CN111732287A

CN111732287A - High-salinity heavy metal refractory shale gas exploitation wastewater treatment system and treatment method

Info

Publication number: CN111732287A
Application number: CN202010704864.7A
Authority: CN
Inventors: 蒲柳; 杨红梅; 杨汉军; 黄莉; 唐俊; 田智; 刘世林; 王建强; 郑庆生; 杜洪飞; 龚斌; 文葵; 姚铭; 肖德龙; 赵绍燕; 王科慧
Original assignee: Sichuan Entech Environment Technology Co ltd
Current assignee: Sichuan Entech Environment Technology Co ltd
Priority date: 2020-07-21
Filing date: 2020-07-21
Publication date: 2020-10-02
Anticipated expiration: 2040-07-21
Also published as: CN111732287B

Abstract

The invention discloses a high-salinity heavy metal refractory shale gas exploitation wastewater treatment system and a treatment method. The processing method comprises the following steps: (1) pretreating wastewater; (2) MVR evaporation treatment; (3) carrying out deep treatment; (4) and (5) membrane treatment. The method disclosed by the invention is used for treating the high-salinity heavy metal refractory shale gas exploitation wastewater, so that the problem of high salt content in the wastewater can be effectively solved, the requirement of ultralow emission of the wastewater can be met, the resource utilization of intermediate products can be realized, good economic benefits are generated, and the requirement of sustainable development is met.

Description

High-salinity heavy metal refractory shale gas exploitation wastewater treatment system and treatment method

Technical Field

The invention belongs to the technical field of wastewater treatment, and particularly relates to a high-salinity heavy metal refractory shale gas exploitation wastewater treatment system and a treatment method.

Background

Shale gas resources in China are abundant, but the development of shale gas is still in the initial stage, and the development and utilization of shale gas is actively promoted in China at present. The shale gas exploitation wastewater is mainly from drilling operation wastewater, including drilling wastewater, well washing wastewater, acidification operation wastewater and fracturing flowback fluid. The water quality and the water quantity of the wastewater generated in the shale gas exploitation process fluctuate greatly, and main pollutants in the wastewater comprise oils, salts (chloride and sulfate), hardness (calcium ions and magnesium ions), heavy metal ions (such as arsenic) and some high molecular polymers, wherein the polymers are different in shale gas exploitation process, the used medicaments are mostly high molecular polymers with long chains or annular structures although the types of the used medicaments are different, and the polymers are slightly soluble or insoluble in water, have good stability, have biotoxicity and are difficult to biodegrade.

According to the water quality characteristics of the shale gas exploitation wastewater, the wastewater treatment has the following four difficulties:

(1) the organic pollutants contained in the wastewater have high stability, high oxidative decomposition difficulty, low B/C value and poor biodegradability, and meanwhile, the wastewater contains very high salt which brings fatal influence on the biodegradation of organic matters.

(2) Because shale gas exploitation wells are distributed dispersedly, the geological conditions of the exploitation wells have difference, so that the change of the water quality and the water quantity of the wastewater is large, the design of a process scheme for wastewater treatment is difficult, and the stable standard operation of a wastewater treatment system can be ensured only by comprehensively considering the design of the quality and the design allowance of the inlet water.

(3) The waste water contains a certain amount of heavy metals, such as arsenic compounds, and arsenic has extremely strong toxicity and is one of the most serious pollutants harmful to human health, so the arsenic-containing waste water can be discharged after being treated to reach the discharge standard. As removal of arsenic is generally carried out by a chemical method, but the limit of arsenic treatment by the chemical method is about 0.10mg/L, and the arsenic removal method cannot meet the requirements of the III-class standard of surface water environment quality standard (GB3838-2002), and other effective treatment means are also needed for removal of low-concentration arsenic.

(4) At present, the national control standard for shale gas mining wastewater is more and more strict, some regions have implemented the requirements of 'surface water environment quality standard' (GB3838-2002) surface water III standard and Chinese drinking water surface water source region supplement project standard limit values for shale gas mining wastewater, the wastewater treatment discharge standard requirement is strict, and representative indexes such as COD (chemical oxygen demand) are_cr≤20mg/L，BOD₅≤4mg/L，NH₃N is less than 1mg/L, TN is less than or equal to 1mg/L, arsenic is less than or equal to 0.05mg/L, sulfate (in terms of SO)₄ ^2-) Less than or equal to 250mg/L of chloride salt (in terms of Cl)^-Calculated) is less than or equal to 250 mg/L. Stringent discharge standards place higher demands and challenges on the treatment of such wastewaters.

In view of the above difficulties in treating shale gas exploitation wastewater, it is urgently needed to find a more optimized process method for treating the high-salinity heavy metal refractory shale gas exploitation wastewater.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a high-salinity heavy metal refractory shale gas exploitation wastewater treatment system and a treatment method, and aims to solve the problems that the existing treatment process is high in operation cost, poor in system stability and incapable of recycling intermediate products.

In order to achieve the purpose, the technical scheme adopted by the invention for solving the technical problems is as follows:

a treatment method of high-salinity heavy metal refractory shale gas exploitation wastewater comprises the following steps:

(1) pretreatment of

After oil removal treatment is carried out on the wastewater, the pH value is adjusted to 8-9, and then a pretreatment solution is obtained after integrated air flotation treatment, de-hardening precipitation, advanced chemical oxidation and coagulating precipitation;

wherein the pH adjustment is to adjust the pH of the wastewater to 8-9 by using alkali liquor; in the air flotation, after a medicament is added into the wastewater, an air flotation device is used for carrying out air flotation treatment on the wastewater to remove micro suspended substances and colloids in the wastewater; the air floatation effluent enters a de-hardening system, and the hardness in the wastewater is removed by using a de-hardening agent; carrying out advanced oxidation on the wastewater after the hardness removal, firstly carrying out oxidation pretreatment on refractory organic matters in the wastewater by using an oxidant, then adding a precipitator, removing a medicament added in the advanced oxidation process through precipitation treatment, carrying out coagulating sedimentation on effluent, and removing micro suspended matters and colloidal substances in the wastewater again by using a coagulant to finish the pretreatment process of the process;

(2) MVR evaporation treatment

Adjusting the pH value of the pretreatment solution to 5-6, and performing two-stage low-temperature-rise MVR evaporation concentration at an evaporation temperature of less than 75-80 ℃; then entering a high temperature rising MVR system with the evaporation temperature of less than 90-105 ℃, evaporating and crystallizing, and separating out crystal salt;

salt substances in the wastewater are mainly removed, meanwhile, a certain interception effect is also realized on pollutants such as COD (chemical oxygen demand), ammonia nitrogen, total nitrogen, arsenic and the like, condensate generated in the process is sent to a rear-section unit for continuous treatment, and the crystallized salt is recycled;

the condensate generated in the processes of low temperature rise MVR and high temperature rise MVR enters the next step for treatment;

(3) advanced treatment

Treating the condensate generated in the step (2) by adopting an A/O + MBR process to further remove the residual pollutants such as ammonia nitrogen, total nitrogen, COD and the like in the wastewater, wherein nutrient solution needs to be supplemented in the process;

(4) membrane treatment

Then treating the condensate treated in the step (3) by adopting a two-stage RO membrane treatment process; and pollutants such as ammonia nitrogen, total nitrogen, salt, arsenic, COD and the like in the wastewater are intercepted with high efficiency so as to meet the requirement of ultralow wastewater discharge.

