Landfill leachate pretreatment hardness removal process and system

Abstract

The invention relates to a landfill leachate pretreatment hardness removal process and a landfill leachate pretreatment hardness removal system, which are specifically characterized in that at the front end of landfill leachate anaerobic reaction treatment of a landfill power plant, landfill leachate raw water and alkaline anaerobic reactor reflux water are fully mixed, the pH value of the mixed liquid is monitored in real time, and the reflux quantity of an anaerobic reactor is adjusted in real time, so that the landfill leachate is subjected to alkali adjustment treatment (pHgt; 7.5), then adding sodium carbonate to generate calcium and magnesium precipitates, then adding polymeric ferric sulfate, activated sludge and polyacrylamide to improve the precipitation effect, enabling the effluent to selectively pass through sand filtration to further remove the calcium and magnesium precipitates in the leachate, and removing the calcium and magnesium precipitates in the leachate subjected to hardness removal treatment, the leachate can be further treated by adopting an anaerobic-AOAO-membrane treatment method. The invention provides a device based on the process, the problems of high cost and the like of hardness removal by a dual-alkali method are solved, the activity of anaerobic sludge and aerobic sludge in the later period can be improved, and the service life of a membrane device is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and particularly relates to a garbage leachate pre-treatment hardness removal process and system. Background Art

[0002] Garbage leachate is an organic wastewater with high concentration of COD, high hardness, and high ammonia nitrogen. It has the characteristics of complex composition, large changes in water quality and quantity, high treatment cost, and great difficulty in treatment. Generally, in urban domestic waste power plants that do not carry out waste sorting, the amount of garbage leachate produced is 10% to 30% of the amount of garbage. As waste power plants gradually complete the process replacement of landfills in China, the treatment of fresh domestic waste leachate has become an important part of the normal production of waste power plants.

[0003] At present, the commonly used leachate treatment process in waste-to-energy plants is screen + regulating tank + anaerobic treatment + biochemical treatment + membrane treatment. However, the high hardness of the leachate will cause many problems in the leachate treatment process, as follows: 1) The anaerobic reactor outlet pipe and the anaerobic reactor internal circulation pipe are seriously scaled and blocked. In production, high-pressure backwashing is usually used to dredge the anaerobic reactor outlet pipe and the anaerobic reactor circulation pipe to reduce pipe scaling and blockage. This requires more manpower and material resources, making the facility maintenance cost high. When used for a long time, some internal circulation pipes are difficult to dredge, and some anaerobic circulation pipes will lose their circulation function; 2) 70% to 90% of the calcium and magnesium ions in the leachate raw water will remain in the anaerobic reactor as insoluble particles. There are a large number of calcified particles at the bottom and middle and lower parts of the anaerobic reactor, which increases the inorganic matter in the anaerobic sludge and the anaerobic sludge. The activity is significantly reduced, and the methane production rate per unit mass of sludge is reduced by about 15% to 40%, which prolongs the hydraulic retention time, significantly reduces the volume load, and reduces the operating efficiency of the anaerobic equipment; 3) Under normal circumstances, the calcium ion concentration of the leachate discharged from the anaerobic reactor is 200-700 mg / L. When entering the subsequent aerobic and anoxic process section for denitrification, the calcium and magnesium ion concentrations are still high at this time, and the nitrification capacity of the sludge in the aerobic and anoxic process section is reduced by 20% to 30%, and the aeration time needs to be increased by 20% to 30%, which increases the production cost; 4) The calcium ion concentration of the leachate discharged from the aerobic and anoxic process section is generally 100-300 mg / L, which is easy to cause blockage of nanofiltration membranes and reverse osmosis membranes during membrane treatment, reducing the life of the membrane. Based on the above analysis, it can be concluded that the high hardness of the garbage leachate will cause systematic process problems in the leachate treatment process.

[0004] In view of the fact that too high hardness of landfill leachate treatment process may cause systemic problems in leachate treatment, the inventor has proposed to use an improved double alkali method to reduce the hardness at the front end of leachate treatment, that is, to add an optimized combination of reagents (NaOH, Na 2 CO 3, polyferric sulfate and polyacrylamide and other drugs) are used to remove hardness from leachate. Although this method can effectively reduce the hardness of the leachate and alleviate the systemic process problems caused by the high hardness of the above-mentioned landfill leachate during the treatment process, the salinity of the leachate will increase due to the main reliance on the addition of NaOH when adjusting the alkali. However, it is costly and still has certain negative effects on subsequent anaerobic digestion and nitrification and denitrification. For example, the high salinity slightly reduces the activity of aerobic sludge and anaerobic sludge. Therefore, it is necessary to further improve and design a landfill leachate hardness removal process that can effectively avoid the above-mentioned hardness removal problems. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a more optimized landfill leachate pre-treatment and hardness removal process and system, so as to achieve the purpose of treating waste with waste. It not only solves the problem of high salinity of traditional double alkali method hardness removal agents, but also further reduces the cost of agents.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The implementation scheme provided by the present invention is to provide a process for removing hardness from landfill leachate, comprising the following steps:

[0008] Before flocculation and sedimentation, the landfill leachate raw water and the alkaline anaerobic reactor return water are mixed to obtain a mixed solution, and the pH values ​​of the anaerobic reactor return water and the mixed solution are monitored in real time. According to the pH value of the mixed solution and the pH value of the anaerobic reactor return water, the flow rate ratio of the landfill leachate raw water and the anaerobic reactor return water is calculated and controlled in real time to stabilize the pH value of the mixed solution between 7.5 and 8.0, and then sodium carbonate is added to the mixed solution to react and generate calcium and magnesium insoluble substances;

[0009] Then, flocculants, activated sludge from the mud press room, flocculants and part of the recycled activated sludge from the sedimentation tank are added into the mixed liquid for flocculation and sedimentation. The netting and flocculation effects of the sludge and flocculants are used to make the newly generated calcium and magnesium insoluble substances adhere to the flocs, and as the flocs grow larger and sink, the calcium and magnesium ions are removed from the landfill leachate raw water in the form of sludge, thereby reducing the hardness of the landfill leachate raw water.

