CN108117224B

CN108117224B - Pretreatment method of desulfurization wastewater

Info

Publication number: CN108117224B
Application number: CN201611073715.5A
Authority: CN
Inventors: 高会杰; 孙丹凤; 郭志华; 赵胜楠; 陈明翔
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: 2021-01-05
Anticipated expiration: 2036-11-29
Also published as: CN108117224A

Abstract

The invention relates to a pretreatment method of desulfurization wastewater, which mainly comprises the following steps of (1) a neutralization unit: mainly removing Mg in wastewater²⁺、Zn²⁺、Cu²⁺、Ni²⁺、Cr³⁺Most heavy metal ions; (2) sulfate reduction unit: mainly removing residual metal ions in the wastewater after neutralization treatment; (3) a denitrification unit: mainly removing nitrogen-containing pollutants and organic pollutants in a high-salt environment, and refluxing a part of effluent to the step (2); (4) a settling unit: and (4) after mud-water separation, the supernatant enters a subsequent unit for treatment. The method removes heavy metal ions, organic pollutants and nitrogen-containing pollutants in the wastewater by combining a chemical precipitation method and a biological method, ensures the subsequent zero emission and resource utilization of the desulfurization wastewater because the total nitrogen concentration in the treated wastewater is lower than 15mg/L and the COD concentration is lower than 60mg/L, and has the characteristics of simplicity, feasibility, low investment, low medicament cost, good effect and the like.

Description

Pretreatment method of desulfurization wastewater

Technical Field

The invention belongs to the technical field of environment-friendly wastewater treatment, and particularly relates to a pretreatment method of desulfurization wastewater.

Background

In order to maintain the balance of the slurry circulation system of the desulfurization apparatus during the flue gas desulfurization process, it is necessary to discharge waste water, i.e., desulfurization waste water, from the absorption tower at regular times. The wastewater contains a large amount of impurities, such as suspended matters, inorganic salt ions, heavy metal ions and the like, and can be discharged only by purification treatment. At present, the most common domestic desulfurization wastewater treatment method is a chemical precipitation method, and most of suspended matters, heavy metal ions and the like in the desulfurization wastewater are removed by physical and chemical methods through means of neutralization, sedimentation, flocculation clarification and the like, so that the desulfurization wastewater reaches the current national discharge standard.

In recent years, a plurality of desulfurization wastewater treatment processes, such as evaporation, recycling, clarification and the like, are newly developed. In the Danish Aiwude power plant, the fluidized bed is used to replace the chemical precipitation method to treat the desulfurization wastewater, a certain amount of potassium permanganate is added into the fluidized bed system to oxidize a large amount of bivalent manganese and ferrous ions contained in the desulfurization wastewater into manganese dioxide and ferric hydroxide, a covering layer is formed on the surface of heavy metal, and the heavy metal in the wastewater is removed. The chemical precipitation-microfiltration membrane method is adopted in advanced Europe such as Netherlands to treat the desulfurization wastewater, and NaOH or Ca (OH) is added into a precipitation tank₂And Na₂S and other substances enable most of metal and heavy metal ions in the wastewater to form substances which are difficult to dissolve in water and are removed by precipitation. Although the comprehensive application of the technologies obtains good treatment effect, the treated wastewater can meet strict pollutant discharge standards, and some of the treated wastewater can realize zero discharge and resource utilization of the desulfurization wastewater, the heavy metal ions can be removed only by adding a chemical agent, so that the salt concentration in the wastewater is additionally increased, and the treatment difficulty of a subsequent unit is increased; meanwhile, the risk of more serious wastewater pollution caused by improper use of sulfides exists; and the existing method does not relate to the removal of organic pollutants and nitrogen-containing pollutants in the wastewater.

Some flue gas desulfurization technologies adopt an oxygen-deficient regeneration mode in the application process, and nitrogen elements are reduced into ammonia gas due to the loss of oxygen, so that a large amount of ammonia nitrogen exists in waste liquid. In particular, some ozone oxidation denitration and sodium desulfurization technologies can generate a large amount of nitrate in the waste liquid. The existence of the nitrogen-containing pollutants brings difficulty to the treatment of the desulfurization wastewater, and further limits the zero emission and resource utilization of the wastewater.

