Method for treating domestic garbage leachate membrane concentrate

Abstract

A method for treating membrane concentrate from municipal solid waste leachate. The nanofiltration and reverse osmosis concentrate undergoes coagulation and activated carbon adsorption under acidic conditions in a humic acid recovery unit, resulting in precipitation and separation. The bottom layer is a humic acid-rich precipitate, while the upper layer is clear treated water. The recovered humic acid is mixed with organic fertilizer and used for soil improvement. The effluent undergoes electrochemical oxidation treatment using iron-manganese-loaded graphite plates as electrodes. Under the action of a DC power supply, a redox reaction produces chlorine and hydrogen as byproducts. The chlorine and hydrogen are recovered in the chlorine recovery unit. The separated hydrogen and effluent enter an autotrophic denitrification unit, where sodium thiosulfate is added. Sulfur-autotrophic denitrifying bacteria use the hydrogen and sodium thiosulfate to reduce nitrate to nitrogen. The effluent from the autotrophic denitrification unit enters an aerated activated carbon adsorption unit, where aeration oxidizes residual sodium thiosulfate and the activated carbon adsorbs trace chlorinated organic matter. This simultaneously removes COD and TN, recovers humic acid and chlorine resources, and eliminates the need for an external carbon source.

Description

Technical Field

[0001] The invention relates to a process for treating domestic waste leachate membrane concentrate, in particular to a COD and TN removal technology using graphite-based electrode electrochemical oxidation coupled with autotrophic denitrification. Background Art

[0002] Combined leachate treatment processes for municipal solid waste landfills typically include membrane filtration technologies such as nanofiltration and reverse osmosis. These technologies produce large amounts of concentrated liquid. Nanofiltration has a water yield of approximately 80%, while RO has a water yield of approximately 75%. The total amount of concentrated liquid produced accounts for approximately 40% of the leachate treatment volume. Nanofiltration concentrate primarily contains divalent salts and humic acid, with a high COD concentration; RO concentrate primarily contains monovalent salts and ammonia nitrogen, with a low COD concentration. Membrane concentrated liquid from landfill leachate contains a large amount of difficult-to-degrade organic pollutants, high salinity, and dark color, making it difficult to treat using biological methods. Currently, treatment methods for membrane concentrated liquid include re-injection, evaporation, and advanced oxidation. The recharge method is the most commonly used treatment method for membrane concentrates because of its economy and simplicity. However, the concentrations of organic matter, ammonia nitrogen, and salinity gradually accumulate, which destroys the normal operation of membrane treatment and increases energy consumption (Ramazan Keyikoglu, Okan Karatas. A review on treatment of membrane concentrates generated from landfill leachate treatment processes. Separation and Purification Technology, 2021, 259: 118182.). The evaporation method can reduce the volume of the concentrate by more than 90%, but the process is complex and the energy consumption is high. In contrast, advanced oxidation technology has the advantages of high oxidation efficiency, fast reaction speed, and thorough oxidation. The Fenton oxidation method is often used in the treatment of landfill leachate membrane concentrates, with a COD removal rate ranging from 26.5% to 79.6%. External electric fields, ultraviolet light, ultrasound and other strengthening measures are required to further improve the organic matter removal rate. Patent publication number CN111170581A proposes an adsorption + evaporation + incineration treatment process, which relies on adsorption materials to remove organic matter from leachate membrane concentrate. After adsorption saturation, it is desorbed by organic solvents, and the desorbed matter is completely removed by evaporation and incineration. Patent publication number 105923800A uses a multi-stage Fenton to treat leachate membrane concentrate. The traditional Fenton treatment unit still adds iron salts, thus generating a large amount of iron sludge hazardous waste. Patent publication number CN110699285A reports that a high-salt-tolerant Balearic Pseudomonas balearicus denitrifies landfill leachate membrane concentrate. Due to the lack of sufficient carbon source, an external carbon source is added under anoxic / aerobic conditions for denitrification. The electrochemical oxidation method (titanium-based ruthenium-iridium coated electrode (DSA) as anode and 316L stainless steel plate as cathode) is used to treat landfill leachate nanofiltration concentrate. The optimal operating conditions are as follows: hydraulic retention time of 3h, inlet flow rate of 1m 3 / h, circulation flow rate is 15m 3 / h, the current intensity is 420A, the COD concentration is reduced from 3100mg / L to 1311mg / L, and the power consumption per ton of water is 12kwh (Wang Qingguo, Le Chen, Zhuo Ruifeng. Treatment of landfill leachate nanofiltration concentrate by electrochemical oxidation. Journal of Environmental Engineering, 2015, 9(3): 1308-1312.). Boron-doped diamond (BDD) is used as the anode and stainless steel is used as the cathode. The current density is 50-100mA / cm 2 The initial COD is 3778mg / L, the COD removal rate after 6h electrolysis is 87.5%, and the power consumption per ton of water is 223.3kWh / m 3 (Z. Li, L. Zhen, X. Li. Anodic oxidation of landfill leachate nanofiltration concentrates using BDD electrode. Chinese Journal of Environmental Engineering, 2014, 8: 4662-4668). A dual anode system (DSA and iron plate) was used to treat waste incineration leachate membrane concentrate (COD: 1300-1600 mg / L). The electrochemical parameters were: current density 30 mA / cm 2 , voltage 7V, electrode plate spacing 1-2cm, COD and ammonia nitrogen removal rates are 57% and 60% respectively, and the power consumption per ton of water is 49kWh / m 3 (Jing Ding, Miao Jiang, Guanshu Zhao. Treatment of leachate concentrate by electrocoagulation coupled with electro-Fenton-like process: Efficacy and mechanism. Separation and Purification Technology, 2021, 255: 117668.). However, DSA and BDD are expensive and difficult to use on a large scale in sewage treatment. The present invention proposes a graphite-based electrochemical oxidation coupled with autotrophic denitrification leachate membrane concentrate treatment technology, and the process flow is as follows: humic acid recovery S1→electrochemical oxidation S2→chlorine recovery S3→autotrophic denitrification S4→aeration activated carbon adsorption S5. Compared with existing treatment technologies, the present invention can achieve low-cost and high-efficiency removal of COD and TN in leachate membrane concentrate, meeting the "Pollution Control Standards for Municipal Waste Landfills" GB16889-2008. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for treating membrane concentrate of domestic waste leachate, an economical and efficient method for treating COD and TN, which relies on graphite-based electrode electrochemical oxidation to deeply purify refractory organic matter, and omits the addition of carbon source based on autotrophic denitrification.