[0010] The landfill leachate raw water after flocculation and sedimentation is subsequently subjected to anaerobic digestion reaction, aerobic nitrification, anoxic denitrification reaction and membrane treatment.

[0011] Preferably, the calcium ion concentration of the landfill leachate raw water is 1800mg / L~3600mg / L, the hardness of the landfill leachate raw water is 8000mg / L~16000mg / L, the pH value of the landfill leachate raw water is 5.3~6.0, and the COD value of the landfill leachate raw water is 30000mg / L~80000mg / L.

[0012] Preferably, the landfill leachate raw water and the anaerobic reactor return water are mixed in a volume ratio of 1:4 to 1:10.

[0013] Preferably, the sodium carbonate dosage is 3.0 kg / m 3 ~7.0kg / m 3 Raw water leachate, reaction time is 10min~30min.

[0014] Preferably, the flocculants are polyferric sulfate and polyacrylamide, the dosage of the polyferric sulfate is 100g / L to 200mg / L, the reaction time is 15min to 30min, the dosage of the polyacrylamide is 100g / L to 200mg / L, and the reaction time is 15min to 30min.

[0015] Preferably, the dry weight addition amount per ton of water sludge is 0.05g to 0.50g.

[0016] Preferably, the hardness removal rate at the front end of the anaerobic reactor is 30% to 90%.

[0017] The second implementation scheme provided by the present invention is to provide a landfill leachate pre-treatment and hardness removal system, comprising:

[0018] A reaction mixing tank, the inlet of which is connected to a water inlet pipe, the water inlet pipe is connected to the raw water inlet pipe of the landfill leachate and the anaerobic reactor reflux outlet pipe, the water inlet pipe and the anaerobic reactor reflux outlet pipe are both provided with a pH detector, the reaction mixing tank is connected to a sodium carbonate dosing pipe, and the anaerobic reactor reflux outlet pipe is provided with an electric control valve;

[0019] The flocculation tank is connected to the bottom of the reaction mixing tank, and the flocculation tank is provided with a polyferric sulfate dosing pipe, a polyacrylamide dosing pipe and a sludge dosing pipe;

[0020] A sedimentation tank is connected to the flocculation tank and is used to settle the flocculated garbage leachate. The upper part of the sedimentation tank is connected to the anaerobic reactor through a pipeline, and the bottom of the sedimentation tank is connected to the flocculation tank through a first activated sludge return conveying pipe. The bottom of the sedimentation tank is also connected to the flocculation tank through a second activated sludge return conveying pipe. The first activated sludge return conveying pipe and the second activated sludge return conveying pipe are both provided with sludge pumps.

[0021] The controller has a signal inlet connected to a pH detector and a signal outlet connected to an electric control valve. The received pH feedback signal is compared with the pH setting value on the controller to adjust the opening of the electric control valve, thereby adjusting the flow rate ratio of the landfill leachate raw liquid and the anaerobic reactor return water.

[0022] Preferably, an outlet is provided at the lower portion of the flocculation tank, an inlet is provided at the upper portion of the sedimentation tank, and the inlet and the outlet are connected through a channel.

[0023] Preferably, the sedimentation tank is connected to the anaerobic reactor through a pipeline, a sand filter is provided between the sedimentation tank and the anaerobic reactor, a stirrer is provided in the reaction mixing tank and the flocculation tank, and a sludge scraper is provided in the sedimentation tank.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention adjusts the pH value of the mixed solution to pH>7.5 by mixing the anaerobic reactor reflux water with the landfill leachate raw water for reaction. This is because the anaerobic reactor reflux water contains ammonia nitrogen decomposed from the total nitrogen of the landfill leachate raw water, and the ammonia nitrogen is alkaline. The anaerobic reactor reflux water replaces the externally added sodium hydroxide in the prior art to react with the acidic landfill leachate raw water, so that the anaerobic reactor reflux water and the acidic substances in the landfill leachate raw water can undergo a neutralization reaction. Compared with the externally added sodium hydroxide provided in the prior art, no sodium ions are added to the mixed solution, and further, no sodium ions are reacted with the acidic substances in the landfill leachate raw water to generate sodium salts, and further, no externally added salts are introduced into the mixed solution. Therefore, the salinity in the leachate treatment process is significantly reduced compared with the prior art, which not only increases the sludge activity of the anaerobic reactor and the aerobic reactor, and improves the volumetric load of the anaerobic reactor and the aerobic reactor, but also reduces the cost of using the reagent without adding sodium hydroxide, and saves resources and energy.

