阅读说明：本技术 一种碱渣废水处理及碱回收方法 (Alkali residue wastewater treatment and alkali recovery method ) 是由 杨勇 周吉平 刘笑天 马永学 邓文海 刘辉 李晓新 韩丹 陈素宁 于 2021-09-09 设计创作，主要内容包括：本发明提出一种碱渣废水处理及碱回收方法,包括依序进行的如下处理步骤：均质；脱硫及除油：将均质处理后的碱渣废水泵入氧化塔,加热并向碱渣废水中通入空气,在内循环搅动下进行氧化除硫和气浮去油；碱纯化：将其内的碳酸钠部分转化为氢氧化钠；三维电催化氧化：去除其中的污染物；双膜分离：分离纯化得到回用碱液和膜分离废水；生化处理：双膜分离废水依序调节pH值、稀释、添加营养液后进入MBR膜池,利用MBR膜进行分离以降低COD。本发明综合脱硫醇、碱纯化、高级氧化、膜分离纯化及生化处理多种工艺,对高浓度、难处理的碱渣废水进行处理,最终实现了碱回用和污水有机物达标处理,抗冲击性好且成本低。(The invention provides an alkali residue wastewater treatment and alkali recovery method, which comprises the following treatment steps in sequence: homogenizing; and (3) desulfurization and oil removal: pumping the alkali residue wastewater after the homogenization treatment into an oxidation tower, heating, introducing air into the alkali residue wastewater, and carrying out oxidation desulfurization and air flotation deoiling under internal circulation stirring; alkali purification: partially converting sodium carbonate in the sodium carbonate solution into sodium hydroxide; three-dimensional electrocatalytic oxidation: removing the pollutants in the waste water; double-membrane separation: separating and purifying to obtain recycled alkali liquor and membrane separation wastewater; biochemical treatment: the double-membrane separation wastewater sequentially adjusts the pH value, dilutes, adds nutrient solution, enters an MBR membrane tank, and is separated by using an MBR membrane to reduce COD. The invention integrates a plurality of processes of mercaptan removal, alkali purification, advanced oxidation, membrane separation purification and biochemical treatment, treats the high-concentration and difficult-to-treat alkali residue wastewater, finally realizes alkali recycling and standard treatment of sewage organic matters, and has good impact resistance and low cost.)

1. A method for treating alkaline residue wastewater and recovering alkali is characterized in that: comprises the following processing steps which are sequentially carried out:

1) homogenizing: collecting the caustic sludge wastewater to be treated and adjusting the water quality;

2) and (3) desulfurization and oil removal: pumping the alkali residue wastewater after the homogenization treatment into an oxidation tower, heating, introducing air into the alkali residue wastewater, and carrying out oxidation desulfurization and air flotation deoiling under internal circulation stirring;

3) alkali purification: firstly, the alkali residue wastewater after desulfurization and oil removal treatment is put into water to be dissolved in water to generate OH^—Reacting for a period of time, and then performing filter pressing;

4) three-dimensional electrocatalytic oxidation: carrying out electrocatalytic oxidation treatment on the filter-pressed effluent to remove pollutants in the filter-pressed effluent to obtain oxidized effluent;

5) double-membrane separation: separating and purifying the oxidized effluent through an inorganic membrane unit and an organic membrane unit to obtain recycled alkali liquor and membrane separation wastewater;

6) biochemical treatment: the membrane separation wastewater sequentially adjusts the pH value, dilutes, adds nutrient solution and then enters an MBR membrane tank, uses the MBR membrane to separate to reduce COD, detects the COD concentration of the effluent after biochemical treatment, discharges the effluent if the effluent reaches the standard, and carries out biochemical treatment again if the effluent does not reach the standard.