[0004] The present invention comprises the following steps:

[0005] 1) The nanofiltration and reverse osmosis concentrates are coagulated and adsorbed on activated carbon under acidic conditions in the humic acid recovery unit, followed by precipitation and separation. The bottom layer is a humic acid-rich precipitate, and the upper layer is clear treated water. The humic acid recovery can be mixed with organic fertilizer for soil improvement.

[0006] 2) The effluent from step 1) is subjected to electrochemical oxidation treatment, with the electrodes being iron-manganese loaded graphite plates, undergoing redox reactions under the action of a DC power supply, while simultaneously producing chlorine and hydrogen as byproducts;

[0007] 3) The chlorine and hydrogen produced in step 2) are recovered in a chlorine recovery unit, and the separated hydrogen is fed to the next step;

[0008] 4) The hydrogen separated in step 3) and the effluent from step 2) enter the autotrophic denitrification unit, and sodium thiosulfate is added at the same time. Sulfur autotrophic denitrifying bacteria use the hydrogen and sodium thiosulfate to reduce nitrate to nitrogen;

[0009] 5) The effluent from the autotrophic denitrification unit enters the aeration activated carbon adsorption unit, where the residual sodium thiosulfate is oxidized under the action of aeration, and the activated carbon adsorbs some trace chlorinated organic matter.

[0010] In step 1), coagulation and activated carbon adsorption are carried out under acidic conditions. First, acid is added to adjust the pH to a strong acidic state, and then polyaluminum chloride and powdered activated carbon are added. The amount of polyaluminum chloride added can be 500-1000 mg / L, and the amount of powdered activated carbon added can be 100-300 mg / L.

