Comprehensive treatment method of photovoltaic silver powder wastewater

Abstract

The invention discloses a comprehensive treatment method of photovoltaic silver powder wastewater, which is characterized in that the photovoltaic silver powder wastewater is treated through ammonia nitrogen stripping, ultrafiltration silver recovery, polyacid PVP (Polyvinyl Pyrrolidone) precipitation, evaporation and coagulation biochemistry, and the ultrafiltration silver recovery technology and the polyacid PVP precipitation technology are combined with the traditional evaporation and biochemical processes. The industrial problems of unstable operation of an evaporation system and high operation cost of a wastewater system in a traditional photovoltaic silver powder wastewater system can be effectively solved, and the method is an effective way for realizing resource utilization of silver in the silver powder wastewater.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial wastewater treatment and resource utilization, and particularly relates to a comprehensive treatment method for photovoltaic silver powder wastewater. BACKGROUND

[0002] One of the most important raw materials in the production of solar cells is conductive silver paste, the performance of which directly affects the photoelectric conversion efficiency of solar cells, and ultra-fine silver powder is the core material of conductive silver paste, so the market demand for ultra-fine silver powder is increasing year by year.

[0003] At present, the preparation methods of ultra-fine silver powder include liquid phase reduction method, mechanical ball milling method, thermal decomposition method, electrochemical method and emulsion method, among which the liquid phase reduction method is widely used in the preparation of ultra-fine silver powder in industry due to its simple production equipment, convenient operation and low running cost. The wastewater produced in the process of preparing silver powder by liquid phase reduction method contains high concentrations of COD, nitrate, ammonia nitrogen and silver, and is a kind of difficult-to-treat industrial wastewater. This kind of wastewater has the characteristics of high COD, high salt and difficult biodegradation. At present, the traditional treatment process is mainly high-temperature evaporation method. Although the high-temperature evaporation method can remove most of the organic matter and salt substances, this method has certain limitations, and there are problems of low running efficiency of evaporator, poor evaporation effect and non-resource utilization of valuable substances in wastewater. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application aims to provide a comprehensive treatment method for photovoltaic silver powder wastewater.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0006] A comprehensive treatment method for photovoltaic silver powder wastewater, comprising the following steps:

[0007] Step 1, ammonia nitrogen stripping: adjusting the pH value of the photovoltaic silver powder wastewater to 10-12 by using flaked alkali, then blowing air into the photovoltaic silver powder wastewater to strip out NH3, obtaining a post-ammonia stripping liquid, and absorbing the stripped NH3 with sulfuric acid to obtain an ammonium sulfate concentrated liquid;

[0008] Step 2, ultrafiltration silver recovery: adding sulfuric acid to the post-ammonia stripping liquid obtained in step 1 to adjust the pH value to 6-8, then concentrating and separating the post-ammonia stripping liquid by using an ultrafiltration device to obtain a silver-containing concentrated water and a post-silver recovery liquid, then centrifuging the silver-containing concentrated water to obtain a post-centrifugation silver powder and a post-centrifugation liquid, returning the post-centrifugation liquid to the ultrafiltration device for repeated silver recovery, and washing and drying the post-centrifugation silver powder;

[0009] Step 3, PVP removal by polybasic acid: polybasic organic acid is added to the silver collection liquid obtained in step 2 to precipitate PVP, and after solid-liquid separation, PVP solid residue and pretreated liquid are obtained, the PVP solid residue enters the sludge treatment system, and the pretreated liquid is a mixture of VC, dehydrogenated VC and sodium nitrate;

[0010] Step 4, evaporation: the pretreated liquid obtained in step 3 is evaporated by using a MVR simulation evaporator, the evaporation mother liquor is solidified by using a drying device and then enters the sludge treatment system, and the condensed water is collected separately;

[0011] Step 5, coagulation and sedimentation: the condensed water collected in step 4 is sent into a coagulation tank, and PAC solution and PAM solution are added for coagulation and sedimentation, and after solid-liquid separation, flocculated precipitate and coagulation liquid are obtained, and the flocculated precipitate enters the sludge treatment system;

[0012] Step 6, hydrolysis acidification-oxygen MBR biochemical system: the coagulation liquid obtained in step 5 is first sent into a hydrolysis acidification tank for chain breaking degradation of macromolecular organic matter to improve biodegradability, and then the effluent of the hydrolysis acidification tank is sent into an oxygen MBR system for further removal of COD and TN in water, and the effluent of the oxygen MBR system is discharged up to standard; the sludge discharged from the entire biochemical system enters the sludge treatment system.

