Treatment process of silver powder wastewater and adopted treatment system

Abstract

The invention belongs to the field of water treatment, and particularly provides a silver powder wastewater treatment process and an adopted treatment system. The treatment process of the silver powder wastewater comprises the following steps: pre-concentration: regulating the pH value of a silver powder mother solution to 6.5-7.5, and then carrying out reverse osmosis treatment; deamination: regulating the pH value of the reverse osmosis concentrated water to 10-12, and performing steam stripping ammonia distillation treatment to obtain free ammonia and deaminated liquid; membrane separation: adjusting the pH value of the deaminated liquid to 4-6, and carrying out ultrafiltration membrane separation; evaporation reduction: carrying out evaporation treatment on the ultrafiltration membrane produced water to obtain evaporation condensate water and evaporation mother liquor; drying: drying the ultrafiltration membrane concentrated water and the evaporation mother liquor; and biochemical treatment: carrying out biochemical reaction on the reverse osmosis produced water, the evaporation condensate water and the like with the silver powder washing water to obtain biochemical produced water. According to the treatment process, the cost of environmental protection treatment of the silver powder wastewater can be reduced, and the safety and stability in treatment are improved.

Description

Technical Field

[0001] The invention belongs to the field of water treatment, and in particular provides a treatment process for silver powder wastewater and a treatment system adopted therein. Background Art

[0002] Solar energy is recognized by the world as the most important clean, environmentally friendly and pollution-free renewable energy. For many years, the photovoltaic industry has been one of the fastest growing and most stable fields in the world. In the manufacturing process of solar cells, battery paste, as an important material, greatly affects the conversion efficiency, weldability, tension, printing, aging and other electrical performance indicators of the battery. Silver powder, as the main component of battery paste, is an essential material for modern electronic devices. With the rapid development of my country's electronics industry, a number of ultra-fine silver powder production projects have been developed in succession in recent years.

[0003] At present, the mainstream process for silver powder production is the liquid phase reduction method. Its reaction principle is that reducing agents such as VC, formaldehyde, and hydrazine hydrate react with silver nitrate to generate silver element and nitric acid. Polyvinyl pyrrolidone (PVP) is introduced as a dispersant during the reaction. Ammonia water is also introduced into some reaction systems to control the reaction rate. After the reaction, in order to improve the quality of the silver powder, the silver powder will be cleaned and other post-treatment processes. The entire silver powder production process will produce a silver powder mother liquor and a wash water. The silver powder mother liquor contains high concentrations of COD, nitrate, and ammonia nitrogen; the main components of the silver powder wash water are similar to those of the mother liquor, but the pollutant content is much lower than that of the mother liquor. For silver powder wastewater (mother liquor + wash water), due to its imbalance in carbon-nitrogen ratio, complex organic components, and high salt content, it cannot be treated by traditional biochemical methods.

[0004] CN115872574A discloses a process for treating wastewater from silver powder production, including: adjusting the pH of the wastewater to weak acidity, and then evaporating and concentrating the wastewater with a multiple-effect evaporator to obtain a concentrated mother liquor; drying the concentrated mother liquor, and incinerating the dried solid; spraying the waste gas from the multiple-effect evaporator and the waste gas after incineration; and finally subjecting the condensed water from the multiple-effect evaporator, the mother liquor drying condensed water, and the sprayed waste liquid to biochemical treatment, membrane biological reaction, and activated carbon filtration to obtain wastewater that meets the standards and can be discharged. The process is centered on multi-stage evaporation, aiming to reduce the amount of silver powder wastewater as much as possible, which is beneficial to the environmentally friendly production of silver powder, but the entire water volume is treated by evaporation, and the environmental protection cost is extremely high.

[0005] CN220845807U discloses a treatment process for silver powder wastewater, including: before the silver powder mother liquor enters the MVR system for evaporation, reverse osmosis concentration and reduction are first used, MVR distilled water, reverse osmosis produced water, and silver powder washing water are mixed and enter a two-stage AO biochemical device for deep treatment. The silver powder wastewater in this process is operated based on membrane + evaporation, but ammonia nitrogen removal is not considered, and ammonium nitrate in the water has a great risk of explosion during high-temperature evaporation.

[0006] In summary, there is an urgent need to develop a treatment method with lower cost, higher safety and capable of meeting the standards for silver powder production wastewater. SUMMARY OF THE INVENTION

[0007] The purpose of the present invention is to provide a treatment process for silver powder wastewater and a treatment system adopted thereby. The treatment process of the present invention can reduce the cost of environmental protection treatment of silver powder wastewater and improve the safety and stability during treatment.

[0008] In a first aspect, the present invention provides a treatment process for silver powder wastewater, the silver powder wastewater including a silver powder mother liquor and silver powder washing water, and the silver powder mother liquor and silver powder washing water containing COD, ammonia nitrogen, nitrate radical and PVP respectively; the treatment process includes the following processes,

[0009] Pre-concentration: After adjusting the pH of the silver powder mother liquor to 6.5 - 7.5, it is used as a stream of influent for reverse osmosis treatment to obtain reverse osmosis concentrate and reverse osmosis product water;

[0010] Deammoniation: After adjusting the pH of the reverse osmosis concentrate to 10 - 12, it is subjected to steam stripping and ammonia distillation treatment to obtain free ammonia and deammoniated liquid;

[0011] Membrane separation: After adjusting the pH of the deammoniated liquid to 4 - 6, it is subjected to ultrafiltration membrane separation to obtain membrane product water and PVP-rich membrane concentrate;

[0012] Evaporation and reduction: The membrane product water is subjected to evaporation treatment to obtain evaporation condensate and evaporation mother liquor;

[0013] Drying: The PVP-rich membrane concentrate and evaporation mother liquor are subjected to drying treatment to obtain solid residue and drying condensate;

[0014] Biochemical treatment: The reverse osmosis product water, evaporation condensate and drying condensate are mixed with the silver powder washing water, and then a carbon source is supplemented for biochemical reaction to obtain biochemical product water.

