Landfill leachate

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Landfill leachate mainly comes from landfills and incineration plants. However, with the development of garbage classification, biogas slurry after anaerobic fermentation of wet garbage and wastewater from garbage transfer stations has also become one of the primary sources of landfill leachate. The water quality of leachate is very complex, contains high concentrations of pollutants, and is challenging to treat. With the continuous development of various technologies, leachate treatment technology has formed a diversified situation.

Table of contents（Click to go to where you want to see）

6.1. Coagulation-flotation pretreatment landfill leachate pretreatment ( Our company’s main products and cases)

6.2 biological methods

6.2.1 Aerobic biological treatment

6.2.2 Anaerobic biological treatment system

6.3 Physical and chemical method

6.3.1 Dismissal method

6.3.2 coagulation sedimentation method

6.3.3 advanced oxidation method

6.3.4 Nanofiltration technology

6.3.5 reverse osmosis

6.4 Land disposal

6.4.1 Leachate recharge

6.4.2 Constructed Wetland Method

What is landfill leachate?

Landfill leachate refers to the water produced by the decomposition of organic matter in the garbage during the landfill and stacking process, as well as the free water in the trash, precipitation, and infiltrated groundwater, and is sewage formed through leaching.

The amount of leachate produced is affected by many factors, such as precipitation, evaporation, ground loss, groundwater infiltration, garbage characteristics, underground structures, surface covering soil, underlying drainage facilities, etc. The calculation methods for leachate production include the water balance, empirical formula, and empirical statistics.

As a water-soluble component, the properties of landfill leachate have been understood. The COD and BOD values of leachate are very high, and it contains a large amount of organic matter, nitrogen, phosphorus, heavy metals, etc., with high concentration and deep color. Landfill leachate will cause severe environmental pollution to surrounding groundwater and surface water. Many groundwater pollution incidents in landfills indicate that leachate is the most important source of groundwater pollution. Leachate contains many toxic substances, and the concentration is high, becoming a massive environmental threat. The leachate is completely discharged into rivers and lakes without treatment. The organic and inorganic pollutants in it will pollute aquatic life and crops. , and cause harm to human health through the food chain and ecological environment.

Therefore, landfill leachate must be effectively treated to minimize its environmental impact. However, due to the complexity of its properties, the treatment of landfill leachate has become one of the more challenging scientific problems in the world.

Source of landfill leachate

The sources of landfill leachate mainly include the following aspects:

1. Rainwater infiltration.
Silt landfill is related to the amount of precipitation. Part of the precipitation flows out, part of it flows out of the landfill, and part of it leaks out of the leachate. Leachate accounts for most of the mainstream water formed during the landfill process. The amount of sludge buried in areas with high precipitation is also more significant for landfills.

2. Surface runoff.
Wastewater generated on the landfill surface affects its permeability. The topography of the fill, vegetation conditions, soil type, permeability, and drainage facilities all impact surface runoff.

3. Surface irrigation.
Surface irrigation water affects the formation of leachate treatment systems and is related to the type of soil and vegetation surrounding the landfill.

4. Groundwater in the site.
If the filling depth is small, groundwater may penetrate the landfill. The contact time of leachate and the landfill's topographic conditions will affect the filter's formation. If landfill filtration measures are used, leachate infiltration can be reduced.

5. The garbage contains some moisture

which may come from the trash, rain, or the atmosphere. The water produced during the waste degradation process is also one of the main components of landfill leachate. The composition of the waste products, pH value, temperature, bacteria, and other factors may affect the properties of landfill leachate.

What are the characteristics of landfill leachate water quality?

The composition of landfill leachate is affected by living standards, collection methods, regions, and climate, but in general, landfill leachate mainly has the following characteristics:

The concentration of organic pollutants is high, with COD and BOD5 reaching tens of thousands of mg per liter;
The ingredients are complex, and the heavy metal ions and toxic organic matter in them will have a poisonous and inhibitory effect on microorganisms;
The ammonia nitrogen content is high, up to several thousand to tens of thousands of mg per liter, which seriously inhibits and reduces the activity of microorganisms in biological treatment;
The C/N ratio is imbalanced and phosphorus is lacking;
Water quality changes with landfill time and stability. Water quality changes considerably. As the age of the landfill increases, the biodegradability of landfill leachate shows a decreasing trend.