[0013] Further, the PVP solid residue in step 3, the solidified product of the evaporation mother liquor in step 4, the flocculated precipitate in step 5 and the sludge in step 6 are respectively pressure-filtered in the sludge treatment system and then outsourced for treatment.

[0014] Further, in step 1, the temperature of the photovoltaic silver powder wastewater is maintained at 30-50℃, the gas-liquid volume ratio in stripping NH3 is 1500:1-4000:1, and the stripping time is 0.5-2.0h.

[0015] Further, in step 2, the concentration multiple of the deamination liquid by the ultrafiltration device is 15-25 times.

[0016] Further, in step 3, the polybasic acid is tannic acid or tannic acid, and the amount is 2-8g / L of the silver collection liquid.

[0017] Further, in step 4, the amount of evaporation mother liquor is 15-25% of the total liquid mass of the pretreated liquid entering the MVR simulation evaporator; the drying device is one of a drum dryer, a scraper dryer and an evaporation crystallizer, and the boiling point is 90-100℃.

[0018] Further, in step 5, the preparation mass concentration of the PAC solution is 10%-30%, the preparation mass concentration of the PAM solution is 1 ‰-3 ‰, the PAC agent dosage is 1-3g / L of the condensed water, and the PAM agent dosage is 2-10mg / L of the condensed water.

[0019] Further, in step 6, in the hydrolysis acidification tank, the pH value is maintained at 6-8, the hydraulic retention time is controlled to be 2-4h, the sludge concentration is maintained at 10-20g / L, and the water level rising flow rate in the hydrolysis acidification tank is 0.8-1.8m / s; in the aerobic MBR system, the pH value is maintained at 6-8, the dissolved oxygen concentration is controlled to be 2-4mg / L, the membrane surface flow rate is controlled to be 3-5m / s, the sludge concentration is controlled to be 3000-20000mg / L, and the clean water backwashing time is 10min-360min.

[0020] Further, in step 6, in the hydrolysis acidification tank, the pH value is maintained at 6-8, the hydraulic retention time is controlled to be 2-4h, the sludge concentration is maintained at 10-20g / L, and the water level rising flow rate in the hydrolysis acidification tank is 0.8-1.8m / s; in the aerobic MBR system, the pH value is maintained at 6-8, the dissolved oxygen concentration is controlled to be 2-4mg / L, the membrane surface flow rate is controlled to be 3-5m / s, the sludge concentration is controlled to be 3000-20000mg / L, and the clean water backwashing time is 10min-360min.

[0021] Further, the solid content rate of the material after pressure filtration reaches 55%-75%.

[0022] The beneficial effects of the present application are as follows:

[0023] 1) The present application provides a comprehensive treatment method for photovoltaic silver powder wastewater, the treated wastewater has stable water quality, the water quality reaches the first level standard of the Integrated Wastewater Discharge Standard, the indirect discharge standard of the Inorganic Chemical Industry Pollutant Discharge Standard, and the safe and stable operation of the wastewater system and the efficient recovery of silver are realized.

[0024] 2) The present application recovers silver in wastewater by using an ultrafiltration device, which not only can efficiently recover silver powder in wastewater with low silver content, but also solves the problems of low silver recovery rate and high water quality requirement existing in the traditional chemical silver deposition.

[0025] 3) The present application uses multiple organic acids to effectively settle PVP high molecular polymers, avoids the adhesion of the evaporator due to PVP high-temperature concentration, affects the evaporation efficiency and operation stability, and further reduces the operation energy consumption of the evaporation equipment.

[0026] 4) The present application uses an ammonia nitrogen stripping system to remove a small amount of ammonia nitrogen in wastewater in advance, eliminates the escape of NH3 during evaporation, affects the normal operation of the evaporator, and the ammonium sulfate concentrated solution after absorbing NH3 by sulfuric acid can be sold to create economic benefits.

