; 4) Performing Fenton reaction on the supernatant obtained in the step 3); 5) Flocculating and precipitating the water body obtained in the step 4); 6) Carrying out anaerobic treatment on the supernatant obtained in the step 5); 7) Carrying out aerobic treatment on the water body obtained in the step 6).

Raw (raw) sewage (W) with high salt content and high COD value from industrial fields of coal chemical industry, mining and mineral processing, fluorine chemical industry, metallurgy, pharmacy, petrochemical industry and the like ₀ ) All need to be purified before being discharged or recycled.

In the enterprises in the industrial fields (such as coal chemical industry), pollutants such as COD, ammonia nitrogen, total phosphorus, suspended matters and the like in all sewage in a factory area of a production enterprise are mainly and intensively treated by a factory area sewage treatment station (WT), and inorganic salts, trace pollutants (COD, ammonia nitrogen, total phosphorus, suspended matters) and the like in various waste water streams such as sewage (circulating water up to the standard), circulating water system drainage, boiler system drainage, water purification station drainage and the like after the sewage is treated up to the standard are and intensively treated by a factory area reuse water station (WR).

The sewage received by the sewage treatment station mainly comprises factory sewage pipe network sewage (mixed sewage W) ₀₃ ) Rainwater pipe network earlier stage rainwater and sludge plate-and-frame filter press drainage (W) ₀₄ ) Low concentration sewage (W) in workshop ₀₂ ) High concentration sewage (W) in workshop ₀₁ ) The sewage is collected in a regulating tank to form raw sewage (W) ₀ ). Sewage of a sewage pipe network (mixed sewage) mainly comprises domestic cleaning water in workshops, offices, dormitories, dining halls and the like; the low-concentration sewage of the workshop mainly refers to sewage with lower pollutant concentration and more stable discharge index, wherein the pollutant index COD of the main index is less than 5000mg/L, and B/C is more than 0.3; the high-concentration sewage mainly refers to higher pollution concentration and dischargeThe standard is unstable sewage, wherein the COD index of main pollutants is more than 5000mg/L, and the water volume of the waste water is usually smaller.

The water received by the reuse water treatment station mainly comprises standard discharge water of the sewage treatment station and clean drainage (RW) of a circulating water system ₀₁ ) Boiler system drain (RW) ₀₂ ) And water purification station drainage (RW) ₀₃ ). The effluent standard of the sewage treatment station is required to reach above first-level A discharge standard in GB 18918-2002, the water discharge of a circulating water system is mainly quantitative water discharge generated by the enrichment of pollutants in the system after the loss of evaporated water of the circulating water system is avoided, the boiler water discharge is mainly quantitative water discharge generated by the enrichment of pollutants in the system after the loss of evaporated water of a boiler water system, and the water discharge of a water purification station is mainly salt-containing concentrated water generated by a multistage membrane concentration process when desalted water is produced by a water purification station of a plant area.

However, for the sewage with high salt content and high COD value in the fields of coal chemical industry, mining and mineral separation, fluorine chemical industry, pharmacy, petrochemical industry and the like, especially for the sewage with high salt content (especially fluorine-containing and silicon-containing) and high COD value in the fields of coal chemical industry, mining and mineral separation and fluorine chemical industry, the treatment method in the prior art cannot achieve ideal purification effect, and the treatment cost is too high.

Disclosure of Invention

Raw (raw) sewage (W) with high salt content (too high sulfate content) and high COD value from industrial fields of coal chemical industry, mining and mineral processing, fluorine chemical industry, metallurgy, pharmacy, petrochemical industry and the like ₀ ) In particular raw (raw) sewage (W) with high sulphate content and high COD value, from the fields of coal chemistry, mining and beneficiation, fluorine chemistry and metallurgical industry ₀ ) Typically contain complex contaminant components and are often collected in catchments and conditioning ponds in the plant area.

Such sewage (W) to be treated in a conditioning tank ₀ ) Not only contains Ca ²⁺ And Mg ²⁺ Also containing heavy metal cations, e.g. Fe ³⁺ ，Fe ²⁺ ，Cu ²⁺ ，Ni ²⁺ ,Cd ²⁺ ,Zn ²⁺ ,Hg ⁺ ,Hg ²⁺ ，Cr ³⁺ ,Pb ²⁺ ,Mn ²⁺ And so on. In addition, such effluents often contain refractory aromatic organic compounds and organic polymers (COD), and may also contain ammonia-nitrogen-type impurities (e.g., NH) ₄ ⁺ ). In addition, such effluents may also contain arsenic (arsenate AsO) ₄ ^3- Arsenite radical AsO ₃ ^3- ) And, such effluents may also contain TP total phosphorus (e.g., PO) ₄ ^3- Or organophosphorus) (total P content)>0.5 ppm). In addition, such effluents may also contain F ^- (content thereof)>1ppm)，SO ₄ ^2- ，S ^2- (content thereof)>1ppm)，SiO ₄ ^4- ,SiO ₃ ^2- ，PO ₄ ^3- ，CO ₃ ^2- ，HCO ₃ ^- And (4) plasma.

In the present application, a 1ppm content or concentration =1mg/L content or concentration.

In general, such raw sewage (W) is treated in the process of the invention ₀ ) In (SO) ₄ ^2- In an amount of 2000-50000ppm (mg/L), preferably 2500-35000ppm, such as 3000 or 4000 or 5000 or 10000 or 20000ppm; in addition, the Chemical Oxygen Demand (COD) is generally greater than or equal to 1000mg/L, even greater than or equal to 4000mg/L, for example from 1g/L to 10g/L; total hardness of calcium and magnesium (Ca) ²⁺ +Mg ²⁺ ) Typically at least 300ppm, even at least 1000 or 1500ppm, for example from 300ppm to 20000ppm, for example from 800 to 5000ppm; f ^- In an amount of 1ppm or more, for example 1ppm to 500ppm, such as 4 or 6 or 20 or 40 or 100ppm; siO in raw sewage of this type ₃ ^2- +SiO ₄ ^4- Is generally greater than or equal to 3ppm, for example from 3ppm to 750ppm, such as 5 or 12 or 20 or 50 or 150 or 300ppm. In addition, the Total Phosphorus (TP) content is generally ≥ 0.5ppm, for example 0.5ppm to 700ppm, such as 4 or 12 or 20 or 50 or 100 or 200ppm. In addition, it is possible that Fe is present in such raw sewage ³⁺ ，Fe ²⁺ ，Cu ²⁺ ，Ni ²⁺ ,Cd ²⁺ ,Zn ²⁺ ,Hg ⁺ ,Hg ²⁺ ，Cr ³⁺ ,Pb ²⁺ Or Mn ²⁺ The content of each heavy metal cation in the aqueous solution is more than or equal to 1ppm, more often more than or equal to 3 or more than or equal to 5ppm, but less than or equal to 30ppm or less than or equal to 20ppm. In addition, it is possible that,ammonia Nitrogen (NH) ₃ N) in an amount of 0.5ppm or more, for example from 0.5ppm to 1200ppm, such as 5 or 20 or 50 or 100 or 200 or 500ppm. It is possible that S ^2- The content is ≥ 0.2ppm, for example from 0.2 to 70ppm, such as 2 or 10 or 20ppm. It is possible that the AsO ₄ ^3- +AsO ₃ ^3- The content is ≥ 0.2ppm, for example 0.2-50ppm, such as 2 or 7 or 15ppm. In addition, the contents of other ions in the raw sewage are as follows: na (Na) ⁺ In an amount of from 300 to 11000ppm, preferably from 500 to 9500ppm, such as 900 or 1500 or 2000 or 4000ppm; cl ^- The content is 450-9500ppm, preferably 700-8000ppm, such as 1200 or 2000 or 3000 or 4000 or 6000ppm. In addition, CO ₃ ^2- The content is 70-6500ppm, such as 100 or 300 or 500 or 800 or 1200 or 1500 or 2000 or 3000ppm.

In the present application, the term "wastewater having a high sulfate content and a high COD value (containing fluorine and silicon)" means a raw wastewater (W) ₀ ) In which sulfate radical SO ₄ ^2- The content is 2000-50000ppm (mg/L), the chemical oxygen demand COD is more than or equal to 1000mg/L, such as 1g/L-10g/L; total hardness of calcium and magnesium (Ca) ²⁺ +Mg ²⁺ ) At 300ppm or more, even 1000ppm or more, for example 300ppm to 20000ppm, such as 800 to 5000ppm; f ^- In an amount of 1ppm or more, for example 1ppm to 500ppm, such as 4 or 6 or 20 or 40 or 100ppm; in such raw sewage (W) ₀ ) SiO 2 ₃ ^2- (+ optional SiO) ₄ ^4- ) Is generally greater than or equal to 3ppm, for example from 3ppm to 750ppm, such as 5 or 12 or 20 or 50 or 150 or 300ppm.

Generally, raw sewage of coal chemical industry is from coal to prepare ethylene glycol, methanol and coal gas (CO + H) ₂ ) Ammonia, urea, etc. It is a high COD, high salt waste water, especially containing fluorine, silicon and heavy metals.

In addition, the effluent of certain metallurgical processes also often contains fluorine, silicon and heavy metals.

In the multiple treatment steps of the sewage, the mutual interference effect of more types of the pollution components (impurities) exists, and the separation and purification effects of the sewage are seriously influenced. For example, organic macromolecular impurities (COD) often wrap or complex the above-mentioned heavy metal ions and anions, and further, in a method for purifying sewageThe metal ions also interfere with each other in each step. Due to the strong hydrogen bonding between HF molecules and the not too high concentration of certain cations in the effluent, a portion of the HF in the effluent is often present in the form of aggregates or associations "(HF) n", which do not necessarily have to be associated with the free Ca contained in the effluent ²⁺ Ion formation of CaF ₂ And (4) precipitating. Also, silicate Ion (SiO) ₃ ^2- Or SiO ₄ ^4- ) Also as aggregates or associated compounds (H) ₂ SiO ₃ ) n and (H) ₄ SiO ₄ ) n is present in the form of not necessarily in association with free Ca contained in the waste water ²⁺ The ions form calcium orthosilicate or calcium metasilicate precipitates. Phosphate radical (PO) like silicate radical ₄ ^3- ) It is also possible to use aggregates or associations (H) ₃ PO ₄ ) n is not necessarily present in combination with free Fe contained in the wastewater ³⁺ Ion formation of precipitate (Fe) ³⁺ +PO ₄ ^3- →FePO ₄ ). In addition, in the sewage, anions, water (or OH) ^- Or NH ₃ ) With certain heavy metal cations (e.g. Cu) ²⁺ 、Cd ²⁺ ,Hg ²⁺ ，Cr ³⁺ ) It is possible to form complexes, and therefore, these heavy metal cations do not necessarily form precipitates with specific anions. The term "aggregate" or "association" as used herein is also considered to be equivalent to "aggregate". The above-mentioned impurities of fluorine, silicon and phosphorus species easily clog a porous filtration membrane such as an ultrafiltration membrane or a reverse osmosis membrane.

On the one hand, in general, the above-mentioned effluents (in particular effluents with high salt content and high COD values in the fields of coal chemical industry, mining and beneficiation, fluorine chemical industry and metallurgy) may contain toxic heavy metals such as cadmium, chromium, mercury and arsenic, etc., and may contain fluorine, silicon and phosphorus elements (such as F present in the effluents) ^- Silicate or phosphate tends to clog the pores of the filtration membrane, because these anions form hard "fouling" precipitates with cations such as calcium and magnesium ions), and thus, this type of wastewater is an extremely difficult type of wastewater to treat, and the purification treatment of this type of wastewater is a worldwide problem. On the other handEnvironmental regulations are also very strict on the heavy metal content and fluorine content in the water obtained after the sewage is purified and discharged to the environment.

In order to treat the sewage, the invention provides a method for treating the sewage containing fluorine and silicon impurities (such as F) ^- The content is more than or equal to 1ppm, even F ^- The content is more than or equal to 2ppm or more than or equal to 3ppm; and SiO ₄ ^4- +SiO ₃ ^2- Content of more than or equal to 2ppm, even more than or equal to 3ppm or more than or equal to 4 ppm). The invention aims to provide a zero-emission sewage treatment process and a zero-emission sewage treatment system.

Since the flow rate of the wastewater containing fluorine and silicon impurities to be treated is large, the fluorine and silicon impurities in the wastewater are very likely to block the pores of various filtration membranes (such as ultrafiltration membranes, reverse osmosis membranes and electrodialysis membranes), and therefore, the purification treatment of wastewater containing high content of fluorine and silicon impurities is a worldwide problem.

Through years of research, the inventor of the application finds that most of fluorine and silicon impurities in the sewage can be removed by combining a biochemical treatment process and an electrochemical impurity removal process adopting a double anode (combined anode or composite anode) containing iron and/or aluminum.

In addition, the inventors have found that the combined use of these two processes also desirably removes most of the heavy metals, but also most of the other harmful anions (e.g., phosphate, arsenate and S) ^2- ) At the same time, it is also possible to additionally (or incidentally) remove a portion of the other "hardness" cations (e.g. calcium, magnesium ions).

Firstly, in the biochemical treatment process, the sewage to be treated is subjected to at least two biochemical treatment processes comprising an anaerobic section (zone) and an aerobic section in sequence. Wherein the main function of the anaerobic segment is denitrification by denitrification of microorganisms [ e.g. heterotrophic bacteria ammoniate contaminants such as proteins, fats (N in the organic chain or amino groups in amino acids) to free ammonia (NH) ₃ 、NH ₄ ⁺ ) While the denitrification of the heterotrophic bacteria converts NO ₃ ^- Reduced to molecular nitrogen (N) ₂ )]Simultaneously with waterDecomposing macromolecular organic matters; the aerobic section is used for removing organic matters in water and simultaneously removing ammonia nitrogen through the nitrification of microorganisms [ nitrification of autotrophic bacteria is used for removing NH ₃ -N(NH ₄ ⁺ ) Oxidation to NO ₃ ^- ]. Anaerobic treatment and aerobic treatment degrade or decompose most COD (namely organic impurities) contained in the sewage to expose or keep heavy metal ions or anions in a free state, so that the problem that the heavy metal ions and the anions are wrapped or complexed by the organic impurities in the sewage purification method in the prior art is solved.

Secondly, (HF) n, (H) in the form of aggregates or associations under the action of an electric field during electrochemical decontamination using a double anode (combined anode or composite anode) comprising iron and/or aluminium ₄ SiO ₄ )n、(H ₂ SiO ₃ ) n or (H) ₃ PO ₄ ) n is dissociated or ionized, a specific anion (e.g. F) ^- 、SiO ₃ ^2- 、PO ₄ ^3- Or AsO ₄ ^3- ) Form a precipitate with the corresponding heavy metal cation. The current action between the polar plates can change the molecular aggregation state of silicon dioxide, silicic acid (radical) and fluoride compounds in the sewage to make SiO ₂ Silicic acid radical, F ^- The plasma is combined with the calcium and magnesium ions to precipitate and coprecipitate, thereby reducing SiO ₂ Silicic acid radical, F ^- And the like.