[0011] In step 2), the electrochemical oxidation treatment is carried out in a closed reactor, and a gas collection pipe is provided on the top of the reactor to collect and discharge the generated chlorine and hydrogen. The mass ratio of iron, manganese and carbon in the loaded iron-manganese graphite plate can be 1:1:85-95. The cathode and anode are made of the same material, and the cathode and anode are alternately arranged to form multiple groups of cathode-anode pairs. The plate spacing can be 3-5 cm. The electrochemical oxidation process does not require the addition of any chemical agents, and the current density is 100-300 A / m 2 , reaction time 2 to 4h; 2) humic acid recovery unit S1 effluent enters electrochemical oxidation unit S2, the electrode plate is loaded with iron-manganese graphite plate, cathode and anode are arranged alternately, the plate spacing is 3 to 5cm, the current density is 100 to 300A / m 2 , reaction time 2 to 4 hours.

[0012] In step 3), the chlorine and hydrogen are recovered in the chlorine recovery unit by passing the mixed gas into a sodium hydroxide solution, and the chlorine and the sodium hydroxide aqueous solution generate a sodium hypochlorite solution to achieve chlorine resource recovery. The gas residence time can be 5 to 15 minutes.

[0013] In step 4), the amount of sodium thiosulfate added can be 5 to 10 mmol / L; the sulfur autotrophic denitrifying bacteria can be sulfur oomycetes (Sulfurovumindicum ST-419), sulfur oomycetes (Sulfurovumindicum ST-419) form a biofilm on the filler, and use sodium thiosulfate and hydrogen to reduce nitrate to nitrogen, and the hydraulic retention time is 8 to 24 hours; the sulfur oomycetes (Sulfurovumindicum ST-419) has been deposited in Guangdong Provincial Microbial Culture Collection Center on March 31, 2021, address: Guangdong Provincial Institute of Microbiology, Postal Code: 510070, and the collection center collection number is GDMCC No.61588; sulfur oomycetes (Sulfurovumindicum ST-419)1A17954 can carry out denitrification under aerobic and anaerobic conditions with nitrate and / or nitrite as the sole nitrogen source, and the final denitrification product is N2 without releasing N2O.

[0014] In step 5), the activated carbon adsorption may be performed using an activated carbon filter tank equipped with bottom aeration, the activated carbon filling layer may be 1 to 2 m, and the hydraulic retention time may be 0.5 to 2 h.

[0015] Compared with the prior art, the present invention has the following outstanding advantages and technical effects:

[0016] The present invention provides an economical and efficient method for treating COD and TN in a membrane concentrate of municipal solid waste leachate. The method utilizes graphite-based electrodes for electrochemical oxidation to deeply purify refractory organic matter, and utilizes sulfur-based autotrophic denitrification to remove nitrogen without adding a carbon source. The process has the following advantages: (1) COD and TN are removed simultaneously, humic acid and chlorine resources are recovered, and the effluent meets the "Standard for Pollution Control of Municipal Solid Waste Landfills" (GB16889-2008); (2) Graphite-based electrodes are used, which are low-cost and have a long lifespan; and (3) Sulfur-based autotrophic denitrifying bacteria utilize hydrogen and thiosulfate for denitrification, eliminating the need for an external carbon source. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the process flow of the present invention.

[0018] Figure 2 Effect of ferrous iron dosage on electrochemical oxidation.

[0019] Figure 3 Effect of current density on electrochemical oxidation. DETAILED DESCRIPTION

[0020] The following embodiments will further illustrate the present invention with reference to the accompanying drawings.

[0021] like Figure 1 The method for treating the membrane concentrate of the domestic waste leachate described in the embodiment of the present invention has a process flow of: humic acid recovery S1 → electrochemical oxidation S2 → chlorine recovery S3 → autotrophic denitrification S4 → aeration activated carbon adsorption S5; the humic acid recovery S1 includes pH adjustment, addition of coagulant and powdered activated carbon, and precipitation separation; the electrochemical oxidation S2 is an electrochemical oxidation based on loaded iron-manganese graphite plates as electrodes, and the process does not require the addition of any chemical agents; the chlorine recovery S3 is the absorption of chlorine generated by the electrochemical oxidation S2 through alkaline solution dissolution; the autotrophic denitrification S4 relies on sulfur autotrophic denitrifying bacteria to reduce nitrate to nitrogen under hydrogen and thiosulfate conditions; the aeration activated carbon adsorption S5 is a granular activated carbon filter with air aeration.