Further, the specific process of the pretreatment is as follows:

(1) oil removal regulation: discharging the wastewater into an oil separation tank to treat oil substances in the wastewater, feeding the wastewater after oil removal into a regulating tank, and homogenizing and uniformly measuring the wastewater to form a first wastewater;

(2) and (3) pH adjustment: adjusting the pH value of the waste liquid I to 8-9 by using sodium hydroxide to form a waste liquid II containing a large amount of fine suspended particles;

(3) integrated air flotation treatment: adding PAC and PAM into the waste liquid II by using a metering pump, wherein the dosage of PAC is 100-150 mg/L, the dosage of PAM is 5-10 mg/L, and removing micro suspended substances and colloid in the waste liquid II by air floatation treatment to form a waste liquid III;

(4) de-hardening and precipitating: sequentially adding sodium carbonate, PAC and PAM into the waste liquid III by using a metering pump, wherein the adding amount of the sodium carbonate is 0.01-0.02 mg/L (can be adjusted according to the hardness of the incoming water), the adding amount of the PAC is 100-150 mg/L, the adding amount of the PAM is 5-10 mg/L, and after mud-water separation in a sedimentation tank, obtaining a supernatant liquid IV;

(5) advanced chemical oxidation: regulating the pH value of the waste liquid IV to 3 by using sulfuric acid, then sequentially adding ferrous sulfate heptahydrate and hydrogen peroxide by using a metering pump, wherein the dosage of the ferrous sulfate heptahydrate is 1300-1500 mg/L, the dosage of the hydrogen peroxide is 1400-1500 mg/L, treating for 4-5 h, adding sodium hydroxide, regulating the pH value to 8-9, finally adding PAM (polyacrylamide), the dosage of the PAM is 5-10 mg/L, removing iron ions after passing through a high-grade oxidation sedimentation tank, and obtaining a supernatant liquid V;

(6) coagulating sedimentation: and (3) adding PAC and PAM into the waste liquid V in sequence by using a metering pump, wherein the dosage of PAC is 100-150 mg/L, and the dosage of PAM is 5-10 mg/L, performing coagulating sedimentation, and performing mud-water separation in a sedimentation tank to obtain a supernatant liquid, namely a pretreatment solution.

Further, the specific process of the two-stage low temperature rise MVR is as follows:

adding the pretreatment solution with the pH value of 5-6 into a low-temperature-rise MVR with the temperature rise of 10-15 ℃, the evaporation temperature of less than 75 ℃ and the steam pressure of 0.4MPa to perform falling film evaporation in the first stage to obtain a solution with the salt content of 6-8%, and then continuing to perform forced circulation evaporation in the second stage under the same conditions to obtain a solution with the salt content of 18-21%; the steam consumption in stable operation is 100 kg/h.

The operating conditions of falling film evaporation and forced circulation type evaporation are that the temperature rise is 10-15 ℃, the evaporation temperature is less than 75 ℃ and the steam pressure is 0.4 MPa.

Further, the low temperature rise MVR has a temperature rise of 10 ℃.

Further, the specific process of the high temperature rise MVR is as follows:

the high-temperature-rise MVR evaporation temperature is less than 93 ℃, the steam pressure is 0.4MPa, the temperature rise is 15-18 ℃, the solution subjected to low-temperature-rise MVR evaporation treatment is subjected to forced circulation type evaporation treatment, the steam consumption is 100kg/h in stable operation, the main components of the finally precipitated crystal salt are sodium chloride and sodium sulfate, the arsenic content is about 0.0003g/kg, the limit requirement (total arsenic is less than or equal to 0.0005g/kg) for edible salt pollutant arsenic in GB2762-2017 can be met, and resource utilization can be carried out.

Further, the temperature rise of the high temperature rise MVR was 18 ℃.

Further, in the step (3), the condensate is treated by adopting an A/O + MBR process, and the temperature of the condensate is less than 32 ℃.

Furthermore, an MBR membrane used in the MBR process is an immersed ultrafiltration membrane with the pore size of less than 0.04 μm, the temperature of the membrane is about 32 ℃ in summer, and the SDI (standard deviation) of the membrane effluent is less than 3.

Furthermore, when the condensate is treated by adopting an A/O + MBR process, a nutrient solution needs to be added during the A/O treatment, and the nutrient solution is preferably sodium acetate.

Furthermore, a reducing agent is required to be added in the MBR process, and the reducing agent is preferably sodium bisulfite.

Further, the membrane used in the step (4) is an RO membrane, and two stages of RO membranes are adopted to efficiently remove pollutants such as ammonia nitrogen, total nitrogen, COD, arsenic and the like in the waste liquid after advanced treatment, and the specific process of the two-stage membrane treatment process is as follows:

separating the solution treated in the step (3) by a primary RO membrane system, feeding the separated fresh water into a secondary RO membrane system, and feeding the concentrated water into a primary RO membrane system for continuous separation; concentrated water is separated by a section of RO membrane, the concentrated water obtained by separation enters an MVR evaporation system to be continuously treated, fresh water enters a second-level RO membrane system to be continuously separated, the fresh water enters a mixed water tank after the separation of the second-level RO membrane, and the concentration of the fresh water enters a first-level RO membrane to be continuously treated.

And (4) detecting the fresh water in the mixed water tank, discharging or recycling the fresh water in the system when the fresh water reaches the standard, or returning to the step (3) to continue processing.

Furthermore, the interception rate of ammonia nitrogen and total nitrogen can reach 97 percent by adopting the anti-pollution RO membrane.

Furthermore, reducing agents of sodium bisulfite, scale inhibitor and dilute sulfuric acid are added during the treatment of the primary RO membrane system; adding a scale inhibitor during treatment of both the first-stage RO membrane system and the second-stage RO membrane system; and adding dilute alkali into the fresh water in the mixing water tank, and adjusting the pH value of the fresh water to 6-9.

A system for treating high-salinity heavy metal refractory shale gas exploitation wastewater comprises a pretreatment unit, an MVR evaporation unit, a deep treatment unit and a membrane treatment unit which are sequentially communicated;

the pretreatment unit comprises an oil separation adjusting tank, a pH adjusting tank 1, an integrated air flotation tank, a de-hardening sedimentation tank, an advanced chemical oxidation tank, an p H adjusting tank 2, an advanced chemical oxidation sedimentation tank and a coagulating sedimentation tank which are sequentially communicated;

wherein, an intermediate water tank 1 is arranged between the coagulating sedimentation tank and the low temperature-rising MVR system;

the MVR evaporation unit comprises a low-temperature-rise MVR system and a high-temperature-rise MVR system; an intermediate water tank 2 is arranged between the low-temperature-rise MVR system and the high-temperature-rise MVR system; the high temperature rise MVR system is also communicated with the advanced chemical oxidation tank; the low temperature rise MVR system and the high temperature rise MVR system are respectively communicated with the A/O + MBR system;

the deep processing unit comprises an A/O + MBR system; the A/O + MBR system is also communicated with a backwashing water tank;

the membrane treatment unit comprises a first-stage RO membrane system, a first-stage RO membrane system and a second-stage RO membrane system which are communicated;

the first-stage RO membrane system is communicated with the second-stage RO membrane system; the first-stage RO membrane system is communicated with the intermediate water tank 1, and the second-stage RO membrane system is communicated with the mixed water tank;

the mixing tank is also in communication with an A/O + MBR system.

Further, the system also comprises a sludge concentration tank.

The invention has the beneficial effects that:

1. the pretreatment unit adopts a combined process, on one hand, oil, hardness, suspended matters and other pollutants in the wastewater are removed, and favorable conditions are provided for the post-treatment, on the other hand, the refractory macromolecular substances in the wastewater are oxidized into micromolecular substances by utilizing a high-grade oxidation means, so that the stable, efficient and energy-saving operation of an MVR evaporation system is ensured, the impurities in the crystallized salt are reduced, the resource utilization of the crystallized salt is facilitated, and the economic benefit is provided;

2. the evaporation desalination method is a currently recognized effective desalination method, and can separate salt in water from wastewater, wherein the MVR evaporation method is widely applied due to the advantages of high steam utilization efficiency, small steam consumption and low investment and operation cost. According to the water quality characteristics and the discharge requirements of the wastewater, the method has higher requirements on the removal of salt in the wastewater, and the removal rate requirement reaches more than 90 percent. Although other methods commonly used in engineering, such as an ion exchange method, an electrodialysis method, an RO reverse osmosis method, an electro-adsorption method and the like, can separate salt from wastewater, so that the salt concentration in fresh water is low, concentrated water with high salt concentration is formed at the same time, and the salt in the concentrated water can be removed only by an evaporation desalination method finally, so that the discharge requirement of high-salinity wastewater can be met. Therefore, for such high salinity wastewater, the MVR evaporation unit is the core unit, with irreplaceability. The process adopts an evaporation process combining low temperature rise MVR and high temperature rise MVR to treat high salinity wastewater, namely, the low temperature rise MVR is firstly used for evaporation to concentrate the wastewater, and then the high temperature rise MVR is used for evaporation to crystallize salts in the wastewater, and the MVR process combining low temperature rise concentration and high temperature rise crystallization is used for obviously saving energy consumption, thereby saving the operation cost.

