CN108117227B

CN108117227B - Method for concentrating salt-containing wastewater and method for recycling salt-containing wastewater

Info

Publication number: CN108117227B
Application number: CN201611073773.8A
Authority: CN
Inventors: 郭志华; 陈明翔; 高会杰; 孙丹凤; 赵胜楠; 李宝忠
Original assignee: China Petroleum and Chemical Corp; Sinopec Fushun Research Institute of Petroleum and Petrochemicals
Current assignee: China Petroleum and Chemical Corp; Sinopec Fushun Research Institute of Petroleum and Petrochemicals
Priority date: 2016-11-29
Filing date: 2016-11-29
Publication date: 2020-05-19
Anticipated expiration: 2036-11-29
Also published as: CN108117227A

Abstract

The invention relates to a method for concentrating salt-containing wastewater and a method for recycling salt-containing wastewater, which comprises the following steps: (1) pre-treating; (2) reverse osmosis treatment; (3) biochemical treatment; (4) electrodialysis concentration; (5) and (5) circulating and crystallizing. Compared with the prior art, the method for treating the salt-containing wastewater in a recycling manner provided by the invention realizes zero discharge of wastewater while realizing the recycling of wastewater, improves the quality and the recovery rate of salt, realizes the recycling treatment of wastewater and the comprehensive utilization of crystallized salt, further removes COD (chemical oxygen demand) and nitrate ions by the biochemical unit, reduces the difficulty of salt separation, and has the advantages of stable process of the membrane treatment unit, long running period, low cost and good economical efficiency of the whole process.

Description

Method for concentrating salt-containing wastewater and method for recycling salt-containing wastewater

Technical Field

The invention belongs to the technical field of environmental protection, and particularly relates to a method for concentrating salt-containing wastewater and a method for recycling the salt-containing wastewater, in particular to a method for concentrating high-salt-containing wastewater in the coal chemical industry and a method for recycling the high-salt-containing wastewater.

Background

Concentration treatment is generally required for improving the economy of the end treatment process before final treatment of the salt-containing wastewater, and methods which can be used for concentration of the salt-containing wastewater include evaporation, forward osmosis, reverse osmosis, electrodialysis, nanofiltration and the like. However, for most of the salt-containing wastewater, the pollutants are not only salts, but also pollutants such as COD, and the salts in the salt-containing wastewater are generally complex components, and in order to reduce the difficulty of the terminal treatment, some salts need to be removed in the concentration pretreatment process. Therefore, the method for concentrating the salt-containing wastewater is an important foundation for ensuring the economical efficiency of the whole treatment process.

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 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. Particularly, the technology of the concentration process of the salt-containing wastewater with high efficiency and stability needs to be further optimized.

Disclosure of Invention

Aiming at the defects of the existing salt-containing wastewater treatment process, the invention provides a concentration method of salt-containing wastewater and a recycling treatment method of salt-containing wastewater, so that the salt-containing wastewater is economically and stably concentrated, the zero discharge of the coal chemical wastewater is realized, the salt recovery rate is improved, the recycling of crystallized salt is realized, the salt separation difficulty of a biochemical unit is reduced, the multi-stage membrane treatment unit has stable process, long running period and low cost, and the whole process has good economical efficiency.

The process of the method for concentrating the salt-containing wastewater comprises the following steps: concentrating the salt-containing wastewater by adopting a method combining reverse osmosis and electrodialysis, wherein the combination mode of reverse osmosis and electrodialysis is as follows: the reverse osmosis adopts at least two stages, namely medium-pressure reverse osmosis and high-pressure reverse osmosis, the high-pressure reverse osmosis inlet water comprises medium-pressure reverse osmosis concentrated water and at least part of electrodialysis fresh water, the high-pressure reverse osmosis concentrated water is further concentrated by an electrodialysis method after at least part of the high-pressure reverse osmosis concentrated water is subjected to biochemical treatment, and the electrodialysis concentrated water is final concentrated outlet water; at least part of the high-pressure reverse osmosis concentrated water is subjected to biochemical treatment before the electrodialysis is carried out, wherein the biochemical treatment method comprises the following steps:

introducing the high-pressure reverse osmosis concentrated water into a membrane bioreactor, and reducing the nitrate content and the COD content in the reverse osmosis concentrated water by adopting a method of adding a compound microbial agent; the composite biological bacterial agent contains paracoccus (paracoccus)Paracoccus sp.) FSTB-2, Microbacterium beiense (F.), (Microbacterium kitamiense) FSTB-4, Pseudomonas stutzeri (Pseudomonas stutzeri) At least one of FSTB-5, and Paracoccus denitrificans (B)Paracoccus denitrificans) DN-3 and Methylobacterium (M) ((M))Methylobacterium phyllosphaerae) At least one of SDN-3, wherein Paracoccus FSTB-2, Microbacterium beijerinckii FSTB-4 and Pseudomonas stutzeri FSTB-5 have been deposited in "China general microbiological culture Collection center of China Committee for culture Collection of microorganisms" at 6 months and 1 days 2015, and the deposit is compiledThe numbers are respectively CGMCC No.10938, CGMCC No.10939 and CGMCC No. 10940; the paracoccus denitrificans DN-3 and the methylobacterium SDN-3 are already preserved in China general microbiological culture Collection center (CGMCC) on 11.03.2010, and the preservation numbers are CGMCC No.3658 and CGMCC No.3660 respectively.

The preservation number of the paracoccus FSTB-2 is CGMCC No.10938, which is applied for publication in CN201510737219.4 and submits preservation and survival evidence; the preservation numbers of the Peganella taishanensis FSTB-4 are CGMCC No.10939, which is applied and published in CN201510737150.5 and submits preservation and survival evidence; the preservation number of the Pseudomonas stutzeri FSTB-5 is CGMCC No.10940, which is filed in CN201510737176.X and submits preservation and survival evidence. The preservation number of the paracoccus denitrificans DN-3 is CGMCC No.3658, which is disclosed in CN102465104A and submits preservation and survival evidence; the preservation numbers of the methylobacterium SDN-3 are CGMCC No.3660 and are disclosed in CN102465103A, and a preservation and survival certificate is submitted.

The membrane bioreactor can be a Biological Aerated Filter (BAF), a Membrane Bioreactor (MBR), a moving bed membrane bioreactor (MBBR) and the like, and BAF is preferably adopted. 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.

In the compound microbial agent, the volume ratio of the paracoccus denitrificans DN-3 and/or the methylobacterium SDN-3 to at least one of paracoccus FSTB-2, the Microbacterium beiense FSTB-4 and the Pseudomonas stutzeri FSTB-5 is 1: 1-1: 5. (the cell volume is the cell volume obtained by centrifugation at 1 ten thousand rpm for 5 minutes after the culture, based on the cell volume, the same applies hereinafter). Paracoccus denitrificans DN-3 and methylobacterium SDN-3 can be one of the two or can be mixed thallus of the two in any proportion. Preferably contains both Paracoccus FSTB-2 and Pseudomonas stutzeri FSTB-5. More preferably, five strains of paracoccus denitrificans DN-3, methylobacterium SDN-3, paracoccus FSTB-2, Microbacterium beiense FSTB-4 and Pseudomonas stutzeri FSTB-5 are simultaneously contained. When the microbial inoculum only contains any one of the two strains, the COD can be treated to be less than 60mg/L, and the total nitrogen can be treated to be 20-25 mg/L; when the bacillus subtilis simultaneously contains two strains of paracoccus FSTB-2 and pseudomonas stutzeri FSTB-5, COD can be treated to be less than 50mg/L, and total nitrogen can be treated to be 10-25 mg/L; when the five strains are contained, COD can be treated to be less than 40mg/L, and total nitrogen can be treated to be less than 15 mg/L. The formula of the compound microbial agent can be specifically selected according to the requirements of the water quality of inlet water, the index requirement of outlet water, the stability of the whole set of process equipment and the like.

