CN101618922A - Method for processing landfill percolate - Google Patents

Abstract

A method for treating landfill leachate in the technical field of wastewater treatment: step 1, passing the landfill leachate through an iron filings layer, and filtering; step 2, passing the filtrate obtained in step 1 through a mineralized garbage layer and a gravel layer in sequence, Filtration; step 3, then passing the filtrate obtained in step 2 through the mineralized garbage layer and the gravel layer successively, and filtering to obtain purified water. In the present invention, Fe and part of the carbon in the mineralized garbage are combined to form internal electrolysis, and the generated Fe ²⁺ is used as the catalyst and microbial flocculant required by the subsequent mineralized garbage biological reaction bed to strengthen the biological reaction of the mineralized garbage, and finally Reduce the COD _Cr and ammonia nitrogen of the leachate, and reduce the treatment cost on the basis of solving the discharge of the leachate tail water up to the standard.

Description

Treatment methods of landfill leachate

technical field

The invention relates to a treatment method in the technical field of wastewater treatment, in particular to a treatment method for landfill leachate.

Background technique

The volume of urban domestic waste removal and transportation in my country is increasing at an average annual rate of more than 8%. The annual output of leachate from controlled point source discharge of domestic waste is about 29 million tons, and the concentration of pollutants contained in 1 ton of leachate is equivalent to 100 tons of urban Concentration of sewage. Due to the characteristics of high toxicity, complex water quality, large fluctuation of water volume, high concentration of organic matter and ammonia nitrogen, and imbalance of nutrient elements, leachate still has great problems. At present, some leachate in our country is directly discharged without any treatment, which has caused serious pollution to the surrounding environment.

As a necessary process for landfill leachate treatment, biological treatment has been widely used in leachate treatment. Generally, landfills will adopt the treatment process of regulating pond-anaerobic pond-facultative pond, but the COD of the effluent is still at 3000~5000mg/L, ammonia nitrogen effluent is about 100~1000mg/L, and after subsequent conventional aerobic treatment, its COD and ammonia nitrogen are still as high as 500~2000mg·L ^-1 and 100~500mg·L ^-1 respectively, These residual leachates contain a variety of non-biodegradable organic substances, a large amount of inorganic salts, and complex complexes and chelates. The water quality index can only be close to or reach the national leachate collection standard (COD<1000mg/L), and it is often necessary to use physical and chemical treatment processes for advanced treatment, so that it is possible to meet the current general requirements of "Pollution Control of Domestic Waste Landfill Sites" Standard GB 16887-1997 "secondary standard, but some advanced treatment technologies commonly used at present, such as: reverse osmosis, activated carbon adsorption, Fenton (Fenton) oxidation, electrolytic treatment, etc., due to high processing costs and complicated operations, are not large Suitable for the current situation of large-scale treatment of leachate.

After many years of research on landfill stabilization, the applicant found that after several years of landfill closure (generally 8 to 10 years in the southern region), the easily degradable substances in the garbage are completely or nearly completely degraded, and the surface of the landfill is subsiding at this time. The amount is very small (such as less than 1cm/a), the garbage itself has little or no leachate and landfill gas, the biodegradable content (BDM) in the garbage is small (such as <2.55%), and the COD concentration of the leachate is low , The landfill reaches a stable state, that is, a harmless state. At this time, the odor of the decomposed waste is reduced, and it is easy to sieve naturally. The fine materials (Φ≤100mm) are similar to humus in appearance, in the form of micro-aggregates, loose in texture, have numerous extremely micro-pores and huge surface area, and are rich in organic matter, have good permeability and high cation exchange capacity. Due to the special formation process, there are a wide variety of microbial communities with strong adaptability and various active enzymes, which have an innate affinity for refractory organic substances such as cellulose, lignin, and polycyclic aromatic hydrocarbons. and degradation ability, so it is very suitable for use as an excellent and efficient sewage purification substrate.

At the same time, internal electrolysis treatment can effectively change the structure and form of some refractory substances in sewage, thereby improving the biodegradability of wastewater. Internal electrolysis generally uses iron scraps (mostly cast iron scraps) and some other substances (such as C, zeolite, etc.) to form a reaction system. When the cast iron is submerged in the wastewater solution, thousands of small micro-battery circuits are formed. The pure iron is the anode, and the carbide and impurities become the cathode. Internal electrolytic reaction occurs to form a microscopic primary battery inside the iron. At the same time, inert materials such as carbon (graphite, coke, activated carbon, coal, etc.) are in contact with iron filings to form a macroscopic primary battery. During the reaction process of the primary battery, the products generated by the electrode reaction have high chemical activity. In a neutral or acidic environment, the cast iron electrode itself and the new ecology [H] and Fe ²⁺ produced by it can be mixed with the waste water. Certain organic components undergo redox reactions, which split macromolecular substances into small molecules, convert refractory groups into easily degradable groups, and improve the biodegradability of wastewater. Therefore, in general, the internal electrolysis of iron filings is a good treatment unit that integrates redox, flocculation adsorption, catalytic oxidation, complexation, electrodeposition, and co-precipitation, and can improve biodegradability. However, in the process of leachate treatment by mineralized waste bioreactor bed, due to factors such as large area and serious temperature influence, its promotion process is limited to a certain extent. However, during the internal electrolysis reaction process, the investment cost of activated carbon is relatively high, especially the hardening problem of internal electrolysis, which seriously affects its further utilization.