3. By adopting the MBR immersed ultrafiltration membrane, a sedimentation tank at the back end of biochemistry and an ultrafiltration unit at the front section of the RO membrane are saved, and the investment construction and operation cost is effectively reduced; the membrane treatment unit is used as a final treatment unit, the salt substances are intercepted by the anti-pollution RO membrane, the removal rate of the anti-pollution RO membrane to salts such as ammonia nitrogen, total nitrogen and the like can reach 97 percent, the running cost is saved, and the standard discharge of pollutants such as the wastewater salts, the ammonia nitrogen, the total nitrogen, the arsenic and the like can be ensured;

4. the invention treats each pollutant in the waste water by adopting a combined process, and the front means and the rear means are mutually matched, thereby ensuring the stability and the safety of the operation of the whole process system and fully ensuring that the effluent can reach the discharge standard.

5. The method not only effectively solves the problem of emission of pollutants such as high salinity and high COD in the shale gas exploitation wastewater, but also can recover by-product crystalline salt, reduce the enterprise cost, meet the environmental protection requirement, generate good economic benefit and meet the requirement of sustainable development.

Drawings

FIG. 1 is a process flow diagram of the present invention.

Detailed Description

The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.

Example 1

A system for treating high-salinity heavy metal refractory shale gas exploitation wastewater comprises a pretreatment unit, an MVR evaporation unit, a deep treatment unit and a membrane treatment unit which are sequentially communicated; an intermediate water tank 1 is arranged between the coagulating sedimentation tank and the low temperature-rising MVR system.

The pretreatment unit comprises an oil separation adjusting tank, a pH adjusting tank 1, an integrated air flotation tank, a de-hardening sedimentation tank, an advanced chemical oxidation tank, an p H adjusting tank 2, an advanced chemical oxidation sedimentation tank and a coagulating sedimentation tank which are sequentially communicated; the wastewater is subjected to oil removal, adjustment, pH adjustment, air floatation, hardness removal, advanced oxidation and other treatment, oil substances, micro suspended substances, colloid substances and hardness in the wastewater are removed, organic matters in the wastewater are subjected to oxidative degradation, favorable conditions are provided for subsequent treatment units, and the intermediate product of the MVR evaporation unit can be recycled.

The MVR evaporation unit comprises a low-temperature-rise MVR system and a high-temperature-rise MVR system; an intermediate water tank 2 is arranged between the low-temperature-rise MVR system and the high-temperature-rise MVR system; the high temperature rise MVR system is also communicated with the advanced chemical oxidation pond.

The pretreated effluent is firstly subjected to low-temperature-rise MVR treatment for concentration treatment, then is subjected to high-temperature-rise MVR treatment, the concentrated wastewater is subjected to evaporative crystallization, and the separated crystal salt can be recycled; meanwhile, the mother liquor in the high-temperature MVR system needs to be returned to the advanced chemical oxidation pond periodically for oxidation, and then MVR evaporation treatment is continued.

The deep processing unit is an A/O + MBR system; the condensate in the MVR evaporation system is treated, and the condensate also contains pollutants such as COD, ammonia nitrogen, total nitrogen, arsenic and the like with certain concentration, so that the pollutants in the wastewater are continuously treated by the advanced treatment process of 'A/O + MBR'.

The membrane treatment unit comprises a primary RO membrane system, a primary RO membrane system and a secondary RO membrane system which are sequentially communicated; one-level RO membrane system and second grade RO membrane system intercommunication, one section RO membrane system and 1 UNICOM in middle pond, second grade RO membrane system and mixed water tank intercommunication, mixed water tank still with AO + MBR system intercommunication.

And (3) carrying out high-efficiency interception on pollutants such as organic matters, ammonia nitrogen, total nitrogen, arsenic and the like in the wastewater after advanced treatment by using the anti-pollution RO membrane, so that the wastewater meets the emission standard.

In addition, the device also comprises a sludge treatment unit used for treating the sludge, wherein the sludge treatment unit is a sludge concentration tank, sludge generated in the wastewater treatment process is temporarily stored in the sludge concentration tank, is subjected to filter pressing by a diaphragm dehydrator, controls the water content of the sludge to be about 65 percent, and is periodically delivered to a special unit for treatment.

The standard of wastewater reaching standards is the standard of surface water environment quality standard (GB3838-2002) surface water III and the requirement of replenishment project standard limit of surface water source of Chinese style drinking water, the requirement of wastewater treatment discharge standard is strict, and the representative indexes are COD_cr≤20mg/L，BOD₅≤4mg/L，NH₃N is less than or equal to 1mg/L, TN is less than or equal to 1mg/L, arsenic is less than or equal to 0.05mg/L, sulfate (in terms of SO)₄ ^2-) Less than or equal to 250mg/L of chloride salt (in terms of Cl)^-Calculated) is less than or equal to 250 mg/L.

Example 2

(1) pre-processing unit

S1, oil removal regulating reservoir: gas field water enters an oil separation regulating reservoir from the outside of a factory, oil substances in the wastewater are treated by an oil extractor arranged in the oil separation reservoir, the wastewater after oil removal enters the regulating reservoir, and the wastewater is homogenized and metered to form a first waste liquid;

s2, pH adjusting tank 1: adding sodium hydroxide by using a metering pump to adjust the pH value of the waste liquid II, and after adjusting the pH value of the waste water to 9, forming a large amount of waste liquid II with fine suspended particles;

s3, integrated air floatation tank: adding PAC and PAM by using a metering pump, removing micro suspended substances and colloid in the waste liquid II by air floatation treatment, and discharging water to form a waste liquid III; the dosage of PAC is 100mg/L, and the dosage of PAM is 10 mg/L;

s4, a hardening removal sedimentation tank: sequentially adding sodium carbonate, PAC and PAM into the waste liquid III by using a metering pump, and performing mud-water separation by using a sedimentation tank to obtain a supernatant liquid IV; wherein the dosage of sodium carbonate is 0.01-0.02 mg/L (can be adjusted according to the hardness of the incoming water), the dosage of PAC is 150mg/L, and the dosage of PAM is 10 mg/L;

s5, advanced chemical oxidation: regulating the pH value of the waste liquid IV to about 3 by using sulfuric acid, then sequentially adding ferrous sulfate heptahydrate and hydrogen peroxide by using a metering pump, wherein the adding amount of the ferrous sulfate heptahydrate is 1300mg/L, and the adding amount of the hydrogen peroxide is 1500mg/L, performing advanced chemical oxidation treatment on the waste liquid IV for about 5 hours, adding sodium hydroxide by using the metering pump, regulating the pH value of the waste water to 9, finally adding PAM (the adding amount of the PAM is 5mg/L), removing the previously added iron ions through an advanced oxidation sedimentation tank, and forming a supernatant into a waste liquid V;

s6, coagulating sedimentation tank: adding PAC and PAM into the waste liquid V in sequence by using a metering pump, wherein the dosage of PAC is 100mg/L, and the dosage of PAM is 5 mg/L; carrying out coagulating sedimentation treatment, carrying out mud-water separation in a sedimentation tank, and allowing supernatant to enter an intermediate water tank 1 to form waste liquid six;

