CN101863592B - Leachate treatment method for small town household refuse landfill sites - Google Patents

Abstract

The invention discloses a leachate treatment method for small town household refuse landfill sites. The method, which adopts two-stage SBR as a core and is organically integrated a chemicophysical method and a biological method, includes the following specific steps that: leachate first enters a regulating storage tank, the quantity of water is regulated, and the water quality is homogenized; the leachate then enters an anaerobic tank, part of COD in the leachate is degraded, so that biodegradability can be enhanced; the effluent of the anaerobic tank enters a two-stage SBR system, and while more COD is removed, the purpose of denitrification can be achieved; and the effluent of the two-stage SBR system undergoes coagulating sedimentation, so that most of suspended matters and total phosphorus in the water can be removed. The method has the advantages of simple technique, convenient management and maintenance, long-term, stable and reliable treatment effect and moderate construction and operation costs, and is applicable to the treatment of the leachate of small town household refuse landfill sites.

Description

A kind of leachate treatment method of urban small domestic waste landfill

technical field

The invention relates to a method for treating leachate of a small-scale domestic garbage landfill in cities and towns, and belongs to the technical field of environmental protection.

Background technique

With the rapid economic development of small towns in my country and the rapid improvement of people's living standards, the generation of domestic waste is increasing year by year, and the disposal of domestic waste needs to be solved urgently. Sanitary landfill technology is widely used because of low investment and low operating costs. But at the same time, sanitary landfills produce a large amount of landfill leachate with complex components and variable properties containing high concentrations of organic matter and ammonia nitrogen, and the resulting secondary pollution has become a problem that must be solved in landfill construction.

Small urban landfills have small landfill scale and low leachate output, generally around 100 tons/day. Complex leachate treatment technologies require high capital, operation, and personnel requirements. Therefore, for this type of landfill, it is necessary to develop a leachate treatment method with simple process, convenient management and maintenance, long-term stable and reliable treatment effect, and moderate infrastructure and operating costs.

Currently, the commonly used methods for leachate treatment mainly include physical and chemical methods and biological methods.

Physical and chemical methods include coagulation, stripping, activated carbon adsorption, evaporation, chemical precipitation, electrolytic catalytic oxidation, ion exchange, membrane separation and other methods. The physicochemical method is less affected by changes in the water quality and volume of landfill leachate, and the effluent water quality is stable, especially for landfill leachate with low BOD ₅ /COD (5-day biochemical oxygen demand/chemical oxygen demand) that is difficult to biologically treat. The treatment effect is high, but the cost of physical and chemical treatment is high, and it is generally used for pretreatment or advanced treatment of leachate.

Biological methods include activated sludge method, biological contact oxidation method, A ² O, SBR, oxidation pond, land treatment method, leachate recharge, etc. Among them, the traditional SBR process (sequential batch activated sludge process) is stable and mature, and its own characteristics are very suitable for the treatment of small water volume sewage, so traditional SBR is often used for the treatment of leachate in small landfills. However, since various biochemical reactions in traditional SBR are completed in the same sludge system, contradictions among functional flora are caused. For example, the removal of COD and ammonia nitrogen, the purpose of these two processes is different, and the requirements for the composition, basic types and environmental conditions of microorganisms are also different. Therefore, when the traditional SBR process is used for leachate treatment, there are sludge ages of different functional flora Contradictions, contradictions between organic matter concentration and nitrification, etc. These problems limit the treatment effect of the traditional SBR process and make it unable to meet the requirements of landfill leachate treatment.

Comparing the above two methods comprehensively, the traditional biological method alone cannot meet the treatment requirements, and the physical and chemical method alone is too costly and economically unfeasible. Therefore, combined with the characteristics of leachate treatment of small urban landfills, the effective way to solve the problem of leachate treatment is to properly improve the existing biological methods and then organically combine them with appropriate physical and chemical methods.