[0027] 5) The present application adopts the combined mode of "coagulation-hydrolysis acidification-oxygen MBR" to carry out the deep treatment of COD and TN of wastewater, and the increased coagulation tank and hydrolysis acidification tank can not only improve the biodegradability of wastewater, but also can buffer the water quality fluctuation, avoid the influence of unstable influent water quality on the activity of microorganisms in the oxygen MBR system, and avoid the increase of white foam, the decrease of sludge settling performance, and the turbidity of supernatant.

[0028] 6) The present application combines the ultrafiltration recovery silver technology, the multi-acid PVP precipitation technology and the traditional evaporation drying technology, the coagulation sedimentation and the biochemical denitrification and COD removal technology, which can not only achieve stable wastewater treatment effect, but also has simple equipment operation and low running cost, so that the process is easy to realize industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The method flowchart of the present application examples 1-3;

[0030] Figure 2 The scanning electron microscope image and XRD diffraction pattern of the ultrafine silver powder obtained in the present application example 3. DETAILED DESCRIPTION

[0031] The present application will be further described below with reference to the accompanying drawings, and it should be noted that the present embodiment is based on the technical solution, and detailed implementation and specific operation process are given, but the protection scope of the present application is not limited to the present embodiment.

[0032] Example 1

[0033] The wastewater generated in the photovoltaic silver powder preparation process of a company mainly includes: COD 38.97g / L, NO3 - 16.85g / L, NH3-N 0.65g / L, Ag 14.52mg / L, conductivity 73.10ms / cm, pH=0.97.

[0034] The present embodiment provides a comprehensive treatment method for treating the above-mentioned wastewater, as shown in the following formula, which includes the following steps: Figure 1

[0035] Step 1, ammonia nitrogen stripping: the pH value of the photovoltaic silver powder wastewater is adjusted to 11 by using flake alkali, and the dosage of flake alkali is 13.7g / L photovoltaic silver powder wastewater. Then air is blown into the photovoltaic silver powder wastewater to blow out NH3 in the wastewater, the gas-liquid ratio is 2000:1, the stripping time is 0.8h, the stripping temperature is maintained at 30℃, the ammonia-removed liquid is obtained, the stripped NH3 is absorbed by sulfuric acid, and the final ammonium sulfate concentrate can be sold.

[0036] ​Step 2, silver recovery by ultrafiltration: sulfuric acid is added to the deaminated solution obtained in step 1, and the pH value of the deaminated solution is adjusted to 6.5, then the deaminated solution is concentrated 20 times by using an ultrafiltration device to obtain a silver-containing concentrated water and a silver recovery solution, the Ag content in the silver recovery solution is less than 0.1 mg / L, and the silver-containing concentrated water is centrifuged to remove water, and the centrifuged solution is returned to the ultrafiltration device for repeated silver recovery, and the silver powder is dehydrated, washed and dried to obtain superfine silver powder which can be sold externally.

[0037] Step 3, PVP removal by polybasic acid: tannic acid is added to the silver recovery solution obtained in step 2 to precipitate PVP, the amount of organic polybasic acid is 3 g / L, and after solid-liquid separation, PVP solid residue and pretreated solution are obtained, the PVP solid residue enters the sludge treatment system, and the pretreated solution is a mixture of VC, dehydrogenated VC and sodium nitrate.

[0038] Step 4, evaporation: the pretreated solution obtained in step 3 is evaporated by using an MVR simulation evaporator, the evaporation mother liquor is solidified by using a roller dryer and then enters the sludge treatment system, the amount of evaporation mother liquor is 15% (mass ratio) of the total liquid amount of the pretreated solution entering the MVR simulation evaporator, and the condensed water is collected separately.

[0039] Step 5, coagulation and sedimentation: the condensed water collected in step 4 is sent to a coagulation tank, and PAC solution and PAM solution are added for coagulation and sedimentation, the preparation concentration of PAC solution is 10%, the preparation concentration of PAM solution is 1 ‰, the dosages of PAC agent (pure PAC) and PAM agent (pure PAM) are 1 g / L and 5 mg / L respectively, and after solid-liquid separation, flocculated precipitate and coagulated solution are obtained, and the flocculated precipitate enters the sludge treatment system.