Chinese patent CN201510878477.4 discloses a pretreatment method before evaporative crystallization of thermal power plant desulfurization wastewater, which completes pretreatment before evaporative crystallization of the desulfurization wastewater by sequentially carrying out four steps of coagulation reaction, multi-media filter filtration, strong cation type sodium ion exchanger softening and pH value adjustment on the thermal power plant desulfurization wastewater. CN201510625606.9 discloses a desulfurization wastewater resourceful treatment device and a method thereof, which adopt membrane treatment and evaporative crystallization treatment technologies to carry out high-efficiency combined design and comprise a pretreatment system, a membrane concentration treatment system and an evaporative crystallization treatment system. The methods do not consider the treatment of organic pollutants and nitrogen-containing pollutants in the desulfurization wastewater, and have great influence on a membrane system.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a method for pretreating desulfurization wastewater. The method removes heavy metal ions, organic pollutants and nitrogen-containing pollutants in the wastewater by combining a chemical precipitation method and a biological method, ensures the subsequent zero emission and resource utilization of the desulfurization wastewater because the total nitrogen concentration in the treated wastewater is lower than 15mg/L and the COD concentration is lower than 60mg/L, and has the characteristics of simplicity, feasibility, low investment, low medicament cost, good effect and the like.

The pretreatment method of the desulfurization wastewater mainly comprises the following units:

(1) a neutralization unit: adding alkali to adjust pH to 8-10, mainly removing Mg in wastewater²⁺、Zn²⁺、Cu²⁺、Ni²⁺、Cr³⁺Most heavy metal ions;

(2) sulfate reduction unit: an anaerobic sulfate reduction treatment system is adopted to mainly remove Hg remained in the neutralized wastewater²⁺、Pb²⁺、Cr³⁺Plasma metal ions;

(3) a denitrification unit: a denitrification biochemical treatment system is adopted, the removal of nitrogen-containing pollutants and organic pollutants is mainly realized in a high-salt environment, and the effluent part flows back to the step (2);

(4) a settling unit: and (4) carrying out sedimentation treatment, and treating the supernatant after mud-water separation in a subsequent unit.

The pH value is adjusted in the step (1) of the invention mainly by adding NaOH and Ca (OH)₂Alkaline substance is added to control pH to 8-10, preferably 8.5-9.5, and Mg in wastewater²⁺、Zn²⁺、Cu²⁺、Ni²⁺、Cr³⁺The hydroxide precipitate generated by the heavy metal ions is removed.

The sulfate reduction unit in the step (2) of the invention is a conventional anaerobic sulfate reduction treatment system, and is mainly used for reducing partial sulfate to generate hydrogen sulfide and Hg in wastewater²⁺、Pb²⁺、Cr³⁺And generating sulfide precipitate through reaction, and further removing heavy metal ions.

The denitrification unit in the step (3) of the invention mainly realizes the removal of nitrogen-containing pollutants and organic pollutants in a high-salt environment. The existing denitrification biochemical treatment system can be adopted, such as A/O, SBR and the like.

In the invention, the reflux ratio of the step (3) to the step (2) is controlled to be 50-200% according to the specific effluent quality in the step (3). When the removal rate of the heavy metal ions in the effluent obtained in the step (2) is lower than 90 percent, the reflux ratio needs to be gradually increased, the adjustment amplitude is 5-15 percent, and the oxidation-reduction potential (ORP) is kept between-300 and-200 mV until the removal rate of the heavy metal reaches 95 percent. When the concentration of the sulfur ions in the effluent obtained in the step (2) is more than 2.0mg/L, the reflux ratio needs to be gradually reduced, the adjustment range is 5-15 percentage points, the oxidation-reduction potential (ORP) is kept between-200 mV and-50 mV, the activity of sulfate reducing bacteria is partially inhibited, and a small amount of H is generated₂S, until the concentration of the sulfur ions is lower than 0.2 mg/L. Through the regulation and control, the effective removal of heavy metal ions can be ensured, and excessive sulfur ions can not be generated.