Contents of the invention

The purpose of the present invention is to provide a method with simple process, convenient management and maintenance, long-term stable and reliable treatment effect, moderate construction and operation costs, and suitable for leachate treatment of small urban domestic garbage landfills.

The leachate treatment method of urban small domestic waste landfills of the present invention comprises the following steps:

(1) After the landfill leachate is adjusted in water volume and homogenized in the storage tank, it is transported to the anaerobic tank equipped with an underwater thruster for anaerobic treatment;

(2) The leachate after anaerobic treatment enters the two-stage SBR system composed of SBRⅠtank and SBRⅡtank connected in series. The SBRⅠtank mainly performs COD removal treatment, including four operation stages, which are restricted aeration water inflow, aeration During the gas, sedimentation and effluent stages, the SBR Ⅱ tank mainly performs denitrification treatment, including six operation stages, which are unrestricted water inflow, first aeration, methanol anoxic stirring, second aeration, precipitation and Water stage;

(3) The leachate treated by the secondary SBR is transported to the coagulation and sedimentation tank after the water volume is adjusted in the intermediate tank, and the coagulation and sedimentation agent is added for coagulation and sedimentation treatment;

(4) The sludge discharged from the secondary SBR system and the coagulation sedimentation tank enters the sludge concentration tank for concentration, the supernatant is discharged to the anaerobic tank, and the concentrated sludge is backfilled to the landfill.

The anaerobic pond described in the above step (1) can be a rectangular pond, and the underwater flowmaker is installed at the opposite corner of the rectangular pond.

The coagulation and sedimentation agent can be polyaluminum chloride and polyacrylamide, and the mass ratio of polyaluminum chloride and polyacrylamide is 30-50:1.

In order to improve the uniform mixing effect of leachate and chemicals, it is better to use a swirl coagulation sedimentation tank for the coagulation sedimentation tank.

The process flow of the invention is as follows: the landfill leachate is pumped into the storage tank through the water collection well, and then enters the anaerobic tank through the pipeline distributor through the lifting pump to remove part of the COD and improve the biochemical property. The effluent from the anaerobic tank enters the secondary SBR system to achieve the purpose of denitrification while further removing COD. The effluent of the secondary SBR system enters the intermediate pool, and the intermediate pool water together with the coagulation and sedimentation agent is lifted to the coagulation and sedimentation tank for advanced treatment. After coagulation and sedimentation treatment, the effluent enters the urban pipe network. The sludge discharged from the secondary SBR system and coagulation sedimentation tank enters the sludge thickening tank by gravity for treatment. After the sludge is concentrated, the supernatant is discharged to the anaerobic tank for further treatment, and the remaining sludge is backfilled after pressure filtration. Landfill to avoid secondary pollution.

The advantages of the leachate treatment method of small-scale domestic waste landfills in cities and towns according to the present invention:

1. The process is simple, easy to manage and maintain, and the infrastructure and operating costs are moderate, suitable for the treatment of leachate from small urban domestic waste landfills.

2. Good effluent quality: except for COD, BOD ₅ , NH ₄ ⁺ -N, TN, TP, SS, and chromaticity can all meet the requirements in Table 2 of "Standards for Pollution Control of Domestic Waste Landfill Sites" (GB16887-2008).

3. While the two-stage SBR has the advantages of the traditional single-stage SBR, the mixed sludge system in the single-stage SBR is divided into a dual-sludge system that mainly removes COD bacteria and mainly plays a role in denitrification. . In this way, the two sludge systems can operate efficiently under their respective optimal conditions, and solve the problems of the contradiction of sludge age, organic matter concentration and nitrification in the single-stage SBR sludge system.

Description of drawings

Figure 1 is a process flow chart of the leachate treatment method for small-scale domestic waste landfills in cities and towns

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing and example.

Example

Taking the leachate treatment process of a county-level domestic waste landfill as an example, the amount of landfill waste in this landfill is about 100 tons per day, and the leachate output is about 60 tons per day. Before the landfill leachate is treated, the COD peak value reaches 50,000 mg/L, and the ammonia nitrogen peak value reaches 2,000 mg/L.