[0040] Step 6, hydrolysis acidification-oxygen MBR biochemical system: the coagulated solution is first introduced into a hydrolysis acidification tank to break the chain of macromolecular organic matter and improve the biodegradability, the pH value of the hydrolysis acidification tank is 7.5, the hydraulic retention time is 2 h, the sludge concentration is 10 g / L, and the upward flow rate in the tank is 1.0 m / s. The hydrolysis tank effluent is introduced into an oxygen MBR system to further remove COD and TN in the water, the pH value of the oxygen MBR system is 7.5, the dissolved oxygen concentration is 2 mg / L, the membrane surface flow rate is between 3 m / s, the sludge concentration is 8000 mg / L, and the clear water backwashing time is 120 min. The effluent of the oxygen MBR system meets the discharge standard. The hydrolysis acidification tank uses sodium carbonate as an alkalinity agent, the C / N ratio is 10:1, and the sludge discharge period is 5 days; the oxygen MBR system uses sodium carbonate as an alkalinity agent, the C / N ratio is 4:1, and the sludge discharge period is 3 days. The sludge periodically discharged from the entire biochemical system enters the sludge treatment system.

[0041] In this embodiment, the sludge from steps 3, 4, 5 and 6 is periodically transported to a sludge filter press room for filter pressing and then outsourced for treatment. The solid content of the filtered sludge is 60%.

[0042] The influent water quality of silver powder wastewater and the effluent water quality of aerobic MBR system are shown in Table 1, the influent and effluent water quality indexes of step 2 are shown in Table 2, and the product quality of superfine silver powder is shown in Table 3.

[0043] Example 2

[0044] The composition of the wastewater generated in the photovoltaic silver powder preparation process of a certain company is the same as that of Example 1.

[0045] This embodiment provides a comprehensive treatment method for photovoltaic silver powder wastewater, as shown in Figure 1 The method comprises the following steps:

[0046] Step 1, ammonia nitrogen stripping: the pH value of the photovoltaic silver powder wastewater is adjusted to 11 by using flake caustic soda, the dosage of flake caustic soda is 13.7 g / L, air is blown into the solution to strip NH3 in the wastewater, the gas-liquid ratio is 3000:1, the stripping time is 0.8 h, and the stripping temperature is maintained at 30°C. The deamination liquid is obtained, the stripped NH3 is absorbed by sulfuric acid, and the obtained concentrated ammonium sulfate liquid can be sold externally.

[0047] Step 2, silver recovery by ultrafiltration: sulfuric acid is added to the deamination liquid obtained in step 1 to adjust the pH value of the solution to 6.5, and then the deamination liquid is concentrated 20 times by using an ultrafiltration device to obtain a silver-containing concentrated water and a silver recovery liquid, the Ag content in the silver recovery liquid is less than 0.1 mg / L, and the silver-containing concentrated water is centrifuged to obtain a centrifuged liquid which is returned to the ultrafiltration device for repeated silver recovery. The silver powder is dehydrated, washed and dried to obtain superfine silver powder which can be sold externally.

[0048] Step 3, PVP removal by multi-element acid: tannic acid is added to the silver recovery liquid obtained in step 2 to precipitate PVP, the dosage of tannic acid is 3.5 g / L, and after solid-liquid separation, PVP solid residue and pretreated liquid are obtained. The PVP solid residue enters the sludge treatment system, and the pretreated liquid is a mixture of VC, dehydrogenated VC and sodium nitrate.

[0049] Step 4, evaporation: the pretreated liquid obtained in step 3 is evaporated by using an MVR simulation evaporator, the evaporation mother liquor is solidified by using a drum dryer and then enters the sludge treatment system, the amount of evaporation mother liquor is 15% (mass ratio) of the total liquid amount of the pretreated liquid entering the MVR simulation evaporator, and the condensate water is collected separately.

[0050] Step 5, coagulation sedimentation: the condensed water collected in step 4 is sent to a coagulation tank, and PAC solution and PAM solution are added for coagulation sedimentation, the preparation concentration of PAC solution is 10%, the preparation concentration of PAM solution is 1 ‰, the dosages of PAC agent (pure PAC) and PAM agent (pure PAM) are 2 g / L and 8 mg / L respectively, and after solid-liquid separation, flocculated precipitate and coagulated liquid are obtained, and the flocculated precipitate enters a sludge treatment system.

