Landfill

thumb|right|One of several landfills used by [[Dryden, Ontario, Canada]]

A landfill is a site for the disposal of waste materials, including municipal solid waste. It is the oldest and most common form of waste disposal, although the systematic burial of waste with daily, intermediate, and final covers only began in the 1940s. In the past, waste was simply left in piles or thrown into pits (known in archeology as middens).

Landfills take up significant amounts of land and pose environmental risks. Some landfill sites are used for waste management purposes, such as temporary storage, consolidation, and transfer, or for various stages of processing waste material, such as sorting, treatment, or recycling. Unless they are stabilized, landfills may undergo severe shaking or soil liquefaction during an earthquake. Once full, the area over a landfill site may be reclaimed for other uses.

Both active and restored landfill sites can have significant environmental impacts which can persist for many years. These include the release of landfill gases that contribute to climate change and the discharge of liquid landfill leachates containing high concentrations of polluting materials.

Operations

thumb|right|Garbage dumped in the middle of a road in [[Karachi, Pakistan]]

Operators of well-run landfills for non-hazardous waste meet predefined specifications by applying techniques to:

1. confine waste to as small an area as possible
2. Compact waste to reduce volume

They can also cover the waste daily with layers of soil or other materials, such as wood chips and fine particles.

During landfill operations, a scale or weighbridge may weigh waste collection vehicles on arrival and personnel may inspect loads for wastes that do not accord with the landfill's waste-acceptance criteria. several sprayed-on foam products, chemically "fixed" bio-solids, and temporary blankets. Blankets can be lifted into place at night and then removed the following day prior to waste placement. The space that is occupied daily by the compacted waste and the cover material is called a daily cell. Waste compaction is critical to extending the life of the landfill. Factors such as waste compressibility, waste-layer thickness and the number of passes of the compactor over the waste affect the waste densities.

Sanitary landfill life cycle

thumb|upright=1.2|Sanitary landfill diagram

The term landfill is usually shorthand for a municipal landfill or sanitary landfill. These facilities were first introduced early in the 20th century, but gained wide use in the 1960s and 1970s, in an effort to eliminate open dumps and other "unsanitary" waste disposal practices. The sanitary landfill is an engineered facility that separates and confines waste. Sanitary landfills are intended as biological reactors in which microbes will break down complex organic waste into simpler, less toxic compounds over time. These reactors must be designed and operated according to regulatory standards and guidelines covered by the field of environmental engineering.

Aerobic decomposition is often the first stage by which wastes are broken down in a landfill. This process is followed by four stages of anaerobic degradation. Solid organic material typically decays rapidly as larger organic molecules degrade into smaller molecules. These smaller organic molecules begin to dissolve and move to the liquid phase, followed by hydrolysis of the organic molecules, and the hydrolyzed compounds then undergo transformation and volatilization as carbon dioxide (CO₂) and methane (CH₄), with the rest of the waste remaining in solid and liquid phases.

During the early phases, little material volume reaches the leachate as the biodegradable organic matter of the waste undergoes a rapid decrease in volume. Meanwhile, the leachate's chemical oxygen demand rises with increasing concentrations of the more recalcitrant compounds compared to the more reactive compounds in the leachate. Successful conversion and stabilization of the waste depends on how well microbial populations function in syntrophy.

The life cycle of a municipal landfill undergoes five distinct phases, as follows:

Social and environmental impact

thumb|right|250px|Landfill operation in Hawaii. The area being filled is a single, well-defined "cell" and a protective [[landfill liner is in place (exposed on the left) to prevent contamination by leachates migrating downward through the underlying geological formation.]]

Landfills have the potential to cause a number of issues. Infrastructure disruption, such as damage to access roads by heavy vehicles, may occur. Pollution of local roads and watercourses from wheels on vehicles when they leave the landfill can be significant and can be mitigated by wheel washing systems. Pollution of the local environment, such as contamination of groundwater or aquifers or soil contamination may occur as well.

Leachate

When precipitation falls on open landfills, or when water is released from the breakdown of waste, water percolates through the waste and becomes contaminated with suspended and dissolved material, forming leachate enriched with organic matter, heavy metals, organic contaminants, and other contaminants present in the waste. If this is not contained it can contaminate groundwater. All modern landfill sites use a combination of impermeable liners several metres thick, geologically stable sites, and collection systems to contain and capture this leachate. It can then be treated and evaporated. Once a landfill site is full, it is sealed off to prevent precipitation entering the landfill and formation of new leachate. However, liners have a lifespan, often several hundred years or more, but eventually any landfill liner could leak, so the ground around landfills must be tested for leachate to prevent pollutants from contaminating groundwater.

The largest problem in sanitary landfills with regard to leachate quality is nitrogen, particularly in the form of ammonium nitrogen. Hydrolysis of waste results in the release of carbon species such as bicarbonate and acetic acid as well as the release of ammonium. The anaerobic environment present in landfills does not allow for coupled nitrification-denitrification, the typical nitrogen removal pathway in soils, which can lead to an accumulation of ammonium in the leachate and concentrations upwards of several thousand milligrams per liter. The average landfill gas further contains about 5% molecular nitrogen (N₂), less than 1% hydrogen sulfide (H₂S), and low concentrations of non-methane organic compounds (NMOC), about 2700 parts per million by volume.

