CN108117222B - Zero-discharge treatment method for salt-containing wastewater in coal chemical industry - Google Patents
Zero-discharge treatment method for salt-containing wastewater in coal chemical industry Download PDFInfo
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- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
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- C02F1/469—Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis
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- C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
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- C02F2301/08—Multistage treatments, e.g. repetition of the same process step under different conditions
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- C02F2305/026—Fenton's reagent
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- C02F3/02—Aerobic processes
- C02F3/12—Activated sludge processes
Abstract
The invention relates to a zero discharge treatment method of coal chemical industry salt-containing wastewater, which comprises the following steps: (1) pre-treating; (2) reverse osmosis treatment; (3) advanced oxidation treatment; (4) biochemical treatment; (5) electrodialysis concentration; (6) and (5) circulating and crystallizing. Compared with the prior art, the zero-discharge salt separation treatment process method for the salt-containing wastewater provided by the invention improves the recovery rate of salt while realizing zero discharge or near zero discharge of the wastewater in the coal chemical industry, can recover high-quality sodium sulfate, mirabilite and sodium chloride, realizes reclamation of crystallized salt, and has the advantages of stable membrane treatment unit process, long operation period, low cost and good economical efficiency of the whole process.
Description
Technical Field
The invention belongs to the technical field of environmental protection, and particularly relates to a zero-emission treatment method for salt-containing wastewater, in particular to a zero-emission treatment method for high-salt-containing wastewater in the coal chemical industry.
Background
Coal chemical industry is a process of converting coal, which is used as a raw material, into gas, liquid, solid fuel and chemicals through chemical processing. The coal chemical industry mainly comprises coal gasification, liquefaction, dry distillation, tar processing, calcium carbide acetylene chemical industry and the like. The coal chemical engineering project has huge water consumption and high water consumption of the produced wastewater. Most coal chemical engineering projects in China are distributed in northwest areas where water resources are short and nano sewage bodies are short. With the continuous adjustment of the national environmental protection policy, the wastewater of the coal chemical industry enterprises needs to be recycled to the maximum extent, so that zero emission is achieved.
Coal chemical wastewater can be generally divided into organic wastewater and saline wastewater. The salt-containing wastewater mainly comprises circulating sewage, chemical water station drainage and the like, and in order to recycle wastewater to the maximum extent, in general, organic wastewater enters a salt-containing wastewater treatment system after primary treatment, secondary treatment and advanced treatment, and is subjected to further desalting treatment, so that the salt-containing wastewater meets the requirement of quality of circulating water make-up water.
The recycling treatment of the salt-containing wastewater mainly comprises two technologies, one is a membrane separation technology, and the other is a thermal evaporation technology. The method for directly obtaining the reuse water from the salt-containing wastewater by adopting the thermal evaporation technology has huge energy consumption, so that the membrane separation technology is the mainstream technology in the field. The main membrane separation unit technologies include reverse osmosis, forward osmosis, bipolar membrane, dialysis, electrodialysis, microwave membrane, ultrafiltration membrane, nanofiltration membrane, biological membrane, etc., and one or a combination of membrane technologies can be generally adopted to treat wastewater from different sources. The key technical problem of the membrane technology in application is the problem of membrane pollution, and the components of the wastewater are complex, so that the membrane has great influence on the use efficiency and the service life. The prior common method is to carry out advanced pretreatment on the treated wastewater, combine different types of membrane technologies and the like, but the cost of the advanced pretreatment is greatly increased, the prior combined technology does not obtain expected effects, and particularly in the saline wastewater treatment technology in the field of coal chemical industry, the prior combined technology can obtain higher reuse water yield, but does not solve the problems of membrane pollution and membrane service life.
The aim of the salt-containing wastewater treatment technology is zero discharge of wastewater, which needs to recover salt in the wastewater in a solid form, and salt meeting the selling quality standard is difficult to obtain due to complex salt components in the wastewater. The existing method obtains more mixed salt, is difficult to sell and use, and forms solid waste which is difficult to treat. Although theoretically, the salts in the wastewater can be respectively obtained into the monosalts with higher purity by various separation and purification methods, the process is complicated, the cost is increased and the method is difficult to bear economically due to more components. Particularly, the existence of organic pollutants and nitrogen-containing pollutants in the wastewater not only brings membrane pollution, but also brings difficulty to comprehensive treatment and recycling of miscellaneous salts, and can not realize real near zero emission. Therefore, how to adopt a proper technology to efficiently treat the organic pollutants and the nitrogen-containing pollutants in the salt-containing sewage is the premise of ensuring the stable operation of the subsequent membrane reduction unit, and the comprehensive utilization of the finally generated miscellaneous salts is possible only by reducing the pollutant concentration in the concentrated solution as much as possible.
CN104016529A discloses a coal chemical industry salt-containing wastewater treatment method based on a multistage countercurrent reverse-electrode electrodialyzer, which can concentrate concentrated water by more than 10 times and improve the fresh water yield to more than 85%. The technology improves the fresh water recovery rate through ozone oxidation, multistage membrane filtration and multistage countercurrent reverse-electrode electrodialysis technology, and relieves the problem of electrodialyzer membrane pollution to a certain extent, but the pretreatment cost is high, the stability of a pretreatment membrane unit has no good solution, the electrodialyzer still contains a small amount of salt after obtaining the reuse water, the overall effect is general, and the strong brine has no further treatment scheme, and zero emission cannot be realized.