[0022] The method for treating the membrane concentrate of the domestic waste leachate of the present invention comprises the following steps and main operating parameters:

[0023] 1) Humic acid recovery: The landfill leachate nanofiltration concentrate and / or reverse osmosis concentrate enters the humic acid recovery unit, adds acid to adjust the pH to 3-4, adds 500-1000 mg / L of polyaluminum chloride and 100-300 mg / L of powdered activated carbon, and coagulates and settles for 30-90 minutes;

[0024] 2) Electrochemical oxidation: The effluent from the humic acid recovery unit enters the electrochemical oxidation unit. The electrode plates are loaded iron-manganese graphite plates, with cathodes and anodes arranged alternately. The plate spacing is 3-5 cm, and the current density is 100-300 A / m 2 , reaction time 2 to 4 hours; the electrochemical oxidation unit is equipped with a water spray defoaming and gas collection system;

[0025] 3) Chlorine recovery: The chlorine and hydrogen produced by the electrochemical oxidation unit enter the chlorine recovery unit, where the chlorine is absorbed and the hydrogen is separated by the NaOH solution. The gas residence time is 5 to 15 minutes.

[0026] 4) Autotrophic denitrification: 5-10 mmol / L sodium thiosulfate is added to the effluent of the electrochemical oxidation unit and enters the autotrophic denitrification unit. Sulfur oomycetes (Sulfurovumindicum ST-419) form a biofilm on the filler and use sodium thiosulfate and hydrogen to reduce nitrate to nitrogen. The hydraulic retention time is 8-24 hours. The sulfur oomycetes (Sulfurovumindicum ST-419) have been deposited in the Guangdong Provincial Microbial Culture Collection on March 31, 2021. The address is: Guangdong Institute of Microbiology, 5th Floor, Building 59, No. 100 Xianlie Middle Road, Guangzhou, Postal Code: 510070, and the collection number of the collection center is GDMCC No. 61588.

[0027] 5) Aeration activated carbon adsorption: The effluent from the autotrophic denitrification unit enters the aeration activated carbon adsorption unit, which is equipped with an aeration system, a granular activated carbon filling layer of 1 to 2 meters, and a hydraulic retention time of 0.5 to 2 hours.

[0028] Specific examples are given below.

[0029] Example 1

[0030] The embodiment of the present invention includes the following steps

[0031] 1) The nanofiltration concentrate of landfill leachate and / or the reverse osmosis concentrate enters the humic acid recovery unit, acid is added to adjust the pH to 3-4, 500 mg / L of polyaluminum chloride and 100 mg / L of powdered activated carbon are added, and coagulation and sedimentation are carried out for 30 minutes.

[0032] 2) The effluent from the humic acid recovery unit enters the electrochemical oxidation unit. The electrode plates are loaded iron-manganese graphite plates, with cathodes and anodes arranged alternately, the plate spacing is 3 cm, and the current density is 100 A / m 2 , reaction time 2h. The electrochemical oxidation unit is equipped with a water spray defoaming and gas collection system.

[0033] 3) The chlorine and hydrogen produced by the electrochemical oxidation unit enter the chlorine recovery unit, where the chlorine is absorbed and the hydrogen is separated by the NaOH solution, with a gas residence time of 5 minutes.

[0034] 4) 5 mmol / L sodium thiosulfate was added to the effluent of the electrochemical oxidation unit and fed into the autotrophic denitrification unit. Sulfur oomycetes (Sulfurovum indicum ST-419) formed a biofilm on the filler and used sodium thiosulfate and hydrogen to reduce nitrate to nitrogen. The hydraulic retention time was 8 h.

[0035] 5) The effluent from the autotrophic denitrification unit enters the aerated activated carbon adsorption unit, which is equipped with an aeration system, a granular activated carbon filling layer of 1m, and a hydraulic retention time of 0.5h.

[0036] Example 2

[0037] This embodiment includes the following steps:

[0038] 1) The nanofiltration concentrate of landfill leachate and / or the reverse osmosis concentrate enters the humic acid recovery unit, acid is added to adjust the pH to 3, 600 mg / L of polyaluminum chloride and 150 mg / L of powdered activated carbon are added, and coagulation and sedimentation are carried out for 40 minutes.