2. The caustic sludge wastewater treatment and alkali recovery method according to claim 1, wherein: 2) in the desulfurization and oil removal, the caustic sludge wastewater is heated to 95-100 ℃, and air is pumped into the caustic sludge wastewater, wherein the volume ratio of the air inflow to the caustic sludge wastewater is (1-50): 10, the internal circulation period of the caustic sludge wastewater in the oxidation tower is 0.5-1 h.

3. The caustic sludge wastewater treatment and alkali recovery method according to claim 1, wherein: 3) the alkali purification comprises primary alkali purification treatment, secondary alkali purification treatment and tertiary alkali purification treatment which are carried out at the temperature of 80-90 ℃ under stirring, wherein the molar ratio of the medicament added in the primary alkali purification treatment to the carbonate in the alkali residue wastewater is (1-2) to 1, and the molar ratio of the medicament added in the primary alkali purification treatment, the secondary alkali purification treatment and the tertiary alkali purification treatment is 4:2: 2.

4. The caustic sludge wastewater treatment and alkali recovery method according to claim 3, wherein: 1) the homogeneous residence time is 5-10d, 2) the residence time of desulfurization and deoiling is 3-7h, and 3) the residence time of the first-stage alkali purification treatment, the second-stage alkali purification treatment and the third-stage alkali purification treatment in the alkali purification is 1-3 h; 4) the electrocatalytic oxidation temperature is 30-45 ℃, the retention time is 1-2h, and the water outlet temperature is not more than 40 ℃; 5) after double-membrane separation, carrying out biochemical treatment until the alkali recovery rate is not less than 70%, the COD content of the recycled alkali liquor is not more than 6000mg/L, and the COD content of the recycled alkali liquor is less than the COD content of the oxidized effluent by at least 8%; 6) in the biochemical treatment, the pH value is adjusted, the dilution and the nutrient solution addition are respectively carried out in a pH adjusting tank, a dilution tank and a nutrient solution tank, and the retention time of the double-membrane separation wastewater in the pH adjusting tank, the dilution tank, the nutrient solution tank and an MBR membrane tank is respectively as follows: 1h, 2h and 48-72 h.

5. The caustic sludge wastewater treatment and alkali recovery method according to claim 1, wherein: 5) in the double-membrane separation, the filtration range of the inorganic membrane unit is not more than 1000nm, the organic membrane unit takes pure water as softening liquid, and the caustic sludge wastewater entering the organic membrane unit and the softening liquid flow in a countercurrent mode.

6. The caustic sludge wastewater treatment and alkali recovery method according to claim 1, wherein: 6) in the biochemical treatment, the pH value of the double-membrane separation is adjusted to 7-8.5, then the domestic sewage is adopted for dilution, the mass percentage of the salt content after dilution is not more than 1%, and the C: N: P (100-.

7. The caustic sludge wastewater treatment and alkali recovery method according to any one of claims 1 to 6, wherein: 1) after homogenizing treatment, the COD of the alkaline residue wastewater is less than or equal to 120000 mg/L; 2) after desulfurization and oil removal treatment, the COD of the alkaline residue wastewater is less than or equal to 80000 mg/L; 3) after alkali purification treatment, the COD of the alkali residue wastewater is less than or equal to 40000 mg/L; 4) after the electrocatalytic oxidation treatment, the COD of the alkaline residue wastewater is less than or equal to 15000 mg/L; 6) the COD of the alkali residue wastewater after biochemical treatment is less than or equal to 3000 mg/L.

8. The caustic sludge wastewater treatment and alkali recovery method according to claim 7, wherein: and collecting the waste gas in each treatment step and discharging the waste gas into a waste gas treatment system for treatment.

Technical Field

The invention belongs to the technical field of alkali residue wastewater treatment, and particularly relates to an alkali residue wastewater treatment and alkali recovery method.