Further, denitrification activated sludge or denitrification bacteria can be inoculated in the denitrification unit, preferably denitrification bacteria are used, such as various denitrification bacteria disclosed currently, more preferably salt-tolerant bacteria are adopted, and the bacteria contain at least one of paracoccus FSTB-2, Microbacterium beijerinckii FSTB-4 and Pseudomonas stutzeri FSTB-5, and simultaneously contain Coccocus palustris (C.palustris)Kocuria palustris) FSDN-A and Staphylococcus cohnii (II)Staphylococcus cohnii) FSDN-C, whileComprises Arthrobacter bacteria (A), (B), (C)Arthrobacter creatinolyticus) FDN-1 and Flavobacterium aquatile (F: (F;)Flavobacterium mizutaii) At least one of FDN-2, and Paracoccus denitrificans (B)Paracoccus denitrificans) DN-3 and Methylobacterium (M) ((M))Methylobacterium phyllosphaerae) At least one of SDN-3.

In the salt-tolerant microbial inoculum, paracoccus FSTB-2, micrococcus beige FSTB-4 and pseudomonas stutzeri FSTB-5 are preserved in the 'common microorganism center of China Committee for culture Collection of microorganisms' in 2015 at 6 months and 1 days, the preservation numbers are CGMCC No.10938, CGMCC No.10939 and CGMCC No.10940, and the preservation addresses are as follows: the institute of microbiology, national academy of sciences No.3, Xilu No.1, Beijing, Chaoyang, Beijing. Wherein the paracoccus FSTB-2 is published in CN201510737219.4 and submitted with a deposit and a survival certificate; microbacterium beijerinckii FSTB-4 was filed in CN201510737150.5 and submitted for preservation and proof of survival; pseudomonas stutzeri FSTB-5 was filed in CN201510737176.X and submitted for deposit and proof of survival. The preservation numbers of the Coicoccus palustris FSDN-A, the Staphylococcus cohnii FSDN-C, the Arthrobacter FDN-1, the Flavobacterium aquatile FDN-2, the paracoccus denitrificans DN-3 and the methylobacterium SDN-3 are CGMCC NO.5061, CGMCC NO.5062, CGMCC NO.3657, CGMCC NO.3659, CGMCC NO.3658 and CGMCC NO.3660 respectively, which are disclosed in CN103103141A, CN103014128A, CN102465106A, CN102465105A, CN102465104A and CN 102465103.

In the salt-tolerant microbial inoculum, the volume ratio of at least one of paracoccus FSTB-2, Microbacterium beijerinckii FSTB-4 and Pseudomonas stutzeri FSTB-5, at least one of Coccocus swartyi FSDN-A, Staphylococcus cohnii FSDN-C, Arthrobacter FDN-1 and Flavobacterium aquatile FDN-2, and at least one of paracoccus denitrificans DN-3 and Methylobacterium SDN-3 is 1-5:1:1:0.1-10: 0.1-10. (the cell volume was obtained by centrifugation at 1 ten thousand rpm for 5 minutes after the culture, based on the cell volume, the same applies hereinafter). Preferably contains Paracoccus FSTB-2, Pseudomonas stutzeri FSTB-5, Coccocus palustris FSDN-A and Staphylococcus cohnii FSDN-C. Specifically, the formula of the salt-tolerant microbial inoculum is 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.

In the salt-tolerant microbial agent, the Paracoccus FSTB-2, the Microbacterium northern Erythroseum FSTB-4 and the Pseudomonas stutzeri FSTB-5 can be independently applied to the efficient removal of COD in the salt-containing wastewater with the salt content of 10000-50000 mg/L. Seed solutions of three bacteria of Paracoccus FSTB-2, Microbacterium beijerinckii FSTB-4 and Pseudomonas stutzeri FSTB-5 can be independently amplified and cultured, or the seed solutions of the three bacteria can be mixed and then amplified and cultured. Seed solutions of the Coicoccus palustris FSDN-A and the Staphylococcus cohnii FSDN-C need to be separately amplified and cultured; seed solutions of arthrobacter FDN-1 and flavobacterium brucellosis FDN-2 can be independently amplified and cultured, or the seed solutions of the two bacteria can be mixed and amplified and cultured together; seed solutions of paracoccus denitrificans DN-3 and methylobacterium SDN-3 can be independently amplified and cultured or seed solutions of two kinds of bacteria are mixed and amplified and cultured together.

In the invention, the salt-tolerant microbial inoculum of the step (3) is added according to 0.001-0.1%, preferably 0.005-0.05% of the volume of the wastewater treated per hour. Can be specifically adjusted according to the water quality and the index requirements of treated effluent.