[0039] 2) The effluent from the humic acid recovery unit enters the electrochemical oxidation unit. The electrode plates are loaded iron-manganese graphite plates, with cathodes and anodes arranged alternately. The plate spacing is 3.5 cm, and the current density is 130 A / m 2 , reaction time 2.5h. The electrochemical oxidation unit is equipped with a water spray defoaming and gas collection system.

[0040] 3) The chlorine and hydrogen produced in step 2) enter the chlorine recovery unit, where the chlorine is absorbed and the hydrogen is separated by a NaOH solution, with a gas residence time of 8 minutes.

[0041] 4) 6 mmol / L sodium thiosulfate was added to the effluent of the electrochemical oxidation unit and fed into the autotrophic denitrification unit. Sulfur oomycetes (Sulfurovum indicum ST-419) formed a biofilm on the filler and used sodium thiosulfate and hydrogen to reduce nitrate to nitrogen. The hydraulic retention time was 12 h.

[0042] 5) The effluent from the autotrophic denitrification unit enters the aeration activated carbon adsorption unit, which is equipped with an aeration system, a granular activated carbon filling layer of 1.5m, and a hydraulic retention time of 1h.

[0043] Example 3

[0044] This embodiment includes the following steps:

[0045] 1) The nanofiltration concentrate of landfill leachate and / or the reverse osmosis concentrate enters the humic acid recovery unit, acid is added to adjust the pH to 4, 700 mg / L of polyaluminum chloride and 200 mg / L of powdered activated carbon are added, and coagulation and sedimentation are carried out for 60 minutes.

[0046] 2) The effluent from the humic acid recovery unit enters the electrochemical oxidation unit. The electrode plates are loaded iron-manganese graphite plates, with cathodes and anodes arranged alternately, the plate spacing is 4 cm, and the current density is 200 A / m 2 , reaction time 3h. The electrochemical oxidation unit is equipped with a water spray defoaming and gas collection system.

[0047] 3) The chlorine and hydrogen produced in step 2) enter the chlorine recovery unit, where the chlorine is absorbed and the hydrogen is separated by a NaOH solution, with a gas residence time of 10 minutes.

[0048] 4) 8 mmol / L sodium thiosulfate was added to the effluent of the electrochemical oxidation unit and fed into the autotrophic denitrification unit. Sulfur oomycetes (Sulfurovum indicum ST-419) formed a biofilm on the filler and used sodium thiosulfate and hydrogen to reduce nitrate to nitrogen. The hydraulic retention time was 15 h.

[0049] 5) The effluent from the autotrophic denitrification unit enters the aeration activated carbon adsorption unit, which is equipped with an aeration system, a granular activated carbon filling layer of 1m, and a hydraulic retention time of 0.8h.

[0050] Example 4

[0051] This embodiment includes the following steps:

[0052] 1) The nanofiltration concentrate of landfill leachate and / or the reverse osmosis concentrate enters the humic acid recovery unit, acid is added to adjust the pH to 3-4, 800 mg / L of polyaluminium chloride and 250 mg / L of powdered activated carbon are added, and coagulation and sedimentation are carried out for 70 minutes.

[0053] 2) The effluent from the humic acid recovery unit enters the electrochemical oxidation unit. The electrode plates are loaded iron-manganese graphite plates, with cathodes and anodes arranged alternately. The plate spacing is 4.5 cm, and the current density is 270 A / m 2 , reaction time 3.5h. The electrochemical oxidation unit is equipped with a water spray defoaming and gas collection system.

[0054] 3) The chlorine and hydrogen produced in step 2) enter the chlorine recovery unit, where the chlorine is absorbed and the hydrogen is separated by a NaOH solution, with a gas residence time of 12 minutes.

[0055] 4) 9 mmol / L sodium thiosulfate was added to the effluent of the electrochemical oxidation unit and fed into the autotrophic denitrification unit. Sulfur oomycetes (Sulfurovum indicum ST-419) formed a biofilm on the filler and used sodium thiosulfate and hydrogen to reduce nitrate to nitrogen. The hydraulic retention time was 18 h.

