Under The Landfill

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How Landfills Work

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Retrieved from " https: Views Read Edit View history. In other projects Wikimedia Commons Wikiquote. Rainwater that falls on the landfill runs through the layer of dirt and vegetation and over the protective plastic to collection pools. Inside the landfill, the trash layer forms a gently sloped hill, which can reach more than feet 46 meters thick, according to New York's DEC.

According to the NSWMA, modern landfills require soil to be added to cover fresh additions of waste every day. The solid waste layer becomes laced with these strips of dirt. But garbage in a landfill does decompose, albeit slowly and in a sealed, oxygen-free environment. Because of the lack of oxygen, bacteria in the waste produce methane gas, which is highly flammable and dangerous if allowed to collect underground. It is also a potent greenhouse gas and contributes to global warming. This relationship helps maintain a healthy operation.

Sump pumps can function with preset phase times. If the flow is not predictable, a predetermined leachate height level can automatically switch the system on. Other conditions for sump planning are maintenance and pump drawdown. Collection pipes typically convey the leachate by gravity to one or more sumps, depending upon the size of the area drained.

Leachate collected in the sump is removed by pumping to a vehicle, to a holding facility for subsequent vehicle pickup, or to an on-site treatment facility. Sump dimensions are governed by the amount of leachate to be stored, pump capacity, and minimum pump drawdown. The volume of the sump must be sufficient to hold the maximum amount of leachate anticipated between pump cycles, plus an additional volume equal to the minimum pump drawdown volume.

What is a Landfill? - How Landfills Work | HowStuffWorks

Sump size should also consider dimensional requirements for conducting maintenance and inspection activities. Sump pumps may operate with preset cycling times or, if leachate flow is less predictable, the pump may be automatically switched on when the leachate reaches a predetermined level. More modern landfills in the developed world have some form of membrane separating the waste from the surrounding ground, and in such sites there is often a leachate collection series of pipes laid on the membrane to convey the leachate to a collection or treatment location.

An example of a treatment system with only minor membrane use is the Nantmel Landfill Site. All membranes are porous to a limited extent so that, over time, low volumes of leachate will cross the membrane. The design of landfill membranes is at such low volumes that they should never have a measurable adverse impact on the quality of the receiving groundwater.

A more significant risk may be the failure or abandonment of the leachate collection system. Such systems are prone to internal failure as landfills suffer large internal movements as waste decomposes unevenly and thus buckles and distorts pipes. If a leachate collection system fails, leachate levels will slowly build in a site and may even over-top the containing membrane and flow out into the environment.

What Happens Inside a Landfill?

Rising leachate levels can also wet waste masses that have previously been dry, triggering further active decomposition and leachate generation. Thus, what appears to be a stabilised and inactive site can become re-activated and restart significant gas production and exhibit significant changes in finished ground levels. One method of leachate management that was more common in uncontained sites was leachate re-circulation, in which leachate was collected and re-injected into the waste mass. This process greatly accelerated decomposition and therefore gas production and had the impact of converting some leachate volume into landfill gas and reducing the overall volume of leachate for disposal.

However, it also tended to increase substantially the concentrations of contaminant materials, making it a more difficult waste to treat. The most common method of handling collected leachate is on-site treatment. When treating leachate on-site, the leachate is pumped from the sump into the treatment tanks. The leachate may then be mixed with chemical reagents to modify the pH and to coagulate and settle solids and to reduce the concentration of hazardous matter.

Traditional treatment involved a modified form of activated sludge to substantially reduce the dissolved organic content. Nutrient imbalance can cause difficulties in maintaining an effective biological treatment stage. The treated liquor is rarely of sufficient quality to be released to the environment and may be tankered or piped to a local sewage treatment facility; the decision depends on the age of the landfill and on the limit of water quality that must be achieved after treatment.

With high conductivity, leachate is hard to treat with biological treatment or chemical treatment. Treatment with reverse osmosis is also limited, resulting in low recoveries and fouling of the RO membranes. Reverse osmosis applicability is limited by conductivity, organics, and scaling inorganic elements such as CaSO4, Si, and Ba. In some older landfills, leachate was directed to the sewers , but this can cause a number of problems. Toxic metals from leachate passing through the sewage treatment plant concentrate in the sewage sludge, making it difficult or dangerous to dispose of the sludge without incurring a risk to the environment.

In Europe , regulations and controls have improved in recent decades, and toxic wastes are now no longer permitted to be disposed of in the Municipal Solid Waste landfills, and in most developed countries the metals problem has diminished.

Paradoxically, however, as sewage treatment plant discharges are being improved throughout Europe and many other countries, the plant operators are finding that leachates are difficult waste streams to treat. This is because leachates contain very high ammoniacal nitrogen concentrations, are usually very acidic, are often anoxic and, if received in large volumes relative to the incoming sewage flow, lack the Phosphorus needed to prevent nutrient starvation for the biological communities that perform the sewage treatment processes.

The result is that leachates are a difficult-to-treat waste stream. However, within ageing municipal solid waste landfills, this may not be a problem as the pH returns close to neutral after the initial stage of acidogenic leachate decomposition. Many older leachate streams also contained a variety of synthetic organic species and their decomposition products, some of which had the potential to be acutely damaging to the environment. The risks from waste leachate are due to its high organic contaminant concentrations and high concentration of ammonia.

Pathogenic microorganisms that might be present in it are often cited as the most important, but pathogenic organism counts reduce rapidly with time in the landfill, so this only applies to the freshest leachate. Toxic substances may, however, be present in variable concentrations, and their presence is related to the nature of the waste deposited. Most landfills containing organic material will produce methane , some of which dissolves in the leachate. This could, in theory, be released in poorly ventilated areas in the treatment plant. The most important requirement is the prevention of the discharge of dissolved methane from untreated leachate into public sewers, and most sewage treatment authorities limit the permissible discharge concentration of dissolved methane to 0.

This entails methane stripping from the leachate. The greatest environmental risks occur in the discharges from older sites constructed before modern engineering standards became mandatory and also from sites in the developing world where modern standards have not been applied.

There are also substantial risks from illegal sites and ad-hoc sites used by organizations outside the law to dispose of waste materials. Leachate streams running directly into the aquatic environment have both an acute and chronic impact on the environment, which may be very severe and can severely diminish bio-diversity and greatly reduce populations of sensitive species.

Where toxic metals and organics are present this can lead to chronic toxin accumulation in both local and far distant populations. Rivers impacted by leachate are often yellow in appearance and often support severe overgrowths of sewage fungus. The contemporary research in the field of assessment techniques and remedial technology of environmental issues originating from landfill leachate has been reviewed in an article published in Critical Reviews in Environmental Science and Technology journal [11].

Leachate collection systems can experience many problems including clogging with mud or silt. Bioclogging can be exacerbated by the growth of micro-organisms in the conduit. The conditions in leachate collection systems are ideal for micro-organisms to multiply.

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