[0015] In the treatment process of the present invention, first, reverse osmosis pre-concentration is carried out on the silver powder wastewater, which can effectively reduce the investment scale and operating energy consumption of the subsequent stripping ammonia distillation and evaporation, significantly reduce the operating cost of the entire process, and improve the economy. In addition, the introduction of stripping ammonia distillation treatment can convert the ammonium nitrate component with flammable and explosive properties in the wastewater into other relatively more stable and safe nitrates (such as sodium nitrate), ensuring the safety of silver powder production to the greatest extent; and, ultrafiltration membrane separation is carried out on the water after ammonia removal, which can effectively remove macromolecular organic components such as PVP therein, avoiding its gelling in the subsequent evaporation system and affecting the continuous operation of evaporation. Finally, the produced water from reverse osmosis, evaporation, ammonia stripping, and ultrafiltration and the silver powder washing water are jointly subjected to biochemical treatment, achieving the up-to-standard discharge of the system-produced water. The treatment process of the present invention can not only realize the resource utilization and environmental protection treatment of silver powder wastewater, but also effectively reduce the equipment investment and operating energy consumption compared with traditional treatment methods such as multi-effect evaporation, improving the stability and safety of the production process.

[0016] In the second aspect, the present invention provides a treatment system for silver powder wastewater. The treatment process described in the first aspect of the present invention is implemented using this treatment system. The treatment system includes: a pre-concentration unit, a deammoniation unit, a membrane separation unit, an evaporation reduction unit, a drying unit, and a biochemical unit; wherein,

[0017] The pre-concentration unit includes a pH adjustment tank and a reverse osmosis concentration device for sequentially adjusting the pH of the silver powder mother liquor and performing reverse osmosis treatment to obtain reverse osmosis concentrated water and reverse osmosis produced water;

[0018] The deammoniation unit includes an alkali adjustment tank and a stripping ammonia distillation device for sequentially adjusting the pH of the reverse osmosis concentrated water and performing stripping ammonia distillation treatment to obtain free ammonia and the liquid after ammonia removal;

[0019] The membrane separation unit includes an acid adjustment tank and an ultrafiltration membrane separation device for sequentially adjusting the pH of the liquid after ammonia removal and performing ultrafiltration separation to obtain membrane-produced water and PVP-rich membrane concentrated water;

[0020] The evaporation reduction unit includes a buffer tank and an evaporation device. The buffer tank is used to collect and homogenize the membrane-produced water, and the evaporation device is used to evaporate the membrane-produced water collected by the buffer tank to obtain evaporation condensate and evaporation mother liquor;

[0021] The drying unit is used to dry the membrane concentrated water and the evaporation mother liquor to obtain solid slag and drying condensate;

[0022] The biochemical unit includes a biochemical adjustment tank and a biochemical reaction device. The biochemical adjustment tank is used to collect reverse osmosis produced water, evaporation condensate, drying condensate, and reverse osmosis produced water and supplement a carbon source to obtain adjusted mixed water; the biochemical reaction device is used to perform a biochemical reaction on the adjusted mixed water to obtain biochemical produced water and biochemical sludge.

[0023] In the treatment system of the present invention, the adoption of reverse osmosis pre-concentration + ammonia removal treatment + ultrafiltration membrane separation can not only realize the resource treatment of silver powder wastewater, but also effectively reduce the investment scale and energy consumption of the evaporation device, and the treatment system enables the treatment process of silver powder wastewater to proceed in a safer and more stable manner.

[0024] Some of the additional aspects and advantages of the present invention will be given in the following description, some will become obvious from the following description, or will be understood through the practice of the present invention. Description of the Drawings

[0025] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, wherein:

[0026] Figure 1 It is a schematic flow chart of the silver powder wastewater treatment process in an embodiment of the present invention.

[0027] Description of the Reference Numerals in the Drawings

[0028] 1: pH adjustment tank; 2-1: primary DTRO device; 2-2: secondary DTRO device; 3: alkali adjustment tank; 4: stripping and ammonia evaporation device; 5: acid adjustment tank; 6: ultrafiltration membrane separation device; 7: buffer tank; 8: single-effect MVR evaporation device; 9: scraper drying device; 10: biochemical adjustment tank; 11: membrane bioreactor. Detailed Embodiments

[0029] The embodiments of the present invention are described in detail below. The described embodiments are exemplary and are only used to explain the present invention and should not be construed as a limitation to the present invention.

[0030] The "range" disclosed in the present invention is defined in the form of a lower limit and / or an upper limit. A given range is defined by selecting a lower limit and / or an upper limit. The range defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range not explicitly recorded, and any lower limit can be combined with other lower limits to form a range not explicitly recorded. Similarly, any upper limit can be combined with any other upper limit to form a range not explicitly recorded. In addition, each separately disclosed point or single value itself can be used as a lower limit or an upper limit and combined with any other point or single value or combined with other lower limits or upper limits to form a range not explicitly recorded.

[0031] If there is no special instruction, all embodiments and optional embodiments of the present invention can be combined with each other to form a new technical solution, and such a technical solution should be considered to be included in the disclosure of the present invention.

[0032] In the process of preparing silver powder, it is usually necessary to add polyvinylpyrrolidone (PVP) as a dispersant to improve the particle size of silver powder, and then wash the silver powder to improve its quality. A large amount of silver powder wastewater containing PVP will be generated during the washing process of silver powder, and this wastewater will also contain components such as dehydro-VC and sodium nitrate dissolved in water. PVP is evenly dispersed in the aqueous solution, making the wastewater have characteristics such as high COD and high total nitrogen, and it is difficult for traditional biochemical reactions to reduce the COD and total nitrogen in this type of wastewater to the discharge standard. Related technologies use a multi-stage evaporation system or combine reverse osmosis with multi-stage evaporation to reduce the amount of wastewater treated in subsequent biochemical reactions. However, using a multi-stage evaporation system results in a large equipment investment and high energy consumption, and PVP during the treatment process also has an obvious tendency to form gels and contaminate the membrane system, affecting the stable operation of the system. Moreover, for silver powder wastewater controlled by ammonia water to regulate the reaction rate, its ammonia nitrogen content is very high, and high-concentration ammonia nitrogen usually exists in the form of ammonium nitrate, and ammonium nitrate has high danger during the evaporation process, which is likely to bring potential safety hazards.

[0033] For this reason, the present invention provides a treatment process for silver powder wastewater, including:

[0034] Pre-concentration: After adjusting the pH of the silver powder mother liquor to 6.5 - 7.5, it is used as a stream of influent for reverse osmosis treatment to obtain reverse osmosis concentrate (RO concentrate) and reverse osmosis permeate (RO permeate);

[0035] Ammonia removal: After adjusting the pH of the reverse osmosis concentrate to 10 - 12, it is subjected to stripping and ammonia distillation treatment to obtain free ammonia and ammonia-removed liquid;

[0036] Membrane separation: After adjusting the pH of the ammonia-removed liquid to 4 - 6, it is subjected to ultrafiltration membrane separation to obtain membrane permeate and PVP-rich membrane concentrate;

[0037] Evaporation and reduction: The membrane permeate is subjected to evaporation treatment to obtain evaporation condensate and evaporation mother liquor;

[0038] Drying: The membrane concentrate and evaporation mother liquor are subjected to drying treatment to obtain solid residues and drying condensate;

[0039] Biochemical treatment: The reverse osmosis permeate, evaporation condensate and drying condensate are mixed with the silver powder washing water, and then a carbon source is supplemented for biochemical reaction to obtain biochemical effluent.