CN104230124A discloses a process and special equipment for classifying, collecting and quality-dividing treatment of coal chemical wastewater, which can improve the recovery rate of water and obtain industrial salt. However, in the process, three independently used reverse osmosis units are adopted, and pretreatment is carried out by adopting an ion exchange and other deep pretreatment modes; the membrane separation unit for separating and purifying water and organic concentrated solution is difficult to obtain ideal effect at present; the industrial salt is mixed salt and is difficult to sell or use.
CN103508602A discloses a membrane and evaporative crystallization integrated process for zero discharge of high salinity industrial wastewater, which comprises the steps of carrying out ultrafiltration pretreatment on industrial wastewater, conveying the industrial wastewater to a reverse osmosis unit through a high-pressure pump, recycling effluent at the permeation side, carrying out electrodialysis treatment on a concentrated solution after filtration for multiple times, evaporating and crystallizing a material after electrodialysis concentration to obtain salt mud and condensate water, carrying out aftertreatment on the salt mud, recycling the condensate water and recycling electrodialysis fresh water. The method simply combines reverse osmosis and electrodialysis for use, and plays a role independently, the electrodialysis fresh water needs to meet the recycling requirement, the treatment difficulty is high, the energy consumption is high, the membrane pollution is serious, the stability of the whole device is insufficient, and in addition, the obtained solid salt is still mixed salt.
CN105565569A discloses a high-salt industrial wastewater enhanced deep concentration system and a process thereof, wherein the high-salt industrial wastewater is adjusted by an adjusting tank, precipitated by a softening sedimentation tank, filtered by a V-shaped filter tank, enhanced filtered by an ultrafiltration device, concentrated by a first-stage reverse osmosis device, concentrated by an ion exchange resin device, removed by hardness, and separated by a nanofiltration device; wherein: the nanofiltration device concentrates water, the frequent electrode-reversing electrodialysis device concentrates water, the advanced oxidation device oxidizes water, the total production water tank crystallizes in a concentrated water-freezing crystallization system, and sodium sulfate crystallizes; the method comprises the steps of nanofiltration device water production, two-section reverse osmosis device concentration, frequent reversed-pole electrodialysis device reconcentration, water production, advanced oxidation device oxidation, total production water tank, concentrated water, MVR evaporative crystallization device crystallization and sodium chloride crystallization. The method combines membrane technologies such as nanofiltration, frequent reverse electrodialysis, reverse osmosis and the like, but the functions of different membrane technologies are not effectively integrated, advanced treatment such as ion exchange is needed for pretreatment, and the cost is high; although sodium chloride crystals and sodium sulfate crystals are obtained respectively, analysis and experiments prove that if the purity of the obtained crystallized salt needs to be ensured, a certain amount of high-concentration salt-containing wastewater needs to be discharged, zero emission cannot be realized, and the salt recovery rate needs to be further improved.
In summary, the treatment process of salt-containing wastewater, especially salt-containing wastewater in coal chemical industry, needs further optimization in terms of comprehensive technical effects such as wastewater recovery rate, industrial salt recycling, salt recovery rate, stable operation of membrane units, reduction of production cost, realization of zero discharge, and the like.
Disclosure of Invention
Aiming at the defects of the existing salt-containing wastewater treatment process, the invention provides a zero-discharge treatment method for salt-containing wastewater, in particular to a zero-discharge treatment method for coal chemical industry salt-containing wastewater, which improves the recovery rate of salt while realizing zero discharge or near zero discharge of the coal chemical industry wastewater, can recover high-quality sodium sulfate, mirabilite and sodium chloride, realizes the recycling of crystallized salt, and has the advantages of stable multi-stage membrane treatment unit process, long running period, low cost and good economical efficiency of the whole process.
The invention relates to a zero discharge treatment method of coal chemical industry salt-containing wastewater, which comprises the following steps:
(1) and (4) preprocessing. The pretreatment comprises softening, coagulating sedimentation, rough filtration and ultrafiltration, and the pretreated effluent is subjected to reverse osmosis treatment. The pretreatment can also comprise the processes of oil removal, biochemical treatment, homogeneous and uniform treatment and the like according to the quality of the incoming water.
(2) And (5) reverse osmosis treatment. The membrane pollution resisting combined membrane process combining medium pressure reverse osmosis and high pressure reverse osmosis is adopted, pretreated effluent is firstly subjected to medium pressure reverse osmosis, produced water of the medium pressure reverse osmosis is recycled, concentrated water of the medium pressure reverse osmosis and fresh water of an electrodialysis unit are subjected to high pressure reverse osmosis together, produced water of the high pressure reverse osmosis is recycled, and concentrated water of the high pressure reverse osmosis is subjected to electrodialysis concentration. Recycle refers to the need for reuse in industrial settings or other uses.
(3) Advanced oxidation treatment: the high-pressure reverse osmosis concentrated water is firstly subjected to advanced oxidation treatment, and the biodegradability of organic pollutants in the salt-containing wastewater is improved mainly by adopting a Fenton oxidation mode.
(4) And (4) performing biochemical treatment. The effluent of the advanced oxidation unit enters a biochemical unit, and COD and total nitrogen are removed by adding a salt-tolerant microbial inoculum and a microorganism growth promoter into the conventional membrane bioreactor. The microbial inoculum is a salt-tolerant microbial inoculum. The microbial growth promoter comprises metal salt, polyamine substances and organic acid hydroxylamine, wherein the metal salt consists of calcium salt, copper salt, magnesium salt and/or ferrous salt.
(5) And (4) electrodialysis concentration. After the effluent of the biochemical unit is pretreated by softening, coagulating sedimentation, rough filtration and ultrafiltration, electrodialysis is carried out for further concentration, electrodialysis fresh water is circulated as high-pressure reverse osmosis inlet water, and the generated concentrated water is circulated and crystallized.