The dosage of the compound microbial inoculum is 0.01-1 percent of the volume of the treated wastewater, and preferably 0.05-0.5 percent. Can be specifically adjusted according to the water quality and the index requirements of treated effluent.

The biochemical treatment method of the reverse osmosis concentrated water can be suitable for biochemical treatment of one-stage or multi-stage reverse osmosis concentrated water, the salt content of inlet water can reach 100000 mg/L, COD can reach 1500 mg/L, nitrate can reach 1000 mg/L, and the numerical value is preferably taken as the upper limit control condition.

The colony color of the paracoccus FSTB-2 is beige, the individual strain is spherical, gram staining is negative, oxidase is positive, catalase is negative, various carbon sources can be decomposed and utilized, and nitrate reduction activity is realized. The colony color of the Peganella taiwanensis FSTB-4 is light grayish brown, the individual strain is rod-shaped, gram-positive, oxidase-negative and catalase-positive, can decompose and utilize various carbon sources, and has the nitrate reduction characteristic. The colony color of the pseudomonas stutzeri FSTB-5 is light ginger yellow, the individual strain is rod-shaped, gram-negative, oxidase-negative and catalase-positive, has nitrate reduction performance, and can decompose and utilize various carbon sources. The paracoccus FSTB-2, the Microbacterium beijerinckii FSTB-4 and the Pseudomonas stutzeri FSTB-5 can be independently applied to the high-efficiency removal of COD in the salt-containing wastewater with the salt content of 1.0-5.0 wt%.

The formula of the FSTB liquid culture medium used for activating the thallus of the paracoccus FSTB-2, the Microbacterium beijerinckii FSTB-4 and the Pseudomonas stutzeri FSTB-5 related by the compound microbial agent and culturing the seed liquid comprises the following components: FeSO₄•7H₂O 25mg/L，NH₄NO₃286mg/L，KCl 929mg/L，CaCl₂2769mg/L, NaCl 21008mg/L, beef extract 5g/L, peptone 10g/L, and pH 6.0-8.0. Paracoccus denitrificans DN-3 the culture medium formula used for thallus activation and seed liquid culture is as follows: KNO₃1g/L, sodium succinate 8g/L, KH₂PO₄1g/L，FeCl₂0.5 g/L. The formula of a culture medium for activating methylobacterium SDN-3 thalli and culturing a seed solution is as follows: ammonium sulfate 0.5g/L, methanol 0.75mL/L, KH₂PO₄1g/L，FeCL₂0.5 g/L. The solid medium was the liquid medium described above to which 2% agar was added.

In the method, the reverse osmosis treatment is preferably a two-stage anti-membrane pollution combined membrane process combining medium-pressure reverse osmosis and high-pressure reverse osmosis, and the method comprises the steps of firstly carrying out medium-pressure reverse osmosis, 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 the electrodialysis unit together, recycling the produced water of the high-pressure reverse osmosis, and carrying out biochemical treatment on the concentrated water of the high-pressure reverse osmosis. Recycle refers to the need for reuse in industrial settings or other uses. 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 subjected to cross flow filtration. The medium-pressure membrane and the high-pressure membrane can be selected from membranes for reverse osmosis commonly used in the field. After the two-stage reverse osmosis membrane separation process, the TDS of the generated concentrated water can reach more than 50000 mg/L.

In the method, biochemical treatment effluent is firstly pretreated by softening, coagulating sedimentation, rough filtration and ultrafiltration, and then is further concentrated by electrodialysis, electrodialysis fresh water is circulated as high-pressure reverse osmosis inlet water, and the generated concentrated water is circulated and crystallized. The softening and flocculating settling processes are carried out in a high-density clarification tank, the 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. 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. The softener is one or more of calcium hydroxide, sodium hydroxide and sodium carbonate with different concentrations which are added according to the water quality of the high-pressure reverse osmosis concentrated water; the flocculant is a PFS and PAM composite coagulant, the concentration of PFS is 10-300 mg/L, and the concentration of PAM is 0.5-12 mg/L. The electrodialytic water inlet index is controlled to be less than 50mg/L, COD and less than 400 mg/L, and the turbidity is less than 3 NTU.