[0026] In addition, Na 2 CO 3 After that, calcium and magnesium insolubles are generated under alkaline conditions. Activated sludge is used as a biological flocculant. Since the sludge itself contains already formed flocs, these flocs can be used as new flocculation cores to accelerate the flocculation reaction. The newly generated calcium and magnesium insolubles, i.e., precipitated substances, are more likely to adhere to these existing flocculation cores, thereby improving the flocculation effect and reducing the amount of polyacrylamide, etc. In addition, activated sludge is used to replace part of the flocculant, reducing the amount of polyferric sulfate added, further reducing the cost of drugs and reducing the technical cost.

[0027] Due to the sludge return, there are more types of flocculation active substances and a stable flocculation environment in the reaction system. The large number of floccules brought by the sludge return accelerates the formation of larger floccules. According to Stokes' law, the larger the particles, the faster the sedimentation rate, which helps to improve the solid-liquid separation efficiency in the hardness removal process, reduce the sedimentation time, and increase the surface load of the treatment equipment (such as sedimentation tanks). Even if the inlet water hardness fluctuates to a certain extent, the entire hardness removal system can operate more stably to ensure that the outlet water hardness continues to be stable at a low level.

[0028] Sludge return flocculation allows the sludge to be recycled within the system to a certain extent, reducing the amount of sludge that needs to be disposed of in the end. This is because the newly generated sediment is more attached to the return sludge rather than forming new independent sludge. This has positive significance for reducing the environmental pressure caused by sludge disposal (such as the occupation of sludge landfills, energy consumption in the sludge disposal process, etc.).

[0029] A certain concentration of carbon dioxide is dissolved in the effluent water from the anaerobic reactor. Carbon dioxide dissolves in water to form carbonate ions. The carbonate ion liquid reacts with the calcium ions and magnesium ions in the mixed liquid to generate calcium and magnesium insoluble substances. On the one hand, it reduces the amount of sodium carbonate added, and on the other hand, it fixes carbon, which is green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a device diagram of a landfill leachate pre-treatment and hardness removal process.

[0031] Reference numerals

[0032] 1. Reaction mixing tank; 2. Water inlet pipe; 3. Raw water inlet pipe of landfill leachate; 4. Backflow outlet pipe of anaerobic reactor; 5. Sodium carbonate dosing pipe; 6. Flocculation tank; 7. Polyferric sulfate dosing pipe; 8. Polyacrylamide dosing pipe; 9. Sludge dosing pipe; 10. Sedimentation tank; 11. Sand filter. DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are conventional methods unless otherwise specified.

[0034] The present invention provides a more optimized landfill leachate pretreatment hardness removal process and system, changes the process composition, and changes the reagent composition from the original NaOH, Na 2 CO 3 , polyferric sulfate and polyacrylamide become Na 2 CO 3, Polyferric sulfate, polyacrylamide and activated sludge are used. By using the principle that the total nitrogen in the anaerobic reactor is hydrolyzed into ammonia nitrogen, causing the pH value to rise rapidly (the pH value generally rises to 7.9 < pH < 8.5), the effluent of the anaerobic reactor is refluxed to replace the externally added NaOH for adjusting the alkalinity of the leachate. Thus, the addition of NaOH is completely replaced, significantly reducing the salinity of the leachate in the subsequent treatment process, reducing the chemical agent cost, saving resources and energy, increasing the sludge activity of the anaerobic reactor and the aerobic reactor, and enhancing the volume load of the anaerobic reactor and the aerobic reactor. At the same time, the flocculation characteristics of the activated sludge are used to replace part of the flocculants such as polyacrylamide.

[0035] In addition, the present invention uses the pH value to regulate the flow rate of the refluxed effluent of the anaerobic reactor for adjusting the alkalinity of the newly fed landfill leachate, so that the landfill leachate reacts with the added Na 2 CO 3 under alkaline conditions (7.5 < pH < 8.0), removing 30% - 60% of Ca 2+ and Mg 2+ Thereby reducing the hardness of the leachate; then using polyferric sulfate, polyacrylamide, activated sludge and reflux sludge to partially replace the flocculant to flocculate and precipitate the precipitate particles generated during the hardness removal process; finally, filtering the leachate after hardness removal through a sand filter and discharging it. By pretreating and removing hardness through this process, the hardness of the anaerobic reactor inlet can be significantly reduced, effectively preventing the scaling of the anaerobic reactor circulation and reflux pipelines, enhancing the sludge activity of the anaerobic reactor, improving the ammonia oxidation efficiency and denitrification rate of the biochemical reaction mixing tank, and further effectively extending the service life of the membrane. Finally, ensuring the stable operation of the process and the effluent quality meeting the discharge and reuse standards.

[0036] As Figure 1 shown, the present invention provides a system for pretreating and removing hardness from landfill leachate, including:

[0037] The inlet of the reaction mixing tank 1 is connected to a water inlet pipe 2, the water inlet pipe 2 is communicated with the raw water inlet pipe 3 of the landfill leachate and the outlet pipe 4 of the anaerobic reactor return flow. pH detectors are provided on both the water inlet pipe 2 and the outlet pipe 4 of the anaerobic reactor return flow. The reaction mixing tank 1 is connected to a sodium carbonate dosing pipe 5, and an electric control valve is provided on the outlet pipe 4 of the anaerobic reactor return flow;

[0038] The flocculation tank 6 is communicated with the bottom of the reaction mixing tank 1, and a polyferric sulfate dosing pipe 7, a polyacrylamide dosing pipe 8 and a sludge dosing pipe 9 are provided on the flocculation tank 6;

[0039] The sedimentation tank 10 is connected to the flocculation tank 6 and is used to settle the flocculated landfill leachate. The upper part of the sedimentation tank 10 is connected to the anaerobic reactor through a pipeline, and the bottom of the sedimentation tank 10 is connected to the flocculation tank 6 through a first activated sludge return conveying pipe. The bottom of the sedimentation tank 10 is also connected to the flocculation tank 6 through a second activated sludge return conveying pipe. The first activated sludge return conveying pipe and the second activated sludge return conveying pipe are both provided with sludge pumps.