It is found through document retrieval of the prior art that the Chinese patent authorization announcement number is CN1120131C (announcement date: 2003.9.3) patent specification discloses the following content: use landfill stabilized garbage or mineralized garbage to form a bioreactor bed, and then Use the pump to spray the garbage percolation water on the mineralized garbage in the reaction bed through the water distributor. The percolation water achieves the purification effect through the adsorption and degradation of the mineralized garbage, which partially solves the problem of substandard leachate treatment. The technical problems to be solved by the present invention are: the removal effect of refractory substances is poor, and the cost of treatment after purification of landfill leachate is relatively high.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a treatment method for landfill leachate. In the present invention, Fe and part of the carbon in the mineralized garbage are combined to form internal electrolysis, and the generated Fe ²⁺ is used as the catalyst and microbial flocculant required by the subsequent mineralized garbage biological reaction bed to strengthen the biological reaction of the mineralized garbage, and finally Reduce the COD _Cr and ammonia nitrogen of the leachate, and reduce the treatment cost on the basis of solving the discharge of the leachate tail water up to the standard.

The present invention is achieved through the following technical solutions:

The present invention relates to a kind of treatment method of landfill leachate, comprising the following steps:

Step 1, filtering the landfill leachate through the iron filings layer;

In step 2, the filtrate obtained in step 1 is passed through the mineralized garbage layer and the gravel layer successively, and filtered;

In step 3, the filtrate obtained in step 2 is passed through the mineralized garbage layer and the gravel layer successively, and filtered to obtain purified water.

In step 1, the landfill leachate: COD is 700-5000 mg/L, ammonia nitrogen concentration is 100-400 mg/L, SS value<600 mg/L.

In step 1, the iron filings layer, wherein the iron flakes are treated with dilute acid, the dimensions of the iron flakes are: 0<width<1cm, 1<length<5cm.

In step 1, a water-permeable support plate is provided at the bottom of the iron filings layer, and holes with a diameter of 5-10 mm are distributed on the support plate.

In step 2 and step 3, the mineralized waste is the mineralized waste that has been buried for 6-10 years.

In step 2 and step 3, the mineralized waste is: sieved fine material of mineralized waste with 0<particle size<100cm.

In step 2 and step 3, the mineralized waste is: 40<particle size<60mm mineralized waste sieved fine material.

The ratio of the sum of the mass of the mineralized garbage layer in step 2 and step 3 to the mass of the iron filings layer in step 1 is (10-20):1.

In the present invention, iron reduces some pollutants in landfill leachate, destroys the structure of chromophoric and auxochrome groups, and improves the biodegradability of landfill leachate. As the corrosion and oxidation of iron continue to increase, part of the ammonia nitrogen in the leachate may be directly oxidized to nitrogen and removed. The specific reaction is shown in the formula:

6Fe ³⁺ +2NH ₄ ⁺ →6Fe ²⁺ +N ₂ +8H ⁺ ΔG ^Θ ＝-100kJ

Iron can also generate cathode hydrogen through the action of the primary battery as a hydrogen supply source, and promote the bioautotrophic denitrification reaction of nitrate nitrogen. As the metal iron corrosion reaction proceeds, autotrophic denitrifying bacteria continue to grow and reduce nitrate nitrogen.

The overall equation can be expressed with the formula:

5Fe ⁰ +2NO ₃ ^- +6H ₂ O→5Fe ²⁺ +N ₂ +12OH ^- ΔG ^Θ = -1147kJ

In the internal electrolysis reaction system of biological iron, the ferrous ions and ferric ions produced can all precipitate with PO ₄ ^3- , and the strong affinity between Fe ³⁺ and OH ^- and PO ₄ ^3- may cause Generate insoluble complexes such as Fe _2.5 PO ₄ (OH) ₄₅ and Fe _1.5 H ₂ PO ₄ (OH) _3.8 , and the surface of the generated complexes has a strong adsorption effect, so that the bio-iron electrolytic reaction bed The total phosphorus removal efficiency was further improved.