Background

In oil refineries and chemical plants using petroleum distillate oil as raw material, in order to reduce the sulfur content of fuel oil and raw material or to reach a certain index of oil product (such as acid value, corrosivity, etc.), alkali refining processes (liquid hydrocarbon alkali refining, gasoline, especially catalytic gasoline alkali refining, diesel oil alkali refining, ethylene cracking gas alkali refining, etc.) are adopted in many oil product refining processes. The alkaline waste liquid with high pollutant content discharged in the refining process has small waste water amount, and the types and the concentrations of pollutants are greatly different according to the types of crude oil to be processed and the processing process. The alkaline residue wastewater belongs to high-concentration organic wastewater in a refinery, contains a large amount of COD, volatile phenol, sulfide and the like, has high concentration, influences the normal operation of wastewater treatment facilities of a petrochemical plant and the qualification rate of wastewater treatment, has high toxicity, and is a highly toxic substance because phenols enter organisms and human bodies to be combined with proteins to cause permanent damage. Therefore, caustic sludge wastewater is one of the most difficult wastewater to effectively treat. In the prior art, the most effective and economic method of the wastewater is to carry out combined treatment by an advanced oxidation method and a biological treatment method, remove most organic matters in the wastewater by the advanced oxidation method, improve the biodegradability of the wastewater, and degrade the wastewater by the biological method to meet the discharge requirement. However, the waste is caused by directly discharging the wastewater after the treatment by the combined treatment mode without recycling and reusing resources and substances in the wastewater, and the waste is contradictory to the current development strategy of energy conservation, emission reduction and resource conservation. Therefore, improvements are needed.

Disclosure of Invention

In order to solve the defects of the prior art, the invention provides an alkali residue wastewater treatment and alkali recovery method, which aims to solve the problem that the alkali in the wastewater cannot be recovered and reused when the alkali residue wastewater is treated by the prior art.

The technical scheme of the invention is realized as follows:

an alkali residue wastewater treatment and alkali recovery method comprises the following treatment steps in sequence:

1) homogenizing: collecting the caustic sludge wastewater to be treated, storing for a period of time, and homogenizing;

2) and (3) desulfurization and oil removal: pumping the alkali residue wastewater after the homogenization treatment into an oxidation tower and heating, arranging an internal circulation pipeline between the upper part and the lower part of the oxidation tower, arranging a gas-liquid mixing pump and an air inlet pipeline on the internal circulation pipeline, introducing air from the air inlet pipeline, uniformly dispersing the air in the alkali residue wastewater in the form of micro-nano bubbles under the action of the gas-liquid mixing pump, and oxidizing sodium mercaptan into disulfide and sodium hydroxide under the action of a catalyst by the micro-nano bubbles (reaction equation: 2NaSR + 1/2O)₂+H₂O → 2NaOH + RSSR), the disulfide is coalesced under the action of the micro-bubble air flotation to form the disulfide with larger liquid drops and is suspended at the upper part of the main oxidation tower for removing the mercaptan, and finally, the disulfide is discharged out of the oxidation tower through the flow guide pipe;

3) alkali purification: firstly, the alkali residue wastewater after desulfurization and oil removal treatment is put into water to be dissolved in water to generate OH^—The medicament (the medicament is a pure substance or a mixture, and the specific components are not limited), the medicament reacts with sodium carbonate in the caustic sludge wastewater to generate carbonate precipitate and sodium hydroxide, the concentration of the sodium hydroxide in the regenerated alkali is improved, the medicament which does not participate in the reaction, the carbonate precipitate generated by the reaction and other solid wastes are removed by filter pressing, and the caustic sludge wastewater after the filter pressing enters a water storage tank for further treatment;

4) three-dimensional electrocatalytic oxidation: according to the type and property of pollutants to be removed from water, a three-dimensional electrocatalytic oxidation device is adopted, catalytic particles are filled between two main electrodes of the three-dimensional electrocatalytic oxidation device, when wastewater to be treated flows through the three-dimensional electrocatalytic oxidation device, a certain amount of hydroxyl radicals and nascent state coagulant are generated in the device under certain operation conditions, and the pollutants in the wastewater can generate the effects of catalytic oxidative decomposition, coagulation, adsorption, complexation, replacement and the like, so that the pollutants in the wastewater are rapidly removed to obtain oxidized effluent; the three-dimensional electrocatalytic oxidation equipment is preferably equipment produced by the southern Chuangye (Tianjin) science and technology limited company, a plurality of three-dimensional electrocatalytic oxidation equipment can be connected in series or in parallel, and the working voltage of each three-dimensional electrocatalytic oxidation equipment is 7-12V;