(6) And (5) circulating and crystallizing. The electrodialysis concentrated water is firstly subjected to primary evaporation crystallization to obtain sodium sulfate crystals and primary mother liquor, the primary mother liquor is subjected to freezing crystallization to obtain mirabilite and secondary mother liquor, the secondary mother liquor is subjected to secondary evaporation crystallization to obtain sodium chloride crystals and tertiary mother liquor, and the tertiary mother liquor is circulated to the primary evaporation crystallization to realize zero discharge of sewage.
Further, in the step (1), the softening, flocculation and precipitation processes are carried out in a high-density clarification tank, the coarse filtration process is carried out in a V-shaped filter tank, and the average pore diameter of the ultrafiltration membrane is 1-100 nm. The homogenizing and homogenizing process is carried out in a regulating tank.
Further, in the step (1), a dosing device is arranged at the front end of the high-density clarification tank, a softening agent and a flocculating agent are added, a dosing device is also arranged at the outlet of the high-density clarification tank, hydrochloric acid or sulfuric acid is respectively added to adjust the pH value to 6.5-7.5, and a non-oxidizing bactericide is added.
Further, in the step (1), the softener is one or more of calcium hydroxide, sodium hydroxide and sodium carbonate with different concentrations according to different water qualities of the salt-containing wastewater in the coal chemical industry; the coagulant is a composite coagulant of polyferric sulfate (PFS) and Polyacrylamide (PAM) according to different water qualities of the salt-containing wastewater in the coal chemical industry, wherein the concentration of PFS is 5-200 mg/L, and the concentration of PAM is 0.5-12 mg/L.
Further, in the step (1), after the pretreatment process, the wastewater index is controlled to be less than 200mg/L, COD and less than 70 mg/L, and the turbidity is less than 3 NTU.
Further, in the step (2), the operating pressure of the medium-pressure reverse osmosis membrane is 1-3 MPa, the operating pressure of the high-pressure reverse osmosis membrane is 3-6 MPa, and the medium-pressure membrane and the high-pressure membrane are both filtered by cross flow. The medium-pressure membrane and the high-pressure membrane can be selected from membranes for reverse osmosis commonly used in the field.
Further, in the step (2), after the two-stage reverse osmosis separation process, the TDS of the high-pressure reverse osmosis produced concentrated water can reach more than 50000 mg/L.
Further, in the step (3), the high-grade oxidation is Fenton oxidation, the high-grade oxidation is performed in a Fenton reaction tank, a medicine adding device is arranged at an inlet of the Fenton reaction tank, any one of hydrochloric acid and sulfuric acid is added, the pH value of the high-pressure membrane concentrated water is adjusted to 2-4, ferrous salts and hydrogen peroxide with different concentrations are added according to the concentration of COD in the water, the ferrous salts and the hydrogen peroxide can be added into the wastewater sequentially or simultaneously, but the ferrous salts and the hydrogen peroxide must be added into the wastewater independently from each other, and the mode that the ferrous salts and the hydrogen peroxide are mixed firstly and then added into the wastewater cannot be adopted. The total reaction time is 1-4 hours.
Further, in the step (4), a membrane bioreactor is mainly adopted, and a specific salt-tolerant microbial inoculum and a microorganism growth promoter are added to realize deep removal of organic pollutants in the high-salt-content sewage. The existing membrane bioreactor may be a Biological Aerated Filter (BAF), a Membrane Bioreactor (MBR), a moving bed membrane bioreactor (MBBR), etc., and BAF is preferably used. The operating conditions of the membrane bioreactor are as follows: the temperature is 20-40 deg.C, pH is 7-9, and dissolved oxygen concentration is 0.5-1.5 mg/L.
The microbial inoculum in the step (4) of the invention adopts a salt-tolerant microbial inoculum described in CN201210130645.8 or CN201210130644.3, and the dosage of the salt-tolerant microbial inoculum is 0.01-0.1% of the volume of the wastewater treated per hour. Microbial growth promoters may be prepared according to the methods described in CN201410585430.4, CN201410585449.9 and CN 201410585485.5.
The proportion of effective components in the microbial growth promoter in the step (4) of the invention is as follows: 40-100 parts of metal salt, preferably 50-80 parts of metal salt, 5-30 parts of polyamine substance, preferably 10-20 parts of polyamine substance and 0.5-15 parts of hydroxylamine organic acid, preferably 2-10 parts of polyamine substance. The metal salt is composed of calcium salt, copper salt, magnesium salt and/or ferrous salt, wherein the metal salt can be calcium salt, magnesium salt and copper salt, wherein Ca2+、Mg2+And Cu2+The molar ratio of (5-15): (5-25): 0.5-5), preferably (8-12): 10-20): 1-4; or salts of calcium, ferrous and copper, where Ca2+、Fe2+And Cu2+The molar ratio of (5-15): (1-8): 0.5-5, preferably (8-12): 2-6): 1-4; or calcium, magnesium, ferrous and copper salts, of which Ca is present2+、Mg2+、Fe2+And Cu2+The molar ratio of (5-15): (5-25): 1-8): 0.5-5, preferably (8-12): 10-20): 2-6): 1-4.
In the invention, the calcium salt in the growth promoter is CaSO4Or CaCl2Preferably CaSO4(ii) a The magnesium salt is MgSO4Or Mg Cl2Preferably MgSO (MgSO)4(ii) a The ferrous salt is FeSO4Or FeCl2Preferably FeSO4(ii) a The copper salt being CuSO4Or CuCl2Preferably CuSO4。
In the invention, the polyamine substance in the growth promoter is spermine, spermidine or a mixture of spermine and spermidine. The organic acid hydroxylamine is hydroxylamine formate, hydroxylamine acetate or a mixture of the two.