[0040] In the present invention, the silver powder wastewater includes silver powder mother liquor and silver powder washing water, and the silver powder mother liquor and silver powder washing water contain COD, ammonia nitrogen, nitrate and PVP respectively.

[0041] In some embodiments, in the silver powder mother liquor, the concentration of COD is 30,000 to 70,000 mg / L, such as 30000 mg / L, 35400 mg / L, 40000 mg / L, 40500 mg / L, 50000 mg / L, 51500 mg / L, 52000 mg / L, 55000 mg / L, 60000 mg / L, 65000 mg / L, etc.; the concentration of nitrate in terms of nitrate nitrogen is 3000 to 5000 mg / L, such as 3000 mg / L, 3300 mg / L, 3500 mg / L, 3800 mg / L, 3900 mg / L, 4000 mg / L, 4200 mg / L, 4400 mg / L, 4500 mg / L, 4700 mg / L, etc.; the concentration of ammonia nitrogen (NH 3 -N) is 1000 to 10000 mg / L, such as 1000 mg / L, 2000 mg / L, 2500 mg / L, 3000 mg / L, 6000 mg / L, 7000 mg / L, 7500 mg / L, 8000 mg / L, 8400 mg / L, 9000 mg / L, 9500 mg / L, 10000 mg / L, etc.; the concentration of PVP is 5000 to 10000 mg / L, such as 5000 mg / L, 5300 mg / L, 5800 mg / L, 6000 mg / L, 6050 mg / L, 6200 mg / L, 6600 mg / L, 7000 mg / L, 7100 mg / L, 7500 mg / L, 7700 mg / L, 7800 mg / L, 8100 mg / L, 8600 mg / L, 9000 mg / L, 9500 mg / L, etc.

[0042] In some embodiments, the concentration of COD in the silver powder washing water is 500 to 5000 mg / L, such as 500 mg / L, 1000 mg / L, 1100 mg / L, 1300 mg / L, 1500 mg / L, 1800 mg / L, 2000 mg / L, 2200 mg / L, 3000 mg / L, 3300 mg / L, 4000 mg / L, etc.; the concentration of nitrate in terms of nitrate nitrogen is 300 to 500 mg / L, such as 300 mg / L, 350 mg / L, 400 mg / L, 500 mg / L, etc.; the concentration of ammonia nitrogen is 100 to 1000 mg / L, such as 100 mg / L, 200 mg / L, 300 mg / L, 600 mg / L, etc.; the concentration of PVP is 50 to 100 mg / L, such as 50 mg / L, 70 mg / L, 80 mg / L, etc.

[0043] In the present invention, through reverse osmosis treatment, most of the COD, ammonia nitrogen, and nitrate in the silver powder mother liquor can be concentrated in the RO concentrated water, and subsequent ammonia removal and evaporation treatments are carried out to achieve the reduction of the influent of both. In order to avoid problems such as shortening the service life of the reverse osmosis membrane and deterioration of the membrane rejection performance caused by directly concentrating the silver powder mother liquor, the pH of the silver powder mother liquor needs to be adjusted to a slightly neutral value (pH = 6.5 - 7.5) by a pH regulator. The pH regulator can be an alkaline solution or an acidic solution, and can be specifically selected according to the pH of the silver powder mother liquor to be treated. When the pH of the mother liquor to be treated > 7.5, an acidic solution can be used for adjustment; when the pH of the mother liquor to be treated < 6.5, an alkaline solution can be used for adjustment. The alkaline solution can be, for example, an aqueous solution of sodium hydroxide, and the mass concentration of sodium hydroxide can be 20% - 35%. The acidic solution can be a sulfuric acid solution or a nitric acid solution. The mass concentration of the sulfuric acid solution can be 40% - 60%, and the mass concentration of the nitric acid solution can be 20% - 30%.

[0044] In some embodiments, the reverse osmosis treatment includes primary reverse osmosis treatment and secondary reverse osmosis treatment. Among them, the pH-adjusted silver powder mother liquor is used as one influent for primary reverse osmosis treatment to obtain primary reverse osmosis product water and reverse osmosis concentrated water for subsequent ammonia removal treatment (i.e., primary reverse osmosis concentrated water); the primary reverse osmosis product water is subjected to secondary reverse osmosis treatment to obtain reverse osmosis product water for subsequent biochemical treatment (i.e., secondary reverse osmosis product water) and secondary reverse osmosis concentrated water, and the secondary reverse osmosis concentrated water is recycled as another influent for the primary reverse osmosis treatment. Using two-stage reverse osmosis treatment can reasonably control the operation cost of the system while ensuring the rejection effect. Preferably, the operating conditions of the primary reverse osmosis treatment include: temperature 15 - 40 °C (such as 20 °C, 25 °C, 30 °C, or 35 °C), pressure 40 - 60 bar (such as 40 bar, 45 bar, 50 bar, 55 bar, or 60 bar), and membrane flux 10 - 15 LMH (such as 10 LMH, 12 LMH, 13 LMH, 14 LMH, or 15 LMH); the operating conditions of the secondary reverse osmosis treatment include: temperature 5 - 40 °C (such as 20 °C, 25 °C, 30 °C, or 35 °C), pressure 10 - 15 bar (such as 10 bar, 12 bar, 13 bar, 14 bar, or 15 bar), and membrane flux 30 - 35 LMH (such as 30 LMH, 32 LMH, 33 LMH, or 35 LMH).

[0045] In some embodiments, the recovery rate of the reverse osmosis treatment is 40% - 60%, and the rejection rate of DOD in the silver powder mother liquor > 95%, the rejection rate of nitrate (calculated as nitrate nitrogen) > 94%, and the rejection rate of ammonia nitrogen > 92%.

[0046] In the present invention, in order to convert the ammonium salt in the wastewater into free ammonia, an alkaline solution can be used to adjust the RO concentrated water to be alkaline (pH = 10 - 12). Through deammoniation, the ammonium nitrate component can be converted into other relatively safe nitrate components, and at the same time, free ammonia is separated. Among them, the type of the nitrate can be determined according to the type of the alkaline solution. For example, when the alkaline solution is an aqueous NaOH solution, the nitrate is sodium nitrate.