5) double-membrane separation: separating and purifying the oxidized effluent through an inorganic membrane unit and an organic membrane unit to obtain recycled alkali liquor and membrane separation wastewater, wherein the organic membrane unit comprises a plurality of organic membrane devices which are arranged in parallel, each organic membrane device is provided with a deionized water inlet and a recycled alkali liquor outlet, and the oxidized effluent and the deionized water preferably flow in a counter-current manner;

6) biochemical treatment: the double-membrane separation wastewater is sequentially subjected to pH value adjustment, dilution and nutrient solution addition and then enters an MBR membrane tank, the MBR membrane is used for separation to reduce COD, the COD concentration of the effluent is detected after biochemical treatment, if the COD concentration reaches the standard, the effluent is discharged outside, and if the COD concentration does not reach the standard, the biochemical treatment is carried out again from the dilution step.

The working principle is as follows: the alkaline residue wastewater is homogenized and then sequentially pumped into an oxidation tower for oxidation desulfurization and air flotation oil removal, medicament is added for alkali purification, three-dimensional electrocatalytic oxidation equipment is adopted for removing pollutants, and double-membrane separation purification and biochemical treatment are adopted for reducing COD. Through tests, the pH value is 12-13, the COD is 50000-120000mg/L, and the salt content is less than or equal to 120000mg/L, c (OH)^-)≥17g/L、c(CO₃ ^2-) After the alkaline residue wastewater which is not less than 27g/L and sodium mercaptan is not more than 1000mg/L is treated by the method provided by the invention, the alkaline residue wastewater is purified to generate recycled alkali liquor: the mass percentage of NaOH is more than or equal to 7 percent, and the COD is less than or equal to 6000 mg/L; the COD of the alkali residue wastewater after alkali extraction is less than or equal to 500mg/L, the pH is 6-9, and the discharge is metAnd (4) standard.

The invention firstly adopts methods of high-efficiency oxidation, low disturbance, disulfide self-phase coalescence and the like to separate and recover disulfide, then adds a medicament to convert sodium carbonate in wastewater into sodium hydroxide, then removes pollutants through electrocatalytic oxidation, and then uses an inorganic membrane unit and an organic membrane unit to separate and purify, and finally reduces COD through biochemical treatment. The regeneration of the alkali liquor does not need the hydrogenation treatment of extracting the sulfur-containing solvent from the solvent, the oxidation of the alkali liquor is carried out at the temperature of 30-45 ℃, the efficiency is high, the energy consumption is low, and the quality of the regenerated alkali is good. Compared with the prior art, the process has the advantages of high efficiency, high quality and good impact resistance, the obtained regenerated alkali liquor has good quality, can be directly used for production, and has low construction cost and operation cost, thereby being worthy of popularization and application.

Preferably, 2) in the desulfurization and the oil removal, the caustic sludge wastewater is heated to 95-100 ℃, air is pumped into the caustic sludge wastewater, the air is dispersed in the caustic sludge wastewater in a micro-nano bubble form, and the volume ratio of the air inflow to the caustic sludge wastewater is (1-50): 10, the internal circulation period of the caustic sludge wastewater in the oxidation tower is 0.5-1 h. The desulfurization and oil removal of the oxidation tower belong to gas-liquid two-phase reaction, the air is dispersed in a micro-nano bubble form, so that the contact area between the air and the alkaline residue wastewater is increased by orders of magnitude, the oxidation conversion rate of sodium mercaptide is greatly improved, after the treatment by adopting the technical parameters, the concentration of the sodium mercaptide in the alkaline residue wastewater can be reduced to be below 0.05 percent by weight, and the content of disulfide in regenerated alkali liquor is reduced to be below 100 ppm.