[0051] Step 6, hydrolysis acidification-oxygen MBR biochemical system: the coagulated liquid first enters a hydrolysis acidification tank to break the chain of macromolecular organic matter and improve the biodegradability, the pH value of the hydrolysis acidification tank is 7.5, the hydraulic retention time is 4 h, the sludge concentration is 15 g / L, and the upward flow rate in the tank is 1.0 m / s. The hydrolysis acidification tank effluent enters an oxygen MBR system to further remove COD and TN in the water, the pH value of the oxygen MBR system is 7.5, the dissolved oxygen concentration is 3 mg / L, the membrane surface flow rate is between 3 m / s, the sludge concentration is 10000 mg / L, and the clear water backwashing time is 120 min. The oxygen MBR system effluent meets the discharge standard. The hydrolysis acidification tank uses sodium carbonate as an alkalinity agent, the C / N ratio is 10:1, and the sludge discharge period is 5 d; the oxygen MBR system uses sodium carbonate as an alkalinity agent, the C / N ratio is 5:1, and the sludge discharge period is 3 d. The sludge regularly discharged from the entire biochemical system enters a sludge treatment system.

[0052] In this embodiment, the sludge from steps 3, 4, 5 and 6 is regularly transported to a sludge filter pressing room for filter pressing and then outsourced treatment. The solid content of the sludge after filter pressing is 60%.

[0053] The silver powder wastewater influent water quality and the oxygen MBR system effluent water quality are shown in Table 1, the ultrafiltration influent and product water quality indexes in step 2 are shown in Table 2, and the superfine silver powder product quality is shown in Table 3.

[0054] Example 3

[0055] The wastewater generated in the photovoltaic silver powder preparation process of a company has the same composition as that of example 1.

[0056] This embodiment provides a comprehensive treatment method for photovoltaic silver powder wastewater, as shown in Figure 1 The method comprises the following steps:

[0057] Step 1, ammonia nitrogen stripping: the pH value of the photovoltaic silver powder wastewater is adjusted to 11 by using flake caustic soda, the dosage of flake caustic soda is 13.7 g / L, air is blown into the photovoltaic silver powder wastewater to strip NH3 in the wastewater, the gas-liquid ratio is 3500:1, the stripping time is 0.8 h, the stripping temperature is maintained at 30℃, and the ammonia-stripped liquid is obtained. The stripped NH3 is absorbed by sulfuric acid, and the obtained concentrated ammonium sulfate solution can be sold.

[0058] Step 2, silver recovery by ultrafiltration: sulfuric acid is added to the deaminated solution obtained in step 1 to adjust the pH value of the solution to 6.5, and then the deaminated solution is concentrated 20 times by using an ultrafiltration device to obtain concentrated silver-containing water and a silver-recovered solution, the Ag content in the concentrated water is less than 0.1 mg / L, and then the concentrated silver-containing water is centrifuged to remove water, and the centrifuged solution is returned to the ultrafiltration device for repeated silver recovery, and the silver powder is dehydrated, washed and dried to obtain superfine silver powder which can be sold externally.

[0059] Step 3, PVP removal by polybasic acid: tannic acid is added to the silver-recovered solution obtained in step 2 to precipitate PVP, the amount of tannic acid is 4 g / L, and after solid-liquid separation, PVP solid residue and pretreated solution are obtained, the PVP solid residue enters the sludge treatment system, and the pretreated solution is a mixture of VC, dehydrogenated VC and sodium nitrate.

[0060] Step 4, evaporation: the pretreated solution obtained in step 3 is evaporated by using an MVR simulation evaporator, the evaporation mother liquor is solidified by using a roller dryer and then enters the sludge treatment system, the amount of evaporation mother liquor is 15% (mass ratio) of the total liquid amount of the pretreated solution entering the MVR simulation evaporator, and the condensed water is collected separately.

[0061] Step 5, coagulation and sedimentation: the condensed water collected in step 4 is sent to a coagulation tank, and PAC solution and PAM solution are added for coagulation and sedimentation, the preparation concentration of PAC solution is 10%, the preparation concentration of PAM solution is 1 ‰, the dosages of PAC agent (pure PAC) and PAM agent (pure PAM) are 3 g / L and 10 mg / L respectively, and after solid-liquid separation, flocculated precipitate and coagulated solution are obtained, and the flocculated precipitate enters the sludge treatment system.