In the method, after electrodialysis concentration, the TDS in the concentrated water can reach over 200000 mg/L. The electrodialytic fresh water TDS is less than 25000mg/L, generally more than 10000 mg/L, preferably more than 15000 mg/L.

The method for recycling the salt-containing wastewater sequentially comprises pretreatment, concentration treatment and crystallization, wherein the concentration treatment adopts the method for concentrating the salt-containing wastewater.

The invention relates to a specific salt-containing wastewater recycling treatment method, 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. According to the quality of the incoming water, the pretreatment can also comprise the processes of oil removal, biochemical treatment, homogeneous and uniform treatment and the like;

(2) and (5) concentrating. The concentration treatment method of the invention is adopted.

(3) Carrying out ozone catalytic oxidation on concentrated water generated by concentration treatment, then carrying out primary evaporation crystallization to obtain sodium sulfate and primary mother liquor, carrying out freezing crystallization on the primary mother liquor to obtain mirabilite and secondary mother liquor, carrying out secondary evaporation crystallization on the secondary mother liquor to obtain sodium chloride and tertiary mother liquor, and circulating crystallization from the tertiary mother liquor to the primary evaporation crystallization step.

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 size 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), 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 70mg/L, and the turbidity is less than 3 NTU.

Further, in the step (3), the catalytic oxidation by ozone can adopt the prior art, for example, the catalyst can adopt one or more of the published patents CN105709737A, CN105709743A or CN 105709744A. COD in the ozone catalytic oxygen effluent is controlled below 500 mg/L.

Further, in the step (3), 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 (3), 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 (3), 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 concentration 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 for concentrating and treating the salt-containing wastewater has the following 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 biochemical unit can remove nitrate in sewage by adding the salt-resistant COD-removing denitrification microbial agent, 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, so that the treatment cost of the subsequent precipitation and ozone catalytic oxidation unit is reduced.

3. The operation cost of the pretreatment unit is low. The flow and conditions of the membrane unit in the concentration method are cooperated, so that the severity requirement of the water inlet index of the membrane unit is reduced, and the operation cost can be greatly reduced by the pretreatment operation of the inlet water. 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.

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 preparation method of the salt-tolerant COD-removing denitrification microbial agent in the invention (3) comprises the following steps:

(1) respectively inoculating paracoccus FSTB-2, Microbacterium beijerinckii FSTB-4 and Pseudomonas stutzeri FSTB-5 on an FSTB solid culture medium for activation; respectively inoculating paracoccus denitrificans DN-3 and methylobacterium SDN-3 on corresponding solid culture media for activation;

(2) taking colonies of paracoccus FSTB-2, Microbacterium beiense FSTB-4 and Pseudomonas stutzeri FSTB-5 on the plate by using an inoculating ring, respectively inoculating colonies of paracoccus denitrificans DN-3 and Methylobacterium SDN-3 on the plate by using the inoculating ring into corresponding liquid culture solutions, respectively culturing for 24-72 hours to logarithmic growth phase at the temperature of 20-40 ℃ and the speed of 150-240rpm, and obtaining liquid microbial inoculum seed liquid;

(3) the seed solution is amplified and cultured, thallus is collected, and paracoccus FSTB-2, microbacterium beige FSTB-4, pseudomonas stutzeri FSTB-5, paracoccus denitrificans DN-3 and methylobacterium SDN-3 are prepared according to the proportion shown in table 1, and the proportion is specifically shown in table 1.