What are the water quality characteristics of different landfill leachates?

Landfill leachate

Landfill leachate originates from landfill areas, garbage storage pits of garbage incineration plants, and garbage compression transfer stations. It has complex and changeable water quality components, high organic matter concentration, high ammonia nitrogen concentration, high color, high conductivity, and contains Polycyclic aromatic hydrocarbons (PAHs), adsorbable organic halides (AOXs), polychlorinated biphenyls (PCBs) and other toxic substances have common characteristics. However, due to different sources of landfill leachate, its water quality characteristics are not entirely consistent.
Domestic waste landfill leachate

The water quality of landfill leachate is complex and rich in organic matter, ammonia, nitrogen, and heavy metals, and the proportion of nutrients is unbalanced. It is easy to change with changes in landfill scale, regulatory reservoir volume, landfill age, season, and weather.

Generally speaking, the concentration of pollutants in the same landfill is higher in the dry season than in the rainy season, and the concentration difference can be 2 to 3 times. The ammonia nitrogen concentration and biodegradability of landfills change irreversibly with the service life of the landfill, which is mainly reflected in the increase in ammonia nitrogen concentration and the decrease in biodegradability. The ammonia nitrogen concentration will gradually increase from 800 to 1500mg/L in the early stage of the landfill to 2000 to 3000mg/L, and even as high as 4000mg/L in some landfills, while the BOD/COD of the leachate will drop from 0.5 to 0.6 in the early stage to 0.1 ~0.2.
Domestic waste incineration plant leachate

Domestic waste contains a large amount of kitchen waste. To increase the calorific value of the waste entering the incinerator, fresh domestic waste will be placed in the garbage storage pit for 3 to 7 days. After fermentation and maturation, the moisture in the waste will be filtered out before entering the incinerator. Carry out burning.

The amount of leachate produced in a waste incineration plant is greatly affected by the composition of the waste and is usually 10% to 25% of the daily treatment scale. The leachate of domestic waste incineration power plants is fresh garbage leachate. Its water quality is relatively stable, and its organic pollution load is high, up to 70,000 mg/L. It has good biodegradability, with a BOD/COD of 0.5 to 0.6; the ammonia nitrogen concentration is generally 800 ~1500 mg/L; chloride ion concentration is approximately 3500 mg/L.
Ash landfill leachate

The water quality characteristics of this type of leachate are pretty different from those of domestic waste landfills and incineration plants. The pollutants of concern are mainly heavy metals, ammonia, nitrogen, and inorganic salts. Affected by the ignition rate of incineration, there will be a specific concentration of COD in the leachate, but the concentration is much lower than that in domestic waste landfills, the biodegradability is poor, and the water quality does not change much with age of the landfill. However, if membrane concentrate is used to cool the ash and prepare lime slurry in the incineration plant, the COD concentration of the ash leachate will be high. Under normal circumstances, the concentration of heavy metals such as mercury, copper, zinc, lead, cadmium, beryllium, barium, nickel, arsenic, total chromium, hexavalent chromium, selenium, and other heavy metals is lower than the leaching concentration limit specified by the standard. Still, in acid rain areas and fly ash stabilization, sites that are not cured in place will have problems with excessive heavy metals. Leachate from ash landfills is mainly treated through physical and chemical methods, and the process route should be determined based on actual monitoring of water quality.

Comparison table of typical water quality of various types of leachate

Typical water quality of various types of leachate
leachate	COD/g·L⁻¹	BOD/g·L⁻¹	Ammonia nitrogen/g·L⁻¹	Total nitrogen/g·L⁻¹	TP/mg·L⁻¹	Cl⁻/g·L⁻¹	pH
Domestic waste landfill leachate	10~25	5~8	1.5~3.5	1.8~4.0	15	-	6~8
Domestic waste incineration plant leachate	40~70	30~4.	0.8~1.5	1.0~2.0	80~150	3.5	6~8
Fly ash landfill leachate	0.5~2.0	0.1~0.3	0.1~0.15	0.12~0.2	-	15~50	7~10

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What are the domestic and international discharge standards for landfill leachate?