[0056] 5) The effluent from the autotrophic denitrification unit enters the aerated activated carbon adsorption unit, which is equipped with an aeration system, a 2m granular activated carbon filling layer, and a hydraulic retention time of 1.5h.

[0057] Example 5

[0058] This embodiment includes the following steps:

[0059] 1) The nanofiltration concentrate of landfill leachate and / or the reverse osmosis concentrate enters the humic acid recovery unit, acid is added to adjust the pH to 3-4, 1000 mg / L of polyaluminium chloride and 300 mg / L of powdered activated carbon are added, and coagulation and sedimentation are carried out for 90 minutes.

[0060] 2) The effluent from the humic acid recovery unit enters the electrochemical oxidation unit. The electrode plates are loaded iron-manganese graphite plates, with cathodes and anodes arranged alternately. The plate spacing is 5 cm, and the current density is 300 A / m 2 , reaction time 4h. The electrochemical oxidation unit is equipped with a water spray defoaming and gas collection system.

[0061] 3) The chlorine and hydrogen produced in step 2) enter the chlorine recovery unit, where the chlorine is absorbed and the hydrogen is separated by a NaOH solution, with a gas residence time of 15 minutes.

[0062] 4) 10 mmol / L sodium thiosulfate was added to the effluent of the electrochemical oxidation unit and fed into the autotrophic denitrification unit. Sulfur oomycetes (Sulfurovum indicum ST-419) formed a biofilm on the filler and used sodium thiosulfate and hydrogen to reduce nitrate to nitrogen. The hydraulic retention time was 24 h.

[0063] 5) The effluent from the autotrophic denitrification unit enters the aeration activated carbon adsorption unit, which is equipped with an aeration system, a granular activated carbon filling layer of 2m, and a hydraulic retention time of 2h.

[0064] Example 6: Humic acid recovery from leachate membrane concentrate + electrochemical oxidation + activated carbon adsorption treatment

[0065] The landfill leachate nanofiltration and reverse osmosis mixed concentrate was adjusted to pH 4 by adding sulfuric acid, and then 500 mg / L polyaluminium chloride and 200 mg / L powdered activated carbon were added. The mixture was stirred for 15 minutes and allowed to settle for 30 minutes. A humic acid-rich sediment layer was formed at the bottom. After humic acid recovery pretreatment, the COD of the mixed concentrate was removed to a certain extent. The experimental results of 6 batches are as follows: the initial COD of the concentrate was 880, 867, 1137, 939, 867, and 889 mg / L, and the COD after humic acid recovery was 686, 729, 796, 757, 677, and 731 mg / L, respectively. The average COD removal rate was 21%. Electrochemical oxidation treatment conditions: the mass ratio of iron, manganese, and carbon in the loaded iron-manganese graphite plate was 1:1:85, the plate spacing was 5 cm, and the current density was 100 A / m 2The experimental results for four batches of five groups were as follows: The COD before electrochemical treatment was 691, 733, 769, and 634 mg / L, and after treatment it was 82, 55, 76, and 35 mg / L, respectively, for an average COD removal rate of 91%. The ammonia nitrogen before electrochemical treatment was 14, 12, 14, and 15 mg / L, and after treatment it was 7, 5, 5, and 6 mg / L, for an average ammonia nitrogen removal rate of 58%. The activated carbon adsorption treatment conditions were: granular activated carbon with a diameter of 2-3 mm and a length of 5-10 mm, bottom aeration, and a hydraulic retention time of 1 hour. The average COD before treatment was 65 mg / L, and the average COD after treatment was 23 mg / L, for an average removal rate of 65%.

[0066] Example 7: Effect of ferrous iron dosage on electrochemical oxidation

[0067] Electrochemical oxidation treatment conditions: The mass ratio of iron, manganese and carbon in the iron-manganese graphite plate is 1:1:95, the plate spacing is 3 cm, and the current density is 150 A / m 2 , voltage 8V, reaction time 2h, cathode and anode alternately arranged in 5 groups, and ferrous iron dosages of 0, 0.5, 0.75, 1.0, and 2.0mM respectively. Figure 2 As shown, the COD removal rates after 2 h of treatment were 88%, 80%, 92%, 90%, and 94%, respectively, and the corresponding zero-order COD removal rate constants were 5.24±0.34, 4.60±0.28, 5.10±0.55, 5.10±0.55, and 5.03±0.24 mg-COD (L.min) respectively. -1 When the initial COD concentrations were basically the same, the COD removal rate of 0.5 mM ferrous iron dosage decreased by 10% compared with 0.75 and 1.0 mM ferrous iron dosage.