In the invention, the adding amount of the growth promoter is 1-20mg/L, preferably 5-15mg/L, of the total concentration of effective components of the promoter in the sewage treatment system.
Further, in the step (5), the softening and flocculation precipitation processes are carried out in a high-density clarification tank, the coarse filtration process is carried out in a V-shaped filter tank, and the average pore diameter of the ultrafiltration membrane is 1-100 nm. The front end of the high-density clarification tank is provided with a dosing device, a softening agent and a flocculating agent are added, a dosing device is also arranged at the outlet of the high-density clarification tank, a pH regulator is added to adjust the pH to 6.5-7.5, and a non-oxidizing bactericide is added according to the requirement.
Further, in the step (5), the softener is one or more of calcium hydroxide, sodium hydroxide and sodium carbonate with different concentrations according to different water qualities of the biochemical treatment effluent; PAM is adopted as the flocculating agent, and the concentration is 2-16 mg/L. After the pretreatment, the electrodialytic water inlet index is controlled to be less than 50 mg/L, COD and less than 70 mg/L, and the turbidity is less than 3 NTU.
Further, in the step (5), after concentration by electrodialysis, TDS in the concentrated water will reach over 200000 mg/L. The electrodialytic fresh water TDS is less than 25000 mg/L, generally more than 10000 mg/L, preferably more than 15000 mg/L.
Further, in the step (6), when the primary evaporation crystallization is carried out, the evaporation concentration temperature is 50-150 ℃, and the crystallization temperature is 50-100 ℃; during secondary evaporation crystallization, the temperature of evaporation concentration is 50-150 ℃, and the crystallization temperature is 30-50 ℃; the temperature of freezing crystallization is 0 to-8 ℃.
Further, in the step (6), the device used for evaporative crystallization comprises an evaporator and a crystallizer. The evaporator is any one of a natural circulation evaporator, a forced circulation evaporator, a climbing-film evaporator or a falling-film evaporator; the crystallisers are any of an Oslo crystalliser, a DP crystalliser or a variation of the above types, respectively. The evaporator and crystallizer may be prior art devices or designed according to the prior art.
Further, in the step (6), the generated sodium sulfate, mirabilite and sodium chloride are collected by a centrifugal dehydrator. The purity of the generated sodium sulfate can reach more than 95 percent, and the product quality reaches the quality standard of national standard industrial anhydrous sodium sulfate III qualified products. The purity of the generated sodium chloride can reach more than 98 percent, and the product quality reaches the secondary quality standard of national standard refined industrial salt. The quality of the mirabilite product is more than 90%. The purity of the product is calculated by mass percent.
The method of the invention obtains the following comprehensive technical effects:
1. the combination of measures ensures stable operation of the membrane unit (reverse osmosis and electrodialysis). The reverse osmosis units with two stages and different pressures are adopted, and the electrodialysis units (still having relatively high salt content in fresh water) with specific operation modes are organically integrated into the reverse osmosis process, and the processes and conditions of the three processes are cooperatively matched, so that the long-period stable operation of the membrane units is realized while the concentration multiple and the water outlet speed are ensured, the membrane pollution problem is effectively controlled, and the membrane service life is reduced due to frequent regeneration of the membrane. When the scheme of the invention is adopted, the membrane unit can stably run for more than 3 years, and tests and simulations show that the membrane unit can only run for 1-1.5 years under the same pretreatment condition if the cooperation of the synergistic combination process and conditions is not adopted.
2. The operation cost of the pretreatment unit is low. The flow and the conditions of the membrane unit are cooperated, so that the severity requirement of the water inlet index of the membrane unit is reduced, and the operation cost of the water inlet pretreatment operation can be greatly reduced. For example, the invention can use the modes of softening, flocculation precipitation, rough filtration, ultrafiltration and the like with lower cost, and the methods have low cost and stable operation and do not need the pretreatment units with high cost such as ion exchange, nanofiltration and the like in the prior art.
3. The biochemical unit can remove nitrate in sewage by matching the salt-tolerant microbial inoculum and the accelerator, remove sodium nitrate in subsequent miscellaneous salt and reduce the difficulty in processing miscellaneous salt. Meanwhile, the biochemical unit can also remove part of organic pollutants, and the treatment cost of operations such as a front-end Fenton oxidation unit and subsequent precipitation is reduced.
4. The salt separation scheme does not discharge waste liquid on the basis of ensuring the purity of the crystallized salt, and really realizes zero discharge. The sodium sulfate is crystallized by adopting two crystallization modes, and the sodium sulfate and the mirabilite are crystallized to reasonably distribute other impurities in the wastewater into different crystallized products, so that the problem of unqualified purity of the crystallized salt caused by full circulation of the mother solution is avoided, and zero discharge of the wastewater is realized on the premise of ensuring qualified quality of the crystallized salt. If the sodium sulfate is separated in a crystal salt form, tests show that the two crystal salts (sodium sulfate and sodium chloride) are unqualified in purity; if the purity of the two kinds of crystal salt is qualified, salt-containing waste liquid needs to be discharged. Therefore, the scheme of the invention improves the recovery rate of the salt while realizing zero discharge or near zero discharge of the wastewater in the coal chemical industry, and can recover high-quality sodium sulfate, mirabilite and sodium chloride to realize the recycling of the crystallized salt. Meanwhile, the process of the quality-divided salt is at the tail end, so that the process is simplified, and the construction cost is reduced.