(2) MVR evaporation unit

S7, low-temperature-rise MVR system: adding sulfuric acid into the waste liquid six by using a metering pump, adjusting the pH value to 6, ensuring that the waste liquid six enters a low-temperature-rise MVR system (the temperature rise of a vapor compressor is 10 ℃, the vapor pressure is 0.4MPa, and the evaporation temperature is less than 75 ℃) under an acidic condition, and performing falling film evaporation concentration treatment at a first stage to obtain a solution with the salt content of 6-8%; and then continuing to perform forced circulation type evaporation treatment of a second section, and finally obtaining a solution with the salt content of 18-21%. The step is characterized in that water is fed under an acidic condition, so that the waste liquid six is prevented from scaling and blocking equipment in a low-temperature-rise MVR system. When the salt content of the wastewater in the low-temperature-rise MVR system reaches about 18-21%, the wastewater can enter the intermediate water tank 2 to form a seventh waste liquid, and a eighth waste liquid is formed by the condensate generated in the concentration process;

s8, high temperature rising MVR system: pumping the waste liquid seven into a high-temperature-rise MVR system by using a pump (the temperature rise of a vapor compressor is 18 ℃, the vapor pressure is 0.4MPa, and the evaporation temperature is less than 93 ℃) to carry out crystallization treatment, wherein in the process, the generated crystallized salts are uniformly stacked for resource utilization; the generated condensate forms a waste liquid nine; mixing the waste liquid eight and the waste liquid nine to form waste liquid ten, passing through a heat exchanger and a cooling tower, controlling the temperature of condensate liquid at 32 ℃, and meeting the requirements of a rear-end biochemical unit;

(3) deep processing unit

S8, A/O unit: enabling the waste liquid ten to enter an A/O unit, carrying out denitrification treatment in an anoxic tank, and carrying out nitrification treatment in an aerobic tank to remove pollutants such as ammonia nitrogen, total nitrogen, COD and the like in the waste liquid ten; because the carbon-nitrogen ratio in the waste liquid is insufficient, sodium acetate is added into an anoxic tank by using a metering pump to provide a carbon source for the growth of microorganisms, and the waste liquid eleven is formed after the treatment of an A/O unit;

s9, MBR membrane tank: and enabling the waste liquid eleven to enter an MBR membrane tank, wherein an immersed ultrafiltration membrane is adopted in the membrane tank, the aperture of the membrane tank is less than 0.04 mu m, the temperature in summer is about 32 ℃, and the effluent of the MBR membrane requires SDI to be less than 3. On one hand, the sludge concentration can be improved, the removal of pollutants such as COD, ammonia nitrogen and total nitrogen in the waste liquid eleven is facilitated, on the other hand, the ultrafiltration can be carried out on the waste liquid eleven, the direct entering of the waste water into a rear-end membrane treatment unit is facilitated, and the investment and the operation cost are reduced. And adding a reducing agent sodium bisulfite into the effluent of the MBR membrane tank through a metering pump to form waste liquid twelve.

S10, backwashing the water pool: enabling the waste liquid twelve to enter a backwashing water tank to provide backwashing water for the MBR membrane group, and facilitating the cleaning of the MBR ultrafiltration membrane;

(4) membrane treatment unit

S11, a primary RO membrane system: feeding the waste liquid twelve into a first-stage RO membrane water inlet tank, adding sodium bisulfite, a scale inhibitor and dilute acid by using a metering pump, and then feeding into a first-stage RO membrane for filtering to form concentrated water I and fresh water I;

s12, a first-stage RO membrane system: the first concentrated water enters a first section of RO membrane water inlet tank, and enters a first section of RO membrane for filtration after the scale inhibitor is added by a metering pump, so as to form a second concentrated water and a second fresh water, wherein the second concentrated water enters an intermediate water tank 1 in S6;

s13, enabling the fresh water I and the fresh water II to enter a two-stage RO membrane system together for filtering to form a concentrated water III and a fresh water III, wherein the concentrated water III enters a first-stage RO membrane water inlet tank, and the fresh water III enters a mixed water tank;

s14, mixing water tank: when the fresh water III enters the mixed water tank, dilute alkali is added by using a metering pump, the pH value of the mixed fresh water is adjusted to 9, the mixed fresh water enters the mixed water tank for temporary storage, and after detection, the quality of the mixed fresh water meets the requirements of the surface water III standard (GB3838-2002) and the surface water source supplement project standard limit value of the centralized domestic drinking water, so that the mixed fresh water can be discharged up to the standard and can be reused as process water in a plant area, and if the mixed fresh water does not meet the requirements, the mixed fresh water enters an A/O unit in S8 for continuous treatment.

Example 3

(1) pre-processing unit

s2, pH adjusting tank 1: adding sodium hydroxide by using a metering pump to adjust the pH value of the waste liquid II, and after adjusting the pH value of the waste water to 8-9, forming a large amount of waste liquid II with fine suspended particles;

s3, integrated air floatation tank: adding PAC and PAM by using a metering pump, removing micro suspended substances and colloid in the waste liquid II by air floatation treatment, and discharging water to form a waste liquid III; the dosage of PAC is 100mg/L, and the dosage of PAM is 5 mg/L;

s4, a hardening removal sedimentation tank: sequentially adding sodium carbonate, PAC and PAM into the waste liquid III by using a metering pump, and performing mud-water separation by using a sedimentation tank to obtain a supernatant liquid IV; wherein the dosage of sodium carbonate is 0.01-0.02 mg/L (can be adjusted according to the hardness of the incoming water), the dosage of PAC is 100mg/L, and the dosage of PAM is 10 mg/L;

s5, advanced chemical oxidation: regulating the pH value of the waste liquid IV to about 3 by using sulfuric acid, then sequentially adding ferrous sulfate heptahydrate and hydrogen peroxide by using a metering pump, wherein the adding amount of the ferrous sulfate heptahydrate is 1300mg/L, and the adding amount of the hydrogen peroxide is 1500mg/L, performing advanced chemical oxidation treatment on the waste liquid IV for about 4 hours, adding sodium hydroxide by using the metering pump, regulating the pH value of the waste water to 8, finally adding PAM (the adding amount of the PAM is 10mg/L), removing the previously added iron ions through an advanced oxidation sedimentation tank, and forming a supernatant into a waste liquid V;

s6, coagulating sedimentation tank: adding PAC and PAM into the waste liquid V in sequence by using a metering pump, wherein the dosage of PAC is 150mg/L, and the dosage of PAM is 10 mg/L; carrying out coagulating sedimentation treatment, carrying out mud-water separation in a sedimentation tank, and allowing supernatant to enter an intermediate water tank 1 to form waste liquid six;

(2) MVR evaporation unit

S7, low-temperature-rise MVR system: adding sulfuric acid into the waste liquid six by using a metering pump, adjusting the pH value to 5, ensuring that the waste liquid six enters a low-temperature-rise MVR system (the temperature rise of a vapor compressor is 15 ℃, the vapor pressure is 0.4MPa, and the evaporation temperature is less than 80 ℃) under an acidic condition, and performing falling film evaporation concentration treatment at a first stage to obtain a solution with the salt content of 6-8%; and then continuing to perform forced circulation type evaporation treatment of a second section, and finally obtaining a solution with the salt content of 18-21%. The step is characterized in that water is fed under an acidic condition, so that the waste liquid six is prevented from scaling and blocking equipment in a low-temperature-rise MVR system. When the salt content of the wastewater in the low-temperature-rise MVR system reaches about 18-21%, the wastewater can enter the intermediate water tank 2 to form a seventh waste liquid, and a eighth waste liquid is formed by the condensate generated in the concentration process;

s8, high temperature rising MVR system: pumping the waste liquid seven into a high-temperature-rise MVR system by using a pump (the temperature rise of a vapor compressor is 18 ℃, the vapor pressure is 0.4MPa, and the evaporation temperature is less than 90 ℃), and carrying out crystallization treatment, wherein in the process, the generated crystallized salts are uniformly stacked and are recycled; the generated condensate forms a waste liquid nine; mixing the waste liquid eight and the waste liquid nine to form waste liquid ten, passing through a heat exchanger and a cooling tower, controlling the temperature of condensate liquid at 32 ℃, and meeting the requirements of a rear-end biochemical unit;

(3) deep processing unit

s9, MBR membrane tank: and enabling the waste liquid eleven to enter an MBR membrane tank, wherein an immersed ultrafiltration membrane is adopted in the membrane tank, the aperture of the membrane tank is less than 0.04 mu m, the temperature in summer is about 32 ℃, and the effluent of the MBR membrane requires SDI to be less than 3. On one hand, the sludge concentration is improved, the removal of pollutants such as COD, ammonia nitrogen and total nitrogen in the waste liquid eleven is facilitated, on the other hand, the ultrafiltration can be carried out on the waste liquid eleven, the direct entering of the waste water into a rear-end membrane treatment unit is facilitated, and the investment and the operation cost are reduced. And adding a reducing agent sodium bisulfite into the effluent of the MBR membrane tank through a metering pump to form waste liquid twelve.