[0062] Step 6, hydrolysis acidification-oxygen MBR biochemical system: the coagulated solution is first introduced into a hydrolysis acidification tank for chain breaking degradation of macromolecular organic matter to improve biodegradability, the pH value of the hydrolysis acidification tank is 7.5, the hydraulic retention time is 4 h, the sludge concentration is 20 g / L, and the upward flow rate in the tank is 1.0 m / s. The hydrolysis acidification tank effluent enters an oxygen MBR system for further removal of COD and TN in the water, the pH value of the hydrolysis acidification tank is 7.5, the dissolved oxygen concentration is 4 mg / L, the membrane surface flow rate is between 3 m / s, the sludge concentration is 15000 mg / L, and the clear water backwashing time is 120 min. The oxygen MBR system effluent meets the discharge standard. The hydrolysis acidification tank uses sodium carbonate as an alkalinity agent, the C / N ratio is 10:1, and the sludge discharge period is 5 days; the oxygen MBR system uses sodium carbonate as an alkalinity agent, the C / N ratio is 6:1, and the sludge discharge period is 3 days. The sludge periodically discharged from the entire biochemical system enters the sludge treatment system.

[0063] In this embodiment, the sludge from steps 3, 4, 5 and 6 is periodically transported to a sludge filter press room for pressure filtration and then outsourced for treatment, and the sludge solid content is 60%.

[0064] The influent water quality of silver powder wastewater and the effluent water quality of aerobic MBR system are shown in Table 1, the ultrafiltration influent and effluent water quality indexes in step 2 are shown in Table 2, and the quality of superfine silver powder product is shown in Table 3. The scanning electron microscope image and XRD diffraction pattern are shown in Figs. (a) and (b) of Fig. 1, respectively. Figure 2

[0065] Table 1 Influent water quality and effluent water quality of aerobic MBR system (mg / L)

[0066]

[0067] Note: GB8978-1996 is the comprehensive wastewater discharge standard, and GB31573-2015 is the inorganic chemical industry pollutant indirect discharge standard.

[0068] Table 2 Ultrafiltration influent and effluent water quality indexes

[0069] Influent Ag concentration (mg / L) Effluent Ag concentration (mg / L) Ag recovery (%) Example 1 14.52 0.07 97.5 Example 2 14.52 0.09 99.4 Example 3 14.52 0.07 96.5

[0070] Table 3 Indexes of superfine silver powder product (%)

[0071]

[0072] Note: GB1774-2009 is the national standard for superfine silver powder, and D50 unit is μm.

[0073] It can be seen that the effluent water quality of Examples 1, 2 and 3 all meet the first level standard of the comprehensive wastewater discharge standard and the indirect discharge standard of the inorganic chemical industry pollutant discharge standard, indicating that the method of Examples 1-3 can effectively treat the photovoltaic silver powder wastewater to reach the discharge standard. The quality of the superfine silver powder product recovered in Examples 1, 2 and 3 not only meets the requirements of the national standard for superfine silver powder, but also has a silver recovery rate of more than 95% in the wastewater, indicating that the resource utilization efficiency of Examples 1-3 is high and has certain economic benefits.

[0074] For those skilled in the art, various corresponding changes and modifications can be given according to the above technical solutions and concepts, and all these changes and modifications should be included in the protection scope of the claims of the present application.​