Drawings
FIG. 1 is a schematic diagram of the components and connection relationship of unit devices for implementing the method of the present invention.
Detailed Description
The following detailed description is further provided with reference to fig. 1, and the scope of the present invention is not limited to the following embodiments. The units are conventional devices or equipment in the field, and referring to the following specific implementation mode of the invention, technicians in the field can perform conventional adjustment according to the quality of wastewater to obtain optimal treatment control conditions of different water qualities, so that each unit meets the requirement of the controlled effluent quality, and the final process effect is realized.
The microbial growth promoter is prepared according to the proportion and the formula shown in the table 1, and the concentration of the promoter is 0.5 g/L.
TABLE 1 formulation and proportions of microbial growth promoters
The salt-tolerant microbial inoculum related to the invention is prepared according to the mixture ratio shown in table 2, and the related bacteria are fully disclosed in CN201210130645.8 and CN 201210130644.3.
TABLE 2 compositions and ratios of different bacterial agents
| Microbial inoculum | Composition of thallus | Proportioning |
| Ⅱ-A | FSDN-A:SDN-3:DN-3: FDN-1:FDN-2 | 1:0.5:0.5:0.5:0.5 |
| Ⅱ-B | FSDN-C:SDN-3:DN-3: FDN-1:FDN-2 | 1:0.5:0.5:0.5:0.5 |
Example 1
The average concentration of each pollutant of the high-salt industrial wastewater is as follows: COD is 80mg/L, total hardness is as CaCO3Calculated as CaCO) of 1500 mg/L and total alkalinity3Calculated) is 800 mg/L, 30 mg/L, TDS is 5000 mg/L, wherein, the concentration of nitrate ions is 40mg/L, the concentration of chloride ions is 700 mg/L, the concentration of sulfate ions is 1000 mg/L, and the pH value is 8. As shown in fig. 1, the zero discharge treatment process for the salt-containing wastewater in the coal chemical industry comprises the following steps:
(1) the method comprises the steps of enabling salt-containing wastewater to enter a high-density clarification tank, adding 1.8 g/L calcium hydroxide into a reaction zone of the high-density clarification tank according to the quality of the salt-containing wastewater to enable the pH value to be maintained at 10.5-11.0, adding 2.0 g/L sodium carbonate, adding 10 mg/L PFS for coagulation, adding 1mg/L PAM for coagulation assistance, enabling the mixture to enter a clarification zone of the high-density clarification tank for precipitation after the reaction zone is fully coagulated, finally adding hydrochloric acid or sulfuric acid into an outlet of the high-density clarification tank to adjust the pH value to about 7, and adding a non-oxidative bactericide to prevent membrane pollution. After treatment, the hardness of the effluent of the high-density clarification tank is less than 200 mg/L.
(2) The effluent of the high-density clarification tank is treated by a V-shaped filter to remove suspended matters, colloid particles and the like in the water, and finally the turbidity of the wastewater is controlled to be about 3 NTU and the COD is controlled to be about 50 mg/L, and the wastewater enters an ultrafiltration device. The operating pressure of the ultrafiltration device is 0.05 MPa, and after further treatment of ultrafiltration, the wastewater index finally reaches the hardness of less than 200mg/L, COD and less than 50 mg/L, the nitrate ion concentration is 40mg/L, and the turbidity is less than 1 NTU.
(3) The pretreated wastewater enters a reverse osmosis device for concentration, wherein the reverse osmosis device comprises medium-pressure reverse osmosis and high-pressure reverse osmosis, and is provided with a microporous filter of 25 mu m as a guarantee measure for water inlet. The medium-pressure reverse osmosis device adopts an anti-pollution medium-pressure reverse osmosis membrane, and the operating pressure is about 2 MPa; concentrated water of medium-pressure reverse osmosis and fresh water of an electrodialysis unit enter a high-pressure reverse osmosis device, the operating pressure of the high-pressure reverse osmosis device is about 3.5 MPa, the COD (chemical oxygen demand) of the fresh water of the medium-pressure reverse osmosis and the high-pressure reverse osmosis is less than 30 mg/L, the TDS (total dissolved solids) is less than 300 mg/L, and the hardness is less than 10 mg/L, so that the water quality index requirement of the circulating water is met. The service life of the reverse osmosis membrane component can reach more than 3 years. The TDS of the reverse osmosis concentrated water reaches 50000 mg/L, the average concentration of COD contained in the reverse osmosis concentrated water is 530 mg/L, and the average concentration of nitrate ions is 380 mg/L.
(4) And (2) allowing the high-pressure reverse osmosis concentrated water to enter a Fenton reaction tank, adding hydrochloric acid or sulfuric acid at an inlet of the Fenton reaction tank to adjust the pH value to be about 3, sequentially adding hydrogen peroxide and ferrous ions in a mass ratio of 20:1 into the Fenton reaction tank, enabling the mass ratio of the hydrogen peroxide to the COD to reach 2:1, and reacting for 2 hours. After Fenton oxidation, the COD concentration in the water was 500 mg/L, and the average nitrate ion concentration was 380 mg/L.