The electrode reactions in the cell are as follows:

anode: fe-2e ^- →Fe ²⁺

2H ₂ O-4e ^- →O ₂ +4H ⁺

2Cl ^- →Cl ₂ +2e

MO _X +H ₂ O→MO _X (HO·)+H ⁺ +e ^- (direct Oxidation reaction)

In the formula MO _X Represents a metal oxide

Cathode: 2H ₂ O+2e-＝H ₂ +2OH ^- (direct reduction reaction)

The following reactions take place in solution: for example

Ca ²⁺ +HCO ₃ ^- +OH ^- →CaCO ₃ ↓+H ₂ O

Mg ²⁺ +2OH ^- →Mg(OH) ₂ ↓

Fe ³⁺ +3OH ^- →Fe(OH) ₃ ↓

Cu ²⁺ +2OH ^- →Cu(OH) ₂ ↓

Ni ²⁺ +2OH ^- →Ni(OH) ₂ ↓

Cd ²⁺ +2OH ^- →Cd(OH) ₂ ↓

Zn ²⁺ +2OH ^- →Zn(OH) ₂ ↓

Fe ³⁺ +PO ₄ ^3- →FePO ₄ ↓

Mn ²⁺ +2OH ^- →Mn(OH) ₂ ↓

Ca ²⁺ +2F ^- →CaF ₂ ↓

2Ca ²⁺ +SiO ₄ ^4- →Ca ₂ SiO ₄ ↓

Ca ²⁺ +SiO ₃ ^2- →CaSiO ₃ ↓

Mg ²⁺ +SiO ₃ ^2- →MgSiO ₃ ↓

Cr ³⁺ +AsO ₄ ^3- →CrAsO ₄ ↓

Hg ²⁺ +S ^2- →HgS↓

Pb ²⁺ +2OH ^- →Pb(OH) ₂ ↓

Thirdly, using a sacrificial anode and an inert anode as a combined anode or using ferrotitanium alloy, aluminum-titanium alloy or ferroaluminum-titanium alloy as a composite anode in an electrochemical treatment tank, and using iron ions and/or aluminum ions in the sewage as or to form a flocculating agent or a flocculating substance; on the one hand, the flocculant is beneficial to the agglomeration and flocculation of inorganic salt precipitates and small particles of organic matters (COD), and on the other hand, the flocculant promotes the further agglomeration and sedimentation of particulate matters in sewage. In addition, fe produced ³⁺ Ion orAl ³⁺ The ions also facilitate removal of phosphate by forming a precipitate. In the electrochemical treatment cell [ FeF ] is also formed ₆ ] ^3- And [ AlF ₆ ] ^3- Ions, which settle by flocculation or are adsorbed by activated carbon in a subsequent stage.

Fourth, the inventors of the present application found through experiments that chlorine-containing oxidants (i.e.: cl, cl) were generated on-site (in situ) in the wastewater ₂ And/or hypochlorite) is much higher than the chlorine-containing oxidizing agent (Cl) added in the contaminated water ₂ Gas or hypochlorite), and thus the high oxidation activity of the former is capable of oxidizing COD impurities (e.g., ammonia nitrogen impurities, certain inorganic anions or cations that can be oxidized, and organic impurities, etc.) as impurities that are difficult to (sufficiently) oxidize, decompose, or degrade in the previous biochemical treatment. In particular, during electrolysis (i.e., electrochemical treatment), highly active free chlorine and hypochlorite are generated in situ (in situ) in the wastewater, with much higher oxidation activity than Cl ₂ (or added Cl) ₂ ) Oxidizing property of (2), which can oxidatively decompose a linear, branched or cyclic alkane organic compound (i.e., a non-aromatic hydrocarbon organic compound) or a derivative thereof (e.g., C) ₁ -C ₇ Linear alkylcarboxylic acids), benzene and other aromatic and heteroaromatic compounds, and also ammonia nitrogen to nitrogen.

Therefore, the invention can remove most of fluorine and silicon impurities at low cost and high efficiency, and the impurities are difficult to remove by the sewage treatment method in the prior art. Meanwhile, the total hardness (calcium and magnesium) in the sewage is greatly reduced. Although the prior art sewage treatment methods employ more treatment steps, it is still difficult to effectively remove fluorine and silicon impurities, and in addition, the removal effect of such methods on ammonia nitrogen impurities, inorganic salts (in the form of precipitates and/or flocs) and COD (i.e., organic impurities) is also unsatisfactory.

In the present application, various wastewaters (including factories) from various segments of the production enterprises in the above-mentioned industrial fieldsDomestic wash water) is collected in a conditioning tank to form raw sewage or raw wastewater, which is referred to as raw sewage or raw wastewater (W) ₀ )。

According to a first embodiment of the present invention, there is provided a method for treating wastewater having a high sulfate content and a high COD value, which comprises:

(1) Biological desulfurization: raw sewage (W) is treated under anaerobic conditions in a biological desulfurization tank using sulfate-reducing bacteria ₀ ) Biological desulfurization is carried out through biological reduction reaction; and

(2) Optional anaerobic treatment: the sewage after biological desulfurization is treated anaerobically in a UASB anaerobic reactor,

obtaining raw sewage (W) from which a part of sulfate is removed ₀ ) (ii) a Then the

(B) Biochemical treatment: raw sewage (W) from which a part of sulfate is removed ₀ ) Biochemical treatment is carried out in a biochemical treatment tank;

(C) Separation: the biochemically treated sewage is separated to remove solid impurities in the form of sludge (i.e., sludge containing COD), and first-stage purified sewage (W) is obtained ₁ ) (ii) a And

(D) Electrochemical impurity removal: the first stage purified wastewater (W) ₁ ) Electrochemical treatment (or electrolysis) is carried out in an electrochemical treatment tank or in an electrochemical impurity removal system comprising an electrochemical treatment tank in order to remove ammonia nitrogen impurities, inorganic salts (in the form of precipitates and/or flocs) and COD (i.e. organic impurities) to obtain second-stage purified wastewater (W) ₂ )；

Wherein a sacrificial anode and an inert anode are used as a combined anode or an alloy material containing a sacrificial metal and an inert metal is used as a composite anode in an electrochemical treatment cell, and a wastewater (W) in the electrochemical treatment cell ₁ ) The content or concentration of alkali metal chloride (such as NaCl and KCl) is sufficient to allow the application of DC voltage between the anode and cathode ₁ ) In situ (in situ) to generate highly active chlorine-containing oxidants [ i.e.: cl, cl ₂ And/or hypochlorite (or salt thereof)](ii) a And

wherein a voltage (V) applied between an inert anode or a composite anode and a cathode as an electrode pair by a DC power supply is used ₁ ) Enough to cause the sewage (W) to flow ₁ ) In situ (in situ) to generate highly active chlorine-containing oxidants [ i.e.: cl, cl ₂ And/or hypochlorite (or salt thereof)]And optionally an oxygen-containing oxidizing agent (i.e.,. O,. OH and O) ₂ ) (when the content or concentration of chloride ions in the sewage is low, oxygen with lower activity is generated in the electrolysis process), and simultaneously, a voltage (V) is applied between a sacrificial anode or a composite anode and a cathode which are used as an electrode pair by a direct current power supply ₂ ) Enough to make the metal simple substance (oxidized) of the sacrificial anode or the composite anode lose electrons and enter the sewage (W) in the form of metal cations ₁ ) And the metal ions form a flocculant or exert a flocculation action in the wastewater contained in the electrochemical treatment cell.

Generally, the COD of the inlet water of the electrochemical treatment tank is less than or equal to 450mg/L. Effluent (W) of electrochemical impurity removal system ₂ ) The total hardness of (A) can be less than 80mg/L, generally between 20 and 78mg/L, and in addition, the COD is between 12 and 30 or between 15 and 20.

In the raw sewage (W) from which a part of the sulfate is removed ₀ ) In the middle, the content of sodium sulfate has been reduced to<1500mg/L or<1700mg/L。

And respectively collecting sediment at the bottom of the electrochemical treatment tank and scum on the surface of the sewage, and sending the sediment and the scum to a sludge collection tank.

The electrochemical treatment can effectively remove fluorine and silicon impurities. In addition, the hardness is also significantly reduced (total hardness based on calcium and magnesium ions is less than 80 mg/L) and heavy metals are removed. The electrochemical treatment method has the advantages of low cost and good effect.

In this application, "optional" means with or without. In the present application, "electrochemical" has the same meaning as "electrolysis" and is used interchangeably. An "electrochemical treatment cell" may also be referred to as an "electrolysis cell". "hardness" and "(calcium and magnesium) total hardness" are used interchangeably.

The power supply used in the present invention is preferably a dc pulsed power supply, more preferably a pulsed adaptive power supply. The power supply parameters can be automatically adjusted according to the work reflection condition. If necessary, a plurality of flow deflectors (or water blocking plates) are provided in the electrochemical treatment cell to guide the sewage to meander (zigzag) flow between all the anodes and cathodes.

The biochemical treatment process comprises the step of sequentially carrying out anaerobic zone (zone) treatment and aerobic zone treatment on the sewage. In addition, in the biochemical treatment process, the treatment of the anaerobic zone (zone) and the treatment of the aerobic zone can be each independently performed a plurality of times. For example, the anaerobic treatment and the aerobic treatment are each carried out 2 times or 3 times or 4 times or 5 times or 6 times, that is, each may be divided into 2, 3, 4 or 5 or 6 stages, respectively. In addition, anaerobic treatment and aerobic treatment may be alternately performed.

Anaerobic bacteria generate denitrification to change organic matters (amino acid and protein) and nitrate radicals into ammonia nitrogen. Typically, nitrates (NO) ₃ ^- ) Nitrogen (N) in (A) is passed through a series of intermediates (NO) ₂ ^- 、NO、N ₂ O) reduction to nitrogen (N) ₂ ). The aerobic section is used for removing organic matters in the sewage and removing ammonia nitrogen through nitration.

Anaerobic and aerobic treatment can greatly reduce the COD value in the sewage. For the selection of anaerobic bacteria or aerobic bacteria, corresponding bacteria sources are selected according to different specific sewage for cultivation. Selecting a plurality of bacteria to cultivate in the specific sewage; then, the number and activity of microorganisms suitable for biochemical treatment are observed under a microscope, and water indexes are detected, so that bacteria which propagate fast in corresponding sewage are selected. For example, the aerobic bacteria used in the aerobic zone include one or more of escherichia coli, bacillus subtilis, pichia pastoris, aspergillus niger and penicillium chrysogenum, and the anaerobic bacteria used in the anaerobic zone are bifidobacterium and/or clostridium butyricum. In addition, heterotrophic bacteria can be used in both the anaerobic and aerobic sections, including one or more of rhizopus and/or penicillium. Autotrophic bacteria may be used in the anaerobic zone and include facultative autotrophic rhizobia (Rhizobium species F43bT, CN 105925516A), thiobacillus ferrooxidans (Thiobacillus ferrooxidans), thiobacillus thiooxidans (Thiobacillus thiooxidans) or Alcaligenes eutrophus (Alcaligenes).

According to the characteristics of sewage, a biochemical treatment process is designed and proper bacteria are selected, and the process has the advantages of low cost, high efficiency, small side effect, less generated secondary pollutants and particularly reduced influence on the following procedures.

The biochemical treatment can degrade harmful organic impurities (such as impurities at the molecular level, such as benzene, methanol, formaldehyde or other micromolecular organic matters, and biological macromolecules), and greatly reduce indexes of COD, ammonia nitrogen, total phosphorus and the like of the sewage.

Above V ₁ And V ₂ May be the same or different. The direct voltage (V) ₁ ) Or (V) ₂ ) Is between 5 and 100V, preferably between 7 and 70V, more preferably between 10 and 36V. Preferably, the voltage V is such that it is necessary to remove different types of impurities ₁ Or V ₂ Kept constant or regulated or stepped up, preferably the voltage V ₁ Or V ₂ Are gradually turned up.

Preferably, wherein the wastewater (W) in the electrochemical treatment tank ₁ ) The content or concentration of alkali metal chloride (e.g., naCl and/or KCl) is between 600mg/L and 70g/L (i.e., between 600ppm and 70000 ppm), preferably between 700mg/L and 60g/L, preferably between 800mg/L and 50g/L, more preferably between 850mg/L and 40g/L, and more preferably between 900mg/L and 30g/L. It has been found experimentally that the above-mentioned chloride content can result in the generation of a sufficient amount of active chlorine in the region near the inert anode of the electrochemical treatment cell.

Preferably, to generate more free chlorine (. Cl), cl ₂ Or hypochlorite, alkali metal chloride (e.g., naCl + KCl) is present in a concentration or concentration of 950mg/L or more, preferably 1.0g/L or more, e.g., 1.1g/L or 1.2g/L or 1.5g/L or 2.0g/L or more, and in general, 20g/L or less, preferably 15g/L or more, more preferably 10g/L or less.

When the content or concentration of alkali metal chloride (e.g., naCl + KCl) in the wastewater is low, a voltage (V) is applied between the anode and the cathode ₁ Or V ₂ ) Is higher but still cannot produceA sufficient amount of active chlorine. The voltage is gradually adjusted from low to high until the presence of free Cl or Cl is detected ₂ The "chlorine" smell is generated or smelled, and the actual voltage or current density is determined.

In general, for domestic tap water disinfected with chlorine, people often smell tap water with a "chlorine" smell.

In general, when the above-mentioned waste water (W) is treated in an electrochemical treatment tank ₁ ) The content of alkali metal chloride of (A) is<600ppm (wt), i.e.<600mg/L, in the sewage (W) ₁ ) To which an alkali metal chloride (e.g., sodium chloride and/or potassium chloride), magnesium chloride and/or calcium chloride is added, preferably an alkali metal chloride and/or magnesium chloride, more preferably an alkali metal chloride.

The alkali metal chloride includes or is: naCl, KCl and/or LiCl. Preferably NaCl and/or KCl, more preferably NaCl.

Preferably, in the electrochemical treatment tank, the wastewater (W) ₁ ) The medium electrolyte concentration is between 0.02mol/L and 0.6mol/L, preferably between 0.035mol/L and 0.5mol/L, preferably between 0.05mol/L and 0.4mol/L, more preferably between 0.06mol/L and 0.3mol/L, more preferably between 0.08mol/L and 0.2mol/L. For example, 0.09, 0.10, 0.12, 0.14 or 0.18mol/L.

For the case of using a sacrificial anode and an inert anode as the combined anode in an electrochemical treatment cell, it is preferred to use iron or aluminum or an iron-aluminum alloy as the sacrificial anode. However, in the case where an alloy material containing a sacrificial metal (e.g., iron and/or aluminum) and an inert metal (e.g., titanium) is used as the composite anode in the electrochemical treatment cell, it is preferable to use an iron-titanium alloy, an aluminum-titanium alloy, or an iron-aluminum-titanium alloy as the composite anode, in which the iron, aluminum, or iron-aluminum element (referred to as the sacrificial metal) contained in the composite anode functions as the sacrificial anode, and titanium (referred to as the inert metal) functions as the inert anode.

There is no limitation on the material for forming the cathode, and materials commonly used in the art for forming the cathode may be used in the present application, for example, materials for forming the cathode include graphite, iron, titanium, and the like. The inert anode comprises graphite or titanium metal and, therefore, the inert anode plate comprises a graphite plate or a titanium metal plate.

In general, the anode or the cathode is generally shaped as a flat plate (e.g., an iron plate, an aluminum plate, or an iron-aluminum alloy plate), a perforated plate (plate with openings), a grid (grate), a fence (grate), a wire mesh, or the like. These anodes or cathodes generally have one or two main faces (i.e. front or rear faces) with a large area. The major face is in the form of a flat or curved surface. For example, when the anode or cathode is in the form of a fence, in the fence-shaped anode or cathode, a plurality of anodes in the shape of rods or bars are arranged upright on a plane or on a curved surface, or a plurality of cathodes in the shape of rods or bars are arranged upright on a plane or on a curved surface. Typically, the major surface (or front surface) of the anode faces the cathode or faces the major surface (or front surface) of the cathode. Preferably, an iron, aluminum or iron-aluminum alloy plate is used as the anode, with the major plane (or face) of the anode facing the cathode or facing the major plane (or face) of the cathode. When iron or aluminum or an iron-aluminum alloy (e.g., an iron plate or an aluminum plate or an iron-aluminum alloy plate) is used as the sacrificial anode, or when an alloy material containing a sacrificial metal and an inert metal is used as the composite anode, a flocculant (or a substance having a flocculation effect) is formed from iron ions, aluminum ions, or iron ions + aluminum ions in the wastewater contained in the electrochemical treatment tank. Such flocculants include, but are not limited to, fe ²⁺ (e.g., [ Fe (H)) ₂ O) ₆ ] ²⁺ )、Fe ³⁺ (e.g., [ Fe (H)) ₂ O) ₆ ] ³⁺ )、Al ³⁺ (e.g., [ Al (H) ] ₂ O) ₆ ] ³⁺ ) And corresponding inorganic high molecular polymers (such as polymeric ferric chloride, polymeric ferric sulfate, polymeric aluminum chloride) or composite inorganic high molecular polymers (such as polymeric aluminum ferric chloride, polymeric aluminum ferric sulfate, polymeric sulfuric acid (chloride) silicon aluminum ferric), and the like.