[0040] The controller has a signal inlet connected to a pH detector and a signal outlet connected to an electric control valve. The received pH feedback signal is compared with the pH setting value on the controller to adjust the opening of the electric control valve, thereby adjusting the flow rate ratio of the landfill leachate raw liquid and the anaerobic reactor return water.

[0041] The high-density sedimentation tank includes a reaction mixing tank 1 , a flocculation tank 6 and a sedimentation tank 10 .

[0042] Specifically, an outlet is provided at the bottom of the flocculation tank 6, and an inlet is provided at the top of the sedimentation tank 10, and the inlet and the outlet are connected through a channel. The flow path of the flocculated landfill leachate is increased, thereby further increasing the contact time of calcium carbonate and magnesium carbonate adhering to the sludge, further precipitating calcium carbonate and magnesium carbonate, and reducing the hardness of the landfill leachate.

[0043] Specifically, the sedimentation tank 10 is connected to the anaerobic reactor through a pipeline, and a sand filter 11 is provided between the sedimentation tank 10 and the anaerobic reactor. The use of the sand filter 11 can separate the generated calcium and magnesium precipitates, which not only fundamentally reduces the hardness of the landfill leachate, but also prevents the calcium and magnesium precipitates from entering the anaerobic reactor; agitators are provided in the reaction mixing tank 1 and the flocculation tank 6, and a sludge scraper is provided in the sedimentation tank 10.

[0044] The present invention provides a process for pre-treatment and hardness removal of landfill leachate, comprising the following steps:

[0045] Before flocculation and sedimentation, the landfill leachate raw water and alkaline anaerobic reactor return water are mixed to obtain a mixed solution, and the pH values ​​of the anaerobic reactor return water and the mixed solution are monitored in real time. According to the pH value of the mixed solution and the pH value of the anaerobic reactor return water, the flow rate ratio of the landfill leachate raw water and the anaerobic reactor return water is calculated and controlled in real time to stabilize the pH value of the mixed solution between 7.5 and 8.0, so as to perform alkali adjustment treatment on the landfill leachate raw water, and then sodium carbonate is added to the uniform mixed solution to react and generate calcium and magnesium insoluble substances;

[0046] Then, polyferric sulfate, activated sludge, part of the activated sludge recycled from the sedimentation tank, polyacrylamide, etc. are added for flocculation and precipitation, and the flocculants in the sludge are used to make the newly generated calcium and magnesium precipitates adhere to the flocculants in the sludge to accelerate the precipitation of calcium and magnesium, and the calcium and magnesium precipitates are filtered to separate them from the landfill leachate;

[0047] The landfill leachate after flocculation and sedimentation is subsequently subjected to anaerobic digestion reaction, aerobic nitrification, anoxic denitrification reaction and membrane treatment.

[0048] Specifically, the calcium ion concentration of the final effluent is 600 mg / L to 1800 mg / L, and the calcium ion removal rate is 30% to 90%.

[0049] Specifically, the calcium ion concentration of the landfill leachate raw water is 1800 mg / L to 3600 mg / L, the pH value is 5.3 to 6.0, and the COD value is 30000 mg / L to 80000 mg / L.

[0050] Specifically, the dosage of sodium carbonate is 3kg / m 3 ~7kg / m 3 The leachate has a reaction time of 10 to 30 minutes. The flocculants are polyferric sulfate and polyacrylamide. The dosage of the polyferric sulfate is 100 g / L to 200 mg / L, and the reaction time is 15 to 30 minutes. The dosage of the polyacrylamide is 100 g / L to 200 mg / L, and the reaction time is 15 to 30 minutes.

[0051] Specifically, the dry weight addition amount per ton of water sludge is 0.05g to 0.50g.

[0052] Specifically, the landfill leachate raw water and the anaerobic reactor effluent water are mixed in a volume ratio of 1:4 to 1:10, and the pH value after mixing is 7.5 to 8.0.

[0053] Several specific embodiments are given below based on the above-mentioned landfill leachate pre-treatment and hardness removal process.

[0054] Example 1

[0055] The waste sources of a waste incineration power plant are urban domestic waste and dried sludge from urban industrial sewage treatment plants. The raw water of the leachate has been measured to have a calcium ion concentration of 2040 mg / L, a pH value of 6.06, and a COD of 44190 mg / L; the calcium ion concentration of the anaerobic reactor effluent is 550 mg / L, the COD is 6575 mg / L, and the pH value is 8.18. The daily water intake is 400 m 3 .

[0056] When the raw water of the leachate from the waste incineration power plant and the reflux water from the anaerobic reactor are mixed in a theoretical volume ratio of 1:6, the pH value of the leachate to be treated after mixing is 8.01, and the temperature of the mixed leachate is 30°C.