[0047] In the present invention, the stripping and ammonia distillation treatment can be negative pressure stripping and ammonia distillation. According to some embodiments, the operating conditions of the stripping and ammonia distillation treatment include: the vacuum degree is 0.05 - 0.06 MPa, and the stripping temperature is 80 - 90 °C. In order to realize the recovery of free ammonia, preferably, the treatment process further includes: mixing free ammonia with water to obtain ammonia water with a mass concentration of 15% - 28%.

[0048] In the present invention, by performing ultrafiltration membrane separation on the water after deammoniation, PVP can be enriched to obtain concentrated membrane water, and other small molecules (such as VC) can be promoted to enter the membrane permeate water, reducing the possibility of evaporation blockage. In order to meet the use environment of the ultrafiltration membrane, an acid solution (such as 68 wt% nitric acid) can be used to adjust the pH of the water after deammoniation to be acidic (pH = 4 - 6). The ultrafiltration membrane can be a polymer membrane, preferably a polyamide ultrafiltration membrane. Compared with inorganic ultrafiltration membranes such as ceramic membranes, the polyamide ultrafiltration membrane has a good pore size distribution and can effectively separate polymers and organic small molecules. Preferably, the cut-off molecular weight of the ultrafiltration membrane is 2200 - 3000 Da, such as 2300 Da, 2500 Da, 2700 Da, 2800 Da, 3000 Da, etc. If the cut-off molecular weight is too small, small molecules may be retained, affecting the recovery rate and increasing the operating energy consumption. If the cut-off molecular weight is too large, it is easy to form a membrane surface that retains macromolecules (the membrane cut-off pore size usually has a normal distribution), and the existence of this membrane surface will reduce the PVP retention rate.

[0049] In some embodiments, the operating conditions of the ultrafiltration membrane separation include: the temperature is 15 - 40 °C, the pressure is 5 - 25 bar, the membrane flux is 15 - 30 LMH, and the recovery rate is 85% - 95%. Preferably, the retention rate of PVP in the liquid after deammoniation by the ultrafiltration membrane separation treatment is ≥99%.

[0050] In the present invention, by evaporation and water reduction, the water volume can be compressed, reducing the operating cost of the drying system. Since the ultrafiltration membrane permeate water to be evaporated almost does not contain macromolecular organic matters such as PVP, the evaporation device can operate stably. By evaporation and water reduction, an evaporation mother liquor mainly composed of dehydro-VC and nitrate, and evaporation condensate water of some small molecules with lower boiling points can be obtained. Preferably, the evaporation treatment is carried out in a single-effect MVR evaporation device, and the evaporation treatment temperature is 85 - 95 °C, and the discharge density is 1.2 - 1.3 t / m 3 .

[0051] In some embodiments, the evaporation treatment results in a mass ratio of the obtained evaporation mother liquor to the evaporation condensate water of (2 - 5):1.

[0052] In the present invention, through the drying treatment, recoverable solid residues and drying condensate water can be obtained. Preferably, the drying treatment is carried out in a scraper drying device, the temperature of the scraper drying is 40 - 80 °C, such as 40 °C, 45 °C, 50 °C, 60 °C, 70 °C, 80 °C, etc., and the moisture content (mass percentage) of the solid residues is controlled to be 10% - 20%, such as 12%, 15%, etc. Additionally, in the scraper drying treatment, the steam consumption can be 1.2 - 1.4 t / m 3 Wastewater.

[0053] In the present invention, the mixed water of reverse osmosis product water, evaporation condensate water, drying condensate water and silver powder washing water is subjected to biochemical treatment, which can convert the COD and total nitrogen in the mixed water into carbon dioxide, nitrogen and the components of the biochemical sludge itself to obtain reaction product water and biochemical sludge. In the biochemical treatment, a carbon source needs to be added to adjust the carbon-nitrogen ratio. Preferably, the added carbon source makes the nitrogen ratio of the reaction system (28 - 33):1, such as 30:1. The present invention has no particular limitation on the carbon source, and it can be a conventional choice in sewage biochemical treatment, for example, but not limited to, composite carbon source, glucose, etc.

[0054] In some embodiments, the total mass of the evaporation condensate water and the drying condensate water is 30% - 55% of the mass of the silver powder washing water, such as 30%, 40%, 45%, 50%, 51%, 52%, etc.; the mass of the reverse osmosis product water is 40% - 60% of the mass of the silver powder washing water, such as 40%, 43%, 48%, 50%, 51%, 55%, etc.

[0055] In some embodiments, the biochemical reaction is carried out in a membrane bioreactor, and the membrane bioreactor includes two - stage A / O pools and a membrane pool, that is, the biochemical treatment adopts a two - stage A / O - MBR process. Generally, the dissolved oxygen concentration in the first - stage anoxic pool (A1) can be 0.2 - 0.5 mg / L, the hydraulic retention time can be 1 - 4 h, the dissolved oxygen (DO) concentration in the first - stage aerobic pool (O1) can be 2 - 5 mg / L, the hydraulic retention time can be 4 - 10 h, the dissolved oxygen concentration in the second - stage anoxic pool (A2) can be 0.2 - 0.5 mg / L, the hydraulic retention time can be 1 - 3 h, the dissolved oxygen concentration in the second - stage aerobic pool (O2) can be 1 - 4 mg / L, and the hydraulic retention time can be 3 - 7 h. The sludge concentration in the membrane pool can be 3000 - 12000 mg / L.

[0056] The present invention also provides a treatment system for silver powder wastewater used in the above treatment process, including: a pre-concentration unit, a deammoniation unit, a membrane separation unit, an evaporation reduction unit, a drying unit, and a biochemical unit.

[0057] In the present invention, the pre-concentration unit includes a pH adjustment tank and a reverse osmosis concentration device, which are used to adjust the pH of the silver powder mother liquor and perform reverse osmosis treatment in sequence to obtain reverse osmosis concentrated water and reverse osmosis product water.

[0058] In some embodiments, the reverse osmosis concentration device includes a first-stage disk tube reverse osmosis device (first-stage DTRO device) and a second-stage disk tube reverse osmosis device (second-stage DTRO device), which can perform the above-mentioned first-stage reverse osmosis treatment and second-stage reverse osmosis treatment respectively. Using the DTRO device can delay membrane fouling and extend the service life of the membrane.