(4) membrane treatment unit

Example 4

(1) pre-processing unit

s3, integrated air floatation tank: adding PAC and PAM by using a metering pump, removing micro suspended substances and colloid in the waste liquid II by air floatation treatment, and discharging water to form a waste liquid III; the dosage of PAC is 120mg/L, and the dosage of PAM is 8 mg/L;

s4, a hardening removal sedimentation tank: sequentially adding sodium carbonate, PAC and PAM into the waste liquid III by using a metering pump, and performing mud-water separation by using a sedimentation tank to obtain a supernatant liquid IV; wherein the dosage of sodium carbonate is 0.01-0.02 mg/L (can be adjusted according to the hardness of the incoming water), the dosage of PAC is 130mg/L, and the dosage of PAM is 8 mg/L;

s5, advanced chemical oxidation: regulating the pH value of the waste liquid IV to about 3 by using sulfuric acid, sequentially adding ferrous sulfate heptahydrate and hydrogen peroxide by using a metering pump, wherein the dosage of the ferrous sulfate heptahydrate is 1300mg/L, the dosage of the hydrogen peroxide is 1400mg/L, performing advanced chemical oxidation treatment on the waste liquid IV for about 4-5 hours, adding sodium hydroxide by using the metering pump, regulating the pH value of the waste water to 8, finally adding PAM (PAM dosage of 6mg/L), removing the previously added iron ions by using an advanced oxidation sedimentation tank, and forming a supernatant into a waste liquid V;

s6, coagulating sedimentation tank: adding PAC and PAM into the waste liquid V in sequence by using a metering pump, wherein the dosage of PAC is 120mg/L, and the dosage of PAM is 6 mg/L; carrying out coagulating sedimentation treatment, carrying out mud-water separation in a sedimentation tank, and allowing supernatant to enter an intermediate water tank 1 to form waste liquid six;

(2) MVR evaporation unit

S7, low-temperature-rise MVR system: adding sulfuric acid into the waste liquid six by using a metering pump, adjusting the pH value to 5, ensuring that the waste liquid six enters a low-temperature-rise MVR system (the temperature rise of a vapor compressor is 10 ℃, the vapor pressure is 0.4MPa, and the evaporation temperature is less than 75 ℃) under an acidic condition, and performing falling film evaporation concentration treatment at a first stage to obtain a solution with the salt content of 6-8%; and then continuing to perform forced circulation type evaporation treatment of a second section, and finally obtaining a solution with the salt content of 18-21%. The step is characterized in that water is fed under an acidic condition, so that the waste liquid six is prevented from scaling and blocking equipment in a low-temperature-rise MVR system. When the salt content of the wastewater in the low-temperature-rise MVR system reaches about 18-21%, the wastewater can enter the intermediate water tank 2 to form a seventh waste liquid, and a eighth waste liquid is formed by the condensate generated in the concentration process;

s8, high temperature rising MVR system: pumping the waste liquid seven into a high-temperature-rise MVR system by using a pump (the temperature rise of a vapor compressor is 16 ℃, the vapor pressure is 0.4MPa, and the evaporation temperature is less than 90 ℃), and carrying out crystallization treatment, wherein in the process, the generated crystallized salts are uniformly stacked and are recycled; the generated condensate forms a waste liquid nine; mixing the waste liquid eight and the waste liquid nine to form waste liquid ten, passing through a heat exchanger and a cooling tower, controlling the temperature of condensate liquid at 32 ℃, and meeting the requirements of a rear-end biochemical unit;

(3) deep processing unit

(4) membrane treatment unit

s12, a first-stage RO membrane system: the concentrated water I enters a section of RO membrane water inlet tank, after the scale inhibitor is added by a metering pump, the concentrated water I enters a section of RO membrane for filtration to form concentrated water II and fresh water II, wherein the concentrated water II enters an intermediate water tank 1 in S6, and the fresh water II enters a mixed water tank;

s14, mixing water tank: when the third fresh water enters the mixed water tank, dilute alkali is added by using a metering pump, the pH value of the mixed fresh water is adjusted to 6-9, the mixed fresh water enters the mixed water tank for temporary storage, and after detection, the quality of the mixed fresh water meets the requirements of the 'surface water environmental quality standard' (GB3838-2002) surface water III standard and the supplement project standard limit value of the surface water source of the centralized domestic drinking water, so that the mixed fresh water can be discharged up to the standard and can be recycled, and if the quality of the mixed fresh water does not meet the requirements, the mixed fresh water enters an A/O unit in S8 to be continuously treated.

Example 5

A method for treating high-salinity heavy metal refractory shale gas exploitation wastewater, wherein the components of the wastewater are the same as those of the wastewater in example 9, comprises the following steps:

(1) pretreatment Unit (dosage of each step in pretreatment Unit is in accordance with example 2)

s3, integrated air floatation tank: adding PAC and PAM by using a metering pump, removing micro suspended substances and colloid in the waste liquid II by air floatation treatment, and discharging water to form a waste liquid III;

s4, a hardening removal sedimentation tank: sequentially adding sodium carbonate, PAC and PAM into the waste liquid III by using a metering pump, and performing mud-water separation by using a sedimentation tank to obtain a supernatant liquid IV;

after pretreatment, the oil content, suspended matter content, hardness, COD content, ammonia nitrogen content, total nitrogen content, arsenic content and salt content in the wastewater are respectively 4.50mg/L, 52.00mg/L, 98.00mg/L, 432.00mg/L, 27.00mg/L, 58.00mg/L, 0.7904mg/L and 20460 mg/L.

(2) MVR evaporation unit

S5, low-temperature-rise MVR system: adding sulfuric acid into the waste liquid five by using a metering pump, adjusting the pH value to 5, ensuring that the waste liquid five enters a low temperature rise MVR system (the temperature rise of a vapor compressor is 10 ℃, the vapor pressure is 0.4MPa, and the evaporation temperature is less than 75 ℃) under an acidic condition, and concentrating. Water is fed under an acidic condition, so that the waste liquid five is prevented from scaling and blocking equipment in a low-temperature-rise MVR system. When the salt content of the wastewater in the low-temperature-rise MVR system reaches about 18-21%, the wastewater can enter the intermediate water tank 2 to form a waste liquid six, and a condensate liquid generated in the concentration process forms a waste liquid seven;

after low temperature rise MVR treatment, the COD, ammonia nitrogen, total arsenic and salt content concentration in the waste liquid seven are 250.66mg/L, 6.18mg/L, 15.62mg/L, 0.1417mg/L and 998mg/L respectively.

S6, high temperature rising MVR system: pumping the waste liquid six into a high-temperature-rise MVR system by using a pump (the temperature rise of a vapor compressor is 16 ℃, the vapor pressure is 0.4MPa, and the evaporation temperature is less than 90 ℃), and carrying out crystallization treatment, wherein in the process, the generated crystallized salts are uniformly stacked and are recycled; the generated condensate forms waste liquid eight; mixing the waste liquid seven and the waste liquid eight to form a waste liquid nine, passing through a heat exchanger and a cooling tower, controlling the temperature of a condensate below 32 ℃, and entering a back-end biochemical unit;

after the high-temperature-rise MVR treatment, the COD, ammonia nitrogen, total arsenic and salt content concentration in the waste liquid are 1006.51mg/L, 33.07mg/L, 83.63mg/L, 0.8535mg/L and 1000mg/L respectively.

