Leachate is formed when water passes through the waste in the landfill cell. The precipitation can be from rain, melted snow or the waste itself. As the liquid moves through the landfill many organic and inorganic compounds, like heavy metals, are transported in the leachate.1 This moves to the base of the landfill cell and collects.
The amount of leachate produced is directly linked to the amount of precipitation around the landfill.2 The amount of liquid waste in the landfill also affects the quantity of leachate produced. A large landfill site will produce greater amount of leachate than a smaller site.
How the landfill has been constructed determines whether the leachate pollutes groundwater. In landfill sites which have been created recently, liners are present and so this greatly limits the leachate leaking and the only way it will leave the cell is if the liner tears.2
The type of waste material put into the landfill
Landfill conditions include the pH, temperature, moisture, age and climate
Characteristics of precipitation entering the landfill
Leachate is collected at the base of the landfill and instead of being sent away for treatment it is flushed back through the landfill waste many times. This increases the rate at which the waste material decomposes.
Table 1. Pros and cons of leachate recycling3
Pros |
Cons |
Enhances landfill stabilisation because rate of landfill gas production is increased due to increase waste moisture content. |
Increase rate of groundwater pollution if used in a landfill with single-composite-lining. |
Provides a means of leachate disposal. |
|
Reduce volume of municipal solid waste leachates. |
Increases toxicity of leachate by concentrating it. |
However, groundwater pollution is minimal with a double-composite-lined landfill and so recycling is now in practice in some landfill sites.4 Dunbar landfill site recycle their leachates as they have a double-composite-lined landfill. They carefully monitor the groundwater and a stream which is checked before it reaches the landfill, as it passes and also after the landfill. There has been no evidence of pollution caused by the leachate recycling.
Leachate is collected from the bottom of modern landfills by a series of collection pipes installed into the base of the landfill. The leachate percolates through the waste and into the pipes where it collects. The leachate can then be recycled or pumped out of the landfill and placed in storage areas or directly into the leachate treatment plant.
Borehole pumps6 These pump extracted leachate only to the point of collection. Borehole pumps only run when leachate are present so there is a low energy demand. Individual sensors are required in wells to switch the pumps on and off.
Eductors6 - These function no matter whether liquid is present or not. Eductors are part of a circuit collection system. They are simple and reliable but use more energy, however, this is still within acceptable limits as it is not necessary to run the eductor for 24 hours a day. This makes this option the favoured choice for leachate extraction.
Before treating leachate it is necessary to know the following information;
The anticipated flow rate that will require treatment. This mainly depends on the water inflow into the landfill.
Composition of leachate at source which is carried out in an equipped laboratory
Discharge composition required by the authorities
If the water table is low (far below the ground surface), water will become partially filtered as it percolates downward through the soil so contamination is less. If the water table is high (close to the ground surface), contaminants can enter the groundwater directly, without filtration by soil.
The higher the concentration of contaminants in the leachate the higher the likelihood of groundwater pollution.
Permeability of the ground below the landfill affects the rate of leachate escape. Sand has large pore spaces and so it allows greater groundwater flow. Clay is tightly packed and so prevents the movement of groundwater and it is also more effective at filtering out contaminants.
Depending on characteristics of the landfill and the waste it contains, the leachate may be relatively harmless or extremely toxic. Generally leachate has a high biochemical oxygen demand (BOD) and high concentrations of organic carbon, nitrogen, chloride, iron, manganese, and phenols. Many other chemicals may be present, including pesticides, solvents, and heavy metals.
Many studies have investigated the possible health effects caused by landfill sites. No direct links between diseases, like cancer, and landfill have been found. (See studies into health hazards). The tables below show the possible health effects of some chemicals that can be found in household waste and which are dumped into the landfill and if not properly controlled could leak out as leachate.
Chemical |
Source |
Health effects from acute exposure |
Toluene/xylene |
Glues and paints |
Euphoria, excitement, tremor, CNS depression, convulsions, coma |
Phenols and cresols |
Paint |
Burning pain in mouth and throat, nausea, vomiting, diarrhoea, pallor, sweating, shock, coma, |
Benzene |
Solvent, starting material in chemical manufacture |
Single exposure unlikely to cause problem |
Nickel |
Manufacture of batteries, colouring ceramics and glass |
Skin – irritation and dermatitis Ingestion – stomatitis, gingivitis and possible diarrhoea |
Cadmium compounds |
Paint and batteries |
Inhalation- delayed features 12-36 hrs, hypersalivation, metallic taste, cough, dysponea, chest pain. Pneumonitis and pulmonary oedema develop within 1-4 days Ingestion – small amounts ingested GI irritation, nausea and diarrhoea within 15-30 mins. Larger amounts affect calcium and zinc metabolism, cause facial and pulmonary oedema. Skin – irritation |
Lead |
Lead paint (apply to older landfill sites), pottery, cosmetics and some ethnic remedies |
Severe abdominal pain, diarrhoea with black stools, vomiting, hypotension, cramps, headache, confusion, drowsiness, coma and seizures secondary to cerebral oedema. |
Mercury |
Lamps, thermometers |
Bloody diarrhoea, intestinal mucosal necrosis, dehydration, circulatory collapse, proteinuria and renal failure |
Chemical |
Health effects from chronic exposure |
Toluene/xylene |
Ventricular arrhythmias, hepatic and renal necrosis |
Phenols and cresols |
Renal failure |
Benzene |
Haematological abnormalities |
Nickel |
|
Cadmium compounds |
Fumes – anaemia, kidney damage, possible prostate and lung cancer. |
Lead |
Anorexia, abdominal pain and constipation. Toxic megacolon, headaches, fatigue, depression, dropped wrist, proximal renal tubular dysfunction, chronic nephropathy and hypertension. |
Mercury |
CNS - irritability, tremour, memory loss, seizures, coma
Respiratory – necrotising bronchitis, pulmonary oedema, ARDS, pulmonary haemorrhage.
GI – metallic taste, vomiting, diarrhoea, stomatatis, blue-line along gum margin
Renal – proteuria, haematuria and acute renal failure
Eyes – grey or brown lens discolouration, band shaped corneal opacities
Haematological – thrombocytopenia, anaemia secondary to GI bleed. |
Leachates are a potential hazardous waste from landfill sites. If not dealt with properly they can cause pollution to groundwater, health problems and effect the environment. It is important that leachates are treated and contained to prevent these occurrences.
Monroe, M. Landfill leachate treatment: VSEP offers a revolutionary solution. Feb 2001. www.vsep.com/company/articles/2.html [Accessed 19.12.02]
Leachate. www.foe.org/site1/ptp/chapter3.html [Accessed 05.12.02]
Fred Lee, G. and Jones-Lee, A. Leachate recycle offers pros and cons to groundwater pollution. August 1994. www.gfredlee.com/slov_rcy.htm [Accessed 19.12.02]
Fred Lee, G. and Jones-Lee, A. Appropriate use of municipal solid waste (MSW) leachate recycling in MSW landfilling. www.gfredlee.com/leachatepapsli.pdf [Accessed 19.12.02]
Leachate treatment method. http://www.cee.vt.edu/program_areas/environmental/teach/gwprimer/group10/leachate.htm
Eden, R D. Landfill gas and leachate – The selection of technologies to meet the objectives of integrated pollution control. www.leachate.com/Main%20Index.htm [Accessed 19.12.02]
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