A deep denitrification process for electroplating comprehensive wastewater

Abstract

The present invention discloses a deep denitrification process for electroplating wastewater. The present invention uses Fenton rare earth catalytic oxidation and anaerobic biology as pretreatment, combines aerobic partial nitrification APN and aerobic synchronous denitrification ASD with a modified anaerobic sludge bed ASB, inoculates ASD bio-bacteria in the aerobic pool, and realizes partial nitrification of ammonia nitrogen and aerobic synchronous denitrification under low carbon-nitrogen ratio conditions; adds sulfur autotrophic denitrifying bacteria SAD, sulfur and trace elements to the anaerobic sludge bed ASB, and realizes efficient removal of total nitrogen and organic matter without an external carbon source, thereby reducing treatment costs. The present invention can solve the problems of strong biological toxicity, insufficient carbon source, poor denitrification efficiency, high cost of external carbon source, and serious secondary pollution in electroplating wastewater, and provides technical support for deep denitrification and carbon removal of electroplating wastewater.

Description

Technical Field

[0001] This invention relates to a deep denitrification and carbon removal treatment technology for electroplating wastewater. This technology utilizes Fenton catalytic oxidation and anaerobic biological pretreatment, combining aerobic partial nitrification (APN) and aerobic simultaneous denitrification (ASD) with a modified anaerobic sludge blanket (ASB) to achieve deep denitrification and carbon removal for electroplating wastewater. This technology belongs to the field of sewage and wastewater treatment technology. Background Art

[0002] The electroplating industry is a highly polluting sector in modern industry. The large amounts of auxiliary materials and fresh water consumed during the electroplating process ultimately become electroplating wastewater. Electroplating wastewater consists of plating solution, rinsing water, and various other wastewaters. Based on the heavy metal content, wastewater can be categorized as chromium (Cr), nickel (Ni), cadmium (Cd), copper (Cu), zinc (Zn), gold (Au), and silver (Ag). Wastewater generated under different production conditions has varying properties. The heavy metal ions, cyanide, and organic matter contained in it can harm microorganisms, making treatment of this wastewater difficult and costly. Therefore, electroplating wastewater treatment has become a major environmental challenge.

[0003] Currently, electroplating wastewater is mostly treated with Fenton oxidation and anaerobic treatment (acidification and hydrolysis reactors) to improve biodegradability, followed by multi-stage or single-stage AO denitrification and carbon removal. Traditional Fenton oxidation consumes large amounts of chemicals, produces large amounts of sludge, and has poor treatment effectiveness. Traditional biological multi-stage AO denitrification processes connect separate reactors in series to perform nitrification and denitrification, respectively, thereby achieving autotrophic nitrification to remove ammonia nitrogen and heterotrophic denitrification (under anoxic conditions) to remove nitrate nitrogen. However, the biotoxicity of heavy metal ions and various additives (such as brighteners, smoothing agents, leveling agents, wetting agents, modifiers, and lubricants) in electroplating wastewater leads to a shortage of bioavailable carbon sources. Traditional denitrification processes rely on the addition of external carbon sources, increasing aeration energy consumption, sludge production, and treatment costs. Despite this, they cannot meet the required total nitrogen and organic matter removal requirements, and cannot ensure that the wastewater consistently meets discharge standards.

[0004] Compared with traditional processes, the present invention first uses Fenton catalytic oxidation and anaerobic biological pretreatment to remove heavy metals and difficult-to-degrade organic matter in wastewater that are harmful to microorganisms, and then uses aerobic partial nitrification and synchronous denitrification processes to remove ammonia nitrogen and organic matter. In other words, a new type of microbial flora is constructed in the same aerobic reaction tank, which can simultaneously achieve partial nitrification and denitrification reactions. This process step does not require the addition of alkalinity, can reduce additional carbon sources, and maintain a stable pH in the reactor. It can reduce aeration energy consumption by 25%, carbon source by 40%, and residual sludge production by 63%, thereby improving the removal rate of total nitrogen. The addition of rare earth catalysts during the Fenton oxidation process reduces reagent consumption, reduces sludge production, and improves the removal effect of harmful substances.

[0005] The modified anaerobic sludge blanket (ASB) incorporates sulfur-autotrophic denitrifying bacteria (SAD) and powdered sulfur to form a sulfur-autotrophic denitrifying community. Regular addition of the trace element Co (CoCl2) enhances biological activity, eliminating the need for an external carbon source, generating no sludge, and reducing energy consumption, thereby enhancing denitrification efficiency.

[0006] The improved anaerobic sludge blanket (ASB) uses a conical reactor. The wastewater passes through the reaction zone, sedimentation zone and clear water zone from bottom to top, and then passes through an external filter before being discharged in compliance with the standards, forming a denitrification device with simple process, easy operation and low operating cost.