The sedimentation treatment in the step (4) can adopt sedimentation modes such as inclined plate sedimentation, gravity sedimentation and the like to realize mud-water separation. And (3) when the supernatant in the step (4) does not meet the requirements of subsequent treatment, refluxing to the step (2), and entering a subsequent unit for treatment or recycling after meeting the requirements, wherein the supernatant can be subjected to evaporation crystallization after concentration treatment.

The specific water quality of the desulfurization wastewater of the invention is as follows: pH is 4-6, SS (suspended substance) is 5000-15000mg/L, Ca²⁺Is 1000-2000mg/L, Mg²⁺3000-7000mg/L, Cl^-7000-₄ ^2-Is 4000-8000mg/L, SiO₂5-50mg/L, TDS (total dissolved solids) is 16000-36000mg/L, COD concentration of 400-1000mg/L, total nitrogen concentration of 100-300mg/L, and heavy metal ions such as mercury, chromium, cadmium, nickel, lead, zinc, copper and the like are contained.

The method provided by the invention adopts a chemical precipitation method and a biological method to remove heavy metal ions, organic pollutants and nitrogen-containing pollutants in the wastewater, and realizes the purpose of efficiently removing heavy metal, total nitrogen and COD through the control of a reflux ratio and an oxidation-reduction potential, the concentration of the total nitrogen in the treated wastewater is lower than 15mg/L, the concentration of the COD is lower than 60mg/L, and the concentration of the heavy metal ions is lower than the limit value specified by a sewage comprehensive discharge standard, so that the guarantee is provided for the subsequent zero discharge and resource utilization of the desulfurization wastewater, and the method has the characteristics of simplicity, feasibility, low investment, low medicament cost, good effect and the like. The invention further realizes the purpose of efficiently removing heavy metal, total nitrogen and COD by adding the synergistic effect of the denitrifier.

The wastewater pretreated by the method enters a subsequent concentration evaporation crystallization unit, so that the operation load of the membrane can be reduced, and the service life of the membrane can be prolonged. The invention solves the problems of cost increase and secondary pollution caused by using chemical agents to treat heavy metals in the prior art, and solves the problems that organic pollutants and nitrogen-containing pollutants in desulfurization wastewater cannot be treated by the prior art.

Drawings

FIG. 1 is a schematic flow diagram of pretreatment of desulfurization waste water according to the present invention;

wherein, the device comprises a 1-neutralization unit, a 2-sulfate reduction unit, a 3-denitrification unit and a 4-sedimentation unit.

Detailed Description

The following detailed description of the specific processes and effects of the present invention is made with reference to the accompanying fig. 1 and examples, but the scope of the present invention is not limited thereby.

By adopting the treatment flow shown in the attached figure 1, the desulfurization waste water firstly enters a neutralization unit 1 and is added with NaOH or Ca (OH)₂Controlling pH to be between 8 and 10 by using alkaline substances, and desulfurizing Mg in the wastewater²⁺、Zn²⁺、Cu²⁺、Ni²⁺、Cr³⁺And removing most of the heavy metal ions to generate hydroxide precipitate. The waste water after alkali neutralization still contains most Hg existing in the form of ions²⁺、Pb²⁺、Cr³⁺Etc. into the sulfate reduction unit 2, S produced by sulfate reduction^2-With Hg²⁺、Pb²⁺Reaction of heavy metals to form sulfidesAnd (4) precipitating. The treated wastewater enters a denitrification unit 3 to further remove nitrogen-containing pollutants and COD, the effluent of the denitrification unit partially flows back to a sulfate reduction unit, and the reflux ratio is controlled to be 50-200%. When the removal rate of the heavy metal ions in the effluent of the sulfate reduction unit is lower than 90 percent, the reflux ratio needs to be gradually increased, the adjustment amplitude is 5-15 percent, and the oxidation-reduction potential (ORP) is kept between-300 and-200 mV until the removal rate of the heavy metal reaches 95 percent. When the concentration of the sulfur ions in the effluent obtained in the step (2) is more than 2.0mg/L, the reflux ratio needs to be gradually reduced, the adjustment range is 5-15 percentage points, the oxidation-reduction potential (ORP) is kept between-200 mV and-50 mV, the activity of sulfate reducing bacteria is partially inhibited, and a small amount of H is generated₂S, until the concentration of the sulfur ions is lower than 0.2 mg/L. Through the regulation and control, effective removal of heavy metal ions can be ensured. The wastewater treated by the three units enters the sedimentation unit 4, the supernatant is discharged after all indexes are qualified, and if the supernatant is not qualified, the supernatant flows back to the sulfate reduction unit 2 for continuous treatment, so that the heavy metals, the organic pollutants and the nitrogen-containing pollutants in the desulfurization wastewater are effectively removed.