TABLE 1 composition and ratio of salt-tolerant COD-removing denitrifying microbial agent

Microbial inoculum	Composition of thallus	Proportioning
			A	FSTB-2:FSTB-5:SDN-3	3:1:1
B	FSTB-2:FSTB-4:FSTB-5:DN-3: SDN-3:	1:1:1:1:1

Example 1

The average concentration of each pollutant of the industrial wastewater with high salt content is as follows: COD 75mg/L, total hardness (as CaCO)₃Calculated as CaCO) of 1000 mg/L and total alkalinity₃Calculated) is 400 mg/L, the silicon dioxide is 30 mg/L, TDS is 5000mg/L, the nitrate ion concentration is 70mg/L, the chloride ion concentration is 700 mg/L, the sulfate ion concentration is 1000 mg/L, and the pH value is 7.8. 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 following steps of enabling salt-containing wastewater to enter a high-density clarification tank, adding 1.8 g/L of calcium hydroxide in a reaction zone of the high-density clarification tank according to the quality of the salt-containing wastewater to maintain the pH value at 11.0-11.5, adding 2.4 g/L of sodium carbonate, adding 50mg/L of PFS for coagulation, adding 4 mg/L of 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 at an outlet of the high-density clarification tank to adjust the pH value to about 7, removing suspended matters, colloid particles and the like in water from the water discharged from the high-density clarification tank through a V-shaped filter tank, and enabling the water to enter an. The operating pressure of the ultrafiltration device is 0.05 MPa, and the ultrafiltration is carried out for further treatment. The hardness of the final wastewater was 200mg/L, COD at a concentration of 70mg/L, turbidity was less than 1 NTU, and nitrate ion concentration was 68 mg/L.

(2) 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 operating pressure of the medium-pressure reverse osmosis device is about 1.5 MPa; concentrated water of medium-pressure reverse osmosis and fresh water of the electrodialysis unit enter a high-pressure reverse osmosis device, and the operating pressure of the high-pressure reverse osmosis device is about 3.5 MPa. The COD of the fresh water obtained by the medium-pressure reverse osmosis and the high-pressure reverse osmosis is less than 20mg/L, the TDS is less than 300 mg/L, and the hardness is less than 10mg/L, so that the water quality index requirement of the circulating water replenishing 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 50000mg/L, the average concentration of COD contained in the reverse osmosis concentrated water is 520 mg/L, and the average concentration of nitrate ions is 650 mg/L.

(3) And (4) enabling concentrated water of the reverse osmosis unit to enter the biological aerated filter for removing COD 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 COD-removing denitrifying microbial inoculum A which is 0.1 percent of the volume of the wastewater treated per hour into the biological aerated filter. The COD concentration of the effluent treated by the biological aerated filter is less than 180 mg/L, and the nitrate ion concentration is less than 70 mg/L.

(4) And (2) feeding the effluent of the biological aerated filter into a high-density clarification tank, adding 0.50 g/L of 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 11.55, adding 2.0 g/L of sodium carbonate, adding 80mg/L of PFS for coagulation, adding 6 mg/L of PAM for coagulation assistance, fully coagulating in the reaction zone, feeding the effluent into a clarification zone of the high-density tank for precipitation, and finally adding hydrochloric acid or sulfuric acid into an outlet of the high-density clarification tank to adjust the pH value to about 7.

(6) 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 further treatment of ultrafiltration, the index hardness of the wastewater is finally less than 50mg/L and the turbidity is less than 1 NTU.

(7) 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 15000 mg/L, and the produced water enters a high-pressure reverse osmosis membrane for further desalination treatment; TDS in the concentrated water reaches 220000 mg/L. 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.

(8) The electrodialysis concentrated water enters an advanced catalytic oxidation device to reduce the COD which is difficult to degrade in the water to about 400 mg/L, and then enters an evaporation crystallization unit.