As shown in Figure 1, the landfill leachate first enters the storage tank, and the effective volume of the storage tank is about 5000m ³ . The adjustment storage tank mainly plays the role of adjusting the leachate water volume and uniform water quality. At the same time, under the anaerobic action of the adjustment storage tank, the COD removal rate is 10% to 15%.

Then the leachate enters the rectangular anaerobic tank through the lift pump through the pipeline distributor. An underwater pusher is installed at the opposite corner of the rectangular anaerobic tank, and the bottom water is used to make the water flow rise slowly, forming a good environment for anaerobic biological reproduction. At the same time, the underwater pusher set in the anaerobic tank is Muddy water has a better stirring effect. The effective pool volume of the anaerobic pool is 320m ³ , and the water retention time is 128h. After the leachate passes through the anaerobic tank, the COD removal rate is 20% to 30%, and the BOD ₅ /COD increases from about 0.4 to about 0.5.

The effluent from the anaerobic tank enters the SBRⅠpool. The effective volume of the SBRⅠpool is 192m ³ , the sludge concentration in the pool is about 5g/L, and the sludge age is about 10d. The way of restricting aeration is used to enter water to achieve a certain denitrification and denitrification effect, and the water intake time is 1h. After the water intake is completed, aeration is performed by the microporous aerator. When the COD is degraded to a lower level, nitrification gradually dominates, and because the nitrification reaction will consume a large amount of alkalinity, the pH will show an obvious downward trend. Therefore, the change of pH is used to control the nitrification reaction. When the pH shows a significant downward trend, the aeration is stopped to prevent the further progress of the nitrification reaction. After being treated in the SBR Ⅰ pool, the COD removal rate of the leachate is 40% to 60%, and the conversion rate of ammonia nitrogen is about 10% to 20%.

After the SBRⅠpool settles for 1 hour, the supernatant is discharged to the SBRⅡpool, which is the water inflow of the SBRⅡpool. The effective pool capacity of the SBRⅡ pool is 160m ³ , the sludge concentration in the pool is about 5g/L, and the sludge age is about 25 days. The water is fed in an unrestricted aeration method, and the water feeding time is 1h. After the water inflow is completed, the first aeration is carried out. When the ammonia nitrogen is basically converted, the consumption of oxygen by microorganisms will be greatly reduced, resulting in a significant increase in dissolved oxygen in water. In addition, when the nitrification reaction is over, the alkalinity consumption will also be significantly reduced, showing that the pH stops falling and remains within a certain range. Therefore, the nitrification reaction can be controlled by the change of dissolved oxygen and pH. Therefore, when the dissolved oxygen in the SBRⅡ tank shows a sharp upward trend and the pH value drops to a stable value, stop the first aeration. Then turn on the submersible mixer in the SBRⅡ pool, and add methanol as the denitrification carbon source. The amount of methanol added is 3 times the total amount of nitrate and nitrite in the water. Alkalinity will be generated during denitrification, so the time of denitrification stirring can be controlled by pH change. Therefore, when the pH rises to a stable value, it means that the denitrification has been basically completed. At this time, the stirring is stopped and the aeration is turned on again to blow off the nitrogen generated by denitrification in the floating sludge to make the sludge settle. Finally, the second aeration is stopped, and the SBRⅡ pool enters the sedimentation stage. After the leachate is treated by the SBRⅡ pool, the ammonia nitrogen is reduced to below 25mg/L, and the total nitrogen is below 40mg/L.

The above two-stage SBR system not only has the advantages of traditional single-stage SBR, but also divides the mixed sludge system in single-stage SBR into a dual-sludge system that mainly removes COD bacteria and mainly plays a role in denitrification. . The two sludge systems can operate efficiently under their respective optimal conditions, and solve the problems of the contradiction of sludge age, organic matter concentration and nitrification in the single-stage SBR sludge system.