Further preferably, the 3) alkali purification comprises primary alkali purification treatment, secondary alkali purification treatment and tertiary alkali purification treatment which are carried out at the temperature of 80-90 ℃ under stirring, the molar ratio of the added medicament in the primary alkali purification treatment to the carbonate in the alkali residue wastewater is (1-2):1, and the molar ratio of the added medicament in the primary alkali purification treatment, the secondary alkali purification treatment and the tertiary alkali purification treatment is 4:2: 2. Multiple creative experiments prove that: when the reaction temperature is higher than 80 ℃, the reaction can reach balance in a short time by adopting the adding proportion, sodium carbonate (the content of sodium carbonate in the caustic sludge wastewater is about 8-10%) in the caustic sludge wastewater is quickly converted into sodium hydroxide, and the conversion rate is more than 70%.

Further preferably, 1) the retention time of homogenization is 5-10d, 2) the retention time of desulfurization and oil removal is 3-7h, and 3) the retention time of primary alkali purification treatment, secondary alkali purification treatment and tertiary alkali purification treatment in alkali purification is 1-3 h; 4) the three-dimensional electrocatalytic oxidation temperature is 30-45 ℃, the retention time is 1-2h, and the water outlet temperature is not more than 40 ℃; 5) after double-membrane separation, biochemical treatment can be carried out until the alkali recovery rate is not less than 70%, the COD content of the recycled alkali liquor is not more than 6000mg/L and the COD content of the recycled alkali liquor is at least 8% less than the COD content of the oxidized effluent, the mass percentage of NaOH in the finally obtained recycled alkali is not less than 7%, and compared with the prior art, the mass percentage is increased by 10% -50%; 6) in the biochemical treatment, the pH value is adjusted, the dilution and the nutrient solution addition are respectively carried out in a pH adjusting tank, a dilution tank and a nutrient solution tank, and the retention time of the double-membrane separation wastewater in the pH adjusting tank, the dilution tank, the nutrient solution tank and an MBR membrane tank is respectively as follows: 1h, 2h and 48-72 h.

Further preferably, in 5) double-membrane separation, the filtration range of the inorganic membrane unit is not more than 1000nm, the organic membrane unit takes pure water as softening liquid, each organic membrane unit comprises 3-10 membrane devices connected in parallel, each membrane device is internally divided into a dialysis chamber and a diffusion chamber through an organic membrane, and caustic sludge wastewater entering the organic membrane unit and the softening liquid flow in a counter-current mode. After the organic membrane treatment, the mass percent of sodium hydroxide in the regenerated alkali liquor in the diffusion chamber is not less than 7 percent, and the COD is not more than 6000mg/L, and the regenerated alkali liquor can be discharged to a reuse water tank for standby; and the effluent of the dialysis chamber is subjected to subsequent biochemical treatment.

Further preferably, 6) in the biochemical treatment, the pH value of the double-membrane separation is adjusted to 7-8.5, then the domestic sewage is adopted for dilution, the mass percentage of the salt content after dilution is not more than 1%, and the nutrient solution is added, so that the C: N: P (100-.

More preferably, 1) after homogenizing treatment, the COD of the alkaline residue wastewater is less than or equal to 120000 mg/L; 2) after desulfurization and oil removal treatment, the COD of the alkaline residue wastewater is less than or equal to 80000 mg/L; 3) after alkali purification treatment, the COD of the alkali residue wastewater is less than or equal to 40000 mg/L; 4) after the electrocatalytic oxidation treatment, the COD of the alkaline residue wastewater is less than or equal to 15000 mg/L; 6) after biochemical treatment, the COD of the alkaline residue wastewater is less than or equal to 3000mg/L, and obviously, the COD of the alkaline residue wastewater is gradually and obviously reduced under the treatment of the method.