The following table lists the leachate discharge standards in different countries and regions. Compared with other countries and regions, my country's landfill leachate treatment standards are more stringent, mainly reflected in CODCr, TN and TP discharge concentrations, of which the TN indicator is 40 mg. /L is significantly lower than that of Germany, the United Kingdom and Japan.

According to the overall requirements of the central environmental protection inspection in 2016~2017, landfills and incineration plants in my country need to process leachate themselves or combine it, and the effluent must meet the "Pollution Control Standard for Domestic Waste Landfills" (GB16889-2008). After treatment, the effluent indicators CODCr, BOD5, TN, and TP are not higher than 100, 30, 40, and 3 mg/L, and the emission standards are raised from the management standard of COD ≤ 500 mg/L to the control standard of COD < 100 mg/L. As our country's ecological civilization construction and environmental protection policies become increasingly strict, various places have put forward higher requirements for sewage discharge, and even require all wastewater to be reused to achieve the goal of zero discharge.

Leachate discharge standards of different countries and regions mg/L
Emission Standards	CODCr	BOD5	SS	TN	TP
China	100	30	30	40	3.0
European Union	125	25	35	15	2.0
France	120	30	-	30	-
Germany	200	20	-	70	3
U.K.	50	10	-	75	-
Japan	120	120	150	120	8
Singapore	100	50	50	-	-

Landfill leachate treatment process

Coagulation-flotation pretreatment landfill leachate pretreatment(Our company’s main products and cases)

The treatment methods of landfill leachate mainly adopt advanced treatment technologies such as biological, physical, chemical, and land treatment methods. Although there is a specific treatment effect, due to the significant investment in treatment facilities and high operating costs, many landfills are still unable to build treatment systems to ensure that leachate is discharged up to standard. In recent years, some scholars have proposed a process that combines chemical and biological methods, and some experts have suggested a multi-stage treatment process that incorporates biological methods (activated sludge method and biofilm method) with physical methods and has achieved good results.

Research results also show that coagulation, as a physical and chemical treatment method, can effectively reduce suspended solids, color, heavy metal ions, and COD in leachate and reduce subsequent treatment costs;

The air flotation method is also widely used in sewage treatment to reduce COD and SS, improve the biodegradability of leachate, and ensure the operation of subsequent processes, thereby truly realizing the sanitary landfill of domestic waste.

Coagulation-flotation treatment effect

Coagulation-air flotation treatment has a good pretreatment effect on domestic waste leachate. Under optimized conditions, the removal rates of COD and BOD5 in landfill leachate reached 81.9% and 73.3%, respectively, and the effluent concentration complied with the third-level standard in 5 Domestic Waste Landfill Pollution Control Standard . It is a practical method for pretreatment of landfill leachate.
The ratio of BOD5/COD is called the biodegradability index, which is often used as a criterion for judging whether sewage is suitable for biological treatment. Generally speaking, sewage with a BOD5/COD ratio greater than 0.3 is biodegradable and should be treated biologically; when BOD5/COD is less than 0.25, biochemical treatment should not be used, but physical and chemical methods should be used; when BOD5/COD is between At 01 25 ~ 013 hours, it isn't accessible to biochemical treatment. The coagulation-air flotation treatment increased landfill leachate's BOD5/COD ratio from 0.26 to 0.40, completing the transformation from difficult to suitable for biological treatment and laying a good foundation for subsequent treatment.

Application case(Preprocessing-physical method)

Case Studies-Landfill Leachate Treatment

This case study introduces how the Taizhou Jiangyan Biochemical Treatment Center Project uses our factory's high-efficiency dissolved air flotation to Reduce the content of organic matter and suspended solids in landfill leachate. After air flotation pretreatment, the concentration removal rate of suspended solids reaches more than 90%, and the grease removal rate reaches more than 95%, significantly reducing the burden of subsequent biochemical treatment.