[0007] The deep denitrification process proposed in the present invention, which combines Fenton rare earth catalytic oxidation with anaerobic pretreatment, aerobic partial nitrification, and simultaneous denitrification (APN+ASD) with anaerobic sludge blanket (ASB), can solve the problems of difficult removal of harmful substances, large sludge volume, high treatment cost, and low denitrification efficiency in traditional processes. It can ensure that the comprehensive electroplating wastewater is discharged in compliance with discharge standards and has great potential for engineering application. Summary of the Invention

[0008] In view of the characteristics of electroplating comprehensive wastewater, such as strong biological toxicity, high nitrogen content, low carbon-nitrogen ratio, high concentration of organic pollutants and poor biodegradability, the present invention proposes a method that can reduce biological toxicity, reduce external carbon source, save aeration energy consumption, reduce sludge production and improve denitrification and carbon removal efficiency under low carbon-nitrogen ratio conditions.

[0009] The technical solutions of the present invention are as follows.

[0010] The present invention uses Fenton rare earth catalytic oxidation and anaerobic biochemical treatment as pretreatment, combines aerobic partial nitrification (APN) and aerobic simultaneous denitrification (ASD) with a modified anaerobic sludge bed (ASB). ASD biogenic bacteria are inoculated in the aerobic tank to achieve partial nitrification of ammonia nitrogen and aerobic simultaneous denitrification under low carbon-nitrogen ratio conditions. Sulfur autotrophic denitrification bacteria (SAD), sulfur and trace elements are added to the anaerobic sludge bed (ASB) to achieve efficient removal of total nitrogen and organic matter without an external carbon source, thereby reducing treatment costs.

[0011] The present invention targets homogenized electroplating wastewater, firstly adopts Fenton catalytic oxidation and anaerobic biochemical treatment to reduce biological toxicity and destroy refractory organic matter, then performs aerobic partial nitrification and simultaneous denitrification (APN+ASD), and finally performs anaerobic autotrophic denitrification (anaerobic ammonium oxidation) to achieve high-efficiency, energy-saving, low carbon-nitrogen ratio and low-cost treatment of electroplating wastewater.

[0012] The process is as follows: wastewater regulating tank → Fenton catalytic oxidation tank → hydrolysis acidification tank → aerobic reaction tank (APN+ASD) → improved anaerobic sludge blanket (ASB) → effluent (see Figure 1 ).

[0013] The purpose of the present invention is achieved through the following technical solutions:

[0014] 1) Electroplating wastewater first enters the regulating tank

[0015] Wastewater from various enterprises or electroplating workshops undergoes chemical treatment to remove heavy metals before entering a regulating tank for water quality and quantity equalization. The hydraulic retention time is 8-12 hours, the pH is controlled at 6.5-7.5, and an underwater agitator is installed for mixing to ensure uniform effluent quality.

[0016] 2) Electroplating comprehensive wastewater enters the Fenton catalytic oxidation tank after homogenization and adjustment

[0017] The Fenton catalytic oxidation tank chemically oxidizes organic matter (including various electroplating additives) in wastewater under acidic conditions, destroying high-molecular-weight organic matter harmful to microorganisms while also performing chemical phosphorus removal. The Fenton catalytic oxidation tank consists of three parts: a reaction tank, a sedimentation tank, and a pH adjustment tank. Acid is first added to the reaction tank to adjust the pH to 2-5. A rare earth catalyst, Fenton reagent (FeSO₄ and H₂O₂), and a flocculant (PAM) are then added to form floccules, which are then fed into the sedimentation tank for sludge-water separation. The supernatant from the sedimentation tank is then adjusted to a pH of 6-8 with alkali before entering the anaerobic reaction tank. The chemical sludge produced in the sedimentation tank is dewatered and transported to an external location. The reaction tank and pH adjustment tank are each equipped with agitators to ensure thorough mixing of the added reagents with the wastewater. The hydraulic retention times for the reaction tank, sedimentation tank, and pH adjustment tank are 1-2.0 hours, 4-5 hours, and 0.5-0.8 hours, respectively, and the temperature ranges from 15°C to 35°C. The concentration of heavy metals in the effluent is controlled within the limit values ​​of Guangdong Province's "Electroplating Water Pollutant Discharge Standard (DB 44 / 1597-2015)".

[0018] 3) Electroplating comprehensive wastewater enters the hydrolysis acidification tank after chemical oxidation

[0019] The hydrolysis and acidification tank is designed to destroy macromolecular organic matter that is harmful to microorganisms and difficult to degrade, thereby improving biodegradability. A stirring device is installed within the reaction tank to ensure thorough mixing of sludge and water. The hydrolysis and acidification tank maintains a hydraulic retention time of 10 to 24 hours, a pH of 6.5 to 7.5, a temperature of 15 to 35°C, a sludge concentration of 3,000 to 4,000 mg / L, and an effluent dissolved oxygen concentration below 0.2 mg / L.