(5) And (4) the effluent of the Fenton reaction tank enters an aeration biological filter for removing COD (chemical oxygen demand) and nitrate radicals. Activated sludge is inoculated in the biological aerated filter in advance according to the sludge concentration of 4000mg/L for starting. The operating conditions were: the temperature was 27 ℃, the pH was 7.5, and the dissolved oxygen concentration was 1.0 mg/L. Adding a salt-tolerant microbial inoculum II-A in an aeration biological filter according to 0.1 percent of the volume of the wastewater treated per hour, and simultaneously adding a microorganism growth promoter I-A according to the total concentration of effective components of the promoter in a sewage treatment system of 15 mg/L. The COD concentration of the effluent treated by the biological aerated filter is less than 200mg/L, and the nitrate ion concentration is less than 100 mg/L.
(6) And (2) enabling the effluent of the biochemical unit to enter a high-density clarification tank, adding sodium hydroxide into a reaction zone of the high-density clarification tank according to the water quality of the effluent to maintain the pH value at about 11.5, then adding 2.2 g/L sodium carbonate, then adding 50 mg/L PFS for coagulation, adding 5mg/L PAM for coagulation assistance, after the reaction zone is fully coagulated, entering a clarification zone of the high-density tank for precipitation, finally adding hydrochloric acid or sulfuric acid into an outlet of the high-density clarification tank to adjust the pH value to about 7, and adding a non-oxidative bactericide to prevent membrane pollution. After treatment, the hardness of the effluent of the high-density clarification tank is less than 50 mg/L.
(7) The effluent of the high-density clarification tank is treated by a V-shaped filter to remove suspended matters, colloid particles and the like in the water, and finally the turbidity in the wastewater is controlled to be about 3 NTU and enters an ultrafiltration device. The operating pressure of the ultrafiltration device is 0.05 MPa, and after the further treatment of ultrafiltration, the index hardness of the wastewater is finally less than 50 mg/L, COD and less than 70 mg/L, and the turbidity is less than 1 NTU.
(8) The wastewater enters an electrodialysis device for further concentration, the operating voltage of the electrodialysis device is 40V, in order to ensure the long-period stable operation of electrodialysis, the TDS of the produced water (fresh water) is set to be about 15000 mg/L, and the produced water enters a high-pressure reverse osmosis membrane for further desalination treatment; TDS in the concentrated water reaches over 200000mg/L and enters an evaporative crystallization unit. The water produced by the electrodialysis device is controlled to have higher salt content and is organically combined with the reverse osmosis unit, so that the long-period stable operation of the reverse osmosis unit is realized, and meanwhile, the long-period stable operation of the electrodialysis unit is ensured.
(9) In a primary evaporation crystallization device, obtaining sodium sulfate with the product quality reaching the quality standard of national standard industrial anhydrous sodium sulfate III qualified products at an evaporation temperature of 100 ℃ and a crystallization temperature of 50-80 ℃; the mother liquor left after crystallization enters a freezing crystallization device to be further obtained at the crystallization temperature of about minus 5 ℃, and the mirabilite with the purity of more than 90 percent is obtained; and the residual liquid enters a secondary evaporation crystallization device again, sodium chloride with the product quality reaching the secondary quality standard of national standard refined industrial salt is obtained at the evaporation temperature of 100 ℃ and the crystallization temperature of 30-50 ℃, the TDS of the residual crystallization mother liquor of the secondary evaporation crystallization is controlled to be above 400000 mg/L, the residual salt in the crystallization mother liquor is evaporated again after the residual liquid is circulated to the primary evaporation crystallization, the purity of three crystallization products is qualified through the circulation process and condition control, and the recovery rate of water and salt is improved. When the COD accumulation of the circulating mother liquor is too high (about 10000 mg/L for example), the circulating mother liquor can be recycled to a Fenton reaction tank or treated by other methods.
Example 2
As shown in fig. 1, the treatment of the wastewater same as that in example 1 by using the zero discharge treatment process for the salt-containing wastewater in the coal chemical industry includes the following steps:
(1) the method comprises the steps of enabling salt-containing wastewater to enter a high-density clarification tank, adding 1.8 g/L calcium hydroxide into a reaction zone of the high-density clarification tank according to the quality of the salt-containing wastewater to enable the pH value to be maintained at 11.0-11.5, adding 2.5 g/L sodium carbonate, adding 50 mg/L PFS for coagulation, adding 5mg/L PAM for coagulation assistance, enabling the mixture to enter a clarification zone of the high-density clarification tank for precipitation after the reaction zone is fully coagulated, finally adding hydrochloric acid or sulfuric acid into an outlet of the high-density clarification tank to adjust the pH value to about 7, and adding a non-oxidative bactericide to prevent membrane pollution. After treatment, the hardness of the effluent of the high-density clarification tank is less than 200 mg/L.
(2) The effluent of the high-density clarification tank is treated by a V-shaped filter to remove suspended matters, colloid particles and the like in the water, and finally the turbidity of the wastewater is controlled to be about 3 NTU and the COD is controlled to be about 50 mg/L, and the wastewater enters an ultrafiltration device. The operating pressure of the ultrafiltration device is 0.05 MPa, and after further treatment of ultrafiltration, the wastewater index finally reaches the hardness of less than 200mg/L, COD and less than 50 mg/L, the nitrate ion concentration is 40mg/L, and the turbidity is less than 1 NTU.