[0059] In the present invention, the deammoniation unit includes an alkali adjustment tank and a stripping and ammonia distillation device, which can be used to adjust the pH of the reverse osmosis concentrated water and perform stripping and ammonia distillation treatment in sequence to obtain free ammonia and deammoniated liquid.

[0060] In the present invention, the membrane separation unit includes an acid adjustment tank and an ultrafiltration membrane separation device, which can be used to adjust the pH of the deammoniated liquid and then perform ultrafiltration separation to obtain membrane product water and membrane concentrated water rich in PVP.

[0061] In the present invention, the evaporation reduction unit includes a buffer tank and an evaporation device. The buffer tank is used to collect the membrane product water, and the evaporation device is used to evaporate the membrane product water to obtain evaporation condensate water and evaporation mother liquor.

[0062] In some embodiments, the evaporation device is a single-effect MVR evaporator. In this case, the evaporation device of the treatment system has low investment and low energy consumption.

[0063] In the present invention, the drying unit is used to dry the membrane concentrated water and the evaporation mother liquor to obtain solid residues and drying condensate water.

[0064] In some embodiments, the drying unit includes a scraper drying device.

[0065] In the present invention, the biochemical unit includes a biochemical adjustment tank and a biochemical reaction device. The biochemical adjustment tank is used to collect reverse osmosis product water, evaporation condensate water, drying condensate water and reverse osmosis product water and supplement a carbon source to obtain adjusted mixed water; the biochemical reaction device is used to perform a biochemical reaction on the adjusted mixed water to obtain biochemical product water.

[0066] In some embodiments, the biochemical reaction device includes a membrane bioreactor.

[0067] According to some specific embodiments, in combination with Figure 1 As shown, the treatment process of silver powder wastewater using the said treatment system includes the following processes:

[0068] Two-stage DTRO pre-concentration: Feed the silver powder mother liquor into the pH adjustment tank 1, add liquid caustic soda to adjust the pH to 6.5 - 7.5, and then enter the first-stage DTRO device 2-1 for first-stage reverse osmosis concentration to obtain first-stage RO product water and first-stage RO concentrated water;

[0069] The first-stage RO product water enters the second-stage DTRO device 2-2 for second-stage reverse osmosis concentration to obtain second-stage RO concentrated water and second-stage RO product water. The second-stage RO concentrated water is returned to the first-stage DTRO device;

[0070] Stripping and ammonia removal: Feed the first-stage RO concentrated water into the alkali adjustment tank 3, add alkali solution to adjust the pH to 10 - 12, and then feed it into the stripping and ammonia distillation device 4, and introduce steam for ammonia removal treatment to obtain free ammonia and ammonia-removed water. The free ammonia is mixed with water to obtain ammonia water;

[0071] Ultrafiltration separation for removing PVP: Feed the ammonia-removed liquid into the acid adjustment tank 5, add nitric acid to adjust the pH to 4 - 6, and then feed it into the ultrafiltration membrane separation device 6 for ultrafiltration separation to obtain ultrafiltration membrane concentrated water and ultrafiltration membrane product water;

[0072] Evaporation for volume reduction: Feed the ultrafiltration membrane product water into the buffer tank 7 for buffering and homogenization, and then feed it into the single-effect MVR evaporation device 8, and introduce steam for evaporation treatment to obtain evaporation condensate water and evaporation mother liquor;

[0073] Drying: Feed the ultrafiltration membrane concentrated water and evaporation mother liquor into the scraper drying device 9, and introduce steam for drying treatment to obtain solid residue and drying condensate water;

[0074] Biochemical treatment: Feed the silver powder washing water, second-stage RO product water, evaporation condensate water and drying condensate water into the biochemical adjustment tank to obtain mixed water. Supplement the carbon source to the mixed water, and then feed it into the membrane bioreactor 11 for biochemical reaction to obtain reaction product water.

[0075] The following describes the embodiments of the present invention. The embodiments described below are exemplary and are only used to explain the present invention and should not be construed as a limitation to the present invention.

[0076] The following embodiments in combination with Figure 1 illustrate the treatment process of silver powder wastewater of the present invention. The ultrafiltration membrane used in the ultrafiltration separation device is the AMS membrane of UNISOL company, with the model of A-U301 (polyamide membrane, the cut-off molecular weight is 2500Da). The alkali solution is all NaOH aqueous solution, and the concentration of NaOH is 30wt%.

[0077] Example 1

[0078] Two-stage DTRO pre-concentration: Feed 300 t / d of silver powder mother liquor (main component concentrations: COD = 60000 mg / L, nitrate nitrogen = 3500 mg / L, NH 3 -N = 8400 mg / L, PVP = 9000 mg / L) into the pH adjustment tank. After adding liquid caustic soda to adjust the pH to 6.5, it serves as one stream of reverse osmosis feed water.

[0079] Feed 320.5 t / d of reverse osmosis feed water (silver powder mother liquor + secondary RO concentrated water) into the first-stage DTRO for first-stage reverse osmosis treatment (operating temperature is 25 °C, pressure is 50 bar, and membrane flux is 12 LMH), obtaining 150 t / d of first-stage RO concentrated water and 170.5 t / d of first-stage RO product water;

[0080] Send 170.5 t / d of first-stage RO product water to the second-stage DTRO for second-stage reverse osmosis treatment (operating temperature is 25 °C, pressure is 20 bar, and membrane flux is 30 LMH), obtaining 20.5 t / d of second-stage RO concentrated water and 150 t / d of second-stage RO product water. The second-stage RO concentrated water is returned to the first-stage DTRO as another stream of reverse osmosis feed water;

[0081] Stripping and ammonia removal: Feed 150 t / d of first-stage RO concentrated water into the alkali adjustment tank. After adding alkali liquor to adjust the pH to 11 - 12, send it to the negative pressure stripping and ammonia distillation device, and introduce steam for stripping and ammonia removal treatment (vacuum degree is 0.05 MPa, stripping temperature is 90 °C), obtaining free ammonia and 169.5 t / d of post-ammonia-removal liquid. The free ammonia is mixed with 12.0 t / d of water to obtain 12.5 t / d of ammonia water (concentration is 20 wt%);