Compared with the prior art, the present invention has the following beneficial effects: in the present invention, Fe and part of the carbon substances in the mineralized waste are combined to form internal electrolysis, and the generated Fe ²⁺ is used as the catalyst required by the subsequent mineralized waste bioreactor bed And microbial flocculants, strengthen the biological reaction of mineralized waste, and finally reduce the COD _Cr and ammonia nitrogen of the leachate, and reduce its treatment cost on the basis of solving the discharge of the leachate tail water up to the standard. At the same time, since the iron layer is mainly located on the upper part of the bed body, it is convenient to add the iron layer after it is lost, and once compaction occurs, it is convenient to remove, dig or update the bed body blockage or dense layer.

Description of drawings

Fig. 1 is the schematic diagram of the treatment device of landfill leachate in the prior art;

Fig. 2 Schematic diagram of the relationship between the COD of the effluent COD in the bio-iron internal electrolysis reaction bed with time;

The schematic diagram of the effect of ammonia nitrogen in the effluent of the bio-iron electrolysis reaction bed in Fig. 3;

Figure 4 Schematic diagram of the COD removal performance of the leachate by the bio-iron internal electrolysis reaction bed;

Fig. 5 Schematic diagram of the removal performance of ammonia nitrogen in the leachate by the bio-iron internal electrolysis reaction bed;

Fig. 6 Schematic diagram of the change trend of COD in the effluent of the bio-iron electrolysis reaction bed;

Fig. 7 Schematic diagram of the change trend of ammonia nitrogen in the effluent of the bio-iron electrolysis reaction bed.

Detailed ways

The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings: this embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following the described embodiment.

Example 1

FIG. 1 is a schematic diagram of a treatment device for landfill leachate in the prior art. Before filtering, each filter layer is filled into a barrel, and then filtered. The landfill leachate passes through the filter layer in the barrel, and is filtered to complete the purification. The specific properties of the landfill leachate in this example are shown in Table 1, and the specific properties of the mineralized waste used to build the bed are shown in Table 2.

Table 1 Influent water quality index (mg/L)

Exterior pH COD _Cr TOC TN NH ₃ -N Conductivity black 7.56 937 146.8 551.5 135.3 10120

Table 2 Basic properties of mineralized waste (landfill age 8 years, sieving particle size ≤ 40mm)

nature Bulk density (g/cm3) Porosity(%) Permeability coefficient (cm/min) Cation exchange capacity (mg equivalent/g dry garbage) Organic matter (g/kg) The total number of bacteria (106/g dry garbage) value 0.75 37.25 2.152 65.4 102.5 7.2

Construct the bio-iron internal electrolysis reaction bed with Fe and mineralized waste (referring to the sum of the mineralized waste mass of each layer in the barrel) with a mass ratio of 1:20; the bottom of the iron filings layer is provided with a water-permeable support plate to support Holes with a diameter of 7mm are distributed on the board; 510g of iron filings layer and 10.2Kg of mineralized waste are mixed evenly and filled into the barrel, and the top is sprayed with landfill leachate (SS value is 590mg/L). The flow enters the electrolytic reaction bed in the bio-iron. After the system has been acclimatized by increasing the concentration gradient of the influent for 30 days, it is operated intermittently, the dry-wet ratio=20:1, the solid-liquid ratio=50:1, and the effluent water quality COD and NH ₃ -N are shown in Figures 2 and 3. It can be seen that the leachate effluent can stably meet the secondary discharge standard (COD<300mg/L, ammonia nitrogen<25mg/L).

Example 2

A PVC column with an inner diameter of 10 cm and a height of 1.0 m was used, and each filter layer was filled therein. Wherein the reaction bed body consists of a 5cm high crushed stone support layer, a main reaction layer (wherein the main reaction layer of the reaction bed is composed of mineralized garbage and corresponding scrap iron chips in a mass ratio of 10:1, and the Fe layer is on top of the mineralized garbage layer at the bottom) and 5cm super high; the bottom of the iron filings layer is provided with a water-permeable support plate, and holes with a diameter of 10mm are distributed on the support plate; the particle size of the mineralized waste is 40-60mm, and it will be buried for 10 years. The scrap iron chips used come from the broken iron pieces cut by the lathe when the alloy steel parts are processed in the metal machinery processing factory. The iron chips are about 4mm wide and 1mm thick and in a curled shape. Before use, soak them in 1% hydrochloric acid for 12 hours to wash off the surface. Oxidized substances, and then rinse with clean water repeatedly.