[0068] Example 8: Effect of current density on electrochemical oxidation

[0069] Electrochemical oxidation treatment conditions: the mass ratio of iron, manganese and carbon in the iron-manganese graphite plate is 1:1:85, the plate spacing is 5 cm, the cathode and anode are arranged alternately in 5 groups, the reaction time is 2 h, and the current density is 130 A / m 2 , 200A / m 2 , 270A / m 2 , initial COD is 633~769mg / L. Figure 3 As shown, the COD removal rates after 2 h of treatment were 64%, 94%, and 98%, respectively, and the corresponding zero-order COD removal rate constants were 3.03±0.17, 5.03±0.24, and 4.59±0.32 mg-COD (L.min) -1 . Current density 130A / m 2When the reaction time was extended to 4 h, the COD removal rate was 98%.

[0070] Example 9: Sulfur Oomycete (Sulfurovum indicum ST-419) autotrophic denitrification treatment 1

[0071] The biofilm was formed on the filler with a 5% inoculation amount, and the reaction conditions were: pH 7.0, temperature 37°C, NO3 - The initial concentration of -N was 140 mg / L (potassium nitrate 10 mM), the initial concentration of thiosulfate (Na2S2O3) was 10 mM, and hydrogen was introduced for 12 h and 24 h. NO3 - -N concentration dropped to 55mg / L and 0mg / L; after 24h of culture, S2O3 2- 733 mg / L was consumed and there was no NO2-N accumulation.

[0072] Example 10: Sulfur Oomycete (Sulfurovum indicum ST-419) autotrophic denitrification treatment 2

[0073] The biofilm was formed on the filler with a 20% inoculation amount, and the reaction conditions were: pH 7.5, temperature 25°C, NO3 - The initial concentration of -N was 50 mg / L, the initial concentration of thiosulfate (Na2S2O3) was 5 mM, and hydrogen was introduced for 8 h. NO3 - -N is completely consumed, there is no NO2-N accumulation, the final product of denitrification is N2, and no N2O is released.

[0074] Example 11: Pilot test of electrochemical oxidation of leachate membrane concentrate + autotrophic denitrification

[0075] The electrochemical oxidation pilot plant has the following dimensions: 120 cm long, 40 cm wide, and 100 cm high. It is equipped with 18 electrode plates, each of which has the following dimensions: 70 cm long, 40 cm wide, and 3 cm thick. The mass ratio of iron, manganese, and carbon in the iron-manganese graphite plates is 1:1:85. The batch process is 150-200 L of leachate membrane concentrate. The reaction conditions are as follows: current 250-300 A, voltage 4.5-7 V, and current density 200 A / m 2The reaction time was 2-3 hours, and the spray defoaming circulating water volume was 2000 L / h. After humic acid recovery pretreatment, the residual COD of the membrane concentrate was 854 and 918 mg / L. After 2 hours of electrochemical treatment, the COD was 121 and 153 mg / L, respectively, and after 3 hours of electrochemical treatment, the COD was 65 and 58 mg / L, respectively. The electrochemical treatment process produced a large amount of chlorine gas, which, after collection with a NaOH solution, had an effective chlorine concentration of 260 g / L. The chlorine content of the treated effluent was 1200-2300 mg / L. The dimensions of the autotrophic denitrification reactor are: 40 cm in diameter and 120 cm in height, continuous treatment, hydraulic retention time 8 h, 7 mmol / L sodium thiosulfate is added to the electrochemical oxidation effluent and introduced into the autotrophic denitrification reactor by a peristaltic pump, and at the same time, a vacuum pump is used to introduce hydrogen generated by electrochemical oxidation treatment into the bottom of the reactor. The inlet nitrate nitrogen concentration is 30-65 mg / L, the inlet total nitrogen concentration is 35-78 mg / L, and the outlet total nitrogen is 5-13 mg / L.