[0082] Ultrafiltration separation for PVP removal: Feed 169.5 t / d of post-ammonia-removal liquid (COD = 119712 mg / L, nitrate nitrogen = 6987 mg / L, NH 3 -N = 16722 mg / L, PVP = 17996 mg / L) into the acid adjustment tank. After adding nitric acid (concentration 68 wt%) to adjust the pH to 5, send it to the ultrafiltration membrane separation device for ultrafiltration treatment (operating conditions: temperature is 25 °C, pressure is 15 bar, and membrane flux is 20 LMH), obtaining 17 t / d of ultrafiltration membrane concentrated water (COD = 298919 mg / L, PVP = 118974 mg / L) and 152.5 t / d of ultrafiltration membrane product water (the COD retention rate of the ultrafiltration separation treatment for the post-ammonia-removal liquid is 26.4%, the PVP retention rate is 99.1%, and there is almost no retention for nitrate nitrogen and ammonia nitrogen);

[0083] Evaporation and concentration: Feed 152.5 t / d of ultrafiltration membrane product water into the buffer tank for homogenization, and then send it to the single-effect MVR evaporation device. Introduce steam for evaporation and concentration (evaporation temperature is 90 °C, discharge density is 1.2 t / m 3) 130.5 t / d of evaporation condensate water and 22 t / d of evaporation mother liquor are obtained;

[0084] Drying: Feed 17 t / d of ultrafiltration membrane concentrated water and 22 t / d of evaporation mother liquor into a scraper drying device, introduce steam, and conduct drying treatment at 50 °C to obtain solid slag with a moisture content of 15 wt% and 22 t / d of drying condensate water;

[0085] Biochemical treatment: Feed 300.0 t / d of silver powder washing water (main component concentration: COD = 1500 mg / L, nitrate nitrogen = 300 mg / L, NH 3 -N = 100 mg / L, PVP = 50 mg / L), 150.0 t / d of secondary RO product water, 130.5 t / d of evaporation condensate water, and 22 t / d of drying condensate water into a biochemical regulation pool to obtain mixed water. Supplement a carbon source (glucose) to the mixed water to control the carbon-nitrogen ratio to 30:1, and then feed it into a membrane bioreactor for two-stage AO biochemical reaction and membrane retention to obtain biochemical product water. Among them, the dissolved oxygen concentration in the first-stage anoxic tank (A1) is 0.5 mg / L, the water residence time is 4 h, the dissolved oxygen in the first-stage aerobic tank (O1) is 0.3 mg / L, the water residence time is 2 h, the dissolved oxygen concentration in the second-stage aerobic tank (O2) is 2 mg / L, the water residence time is 5 h, and the sludge concentration in the membrane tank is 5 g / L.

[0086] The main product water (data measured when the device operates stably for 7 days) in Example 1 and its components are shown in Table 1.

[0087] Table 1

[0088] Index COD, mg / L Nitrate nitrogen, mg / L Ammonia nitrogen, mg / L PVP, mg / L Silver powder mother liquor 60000 3500 8400 9000 Secondary DTRO product water 288 13 78 4 Interception rate of two-stage DTRO 99.5％ 99.6％ 99.1％ 99.9％ Biochemical product water 120 5 20 35

[0089] As can be seen from Table 1, the biochemical product water obtained in Example 1 has COD < 200 mg / L and total nitrogen < 40 mg / L, meeting the indirect emission standards in Table 1 of the "Pollutant Discharge Standards for the Inorganic Chemical Industry" (GB 31573-2015). Using reverse osmosis concentration treatment to concentrate silver powder wastewater, first recovering the product water can simplify the evaporation treatment equipment at the back end and reduce evaporation energy consumption; subsequently, using ultrafiltration membrane to separate PVP first can also ensure the stable implementation of evaporation at the back end. This treatment process can operate continuously and stably for 20 days, without phenomena such as pollutant precipitation and colloid fouling in the evaporator.

[0090] Comparative Example 1

[0091] Treat silver powder wastewater according to the method of Example 1, except that ultrafiltration membrane separation treatment is not carried out. Specifically,

[0092] Two-stage DTRO pre-concentration: Feed 300 t / d of silver powder mother liquor into a pH adjustment pool, add liquid caustic soda to adjust the pH to 6.5, and then use it as a reverse osmosis feed water.

[0093] Feed 320.5 t / d of reverse osmosis influent (silver powder mother liquor + secondary RO concentrate) into the first-stage DTRO for first-stage reverse osmosis treatment (operating temperature is 30 °C, pressure is 50 bar), obtaining 150 t / d of first-stage RO concentrate and 170.5 t / d of first-stage RO product water;

[0094] Send 170.5 t / d of first-stage RO product water to the second-stage DTRO for second-stage reverse osmosis treatment (operating temperature is 25 °C, pressure is 20 bar, membrane flux is 30 LMH), obtaining 20.5 t / d of second-stage RO concentrate and 150 t / d of second-stage RO product water;

[0095] Stripping deammoniation: Feed 150 t / d of first-stage RO concentrate into the alkali adjustment tank, add alkali solution to adjust the pH to 11 - 12, then send it to the negative pressure stripping and ammonia distillation device, and introduce steam for stripping deammoniation treatment (vacuum degree is 0.05 MPa, stripping temperature is 90 °C), obtaining free ammonia and 169.5 t / d of deammoniated liquid. Mix the free ammonia with 12.0 t / d of pure water to obtain 12.5 t / d of ammonia water (concentration is 20 wt%);

[0096] Evaporation and concentration: Feed 169.5 t / d of deammoniated liquid into the single-effect MVR evaporation device and introduce steam for evaporation and concentration (evaporation temperature is 90 °C, discharge density is 1.12 t / m 3 ), obtaining 100 t / d of evaporation condensate and 69.5 t / d of evaporation mother liquor;

[0097] Drying: Feed 69.5 t / d of evaporation mother liquor into the scraper drying device, introduce steam, and conduct drying treatment at 50 °C, obtaining solid slag with a moisture content of 15 wt% and 43.5 t / d of drying condensate;

[0098] Biochemical treatment: Feed 300.0 t / d of silver powder washing water, 150 t / d of second-stage RO product water, 100 t / d of evaporation condensate, and 43.5 t / d of drying condensate into the biochemical adjustment tank to obtain mixed water. Supplement a carbon source (glucose) to the mixed water to control the carbon-nitrogen ratio to 30:1, and then send it to the membrane bioreactor for two-stage AO biochemical reaction and membrane retention to obtain biochemical product water. When the device operates stably for 1 day, the COD in the biochemical product water = 120 mg / L, nitrate nitrogen = 5 mg / L, ammonia nitrogen = 20 mg / L, and PVP = 40 mg / L.