[0020] After hydrolysis and acidification, the wastewater enters the anaerobic sludge sedimentation tank for mud-water separation. The surface load of the anaerobic sludge sedimentation tank is 0.5~1.0m 3 / (m 2 h), hydraulic retention time is 3~4 hours, solid load is 30-90kg / m 2 .d. All the sludge produced by sedimentation is returned to the front end of the anaerobic reaction tank for reuse, and the supernatant enters the aerobic tank (APN+ASD).

[0021] 4) The effluent from the anaerobic sludge sedimentation tank enters the aerobic partial nitrification and simultaneous denitrification tank (APN+ASD)

[0022] The aerobic partial nitrification and simultaneous denitrification tank (APN+ASD) utilizes organic carbon in the wastewater under aerobic conditions. Autotrophic nitrifying bacteria complete partial nitrification of ammonia nitrogen, while inoculated aerobic heterotrophic denitrifying bacteria achieve simultaneous removal of ammonia nitrogen and nitrate nitrogen. The inoculation ratio is 2-4%. The hydraulic retention time (HRT) of the aerobic tank is 15-30 hours, the solids retention time (SRT) is 9-12 days, and the activated sludge concentration in the aerobic tank is controlled between 5000-9000 mg / L, the pH is 7.0-7.5, and the temperature is 15-35°C. The aerobic reaction tank is equipped with microporous aeration, with the air volume ensuring that the dissolved oxygen concentration in the reaction tank is controlled between 0.5 and 2.5 mg / L and the ORP is controlled between -10 and +250 mV. The nitrified solution from the aerobic tank is returned from the end to the front end of the aerobic tank, where it is mixed with wastewater from the anaerobic sedimentation tank for further reaction. The nitrified solution return ratio is 200-300%.

[0023] The mud-water mixture in the aerobic reaction tank enters the aerobic sludge sedimentation tank (secondary sedimentation tank) to achieve mud-water separation. The surface load of the aerobic sludge sedimentation tank can be controlled at 0.5~1.2m 3 / (m 2 ·h), hydraulic retention time is 3~4 hours, solid load is 30-90kg / (m 2 .d). The sludge produced in the aerobic sludge sedimentation tank can be fully or partially returned (return ratio 80-100%) to the front end of the aerobic tank according to the reaction effect to mix with the wastewater from the anaerobic sedimentation tank and then react. The remaining sludge is dehydrated and transported out.

[0024] 5) The effluent from the aerobic sludge sedimentation tank (secondary sedimentation tank) enters the improved anaerobic sludge blanket (ASB)

[0025] The improved anaerobic sludge blanket (ASB) further removes nitrate nitrogen and some organic matter. The ASB comprises a conical reaction zone, a cylindrical sludge-water separation zone (sedimentation zone), a cylindrical clear water zone, and an external filter. The ASB has a residence time of 10.5-15 hours. Wastewater first enters the lower portion of the ASB, where it reacts with sludge returned from the sedimentation zone, added powdered sulfur, and supplemented trace elements. Wastewater then flows upward into the sedimentation zone for sludge-water separation, then enters the clear water zone for degassing and clarification. After exiting the sludge bed, it is filtered and discharged to meet discharge standards.

[0026] The inoculation ratio for the anaerobic sludge bed is 5-10%, and the dosage of powdered sulfur is 15-30 mg / L based on the volume of treated water. The trace element Co (CoCl2) is regularly supplemented to the anaerobic sludge at a dosage of 2-5 mg / L based on the volume of treated water. The wastewater in the anaerobic sludge bed has an upward flow rate of 0.3-0.5 m / h, a temperature of 15-25°C, and a pH of 7-8. The filter filtration rate is 4-6 m / h.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1) High catalytic oxidation efficiency. Fenton uses rare earth catalytic oxidation agents with low consumption, low sludge production, good detoxification effect, and high organic matter removal efficiency.

[0029] 2) High denitrification efficiency. As heterotrophic microorganisms, ASD microorganisms have a short metabolic cycle (24-36 h) and a denitrification efficiency (1.4 kg-N m -3 d -1 ) is much higher than conventional aerobic nitrification and anoxic denitrification (0.5 kg-N m -3 d -1 ).

[0030] 3) Low treatment cost. Simultaneous nitrification and denitrification are achieved in the (APN+ASD) reaction tank under low carbon-nitrogen ratio conditions, effectively addressing the different requirements of nitrifying and denitrifying bacteria for carbon source, alkalinity, sludge age, and dissolved oxygen. This saves on external carbon sources, reduces energy consumption, reduces sludge production, and lowers treatment costs.

[0031] 4) Low alkalinity requirement. The (APN+ASD) aerobic reaction tank utilizes the acid produced by nitrification and the alkali produced by denitrification, essentially achieving acid-base balance. This effectively maintains a stable pH in the reactor and reduces alkalinity consumption.