(3) The pretreated wastewater enters a reverse osmosis device for concentration, wherein the reverse osmosis device comprises medium-pressure reverse osmosis and high-pressure reverse osmosis, and is provided with a microporous filter of 25 mu m as a guarantee measure for water inlet. The medium-pressure reverse osmosis device adopts an anti-pollution medium-pressure reverse osmosis membrane, and the operating pressure is about 1.5 MPa; concentrated water of medium-pressure reverse osmosis and fresh water of an electrodialysis unit enter a high-pressure reverse osmosis device, the operating pressure of the high-pressure reverse osmosis device is about 4.0 MPa, the COD (chemical oxygen demand) of the fresh water of the medium-pressure reverse osmosis and the high-pressure reverse osmosis is less than 30 mg/L, the TDS (total dissolved solids) is less than 300 mg/L, and the hardness is less than 10 mg/L, so that the water quality index requirement of the circulating water is met. The service life of the reverse osmosis membrane component can reach more than 3 years. The TDS of the reverse osmosis concentrated water reaches 50000 mg/L, the average concentration of COD contained in the reverse osmosis concentrated water is 530 mg/L, and the average concentration of nitrate ions is 380 mg/L.
(4) And (2) allowing the high-pressure reverse osmosis concentrated water to enter a Fenton reaction tank, adding hydrochloric acid or sulfuric acid at an inlet of the Fenton reaction tank to adjust the pH value to be about 3, sequentially adding hydrogen peroxide and ferrous ions in a mass ratio of 10:1 into the Fenton reaction tank, enabling the mass ratio of the hydrogen peroxide to the COD to reach 2:1, and reacting for 1.5 h. After Fenton oxidation, the COD concentration in the water was 500 mg/L, and the average nitrate ion concentration was 380 mg/L.
(5) And (4) the effluent of the Fenton reaction tank enters an aeration biological filter for removing COD (chemical oxygen demand) and nitrate radicals. Activated sludge is inoculated in the biological aerated filter in advance according to the sludge concentration of 4000mg/L for starting. The operating conditions were: the temperature was 27 ℃, the pH was 7.5, and the dissolved oxygen concentration was 1.0 mg/L. Adding a salt-tolerant microbial inoculum II-B in an aeration biological filter according to 0.1 percent of the volume of the wastewater treated per hour, and simultaneously adding a microbial growth promoter I-B according to the total concentration of effective components of the promoter in a sewage treatment system of 15 mg/L. The COD concentration of the effluent treated by the biological aerated filter is less than 200mg/L, and the nitrate ion concentration is less than 100 mg/L.
(6) And (2) enabling the effluent of the biochemical unit to enter a high-density clarification tank, adding sodium hydroxide into a reaction zone of the high-density clarification tank according to the water quality of the effluent to maintain the pH value at about 11.5, adding 2.5 g/L of sodium carbonate, adding 50 mg/L of PFS for coagulation, adding 5mg/L of PAM for coagulation assistance, after the reaction zone is fully coagulated, entering a clarification zone of the high-density tank for precipitation, finally adding hydrochloric acid or sulfuric acid into an outlet of the high-density clarification tank to adjust the pH value to about 7, and adding a non-oxidative bactericide to prevent membrane pollution. After treatment, the hardness of the effluent of the high-density clarification tank is less than 50 mg/L.
(7) The effluent of the high-density clarification tank is treated by a V-shaped filter to remove suspended matters, colloid particles and the like in the water, and finally the turbidity in the wastewater is controlled to be about 3 NTU and enters an ultrafiltration device. The operating pressure of the ultrafiltration device is 0.05 MPa, and after the further treatment of ultrafiltration, the index hardness of the wastewater is finally less than 50 mg/L, COD and less than 70 mg/L, and the turbidity is less than 1 NTU.
(8) The wastewater enters an electrodialysis device for further concentration, the operating voltage of the electrodialysis device is 40V, in order to ensure the long-period stable operation of electrodialysis, the TDS of produced water (fresh water) is set to be about 20000 mg/L, and the produced water enters a high-pressure reverse osmosis membrane for further desalination treatment; TDS in the concentrated water reaches over 200000mg/L and enters an evaporative crystallization unit. The water produced by the electrodialysis device is controlled to have higher salt content and is organically combined with the reverse osmosis unit, so that the long-period stable operation of the reverse osmosis unit is realized, and meanwhile, the long-period stable operation of the electrodialysis unit is ensured.
(9) In a primary evaporation crystallization device, obtaining sodium sulfate with the product quality reaching the quality standard of national standard industrial anhydrous sodium sulfate III qualified products at an evaporation temperature of 110 ℃ and a crystallization temperature of 80-100 ℃; the residual mother liquid after crystallization enters a freezing crystallization device to further obtain mirabilite with the purity of more than 92 percent at the crystallization temperature of about minus 5 ℃; and the residual liquid enters a secondary evaporation crystallization device again, sodium chloride with the product quality reaching the secondary quality standard of national standard refined industrial salt is obtained at the evaporation temperature of 100 ℃ and the crystallization temperature of 30-50 ℃, the TDS of the residual crystallization mother liquor of the secondary evaporation crystallization is controlled to be above 400000 mg/L, the residual salt in the crystallization mother liquor is evaporated again after the residual liquid is circulated to the primary evaporation crystallization, the purity of three crystallization products is qualified through the circulation process and condition control, and the recovery rate of water and salt is improved. When the COD accumulation of the circulating mother liquor is too high (about 10000 mg/L for example), the circulating mother liquor can be recycled to a Fenton reaction tank or treated by other methods.