[0099] The biochemical effluent obtained in Comparative Example 1 had a COD < 200 mg / L and a total nitrogen < 40 mg / L, meeting the indirect discharge standard in Table 1 of GB 31573-2015. However, although reverse osmosis concentration treatment was used to concentrate the silver powder wastewater and recover the produced water first, before drying, since an ultrafiltration membrane was not used to separate PVP, the energy consumption of the drying system was too high, the steam consumption increased, the evaporation system coked, and the compressor surged; after 3 days of operation, the phenomenon of shutdown due to pollution of the heat exchange tubes of the evaporator occurred, affecting the production efficiency.

[0100] Example 2

[0101] Two-stage DTRO pre-concentration: 300 t / d of silver powder mother liquor (main component concentration: COD = 40000 mg / L, nitrate nitrogen = 3800 mg / L, NH 3 -N = 2000 mg / L, PVP = 5000 mg / L) was sent to the pH adjustment tank, and liquid caustic was added to adjust the pH to 7, and then it was used as a reverse osmosis feed water.

[0102] 320.5 t / d of reverse osmosis feed water (silver powder mother liquor + secondary RO concentrated water) was sent to the first-stage DTRO for first-stage reverse osmosis treatment (operating temperature was 30 °C, pressure was 45 bar, and membrane flux was 15 LMH), obtaining 150 t / d of first-stage RO concentrated water and 170.5 t / d of first-stage RO produced water;

[0103] 170.5 t / d of first-stage RO produced water was sent to the second-stage DTRO for second-stage reverse osmosis treatment (operating temperature was 30 °C, pressure was 25 bar, and membrane flux was 32 LMH), obtaining 20.5 t / d of second-stage RO concentrated water and 150 t / d of second-stage RO produced water;

[0104] Steam stripping for ammonia removal: 150 t / d of first-stage RO concentrated water was sent to the alkali adjustment tank, and liquid caustic was added to adjust the pH to 11 - 12, and then it was sent to a negative-pressure steam stripping ammonia removal device, and steam was introduced for steam stripping ammonia removal treatment (vacuum degree was 0.05 MPa, steam stripping temperature was 90 °C), obtaining free ammonia and 170 t / d of post-ammonia-removal liquid. The free ammonia was mixed with 2.85 t / d of pure water to obtain 3 t / d of ammonia water (concentration was 20 wt%);

[0105] Ultrafiltration separation for PVP removal: 170 t / d of post-ammonia-removal liquid (COD = 79828 mg / L, nitrate nitrogen = 7579 mg / L, NH 3-N = 30 mg / L, PVP = 10000 mg / L) is fed into the acid - adjusting tank. After adjusting the pH to 5.5, it is fed into the ultra - filtration membrane separation device for ultra - filtration treatment (operating conditions: temperature is 30 °C, pressure is 20 Bar, membrane flux is 20 LMH), obtaining 17 t / d of ultra - filtration membrane concentrate (COD = 237846 mg / L, PVP = 66639 mg / L) and 153 t / d of ultra - filtration membrane permeate (the interception rate of COD in the liquid after deamination by ultra - filtration separation treatment is 22.01%, the interception rate of PVP is 99.0%, and there is almost no interception of nitrate nitrogen and ammonia nitrogen);

[0106] Evaporation and concentration: The 153 t / d of ultra - filtration membrane permeate is fed into the buffer tank for homogenization, and then steam is introduced into the single - effect MVR evaporation device for evaporation and concentration (evaporation temperature is 90 °C, the density of the discharged material is 1.2 t / m 3 ) to obtain 130 t / d of evaporation condensate and 23 t / d of evaporation mother liquor;

[0107] Drying: The 17 t / d of ultra - filtration membrane concentrate and 23 t / d of evaporation mother liquor are fed into the scraper drying device, and steam is introduced for drying treatment at 50 °C to obtain solid residue with a moisture content of 15 wt% and 23 t / d of drying condensate;

[0108] Biochemical treatment: 300 t / d of silver powder washing water (main component concentrations: COD = 1500 mg / L, nitrate nitrogen = 300 mg / L, NH 3 -N = 100 mg / L, PVP = 50 mg / L), 150 t / d of secondary RO permeate, 130 t / d of evaporation condensate and 23 t / d of drying condensate are fed into the biochemical adjustment tank to obtain mixed water. Carbon source (glucose) is supplemented into the mixed water to control the carbon - nitrogen ratio to 30:1, and then it is fed into the membrane bioreactor for two - stage AO biochemical reaction and membrane interception to obtain biochemical permeate. Among them, the dissolved oxygen concentration in the first - stage anoxic tank (A1) is 0.2 mg / L, the hydraulic retention time is 2 h, the dissolved oxygen concentration in the first - stage aerobic tank (O1) is 2 mg / L, the hydraulic retention time is 6 h, the dissolved oxygen concentration in the second - stage anoxic tank (A2) is 0.3 mg / L, the hydraulic retention time is 2 h, the dissolved oxygen concentration in the second - stage aerobic tank (O2) is 3 mg / L, and the hydraulic retention time is 5 h. The sludge concentration in the membrane tank is 3 g / L.

[0109] The main produced water (data measured when the device operates stably for 7 days) and its components in Example 2 are shown in Table 2.

[0110] Table 2

[0111] Index COD, mg / L Nitrate nitrogen, mg / L Ammonia nitrogen, mg / L PVP, mg / L Silver powder mother liquor 40000 3800 2000 5000 Secondary DTRO product water 173 21 33 3 Interception rate of two-stage DTRO 99.6％ 99.4％ 98.3％ 99.9％ Biochemical product water 98 5 15 20

[0112] As can be seen from Table 2, the biochemical produced water obtained in Example 2 has a COD < 100 mg / L and a total nitrogen < 40 mg / L, meeting the indirect discharge standard in Table 1 of GB31573-2015. Reverse osmosis concentration treatment is used to concentrate the silver powder wastewater. First, the produced water is recovered, which can simplify the evaporation treatment equipment at the back end and reduce the evaporation energy consumption. Subsequently, ultrafiltration membrane is used to separate PVP first, which can also ensure the stable implementation of evaporation at the back end. This treatment process can operate continuously and stably for 21 days, without phenomena such as pollutant precipitation and colloid fouling in the evaporator.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and the description of the present invention. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present invention is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A process for treating silver powder wastewater, characterized in that: The silver powder wastewater includes silver powder mother liquor and silver powder washing water, and the silver powder mother liquor and silver powder washing water contain COD, ammonia nitrogen, nitrate and PVP respectively; The processing technology comprises: Pre-concentration: After adjusting the pH of the silver powder mother liquor to 6.5-7.5, it is used as an influent for reverse osmosis treatment to obtain reverse osmosis concentrated water and reverse osmosis produced water; Deammoniation: After adjusting the pH of the reverse osmosis concentrated water to 10-12, ammonia stripping treatment is performed to obtain free ammonia and deammoniation liquid; Membrane separation: after adjusting the pH of the deammoniation liquid to 4-6, ultrafiltration membrane separation is performed to obtain membrane produced water and PVP-rich membrane concentrated water; Evaporation reduction: evaporating the membrane produced water to obtain evaporated condensed water and evaporated mother liquor; Drying: drying the membrane concentrated water and evaporation mother liquor to obtain solid residue and dried condensed water; Biochemical treatment: the reverse osmosis produced water, evaporation condensed water and drying condensed water are mixed with the silver powder washing water, a carbon source is added, and a biochemical reaction is carried out to obtain biochemical produced water.