In general, multiple pairs of anodes and cathodes may be used in an electrochemical treatment cell, for example 2-150 pairs, preferably 3-120 pairs, more preferably 4-100 pairs, more preferably 5-90 pairs, more preferably 6-85 pairs, such as 8, 9, 10, 12, 14, 16, 18, 20, 22, 25, 28, 30, 32, 35, 40, 60, 70 or 80 pairs. For example, when one cathode plate (or anode plate) with a larger surface area is paired with two anode plates (or cathode plates) with a smaller surface area, then 2 pairs of anode and cathode are considered to be present; when one cathode plate (or anode plate) with a larger surface area is paired with three anode plates (or cathode plates) with a smaller surface area, then there are 3 pairs of anodes and cathodes. The number of pairs is calculated as an average.

The plurality of anodes and cathodes may be alternately arranged in the electrochemical treatment cell (or electrolytic cell) or may be arranged in pairs or in a set of 2 anodes and 1 cathode. Preferably, a plurality of anodes and cathodes (e.g., 8 anodes and 7 cathodes) are alternately arranged, as shown in fig. 3. In addition, two or more anodes may be adjacent to or electrically connected to each other. Also, two or more cathodes may be adjacent to or electrically connected to each other.

Generally, to generate highly active oxidizing agents, cl and Cl, on site (in situ) in sewage ₂ And/or hypochlorite, the magnitude of the applied direct voltage between the inert anode and cathode as an electrode pair being related to the distance (d) between the anode and cathode. The distance between the anode and the cathode (distance d) is typically between 2 and 40cm, preferably between 3 and 35cm, more preferably between 4 and 30cm, more preferably between 5 and 28cm, such as 6, 7, 8, 9, 10, 11, 12, 13, 15, 16, 17, 20, 22 or 25cm. The larger the pitch, the higher the applied DC voltage (V1 or V2). For a spacing (d) of between 2 and 25cm, the voltage is generally between 1.7V and 30V. In electrochemical processes (otherwise known as electrolysis processes), the DC voltage is generally adjusted from low to high until active chlorine (e.g., free Cl or Cl) is detected ₂ ) Generating or smelling the smell of 'chlorine'.

During the electrochemical treatment, the current density between the anode (plate) and the cathode (plate) was 10mA/cm ² To 60mA/cm ² Preferably between 12mA/cm ² To 55mA/cm ² More preferably between 14mA/cm ² To 50mA/cm ² E.g. 13, 15, 17, 20, 30, 40 or 45mA/cm ² 。

In general comeIn other words, the adjustment of the content or concentration of the alkali metal chloride in the wastewater in the electrochemical treatment tank is also dependent on the content of the reducing impurities (e.g., aromatic organic compounds, organic polymers, and ammonia nitrogen impurities) in the wastewater. That is, the higher the content or concentration of alkali chloride in the wastewater in the electrochemical treatment cell, the more chlorine-containing oxidizing agent (i.e.: cl, cl) is generated by the electrochemical treatment ₂ And/or hypochlorite) to more rapidly fully oxidize the reducing impurities.

In the (D) electrochemical impurity removal process, formed precipitate is scraped off and collected in a sludge collection tank.

Preferably, a filler or three-dimensional filler (filler diameter of, for example, 4 to 8 mm) is placed between the anode and the cathode in the electrochemical treatment cell; for example, a ceramic filler (for example alumina ceramic, silicon carbide ceramic or silicon nitride ceramic), or a wire mesh filler (mesh size of for example 4-8 mm). The filler plays a role of adsorption and provides a reaction interface, a crystallization point at the same time.

Preferably, the wastewater (W) is treated in an electrochemical treatment process ₁ ) In which a coagulant aid (or a flocculant or a sedimentation agent), such as polyacrylamide, is added. Organic floating slag such as oily matter or floating matter floats on the surface of the sewage due to bubbling caused by hydrogen generated by electrolysis in the sewage and air (aeration), so that the organic floating slag is further gathered or precipitated by a coagulant aid (or a flocculant or a sedimentation agent), and the floating slag or the precipitate is conveniently fished out or collected.

In the electrochemical treatment cell, sodium chloride, potassium chloride, sodium carbonate, sodium bicarbonate, sodium hydroxide, or lithium nitrate may be added as a catalyst, and thus, the electrochemical process may also be referred to as "electrocatalytic" electrochemical treatment.

Preferably, during the electrochemical treatment in step (D), the effluent (W) is preferably at the front or inlet end of the electrochemical treatment cell ₁ ) Adding inorganic base (such as Na) ₂ CO ₃ And/or NaOH) for conditioning the waste water (W) ₁ ) To a pH of 7.2-13.5, preferably in the range of 9-13.2, more preferably in the range of 10-13, more preferably 10.5-12.5, preferably 11-12, on sewage (W) ₁ ) IntoAnd performing electrochemical treatment.

The inventors of the present application have surprisingly found that in the electrochemical treatment step (D), although the sacrificial anode produces a flocculant containing iron or aluminum under the action of an electric field, and also to the wastewater (W) in the electrochemical treatment tank (e.g. at the front or inlet end of the electrochemical treatment tank) ₁ ) In which a coagulant aid such as polyacrylamide is added, which is advantageous for removing fluorine and silicon in sewage and for reducing the total hardness of sewage, but if the total hardness (calcium magnesium) of sewage in the treatment tank is excessively reduced, for example, less than 80mg/L, it is rather difficult to completely remove silicon-based impurities, and at the same time, the effect of removing fluorine is also impaired. Thus, the total hardness of calcium and magnesium in the effluent of the basin is maintained above 80mg/L, preferably above 90 or 100mg/L, or even above 200 or 300 or 400 or 500mg/L, but below 1200 or 1100 or 1000 or 900 or 800mg/L, while the effluent (W) is conditioned ₁ ) Has a pH in the above range, and therefore, it is possible to desirably remove silicon-based impurities (SiO) in the wastewater in the electrochemical treatment tank ₃ ^2- ) And fluorine-based impurities (F) ^- )。

In addition, the inventors have also found that, in the case where the pH value of the wastewater in the electrochemical treatment tank is adjusted within the above-mentioned range, and in the wastewater (W) requiring electrochemical treatment ₁ ) With or without the addition of water soluble magnesium salts (e.g., magnesium chloride, magnesium sulfate and/or magnesium nitrate, preferably magnesium chloride) and/or water soluble calcium salts (e.g., calcium chloride and/or calcium nitrate), maintaining the effluent (W) of the treatment tank ₂ ) The total hardness of the calcium and the magnesium is higher than 80mg/L, thereby being capable of leading SiO in sewage ₃ ^2- The removal rate of (a) is higher than 98%, even higher than 99.5% or higher than 99.9%. The reason for this effect may be the magnesium ion Mg ²⁺ With SiO ₃ ^2- And optionally other ions (e.g. PO) ₄ ^3- Or OH ^- ) A precipitate of double salt is formed.

Generally, the above-mentioned sewage in the electrochemical treatment tank contains a sufficient amount of Ca ²⁺ And Mg ²⁺ Ions such that F ^- And SiO ₃ ^2- Precipitates were formed separately. Generally, the wastewater (W) purified in the first stage ₁ ) (e.g. in electrochemical treatment cellsFront end or water inlet end) of the sewage (W) with or without additionally adding a water-soluble magnesium salt (e.g., magnesium chloride) and/or a water-soluble calcium salt (e.g., calcium chloride) ₁ ) Middle Ca ²⁺ And F ^- Is 0.5 (i.e. 0.5, 1), preferably 1, preferably 1.5, preferably 2, preferably 2.5, even 3 or 4 or 5 or 6 or 7 or 8 or 9 or 12 or 15 or 20 or 50 or 100 or 200 or 300 or 400, but 700, preferably 650. At the same time, sewage (W) ₁ ) Medium Mg ²⁺ With SiO ₃ ^2- Is ≥ 1 (i.e. 1), preferably ≥ 1.5, preferably ≥ 2, preferably ≥ 2.5, preferably ≥ 3, preferably ≥ 3.5, even ≥ 4 or 5 or 6 or 7 or 8 or 9 or 12 or 15 or 20 or 50 or 100 or 200 or 300 or 400 or 500 or 600, but the molar ratio is ≤ 900, preferably ≤ 800. When the water-soluble magnesium salt and/or the water-soluble calcium salt is not added to the wastewater in the electrochemical treatment tank, the above molar ratio is maintained by shortening the retention time of the wastewater in the electrochemical treatment tank and/or reducing the amount of the coagulant aid (or flocculant) added.

Preferably, mg (as Mg) is present in the wastewater when electrochemical treatment is required ²⁺ Calculation): si (in SiO) ₃ ^2- Meter) is 2 (i.e. 2) ₁ ) Adding water soluble magnesium salt (preferably magnesium chloride) to increase Si (with SiO) ₃ ^2- Meter) removal rate. After the addition of water soluble magnesium salts, the wastewater should be made Mg (as Mg) ²⁺ Calculation): si (in SiO) ₃ ^2- In terms of) is ≥ 1 (i.e. 1.0), preferably ≥ 1.5, preferably ≥ 2, preferably ≥ 2.5, preferably ≥ 2.7, more preferably ≥ 3, preferably ≥ 3.5, more preferably ≥ 4, more preferably ≥ 5, more preferably ≥ 6, more preferably ≥ 7, more preferably ≥ 8, more preferably ≥ 10, even ≥ 50 or 100 or 200 or 300 or 400 or 500 or 600 or 700 or 800 or 900 or 1000; however, mg (as Mg) should be allowed to exist in the sewage ²⁺ Calculation): si (in SiO) ₃ ^2- In terms of) is generally 1800 or less (i.e. 1800 1), preferably 1500 or less, preferably 1400 or less, preferably 1200 or less.

Preferably, the separation step (C) is a precipitation separation, a filtration separation or a membrane separation, such as MBR membrane bioreactionAnd (4) separating by using a separator, wherein the sewage subjected to biochemical treatment is subjected to MBR treatment in an MBR membrane biological reaction tank (MBR tank). Preferably, the MBR membrane or the MBR membrane module in the MBR tank adopts an anti-pollution PVDF hollow fiber membrane. In the MBR membrane biological reaction tank, the metabolism of aerobic microorganisms is utilized to degrade organic matters into CO ₂ 、H ₂ O and an inorganic compound; clear water is directly pumped out from the MBR membrane through a membrane component suction pump and is discharged to a finished product water tank, and sludge is completely intercepted.

Preferably, the MBR membrane tank effluent of the sewage treatment station needs to use inorganic base (such as Na) before entering the reuse water station ₂ CO ₃ And/or NaOH) to reduce the overall hardness of the influent water to the next process step (i.e., the electrochemical treatment cell). Generally, the COD of the influent water is less than or equal to 450mg/L.

The biochemical sludge separated by the (C) separation step (e.g., separated by an MBR membrane bioreactor) is delivered to a sludge collection tank or a biochemical sludge reduction device.

Because the various impurities in the electrochemical treatment cell interfere with each other, and thus all impurities cannot be completely removed, the inventors have experimentally found that trace amounts of SiO can be completely removed from wastewater by maintaining a high hardness in the effluent of the electrochemical treatment cell ₃ ^2- And F ^- (they are extremely difficult to remove in the prior art), and then the chemical softening tank is adopted to reduce the hardness in the sewage (i.e. the chemical softening tank takes on the task of removing residual calcium and magnesium ions), the strategy of 'one-step removal of silicon, fluorine and heavy metals and two-step reduction of hardness' of the invention obtains very ideal technical effects.

Preferably, the above method of the present invention further comprises the steps of: (E) chemical softening: second stage purified wastewater (W) ₂ ) The electrochemically treated wastewater is fed into a softening reactor (or softening tank) and passed into wastewater (W) with or without the hardness of the wastewater being detected ₂ ) Adding inorganic base (such as Na) ₂ CO ₃ And/or NaOH) to further soften the wastewater (i.e., reduce the hardness of the wastewater, allow calcium and magnesium ions to form precipitates) to obtain a third stage of purified wastewater: (a)W ₃ ) The hardness is generally in the range of 2 to 5mg/L. The formed precipitate is collected in a sludge collection tank for additional solid waste treatment.

Preferably, the above-mentioned (E) chemical softening step includes not only the following substeps:

(E1) Chemical softening: second stage purified wastewater (W) ₂ ) (i.e., the electrochemically treated wastewater) is transferred to a softening reaction tank (or softening reactor) as a chemical softening section, and passed through a wastewater treatment section (W) ₂ ) Adding Na ₂ CO ₃ And/or NaOH to further soften the wastewater (i.e., reduce the hardness of the wastewater, allowing calcium and magnesium ions to form precipitates);

and further comprising one or both of the following sub-steps:

(E2) Coagulation: in the coagulation section, coagulation of calcium and magnesium salts is promoted by adding a coagulant (e.g., polyaluminium chloride, ferric chloride or polyacrylamide) to the wastewater (e.g., wastewater flowing into or overflowing from the softening tank into the coagulation tank), and/or (E3) precipitation: in the settling section, allowing the wastewater (e.g., wastewater flowing from the softening tank into or overflowing into the settling tank) to settle in a settling tank, e.g., allowing the wastewater to settle in the settling tank; obtaining the third-stage purified sewage (W) ₃ ). Wherein, when the above two sub-steps (E2) and (E3) are adopted simultaneously, the order of the two sub-steps (E2) and (E3) may be any order, i.e. the order may be reversed.

In the present application, coagulants, flocculants (such as polyacrylamides) or coagulant aids (such as polyacrylamides) have the same meaning and they may be used interchangeably. In addition, precipitation and sedimentation may be used interchangeably.

If the above E3) precipitation step employs a general method of achieving precipitation by standing, a long precipitation time is required. To accelerate precipitation or shorten the precipitation time, an efficient precipitation method may be used, which is known in the art. For example, chinese utility model CN206995942U discloses a high-efficiency sewage sedimentation tank, CN208413999U and CN204434407U disclose high-efficiency sedimentation tanks respectively, and chinese invention patent publication CN108373206A discloses a high-efficiency sedimentation tank.

In the application, in the E3) precipitation step, calcium salts and magnesium salts in the sewage (such as the sewage flowing into or overflowing from a softening tank or a coagulation tank into a high-efficiency precipitation tank) are subjected to high-efficiency precipitation or high-efficiency sedimentation by using a high-efficiency precipitation tank; thereby obtaining third-stage purified sewage (W) ₃ ). For example, a high-efficiency sewage sedimentation tank disclosed in CN206995942U is adopted. Scraping off the sediment and suspended substances including CaF at the bottom of the sedimentation tank ₂ 、Ca(OH) ₂ 、CaCO ₃ 、Mg(OH) ₂ 、CaSiO ₃ And the like.