The salt-tolerant microbial inoculum used by the invention is prepared by adopting the method described by CN201510737425.5, and the formula of the FSTB liquid culture medium used by paracoccus FSTB-2, Microbacterium beijerinckii FSTB-4 and Pseudomonas stutzeri FSTB-5 is as follows: FeSO₄•7H₂O:25mg/L，NH₄NO₃:286mg/L，KCl:929mg/L，CaCl₂2769mg/L, 21008mg/L NaCl, 5g/L beef extract, 10g/L peptone and 6.0-8.0 pH value; the solid medium is a liquid medium added with 2% agar. The formulA of A culture medium for thallus activation and seed liquid culture of the Coccocus palustris FSDN-A is as follows: 10g/L beef extract, 15g/L peptone and NaNO₂:1.0g/L，KNO₃0.8 g/L. The formula of a culture medium for activating the bacteria and culturing the seed liquid of the staphylococcus cohnii FSDN-C is as follows: 10g/L beef extract, 15g/L peptone and NaNO₂1.0g/L and 1.0mL/L of methanol. The culture medium formula for thallus activation and seed liquid culture of arthrobacter FDN-1 and flavobacterium brucellosis FDN-2 is as follows: 5g/L beef extract, 10g/L peptone and NaNO₂1g/L, adding 1.5-2.5% agar into the solid culture medium. Liquid culture of paracoccus denitrificans DN-3The base formula is as follows: KNO₃1g/L, 8g/L sodium succinate and KH₂PO₄:1g/L，FeCL₂0.5 g/L; 20g/L agar was added to the solid medium. The formula of a liquid culture medium of methylobacterium SDN-3 is as follows: 0.5g/L ammonium sulfate, 0.75mL/L methanol, KH₂PO₄:1g/L，FeCL₂0.5 g/L; solid medium was added with 2% agar. The method specifically 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 the Coicoccus palustris FSDN-A, the Staphylococcus cohnii FSDN-C, the Arthrobacter FDN-1, the Flavobacterium aquatile FDN-2, the Paracoccus denitrificus DN-3 and the methylobacterium SDN-3 on corresponding solid culture mediA for activation; after being evenly coated, the mixture is placed in a constant temperature incubator with the temperature of 35 ℃ for activation.

(2) Bacterial colonies of paracoccus FSTB-2, Microbacterium beijerinckii FSTB-4 and Pseudomonas stutzeri FSTB-5 on the plate are taken by an inoculation ring and inoculated in corresponding FSTB liquid culture mediA respectively, bacterial colonies of Coccocus palustris FSDN-A, Staphylococcus cohnii FSDN-C, Arthrobacter FDN-1, Flavobacterium aquaticum FDN-2, Paracoccus denitrificans DN-3 and Methylobacterium SDN-3 on the plate are taken by the inoculation ring and inoculated in corresponding liquid culture mediA respectively, and shake culture is carried out for 48 hours to logarithmic phase at the temperature of 30 ℃ and 150rpm, so as to obtain liquid microbial inoculum seed liquid.

(3) In A reactor with good aeration and stirring conditions, paracoccus FSTB-2, micrococcus beifolium FSTB-4, pseudomonas stutzeri FSTB-5, cooke bacteriA FSDN-A, staphylococcus cohnii FSDN-C, arthrobacterium FDN-1, flavobacterium brucei FDN-2, paracoccus denitrificans DN-3 and methylobacterium SDN-3 seed solutions are respectively subjected to amplification culture, wherein the COD concentration in the culture solution is 2000mg/L, the total nitrogen concentration is 100mg/L, the salt content is 2.5wt%, and the pH value is 8.0. The culture conditions were all: the temperature is 30 ℃, the dissolved oxygen is 2.0-3.0mg/L, and the culture time is 72 hours, thus obtaining the concentrated bacterial liquid of nine strains.

The concentrated bacterial liquid is collected and prepared according to the proportion shown in the table 1, and the specific composition and the proportion are shown in the table 1.