[0076] The above embodiments are only preferred embodiments of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent of the present invention.

Claims

1. A method for treating a membrane concentrate of a domestic waste leachate, characterized in that The following steps are involved: 1) The nanofiltration and reverse osmosis concentrates are coagulated and adsorbed on activated carbon under acidic conditions in the humic acid recovery unit, followed by precipitation and separation. The bottom layer is a humic acid-rich precipitate, and the upper layer is clear treated water. The humic acid recovery product is mixed with organic fertilizer for soil improvement. 2) The effluent from step 1) is subjected to electrochemical oxidation treatment. The electrodes are iron-manganese loaded graphite plates. Under the action of a DC power supply, a redox reaction is carried out, and chlorine and hydrogen are produced as byproducts. 3) The chlorine and hydrogen produced in step 2) are recovered in a chlorine recovery unit, and the separated hydrogen is fed to the next step; 4) The hydrogen separated in step 3) and the effluent from step 2) enter the autotrophic denitrification unit, and sodium thiosulfate is added at the same time. The sulfur autotrophic denitrifying bacteria use hydrogen and sodium thiosulfate to reduce nitrate to nitrogen; the sulfur autotrophic denitrifying bacteria adopt sulfur oomycetes ( Sulfurovum indicumST-419 ), Sulfur Oomycetes ( Sulfurovum indicumST-419 ) was deposited in Guangdong Provincial Microbiological Culture Collection on March 31, 2021, with the collection number GDMCC No.61588; 5) The effluent from the autotrophic denitrification unit enters the aeration activated carbon adsorption unit, where the residual sodium thiosulfate is oxidized under the action of aeration, and the activated carbon adsorbs some trace chlorinated organic matter.

2. A method for treating a membrane concentrate of a domestic waste leachate according to claim 1, characterized in that In step 1), coagulation and activated carbon adsorption are carried out under acidic conditions, acid is first added to adjust the pH to a strong acidic state, and then polyaluminium chloride and powdered activated carbon are added.

3. A method for treating a membrane concentrate of a domestic waste leachate according to claim 2, characterized in that The added amount of the polyaluminium chloride is 500-1000 mg / L, and the added amount of the powdered activated carbon is 100-300 mg / L.

4. A method for treating a membrane concentrate of a domestic waste leachate according to claim 1, characterized in that In step 2), the electrochemical oxidation treatment is carried out in a closed reactor. A gas collecting pipe is provided on the top of the reactor to collect and discharge the generated chlorine and hydrogen.

5. A method for treating a membrane concentrate of a domestic waste leachate according to claim 1, characterized in that In step 2), the mass ratio of iron, manganese and carbon in the loaded iron-manganese graphite plate is 1:1:85-95, the cathode and the anode are made of the same material, and the cathode and the anode are alternately arranged to form multiple cathode-anode pairs.

6. A method for treating a membrane concentrate of a domestic waste leachate according to claim 1, characterized in that In step 2), no chemical agent is required during the electrochemical oxidation process, and the current density is 100-300 A / m 2 , reaction time 2 to 4 hours.

7. A method for treating a membrane concentrate of a domestic waste leachate according to claim 1, characterized in that In step 3), the chlorine and hydrogen are recovered in the chlorine recovery unit by introducing the mixed gas into a sodium hydroxide solution. The chlorine and the sodium hydroxide aqueous solution generate a sodium hypochlorite solution to achieve chlorine resource recovery. The gas residence time is 5 to 15 minutes.

8. A method for treating a membrane concentrate of a domestic waste leachate according to claim 1, characterized in that In step 4), the amount of sodium thiosulfate added is 5 to 10 mmol / L, and the sulfur oomycetes ( Sulfurovum indicumST-419 ) A biofilm is formed on the filler, and sodium thiosulfate and hydrogen are used to reduce nitrate to nitrogen. The hydraulic retention time is 8 to 24 hours.

9. A method for treating a membrane concentrate of a domestic waste leachate according to claim 1, characterized in that In step 5), the activated carbon adsorption adopts an activated carbon filter tank equipped with bottom aeration, the activated carbon filling layer is 1 to 2 meters, and the hydraulic retention time is 0.5 to 2 hours.

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