Preferably, the high-efficiency sedimentation tank used consists of two parts, namely a reaction zone and a clarification zone. The reaction zone comprises a mixed reaction zone and a plug flow reaction zone; the clarifying zone comprises an inlet pre-settling zone, an inclined tube settling zone and a concentration zone. In the mixing reaction zone, the mud residue, the added medicament (such as flocculant) and the raw water are quickly coagulated (namely, the flocculation is realized by stirring) by the lifting and mixing action of the stirrer, and then the mixture is lifted to the plug flow reaction zone by the impeller to carry out slow flocculation reaction so as to form larger floccules. The whole reaction zone (mixing and plug flow reaction zone) can obtain a large amount of high-density homogeneous alum flocs, and the high-density alum flocs can ensure that the settling speed of the sludge in the settling zone is higher without influencing the quality of effluent.

Typically, a dense packing of inclined tubes is provided in the settling zone. The inclined tube filler is a hexagonal honeycomb filler (as shown in fig. 7) made of polymer material (such as polyethylene or polypropylene). According to Harzhen (Hazen) shallow layer theory, utilize the pipe chute filler to divide into the shallow layer sedimentation layer (pipe chute filler district) with the settling zone, thereby shortened the settling distance of sediment granule, shortened the settling time, the installation angle of pipe chute is generally with the level be 50-70 (like 55, 60 or 65) contained angle, this angle can guarantee that the sludge deposit on the pipe chute can slide to the bottom of the pool and be unlikely to the siltation to a certain extent, the pipe chute has increased the settlement area on settling layer simultaneously, thereby the treatment load of sedimentation tank has been improved, the area of occupation of sedimentation tank has been reduced.

By further concentration sedimentation in the concentration zone, a sludge blanket is formed at the bottom of the sedimentation tank. As a certain amount of flocculating agent is added in the reaction zone before, the flocculating agent utilizes the molecular characteristics of the flocculating agent to sweep insoluble substances or part of macromolecules in water (net catching), so that the flocculating agent is subjected to co-sedimentation and precipitates are formed. The bottom of the sedimentation tank is provided with a concentrated mud scraper, and through the stirring effect of the mud scraper, the bottom of the sedimentation tank contains the precipitate with the characteristic of a flocculating agent, so that the precipitate can be further concentrated, large-particle floccule precipitates are formed, and the precipitate with higher density is further formed by utilizing the gravity of the large-particle precipitates.

In the present application, alum blossom means: alum (aluminum potassium sulfate dodecahydrate) is hydrolyzed and then adsorbed together with impurities in water to form floc, and the floc is bonded with each other into clusters by proper stirring, which is called alum floc. The larger the granularity of the alum blossom is, the larger the formed floc is, the better the sedimentation effect of the floc is, and the clearer the effluent is. Subsequently, alum floc is also used to broadly refer to flocs formed by flocculants such as iron. Thus, alum floc may also be referred to as floc.

Preferably, in the step (E) chemical softening of the method of the present invention, the above-mentioned sub-steps, i.e., (E1) chemical softening and (E2) coagulation and/or (E3) precipitation, may be performed using an integrated apparatus. For example, a chemical de-hardening device or an integrated softening tank comprising a softening reaction zone (zone) and a coagulation and/or sedimentation zone is employed, as shown in fig. 8. In the integrated softening apparatus, softening, coagulation, precipitation and neutralization can be carried out simultaneously. In the chemical softening zone, alkali (sodium hydroxide and/or sodium carbonate) is added to the wastewater in the softening reaction tank to reduce the hardness of the wastewater to, for example, 4mg/L or less. In the coagulation section, a coagulant (e.g., polyaluminum chloride, ferric chloride, or polyacrylamide) is used to further remove contaminants or fine particles in the wastewater. In the precipitation (or settling) zone, the effluent is subjected to a precipitation treatment, preferably, the pH of the effluent is adjusted to 7 ± 0.5 with hydrochloric acid (HCl solution). Preferably, sodium hypochlorite is added to the wastewater in the precipitation (or settling) zone to further remove ammonia nitrogen (i.e., oxidize ammonia nitrogen to nitrogen).

Other treatment steps may also be included between steps (D) and (E) of the present invention, such as filtration steps (e.g. using a ceramic membrane filter or a multi-media filter, more preferably a multi-media filter comprising a quartz sand filter layer) and/or ultrafiltration steps (e.g. using a ceramic membrane ultrafiltration device, more preferably using a ceramic flat sheet membrane ultrafiltration device).

Preferably, the above method according to the present invention further comprises the steps of: (F) a filtration and separation step: for the purified sewage (W) ₃ ) Further filtering and separating to obtain fourth-stage purified sewage (W) ₄ )。

Further preferably, step (F) comprises one or both of the following substeps: (F1) filtering: subjecting the sewage to filtration using a filter (e.g., a general filter, preferably, a ceramic membrane filter or a multimedia filter), separating and removing suspended substances or particulate matters (of micron-sized) in the sewage by filtration; and/or, (F2) ultrafiltration: the wastewater is ultrafiltered using an ultrafilter (preferably, a ceramic membrane ultrafiltration device, such as a ceramic flat membrane ultrafiltration device) to remove micron-sized suspended matter (i.e., fine particulate matter) in the wastewater. When the above two substeps are used simultaneously, the order of the substeps may be reversed in any order.

The raw material (or material) of the ceramic ultrafiltration membrane is generally alumina ceramic, silicon carbide or silicon nitride ceramic.

There is no particular limitation in the multimedia filter used in the present application, and multimedia filters commonly used in the art may be used. The present invention preferably uses a multimedia filter comprising a quartz sand filter layer, for example, a multimedia filter comprising an activated carbon filter layer, a quartz sand filter layer and a porous ceramic particle filter layer. Alternatively, for example, the present invention may adopt a multi-media filter disclosed in CN103239909A, wherein a filter plate is provided at a lower portion of a housing of the filter, a filter layer is provided at an upper side of the filter plate, the filter layer includes, from top to bottom, an anthracite layer, a quartz sand layer, and a pebble layer, the grain size of the particles in the anthracite layer and the pebble layer is larger than that of the particles in the quartz sand layer, and a water outlet is provided at a bottom of the housing.

Multimedia filtration may also be referred to as sand filtration. By using a multimedia filter, tiny or visually invisible particulates, including suspended matter, calcium carbonate particles, or colloidal matter, can be removed from the contaminated water. The multimedia filter can be regenerated by flushing with water, the flushed effluent being returned upstream, or the flushed effluent being collected and subjected to pressure filtration.

The (F2) ultrafiltration step may further filter out fine suspended matter or particulate matter in the contaminated water.

Preferably, the above method according to the present invention further comprises the steps of: (G) reverse osmosis: subjecting fourth-stage purified sewage (W4) (hardness about 0.1 mg/L) from the preceding step to reverse osmosis treatment in one or more stages to obtain fifth-stage purified sewage (W4) as reuse water ₅ ) Simultaneously obtaining Concentrated Water (CW) containing sodium chloride and sodium sulfate ₁ )。

More preferably, the (G) reverse osmosis step comprises: primary and secondary reverse osmosis, and optionally ST reverse osmosis (or electrodialysis). Further preferably, the first-stage reverse osmosis adopts a first-stage two-stage process; for example, the water inlet pressure is less than or equal to 1.4MPa, a booster pump is arranged between the two sections, and the water yield is controlled to be about 75 percent. The second-stage reverse osmosis adopts a first-stage two-stage process; for example, the water inlet pressure is less than or equal to 3.0MPa, a booster pump is arranged between the two sections, the water yield is controlled to be about 50%, and the produced concentrated water enters ST reverse osmosis. In ST reverse osmosis operation, the water inlet pressure is less than or equal to 6.0MPa, and the water yield is controlled to be about 75 percent. The produced water obtained by the first-stage reverse osmosis is used as reuse water, and the obtained concentrated water (the hardness is about 0.2-0.4 mg/L) is subjected to second-stage reverse osmosis; the product water obtained from the secondary reverse osmosis is used as reuse water, and the obtained further concentrated Concentrate (CW) is obtained ₁ ) Without or with further concentration, e.g. by ST reverse osmosis (or electrodialysis), to obtain a more concentrated Concentrate (CW) _1a ) The Concentrated Water (CW) ₁ ) Or Concentrated Water (CW) _1a ) Then, the solution is subjected to the next treatment, for example, nanofiltration using a nanofiltration membrane in the subsequent (H) nanofiltration membrane salt separation step.

Concentrated Water (CW) can be obtained by two-stage reverse osmosis ₁ ) (hardness about 0.5-0.9 mg/L), wherein the mixed salt content (NaCl and sodium sulfate) is generally 3-5wt%. If the Concentrated Water (CW) ₁ ) The direct delivery to evaporation consumes more energy. Thus, the devicePreferably, ST reverse osmosis or electrodialysis is further applied to obtain Concentrated Water (CW) with further concentration _1a ) Wherein the water is Concentrated (CW) _1a ) The content of mixed salts (NaCl and sodium sulfate) in the salt is further increased, for example>10wt%, e.g., 15wt% to 25wt%, and a hardness of about 1 to 4mg/L.

Preferably, the above-mentioned method according to the invention further comprises, between (E) the chemical softening step and (G) the reverse osmosis step, one or more of the following additional steps (EG):

(EG 1) activated carbon adsorption: using active carbon to carry out adsorption treatment on the softened sewage (mainly used for adsorbing COD impurities);

(EG 2) ion exchange treatment: neutralizing the softened sewage before ion exchange treatment (to pH =7 ± 0.5, for example, neutralizing with hydrochloric acid), and then performing ion exchange treatment on the sewage by using ion exchange resin to adsorb trace calcium and magnesium ions in the sewage, so as to further reduce the hardness of the sewage, for example, to make the total hardness of the effluent of the ion exchange equipment about 0.1mg/L;

and/or the presence of a gas in the gas,

(EG 3) carbonate and bicarbonate removal (abbreviated as "decarbonization"): CO is formed by adding hydrochloric acid to the softened effluent in a carbonate and bicarbonate removal plant or decarboniser (typically a water basin) ₂ Removing HCO from gas and alkali metal chloride (NaCl and KCl) ₃ ^- 、CO ₃ ^2- Ions so as to prevent the subsequent evaporator from generating scaling risk after long-time operation, reduce the bubbling degree of the evaporator and reduce the content of miscellaneous salt in the finally produced industrial salt;

and, the order of the following intermediate steps may be any order; (F1) Filtration, (F2) ultrafiltration, (EG 1) activated carbon adsorption, (EG 2) ion exchange treatment and (EG 3) removal of carbonate and bicarbonate.

The use of one or more of these additional steps (EG 1), (EG 2) and (EG 3) is determined based on the results of the detection of the wastewater.

The intermediate steps can be in any order, which is due to the fact that the previous steps (B) and (D) remove fluorine and silicon impurities, and the influence of the fluorine and silicon impurities on the subsequent process is greatly reduced.

Preferably, the (EG 1) activated carbon adsorption step is before or after the (F1) filtration or multimedia filtration step. More preferably, the (EG 1) activated carbon adsorption step is after the (F1) filtration or multimedia filtration step and before the (F2) ultrafiltration step, i.e. step (EG 1) is between step (F1) and step (F2).

(EG 1) activated carbon adsorption step (A) as a complement to the electrochemical impurity removal step (B) for removing organic and inorganic polymers in the wastewater and impurities that could not be removed in the previous step, and also for decoloring, sterilizing, and deodorizing. The active carbon can adsorb and remove residual macromolecular organic matters in water. An adsorption column with activated carbon packing, preferably a vertical adsorption column with a fixed bed of activated carbon, can be used. The activated carbon adsorption method can adsorb organic polymers (such as polyacrylamide as a coagulant), inorganic polymers and heavy metals from sewage, and also adsorb small amounts of magnesium oxide and calcium oxide microparticles. Preferably, 2 or more activated carbon adsorption columns are used in parallel.

(EG 2) ion exchange treatment step to further remove the trace amount of Ca present in the wastewater ²⁺ 、Mg ²⁺ Ions, yielding a sewage with further reduced overall hardness. Preferably, a resin adsorption column having a fixed bed layer of an ion exchange resin is used. Preferably, 2 or more resin adsorption columns are used in parallel. The resin adsorption tower can remove insoluble impurities accumulated inside the resin adsorption tower by back-flushing with pure water. Firstly, washing with hydrochloric acid solution 2-3 times of the volume of resin, washing with pure water to neutrality, then washing with sodium hydroxide solution 2-3 times of the volume of resin, washing with pure water to neutrality, wherein the regenerated liquid generated after resin regeneration mainly contains sodium chloride and a small amount of calcium chloride and magnesium chloride, the mixed solution can be further chemically de-hardened to obtain calcium magnesium type precipitate and sodium chloride solution, and after solid-liquid separation, evaporating the sodium chloride solution to obtain pure water and sodium chloride solid.

The ion exchange resin is preferably an ion exchange resin capable of selectively adsorbing calcium and magnesium ions under high salt conditions, and preferably an ion exchange resin having a chelating action (more preferably a chelating macroporous weakly acidic ion exchange resin). The ion exchange resin is generally selected according to the type of wastewater. More preferably, a double chelate type ion exchange resin is used, or a combination of two single chelate type resins is used.

Preferably, the above method according to the present invention further comprises the following step after the (G) reverse osmosis step: (H) nanofiltration membrane salt separation: use of nanofiltration membranes (i.e. nanofiltration membranes) for Concentrated Water (CW) from a reverse osmosis step ₁ ) Subjecting to salt separation treatment, i.e. separating sulfate and chloride ions to obtain Concentrated Water (CW) containing sodium sulfate ₂ ) And water of production (CW) containing chloride salt ₃ )。

The core original piece of the nanofiltration membrane salt separation device is a nanofiltration membrane, the aperture of the nanofiltration membrane is more than 1nm, generally 1-2nm, and experiments prove that Na is arranged on the concentrated water side of the nanofiltration membrane ₂ SO ₄ The retention rate can reach more than 98 percent, and the water yield of the produced water on the other side can reach about 85 percent.

Preferably, the content of other salt substances in the sewage is controlled before the sewage enters the NF nanofiltration membrane so as to ensure that the obtained industrial-grade NaCl and Na ₂ SO ₄ The purity of (2).

Generally, 6-9L (such as 7.5L) of concentrated water can be obtained from 100L of sewage after reverse osmosis treatment. After the reverse osmosis, the obtained concentrated water is further enriched in impurities (such as COD, ca, mg, F and Si). Therefore, the concentrated water needs to be pretreated before nanofiltration.

Therefore, preferably, the above method according to the present invention further comprises the following steps after the (G) reverse osmosis step and before the (H) nanofiltration membrane salt separation step:

(H ₀ ) Pretreatment before nanofiltration: with or without detection of Concentrated Water (CW) ₁ ) In the case of (A), the wastewater is subjected to a pretreatment before nanofiltration, said (H) ₀ ) The pretreatment step before nanofiltration is one or two or more of the following treatments: 1) Performing the above-mentioned electrochemical treatment (B) again; 2) The above-described (F1) filtration treatment was performed again: using filters (e.g. conventional filters, preferably ceramic membrane filters or multi-media filters)) Filtering the sewage to separate and remove suspended matters or particulate matters (with micron-sized sizes) in the sewage; 3) The above-mentioned (F2) ultrafiltration treatment was performed again: subjecting the wastewater to ultrafiltration using an ultrafilter (preferably, a ceramic membrane ultrafiltration device, such as a ceramic flat membrane ultrafiltration device); 4) Performing the above-mentioned (EG 1) activated carbon adsorption treatment again; and, 5) performing the above-described (EG 2) ion exchange treatment again. When two or more of the above steps are used simultaneously, the order of the steps may be in any order, i.e., the order may be reversed. These steps are selected according to the concentrate (i.e. concentrate CW) to be subjected to nanofiltration ₁ ) Is determined from the results of the contaminant detection. Since the amount of concentrate to be pretreated is small, corresponding equipment with less processing capacity (i.e., miniaturized equipment) can be used in these steps.

