Landfill
[2] Afterward, the waste collection vehicles use the existing road network on their way to the tipping face or working front, where they unload their contents.
The weighing process can assemble statistics on the daily incoming waste tonnage, which databases can retain for record keeping.
Typically, in the working face, the compacted waste is covered with soil or alternative materials daily.
Alternative waste-cover materials include chipped wood or other "green waste",[3] several sprayed-on foam products, chemically "fixed" bio-solids, and temporary blankets.
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.
Sanitary landfills are intended as biological reactors (bioreactors) in which microbes will break down complex organic waste into simpler, less toxic compounds over time.
These smaller organic molecules begin to dissolve and move to the liquid phase, followed by hydrolysis of these organic molecules, and the hydrolyzed compounds then undergo transformation and volatilization as carbon dioxide (CO2) and methane (CH4), with rest of the waste remaining in solid and liquid phases.
The primary electron acceptors during transition are nitrates and sulphates since O2 is rapidly displaced by CO2 in the effluent gas.
The leachate's organic strength, expressed as oxygen demand, decreases at a rapid rate with increases in CH4 and CO2 gas production.
The rate of microbiological activity slows during the last phase of waste decomposition as the supply of nutrients limits the chemical reactions, e.g. as bioavailable phosphorus becomes increasingly scarce.
CH4 production almost completely disappears, with O2 and oxidized species gradually reappearing in the gas wells as O2 permeates downwardly from the troposphere.
When precipitation falls on open landfills, water percolates through the garbage and becomes contaminated with suspended and dissolved material, forming leachate.
In addition to available O2, the fraction of gas constituents will vary, depending on the age of landfill, type of waste, moisture content and other factors.
The gas also contains about 5% molecular nitrogen (N2), less than 1% hydrogen sulfide (H2S), and a low concentration of non-methane organic compounds (NMOC), about 2700 ppmv.
Methane is a greenhouse gas, and is flammable and potentially explosive at certain concentrations, which makes it perfect for burning to generate electricity cleanly.
Poorly run landfills may become nuisances because of vectors such as rats and flies which can spread infectious diseases.
Landfill gas monitoring alerts workers to the presence of a build-up of gases to a harmful level.
The majority of EU member states have laws banning or severely restricting the disposal of household trash via landfills.
[17] However, issues frequently arise due to the alarming growth rate of landfills and poor management by authorities.
In commercial contexts, companies have also discovered landfill sites, and many[quantify] have begun harvesting materials and energy.
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.
[27] Countries including Germany, Austria, Sweden,[28] Denmark, Belgium, the Netherlands, and Switzerland, have banned the disposal of untreated waste in landfills.
[citation needed] In these countries, only certain hazardous wastes, fly ashes from incineration or the stabilized output of mechanical biological treatment plants may still be deposited.