Claims (14)
1. A zero discharge treatment method for salt-containing wastewater in coal chemical industry comprises the following steps:
(1) pre-treating; the pretreatment comprises softening, coagulating sedimentation, rough filtration and ultrafiltration, and the pretreated effluent is subjected to reverse osmosis treatment;
(2) reverse osmosis treatment; adopting a membrane pollution resistant combined membrane process combining medium-pressure reverse osmosis and high-pressure reverse osmosis, firstly carrying out medium-pressure reverse osmosis on pretreated effluent, recycling the produced water of the medium-pressure reverse osmosis, carrying out high-pressure reverse osmosis on the concentrated water of the medium-pressure reverse osmosis and the fresh water of an electrodialysis unit together, and recycling the produced water of the high-pressure reverse osmosis;
(3) advanced oxidation treatment: the high-pressure reverse osmosis concentrated water is firstly subjected to advanced oxidation treatment, mainly in a Fenton oxidation mode, so that the biodegradability of organic pollutants in the salt-containing wastewater is improved;
(4) biochemical treatment; the effluent of the advanced oxidation unit enters a biochemical unit, and COD and total nitrogen are removed by adding a salt-tolerant microbial inoculum and a microorganism growth promoter into a membrane bioreactor; the salt-tolerant microbial inoculum added in the biochemical treatment adopts the salt-tolerant microbial inoculum described in CN201210130645.8 or CN201210130644.3, and the adding amount is 0.01-0.1% of the volume of the wastewater treated per hour; the proportion of effective components in the microorganism growth promoter added in the biochemical treatment is as follows: 40-100 parts of metal salt, 5-30 parts of polyamine substance and 0.5-15 parts of organic acid hydroxylamine; the metal salt consists of calcium salt, copper salt, magnesium salt and/or ferrous salt;
(5) electrodialysis concentration; after the biochemical treatment effluent is pretreated by softening, coagulating sedimentation, rough filtration and ultrafiltration, electrodialysis is carried out for further concentration, electrodialysis fresh water is circulated to be used as high-pressure reverse osmosis inlet water, and the generated concentrated water is circulated and crystallized; TDS in the concentrated water is over 200000 mg/L; the electro-dialysis fresh water TDS is less than 25000 mg/L and more than 10000 mg/L;
(6) circulating crystallization; the electrodialysis concentrated water is firstly subjected to primary evaporation crystallization to obtain sodium sulfate crystals and primary mother liquor, the primary mother liquor is subjected to freezing crystallization to obtain mirabilite and secondary mother liquor, the secondary mother liquor is subjected to secondary evaporation crystallization to obtain sodium chloride crystals and tertiary mother liquor, and the tertiary mother liquor is circulated to the primary evaporation crystallization to realize zero discharge of sewage.
2. The method of claim 1, wherein: in the step (1), softening, flocculation and sedimentation processes are carried out in a high-density clarification tank, a rough filtration process is carried out in a V-shaped filter tank, and the average pore diameter of an ultrafiltration membrane is 1-100 nm.
3. The method of claim 2, wherein: in the step (1), a dosing device is arranged at the front end of the high-density clarification tank, a softening agent and a flocculating agent are added, a dosing device is arranged at the outlet of the high-density clarification tank, hydrochloric acid or sulfuric acid is respectively added to adjust the pH value to 6.5-7.5, and a non-oxidizing bactericide is added.
4. The method of claim 1, wherein: in the step (1), the softening agent is one or more of calcium hydroxide, sodium hydroxide and sodium carbonate; the coagulant is a composite coagulant of polymeric ferric sulfate and polyacrylamide, the concentration of the polymeric ferric sulfate is 5-200 mg/L, and the concentration of the polyacrylamide is 0.5-12 mg/L.
5. The method of claim 1, wherein: in the step (1), after the pretreatment process, the wastewater index is controlled to be that the hardness is less than 200mg/L, COD and less than 70 mg/L, and the turbidity is less than 3 NTU.
6. The method of claim 1, wherein: in the step (2), the operating pressure of the medium-pressure reverse osmosis membrane is 1-3 MPa, and the operating pressure of the high-pressure reverse osmosis membrane is 3-6 MPa.
7. The method of claim 1 or 6, wherein: in the step (2), after the two-stage reverse osmosis separation process, the TDS of the concentrated water generated by the high-pressure reverse osmosis reaches more than 50000 mg/L.
8. The method of claim 1, wherein: 50-80 parts of metal salt, 10-20 parts of polyamine substance and 2-10 parts of organic acid hydroxylamine.
9. The method of claim 1, wherein: in the step (4), the microbial growth promoter added in the biochemical treatment is added according to the total concentration of the effective components of the promoter in the sewage treatment system of 1-20 mg/L.
10. The method of claim 9, wherein: in the step (4), the microbial growth promoter added in the biochemical treatment is added according to the total concentration of effective components of the promoter in the sewage treatment system of 5-15 mg/L.
11. The method of claim 1, wherein: in the step (5), softening and flocculating settling processes are carried out in a high-density clarification tank, a rough filtration process is carried out in a V-shaped filter tank, and the average pore diameter of an ultrafiltration membrane is 1-100 nm.
12. The method of claim 1, wherein: in the step (5), the electrodialytic water inlet index is controlled to be less than 50 mg/L, COD and less than 70 mg/L, and the turbidity is less than 3 NTU.
13. The method of claim 1, wherein: in the step (6), when primary evaporation crystallization is carried out, the temperature of evaporation concentration is 50-150 ℃, and the crystallization temperature is 50-100 ℃, so that sodium sulfate crystals are obtained; during secondary evaporation crystallization, the temperature of evaporation concentration is 50-150 ℃, and the crystallization temperature is 30-50 ℃ to obtain sodium chloride crystals; the temperature of the freezing crystallization is 0 to-8 ℃, and mirabilite crystals are obtained.
14. The method of claim 1, wherein: in the step (6), the purity of the generated sodium sulfate is more than 95% by mass, the purity of the generated sodium chloride is more than 98% by mass, and the purity of the generated mirabilite is more than 90% by mass.
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