Claims

1. A comprehensive treatment method for photovoltaic silver powder wastewater, characterized in that: The following steps are involved: Step 1, ammonia nitrogen stripping: Use caustic soda to adjust the pH value of photovoltaic silver powder wastewater to between 10-12, then blow air into the photovoltaic silver powder wastewater to blow out NH3 to obtain a deammoniated liquid, and absorb the stripped NH3 with sulfuric acid to obtain ammonium sulfate concentrate; Step 2, ultrafiltration to recover silver: sulfuric acid is added to the deaminated liquid obtained in step 1 to adjust the pH value to between 6 and 8, and then the deaminated liquid is concentrated and separated using an ultrafiltration device to obtain a silver-containing concentrated water and a silver-collected liquid. The silver-containing concentrated water is then centrifuged to obtain dehydrated silver powder and a centrifuged liquid. The centrifuged liquid is returned to the ultrafiltration device for repeated silver collection, and the dehydrated silver powder is washed and dried. Step 3, polyacid removal of PVP: polyacid is added to the post-collection liquid obtained in step 2 to precipitate PVP, and after solid-liquid separation, PVP solid residue and pre-treated liquid are obtained. The PVP solid residue enters the sludge treatment system, and the pre-treated liquid is a mixture of VC, dehydrogenated VC and sodium nitrate; Step 4, evaporation: The pretreated liquid obtained in step 3 is evaporated using an MVR simulated evaporator. The evaporated mother liquor is solidified using a drying device and then enters the sludge treatment system. The condensed water is collected separately. Step 5, coagulation and sedimentation: the condensed water collected in step 4 is sent to the coagulation tank, and PAC solution and PAM solution are added for coagulation and sedimentation. After solid-liquid separation, flocculated sediment and coagulated liquid are obtained. The flocculated sediment enters the sludge treatment system; Step 6, hydrolysis acidification-aerobic MBR biochemical system: the coagulated liquid obtained in step 5 is first sent to the hydrolysis acidification tank for chain scission degradation of macromolecular organic matter to improve biodegradability; the effluent from the hydrolysis acidification tank is then sent to the aerobic MBR system to further remove COD and TN in the water, and the effluent from the aerobic MBR system meets the discharge standards; The sludge discharged from the entire biochemical system enters the sludge treatment system.

2. The method according to claim 1, characterized in that The PVP solid residue in step 3, the solidified product of the evaporated mother liquor in step 4, the flocculated precipitate in step 5 and the sludge in step 6 are filtered in the sludge treatment system and then outsourced for treatment.

3. The method according to claim 1, characterized in that In step 1, the inlet temperature of the photovoltaic silver powder wastewater is maintained at 30°C-50°C, the NH3 is stripped, the gas-liquid volume ratio is 1500:1-4000:1, and the stripping time is 0.5-2.0h.

4. The method according to claim 1, wherein In step 2, the ultrafiltration equipment concentrates the deammoniation liquid by 15-25 times.

5. The method according to claim 1, wherein In step 3, the polyacid is tannic acid or tannic acid, and the dosage is 2-8 g / L post-cash liquid.

6. The method according to claim 1, characterized in that In step 4, the amount of evaporated mother liquor is 15-25% of the total liquid mass of the pretreated liquid entering the MVR simulated evaporator; the drying equipment is one of a drum dryer, a scraper dryer, and an evaporation crystallization pot, with a boiling point of 90°C-100°C.

7. The method according to claim 1, characterized in that In step 5, the prepared mass concentration of the PAC solution is 10%-30%, and the prepared mass concentration of the PAM solution is 1‰-3‰; the dosage of the PAC agent is 1-3 g / L condensed water, and the dosage of the PAM agent is 2-10 mg / L condensed water.

8. The method according to claim 1, characterized in that In step 6, in the hydrolysis and acidification tank, the pH value is maintained between 6 and 8, the hydraulic retention time is controlled to 2-4 hours, the sludge concentration is maintained between 10 and 20 g / L, and the water level rising flow rate in the hydrolysis and acidification tank is 0.8-1.8 m / s; in the aerobic MBR system, the pH value is maintained between 6 and 8, the dissolved oxygen concentration is controlled between 2 and 4 mg / L, the membrane surface flow rate is controlled between 3 and 5 m / s, the sludge concentration is controlled between 3000 and 20000 mg / L, and the clean water backwash time is 10 min to 360 min.

9. The method according to claim 1, characterized in that In step 6, the hydrolysis acidification tank uses sodium carbonate as the alkalinity agent, the C / N ratio is 10:1-15:1, and the sludge discharge cycle is 3-7 days; the aerobic MBR system uses sodium carbonate as the alkalinity agent, the C / N ratio is 4:1-6:1, and the sludge discharge cycle is 1-3 days.

10. The method according to claim 2, characterized in that The solid content of the material after filtration reaches 55%-75%.

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