Landfills

A landfill, also called sanitary landfill, is a land disposal site for waste, which is designed to protect from environmental pollution and health risks. It is not the same as an open dump. Landfills are built to concentrate the waste in compacted layers to reduce the volume and monitored for the control of liquid and gaseous effluent in order to protect the environment and human health.

Besides municipal solid waste, faecal sludge can also be discharged into landfills. Well-constructed and maintained landfills are safer than open dumping sites, but even the best sanitary landfill will fill up and, after many years, probably start to leak. Therefore only waste, which cannot be reused further should be disposed of in landfills. To solve current waste problems, prevention of waste in the first place remains a priority. Separation of different types of wastes and reuse is much more sustainable. For instance, the disposal of faecal sludge should only be considered, if there is no need and market for soil conditioner/ fertiliser (see also composting large-scale and small scale, fertiliser from sludge, anaerobic digestion and use of compost).

A basic landfill is a pit with a protected bottom (to prevent contamination of groundwater) where trash is buried in layers, compacted and covered. Ideally, about 0.5 m of soil should cover the deposited refuse at the end of each day to prevent animals from digging up the waste, flies from breeding and to avoid that odour, waste (e.g. plastic bags) or pathogens are spread by the wind (see also HARVEY et al. 2002 Chapter 7.7.1).

The more advanced (“engineered”) landfills consist of a liner system at the bottom and the sides; a leachate removal system, which also includes a treatment of the leachate; groundwater monitoring, gas extraction (the gas is flared or used for energy production) and a cap system (see picture above). The capacity is planned and the site is chosen based on an environmental risk assessment study (UNEP 2002).

There also types of aerobic or anaerobic bioreactor landfill. Bioreactor technology accelerates the biological decomposition of the organic fraction of the waste (e.g. food, plants, paper, etc.) in a landfill by promoting conditions necessary for the microorganisms that degrade the waste and produce biogas. The single most important factor in promoting waste decomposition is the moisture content of the waste. Liquids must be added to the waste mass to obtain optimal moisture content, which ranges from 35 to 45 percent water by weight. Liquids that are added include: the landfill leachate that is previously recovered at the bottom, gas condensate, water, storm water runoff, and faecal sludge or residual sludge from wastewater treatment plants (adapted from WM 2004).

Treatment of Leachate

Landfill leachates will cause environmental problems if not handled properly. One of the most promising methods of treating landfill leachate are constructed wetlands as they require little operation and maintenance (see also horizontal flow, vertical flow, free-surface and hybrid constructed wetlands). The use of constructed wetlands to treat landfill leachates is an environmentally sustainable and cost saving solution (see also SA'AT 2006).

Because building and maintaining a sanitary landfill is a lot of work, it usually needs to be done in partnership with the community, local government, and other organisations, such as churches or businesses (CONTANT and FADEM 2008). Sanitary landfill is the most cost-effective system of solid waste final disposal for most urban areas in developing countries (COINTREAU 2004). If there is no other solution (e.g. separate collection and separate recycling/incineration), landfills are an effective way to discharge solid waste or residual sludge from wastewater treatment plants. With a properly planned landfill it is possible to prevent groundwater contamination and to collect biogas for further use. High-tech landfills, such as bioreactor landfills, will be more expensive in initial costs as well as O&M costs.

A landfill requires a dedicated operator to ensure the management procedures above are carried out (UNEP 2002). Waste has to be covered each day as already described above. Once the capacity of the landfill is reached, it has to be covered correctly and the bottom has to be controlled regularly to make sure no toxic effluent reaches groundwater sources. The cover should resist erosion by wind and water, promote vegetation and satisfy aesthetic, ecological, or end use criteria (GROSS n.y.).

The bioreactor landfill including anaerobic digestion and addition of moisture as described above requires a much higher level of maintenance and operator skill to optimise operations and to modify the system as needed. Consequently, bioreactor landfills require a more complex set of operations and maintenance (O&M) procedures than conventional landfills. Additionally, liquid delivery systems must be designed and installed at various stages of landfill operation. They increase the risk of damage to the liquid delivery system and add to the complexity of conducting day-to-day operations. Therefore, some waste disposal facilities, with limited resources, may find it difficult to retain the appropriate level of design, construction, and operator skills to successfully implement a bioreactor landfill project (adapted from ITRC 2006).

Open dumps can be turned into sanitary landfills. Or a community can build a new sanitary landfill and clean up the old site by transporting trash to the new one. A sanitary landfill protects community health when (CONTANT and FADEM 2008):

• It is built away from where people live.
• It is covered to prevent insects and other disease-carrying animals from breeding.
• It has a lining of hard-packed clay soil and/or plastic to prevent chemicals and germs from contaminating groundwater.

A landfill protects community health only if it is well managed. Good management includes training and support for landfill workers, and working together with resource recovery centres, toxic waste collectors, and local government (CONTANT and FADEM 2008).