(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 the evaporation temperature of 100 ℃ and the crystallization temperature of 60-80 ℃; the mother liquor left after crystallization is put into 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 93 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 crystallization mother liquor of the secondary evaporation crystallization is controlled to be above 400000 mg/L, the sodium chloride is circulated to the primary evaporation crystallization to evaporate the residual salt in the crystallization mother liquor again, the purity of three crystallization products is qualified through the circulation process and condition control, and the recovery rates of water and salt are improved. The circulating mother liquor with too high COD accumulation (such as about 10000 mg/L) can be treated by circulating to an ozone catalytic oxidation device or other modes.

Example 2

The average concentration of each pollutant of the industrial wastewater with high salt content is as follows: COD of 78 mg/L, total hardnessDegree (as CaCO)₃Calculated as CaCO) of 1200 mg/L and total alkalinity₃Calculated) is 500 mg/L, the silicon dioxide is 30 mg/L, TDS is 5500 mg/L, wherein, the nitrate ion concentration is 80mg/L, the chloride ion concentration is 700 mg/L, the sulfate ion concentration is 1500 mg/L, and the pH value is 7.8.

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 sodium hydroxide at a concentration of 2.0 g/L in a reaction zone of the high-density clarification tank according to the quality of the salt-containing wastewater to maintain the pH value at 11.0-11.5, adding 2.5 g/L sodium carbonate, adding 100mg/L PFS for coagulation, adding 10mg/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 at an outlet of the high-density clarification tank to adjust the pH value to about 7.5, removing suspended matters, colloid particles and the like in water from water discharged from the high-density clarification tank through a V-shaped filter tank, and enabling the water to enter an ultrafiltration device. The operating pressure of the ultrafiltration device is 0.05 MPa, and the ultrafiltration is carried out for further treatment. The hardness of the final wastewater was 220 mg/L, COD, the concentration was 70mg/L, the turbidity was less than 1 NTU, and the nitrate ion concentration was 75 mg/L.

(2) 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 3 MPa; concentrated water of medium-pressure reverse osmosis and fresh water of an electrodialysis unit enter a high-pressure reverse osmosis device, the high-pressure reverse osmosis device adopts an anti-pollution high-pressure reverse osmosis membrane, and the operating pressure is about 5 MPa. The COD of the fresh water obtained by the medium-pressure reverse osmosis and the high-pressure reverse osmosis is less than 20mg/L, the TDS is less than 300 mg/L, and the hardness is less than 10mg/L, so that the water quality index requirement of the circulating water replenishing 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 55000 mg/L, the average COD concentration contained in the reverse osmosis concentrated water is 550 mg/L, and the average nitrate ion concentration is 720 mg/L.

(3) And (4) enabling concentrated water of the reverse osmosis unit to enter the biological aerated filter for removing COD and nitrate radicals. Activated sludge is inoculated in the biological aerated filter in advance according to the sludge concentration of 3000mg/L for starting. The operating conditions were: the temperature was 30 ℃, the pH was 8.0, and the dissolved oxygen concentration was 1.0 mg/L. Adding a salt-tolerant COD-removing denitrifying microbial inoculum B which is 0.1 percent of the volume of the wastewater treated per hour into the biological aerated filter. The COD concentration of the effluent treated by the biological aerated filter is less than 180 mg/L, and the nitrate ion concentration is less than 70 mg/L.

(4) And (2) feeding the effluent of the biological aerated filter into a high-density clarification tank, adding 0.70 g/L of 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 11.5, then adding 2.5 g/L of sodium carbonate, then adding 150 mg/L of PFS for coagulation, adding 10mg/L of PAM for coagulation assistance, after fully coagulating in the reaction zone, feeding the effluent into a clarification zone of the high-density tank for precipitation, and finally adding hydrochloric acid or sulfuric acid into an outlet of the high-density clarification tank to adjust the pH value to about 7.5.