2. The treatment process according to claim 1, characterized in that: The COD concentration in the silver powder mother liquor is 30,000 to 70,000 mg / L, the nitrate concentration is 3,000 to 5,000 mg / L in terms of nitrate nitrogen, the ammonia nitrogen concentration is 1,000 to 10,000 mg / L, and the PVP concentration is 5,000 to 10,000 mg / L; Preferably, the COD concentration in the silver powder washing water is 500-5000 mg / L, the nitrate concentration in terms of nitrate nitrogen is 300-500 mg / L, the ammonia nitrogen concentration is 100-1000 mg / L, and the PVP concentration is 50-100 mg / L.

3. The treatment process according to claim 1 or 2, characterized in that: In the ultrafiltration membrane separation, the molecular weight cutoff of the ultrafiltration membrane used is 2200 to 3000Da; Preferably, the ultrafiltration membrane is a polyamide ultrafiltration membrane; Preferably, the operating conditions of the ultrafiltration membrane separation include: temperature of 15-40°C, pressure of 5-25 bar, membrane flux of 15-30 LMH, and recovery rate of 85%-95%; Preferably, the ultrafiltration membrane separation treatment has a retention rate of ≥99% for PVP in the deammoniation liquid.

4. The treatment process according to any one of claims 1 to 3, characterized in that: The recovery rate of the reverse osmosis treatment is 40% to 60%, and the DOD retention rate in the silver powder mother liquor is greater than 95%, the nitrate retention rate is greater than 94%, and the ammonia nitrogen retention rate is greater than 92%; Preferably, the reverse osmosis treatment includes primary reverse osmosis treatment and secondary reverse osmosis treatment, wherein the silver powder mother liquor after pH adjustment is subjected to primary reverse osmosis treatment to obtain primary reverse osmosis produced water and the reverse osmosis concentrated water; The primary reverse osmosis produced water is subjected to secondary reverse osmosis treatment to obtain the reverse osmosis produced water and secondary reverse osmosis concentrated water, and the secondary reverse osmosis concentrated water is circulated as another influent water to be subjected to the primary reverse osmosis treatment; Preferably, the operating conditions of the primary reverse osmosis treatment include: temperature of 15-40°C, pressure of 40-60 bar, and membrane flux of 10-15 LMH; the operating conditions of the secondary reverse osmosis treatment include: temperature of 15-40°C, pressure of 15-25 bar, and membrane flux of 30-35 LMH.

5. The treatment process according to any one of claims 1 to 4, characterized in that: The operating conditions of the stripping and ammonia evaporation treatment include: vacuum degree of 0.05-0.06MPa, stripping temperature of 80-90°C; Preferably, the treatment process further comprises: mixing the free ammonia with water to obtain ammonia water with a mass concentration of 15% to 28%.

6. The treatment process according to any one of claims 1 to 5, characterized in that: The mass ratio of the silver powder washing water to the silver powder mother liquor is 1:(0.8-1.2); Preferably, the total mass of the evaporated condensed water and the dried condensed water is 30% to 55% of the mass of the silver powder washing water; Preferably, the mass of the reverse osmosis produced water is 40% to 60% of the mass of the silver powder washing water.

7. The treatment process according to any one of claims 1 to 6, characterized in that: The evaporation treatment is carried out in a single-effect MVR evaporation device, the evaporation temperature is 85-95°C, and the discharge density is 1.2-1.3 t / m 3 .

8. The treatment process according to any one of claims 1 to 7, characterized in that: The drying treatment is carried out in a scraper drying device, the scraper drying temperature is 40-80° C., and the moisture content of the obtained solid slag is controlled to be 10%-20%.

9. The treatment process according to any one of claims 1 to 8, characterized in that: In the biochemical treatment, the amount of carbon source used is such that the carbon-nitrogen ratio in the resulting reaction system is (28-33):1; Preferably, the biochemical treatment adopts a two-stage A / O-MBR process.

10. The treatment system used in the treatment process of silver powder wastewater according to any one of claims 1 to 9 is characterized in that: include: Pre-concentration unit, deammoniation unit, membrane separation unit, evaporation reduction unit, drying unit and biochemical unit; among which, The pre-concentration unit includes a pH adjustment tank and a reverse osmosis concentration device, which are used to sequentially adjust the pH of the silver powder mother liquor and perform reverse osmosis treatment to obtain reverse osmosis concentrated water and reverse osmosis produced water; The deammoniation unit comprises a alkali adjustment tank and a steam stripping and ammonia evaporation device, which are used to sequentially adjust the pH of the reverse osmosis concentrated water and perform steam stripping and ammonia evaporation treatment to obtain free ammonia and deammoniation liquid; The membrane separation unit includes an acid adjustment tank and an ultrafiltration separation device, which are used to adjust the pH of the deammoniation liquid and perform ultrafiltration separation in sequence to obtain membrane produced water and PVP-rich membrane concentrated water; The evaporation reduction unit includes a buffer tank and an evaporation device, wherein the buffer tank is used to collect and homogenize the membrane produced water, and the evaporation device is used to evaporate the membrane produced water collected by the buffer tank to obtain evaporated condensed water and evaporated mother liquor; The drying unit is used to dry the membrane concentrated water and the evaporation mother liquor to obtain solid residue and dried condensed water; The biochemical unit includes a biochemical regulating pool and a biochemical reaction device. The biochemical regulating pool is used to collect reverse osmosis water, evaporation condensed water, drying condensed water and reverse osmosis water and supplement carbon source to obtain regulated mixed water; The biochemical reaction device is used to cause the regulated mixed water to undergo a biochemical reaction to obtain biochemical produced water and biochemical sludge.

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