[0057] The anaerobic reactor effluent supernatant was mixed with the influent leachate to replace NaOH to adjust the pH of the leachate. Since the raw water of the landfill leachate in the experiment was different from the actual water quality of the raw water of the leachate from the waste incineration power plant in actual application, it was also necessary to accurately calculate and control the reflux flow rate to maintain the initial stability of the pH. The pH online monitoring equipment was installed on the outlet of the inlet pipe 2 and the anaerobic reactor reflux outlet pipe 4. The flow rate of the reflux leachate was accurately calculated according to the pH deviation to ensure that the pH was maintained in an appropriate range of 7.5 to 8.0. 4 kg / m 3 Sodium carbonate (the dosage of sodium carbonate is calculated based on the calcium ion concentration in the raw water of the landfill leachate, m 3 represents the volume of the original water of the landfill leachate), removes Ca from the leachate 2+ and Mg 2+ ; Add 100g / m 3 ~200g / m 3 Polyferric sulfate, 125L / m 3 Activated sludge, 100g / m 3 ~200g / m 3 Polyacrylamide, sludge can partially replace flocculants such as polyacrylamide (the sludge source is the concentrated sludge in the mud pressing room of the garbage power plant, or the sludge precipitated in the sedimentation tank 10, and the dry weight addition amount of sludge per ton of water is 0.05g~0.50g). The flocculation tank 6 is connected to the sludge discharge pipe at the bottom of the sedimentation tank 10. The flocculation effect of the activated sludge and the return sludge is utilized to adsorb into stable suspended particle aggregates in the flocculation tank 6, and settle and remove in the sedimentation tank 10; a sand filter device 11 is added at the outlet for further filtering to effectively remove suspended matter, macromolecular solid particles, colloids and iron ions in the leachate.

[0058] Finally, the high-density sedimentation tank consisting of the reaction mixing tank 1, the flocculation tank 6 and the sedimentation tank 10 operated stably, with a calcium ion removal rate of 36.36%. During stable operation, the calcium ion concentration of the anaerobic reactor inlet was 220 mg / L~250 mg / L, the calcium ion concentration of the anaerobic reactor effluent was 80 mg / L~130 mg / L, and the COD removal rate of the anaerobic reactor was 85.12%.

[0059] Example 2

[0060] The waste sources of a waste incineration power plant are urban domestic waste and biomass resources such as straw collected by enterprises. The leachate collected from the landfill has a calcium ion concentration of 2240 mg / L, a pH value of 6.12, and a COD of 35860 mg / L; the anaerobic effluent has a calcium ion concentration of 460 mg / L, a COD of 6045 mg / L, a pH value of 8.16, and a daily water intake of 600 m 3 .

[0061] The leachate from the waste incineration power plant and the return water from the anaerobic reactor were mixed in a theoretical volume ratio of 1:6. After mixing, the pH value was 8.06 and the temperature was 30°C.

[0062] The anaerobic reactor effluent supernatant was mixed with the influent leachate to replace NaOH to adjust the pH of the leachate. Since the actual water quality of the landfill leachate raw water in the experiment is different from that of the landfill incineration power plant leachate raw water in actual application, it is also necessary to accurately calculate and control the reflux flow rate to maintain the initial pH stability. A pH online monitoring device was installed at the outlet of the inlet pipe 2 to accurately calculate the dosage of the reflux leachate according to the pH deviation to ensure that the pH is maintained in an appropriate range of 7.5 to 8.0; 4 kg / m 3 Sodium carbonate (the dosage of sodium carbonate is calculated based on the calcium ion concentration in the raw water of the landfill leachate, m 3 represents the volume of the original water of the landfill leachate), removes Ca from the leachate 2+ and Mg 2+ ; Add 100g / m 3 ~200g / m 3 Polyferric sulfate, 125L / m 3 Activated sludge, 100g / m 3 ~200g / m 3 Polyacrylamide, sludge can partially replace flocculants such as polyacrylamide (the sludge source is the concentrated sludge in the mud pressing room of the garbage power plant, or the sludge precipitated in the sedimentation tank 10, and the dry weight of the sludge added per ton of water is 0.05g~0.50g). The flocculation tank 6 is connected to the sludge discharge pipe at the bottom of the sedimentation tank 10. The flocculation effect of the activated sludge and the return sludge is utilized to adsorb into stable suspended particle aggregates in the flocculation tank 6, and then settle and remove in the sedimentation tank 10; a sand filter device 11 is added at the outlet for further filtering to effectively remove suspended matter, macromolecular solid particles, colloids and iron ions in the leachate and soften the water.

[0063] Finally, the high-density sedimentation tank consisting of the reaction mixing tank 1, the flocculation tank 6 and the sedimentation tank 10 operated stably, with a calcium ion removal rate of 49.62%. During stable operation, the calcium ion concentration of the anaerobic reactor inlet was 220 mg / L~260 mg / L, the calcium ion concentration of the anaerobic reactor effluent was 100 mg / L~150 mg / L, and the COD removal rate of the anaerobic reactor was 83.14%.

[0064] Example 3

[0065] The raw water of the leachate from a waste incineration power plant was measured to have a calcium ion concentration of 2150 mg / L, a pH value of 6.01, and an influent COD of 25460 mg / L; the calcium ion concentration of the anaerobic effluent was 360 mg / L, the COD was 4445 mg / L, the pH value was 8.11, and the daily influent volume was 600 m 3 .

[0066] The leachate from the waste incineration power plant and the effluent from the anaerobic reactor were mixed in a theoretical volume ratio of 1:5. After mixing, the pH value was 7.88 and the temperature was 30°C.