Preferably, the above method according to the present invention further comprises the steps of: (I) evaporation treatment: for Concentrated Water (CW) containing sodium sulfate ₂ ) (hardness about 0.5-2 mg/L) to obtain industrial-grade sodium sulfate; and/or, for water (CW) containing chloride salts (e.g., naCl or KCl) ₃ ) (hardness about 0.1-0.3 mg/L) to obtain technical grade chloride salt (such as NaCl or KCl). Wherein the evaporated condensed water is recycled as reuse water.

Preferably, the above method according to the present invention further comprises the steps of: (A) sewage pretreatment: and carrying out deslagging treatment on the high-concentration sewage. Preferably, (a) the sewage pretreatment step includes the substeps of: air floatation treatment: in an air floatation device with an air floatation sewage tank, air is introduced into sewage to carry out air floatation treatment, and coarse fiber and granular substances in the form of scum are removed by a physical method. The air flotation treatment can reduce the load of the subsequent biochemical treatment step. The collected scum is conveyed to a sludge collection tank. Preferably, a flocculant, such as polyaluminum chloride, an iron-based flocculant, an aluminum-based flocculant or an iron-aluminum composite flocculant, is added to the sewage in the air flotation sewage tank of the air flotation device.

Depending on the type of effluent and the needs of the particular process, it may be determined whether pH adjustment is required in each step, as is also well known in the art. In addition, in each step, it is generally necessary to detect the impurity content of the wastewater or concentrate.

When sewage (W) ₀ ) Sulfate radical SO (e.g., wastewater from coal chemical industry) ₄ ^2- The content is ≥ 2g/L (e.g. 3g/L ≤ SO) ₄ ^2- The content is less than or equal to 50g/L, in particular less than or equal to 3.2g/L and less than or equal to SO ₄ ^2- The content is less than or equal to 45g/L, even less than or equal to 3.5g/L and less than or equal to SO ₄ ^2- Content ≤ 40 g/L), the method further comprises (1) a biological desulfurization step and optionally an anaerobic treatment step (i.e., subjecting the biologically desulfurized wastewater to anaerobic treatment in a UASB anaerobic reactor (upflow anaerobic sludge blanket, such as an anaerobic tower) before the (B) biochemical treatment step.

The above-mentioned (1) biological desulfurization step and optionally (2) anaerobic treatment step are immediately before the (B) step. When the above-mentioned method of the present invention includes (a) a sewage pretreatment step, the above-mentioned (1) step and optionally (2) step are after (a) the sewage pretreatment step.

The biological desulfurization tank is mainly used for culturing a microbial system mainly containing sulfate reducing bacteria, wherein the following chemical reactions mainly occur in the tank under the anaerobic condition:

8[H]+SO ₄ ^2- →H ₂ S↑+2H ₂ O+2OH ^- 。

in general, at SO ₄ ^2- And (C) after reaching less than or equal to 1500 or 1700mg/L, allowing the sewage to enter a UASB anaerobic treatment system at the rear end or the biochemical treatment system in the step (B).

The sulfate radical content in the sewage is reduced by adopting a biological desulfurization method, so that the generation of H with higher concentration in the later (B) biochemical treatment step is avoided ₂ And (4) S gas.

The sulfur-containing tail gas generated in the biological desulfurization tank and the optional anaerobic tail gas generated in the UASB reactor are collected and conveyed to a tail gas treatment device for treatment, and the treated tail gas is discharged after reaching the discharge standard.

Accordingly, according to a second embodiment of the present invention, there is provided a treatment system for high sulphate content, high COD value sewage, the treatment system comprising the following devices in the following order:

1) An air flotation device with an air flotation sewage tank;

2) Biological desulfurization pool (DS) ₀₁ ) And optionally a UASB reactor (DS) ₀₃ )；

3) The biochemical treatment device comprises a biochemical treatment tank comprising an anaerobic section and an aerobic section, wherein the number of the biochemical treatment tank in the anaerobic section and the number of the biochemical treatment tank in the aerobic section can be 1, 2, 3, 4 or 5 respectively and independently; and

4) An electrochemical decontamination system having an electrochemical treatment cell in which a sacrificial anode and an inert anode are used as a combined anode or an alloy material containing a sacrificial metal and an inert metal is used as a composite anode, and a dc voltage is supplied between the combined anode or the composite anode and a cathode from a dc power supply.

Preferably, the treatment system further comprises means in the following order:

5) The chemical softening reaction tank comprises a chemical softening section, a coagulation section and a precipitation section;

11 A reverse osmosis plant; and

12 Nanofiltration equipment with nanofiltration membranes;

and further comprising one or more of the following, arranged between 4) the chemical softening reaction tank and 10) the reverse osmosis plant, and arranged in any order:

6) A ceramic membrane filter or a multi-media filter, more preferably a multi-media filter comprising a quartz sand filter layer;

7) An activated carbon adsorption tower;

8) An ultrafilter, preferably a ceramic membrane ultrafiltration device, more preferably a ceramic flat membrane ultrafiltration device;

9) An ion exchange device filled with ion exchange resin; and

10 A plant or water tank for removing carbonate and bicarbonate.

Preferably, the sedimentation section comprises a high-efficiency sedimentation tank, the high-efficiency sedimentation tank consists of a reaction zone and a clarification zone, wherein the reaction zone comprises a mixed reaction zone and a plug flow reaction zone, and the clarification zone comprises an inlet pre-sedimentation zone, an inclined tube sedimentation zone and a concentration zone; preferably, the tube-chute packing is arranged in the tube-chute settling zone.

Preferably, the reverse osmosis apparatus comprises: a primary reverse osmosis device, a secondary reverse osmosis device, and optionally an ST reverse osmosis device or an electrodialysis device.

Generally, other processing equipment is also included between 3) the electrochemical decontamination system having an electrochemical processing cell and 4) the chemical softening reaction cell, including but not limited to: filtration equipment (e.g., ceramic membrane filters or multi-media filters); and/or an ultrafiltration device (e.g., a ceramic membrane ultrafiltration device).

The most preferred process and system of the present invention is a process and equipment arrangement in the order shown in fig. 6.

THE ADVANTAGES OF THE PRESENT INVENTION

1. Biological desulfurization treatment is carried out on the original sewage to avoid overhigh H in biochemical treatment ₂ S gas content poisons microorganisms.

2. The original sewage is subjected to biochemical treatment and electrochemical impurity removal treatment in sequence, wherein the biochemical treatment removes most COD (COD is less than or equal to 450 mg/L) in a low-cost and high-efficiency mode, and organic matters are prevented from carrying out F treatment ^- 、SiO ₃ ^2- Encapsulation and complexation of ions and heavy metal ions, and electrochemical treatment of (HF) n and (H) ₂ SiO ₃ ) n, etc. are dissociated (dissociates) with Ca existing in the sewage ²⁺ And Mg ²⁺ The precipitate is formed, so that most of fluorine and silicon impurities are removed, and the phenomenon that the micropores of various filtering membranes are frequently blocked due to the formation of hard scales in the subsequent process, which results in the shortening of the service life of filtering equipment, is avoided. The electrochemical treatment can further degrade organic matters such as benzene and heterocyclic compounds which are difficult to degrade in the biochemical treatment by generating active chlorine, thereby further reducing the COD of the sewage after the biochemical treatment to about 20, for example, in the range of 12-30 or 15-25. In addition, the effluent from the electrochemical treatment cell can reach a total hardness of 20-78ppm, with a COD of around 20, for example between 12-30 or 15-20.

3. During the electrochemical treatment process, when the pH value of the sewage in the electrochemical treatment tank is adjusted to be within the range7.2-13.5, preferably in the range of 9-13.2, more preferably in the range of 10-13, more preferably in the range of 10.5-12.5, more preferably in the range of 11-12, and maintaining the total hardness of calcium and magnesium in the effluent of the cell above 80mg/L, preferably above 100 or 150 or 200 or 300mg/L, allows for the ideal removal of silicon and fluorine-based impurities. In particular, high Ca content is maintained by adding water-soluble calcium and magnesium salts (e.g., calcium chloride and magnesium chloride) to the wastewater in the treatment tank during electrochemical treatment ²⁺ Or Mg ²⁺ With SiO ₃ ^2- In a molar ratio of (a). The inventors have found through experiments that the addition of magnesium chloride to the contaminated water results in a much better removal of fluorine, silicon-based impurities than the addition of calcium chloride to the contaminated water, i.e. silicate and fluoride ions are removed more thoroughly despite the addition of a smaller amount of magnesium chloride.

4. Removing most of calcium and magnesium ions by an electrochemical method so as to enable the effluent of the electrochemical treatment tank to reach the total hardness of 20-78ppm, achieving the outstanding effects of reducing the hardness by more than 99 percent and completely removing heavy metal ions, but still having trace SiO in the effluent ₃ ^2- And F ^- (although their content is almost negligible). Therefore, it is preferable to maintain the total hardness of calcium and magnesium in the effluent of the electrochemical treatment tank to be higher than 80mg/L, so that silicon, fluorine-based impurities and heavy metal ions are completely removed in the electrochemical treatment tank, and at the same time, calcium and magnesium ions are completely removed through two steps, i.e., electrochemical treatment and chemical softening, and trace amounts of calcium and magnesium ions remaining in the wastewater are completely removed by subsequent treatment, e.g., ion exchange.

5. By adding inorganic alkali (such as Na) to the sewage in a chemical softening reaction tank ₂ CO ₃ And/or NaOH), further removing the remaining Ca ²⁺ And Mg ²⁺ Ions.

6. Before the sewage is subjected to nanofiltration, the impurity type of the concentrated sewage is detected, and the corresponding type of pretreatment is adopted, so that the inlet water of the nanofiltration equipment does not contain fluorine, silicon, calcium and magnesium, and does not contain various heavy metals.

7. There is a relevant relationship among the various steps in the sewage treatment process, so-called "moving the whole body by pulling". The invention provides the optimized sewage purification process shown in the figure 6, and has the advantages of lowest cost, highest efficiency, best technical effect and zero discharge of sewage.

Drawings

FIG. 1 is a schematic diagram of the operation principle of the electrochemical impurity removal system of the present invention.

1201: an electrochemical impurity removal reaction tank; 1201a: an anode plate (sacrificial anode and inert anode; or composite anode); 1201b: a negative plate or bipolar plate; 1201c: a three-dimensional filler; 1201d: a water inlet; 1201e: an air inlet; 1201f: a porous air intake pipe (or aeration pipe); 1201g: a water outlet; 1201h: a sewage draining port; 1201i: a reaction tank cover plate; 1202: a sedimentation and clarification tank; 1203: a power supply (pulse adaptive power supply); 1204: a water inlet pump; 1205: an air pump.

FIG. 2 is a front (longitudinal) cross-sectional view of an electrochemical decontamination system of the present invention.

1201j: sediment discharge port equipped with solenoid valve (automatic sediment discharge).

FIG. 3 is a top view of the anode and cathode arrangement in the electrochemical treatment cell of the electrochemical decontamination system of the present invention.

Fig. 4 is a transverse perspective view of the anode and cathode arrangement.

FIG. 5 is a flow chart of wastewater treatment used in example 1 of the present invention.

FIG. 6 is a flow chart of wastewater treatment used in example 4 of the present invention.

1: a high concentration sewage tank; 2: a water collecting tank; 3: a distribution tank; 4: (first) a regulating reservoir; 5: an air floatation device; 6: a water cooling tower; 7: a middle water tank; 8: a biochemical A section (denitrification hydrolysis tank); 9: a biochemical O section (aerobic section); 10: an MBR membrane tank; 11: an MBR water producing tank; 12: an electrochemical impurity removal system; 13: (second) a regulating reservoir; 14: a softening reaction tank; 15: a high-efficiency sedimentation tank; 16: a multi-media filter; 17: an activated carbon adsorption tank; 18: a ceramic membrane ultrafilter; 19: an ion exchange resin adsorption unit; 20: a decarbonizer (pool of carbonate removed water); 21: a reverse osmosis water inlet tank; 22: a first-stage reverse osmosis device; 23: secondary reverse osmosis equipment; 24: (ii) ST reverse osmosis equipment; 25: a super-concentration concentrated water tank; 26: pre-treatment equipment before nanofiltration; 27: a nanofiltration membrane; 28: a nanofiltration concentrated water tank; 29: a sodium sulfate evaporator; 30: a rake dryer; 31: nano-filtering to produce a water tank; 32: a sodium chloride evaporator; RWP: a reuse water tank; SCZ: a sludge collection tank; WT: a sewage treatment station; WR: a recycling water treatment station; w1: MBR water production; w2: and (4) sewage after electrochemical treatment.

W ₀₁ : high-concentration sewage; w ₀₂ : low-concentration sewage; w is a group of ₀₃ : mixing the sewage; w ₀₄ : plate-frame press filtration water (derived from plate-frame press filtration operation of sludge); RW (R-W) ₀₁ : cleaning and draining the circulating water; RW (RW) ₀₂ : draining water from the boiler; RW (R-W) ₀₃ : draining water from a water purifying station; RW (R-W) ₀₄ : circulating water (effluent) of a sewage treatment station reaching the standard.

Fig. 7 is a structural view of a hexagonal honeycomb packing made of PE as a chute packing.

1501: and (5) filling inclined pipes.

Fig. 8 is an integrated apparatus of softening-coagulating-high efficiency precipitation of the present invention.

M: a motor (motor); PAM: polyacrylamide. 14: a softening tank (14) and a coagulation tank (14 a); 15: high-efficiency sedimentation tank (or called as high-efficiency sedimentation tank). The sludge is dewatered after being discharged from the sedimentation tank and then is transported out for treatment.

Fig. 9 is a partial top view showing the arrangement of the fluidic plates, anode, and cathode in an electrochemical treatment cell.

1201k: a deflector (or water barrier).

FIG. 10 is a flow diagram of a biological desulfurization process.

DS01: a biological desulfurization tank; DS02: a desulfurization intermediate water tank; DS03: UASB reactors (i.e., upflow anaerobic sludge blanket); DS04: a tail gas treatment system.

Detailed Description

The present invention will be described in further detail with reference to the following examples, but the present invention is not limited to these examples.

The apparatuses used in the examples are those generally used in the art and commercially available on the market unless otherwise specified.

For the commercially available processing apparatus used in each step, when the processing capacity of a single processing apparatus is low, the parallel use of two or more apparatuses may be considered.

1. Raw materials and reagents

Ion exchange resin 1: feilong brand D463 aminocarboxylic acid chelate resin from Zibo David Chemicals Co.

Ion exchange resin 2: zibo Dong Daochong brand D116 weakly acidic cation exchange resin from chemical Co.

2. Test method

Other impurities can be measured according to Chinese national standard GB 8538-2016.

3. Sewage to be treated

Raw wastewater (W) used in examples 1 to 5 and comparative examples 1 and 2 of the present application ₀ ) Derived from a coal chemical plant in Yangquan City of Shanxi province in China. Ethylene glycol is produced from coal in the plant. The process water is tap water.

Factory sewage pipe network sewage (mainly domestic sewage and workshop cleaning water) (mixed sewage W) ₀₃ ) (sludge) plate and frame filter press discharge water (W) ₀₄ ) Gasification process sewage (workshop low-concentration sewage W) ₀₂ ) Is converged and collected in a collecting tank (2) of a sewage treatment station, and then the converged sewage and the sewage of the process for preparing the glycol by the coal (high-concentration sewage W in a workshop) ₀₁ ) Mixed in a distribution tank, and the mixed sewage is collected in a (first) regulating tank (4) for storage. The waste water collected in the conditioning tank (4) is referred to as raw waste water (W) in the examples ₀ ). Additionally, the water is drained (RW) by circulating water ₀₁ ) Boiler drainage (RW) ₀₂ )、Water purification station drainage (RW) ₀₃ ) And the circulating water up to standard (RW) obtained after the treatment of the sewage treatment station ₀₄ ) The mixed water enters a (second) regulating tank (13) of a reuse water station, and the water obtained after treatment in the reuse water station is conveyed back to each system of the plant area for reuse.