[0032] 5) Denitrification achieves deep denitrification without the need for an external carbon source. The improved anaerobic sludge blanket (ASB) utilizes sulfur-autotrophic denitrification technology. Compared to existing heterotrophic denitrification technologies, this system eliminates the need for an external organic carbon source (methanol, glucose, etc.), achieving extreme denitrification. The residual sludge output is only one-tenth of that of heterotrophic denitrification, reducing operating costs.

[0033] 6) Excellent effluent quality. Fenton catalytic oxidation and anaerobic biological pretreatment effectively address the issue of microbial inhibition by harmful substances. Chemical phosphorus removal is also achieved. Aerobic partial nitrification and simultaneous denitrification (APN+ASD) technology complements the advantages of sulfur-autotrophic denitrification sludge blanket technology, ensuring that total nitrogen concentrations are reduced from 100-200 mg / L to below 20 mg / L, and COD concentrations are reduced from 600-800 mg / L to below 80 mg / L. Compared to existing traditional technologies, effluent quality is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a process flow chart of the present invention for combining Fenton catalytic oxidation with anaerobic pretreatment, aerobic partial nitrification (APN), simultaneous denitrification (ASD) and improved anaerobic sludge blanket (USB) for electroplating wastewater;

[0035] Figure 2This is a diagram of the laboratory setup;

[0036] Figure 3 The following are photos of the sewage treatment site in Example 3. DETAILED DESCRIPTION

[0037] For a better understanding of the present invention, the present invention will be further described below with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.

[0038] Example 1

[0039] like Figure 1 As shown, the structure of this embodiment is as follows: a wastewater regulating tank, a Fenton oxidation tank, an acidification and hydrolysis tank, an aerobic tank APN+ASD, and an anaerobic sludge blanket ASB are used in series. The aerobic tank APN+ASD is an aerobic partial nitrification and synchronous denitrification tank; the anaerobic sludge blanket ASB is a modified sulfur autotrophic denitrification sludge blanket; the Fenton oxidation tank includes a reaction tank, a sedimentation tank, and a pH adjustment tank; the acidification and hydrolysis tank also includes a sedimentation tank, the bottom of which can return anaerobic sludge to the acidification and hydrolysis tank; the aerobic tank is connected to a sedimentation tank, the bottom of which returns anaerobic sludge to the aerobic tank; the bottom of the aerobic tank is also connected to an air buffer tank, a flow meter and an air control valve are connected between the air buffer tank and the aerobic tank, and the bottom of the aerobic tank is also provided with a nitrification liquid return; the anaerobic sludge blanket consists of three parts: a conical reaction zone, a cylindrical sedimentation zone, and a clear water zone, wherein the clear water zone is connected to a filter. Laboratory electroplating comprehensive wastewater treatment experimental device see Figure 2 .

[0040] Example 2: Treatment of comprehensive electroplating wastewater in an industrial park

[0041] The comprehensive electroplating wastewater treatment adopts the use of treatment tanks in series and is implemented according to the following steps.

[0042] 1) Electroplating wastewater first enters the regulating tank

[0043] Electroplating wastewater is mixed to form electroplating comprehensive wastewater after being treated with cyanide breaking, decyanation and secondary chemical precipitation. Daily wastewater output is 5000m 3 This wastewater first enters a regulating tank for water quality and quantity adjustment. The regulating tank has a hydraulic retention time of 10 hours and is equipped with six submersible mixers. After homogenization, the wastewater maintains a pH between 6.5 and 7.5.

[0044] 2) Electroplating comprehensive wastewater enters the Fenton chemical oxidation tank after homogenization and adjustment

[0045] The electroplating park uses two production lines for wastewater treatment. Each line treats 2500m3 of wastewater per day. 3 / d. Sulfuric acid is added to the first reaction tank of the Fenton chemical oxidation tank to adjust the pH to between 2-5, and the residence time is 0.3 hours; the wastewater after pH adjustment flows into the second reaction tank, and rare earth catalyst (ReSO4), FeSO4 and H2O2 are added respectively, with dosages of 35mg / L, 600mg / L and 250mg / L. The residence time is 0.5 hours; the wastewater after the reaction flows into the third reaction tank, and flocculant (PAM) is added at a dosage of 15mg / L, and the residence time is 0.3 hours. A mechanical stirrer is installed in each of the three reaction tanks for stirring. The flocculated wastewater enters the vertical flow sedimentation tank for mud-water separation. The sedimentation tank has a residence time of 4.0 hours and a surface load of 1.0m 3 / (m 2 .h). The supernatant from the sedimentation tank flows by gravity into the pH adjustment tank, where alkali is added to adjust the pH to 7-8 before entering the acidification and hydrolysis tank. The pH adjustment tank is maintained for 0.6 hours with alkali addition and equipped with a mechanical stirrer. The reaction temperature is 15-25°C.