The properties of landfill leachate (SS value 500mg/L) and mineralized waste used are shown in Table 3 and Table 4, respectively. The operating parameters are a solid-liquid ratio of 100:1, an operating cycle of 3 hours, and a hydraulic load of 0.08m ³ /m ³ of mineralized waste. The reaction results are shown in Figures 4 and 5. The COD removal rate reaches 90% to 96.8%, and the effluent is extremely light yellow to white, which can stably meet the secondary discharge standard. When the reaction bed runs for 20 days, the effluent COD meets the GB16889-1997 primary discharge standard, indicating that its temperature is relatively high During the period, the effect is better and can meet higher emission requirements.

Table 3 Influent Water Quality Index (mg/L)

COD BOD ₅ Chroma pH NH ₃ -N TN TP 1150-4750 195-1619 1200-1800 7.4-8.5 100-400 80.5-2359 1.89-29

Note: Except for pH value and chromaticity, the unit used for the above parameters is mg/L.

Table 4 Basic properties of mineralized waste

Saturated hydraulic permeability coefficient (Ks) Moisture content (%) Organic matter content (%) pH Total nitrogen (g/kg) Total phosphorus (g/kg) Cation exchange capacity (milligram equivalent/100g dry garbage) 0.994 30.5 10.25 7.6 5.19 7.42-7.78 66.7

Example 3

The specific properties of landfill leachate are shown in Table 5.

Table 5 Influent water quality index (mg/L)

COD _Cr pH Conductivity Ammonia nitrogen TOC TN Three grade water 701 7.47 10010 135 398.9 510.8

Note: The unit of conductivity is (μs/cm); pH has no unit, and the other indicators are mg/L.

In this implementation, the quality of the iron filings layer is 510g, and the quality of the mineralized garbage layer (the sum of the mineralized garbage quality of each layer in the barrel body) is 4.65Kg; the size of the iron flakes in the used iron filings is: 0＜wide＜1cm, 1<length<5cm; landfill leachate (SS value 400mg/L) enters the barrel, passes through the iron filings layer, mineralized garbage layer and gravel layer, and flows out from the water outlet; the bottom of the iron filings layer A water-permeable support plate is provided, and holes with a diameter of 5mm are distributed on the support plate; among them, the mineralized waste is the mineralized waste that has been buried for 6 years, and the water flow rate: 10mL/h; the reaction property: continuous reaction. It can be seen from Figure 6 that after being treated by the internal electrolytic reaction bed of biological iron, the COD _Cr of the secondary water can be reduced from 701mg/L to below 300mg/L, reaching the secondary index of the national effluent, reflecting a strong treatment ability. It can be seen from Figure 7 that the treatment effect of mineralized waste on ammonia nitrogen is remarkable, from 135.3mg/L to about 10mg/L. This is because of the nitrification reaction, which converts NH ₃ into NO ^2- , and NO ^3- reduces ammonia nitrogen.

From the above three examples, it can be seen that the internal electrolysis reaction process of biological iron has a good COD and ammonia nitrogen removal ability for the leachate tail water after biological treatment, and its effluent can meet the "National Standard of the People's Republic of China---Household Garbage Filling Buried Pollution Control Standards" (GB16889-1997) standards.

Claims (8)

1, a treatment method for landfill leachate, is characterized in that, comprises the steps: Step 1, filtering the landfill leachate through the iron filings layer; In step 2, the filtrate obtained in step 1 is passed through the mineralized garbage layer and the gravel layer successively, and filtered; In step 3, the filtrate obtained in step 2 is passed through the mineralized garbage layer and the gravel layer successively, and filtered to obtain purified water. 2. The method for treating landfill leachate according to claim 1, wherein in step 1, the landfill leachate: COD is 700-5000 mg/L, ammonia nitrogen concentration is 100-400 mg/L , SS value <600mg/L. 3. The method for treating landfill leachate according to claim 1, characterized in that in step 1, the iron filings layer, wherein the iron flakes are treated with dilute acid, the size of the iron flakes is: 0<width <1cm, 1<length<5cm. 4. The method for treating landfill leachate according to claim 1, characterized in that in step 1, the bottom of the iron filings layer is provided with a water-permeable support plate, and the support plate is distributed with 5-10mm in diameter. hole. 5. The method for treating landfill leachate according to claim 1, characterized in that, in Step 2 and Step 3, the mineralized waste is mineralized waste that has been landfilled for 6-10 years. 6. The method for treating landfill leachate according to claim 1, characterized in that, in step 2 and step 3, the mineralized waste is: 0<particle size<100cm fine mineralized waste sieved . 7. The method for treating landfill leachate according to claim 6, characterized in that, in step 2 and step 3, the mineralized waste is: 40<particle size<60mm fine mineralized waste sieved . 8. The treatment method of landfill leachate according to claim 1, characterized in that the ratio of the sum of the quality of the mineralized garbage layer in step 2 and step 3 to the quality of the iron filings layer in step 1 is (10～ 20): 1.

Images