The output water from the secondary SBR system enters the intermediate pool, the volume of which is 120m ³ . The intermediate pool water together with the coagulation and sedimentation agent enters the cyclone coagulation sedimentation tank. The diameter of the tank is 3m, the effective height is 7m, the effective volume is 25m ³ , and the hydraulic retention time is 2h. The medicaments for coagulation and sedimentation are polyaluminum chloride and polyacrylamide, the preparation concentrations are 10% and 0.5% respectively, and the use concentrations are 30mg/L and 1mg/L respectively. In the coagulation sedimentation tank, the leachate passes through the special water distribution holes in the tank to form a vortex in the tank, which promotes the uniform mixing of the dosing agent (polyaluminum chloride and polyacrylamide) and the leachate to achieve the purpose of coagulation. At the same time, under the action of the centripetal force formed by the eddy current, the large particles of impurities contained in the leachate collide with each other, agglomerate into a large volume of mixed solid sediment, and then capture and entrain some small particles of suspended matter to form floc precipitation. After coagulation and sedimentation treatment, the removal rate of suspended solids is about 90%, the effluent SS<30mg/L; the COD removal rate is 20%-50%, the effluent COD<500mg/L; the total phosphorus removal rate is 60%-80% , the effluent TP<3mg/L; the chroma removal rate is about 50%, and the chroma is less than 15 times.

After the leachate is treated by the above process, except for COD, other indicators, such as BOD ₅ , NH ₄ ⁺ -N, TN, TP, SS, and chromaticity can all meet the "Standards for Pollution Control of Domestic Waste Landfill Sites" (GB16887-2008 ) Table II requirements.

The specific treatment effect of this process is as follows

project water ingress out of water COD(mg/L) 5000～20000 ≤500 _BOD5 (mg/L) 2000～10000 ≤30 NH ₄ ⁺ -N (mg/L) 800～2000 ≤25 TN(mg/L) 1000～2500 ≤40 TP (mg/L) 10～20 ≤3 SS(mg/L) 600～1000 ≤30 Chromaticity (times) 60～100 ≤15 pH 6～9 6～9

Claims (4)

1. leachate treatment method for small town household refuse landfill sites is characterized in that may further comprise the steps:

(1) percolate carry out in storage pond that the water yield is regulated and the water quality homogenize after, be transported in the anaerobic pond that impeller under water is housed and carry out anaerobic treatment;

(2) percolate after the anaerobic treatment enters the secondary SBR system that is composed in series by SBRI pond and SBRII pond, the SBRI pond is mainly carried out the removal of COD and is handled, comprise four operation phase, be followed successively by restricted aeration water inlet, aeration, precipitation and water outlet stage, denitrogenation processing is mainly carried out in the SBRII pond, comprise six operation phase, be followed successively by the unlimited aeration mode intake, for the first time aeration, add methyl alcohol anoxia stirring, aeration, precipitation and water outlet stage for the second time;

(3) be transported to the coagulating sedimentation jar behind the middle pond of the percolate process regulating pondage after secondary SBR handles, add the coagulating sedimentation medicament and carry out the coagulating sedimentation processing;

(4) mud of discharging from secondary SBR system and coagulating sedimentation jar enters sludge thickener and concentrates, and supernatant liquor drains into anaerobic pond, and thickened sludge is backfilled to landfill yard.

2. leachate treatment method for small town household refuse landfill sites according to claim 1 is characterized in that: the anaerobic pond described in the step (1) is rectangular-shaped pond, and impeller is installed in the diagonal angle of rectangle form pool under water.

3. leachate treatment method for small town household refuse landfill sites according to claim 1 is characterized in that: described coagulating sedimentation medicament is polymerize aluminum chloride and polyacrylamide, and the mass ratio of polymerize aluminum chloride and polyacrylamide is 30～50: 1.

4. leachate treatment method for small town household refuse landfill sites according to claim 1 is characterized in that: the coagulating sedimentation jar is a whirlwind-type coagulating sedimentation jar.

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