4 C₆H₁₀O₄ + 6 H₂O → 13 CH₄ + 11 CO₂thumb|Waste disposal in Athens, Greece

Landfill gases can seep out of the landfill and into the surrounding air and soil. This makes landfills a significant source of greenhouse gases in the form of CO₂ and particularly CH₄, with landfills being the 3rd largest emitter of CH₄ worldwide and CH₄ having a global warming potential of 29.8 ± 11 relative to CO₂ over a period of 100 years, and 82.5 ± 25.8 over a period of 20 years. Properly managed landfills ensure collection and usage of gases. This can range from simple flaring to get rid of the gas to landfill gas utilization for electricity generation. Monitoring landfill gas alerts workers to the presence of a build-up of gases to a harmful level. In some countries, landfill gas recovery is extensive; in the United States, for example, more than 850 landfills have active landfill gas recovery systems.

Other nuisances

thumb|A group of wild elephants interacting with a trash dump in Sri Lanka

Other potential issues of landfills include wildlife disruption due to occupation of habitat and animal health disruption caused by consuming waste from landfills, dust, odor, noise pollution, and reduced local property values. Poorly run landfills may further become nuisances because of vectors such as rats and flies which can spread infectious diseases. The occurrence of such vectors can be mitigated through the use of daily cover.

Landfill aftercare

thumb|[[Solar arrays on a full landfill in Rehoboth, MA]]

Once a landfill is filled, a top liner or cap is placed on top of the landfill to prevent further inflow of precipitation. The landfill subsequently enters the "aftercare" stage. During aftercare, environmental impacts are minimized through the (re)placement of liners, capture of greenhouse gases, and treatment of contaminant-rich leachates. Estimated duration of aftercare has been estimated between several decades up to eternity with an estimated aftercare cost of more than 20 million euros per landfill in the Netherlands.

Sustainability

Bioreactor landfill

The practice of sanitary landfilling poses challenges with regard to sustainability. Once the lifetime of the landfill is completed, and it enters its aftercare period, the typical practice of sealing the waste with liners restricts contaminants within the landfill and prevents the waste from being subdued to environmental factors. The waste's potential to pollute the environment is thus maintained within the landfill, and the replacement of liners and treatment of leachate is an indefinite requirement. Certain countries, such as the Netherlands, consequently consider the necessity of long-term aftercare, up-to eternal. or recirculating leachate through the waste body. Bioreactor landfills stimulate the removal of contaminants to a point where contaminant emissions no longer threaten the environment. At this point, placement of liners and treatment of gas and leachate is no longer required, significantly limiting costs and reducing the impact on future generations. Additional benefits include a stimulated gas production during the active treatment period, allowing for a more efficient potential for energy generation during a shorter timeframe. Well-known examples include gas-recovery facilities. Other commercial facilities include waste incinerators which have built-in material recovery. This material recovery is possible through the use of filters (electro filter, active-carbon and potassium filter, quench, HCl-washer, SO₂-washer, bottom ash-grating, etc.).

Landfill restoration

Following placement of the cap and closure of the landfill, the area is oftentimes re-purposed. Popular alternative land-uses include recreational purposes (e.g. mountain bike courses), the placement of solar panels to create solar array farms, parks, or living areas.

Regional practice

thumb|right|A landfill in Perth, Western Australia

thumb|right|South East New Territories Landfill, [[Hong Kong]]

Canada

Landfills in Canada are regulated by provincial environmental agencies and environmental protection legislation.

Older facilities tend to fall under current standards and are monitored for leaching. Some former locations have been converted to parkland.

European Union

thumb|The Rusko landfill in [[Oulu|Oulu, Finland]]

In the European Union, individual states are obliged to enact legislation to comply with the requirements and obligations of the European Landfill Directive.

The majority of EU member states have laws banning or severely restricting the disposal of household trash via landfills.

India

Landfilling is currently the major method of municipal waste disposal in India. India also has Asia's largest dumping ground in Deonar, Mumbai. However, issues frequently arise due to the alarming growth rate of landfills and poor management by authorities. On and under surface fires have been commonly seen in the Indian landfills over the last few years.

Permitting a landfill generally takes between five and seven years, costs millions of dollars and requires rigorous siting, engineering and environmental studies and demonstrations to ensure local environmental and safety concerns are satisfied.

Types

• Municipal solid waste: takes in household waste and nonhazardous material. Included in this type of landfill is a Bioreactor Landfill that specifically degrades organic material.
• Industrial waste: for commercial and industrial waste. Other related landfills include Construction and Demolition Debris Landfills and Coal Combustion Residual Landfills.
• Hazardous waste or PCB waste: Polychlorinated Biphenyl (PCB) landfills that are monitored in the United States by the Toxic Substances Control Act of 1976 (TSCA).

Microbial topics

The status of a landfill's microbial community may determine its digestive efficiency.

Bacteria that digest plastic have been found in landfills.

Alternatives

In addition to waste reduction and recycling strategies, there are various alternatives to landfills, including waste-to-energy incineration, anaerobic digestion, composting, mechanical biological treatment, pyrolysis and plasma arc gasification. Depending on local economics and incentives, these can be made more financially attractive than landfills.

The goal of the zero waste concept is to minimize landfill volume.

Restrictions

Countries including Germany, Austria, Sweden, Denmark, Belgium, the Netherlands, and Switzerland, have banned the disposal of untreated waste in landfills.

See also

• (HELP) model

Notes

References

Further reading

• Daniel A. Vallero, Environmental Biotechnology: A Biosystems Approach. 2nd Edition. Academic Press, Amsterdam, Netherlands and Boston MA, Print Book ; eBook . 2015.

External links

• US National Waste & Recycling Association
• Solid Waste Association of North America
• A Compact Guide to Landfill Operation: Machinery, Management and Misconceptions