The sewage treatment station and the reuse water station have the following sewage water volumes:

mixing 8-18m ³ H (e.g. 15 m) ³ Flow/h) of high-concentration waste water (W) ₀₁ ) Collected in a high-concentration sewage tank (1). In addition, 40-60m ³ H (e.g. 50 m) ³ Flow rate of low concentration waste water (W) ₀₂ )、60-100m ³ Flow rate/h (e.g. 83 m) ³ H) mixed sewage (W) ₀₃ ) And 1-3m ³ H (e.g. 2 m) ³ Flow/h) plate and frame press-filtered water (W) ₀₄ ) Are collected in a collecting basin (2). The sewage in the high-concentration sewage tank (1) and the sewage in the water collecting tank (2) are converged in a distribution tank (3), and then the mixed sewage is conveyed to a first regulating tank (4) to be stored as raw sewage.

The amount of treated water at the sewage treatment plant was about 150m ³ /h。

The amount of treated water in the reuse water station is about 400m ³ H is used as the reference value. Wherein the standard circulating water (effluent) of the sewage treatment station is about 150m ³ Per hour, the clean water discharge of the circulating water is about 200m ³ H, the water station discharge is about 40m ³ H and boiler discharge of about 10m ³ H is the ratio of the total weight of the catalyst to the total weight of the catalyst. This water is collected in a second conditioning tank (13).

In the adjusting tank (4), raw (raw) sewage (W) ₀ ) The contents of various impurities in the formula are as follows:

chemical Oxygen Demand (COD): 4510mg/L; ammonia Nitrogen (NH) ₃ -N): 250mg/L; total Phosphorus (TP): 4mg/L; ca ²⁺ ：971.4mg/L；Mg ²⁺ :502.3mg/L. Suspended matters: 510mg/L. The contents of other impurities were: fe ³⁺ +Fe ²⁺ :18.4ppm (i.e., mg/L); cu (copper) ²⁺ ：3.2ppm；Ni ²⁺ ：3.7ppm；Cd ²⁺ ：4.7ppm；Zn ²⁺ ：4.4ppm；Hg ⁺ +Hg ²⁺ ：3.2ppm；Cr ³⁺ ：3.2ppm；Mn ²⁺ ：3.8ppm；F ^- ：5.1ppm；SiO ₃ ^2- ：20.2ppm；S ^2- ：1.5ppm；AsO ₄ ^3- +AsO ₃ ^3- ：1.7ppm；PO ₄ ^3- :11.4ppm. Wherein Mg is ²⁺ With SiO ₃ ^2- Is 77.7, 1,Ca ²⁺ And F ^- Is 90.

In addition, the contents of other ions are as follows: na (Na) ⁺ :651.2ppm (i.e., mg/L); k ⁺ ：29.7ppm；SO ₄ ^2- ：687.6ppm；Cl ^- ：3451.6ppm；CO ₃ ^2- ：360ppm。

4. Electrochemical impurity removal system

In examples 1, 2, 4 and 5 and comparative examples 1 and 2, the anode-to-cathode spacing in the electrochemical treatment cell (sacrificial and inert) was 18cm; 8 iron metal plate anodes, 8 titanium metal plate anodes and 15 graphite cathode plates are arranged in total. The dc voltage typically varies in the range of 10-30V. The current density is generally 10mA/cm ³ To 60mA/cm ³ In between. If necessary, a flow guide plate (or water blocking plate) 1201k is provided in the electrochemical treatment cell, as shown in fig. 9.

Example 1

The process flow is shown in figure 5. The apparatus shown in fig. 1-4 is used. Raw (raw) sewage (W) ₀ ) Is about 150m ³ Therefore, the throughput of the equipment at each step should meet this throughput requirement. In addition, since the average residence time of wastewater in each biochemical treatment tank is about 5 to 7 hours (generally about 6 hours), the capacity of each biochemical treatment tank should be 150m as the above-mentioned average flow rate ³ More than 7 times of the volume of the solution to 1300m ³ 。

The flow rate of the raw sewage to be treated is 150m ³ H is used as the reference value. The raw sewage is conveyed to an air flotation device (5) with an air flotation water tank, and polyaluminium chloride is added into the raw sewage to be used as a flocculating agent. Scum is formed on the surface of the air flotation tank by introducing air into the raw sewage (namely, aeration), and the scum is collected and sent to a sludge collection tank (SCZ). The sewage (COD = 4010) after the air floatation treatment is conveyed to a water cooling tower (6) for cooling and then conveyedTo the intermediate water basin (7). The temperature of the inlet water of the biochemical system is controlled to be less than or equal to 35 ℃.

Raw sewage (W) in the intermediate water tank (7) ₀ ) The sewage is conveyed to 2 anaerobic sections (8) and 2 aerobic sections (9) of a biochemical treatment tank for biochemical treatment. The average residence time of the wastewater in each biochemical treatment tank was about 6 hours. Aerobic bacteria include escherichia coli, bacillus subtilis, and pichia pastoris (number about 1.

Biochemically treated sewage (COD is about 100, ammonia nitrogen content is 10 mg/L) is separated in an MBR membrane tank (10) by using an MBR membrane, and the separated sludge is sent to a sludge collection tank. MBR produced water (W) ₁ ) (COD is about 50, ammonia nitrogen content is 4 mg/L) enters an electrochemical impurity removal system (12).

With NaOH and Na ₂ CO ₃ (weight ratio 2. The direct current power supply is a pulse self-adaptive power supply. And gradually increasing the voltage between the iron metal anode plate and the titanium metal anode plate and the cathode until detecting that active chlorine is generated in the sewage (according to GB/T5750.11-2006), and then maintaining the voltage to carry out electrochemical treatment on the sewage. During the electrochemical treatment, the air pump is activated to ventilate the wastewater through the air inlet pipe (1201 f) to form a large amount of air bubbles. And fishing the floating materials on the surface of the sewage, periodically opening an electromagnetic valve at the bottom of the electrochemical treatment tank to discharge the sediments, and conveying the sediments to a sludge collection tank.

For the effluent (W) of the electrochemical impurity removal system (12) ₂ ) The detection is carried out, and the content of various impurities is as follows:

F ^- the content is as follows: 0.14ppm. SiO 2 ₃ ^2- The content is as follows: 0.28ppm, which indicates SiO ₃ ^2- The content is reduced by 98.6%.

Chemical Oxygen Demand (COD): 22.9mg/L; ammonia Nitrogen (NH) ₃ -N): 0.35mg/L; total Phosphorus (TP): 0.15mg/L. The total hardness of calcium and magnesium is 74mg/L. The contents of other metal impurities are: fe ³⁺ +Fe ²⁺ :0.03ppm (i.e., mg/L); heavy metal ion Cu ²⁺ 、Ni ²⁺ 、Cd ²⁺ 、Zn ²⁺ 、Hg ⁺ +Hg ²⁺ 、Cr ³⁺ And Mn ²⁺ All contents of (a) are below the detection limit. S. the ^2- 、PO ₄ ^3- And AsO ₄ ^3- +AsO ₃ ^3- All contents of (a) are below the detection limit.

Example 2

Example 1 was repeated except that MgCl was added to the wastewater at a concentration of 3M at the front end of the electrochemical treatment cell ₂ The solution was added in an amount of 0.2L per 100L of wastewater.

F ^- the content is as follows:<0.1ppm。SiO ₃ ^2- the contents are as follows: 0.1ppm, which indicates SiO ₃ ^2- The content was reduced by about 99.5%.

Chemical Oxygen Demand (COD): 21.5mg/L; ammonia Nitrogen (NH) ₃ -N): 0.32mg/L; total Phosphorus (TP):<0.1mg/L. The total hardness of the calcium and the magnesium is 81mg/L. The contents of other metal impurities are: fe ³⁺ +Fe ²⁺ :0.04ppm (i.e., mg/L); heavy metal ion Cu ²⁺ 、Ni ²⁺ 、Cd ²⁺ 、Zn ²⁺ 、Hg ⁺ +Hg ²⁺ 、Cr ³⁺ And Mn ²⁺ All contents of (a) are below the detection limit. S ^2- 、PO ₄ ^3- And AsO ₄ ^3- +AsO ₃ ^3- All contents of (a) are below the detection limit.

The above results show that fluorine (F) can be removed ideally by adding magnesium chloride to the wastewater to maintain the total hardness of the effluent of the electrochemical treatment cell above 80mg/L ^- ) And Silicon (SiO) ₃ ^2- )。

Example 3

Example 1 was repeated except that MgCl was added to the wastewater at a concentration of 3M at the front end of the electrochemical treatment cell ₂ The solution was added in an amount of 1.5L per 100L of wastewater.

F ^- the content is as follows: below the detection limit. SiO 2 ₃ ^2- The contents are as follows: below the detection limit, this indicates that SiO ₃ ^2- The content is reduced by at least 99.9%.

Chemical Oxygen Demand (COD): 20.7mg/L; ammonia Nitrogen (NH) ₃ -N): 0.30mg/L; total Phosphorus (TP): below the detection limit. The total hardness of the calcium and the magnesium is 325mg/L. The contents of other metal impurities are: fe ³⁺ +Fe ²⁺ :0.03ppm (i.e., mg/L); heavy metal ion Cu ²⁺ 、Ni ²⁺ 、Cd ²⁺ 、Zn ²⁺ 、Hg ⁺ +Hg ²⁺ 、Cr ³⁺ And Mn ²⁺ All contents of (a) are below the detection limit. S ^2- 、PO ₄ ^3- And AsO ₄ ^3- +AsO ₃ ^3- All contents of (a) are below the detection limit.

The above results show that the addition of magnesium chloride to the wastewater greatly increases Mg ²⁺ With SiO ₃ ^2- And maintaining the total hardness of the effluent of the electrochemical treatment cell higher than 300mg/L, enabling the complete removal of fluorine (F) ^- ) And Silicon (SiO) ₃ ^2- )。

Example 4

Example 1 was repeated except that 8 aluminum metal plate anodes were used as sacrificial anodes, 8 titanium metal plates were used as inert anodes, and 15 graphite plates were used as cathodes in the electrochemical treatment cell. The distance between the anode and the cathode is 18cm. The dc voltage typically varies in the range of 10-30V. The current density is generally 10mA/cm ³ To 60mA/cm ³ In between.

Effluent (W) to an electrochemical decontamination system (12) ₂ ) The detection is carried out, and the content of various impurities is as follows:

F ^- the content is 0.15ppm. SiO 2 ₃ ^2- The content is as follows: 0.7ppm, which indicates SiO ₃ ^2- The content was reduced by about 96.5%.

Chemical Oxygen Demand (COD): 22.9mg/L; ammonia Nitrogen (NH) ₃ -N): 0.29mg/L; total Phosphorus (TP): 0.18mg/L. The total hardness of the calcium and the magnesium is 60mg/L. The contents of other metal impurities are: fe ³⁺ +Fe ²⁺ :0.02ppm (i.e., mg/L); heavy metal ion Cu ²⁺ 、Ni ²⁺ 、Cd ²⁺ 、Zn ²⁺ 、Hg ⁺ +Hg ²⁺ 、Cr ³⁺ And Mn ²⁺ All the contents of (A) are lower than the detection limit. S. the ^2- 、PO ₄ ^3- And AsO ₄ ^3- +AsO ₃ ^3- All contents of (a) are below the detection limit.

Comparative example 1

Example 1 was repeated except that the order of biochemical treatment and electrochemical treatment was reversed, i.e., the electrochemical impurity removal step was performed first, then the sewage was separated, and then the sewage was subjected to the biochemical treatment step.

Detection, sewage after biochemical treatment:

the Chemical Oxygen Demand (COD) was 1521mg/L, which indicates that Cl was generated in the previous electrochemical treatment ₂ And hypochlorite salts, these active chlorides inhibiting bacterial growth in subsequent biochemical processes. The total hardness of calcium and magnesium is 658mg/L. In addition, F ^- ：2.5ppm；SiO ₃ ^2- The content is as follows: 7.8ppm; cr (chromium) component ³⁺ ：1.2ppm；Cd ²⁺ ：2.1ppm；Fe ³⁺ +Fe ²⁺ :2.5ppm. This indicates that the undegraded bulk organic material encapsulates or complexes these ions and does not adequately form a precipitate.

Example 5

The process flow is shown in figure 6. The apparatus shown in fig. 1-4 and fig. 7 and 8 is used.

The previous procedure was the same as in example 1 except that a subsequent treatment step was added after the electrochemical removal step and that MgCl was added to the effluent from the electrochemical treatment cell at a concentration of 3M ₂ The solution was added in an amount of 2L per 100L of wastewater.

An iron metal plate anode was used as the sacrificial anode, a titanium metal plate was used as the inert anode, and a graphite plate was used as the cathode in the electrochemical treatment cell.

And (3) regulating the pH value of the sewage in the electrochemical impurity removal tank to be about 11.5 by using NaOH.

F ^- the content is below the detection limit. SiO 2 ₃ ^2- The contents are as follows:below the detection limit, this indicates that SiO ₃ ^2- The content is reduced by at least 99.9%. Chemical Oxygen Demand (COD): 18.5mg/L; ammonia Nitrogen (NH) ₃ -N): 0.25mg/L; total Phosphorus (TP): 0mg/L.

The total hardness of calcium and magnesium is up to 651mg/L.

The contents of other metal impurities are: fe ³⁺ +Fe ²⁺ :0.02ppm (i.e., mg/L); heavy metal ion Cu ²⁺ 、Ni ²⁺ 、Cd ²⁺ 、Zn ²⁺ 、Hg ⁺ +Hg ²⁺ 、Cr ³⁺ And Mn ²⁺ All contents of (a) are below the detection limit. S. the ^2- 、PO ₄ ^3- And AsO ₄ ^3- +AsO ₃ ^3- All the contents of (A) are lower than the detection limit.

Circulating water (outlet water) reaching the standard of a sewage treatment station (the flow rate is about 150 m) ³ H), clean discharge of circulating water (flow rate about 200 m) ³ H), clean water station discharge (flow rate about 40 m) ³ H), and boiler drain (flow rate about 10 m) ³ H) collected in a second regulating reservoir (13). The quantity of water to be treated in the regulating reservoir (13) of the station for reusing water is about 400m ³ /h。

Effluent (W) of electrochemical decontamination system (12) ₂ ) Further sent to a softening tank (14) of a softening-coagulating-efficient sedimentation integrated device (integrated device) (14 and 15), and simultaneously the circulating water in the regulating tank (13) is sent to a softening reaction tank (14). Detecting the total hardness of the sewage in the softening reaction tank, and adding sufficient sodium carbonate and sodium hydroxide into the sewage in the softening reaction tank for softening treatment so that the sodium carbonate and Ca are mixed ²⁺ To at least 1.05 and sodium hydroxide to Mg ² ⁺ To at least 1.03. The total hardness of the chemically softened sewage was reduced to about 2.5mg/L.

The sewage in the softening tank overflows to a flocculation tank (14 a). Adding a flocculating agent PAM (polyacrylamide) to the sewage in the flocculation tank (14 a). The sewage in the flocculation tank (14 a) overflows into the high-efficiency sedimentation tank (15) for sedimentation, and forms larger-sized flocculation particles under the flow pushing action of the stirring equipment. The sediment is periodically drained from the bottom of the sedimentation basin (15). Wherein the inclined tube filler 1501 in the high-efficiency sedimentation tank (15) is hexagonal honeycomb filler made of polyethylene (as shown in figure 7).