(3) Deep processing unit

S7, A/O unit: the waste liquid nine enters an A/O unit, denitrification treatment is carried out in an anoxic tank, nitrification treatment is carried out in an aerobic tank, and pollutants such as ammonia nitrogen, total nitrogen, COD and the like in the waste liquid nine are removed; adding sodium acetate into an anoxic tank by using a metering pump to provide a carbon source for microbial growth because the carbon-nitrogen ratio in the waste liquid is insufficient, and forming a waste liquid ten after the treatment of an A/O unit;

s8, MBR membrane tank: and enabling the waste liquid to enter an MBR membrane tank, wherein an immersed ultrafiltration membrane is adopted in the membrane tank, the aperture of the membrane tank is less than 0.04 mu m, the temperature in summer is about 32 ℃, and the effluent SDI of the MBR membrane is less than 3. On one hand, the sludge concentration is improved, which is beneficial to removing pollutants such as COD, ammonia nitrogen, total nitrogen and the like in the waste liquid, on the other hand, the waste liquid can be ultrafiltered decimal, which is beneficial to the waste water to directly enter a rear-end membrane treatment unit, and the investment and the operation cost are reduced. And adding a reducing agent sodium bisulfite into the effluent of the MBR membrane tank through a metering pump to form eleven waste liquid.

The detected COD, ammonia nitrogen, total arsenic and salt content concentrations in the waste liquid are 191.91mg/L, 2.90mg/L, 17.12mg/L, 0.2319mg/L and 1000mg/L respectively.

S9, backwashing the water pool: enabling the waste liquid eleven to enter a backwashing water tank to provide backwashing water for an MBR membrane group, and facilitating the cleaning of an MBR ultrafiltration membrane;

(4) membrane treatment unit

S10, a primary RO membrane system: enabling the waste liquid eleven to enter a first-stage RO membrane water inlet tank, adding sodium bisulfite, a scale inhibitor and dilute acid by using a metering pump, and then entering a first-stage RO membrane for filtering to form concentrated water I and fresh water I;

s11, a first-stage RO membrane system: the concentrated water I enters a section of RO membrane water inlet tank, after the scale inhibitor is added by a metering pump, the concentrated water I enters a section of RO membrane for filtration to form concentrated water II and fresh water II, wherein the concentrated water II enters an intermediate water tank 1 in S6, and the fresh water II enters a mixed water tank;

s12, enabling the fresh water I and the fresh water II to enter a two-stage RO membrane system together for filtering to form a concentrated water III and a fresh water III, wherein the concentrated water III enters a first-stage RO membrane water inlet tank, and the fresh water III enters a mixed water tank;

s13, mixing water tank: when the third fresh water enters the mixed water tank, dilute alkali is added by using a metering pump, the pH value of the mixed fresh water is adjusted to 6-9, the mixed fresh water enters the mixed water tank for temporary storage to form a fourth fresh water, and after detection,

the COD, ammonia nitrogen, total arsenic and salt content concentration in the fresh water IV are respectively 35.10mg/L, 0.28mg/L, 0.44mg/L, 0.00417mg/L and 21.64 mg/L.

From the data, in the initial operation stage of the process, the effluent can also meet the requirements of the surface water environmental quality standard (GB3838-2002) surface water III type standard and the supplement project standard limit value of the surface water source of the centralized domestic drinking water, but due to the lack of advanced oxidation for preprocessing macromolecular substances in the wastewater, the MVR evaporation unit can accumulate the macromolecular substances in the MVR evaporation system in the operation process to generate a large amount of mother liquor, the mother liquor can not be continuously processed, and finally the process is collapsed and can not normally operate. In addition, in the initial operation stage, the service life and efficiency of the RO membrane are rapidly reduced due to the high COD concentration entering the membrane treatment unit at the later stage, and the operation cost of the process is increased. Therefore, the above process is not suitable for the treatment of such wastewater.

Example 6

s4, a hardening removal sedimentation tank: sequentially adding sodium carbonate, PAC and PAM into the waste liquid III by using a metering pump, and performing mud-water separation by using a sedimentation tank to obtain a supernatant liquid IV; through detection, the oil content, the suspended matter content, the hardness, the COD content, the ammonia nitrogen content, the total nitrogen content, the arsenic content and the salt content in the waste liquid IV are respectively 4.7mg/L, 54mg/L, 99mg/L, 480.00mg/L, 29.00mg/L, 59.00mg/L, 1.1671mg/L and 20511.00 mg/L.

S5, advanced chemical oxidation: adding ferrous sulfate heptahydrate into the waste liquid IV by using a metering pump, wherein the dosage is about 100mg/L, introducing ozone into the waste liquid IV, performing advanced chemical oxidation treatment on the waste liquid IV for about 4-5 hours, adding sodium hydroxide by using the metering pump, adjusting the pH value of the waste water to 8-9, finally adding PAM, removing the iron ions added in the front by using an advanced oxidation sedimentation tank, and forming a waste liquid V by using the supernatant;

s6, coagulating sedimentation tank: adding PAC and PAM into the waste liquid V in sequence by using a metering pump, performing coagulating sedimentation treatment, performing mud-water separation by using a sedimentation tank, and allowing supernatant to enter an intermediate water tank 1 to form a waste liquid VI;

through detection, the COD, ammonia nitrogen, total nitrogen, arsenic and salt content concentration in the waste liquid six are 345.60mg/L, 28.00mg/L, 58.50mg/L, 0.7937mg/L and 20511.00mg/L respectively.

(2) MVR evaporation unit

S7, low-temperature-rise MVR system: adding sulfuric acid into the waste liquid six by using a metering pump, adjusting the pH value to 5, ensuring that the waste liquid six enters a low temperature rise MVR system (the temperature rise of a vapor compressor is 10 ℃, the vapor pressure is 0.4MPa, and the evaporation temperature is less than 75 ℃) under an acidic condition, and concentrating. Water is fed under an acidic condition, so that the scale formation and equipment blockage of the waste liquid six in the low-temperature-rise MVR system are prevented. When the salt content of the wastewater in the low-temperature-rise MVR system reaches about 18-21%, the wastewater can enter the intermediate water tank 2 to form a seventh waste liquid, and a eighth waste liquid is formed by the condensate generated in the concentration process;

after low-temperature-rise MVR treatment, the COD, ammonia nitrogen, total nitrogen, arsenic and salt content concentration in the waste liquid eight are 232.79mg/L, 6.86mg/L, 16.44mg/L, 0.1425mg/L and 998.00mg/L respectively.

after the treatment of high-temperature MVR, the COD, ammonia nitrogen, total nitrogen, arsenic and salt content in the waste liquid are 934.74mg/L, 36.75mg/L, 88.04mg/L, 0.8582mg/L and 1000mg/L respectively.

(3) Deep processing unit

Through detection, the concentrations of COD, ammonia nitrogen, total nitrogen, arsenic and salt in the waste liquid twelve are 226.83mg/L, 3.22mg/L, 18.03mg/L, 0.2355mg/L and 1000mg/L respectively.

(4) membrane treatment unit

s14, mixing water tank: when the third fresh water enters the mixed water tank, dilute alkali is added by using a metering pump, the pH value of the mixed fresh water is adjusted to 6-9, the mixed fresh water enters the mixed water tank for temporary storage to form a fourth fresh water, and the COD, ammonia nitrogen, total arsenic and salt content concentration in the fourth fresh water are detected to be 31.61mg/L, 0.32mg/L, 0.47mg/L, 0.004233mg/L and 13.54mg/L respectively.