[0046] 3) Electroplating comprehensive wastewater enters the hydrolysis acidification tank after chemical oxidation

[0047] The hydraulic retention time of the hydrolysis and acidification tank is 15 hours, the sludge concentration is 3000-4000 mg / L, the pH is controlled at 6~8, the temperature is 15~25℃, 6 stirring devices are installed in the reaction tank, and the dissolved oxygen concentration of the effluent is less than 0.2 mg / L.

[0048] 4) Electroplating comprehensive wastewater enters the anaerobic sludge sedimentation tank after hydrolysis and acidification

[0049] The anaerobic sludge sedimentation tank adopts a vertical flow sedimentation tank. The hydraulic retention time is 4.5 hours and the surface load is 0.7m 3 / (m 2 ·h), solid load is 50-67kg / (m 2 .d) All the sludge produced by sedimentation flows back to the front end of the hydrolysis and acidification tank, and the supernatant enters the aerobic tank.

[0050] 5) The effluent from the anaerobic sludge sedimentation tank enters the aerobic partial nitrification and simultaneous denitrification tank (APN+ASD)

[0051] The aerobic partial nitrification and simultaneous denitrification tank (APN+ASD) was supplemented with Acinetobacter sp. GDMCC 1.586, Sphingomonas azotifigens GDMCC 1.696, and Bacillus cereus GDMCC 801530 at a ratio of 3%. The hydraulic retention time (HRT) was 20 hours, the sludge concentration was 4000-5000 mg / L, the solids retention time (SRT) was 10-12 days, the pH was 7.0-7.5, and the temperature was 15-25°C. The aerobic reactor was equipped with microporous aeration, with the air volume ensuring the dissolved oxygen concentration in the reactor was controlled between 1.0 and 2.5 mg / L. The nitrified solution was returned from the end of the aerobic tank to the front end of the aerobic tank and mixed with the wastewater from the anaerobic sedimentation tank. The nitrified solution return ratio was 200-300%.

[0052] 6) The sludge-water mixture from the aerobic reaction tank enters the aerobic sludge sedimentation tank (secondary sedimentation tank)

[0053] Aerobic sludge sedimentation tank adopts vertical flow sedimentation tank. The surface load can be controlled at 0.7m 3 / (m 2 ·h), hydraulic retention time is 4 hours, solid load is 67-84kg / (m 2 .d). The sludge return ratio is 90-100%, and the remaining sludge is transported out after dehydration.

[0054] 7) The effluent from the aerobic sludge sedimentation tank enters the improved anaerobic sludge blanket (ASB)

[0055] Wastewater first enters the anaerobic sludge bed (ANAB) where it remains for 10 hours, with an upward flow rate of 0.4 m / h, a temperature of 15-25°C, and a pH of 7-8. Desulfovibrio desulfuricans GDMCC 1.765 and Thauera sp. GDMCC 805944 are inoculated at an 8% inoculum ratio. The wastewater then enters the lower portion of the ANAB, where it reacts with sludge returning from the settling zone, added powdered sulfur, and supplemented trace elements. The dosages of powdered sulfur and trace element CoCl2 are 20 mg / L and 3 mg / L, respectively, based on the treated water volume, resulting in a sludge concentration of 8000 mg / L. The wastewater then flows upstream into the settling zone for sludge-water separation, then into the clear water zone for degassing and clarification before passing through a filter to meet discharge standards. The filter residence time is 1 hour, and the filtration rate is 5 m / h.

[0056] The water quality indicators after treatment using the above steps are shown in Table 1.

[0057] Table 1: Fenton catalytic oxidation + hydrolysis acidification + aerobic (APN + ASD) + anaerobic sludge blanket (ASB) combined process

[0058] Treatment effect of electroplating comprehensive wastewater

[0059]

[0060] *Electroplating wastewater discharge limits in the Pearl River Delta region as stipulated in Guangdong Province’s Electroplating Water Pollutant Discharge Standard (DB 44 / 1597-2015).

[0061] The results shown in Table 1 show that after the process proposed in the present invention treats electroplating comprehensive wastewater, the removal rates of COD, TN, NH4-N, TP, SS and CN reach 81%, 88%, 91%, 91%, 83% and 80%, respectively; the heavy metals and organic pollutants in the effluent can stably meet the emission limits for the Pearl River Delta region in Guangdong Province's "Electroplating Water Pollutant Discharge Standard (DB 44 / 1597-2015)".

[0062] The comparison of the treatment effects of the process proposed by the present invention and the existing traditional process is shown in Table 2. The results shown in Table 2 show that:

[0063] ① The existing traditional process for treating electroplating wastewater cannot consistently meet discharge standards, with COD, TN, NH4-N, TP, SS, and CN all significantly exceeding standards. The process of the present invention can ensure that various indicators of electroplating wastewater meet national emission standards after treatment without adding a carbon source.