[0067] The anaerobic reactor effluent supernatant was mixed with the influent leachate to replace NaOH to adjust the pH of the leachate. Since the actual water quality of the landfill leachate raw water in the experiment is different from that of the landfill incineration power plant leachate raw water in actual application, it is also necessary to accurately calculate and control the reflux flow rate to maintain the initial pH stability. A pH online monitoring device was installed at the outlet of the inlet pipe 2 to accurately calculate the dosage of the reflux leachate according to the pH deviation to ensure that the pH is maintained in an appropriate range of 7.5 to 8.0; 4 kg / m 3 of sodium carbonate, (the dosage of sodium carbonate is calculated based on the calcium ion concentration in the raw water of the landfill leachate, m 3 represents the volume of the original water of the landfill leachate), removes Ca from the leachate 2+ and Mg 2+ ; Add 100g / m 3 ~200g / m 3 Polyferric sulfate, 125L / m 3 Activated sludge, 100-200 g / m 3 ~200g / m 3Polyacrylamide, sludge can partially replace flocculants such as polyacrylamide (the sludge source is the concentrated sludge in the mud pressing room of the garbage power plant, or the precipitated sludge in the sedimentation tank 10, and the dry weight addition amount of sludge per ton of water is 0.05g~0.50g). The flocculation tank 6 is connected to the sludge discharge pipe at the bottom of the sedimentation tank 10. The flocculation effect of the activated sludge and the return sludge is utilized to adsorb into stable suspended particle aggregates in the flocculation tank 6, and settle and remove in the sedimentation tank 10; a sand filter device 11 is added at the outlet for further filtering to effectively remove suspended matter, macromolecular solid particles, colloids and iron ions in the leachate and soften the water.

[0068] Finally, the high-density sedimentation tank consisting of the reaction mixing tank 1, the flocculation tank 6 and the sedimentation tank 10 operated stably, with a calcium ion removal rate of 47.72%. During stable operation, the calcium ion concentration of the anaerobic reactor inlet was 230 mg / L~260 mg / L, the calcium ion concentration of the anaerobic reactor effluent was 120 mg / L-180 mg / L, and the COD removal rate of the anaerobic reactor was 82.54%.

[0069] Example 4

[0070] The raw water of the garbage incineration power plant was measured to have a calcium ion concentration of 3220 mg / L, a pH value of 6.05, and an influent COD of 32050 mg / L; the anaerobic effluent calcium ion concentration was 280 mg / L, COD was 5170 mg / L, pH value was 8.11, and the daily water inflow was 800 m 3 .

[0071] The leachate from the waste incineration power plant and the effluent from the anaerobic reactor were mixed in a theoretical volume ratio of 1:5. After mixing, the pH value was 7.88 and the temperature was 30°C.

[0072] The anaerobic reactor effluent supernatant was mixed with the influent leachate to replace NaOH to adjust the pH of the leachate. Since the raw water of the landfill leachate in the experiment is different from the actual water quality of the raw water of the leachate from the waste incineration power plant in actual application, it is also necessary to accurately calculate and control the reflux flow rate to maintain the initial stability of the pH. A pH online monitoring device was installed at the outlet of the inlet pipe 2 to accurately calculate the dosage of the reflux leachate according to the pH deviation to ensure that the pH is maintained in an appropriate range of 7.5 to 8.0; 5 kg / m 3 of sodium carbonate, (the dosage of sodium carbonate is calculated based on the calcium ion concentration in the raw water of the landfill leachate, m 3 represents the volume of the original water of the landfill leachate), removes Ca from the leachate 2+ and Mg 2+ ; Add 100g / m 3 ~200g / m 3 Polyferric sulfate, 125L / m3 Activated sludge, 100g / m 3 ~200g / m 3 Polyacrylamide, sludge can partially replace flocculants such as polyacrylamide (the sludge source is the concentrated sludge in the mud pressing room of the garbage power plant, or the precipitated sludge in the sedimentation tank 10, and the dry weight addition amount of sludge per ton of water is 0.05g~0.50g). The flocculation tank 6 is connected to the sludge discharge pipe at the bottom of the sedimentation tank 10. The flocculation effect of the activated sludge and the return sludge is utilized to adsorb into stable suspended particle aggregates in the flocculation tank 6, and settle and remove in the sedimentation tank 10; a sand filter device 11 is added at the outlet for further filtering to effectively remove suspended matter, macromolecular solid particles, colloids and iron ions in the leachate and soften the water.

[0073] Finally, the high-density sedimentation tank consisting of the reaction mixing tank 1, the flocculation tank 6 and the sedimentation tank 10 operated stably, with a calcium ion removal rate of 60.71%. During stable operation, the calcium ion concentration of the anaerobic reactor inlet was 250mg / L~280mg / L, the calcium ion concentration of the anaerobic reactor effluent was 120mg / L~180mg / L, and the COD removal rate of the anaerobic reactor was 83.87%.

[0074] Example 5

[0075] The raw water of the leachate from a waste incineration power plant was measured to have a calcium ion concentration of 2980 mg / L, a pH value of 6.01, and an influent COD of 30290 mg / L; the anaerobic effluent calcium ion concentration was 350 mg / L, COD was 4410 mg / L, and the pH value was 8.1. The daily influent volume was 1200 m 3 .

[0076] The leachate from the waste incineration power plant and the effluent from the anaerobic reactor were mixed in a theoretical volume ratio of 1:6. After mixing, the pH value was 8.0 and the temperature was 30°C.