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Biological methods

Aerobic biological treatment

The forms of microorganisms in the aerobic biological treatment system can be divided into two parts: suspended growth and attached growth. The suspended growth system includes aerobic ponds, the traditional activated sludge method, and the SBR method; the attached growth system mainly includes moving bed biofilm—reactor (MBBR).

①Aerobic pond is an effective and low-cost treatment method for pathogens, organic matter, and inorganic matter in leachate. Its operation and maintenance costs are low and suitable for developing countries. MEHMOOD et al. used an aerobic pond to remove COD and ammonia nitrogen by more than 75% and 80%, respectively, when the leachate COD concentration was 1 740 mg/L and the ammonia nitrogen concentration was 1 241 mg/L.

② The traditional activated sludge method is widely used to treat municipal sewage or sewage and leachate mixture. Although the conventional activated sludge method can effectively remove organic carbon, nutrients, and ammonia nitrogen, it is directly used to treat landfill leachate, and the activity The sludge method still has certain limitations, including insufficient sludge stability, requiring a long aerobic time; high energy consumption and sizeable residual sludge production; high concentration of ammonia nitrogen in the leachate has a strong inhibitory effect on microorganisms, etc.

③Aerobic SBR method The SBR system considers both organic carbon oxidation and nitrification and denitrification. This process is widely used for leachate treatment. Studies have shown that the COD treatment efficiency of SBR can reach more than 75%, and the ammonia nitrogen treatment effect can reach 99%. Because the SBR process has excellent flexibility, it is very suitable for treating wastewater such as landfill leachate, which has significant water quality and quantity changes.

The MBBR method attached to the growth system will not cause the loss of active biomass. At the same time, compared with the suspended growth system, low temperature has less impact on nitrification in the attached growth system. The system has a higher sludge concentration, a short settling time, and is toxic. It. has strong material tolerance and can simultaneously remove organic matter and ammonia nitrogen. PICULELL et al. used the MBBR process to achieve an ammonia nitrogen removal efficiency of more than 90%, while the COD removal rate could reach 20%. Some studies have also shown that using granular activated carbon as a carrier can promote biodegradation. HORAN et al.’s research shows that using the MBBR + activated carbon combination process can achieve an ammonia nitrogen removal rate of 85% to 90%. In comparison, the COD removal rate can reach 60% to 81%.

Anaerobic biological treatment system

Anaerobic biological treatment processes can also be divided into suspended and attached growth systems. Compared with aerobic biological treatment, anaerobic biological treatment consumes less energy and leaves less sludge after reaction, but the reaction rate is lower.

① Anaerobic SBR method UYGUR et al. [18] used the anaerobic SBR method to achieve COD, ammonia nitrogen, and phosphate removal rates of 62%, 31%, and 19%, respectively. At the same time, under the action of methanogens and denitrifying bacteria, the reduction of organic components is achieved, thereby simultaneously removing organic matter and ammonia nitrogen.

②UASB method is a typical anaerobic treatment process with high efficiency and short hydraulic retention time. Studies have shown that when the COD concentration of leachate is 45 000 mg/L, after passing through the UASB reactor, the COD concentration drops to 3 000 mg/L, and the removal rate reaches 93%.

③ Anaerobic filter HENRY et al. research shows that when the COD load is 1.26~1.45 kg/m3·d, the anaerobic filter can achieve a COD removal rate of 90%. The total gas production is 400-500 L/kgCOD, of which methane content accounts for 75%-85%.

Physical and chemical method

Dismissal method

The stripping method is very effective for high concentrations of ammonia nitrogen in leachate. Studies have shown that when the surface loads of ammonia nitrogen reach 650, 750, and 850 kg/hm2·d respectively, and the hydraulic retention times are 51.2, 64.9, and 55.6 d respectively, the ammonia nitrogen removal rates exceed 99%, reaching 99.0%, 99.3%, and 99.3% respectively. 99.5%, and the total COD removal rates were 69.2%, 40.1%, and 29.3%, respectively.

coagulation sedimentation method

The coagulation sedimentation method has been successfully used to treat old landfill leachate. This method is suitable for the pretreatment of biological and reverse osmosis methods or for advanced treatment to remove non-biodegradable organic particles. Commonly used coagulants include aluminum sulfate, ferrous sulfate, ferric chloride, etc.