From the data, in the initial operation stage of the process, the effluent can also meet the requirements of the standards of the class III standards of surface water environment quality (GB3838-2002) and the limit values of the supplementary project standards of the surface water of centralized domestic drinking water, but because ozone is used as a high-level oxidation means, the pretreatment effect on the wastewater is weak, macromolecular organic substances cannot be effectively oxidized and degraded, the MVR evaporation unit still can be caused to accumulate in the MVR evaporation system in the continuous operation process, a large amount of mother liquor is generated, the mother liquor cannot be continuously treated, and finally the process can be caused to collapse and not normally operate. In addition, in the initial operation stage, the service life and efficiency of the RO membrane are rapidly reduced due to the high COD concentration entering the membrane treatment unit at the later stage, and the operation cost of the process is increased. Therefore, the above process is not suitable for the treatment of such wastewater.

Example 7

s5, advanced chemical oxidation: regulating the pH value of the waste liquid IV to about 3 by using sulfuric acid, then sequentially adding ferrous sulfate heptahydrate and hydrogen peroxide by using a metering pump, performing advanced chemical oxidation treatment on the waste liquid IV for about 4-5 hours, then adding sodium hydroxide by using the metering pump, regulating the pH value of the waste water to 8, finally adding PAM, removing the previously added iron ions through an advanced oxidation sedimentation tank, and forming a waste liquid V from the supernatant;

through detection, the COD, ammonia nitrogen, total arsenic and salt content concentration in the waste liquid six are 129.60mg/L, 29.00mg/L, 58.00mg/L, 0.0942mg/L and 21256mg/L respectively.

(2) MVR evaporation unit

through detection, the COD, ammonia nitrogen, total arsenic and salt content concentration in the waste liquid eight are 59.59mg/L, 6.90mg/L, 13.79mg/L, 0.0175mg/L and 990mg/L respectively.

through detection, the COD, ammonia nitrogen, total arsenic and salt content concentration in the waste liquid are 239.26mg/L, 36.92mg/L, 73.85mg/L, 0.1043mg/L and 1050mg/L respectively.

(3) Deep processing unit

and S11, detecting the waste liquid twelve, wherein the COD, ammonia nitrogen, total arsenic and salt content concentrations are respectively 60.00mg/L, 3.24mg/L, 15.12mg/L, 0.0285mg/L and 998mg/L, the standard does not meet the requirements of the surface water environment quality standard (GB3838-2002) surface water III type standard and the supplement project standard limit value of the surface water source of the central drinking water, and the waste liquid can not be discharged outside. Therefore, the process cannot be used for the treatment of this type of wastewater.

Example 8

(2) MVR evaporation unit

S7, low-temperature-rise MVR system: adding sulfuric acid into the waste liquid six by using a metering pump, adjusting the pH value to 5, ensuring that the waste liquid six enters a low temperature rise MVR system (the temperature rise of a vapor compressor is 10 ℃, the vapor pressure is 0.4MPa, and the evaporation temperature is less than 75 ℃) under an acidic condition, and concentrating. Water is fed under an acidic condition, so that the scale formation and equipment blockage of the waste liquid six in the low-temperature-rise MVR system are prevented. When the salt content of the wastewater in the low-temperature-rise MVR system reaches about 18-21%, the wastewater can enter the intermediate water tank 2 to form a seventh waste liquid, and a eighth waste liquid is formed by the condensate generated in the concentration process; the COD, ammonia nitrogen, total arsenic and salt content in the waste liquid eight are 65.40mg/L, 6.5mg/L, 14.04mg/L, 0.0530mg/L and 995mg/L respectively.

S8, high temperature rising MVR system: pumping the waste liquid seven into a high-temperature-rise MVR system by using a pump (the temperature rise of a vapor compressor is 16 ℃, the vapor pressure is 0.4MPa, and the evaporation temperature is less than 90 ℃), and carrying out crystallization treatment, wherein in the process, the generated crystallized salts are uniformly stacked and are recycled; the generated condensate forms a waste liquid nine; mixing the waste liquid eight and the waste liquid nine to form waste liquid ten, passing through a heat exchanger and a cooling tower, controlling the temperature of condensate liquid at 32 ℃, and meeting the requirements of a rear-end biochemical unit; the COD, ammonia nitrogen, total arsenic and salt content concentration in the waste liquid are 262.60mg/L, 34.38mg/L, 75.16mg/L, 0.3193mg/L and 1000mg/L respectively.

(3) Deep processing unit

s9, MBR membrane tank: and enabling the waste liquid eleven to enter an MBR membrane tank, wherein an immersed ultrafiltration membrane is adopted in the membrane tank, the aperture of the membrane tank is less than 0.04 mu m, the temperature in summer is about 32 ℃, and the effluent of the MBR membrane requires SDI to be less than 3. On one hand, the sludge concentration is improved, the removal of pollutants such as COD, ammonia nitrogen and total nitrogen in the waste liquid eleven is facilitated, on the other hand, the ultrafiltration can be carried out on the waste liquid eleven, the direct entering of the waste water into a rear-end membrane treatment unit is facilitated, and the investment and the operation cost are reduced. And adding a reducing agent sodium bisulfite into the effluent of the MBR membrane tank through a metering pump to form waste liquid twelve. The COD, ammonia nitrogen, total arsenic and salt content concentration in the waste liquid twelve are 262.60mg/L, 4.02mg/L, 15.39mg/L, 0.0876mg/L and 995.65mg/L respectively.

(4) membrane treatment unit

S11, primary RO membrane unit: feeding the waste liquid twelve into a first-stage RO membrane water inlet tank, adding sodium bisulfite, a scale inhibitor and dilute acid by using a metering pump, and then feeding into a first-stage RO membrane for filtering to form concentrated water I and fresh water I;

s12, one stage RO membrane unit: the concentrated water I enters a section of RO membrane water inlet tank, after the scale inhibitor is added by a metering pump, the concentrated water I enters a section of RO membrane for filtration to form concentrated water II and fresh water II, wherein the concentrated water II enters an intermediate water tank 1 in S6, and the fresh water II enters a mixed water tank;

s12, mixing water tank: after the fresh water I and the fresh water II are mixed, dilute alkali is added by using a metering pump, the pH value of the mixed fresh water is adjusted to 6-9, the mixed fresh water enters a mixed water tank for temporary storage, after detection, the concentrations of COD, ammonia nitrogen, total arsenic and salt in the mixed fresh water are respectively 16.00mg/L, 0.44mg/L, 3.25mg/L, 0.005755mg/L and 108mg/L, the total nitrogen does not meet the requirements of the surface water environment quality standard (GB3838-2002) surface water III type standard and the supplement project limit value of the surface water source of the centralized drinking water, and the discharge cannot be carried out, so the process is not suitable for the treatment of the waste water.

Example 9

The method described in the embodiment 2 of the application is used for treating the wastewater generated by a certain shale gas exploitation project, wherein the wastewater mainly comprises gas field water and fracturing flowback fluid and mainly comprisesThe pollutants are macromolecular organic matters, oils, hardness, salt, arsenic, ammonia nitrogen, total nitrogen and the like, wherein the water volume of the gas field is 320m³D, the water amount of the fracturing flowback fluid is 80m³D, total throughput of 400m³The main pollutants of the waste water are shown in Table 1.

TABLE 1 wastewater contaminant composition

Considering the fluctuation of water quality and water quantity, a safety system with 20% of maximum value of pollutant concentration is designed, and the treatment capacity is designed to be 480m³The pollutant concentration is designed according to a high value.

The pretreatment unit is mainly used for carrying out oil removal, adjustment, pH adjustment, suspended matter removal, hardness removal and oxidation of the degradation-resistant macromolecular polymer into the easily-treated micromolecular substance on the wastewater. After the treatment of the pretreatment unit, the oil content, the suspended matter content, the hardness content, the COD content, the ammonia nitrogen content, the total nitrogen content, the arsenic content and the salt content in the wastewater are respectively 5mg/L, 50mg/L, 100mg/L, 130mg/L, 30mg/L, 60mg/L, 0.0981mg/L and 21256 mg/L.