[0064] ② Using the process proposed in the present invention, the removal efficiencies of COD, TN, NH4-N, TP, SS and CN are increased by 37%, 45%, 6%, 52%, 16% and 40% respectively compared with the existing traditional process without adding an external carbon source.

[0065] ③ Although the existing traditional process improves denitrification efficiency when adding 0.8 kg of glucose per ton of wastewater, it still fails to meet emission standards. The process proposed in this invention not only eliminates the need for an external carbon source but also reduces sludge production by 0.48 kg per ton of wastewater treated, significantly reducing treatment costs.

[0066] In summary, the electroplating comprehensive wastewater treatment process proposed in the present invention has obvious technical and economic advantages.

[0067] Table 2: Fenton catalytic oxidation + hydrolysis acidification + aerobic (APN + ASD) + anaerobic sludge blanket (ASB) combined process

[0068] Comparison table of treatment effects with existing traditional processes

[0069]

[0070] * Substandard water quality indicators

[0071] Example 3 Treatment of comprehensive electroplating wastewater in industrial parks

[0072] The treatment tanks used in the comprehensive electroplating wastewater treatment are used in series and implemented in the following steps:

[0073] 1) Electroplating wastewater first enters the regulating tank

[0074] Electroplating wastewater is mixed and treated with cyanide breaking and chemical precipitation to form electroplating comprehensive wastewater. Daily wastewater output is 2000m 3 This wastewater first enters a regulating tank for water quality and quantity adjustment. The regulating tank has a hydraulic retention time of eight hours and is equipped with four submersible mixers. After homogenization, the wastewater maintains a pH between 6.5 and 7.5.

[0075] 2) Electroplating comprehensive wastewater enters the Fenton catalytic oxidation tank after homogenization and adjustment

[0076] The electroplating park uses two production lines for wastewater treatment. Each line treats 1000m3 of wastewater per day. 3 / d. Sulfuric acid is added to the first reaction tank of the Fenton chemical oxidation tank to adjust the pH to about 4.0, and then rare earth catalyst (ReSO4), FeSO4 and H2O2 are added, with dosages of 25 mg / L, 520 mg / L and 240 mg / L respectively. The residence time is 0.5 hours; the wastewater after pH adjustment flows into the second reaction tank and flocculant (PAM) is added, with a dosage of 13 mg / L and a residence time of 0.5 hours. A mechanical stirrer is installed in each of the two reaction tanks for stirring. The flocculated wastewater enters the vertical flow sedimentation tank for mud-water separation. The residence time in the sedimentation tank is 4.0 hours, and the surface load is 0.9m 3 / (m 2 The supernatant from the sedimentation tank flows by gravity into the pH adjustment tank, where alkali is added to adjust the pH to 7-8 before entering the acidification and hydrolysis reaction tank. The pH adjustment tank has a residence time of 0.6 hours and is equipped with a mechanical stirrer. The reaction temperature is approximately 20°C.

[0077] 3) Electroplating comprehensive wastewater enters the hydrolysis acidification tank after chemical oxidation

[0078] The hydraulic retention time of the hydrolysis and acidification tank is 12 hours, the sludge concentration is 2500-3500 mg / L, the pH is controlled at 6~8, the temperature is about 20℃, there are 4 stirring devices in the reaction tank, and the dissolved oxygen concentration of the effluent is less than 0.1 mg / L.

[0079] 4) Electroplating comprehensive wastewater enters the anaerobic sludge sedimentation tank after hydrolysis and acidification

[0080] The anaerobic sedimentation tank adopts a vertical flow sedimentation tank. The hydraulic retention time is 4.5 hours and the surface load is 0.7m3 / (m 2 ·h), solid load is 42kg / (m 2 .d) All the sludge produced by sedimentation is returned to the hydrolysis and acidification tank, and the supernatant enters the aerobic partial nitrification and simultaneous denitrification tank (APN+ASD).

[0081] 5) The effluent from the anaerobic sludge sedimentation tank enters the aerobic tank

[0082] The aerobic tank (aerobic partial nitrification and simultaneous denitrification tank) is infused with simultaneous denitrifying bacteria at a rate of 3%. The hydraulic retention time (HRT) is 18 hours, the sludge concentration is controlled at approximately 3500-4500 mg / L, the solids retention time is 12 days, the pH is maintained at 7.0-7.5, and the temperature is approximately 20°C. The aerobic reaction tank is equipped with microporous aeration, with the air volume ensuring the dissolved oxygen concentration in the reaction tank is controlled at approximately 1.5-2.5 mg / L. The nitrified liquid is returned from the end of the aerobic tank to the front end of the aerobic tank and mixed with wastewater from the anaerobic sludge sedimentation tank. The nitrified liquid return ratio is 300%. The mixed liquid enters the sedimentation tank for sludge-water separation.