The total hardness of the effluent of the high-efficiency sedimentation tank (15) is reduced to about 2.5mg/L. The effluent of the sedimentation tank (15) is sent to a tower-type multi-media filter (16) for filtration so as to completely remove suspended matters in the sewage. The multi-media filter (16) comprises an activated carbon filter layer, a quartz sand filter layer and a porous ceramic particle filter layer.

The effluent of the multi-medium filter (16) is conveyed to an activated carbon adsorption tower (17) for adsorption to remove trace COD impurities and [ FeF ₆ ] ^3- Ions. Simultaneously, the sewage is decolored, so that the sewage becomes clear.

The effluent of the activated carbon adsorption tower (17) is conveyed to a ceramic membrane ultrafilter (18) for ultrafiltration, and fine particles in the effluent are removed.

The effluent from the ceramic membrane ultrafilter (18) (total hardness approximately 2.5mg/L, turbidity < 0.1NTU, COD 15mg/L) was, after neutralization to pH7 with hydrochloric acid, fed to a column-type ion exchange unit (19), in which the ion exchange resin charged was a Feilong brand D463 aminocarboxylic acid chelate resin from Tbodong chemical GmbH. The total hardness of the effluent after ion exchange was determined to be reduced to about 0.1mg/L.

The effluent of the tank-type ion exchange unit (19) is sent to a decarbonizer (20) (water tank) and hydrochloric acid is added to the effluent to form CO ₂ Gas and alkali chlorides (NaCl and KCl), removing HCO ₃ ^- 、CO ₃ ^2- Ions. Thereafter, the wastewater in the decarbonizer (20) (water tank) is transferred to a reverse osmosis water intake tank (21).

Sewage (total hardness about 0.1mg/L, naCl + Na) in reverse osmosis water intake pool (21) ₂ SO ₄ 2900 mg/L) was fed to a primary reverse osmosis apparatus (22) equipped with an aromatic polyamide composite membrane for primary reverse osmosis. The produced water of the primary reverse osmosis is fed to a reuse water tank (RWP), and the resulting concentrated water (total hardness about 0.4 mg/L) is fed to a secondary reverse osmosis apparatus (23) equipped with an aromatic polyamide composite membrane to perform secondary reverse osmosis. The produced water of the second-stage reverse osmosis is transmittedSent to a reuse water tank (RWP), and the resulting concentrated water (total hardness of about 0.8 mg/L) was sent to an ST reverse osmosis apparatus (24) equipped with a polyamide membrane for ST reverse osmosis. The ST reverse osmosis produced water is sent to a reuse basin (RWP) and the resulting Concentrated Water (CW) ₁ ) (Total hardness about 3.2mg/L, naCl + Na) ₂ SO ₄ Content of 87000 mg/L) is transferred to a super concentrated concentrate tank (25).

The first-stage reverse osmosis adopts a first-stage two-section process, the water inlet pressure is less than or equal to 1.4MPa, a booster pump is arranged between sections, and the water yield is controlled at 75 percent. The second-stage reverse osmosis adopts a first-stage two-section process, the water inlet pressure is less than or equal to 3.0MPa, a booster pump is arranged between sections, the water yield is controlled at 50%, and the produced concentrated water enters ST reverse osmosis. In ST reverse osmosis, the water inlet pressure is less than or equal to 6.0MPa, and the water yield is controlled at 75 percent.

By concentrating the Concentrated Water (CW) in a super concentrated concentrate tank (25) ₁ ) Detection was carried out in Concentrated Water (CW) ₁ ) With an enrichment of trace amounts of particulate impurities (macroions and COD) and a total hardness of up to about 3.2mg/L. Therefore, the dense water (CW) is required ₁ ) Carrying out pretreatment before nanofiltration: the ceramic membrane ultrafilter (18) is used again as a pretreatment device (26) before nanofiltration for Concentrated Water (CW) ₁ ) Ultrafiltration is carried out, and then the concentrated water after ultrafiltration is subjected to ion exchange treatment again by using a miniaturized ion exchange device (19). The ion-exchanged concentrate was again examined, no particulate impurities were detected, and the total hardness was about 0.3mg/L.

The concentrated water pretreated before nanofiltration is conveyed to nanofiltration membrane filtration equipment (27) provided with a polyamide nanofiltration membrane for nanofiltration, so that salt separation is realized. Nanofiltration concentrated water (total hardness of about 1.2 mg/L) is fed to a nanofiltration concentrated water tank (28) for storage, the concentrated water is fed to a sodium sulfate evaporator (29) for evaporation, the evaporated condensate water is fed to a reuse water tank (RWP), and the obtained crystals are detected and judged to be technical grade sodium sulfate based on their purity (purity >98.5 wt%). The obtained mixed salt mother liquor is conveyed to a rake dryer (30) for drying.

Nanofiltration product water (total hardness of about 0.2 mg/L) is fed to a nanofiltration product water tank (31) for storage, the product water is fed to a sodium chloride evaporator (32) for evaporation, the evaporated condensate water is fed to a reuse water tank (RWP), and the obtained crystals are detected and judged to be technical grade sodium chloride based on their purity (purity >98.9 wt%). The obtained mixed salt mother liquor is also conveyed to a rake dryer (30) for drying.

The small amount of mixed salt obtained in the rake dryer (30) is transported to a waste salt treatment station for post-treatment.

The concentrated water obtained after salt evaporation returns to the previous regulating tank or biochemical tank, so that the whole sewage treatment process realizes zero emission.

Example 6

Example 1 was repeated. Inorganic alkali (sodium carbonate and sodium hydroxide, weight ratio 2.

F ^- the content is as follows: 0.16ppm. SiO 2 ₃ ^2- The content is as follows: 0.9ppm, which indicates SiO ₃ ^2- The content was reduced by about 95.5%.

Chemical Oxygen Demand (COD): 23.8mg/L; ammonia Nitrogen (NH) ₃ -N): 0.42mg/L; total Phosphorus (TP): 0.15mg/L.

The total hardness of the calcium and the magnesium is 65mg/L. The contents of other metal impurities are: fe ³⁺ +Fe ²⁺ :0.05ppm ppm ppm (i.e., mg/L); heavy metal ion Cu ²⁺ 、Ni ²⁺ 、Cd ²⁺ 、Zn ²⁺ 、Hg ⁺ +Hg ²⁺ 、Cr ³⁺ And Mn ²⁺ All the contents of (A) are lower than the detection limit. S ^2- 、PO ₄ ^3- And AsO ₄ ^3- +AsO ₃ ^3- All the contents of (A) are lower than the detection limit.

The above data indicate that when water (W) is coming out ₂ ) When the total hardness of the alloy is lower (lower than 80 mg/L), siO is removed ₃ ^2- And F ^- The effect of (c) is also affected.

Comparative example 2

Example 5 was repeated except that (D) the electrochemical impurity removal process was omitted and the effluent obtained from the separation step (C) was directly subjected to the next chemical softening step (E).

The following is a comparison of the flushing and cleaning cycles of the various filtration apparatus of example 5 and comparative example 2:

	example 5	Comparative example 2
			Backwash cycle of ultrafiltration membrane	1 hour	40 minutes
Off-line chemical cleaning cycle for ultrafiltration membranes	1 month	12 days
			Backwash cycle of reverse osmosis membrane	24 hours	8 hours
Off-line chemical cleaning cycle for reverse osmosis membranes	3 months old	1 month
			Backwash cycle of nanofiltration membranes	24 hours	8 hours
Off-line chemical cleaning cycle of nanofiltration membranes	3 months old	1 month
			Service life of ceramic ultrafiltration membrane	For 10 years	For 3 years
Service life of reverse osmosis membrane	5 years old	2 years old
			Service life of nanofiltration membrane	For 3 years	1 year

Example 7 (Pre-desulfation)

During a period of time, the process water of the coal chemical plant adopts different underground water sources, so that the raw sewage (W) in the regulating tank (4) is generated ₀ ) The contents of the various impurities of (a) vary as follows:

chemical Oxygen Demand (COD): 4435mg/L; ammonia Nitrogen (NH) ₃ -N): 246mg/L; total Phosphorus (TP): 3.5mg/L; ca ²⁺ ：621.1mg/L；Mg ²⁺ :340.4mg/L. Suspended matters: 652mg/L. The contents of other impurities were: fe ³⁺ +Fe ²⁺ :19.6ppm (i.e., mg/L); cu ²⁺ ：3.3ppm；Ni ²⁺ ：3.5ppm；Cd ²⁺ ：4.2ppm；Zn ²⁺ ：4.7ppm；Hg ⁺ +Hg ²⁺ ：3.0ppm；Cr ³⁺ ：3.3ppm；Mn ²⁺ ：3.5ppm；F ^- ：5.6ppm；SiO ₃ ^2- ：22.5ppm；S ^2- ：1.6ppm；AsO ₄ ^3- +AsO ₃ ^3- ：1.7ppm；PO ₄ ^3- ：10.6ppm。

In addition, the contents of other ions are as follows: na (Na) ⁺ :1907.5ppm；K ⁺ ：118.3ppm；Cl ^- ：1772.7ppm；CO ₃ ^2- ：301.8ppm。

In particular, raw sewage (W) ₀ ) SO in (1) ₄ ^2- The content reaches 4100mg/L.

This example 7 is used to treat wastewater having a high sulfate content. Raw sewage (W) in the intermediate tank (7) ₀ ) Is similar to that of example 1 except that the sulfate content is higher.

Example 5 was repeated except that after the intermediate basin (7) and before the biochemical treatment (8), a biological desulfurization step was added (as shown in FIG. 10), which included the following substeps: (1) biological desulfurization: the raw sewage in the intermediate pool (7) is conveyed to a biological desulphurization pool (DS) ₀₁ ) In the method, sulfate reducing bacteria are used to treat raw sewage (W) under anaerobic conditions ₀ ) Biological desulfurization is carried out through biological reduction reaction, the retention time is 6 hours, and SO in the desulfurized sewage ₄ ^2- The content of the sewage reaches less than or equal to 1500mg/L, and the sewage is conveyed to another downstream desulfurization intermediate pool (DS) ₀₂ ) Storing; and (2) anaerobic treatment in a UASB anaerobic reactor: then, the sewage in the additional desulfurization intermediate pond is sent to a UASB anaerobic reactor (upflow anaerobic sludge blanket) (DS) ₀₃ ) Anaerobic treatment is carried out in the process, and the retention time is 6 hours. The anaerobic bacteria are bifidobacteria and clostridium butyricum (number about 1. Thereafter, the sewage is sent to a subsequent biochemical treatment tank (8).

Collecting sulfur-containing tail gas generated in the biological desulfurization tank and anaerobic tail gas generated in the UASB reactor, conveying the collected sulfur-containing tail gas and anaerobic tail gas to a tail gas treatment device for treatment, and discharging the treated tail gas after reaching the discharge standard.

In neither the anaerobic zone nor the aerobic zone of the biochemical treatment stage, a situation was observed in which the propagation of microorganisms was affected.

F ^- the content is below the detection limit. SiO 2 ₃ ^2- The content is as follows: below the detection limit.

Chemical Oxygen Demand (COD): 38.8mg/L; ammonia Nitrogen (NH) ₃ -N): 0.36mg/L; total Phosphorus (TP): below the detection limit.

The total hardness of calcium and magnesium is up to 587mg/L.

The contents of other metal impurities are: fe ³⁺ +Fe ²⁺ :0.02ppm (i.e., mg/L); heavy metal ion Cu ²⁺ 、Ni ²⁺ 、Cd ²⁺ 、Zn ²⁺ 、Hg ⁺ +Hg ²⁺ 、Cr ³⁺ And Mn ²⁺ All the contents of (A) are lower than the detection limit. S. the ^2- 、PO ₄ ^3- And AsO ₄ ^3- +AsO ₃ ^3- All contents of (a) are below the detection limit.

Claims

1. A method for treating sewage with high sulfate content and high COD value comprises the following steps:

(A) Pretreatment of sewage: carrying out deslagging treatment on high-concentration sewage; then the

(2) Optional anaerobic treatment: the sewage after biological desulfurization is treated in an UASB anaerobic reactor in an anaerobic manner,

(B) Biochemical treatment: let raw sewage (W) ₀ ) Biochemical treatment is carried out in a biochemical treatment tank; wherein the biochemical treatment process comprises one or more times of treatment of an anaerobic section and one or more times of treatment of an aerobic section;

wherein, raw sewage (W) ₀ ) SO of (A) ₄ ^2- The content is 2000-50000ppm, the Chemical Oxygen Demand (COD) is 4-10 g/L, and the total hardness of calcium and magnesium (Ca) ²⁺ +Mg ²⁺ ) Is 300ppm to 20000ppm, F ^- The content is 1ppm-500ppm, and the raw sewage (W) ₀ ) Middle Fe ³⁺ 、Fe ² ⁺ 、Cu ²⁺ 、Ni ²⁺ 、Cd ²⁺ 、Zn ²⁺ 、Hg ⁺ 、Hg ²⁺ 、Cr ³⁺ 、Pb ²⁺ Or Mn ²⁺ The content of each heavy metal cation in the heavy metal ion is more than or equal to 1ppm;

(C) Separation: separating the biochemically treated effluent, thereby removing solid impurities in the form of sludge, and obtaining a first stage of purified effluent (W1); and

(D) Electrochemical impurity removal: the first stage purified wastewater (W) ₁ ) Electrochemical treatment is carried out in an electrochemical treatment tank or in an electrochemical impurity removal system comprising the electrochemical treatment tank by applying direct current voltage between a combined anode or a composite anode and a cathode so as to remove ammonia nitrogen impurities, inorganic salts and COD, thereby obtaining second-stage purified sewage (W) ₂ )；

Wherein a sacrificial anode and an inert anode are used as a combined anode or an alloy material containing a sacrificial metal and an inert metal is used as a composite anode in an electrochemical treatment cell, and a wastewater (W) in the electrochemical treatment cell ₁ ) The content of alkali chloride is sufficient to allow the application of a DC voltage between the anode and the cathode in the wastewater (W) ₁ ) Can generate chlorine-containing oxidant on site; and

wherein a voltage (V) applied between an inert anode or a composite anode and a cathode as an electrode pair by a DC power supply is used ₁ ) Enough to cause the sewage (W) to flow ₁ ) In which a chlorine-containing oxidizing agent and optionally an oxygen-containing oxidizing agent can be generated in situ, while a voltage (V) is applied between a sacrificial anode or composite anode and a cathode as an electrode pair using a DC power supply ₂ ) Enough to make the metal simple substance of the sacrificial anode or the composite anode lose electrons and enter the sewage (W) in the form of metal cations ₁ ) Wherein the voltage (V) exerts a flocculating effect in the wastewater ₁ ) And voltage (V) ₂ ) The same or different;

wherein a plurality of anodes and a plurality of cathodes are alternately arranged or arranged in pairs in the electrochemical treatment cell, and 8 to 120 pairs of anodes and cathodes are used in the electrochemical treatment cell;

wherein the wastewater (W) in the electrochemical treatment tank ₁ ) The content of NaCl and KCl in the solution is 6Between 00mg/L and 70 g/L;

wherein the wastewater (W) purified in the first stage ₁ ) Adding inorganic alkali to adjust the sewage (W) ₁ ) To a pH in the range of 10-13, for sewage (W) ₁ ) Performing electrochemical treatment, and treating wastewater (W) requiring electrochemical treatment ₁ ) Under the condition of adding water-soluble magnesium salt and/or water-soluble calcium salt, the total hardness of calcium and magnesium of effluent of the electrochemical treatment pool is maintained to be higher than 100mg/L but lower than 900mg/L;

wherein iron or aluminum or an iron-aluminum alloy is used as the sacrificial anode when the sacrificial anode and the inert anode are used as the combined anode, or an iron-titanium alloy, an aluminum-titanium alloy or an iron-aluminum-titanium alloy is used as the combined anode when an alloy material containing the sacrificial metal and the inert metal is used as the combined anode;