ZOUBOULIS et al. used the coagulation precipitation method to reduce the humic acid concentration in the leachate. When the coagulant dosage was 20 mg/L, the humic acid removal rate reached 85%. However, the coagulation sedimentation method also has disadvantages, including increasing sludge production and the concentration of aluminum and iron salts in the liquid phase.

advanced oxidation method

More and more studies are using advanced oxidation methods to treat landfill leachate. Most use strong oxidants in combination, such as (O3 and H2O2); use techniques such as ultraviolet irradiation and ultrasound or catalysts (such as transition metals or photocatalysts). ), stimulate the generation of free radicals, degrade refractory groups in landfill leachate, and improve the biodegradability of leachate.

It has been reported that the removal efficiency of organic matter in leachate treated with O3/H2O2 method can be as high as 90%; after H2O2/UV pretreatment, the BOD5/COD of leachate is increased from 0.1 to 0.45 [26]; the optical Fenton method can increase the initial The landfill leachate with a COD concentration of 8300 mg/L reached a treatment efficiency of 70% after one h of treatment. The dosage of Fe2+ was ten mg/L [27]. The main factors affecting the cost of advanced oxidation treatment are main factors affecting the cost of advanced oxidation treatment are the manufacturing cost and power consumption of ozone generators, UV lamps, and other equip.

Nanofiltration technology

The nanofiltration method can remove organic and inorganic substances in leachate and some micro-pollutants in water to meet the requirements of multiple water quality indicators. Regardless of the membrane material and its geometric properties, when the average flow velocity is three m/s and the pressure difference across the membrane is between 6 and 30 bar, nearly 70% of the COD and 50% of the ammonia nitrogen can be removed by nanofiltration.

Reverse osmosis

Among new methods for leachate treatment, reverse osmosis is a method with good application prospects. In the past few years, reverse osmosis has shown sound treatment effects in laboratories and engineering applications. Landfill leachate is treated through reverse osmosis, and the removal efficiency of COD and heavy metals can be as high as 98%.

Land disposal

The main land treatment methods are leachate recharge, constructed wetlands, etc.

Leachate recharge

The recirculation method is my country's most widely used and lowest-cost method for treating membrane concentrates. It uses surface irrigation, well injection, surface spraying, etc., to return the focus to the garbage pile using its physical and chemical properties. , biological action, filtering, adsorbing, and degrading organic pollutants in concentrated liquid. A focused solution recirculation experiment was carried out for garbage columns with different landfill ages. The experimental time was 24 days. The results showed that the garbage column with a landfill age of 1 year had a strong removal effect on nitrate nitrogen, reaching 88%, but The concentrations of total organic carbon and NH3-N are relatively high; the garbage column that has been landfilled for 15 years has been mineralized and has the best removal effect on heavy metals, COD, NH3-N, and salt.

Constructed Wetland Method

SILVERSTRINI et al. achieved average COD, ammonia nitrogen, and total nitrogen removal rates of 52%, 75%, and 48% in constructed wetlands planted with T. domingens, respectively; MEKY et al. investigated the impact of constructed wetland systems with and without plants on landfill seepage. The removal efficiency of COD, nutrients, and heavy metals in the filtrate showed that after planting plants, the total COD removal rate was 74.19%, respectively; the removal efficiencies of total nitrogen, total Kjeldahl nitrogen, and ammonia nitrogen were 48.78%, 49.34%, and 61.79% respectively. ; The removal rates of Cu2+, Mn2+, Zn2+, Ni2+, Pb2+, and Cd2+ are 94.23%, 92.17%, 88.08%, 74.22%, 81.44%, and 64.55% respectively.

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