[0083] 6) The sludge-water mixture from the aerobic reaction tank enters the aerobic sludge sedimentation tank (secondary sedimentation tank)

[0084] Aerobic sludge sedimentation tank adopts vertical flow sedimentation tank. The surface load is 0.7m 3 / (m 2 h), hydraulic retention time is 4 hours, solid load is 67 kg / (m 2 .d). The sludge return ratio is 100%, and the remaining sludge is transported out after dehydration.

[0085] 7) The effluent from the aerobic sedimentation tank enters the modified anaerobic sludge blanket (ASB)

[0086] Wastewater first enters the anaerobic sludge bed, where it remains for 11 hours. The wastewater has an upward flow rate of 0.5 m / h, a temperature of approximately 20°C, and a pH of 7-8. The inoculation ratio of the sulfur-autotrophic denitrifying bacteria is 7%, and the dosages of powdered sulfur and the trace element CoCl2 are 25 mg / L and 4 mg / L, respectively, based on the treated water volume. The sludge concentration exceeds 7000 mg / L. The wastewater enters the lower portion of the anaerobic sludge bed, where it reacts with sludge returning from the sedimentation zone, the added powdered sulfur, and the supplemented trace elements. The wastewater then flows upward to the sedimentation zone for sludge-water separation. It then enters the clear water zone for degassing and clarification before passing through filters to meet discharge standards. The filter residence time is 1.2 hours, and the filter velocity is 4 m / h.

[0087] See the photos of the sewage treatment site using the above operation. Figure 3 .

[0088] The water quality indicators after the above operation steps are implemented are shown in Table 3. The results shown in Table 3 show that:

[0089] After treating this type of electroplating comprehensive wastewater, the process proposed in the present invention can achieve COD, TN, NH4-N, TP, and CN removal rates of 78%, 82%, 85%, 91%, and 92%, respectively; the heavy metals and organic pollutants in the effluent can stably meet the emission limits for the Pearl River Delta region in Guangdong Province's "Electroplating Water Pollutant Discharge Standard (DB 44 / 1597-2015)."

[0090] Table 3: Fenton catalytic oxidation + hydrolysis acidification + aerobic (APN + ASD) + anaerobic sludge blanket (ASB) combined process

[0091] Treatment effect of electroplating comprehensive wastewater

[0092]

[0093] *Electroplating wastewater discharge limits in the Pearl River Delta region as stipulated in Guangdong Province’s Electroplating Water Pollutant Discharge Standard (DB 44 / 1597-2015).

[0094] The comparison of the treatment effects of the process proposed by the present invention and the existing traditional process is shown in Table 4. The results shown in Table 4 show that:

[0095] ① The existing traditional process for treating electroplating wastewater cannot meet discharge standards, with COD, TN, NH4-N, TP and CN all significantly exceeding the standards. The process of the present invention can ensure that various indicators of electroplating wastewater meet national emission standards after treatment without adding a carbon source.

[0096] ② Using the process proposed in the present invention, the removal efficiencies of COD, TN, NH4-N, TP, SS and CN are increased by 36%, 46%, 8%, 62% and 67% respectively compared with the existing traditional process without adding an external carbon source.

[0097] ③ While the existing conventional process improves denitrification efficiency by adding 0.6 kg of methanol per ton of wastewater, it still fails to meet emission standards. The process proposed in this invention not only eliminates the need for an external carbon source but also reduces sludge production by 0.3 kg per ton of wastewater treated, significantly reducing treatment costs.

[0098] In summary, the electroplating comprehensive wastewater treatment process proposed in the present invention has obvious technical and economic advantages.

[0099] Table 4: Fenton catalytic oxidation + hydrolysis acidification + aerobic (APN + ASD) + anaerobic sludge blanket (ASB) combined process

[0100] Comparison table of treatment effects with existing traditional processes

[0101]