[0077] The anaerobic reactor effluent supernatant was mixed with the influent leachate to replace NaOH to adjust the pH of the leachate. Since the raw water of the landfill leachate in the experiment is different from the actual water quality of the raw water of the leachate from the waste incineration power plant in actual application, it is also necessary to accurately calculate and control the reflux flow rate to maintain the initial stability of the pH. A pH online monitoring device was installed at the outlet of the inlet pipe 2 to accurately calculate the dosage of the reflux leachate according to the pH deviation to ensure that the pH is maintained in an appropriate range of 7.5 to 8.0; 5 kg / m 3 of sodium carbonate, (the dosage of sodium carbonate is calculated based on the calcium ion concentration in the raw water of the landfill leachate, m 3 represents the volume of the original water of the landfill leachate), removes Ca from the leachate 2+ and Mg 2+ ; Add 100g / m3 ~200g / m 3 Polyferric sulfate, 125L / m 3 Activated sludge, 100g / m 3 ~200g / m 3 Polyacrylamide, sludge can partially replace flocculants such as polyacrylamide (the sludge source is the concentrated sludge in the mud pressing room of the garbage power plant, or the sludge precipitated in the sedimentation tank 10, and the dry weight addition amount of sludge per ton of water is 0.05g~0.50g). The flocculation tank 6 is connected to the sludge discharge pipe at the bottom of the sedimentation tank 10. The flocculation effect of the activated sludge and the return sludge is utilized to adsorb into stable suspended particle aggregates in the flocculation tank 6, and settle and remove in the sedimentation tank 10; a sand filter device 11 is added at the outlet for further filtering to effectively remove suspended matter, macromolecular solid particles, colloids and iron ions in the leachate.

[0078] Finally, the high-density sedimentation tank consisting of the reaction mixing tank 1, the flocculation tank 6 and the sedimentation tank 10 operated stably, with a calcium ion removal rate of 45.83%. During stable operation, the calcium ion concentration of the anaerobic reactor inlet was 250mg / L~280mg / L, the calcium ion concentration of the anaerobic reactor effluent was 150mg / L~200mg / L, and the COD removal rate of the anaerobic reactor was 85.36%.

[0079] After being treated by the garbage leachate pretreatment system given in Examples 1 to 5, the hardness of the entire leachate treatment system is effectively reduced. Although the influent calcium ion of the garbage leachate raw water given in Examples 1 to 5 is greater than 2000 mg / L, after being treated by the treatment system and process, the hardness of the leachate from the inlet of the anaerobic reactor is effectively reduced.

[0080] In Examples 1 to 5, the flocculation and sedimentation stage at the front end of the leachate treatment process effectively reduces the leachate hardness by more than 30%, significantly reduces the scaling rate of the subsequent anaerobic reactor circulation and return pipes, increases the activity of anaerobic activated sludge by 10% to 30%, increases the activity of aerobic sludge by 10% to 20%, increases the sludge MLVSS / MLSS, enhances the denitrification efficiency of the aerobic and anoxic biological treatment section, significantly reduces the clogging rate of the membrane treatment system structure, and reduces the operation and maintenance costs.

[0081] In the implementation case, adding activated sludge into the flocculation tank 6 can effectively react with the suspended particles and colloidal substances in the wastewater to form larger flocs, thereby accelerating the aggregation and sedimentation of these particles. 2+ and Mg 2+ Can be adsorbed on sludge, thereby reducing the Ca content in landfill leachate 2+ and Mg 2+ concentration, thereby reducing Ca 2+ and Mg2+ The CO produced in the anaerobic reactor 3 - The amount that combines to form calcium carbonate.

[0082] The use of this process to remove calcium and magnesium ions in the leachate can reduce the hardness of the leachate and effectively reduce scaling of the anaerobic reactor effluent and circulation pipes. Studies have shown that reducing the hardness of the anaerobic reactor inlet water by 50% can reduce the scaling rate by 4 to 5 times, and the specific data varies depending on the water quality and operating conditions.

[0083] After reducing the inorganic components of the leachate, the MLVSS / MLSS ratio of aerobic and anaerobic sludge usually increases by 10% to 20%, and the organic matter content of the sludge increases significantly. Activity detection shows that the sludge activity is enhanced and the degradation rate of organic pollutants is increased.

[0084] After the sludge activity is enhanced, the denitrification efficiency of the aerobic tank can be increased by 10% to 30%, and the oxygen utilization efficiency can be increased by about 20%. The sludge concentration in the tank can be reduced in production. This method will create better conditions for oxygen and pollutant mass transfer. The specific effect can be determined based on the specific system design and operating conditions.

[0085] Lowering hardness can reduce membrane clogging, extend cleaning cycles by 40% to 70%, and reduce maintenance frequency and costs.

[0086] The method for treating the leachate reduces the salinity of the entire system, and the salinity of the treated water can be reduced by 10% to 30%. The treated water can effectively increase the reuse rate.

[0087] Combining the above measures, the use of this pretreatment hardness removal method can reduce the operating and maintenance costs of traditional landfill leachate treatment by 15% to 25%, mainly from the reduced pipeline dredging and replacement, electricity saving, chemical cleaning and membrane replacement costs.