Most preferably, the waste gas in each treatment step is collected and discharged into a waste gas treatment system for treatment, so that pollution to workshops or atmospheric environment is avoided.

The invention treats the high-concentration and difficult-to-treat alkaline residue wastewater by mainly using a physical and chemical treatment method and secondarily using biochemical treatment, finally realizes the alkali recycling and the standard treatment of organic matters in the wastewater, and synchronously realizes the aims of wastewater treatment and resource recovery.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic diagram of the operation of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

Has a pH value of 12.85, a COD of 97950mg/L and a salt content of 188g/L, c (OH)^-)＝17g/L、c(CO₃ ^2-) 68g/L of soda ash wastewater of certain chemical plant in Hunan province with 960mg/L of sodium mercaptide is treated according to the following operation:

1) homogenizing: collecting alkali residue wastewater of certain chemical plant in Hunan with water inflow of 20m³The number of the Chinese medicinal herbs is one day,placing the mixture in a regulating tank and staying for 10 days;

2) and (3) desulfurization and oil removal: pumping the alkali residue wastewater after the homogenization treatment into an oxidation tower to be heated to 95 ℃, pumping air into the alkali residue wastewater, wherein the volume ratio of the air inflow to the alkali residue wastewater is 50: oxidizing to remove sulfur and removing oil by air flotation under internal circulation stirring, wherein the internal circulation period of the caustic sludge wastewater in the oxidation tower is 0.8h, the retention time of desulfurization and oil removal is 6h, and the COD of the effluent is 69200 mg/L;

3) alkali purification: performing primary alkali purification treatment, secondary alkali purification treatment and tertiary alkali purification treatment under stirring at 90 ℃, wherein the medicament adopts calcium hydroxide powder, the molar ratio of the calcium hydroxide powder added in the primary alkali purification treatment to carbonate radicals in the alkaline residue wastewater is 2:1, the molar ratio of the calcium hydroxide powder added in the primary alkali purification treatment, the secondary alkali purification treatment and the tertiary alkali purification treatment is 4:2:2, the retention time of the primary alkali purification treatment, the secondary alkali purification treatment and the tertiary alkali purification treatment is 1h, and finally performing filter pressing, wherein the COD (chemical oxygen demand) of filter pressing effluent is 40000 mg/L;

4) electrocatalytic oxidation: carrying out electrocatalytic oxidation treatment on the filter-pressed effluent by adopting 1 three-dimensional electrocatalytic oxidation device which is produced by southern entrepreneurial (Tianjin) science and technology Limited company and has the model of SOB-2, wherein the working voltage of the three-dimensional electrocatalytic oxidation device is 8.8V, the temperature is 40 ℃, the retention time is 1.5h, and oxidized effluent is obtained, the COD of the oxidized effluent is 11900mg/L, and the temperature of the oxidized effluent is 40 ℃;

5) double-membrane separation: separating and purifying the oxidized effluent by an inorganic membrane unit and an organic membrane unit to obtain recycled alkali liquor and double-membrane separation wastewater, wherein the filtering range of the inorganic membrane unit is not more than 1000nm, the organic membrane unit takes pure water as softening liquid, the alkali residue wastewater entering the organic membrane unit and the softening liquid flow in a countercurrent mode, the retention time of double-membrane separation is 6h, and effluent c (OH) is obtained^-) 55g/L, and the COD is 11000 mg/L;

6) biochemical treatment: sequentially adjusting the pH value of the double-membrane separation wastewater to 7 in a pH adjusting tank, a diluting tank and a nutrient solution tank respectively, diluting the double-membrane separation wastewater to 8g/L salt by adopting domestic sewage, adding the nutrient solution to the double-membrane separation wastewater with the ratio of C: N: P being 200:5:1, then entering an MBR (membrane bioreactor), and separating by utilizing an MBR (membrane bioreactor) membraneIn order to reduce COD, the residence time of the double-membrane separation wastewater in the pH adjusting tank, the diluting tank, the nutrient solution tank and the MBR membrane tank is respectively as follows: 1h, 2h and 48 h; the COD of the effluent is 420mg/L, and the effluent is directly discharged out to recycle the alkali liquor c (OH)^-) 72g/L, COD 880 mg/L.