[0102] * Substandard water quality indicators

Claims

1. A deep denitrification process for electroplating wastewater, which adopts a process of coupling aerobic partial nitrification, synchronous denitrification and improved anaerobic sludge blanket, characterized in that: The wastewater regulating tank, Fenton catalytic oxidation tank, acidification hydrolysis tank, aerobic tank, and anaerobic sludge blanket ASB are used in series. The aerobic tank is an aerobic partial nitrification and synchronous denitrification tank. The anaerobic sludge blanket ASB is an improved sulfur autotrophic denitrification sludge blanket. The steps include: 1) Wastewater regulating tank The hydraulic retention time of the wastewater regulating tank is 8-12 hours, and the pH is controlled at 6.5-7.5; 2) Fenton catalytic oxidation tank The wastewater homogenized in the regulating tank flows into the Fenton catalytic oxidation tank, which destroys high-molecular-weight, refractory organic matter harmful to microorganisms, removes toxic heavy metals, and performs chemical phosphorus removal. The Fenton catalytic oxidation tank adds acid to adjust the pH, and then adds a rare earth catalyst, Fenton reagent, and flocculant in sequence. The supernatant in the sedimentation tank adds alkali to adjust the pH and then enters the acid hydrolysis tank. The rare earth catalyst is ReSO4; the Fenton reagent is FeSO4 and H2O2; and the flocculant is PAM. Acid is added to the Fenton catalytic oxidation tank to adjust the pH to 2-5, and then rare earth catalyst, ferrous sulfate, hydrogen peroxide, and flocculant are added in dosages of 20-50 mg / L, 500-700 mg / L, 200-300 mg / L, and 10-20 mg / L, respectively. The formed alum flocs enter the sedimentation tank for mud and water separation. The supernatant produced in the sedimentation tank is adjusted to a pH of 6-8 with alkali and then enters the acid hydrolysis tank. The hydraulic retention times of the reaction tank, sedimentation tank, and pH adjustment tank in the Fenton catalytic oxidation tank are 1-2.0 hours, 4-5 hours, and 0.5-0.8 hours, respectively, and the temperature is 15-35°C. 3) Acidification and hydrolysis tank After the high-molecular-weight, refractory organic matter is further destroyed in the acidification and hydrolysis tank, the wastewater enters the anaerobic sedimentation tank for sludge-water separation. The sludge produced in the anaerobic sedimentation tank is all returned to the front end of the acidification and hydrolysis tank, and the supernatant enters the aerobic partial nitrification and synchronous denitrification tank. 4) Aerobic pool The aerobic tank partially nitrifies ammonia nitrogen through autotrophic nitrifying bacteria under aerobic conditions, and the inoculated aerobic heterotrophic denitrifying bacteria utilize the organic carbon source in the wastewater to achieve the simultaneous removal of ammonia nitrogen and nitrate nitrogen; the sludge produced in the aerobic sludge sedimentation tank is returned to the front section of the aerobic tank and mixed with the wastewater and the return nitrification liquid before reacting; the supernatant produced in the aerobic sludge sedimentation tank enters the improved anaerobic sludge bed ASB; The aerobic partial nitrification and simultaneous denitrification tanks were inoculated with Acinetobacter GDMCC 1.586, Sphingomonas GDMCC1.696, and Bacillus cereus GDMCC 801530 at an inoculation ratio of 2-4%. The hydraulic retention time of the aerobic tank was 15-30 hours, the solid retention time was 9-12 days, the activated sludge concentration in the aerobic tank was controlled at 5000-9000 mg / L, the pH was 7.0-7.5, the temperature was 15-35°C, the dissolved oxygen concentration was controlled at 0.5-2.5 mg / L, the ORP was controlled at -10-+250 mV, and the aeration method was microporous aeration. The nitrified liquid at the end of the aerobic tank was returned to the front end of the aerobic tank and mixed with the wastewater from the anaerobic sedimentation tank for further reaction. The nitrified liquid return ratio was 200-300%. The surface load of the aerobic sludge sedimentation tank was 0.5-1.2 m 3 / (m 2 h), hydraulic retention time is 3~4 h, solid load is 30-90 kg / m 2 d. The sludge produced by sedimentation is fully or partially returned to the front end of the aerobic tank according to the reaction effect, mixed with the wastewater from the anaerobic sedimentation tank and then reacted; the remaining sludge is dehydrated and transported out; the return ratio of partial return is 80-100%; 5) Anaerobic sludge blanket (ASB) The anaerobic sludge bed ASB further denitrifies and removes nitrate nitrogen. Sulfur autotrophic denitrifying bacteria, powdered sulfur and trace elements are added to the anaerobic sludge bed ASB in proportion. After inoculation and acclimatization, the ASB is used after reaching the required concentration. The effluent from the sludge bed is filtered and discharged in compliance with the standards. Sulfur autotrophic denitrifying bacteria and powdered sulfur are added to the anaerobic sludge bed ASB; the bacteria inoculation ratio is 5-10%, the powdered sulfur dosage is 15-30 mg / L based on the treated water volume, and the trace element Co is regularly added to the anaerobic sludge, with the dosage being 2-5 mg / L based on the treated water volume.

2. The deep denitrification process for electroplating comprehensive wastewater according to claim 1, characterized in that: In step 5), the improved anaerobic sludge blanket (ASB) consists of three parts: a conical reaction zone, a cylindrical sedimentation zone, and a clear water zone; the residence time is 10-15 hours, and the wastewater enters the anaerobic sludge blanket with an upward flow rate of 0.3-0.5 m / h, passing through the lower reaction zone, sedimentation zone, and clear water zone in turn, and then passing through the external filter before meeting the discharge standards.

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