TABLE 1 compositions and proportions of salt-tolerant microbial inoculum

Example 1

The specific water quality of the desulfurization wastewater generated by a certain power plant is as follows: pH is 4-6, SS is 5000-²⁺1000-1200Mg/L, Mg²⁺3000-3500mg/L of Cl^-7000-8000mg/L, SO₄ ^2-4000-5000mg/L of SiO₂15-20mg/L, TDS 16000-18000mg/L, COD 400-500mg/L, and total nitrogen 100-150 mg/L. And also contains some metal ions, wherein the total mercury is 0.3-0.4mg/L, the total chromium is 2-3mg/L, the total cadmium is 0.5-0.6mg/L, the nickel is 2-3mg/L, the lead is 3-4mg/L, and the zinc is 5-6 mg/L.

By adopting the process of the method, the desulfurization wastewater firstly enters a neutralization unit, NaOH is added to control the pH value to be 8.5-9.0, and Mg in the wastewater is removed²⁺、Zn²⁺、Cu²⁺、Ni²⁺、Cr³⁺And (3) heavy metal ions. The wastewater after the alkali neutralization treatment enters an anaerobic sulfate reduction unit, and S generated by sulfate reduction^2-With Hg²⁺、Pb²⁺、Cr³⁺The heavy metals react to generate sulfide precipitate. And the wastewater from which the heavy metal ions are removed enters a denitrification unit, and effluent from the denitrification unit flows back to the sulfate reduction unit according to a reflux ratio of 50%. When the removal rate of heavy metal ions in the effluent of the sulfate reduction unit is lower than 90 percent, gradually reducing the reflux ratio by 10 percent each time to enable the ORP to be between-300 and-250 mV until the removal rate reaches 95 percent; when the concentration of the sulfur ions in the effluent is more than 2.0mg/L, gradually increasing the reflux ratio by 10 percent each time to enable the ORP to be between-100 and-50 mV until the concentration of the sulfur ions is less than 0.2 mg/L. And (3) settling the wastewater treated by the three units, wherein the COD concentration in the supernatant is lower than 60mg/L, the total nitrogen concentration is lower than 15mg/L, and no heavy metal ions can be detected.

Example 2

The wastewater treatment, process and operating conditions were the same as in example 1. The difference lies in that: adding 1# halotolerant microbial inoculum into the denitrification unit according to 0.05% of the volume of the wastewater treated per hour. And (3) settling the wastewater treated by the three units, wherein the COD concentration in the supernatant is lower than 50mg/L, the total nitrogen concentration is lower than 10mg/L, and no heavy metal ions can be detected.

Example 3

The wastewater treatment, process and operating conditions were the same as in example 1. The difference lies in that: adding a salt-tolerant microbial inoculum 2# into the denitrification unit according to 0.005 percent of the volume of the wastewater treated per hour. And (3) settling the wastewater treated by the three units, wherein the COD concentration in the supernatant is lower than 50mg/L, the total nitrogen concentration is lower than 10mg/L, and no heavy metal ions can be detected.

Example 4

The specific water quality of the desulfurization wastewater generated by a certain power plant is as follows: pH: 4-6, SS: 8000-10000mg/L, Ca²⁺：1500-2000mg/L、Mg²⁺：3500-4500mg/L、Cl^-：8000-9000mg/L、SO₄ ^2-：5000-6000mg/L、SiO₂: 15-20mg/L, TDS: 18000-20000mg/L, COD: 500-600mg/L, total nitrogen: 150-200 mg/L. Also contains heavy metals, wherein the total mercury: 0.4-0.5mg/L, total chromium: 3-4mg/L, total cadmium: 0.6-0.7mg/L, nickel: 2-3mg/L, lead: 4-5mg/L, zinc: 6-8 mg/L.

By adopting the process of the method, the desulfurization wastewater firstly enters a neutralization unit, NaOH is added to control the pH value to be 9.0-9.5, and Mg in the wastewater is removed²⁺、Zn²⁺、Cu²⁺、Ni²⁺、Cr³⁺And (3) heavy metal ions. The wastewater after the alkali neutralization treatment enters an anaerobic sulfate reduction unit, and S generated by sulfate reduction^2-With Hg²⁺、Pb²⁺、Cr³⁺The heavy metals react to generate sulfide precipitate. The wastewater without heavy metal ions enters a denitrification unit, and the effluent of the denitrification unit flows back to a sulfate reduction unit according to the 100 percent reflux ratio. After the operation for a period of time, the sulfate reduction unit still contains unremoved heavy metal ions, the removal rate is 88 percent, the reflux ratio is gradually reduced, each time, the reflux ratio is reduced by 10 percent, and the ORP is controlled to be between-250 and-200 mV until the removal rate reaches more than 95 percent; when the concentration of sulfur ions in the effluent is more than 2.0mg/L, the reflux ratio is gradually increased by 1 each time0 percentage point, and the ORP is between-200 and-100 mV until the concentration of the sulfur ions is lower than 0.2 mg/L. And (3) settling the wastewater treated by the three units, wherein the COD concentration in the supernatant is lower than 60mg/L, the total nitrogen concentration is lower than 15mg/L, and no heavy metal ions can be detected.