[0088] In addition, microorganisms or special chemically active substances in the return sludge help maintain the stability of the hardness removal reaction. This is because: special chemically active substances include extracellular polymers (EPS), alkaline substances (such as carbonates, hydroxides) and redox substances (such as aluminum salts and iron salts) in the return sludge. The EPS in the return sludge can absorb hardness ions (such as Ca 2 +, Mg2+), promote precipitation, EPS can increase the hardness removal rate by 10% to 20%; the alkaline substances in the return sludge (such as carbonates, hydroxides) can react with the hardness ions to form precipitates. The addition of alkaline substances can increase the hardness removal rate by 25% to 35%; certain redox substances (such as iron salts, aluminum salts) promote the precipitation of hardness ions through flocculation. The addition of iron salts can increase the hardness removal rate by 15% to 25%.

[0089] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A landfill leachate pretreatment and hardness removal process, characterized in that: The steps include: Before flocculation and sedimentation, the landfill leachate raw water and the alkaline anaerobic reactor return water are mixed to obtain a mixed solution, and the pH values ​​of the anaerobic reactor return water and the mixed solution are monitored in real time. According to the pH value of the mixed solution and the pH value of the anaerobic reactor return water, the flow rate ratio of the landfill leachate raw water and the anaerobic reactor return water is calculated and controlled in real time to stabilize the pH value of the mixed solution between 7.5 and 8.0, and then sodium carbonate is added to the mixed solution to react and generate calcium and magnesium insoluble substances; Then, flocculants, activated sludge from the mud press room and part of the recycled activated sludge from the sedimentation tank are added into the mixed liquid for flocculation and sedimentation to reduce the hardness of the landfill leachate raw water; the landfill leachate raw water after flocculation and sedimentation is subsequently treated.

2. A landfill leachate pretreatment and hardness removal process as claimed in claim 1, characterized in that: The landfill leachate raw water and the anaerobic reactor return water are mixed in a volume ratio of 1:4 to 1:

10.

3. A landfill leachate pretreatment and hardness removal process as claimed in claim 1, characterized in that: The sodium carbonate dosage is 3.0 kg / m 3 ~7.0kg / m 3 Raw water leachate, reaction time is 10min~30min.

4. A landfill leachate pretreatment and hardness removal process as claimed in claim 1, characterized in that: The flocculants are polyferric sulfate and polyacrylamide, the dosage of the polyferric sulfate is 100g / L-200mg / L, the reaction time is 15min-30min, the dosage of the polyacrylamide is 100g / L-200mg / L, and the reaction time is 15min-30min.

5. A landfill leachate pretreatment and hardness removal process as claimed in claim 1, characterized in that: The dry weight addition amount per ton of sewage sludge is 0.05g~0.50g.

6. A landfill leachate pretreatment and hardness removal process as claimed in claim 1, characterized in that: The hardness removal rate at the front end of the anaerobic reactor is 30% to 90%.

7. A landfill leachate pretreatment and hardness removal process as claimed in claim 1, characterized in that: The calcium ion concentration of the landfill leachate raw water is 1800mg / L~3600mg / L, the hardness of the landfill leachate raw water is 8000mg / L~16000mg / L, the pH value of the landfill leachate raw water is 5.3~6.0, and the COD value of the landfill leachate raw water is 30000mg / L~80000mg / L.

8. A landfill leachate pretreatment and hardness removal system, characterized in that: include: A reaction mixing tank (1) has an inlet connected to a water inlet pipe (2), the water inlet pipe (2) is in communication with a landfill leachate raw water inlet pipe (3) and an anaerobic reactor return water outlet pipe (4), a pH detector is provided on the water inlet pipe (2) and the anaerobic reactor return water outlet pipe (4), the reaction mixing tank (1) is connected to a sodium carbonate dosing pipe (5), and an electric control valve is provided on the anaerobic reactor return water outlet pipe (4); A flocculation tank (6) is connected to the bottom of the reaction mixing tank (1), and a polyferric sulfate dosing pipe (7), a polyacrylamide dosing pipe (8) and a sludge dosing pipe (9) are provided on the flocculation tank (6); The sedimentation tank (10) is connected to the flocculation tank (6) and is used to settle the flocculated landfill leachate. The upper part of the sedimentation tank (10) is connected to the anaerobic reactor through a pipeline, and the bottom of the sedimentation tank (10) is connected to the flocculation tank (6) through a first activated sludge return pipe. The bottom of the sedimentation tank (10) is also connected to the flocculation tank (6) through a second activated sludge return pipe. The first activated sludge return pipe and the second activated sludge return pipe are both provided with sludge pumps. The controller has a signal inlet connected to a pH detector and a signal outlet connected to an electric control valve. The received pH feedback signal is compared with the pH setting value on the controller to adjust the opening of the electric control valve, thereby adjusting the flow rate ratio of the landfill leachate raw liquid and the anaerobic reactor return water.

9. A landfill leachate pretreatment and hardness removal system as claimed in claim 7, characterized in that: The lower part of the flocculation tank (6) is provided with an outlet, and the upper part of the sedimentation tank (10) is provided with an inlet, and the inlet and the outlet are connected through a channel.

10. A landfill leachate pretreatment and hardness removal system as claimed in claim 7, characterized in that: The sedimentation tank (10) is connected to the anaerobic reactor via a pipeline, a sand filter (11) is provided between the sedimentation tank (10) and the anaerobic reactor, a stirrer is provided in the reaction mixing tank (1) and the flocculation tank (6), and a sludge scraper is provided in the sedimentation tank (10).

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