(E) Chemical softening: second stage purified wastewater (W) ₂ ) Is transferred to a softening reactor through a pipe to the sewage (W) ₂ ) Adding inorganic alkali to further soften the sewage and obtaining third-stage purified sewage (W) ₃ )；

Wherein the (E) chemical softening step includes not only the following substeps:

(E1) Chemical softening: second stage purified wastewater (W) after electrochemical treatment ₂ ) Is conveyed into a softening reaction tank as a chemical softening section, and is passed through a wastewater (W) with or without detecting the hardness of the wastewater ₂ ) Inorganic alkali is added to further soften the sewage;

and further comprising one or both of the following sub-steps:

(E2) Coagulation: in the coagulation section, coagulation of calcium and magnesium salts is promoted by adding a coagulant to the chemically softened sewage, and, (E3) precipitation: in the sedimentation section, the sewage after the chemical softening treatment is sedimentated in a sedimentation tank; obtaining the third-stage purified sewage (W) ₃ ) (ii) a Wherein, in the E3) precipitation step, calcium salt and magnesium salt in the sewage are subjected to high-efficiency precipitation by using a high-efficiency precipitation tank; thereby obtaining third-stage purified sewage (W) ₃ )；

(F) And (3) filtering and separating: for cleaningThe sewage (W) thus treated ₃ ) Further filtering and separating to obtain fourth-stage purified sewage (W) ₄ )；

Wherein step (F) comprises one or both of the following substeps: (F1) filtering: filtering the sewage by using a filter, and separating and removing suspended matters in the sewage by filtering; and, (F2) ultrafiltration: subjecting the wastewater to ultrafiltration using an ultrafilter to remove suspended matter of micron-sized size;

(G) Reverse osmosis: subjecting the fourth stage purified effluent (W) from the preceding step ₄ ) Performing one or more stages of reverse osmosis treatment to obtain fifth-stage purified wastewater (W) as reuse water ₅ ) While obtaining a Concentrated Water (CW) containing NaCl and sodium sulfate ₁ )；

(H) And (3) separating salt by using a nanofiltration membrane: subjecting the concentrated water (CW 1) from the reverse osmosis step to a salt separation treatment using a nanofiltration membrane, i.e. separating sulfate and chloride ions to obtain Concentrated Water (CW) containing sodium sulfate ₂ ) And water containing chloride salt (CW) ₃ )；

(I) And (3) evaporation treatment: for Concentrated Water (CW) containing sodium sulfate ₂ ) Evaporating to obtain industrial-grade sodium sulfate; and/or, for water production (CW) containing chloride salts ₃ ) Evaporating to obtain industrial chloride salt;

wherein the above process further comprises the following additional steps (EG) between (E) the chemical softening step and (G) the reverse osmosis step:

(EG 1) activated carbon adsorption: carrying out adsorption treatment on the softened sewage by using activated carbon;

(EG 2) ion exchange treatment: before the ion exchange treatment, the softened sewage is neutralized, and then the ion exchange resin is used for carrying out the ion exchange treatment on the softened sewage, so that the hardness of the sewage is further reduced; and the combination of (a) and (b),

(EG 3) removal of carbonate and bicarbonate: by adding hydrochloric acid to the softened sewage, CO is formed ₂ Gas and alkali metal chloride to remove HCO ₃ ^- 、CO ₃ ^2- Ions;

and the sequence of the following intermediate steps can be any sequence: (F1) Filtration, (F2) ultrafiltration, (EG 1) activated carbon adsorption, (EG 2) ion exchange treatment, and (EG 3) removal of carbonate and bicarbonate.

2. The method according to claim 1, wherein the effluent (W) in the electrochemical treatment cell is ₁ ) The content of NaCl and KCl is 850mg/L to 40g/L; and/or

In step (D), the effluent (W) is purified in the first stage ₁ ) Adding inorganic alkali to adjust the sewage (W) ₁ ) pH of 10.5-12.5, for sewage (W) ₁ ) And carrying out electrochemical treatment.

3. The method according to claim 2, wherein the effluent (W) in the electrochemical treatment cell is ₁ ) The content of NaCl and KCl is 900mg/L to 30g/L; and/or

In step (D), the wastewater (W) purified in the first stage ₁ ) Adding inorganic alkali to adjust the sewage (W) ₁ ) To pH 11-12, for sewage (W) ₁ ) And carrying out electrochemical treatment.

4. Method according to claim 1, wherein said direct voltage (V) ₁ ) Or (V) ₂ ) Is between 5 and 100V; and/or

The current density between the anode and the cathode was 10mA/cm ² To 60mA/cm ² In between.

5. Method according to claim 4, wherein said direct voltage (V) ₁ ) Or (V) ₂ ) Is between 7 and 70V; and/or

The current density between the anode and the cathode was 12mA/cm ² To 55mA/cm ² In the meantime.

6. Method according to claim 5, wherein said direct voltage (V) ₁ ) Or (V) ₂ ) Is between 10-36V; and/or

The current density between the anode and the cathode was 14mA/cm ² To 50mA/cm ² In between.

7. The method of claim 1, wherein: the treatment in the anaerobic zone and the treatment in the aerobic zone can be carried out 2, 3, 4 or 5 times independently of one another.

8. The method of claim 1, wherein:

the aerobic bacteria used in the aerobic zone include one or more of escherichia coli, bacillus subtilis, pichia pastoris, aspergillus niger and penicillium chrysogenum, and/or the anaerobic bacteria used in the anaerobic zone are bifidobacteria and/or clostridium butyricum.

9. The method of claim 1 or 8, wherein:

heterotrophic bacteria are used in both the anaerobic and aerobic sections, the heterotrophic bacteria including rhizopus and/or penicillium, and/or autotrophic bacteria are also used in the anaerobic section, the autotrophic bacteria including facultative autotrophic rhizobia, thiobacillus ferrooxidans, thiobacillus thiooxidans or alcaligenes eutrophus.

10. The method according to any one of claims 1 to 8, wherein the effluent (W) is treated in an electrochemical treatment cell ₁ ) The concentration of the medium electrolyte is between 0.02mol/L and 0.6 mol/L.

11. The method according to claim 10, wherein the effluent (W) is treated in an electrochemical treatment cell ₁ ) The concentration of the medium electrolyte is between 0.035mol/L and 0.5 mol/L.

12. The method according to claim 11, wherein the effluent (W) is treated in an electrochemical treatment cell ₁ ) The concentration of the medium electrolyte is between 0.05mol/L and 0.4 mol/L.

13. The method according to claim 12, wherein the effluent (W) is treated in an electrochemical treatment cell ₁ ) The medium electrolyte concentration is between 0.06mol/L and 0.3 mol/L.

14. The method according to claim 13, wherein the effluent (W) is treated in an electrochemical treatment cell ₁ ) The concentration of the medium electrolyte is between 0.08mol/L and 0.2mol/L.

15. The method of claim 1, wherein a filler or three-dimensional filler is placed between the anode and the cathode in the electrochemical treatment cell; and/or

To the sewage (W) in the electrochemical treatment tank ₁ ) Adding coagulant aid or flocculant.

16. The process according to claim 1, wherein the separation step (C) is a precipitation separation, a filtration separation or a membrane separation.

17. The method of claim 16 wherein said step (C) of separating is MBR membrane bioreactor separation.

18. The process of claim 17, wherein the MBR membranes or MBR membrane modules in the MBR tank are anti-fouling PVDF hollow fiber membranes.

19. The method according to claim 1, wherein the high-efficiency sedimentation tank used consists of two parts, a reaction zone and a clarification zone, wherein the reaction zone comprises a mixing reaction zone and a plug flow reaction zone, and the clarification zone comprises an inlet pre-sedimentation zone, a tube-chute sedimentation zone and a concentration zone.

20. The method of claim 19, wherein a tube-chute packing is provided in the tube-chute settling zone.

21. The method according to claim 1 or 19, wherein in the (E) chemical softening step, (E1) chemical softening and (E2) coagulation and/or (E3) precipitation process employs an integrated softening apparatus comprising a softening reaction section and a coagulation section and/or a precipitation section, in which softening, coagulation, sedimentation and neutralization are simultaneously carried out.

22. The method of claim 1 or 19, wherein:

in the chemical softening section, adding alkali into the sewage in the softening reaction tank to reduce the hardness of the sewage; and/or

In the coagulation section, a coagulant is added into the sewage to further remove pollutants or fine particles in the sewage; and/or

In the precipitation section, the wastewater is subjected to a precipitation treatment, and the pH of the wastewater is adjusted to 7. + -. 0.5 with hydrochloric acid.

23. The method of claim 22, wherein:

in the chemical softening section, sodium hydroxide and/or sodium carbonate are/is added into the sewage in the softening reaction tank to reduce the hardness of the sewage to be below 4mg/L; and/or

Wherein: and adding sodium hypochlorite into the sewage in the precipitation section to further remove ammonia nitrogen.

24. The method according to claim 1, wherein the filter used in sub-step (F1) is a ceramic membrane filter or a multimedia filter; and/or

The ultrafilter used in substep (F2) is a ceramic membrane ultrafiltration device.

25. The method according to claim 24, wherein the filter used in sub-step (F1) is a multi-media filter comprising a quartz sand filter layer; and/or

The ultrafilter used in substep (F2) is a ceramic flat membrane ultrafiltration device.

26. The method of claim 1 wherein said (G) reverse osmosis step comprises: primary and secondary reverse osmosis, and optionally ST reverse osmosis or electrodialysis.

27. The process of claim 1, wherein the (EG 1) activated carbon adsorption step is before or after the (F1) filtration or multi-media filtration step.

28. The process of claim 27, wherein (EG 1) the activated carbon adsorption step is after the (F1) filtration or multimedia filtration step and before the (F2) ultrafiltration step, i.e., step (EG 1) is between step (F1) and step (F2).

29. The process of claim 1 wherein the process further comprises the following steps after (G) the reverse osmosis step and before (H) the nanofiltration membrane desalination step:

(H ₀ ) Pretreatment before nanofiltration: (ii) subjecting the contaminated water, with or without detection of concentrated water (CW 1), to a pre-nanofiltration pretreatment, said (H0) pre-nanofiltration pretreatment step being one or two or more of the following treatments:

1) Performing the above-mentioned electrochemical treatment (B) again;

2) The above-described (F1) filtration treatment was performed again: filtering the sewage by using a filter, and separating and removing suspended matters or particulate matters in the sewage by filtering;

3) The above-mentioned (F2) ultrafiltration treatment was performed again: ultrafiltering the sewage by using an ultrafilter;

4) Performing the above-mentioned (EG 1) activated carbon adsorption treatment again; and the number of the first and second groups,

5) The above-mentioned (EG 2) ion exchange treatment was performed again;

when two or more of the pretreatment steps 1) to 5) above are used simultaneously, the order of these steps may be in any order.

30. The method according to claim 29, wherein the filter used is a ceramic membrane filter or a multimedia filter; and

the ultrafilter used is a ceramic membrane ultrafiltration device.

31. The method according to any one of claims 1 to 8, wherein (A) the sewage pretreatment step comprises the substeps of: air floatation treatment: in an air flotation device with an air flotation sewage tank, air is introduced into sewage to carry out air flotation treatment, and coarse fiber and granular substances in the form of scum are removed by a physical method; and adding a flocculating agent into the sewage in the air floatation sewage tank of the air floatation device.

32. The method of claim 31, wherein the flocculant is polyaluminum chloride, an iron-based flocculant, an aluminum-based flocculant, or an iron-aluminum composite flocculant.

33. The method according to claim 1, wherein the raw sewage (W) is ₀ ) In, SO ₄ ^2- The content is 2500-35000ppm; total hardness of calcium and magnesium (Ca) ²⁺ +Mg ²⁺ ) 800-5000ppm; f ^- The content is 4ppm to 500ppm; and, siO in such raw sewage ₃ ^2- +SiO ₄ ^4- The content of (B) is 5ppm to 750ppm.

34. The method of claim 33, wherein the raw sewage (W) is ₀ ) In (SO) ₄ ^2- The content is 3000-20000ppm; f ^- The content is 6ppm to 500ppm; and, siO in such raw sewage ₃ ^2- +SiO ₄ ^4- The content of (B) is 12ppm to 750ppm.

35. The method of claim 34, wherein the raw sewage (W) is ₀ ) In, SO ₄ ^2- The content is 4000-20000ppm; f ^- The content is 20ppm to 500ppm; and, siO in such raw sewage ₃ ^2- +SiO ₄ ^4- The content of (B) is 20ppm to 750ppm.

36. The method of claim 35, wherein the raw sewage (W) is ₀ ) In, SO ₄ ^2- The content is 5000-20000ppm; f ^- The content is 40ppm to 500ppm; and, siO in such raw sewage ₃ ^2- +SiO ₄ ^4- The content of (B) is 50ppm to 750ppm.

37. The method of claim 36, wherein the raw sewage (W) is ₀ ) In, SO ₄ ^2- The content is 5000-10000ppm; f ^- The content is 100ppm to 500ppm; and, siO in such raw sewage ₃ ^2- +SiO ₄ ^4- The content of (B) is 150ppm to 300ppm.

38. The method according to any of claims 33-37, wherein the raw sewage (W) is ₀ ) In the Total Phosphorus (TP) content is 0.5ppm-700ppm; na (Na) ⁺ The content is 300-11000ppm; cl ^- The content is 450-9500ppm; and, CO ₃ ^2- The content is 70-6500ppm.

39. The method of claim 38, wherein the raw sewage (W) is ₀ ) In the Total Phosphorus (TP) content is 4ppm to 200ppm; na (Na) ⁺ The content is 500-9500ppm; cl ^- The content is 700-8000ppm; SO (SO) ₄ ^2- The content is 100-25000ppm; and, CO ₃ ^2- The content is 100-3000ppm.

40. The method of claim 39, wherein the raw sewage (W) is ₀ ) In the Total Phosphorus (TP) content is 12ppm to 200ppm; na (Na) ⁺ The content is 900-4000ppm; cl ^- The content is 1200-6000ppm; SO (SO) ₄ ^2- The content is 300-20000ppm; and, CO ₃ ^2- The content is 300-2000ppm.

41. The method according to claim 40, wherein the raw sewage (W) is ₀ ) In the Total Phosphorus (TP) content is 20ppm to 100ppm; na (Na) ⁺ The content is 1500-2000ppm; cl ^- The content is 2000-4000ppm; SO ₄ ^2- The content is 500-10000ppm; and, CO ₃ ^2- The content is 500-1500ppm.

42. The method according to claim 31, wherein said (1) biological desulfurization step and optionally said (2) anaerobic treatment step are immediately before said (B) step, and when said method comprises said (a) sewage pretreatment step, said (1) step and optionally said (2) step are after said (a) sewage pretreatment step.

43. The method according to claim 1, wherein between steps (D) and (E) further processing steps are included, which are filtration steps and/or ultrafiltration steps.

44. The method according to claim 43, wherein the further treatment step is a filtration step using a ceramic membrane filter or a multi-media filter and/or an ultrafiltration step using a ceramic membrane ultrafiltration device.

45. The process of claim 1, wherein the inorganic base is Na ₂ CO ₃ And/or NaOH.

46. The method of claim 1, wherein

(EG 2) ion exchange treatment: and neutralizing the softened sewage before ion exchange treatment, and then carrying out ion exchange treatment on the softened sewage by using ion exchange resin to further reduce the hardness of the sewage so that the total hardness of the effluent of the ion exchange equipment is lower than 1mg/L.