The method comprises the steps of pretreating wastewater, then feeding the pretreated wastewater into an MVR evaporation unit, concentrating the wastewater by utilizing the indirect heating effect of saturated steam, concentrating the salt content to 18-21%, feeding the wastewater into a high-temperature-rise MVR system, carrying out evaporative crystallization on the wastewater after the wastewater is concentrated, recycling the precipitated crystal salt, and feeding the condensate generated in the MVR evaporation process into a rear-end processing unit for continuous processing. According to the operation experience, the salt content in the condensate is about 1000mg/L, and COD in the wastewater is about 40%, ammonia nitrogen and total nitrogen are about 20%, and arsenic is about 11% entering the condensate. Therefore, after the high-temperature-rise MVR condensate is mixed, the COD, ammonia nitrogen, total nitrogen, arsenic and salt content concentration in the wastewater are respectively 110mg/L, 11mg/L, 26mg/L, 0.0324mg/L and 1000mg/L, and the concentration of arsenic in the crystallized salt is about 0.0003g/kg, so that the limit requirement of GB2762-2017 on arsenic as a pollutant of edible salt (the total arsenic is less than or equal to 0.0005g/kg) is met.

The condensate from the MVR evaporation unit enters an advanced treatment unit, pollutants such as COD, ammonia nitrogen, total nitrogen, arsenic and the like in the condensate are treated by utilizing an A/O + MBR process, and after the advanced treatment, the concentrations of the COD, the ammonia nitrogen, the total nitrogen, the arsenic and the salt content of the wastewater are respectively about 60mg/L, 3.22mg/L, 18mg/L, 0.0320mg/L and 1000 mg/L.

The wastewater after advanced treatment enters a membrane treatment unit, COD, ammonia nitrogen, total nitrogen and arsenic in the wastewater are removed at a terminal, after the wastewater is treated by a secondary special RO membrane, the COD, ammonia nitrogen, total nitrogen, arsenic and salt content in the wastewater are respectively reduced to 6.82mg/L, 0.31mg/L, 0.46mg/L, 0.000576mg/L and 5.08mg/L, the requirements of the surface water environment quality standard (GB3838-2002) surface water III standard and the supplement project standard limit value of the surface water source of the centralized domestic drinking water are met, and standard discharge and the process water recycling in a plant area can be realized.

In conclusion, the process disclosed by the invention is used for treating the high-salinity heavy metal refractory shale gas exploitation wastewater, the treatment effect is better than that of the treatment effects of the processes in examples 5-8, the problem of ultralow emission standard of the wastewater can be effectively solved, the energy consumption can be reduced, the investment operation cost can be saved, the resource utilization of intermediate products can be realized, the environment-friendly requirement is met, good economic benefits are generated, and the sustainable development requirement is met.

Claims

1. A treatment method of high-salinity heavy metal refractory shale gas exploitation wastewater is characterized by comprising the following steps:

(1) pretreatment of

(2) MVR evaporation treatment

Adjusting the pH value of the pretreated solution to 5-6, and performing two-stage low-temperature-rise MVR evaporation concentration under the condition that the evaporation temperature is less than 75-80 ℃; then entering a high temperature rising MVR system with the evaporation temperature of less than 90-105 ℃, evaporating and crystallizing, and separating out crystal salt; the condensate generated in the processes of low temperature rise MVR and high temperature rise MVR enters the next step of treatment;

(3) advanced treatment

Treating the condensate generated in the step (2) to remove ammonia nitrogen, total nitrogen and COD in the wastewater;

(4) membrane treatment

And (4) treating the condensate treated in the step (3) by adopting a two-stage RO membrane treatment process.

2. The method for treating the high-salinity heavy-metal refractory shale gas exploitation wastewater according to claim 1, wherein the pretreatment specifically comprises the following steps:

(3) integrated air flotation treatment: adding PAC and PAM into the waste liquid II, and removing micro suspended substances and colloids in the waste liquid II through air floatation treatment to form a waste liquid III;

(4) de-hardening and precipitating: sequentially adding sodium carbonate, PAC and PAM into the waste liquid III, and performing mud-water separation in a sedimentation tank to obtain a supernatant liquid IV;

(5) advanced chemical oxidation: regulating the pH value of the waste liquid IV to 3 by using sulfuric acid, then sequentially adding ferrous sulfate heptahydrate and hydrogen peroxide, treating for 4-5 h, then adding sodium hydroxide, regulating the pH value to 8-9, finally adding PAM, removing iron ions after passing through an advanced oxidation sedimentation tank, and forming a waste liquid V by using supernatant;

(6) coagulating sedimentation: and sequentially adding PAC and PAM into the waste liquid V for coagulating sedimentation, and performing mud-water separation in a sedimentation tank to obtain a supernatant liquid, namely a pretreatment solution.

3. The method for treating high-salinity heavy-metal refractory shale gas exploitation wastewater according to claim 1, wherein the specific process of the two-stage low-temperature-rise MVR is as follows:

adding the pretreatment solution with the pH value of 5-6 into a low-temperature-rise MVR with the temperature rise of 10-15 ℃, the evaporation temperature of less than 75 ℃ and the steam pressure of 0.4MPa to perform falling film evaporation in the first stage, and then performing forced circulation evaporation in the second stage to obtain a solution with the salt content of 18-21%.

4. The method for treating high-salinity heavy-metal refractory shale gas exploitation wastewater according to claim 1, wherein the specific process of the high temperature rise MVR is as follows:

and (3) carrying out high temperature rise MVR evaporation temperature of less than 93 ℃, steam pressure of 0.4MPa, temperature rise of 15-18 ℃, carrying out forced circulation type evaporation treatment on the solution subjected to low temperature rise MVR treatment, and finally separating out crystal salt capable of being recycled.

5. The method for treating the high-salinity heavy-metal refractory shale gas exploitation wastewater according to claim 1, wherein an A/O + MBR process is adopted to treat the condensate in the step (3).

6. The method for treating high salinity heavy metal refractory shale gas exploitation wastewater according to claim 5, wherein the MBR membrane used in the MBR process is an immersed ultrafiltration membrane with a pore size of less than 0.04 μm, and the effluent SDI is required to be less than 3.

7. The method for treating high salinity heavy metal refractory shale gas production wastewater according to claim 6, wherein a reducing agent is added to the MBR process.

8. The method for treating high-salinity heavy-metal refractory shale gas exploitation wastewater according to claim 1, wherein the specific process of the two-stage RO membrane treatment process in the step (4) is as follows:

separating the solution treated in the step (3) by a primary RO membrane system, feeding the separated fresh water into a secondary RO membrane system, and feeding the concentrated water into a primary RO membrane system for continuous separation; concentrated water is separated by a first-stage RO membrane, the concentrated water obtained by separation enters an MVR evaporation system to be continuously treated, fresh water enters a second-stage RO membrane system and is finally treated by the second-stage RO membrane system, the fresh water enters a mixed water tank, and the concentrated water enters a first-stage RO membrane to be continuously treated;

9. The method for treating high salinity heavy metal refractory shale gas exploitation wastewater according to claim 8, wherein reducing agents sodium bisulfite, scale inhibitor and dilute sulfuric acid are added during the treatment of the primary RO membrane system; adding a scale inhibitor during treatment of both the first-stage RO membrane system and the second-stage RO membrane system; and adding dilute alkali into the fresh water in the mixing water tank, and adjusting the pH value of the fresh water to 6-9.

10. A system for treating high-salinity heavy metal refractory shale gas exploitation wastewater is characterized by comprising a pretreatment unit, an MVR evaporation unit, a deep treatment unit and a membrane treatment unit which are sequentially communicated;

the pretreatment unit comprises an oil separation adjusting tank, a pH adjusting tank 1, an integrated air flotation tank, a de-hardening sedimentation tank, an advanced chemical oxidation tank, a pH adjusting tank 2, an advanced chemical oxidation sedimentation tank and a coagulating sedimentation tank which are sequentially communicated;

the MVR evaporation unit comprises a low-temperature-rise MVR system and a high-temperature-rise MVR system;

the deep processing unit comprises an A/O + MBR system;

the membrane treatment unit comprises a primary RO membrane system, a primary RO membrane system and a secondary RO membrane system which are communicated.