(7) 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 15000 mg/L, and the produced water enters a high-pressure reverse osmosis membrane for further desalination treatment; the TDS in the concentrated water reaches over 200000 mg/L. 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 the evaporation temperature of 120 ℃ and the crystallization temperature of 60-80 ℃; the residual mother liquid after crystallization is put into 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 94 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 crystallization mother liquor of the secondary evaporation crystallization is controlled to be above 400000 mg/L, the sodium chloride is circulated to the primary evaporation crystallization to evaporate the residual salt in the crystallization mother liquor again, the purity of three crystallization products is qualified through the circulation process and condition control, and the recovery rates of water and salt are improved. The circulating mother liquor with too high COD accumulation (such as about 10000 mg/L) can be treated by circulating to an ozone catalytic oxidation device or other modes.

Claims

1. A method for concentrating salt-containing wastewater adopts a method combining reverse osmosis and electrodialysis to concentrate the salt-containing wastewater, and is characterized in that: the combination mode of reverse osmosis and electrodialysis is as follows: the reverse osmosis adopts at least two stages, namely medium-pressure reverse osmosis and high-pressure reverse osmosis, the high-pressure reverse osmosis inlet water comprises medium-pressure reverse osmosis concentrated water and at least part of electrodialysis fresh water, after the two-stage reverse osmosis membrane separation process, the TDS of the generated concentrated water reaches more than 50000mg/L, after at least part of the high-pressure reverse osmosis concentrated water is subjected to biochemical treatment, the high-pressure reverse osmosis concentrated water is further concentrated by adopting an electrodialysis method, and the electrodialysis concentrated water is final concentrated outlet water; after electrodialysis concentration, the TDS in the concentrated water reaches over 200000 mg/L, and the TDS in the electrodialysis fresh water is less than 25000mg/L and more than 10000 mg/L; the biochemical treatment method comprises the following steps of introducing high-pressure reverse osmosis concentrated water into a membrane bioreactor, and reducing the nitrate content and the COD content in the reverse osmosis concentrated water by adopting a method of adding a microbial agent; the microbial agent contains at least one of paracoccus denitrificans DN-3 and methylobacterium SDN-3, wherein the paracoccus denitrificans DN-3 and the methylobacterium SDN-3 are already preserved in China general microbiological culture Collection center on 03-11 2010, and the preservation numbers are CGMCC No.3658 and CGMCC No.3660 respectively.

2. The method of claim 1, wherein: the reverse osmosis treatment adopts a two-stage anti-membrane pollution combined membrane process combining medium-pressure reverse osmosis and high-pressure reverse osmosis, and comprises the steps of firstly carrying out medium-pressure reverse osmosis, 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 the electrodialysis unit together, recycling the produced water of the high-pressure reverse osmosis, and carrying out biochemical treatment on the concentrated water of the high-pressure reverse osmosis.

3. A method according to claim 1 or 2, characterized in that: 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.

4. The method of claim 1, wherein: the biochemical treatment effluent is firstly pretreated by softening, coagulating sedimentation, rough filtration and ultrafiltration, and then is further concentrated by electrodialysis, electrodialytic fresh water is circulated as high-pressure reverse osmosis inlet water, and the generated concentrated water is circulated and crystallized.

5. The method of claim 1, wherein: and after electrodialysis concentration, the TDS of electrodialysis fresh water is over 15000 mg/L.

6. The method of claim 5, wherein: 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.

7. The method of claim 5, wherein: the dosage of the microbial inoculum is 0.01-1 percent of the volume of the treated wastewater.

8. The method of claim 5, wherein: the dosage of the microbial inoculum is 0.05 to 0.5 percent of the volume of the treated wastewater.

9. A method for recycling salt-containing wastewater sequentially comprises pretreatment, concentration treatment and crystallization, and is characterized in that: the method of claim 1 is used for the concentration treatment.

10. A method for recycling salt-containing wastewater 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) concentration treatment; the concentration treatment method according to claim 1;

11. The method of claim 10, wherein: in the step (3), the temperature of evaporation concentration is 50-150 ℃ and the crystallization temperature is 50-100 ℃ during primary evaporation crystallization; 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 ℃.