Example 2

For pH of 12.4, COD of 86550mg/L and salt content of 180g/L, c (OH)^-)＝12g/L、c(CO₃ ^2-) 72g/L and 825mg/L sodium mercaptide, and the alkali residue wastewater of certain petroleum refinery in Shaanxi is treated according to the following operation:

1) homogenizing: collecting alkali residue wastewater of certain chemical plant in Hunan with water inflow of 48m³Placing the mixture in a regulating tank for 5 days;

2) and (3) desulfurization and oil removal: pumping the alkali residue wastewater after the homogenization treatment into an oxidation tower, heating to 98 ℃, pumping air into the alkali residue wastewater, wherein the volume ratio of the air inflow to the alkali residue wastewater is 25: oxidizing to remove sulfur and removing oil by air flotation under internal circulation stirring, wherein the internal circulation period of the caustic sludge wastewater in the oxidation tower is 0.5h, the retention time of the sulfur and oil removal is 3h, and the COD of the effluent is 64350 mg/L;

3) alkali purification: performing primary alkali purification treatment, secondary alkali purification treatment and tertiary alkali purification treatment under stirring at 85 ℃, wherein a medicament is a mixture of limestone and hydrated lime in a mass ratio of 1:1, the molar ratio of the medicament added in the primary alkali purification treatment to carbonate in the caustic sludge wastewater is 1:1, the molar ratio of the medicament added in the primary alkali purification treatment, the secondary alkali purification treatment and the tertiary alkali purification treatment is 4:2:2, the retention time of the primary alkali purification treatment, the secondary alkali purification treatment and the tertiary alkali purification treatment is 3 hours, and finally performing pressure filtration, wherein the COD (chemical oxygen demand) of the pressure filtration effluent is 36800 mg/L;

4) electrocatalytic oxidation: 2 three-dimensional electrocatalytic oxidation devices which are produced by southern venture (Tianjin) science and technology Limited and have the models of SOB-2 are connected in series to carry out electrocatalytic oxidation treatment on the filtered press water, the working voltage of the three-dimensional electrocatalytic oxidation devices is 12V, the temperature is 30 ℃, the retention time is 2 hours, and oxidized water is obtained, the COD of the oxidized water is 11000mg/L, and the temperature of the oxidized water is 38 ℃;

5) double-membrane separation: separating and purifying oxidized effluent by an inorganic membrane unit and an organic membrane unit to obtain recycled alkali liquor and double-membrane separation wastewater, wherein the filtering range of the inorganic membrane unit is not more than 1000nm, the organic membrane unit takes pure water as softening liquid, the caustic sludge wastewater entering the organic membrane unit and the softening liquid flow in a countercurrent mode, the retention time of double-membrane separation is 6h, the mass percent of sodium hydroxide in the effluent is 5.5%, and the COD is 11000 mg/L;

6) biochemical treatment: the pH value of the double-membrane separation wastewater is respectively adjusted to 8.5 in a pH adjusting tank, a diluting tank and a nutrient solution tank in sequence, the domestic sewage is diluted to contain 10g/L of salt, the nutrient solution is added into the double-membrane separation wastewater, C, N, P, is 150:5:1, then the double-membrane separation wastewater enters an MBR membrane tank, the MBR membrane is used for separation to reduce COD, and the retention time of the double-membrane separation wastewater in the pH adjusting tank, the diluting tank, the nutrient solution tank and the MBR membrane tank is respectively as follows: 1h, 2h and 70 h; the COD of the effluent is 500mg/L and is directly discharged, the mass percent of the sodium hydroxide in the recycled alkali liquor is 7 percent, and the COD is 820 mg/L.