Comparative example 1

The wastewater treatment, process and operating conditions were the same as in example 1. The difference lies in that: the effluent reflux ratio of the denitrification unit is always controlled at 50 percent. After the operation is carried out for a period of time, the wastewater treated by the three units is subjected to sedimentation treatment, the COD concentration in the supernatant reaches 80mg/L, the total nitrogen concentration reaches 40mg/L, and 0.1-0.2mg/L of mercury and about 1mg/L of metal ions such as lead can be detected.

Comparative example 2

The wastewater treatment, process and operating conditions were the same as in example 1. The difference lies in that: the ORP of the sulfate reduction unit is always controlled between-300 mV and-200 mV. After the operation is carried out for a period of time, the wastewater treated by the three units is subjected to sedimentation treatment, the COD concentration in the supernatant is lower than 50mg/L, the total nitrogen concentration is lower than 10mg/L, and the concentration of sulfur ions reaches 5.0 mg/L.

Claims

1. A pretreatment method of desulfurization wastewater is characterized by comprising the following units:

(1) a neutralization unit: adding alkali to adjust pH to 8-10, and removing Mg in wastewater²⁺、Zn²⁺、Cu²⁺、Ni²⁺、Cr³⁺Heavy metal ions;

(2) sulfate reduction unit: an anaerobic sulfate reduction treatment system is adopted to remove Hg remained in the neutralized wastewater² ⁺、Pb²⁺、Cr³⁺A metal ion;

(3) a denitrification unit: a denitrification biochemical treatment system is adopted to remove nitrogen-containing pollutants and organic pollutants in a high-salt environment, and part of the effluent flows back to the step (2);

(4) a settling unit: settling, and treating supernatant after mud-water separation in a subsequent unit;

controlling the reflux ratio of the steps (3) to (2) to be 50-200%; when the removal rate of the heavy metal ions in the effluent obtained in the step (2) is lower than 90%, gradually reducing the reflux ratio to ensure that the oxidation-reduction potential is between-300 and-200 mV until the removal rate reaches more than 95%; and (3) when the concentration of the sulfur ions in the effluent obtained in the step (2) is more than 2.0mg/L, gradually increasing the reflux ratio to enable the oxidation-reduction potential to be between-200 and-50 mV until the concentration of the sulfur ions is less than 0.2 mg/L.

2. The method of claim 1, wherein: step (1) adjusting pH, adding NaOH or Ca (OH)₂。

3. The method of claim 1, wherein: the sulfate reduction unit in the step (2) is an anaerobic sulfate reduction treatment system, and part of sulfate is reduced to generate hydrogen sulfide and Hg in the wastewater²⁺、Pb²⁺、Cr³⁺The reaction produces a sulfide precipitate.

4. The method of claim 1, wherein: and (3) adopting the existing A/O or SBR denitrification system for the denitrification unit, and inoculating denitrification activated sludge or denitrification microbial inoculum in the denitrification unit.

5. The method of claim 1, wherein: and (4) adopting inclined plate precipitation or gravity method precipitation for the sedimentation treatment in the step (4), and refluxing to the step (2) when the supernatant in the step (4) does not meet the requirement of subsequent treatment.

6. The method of claim 1, wherein: the specific water quality of the desulfurization wastewater is as follows: pH is 4-6, SS is 5000-²⁺Is 1000-2000mg/L, Mg²⁺3000-7000mg/L, Cl^-7000-₄ ^2-Is 4000-8000mg/L, SiO₂5-50mg/L, TDS is 16000-36000mg/L, COD concentration of 400-1000mg/L, total nitrogen concentration of 100-300mg/L, and mercury, chromium, cadmium, nickel, lead, zinc and copper ions.