Example 3

For 2000 tons, the pH value is 12.7, the COD is 98980mg/L, and the salt content is 210g/L, c (OH)^-)＝13g/L、c(CO₃ ^2-) Treating alkali residue wastewater of certain Shanxi petroleum refinery with 84g/L sodium mercaptide of 960mg/L, specifically according to the following operations:

1) homogenizing: collecting alkali residue wastewater of certain chemical plant in Hunan with water inflow of 50m³Placing the mixture in a regulating tank for 8 days;

2) and (3) desulfurization and oil removal: pumping the alkali residue wastewater after the homogenization treatment into an oxidation tower, heating to 100 ℃, pumping air into the alkali residue wastewater, wherein the volume ratio of the air inflow to the alkali residue wastewater is 1: carrying out oxidation desulfurization and air flotation deoiling under internal circulation stirring, wherein the internal circulation period of the caustic sludge wastewater in the oxidation tower is 1h, the retention time of desulfurization and deoiling is 7h, and the COD of effluent is 68750 mg/L;

3) alkali purification: the method comprises the following steps of performing primary alkali purification treatment, secondary alkali purification treatment and tertiary alkali purification treatment under stirring at 80 ℃, wherein a medicament specifically adopts a mixture of limestone, lime milk and hydrated lime in a mass ratio of 1:2:1, the molar ratio of the medicament added in the primary alkali purification treatment to carbonate in alkaline residue wastewater is 1.5:1, the molar ratio of the medicament added in the primary alkali purification treatment, the secondary alkali purification treatment and the tertiary alkali purification treatment is 4:2:2, the retention time of the primary alkali purification treatment, the secondary alkali purification treatment and the tertiary alkali purification treatment is 2 hours, and finally performing filter pressing, wherein COD (chemical oxygen demand) of filter pressing effluent is 39000 mg/L;

4) electrocatalytic oxidation: 3 three-dimensional electrocatalytic oxidation devices which are produced by southern venture (Tianjin) science and technology Limited and have the models of SOB-2 are adopted to be connected in parallel to carry out electrocatalytic oxidation treatment on the filtered press water, the working voltage of the three-dimensional electrocatalytic oxidation devices is 7V, the temperature is 45 ℃, the retention time is 1h, oxidized effluent is obtained, the COD of the oxidized effluent is 14000mg/L, and the temperature of the oxidized effluent is 35 ℃;

5) double-membrane separation: separating and purifying oxidized effluent by an inorganic membrane unit and an organic membrane unit to obtain recycled alkali liquor and double-membrane separation wastewater, wherein the filtering range of the inorganic membrane unit is not more than 1000nm, the organic membrane unit takes pure water as softening liquid, the alkali residue wastewater entering the organic membrane unit and the softening liquid flow in a countercurrent mode, the retention time of double-membrane separation is 6h, the mass percent of sodium hydroxide in the effluent is 6.7%, and COD is 12800 mg/L;

6) biochemical treatment: the double-membrane separation wastewater is sequentially and respectively subjected to pH value adjustment to 8 in a pH adjusting tank, a diluting tank and a nutrient solution tank, is diluted to contain 8g/L of salt by adopting domestic sewage, is added with nutrient solution to the double-membrane separation wastewater C, N, P is 100:5:1, then enters an MBR membrane tank, is separated by utilizing an MBR membrane to reduce COD, and the retention time of the double-membrane separation wastewater in the pH adjusting tank, the diluting tank, the nutrient solution tank and the MBR membrane tank is respectively as follows: 1h, 2h and 72 h; the COD of the effluent is 500mg/L, the effluent is directly discharged, the mass percent of the sodium hydroxide in the recycled alkali liquor is 8 percent, and the COD is 1100 mg/L.

The technical details which are not described in detail in the above embodiments all adopt the conventional technical means; the above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.