In-vessel composting generally describes a group of methods that confine the

composting Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical, and biological properties. It is commonly prepared by Decomposition, decomposing plant and food waste, recycling organic materials, and man ...

materials within a building, container, or vessel. In-vessel composting systems can consist of metal or plastic tanks or concrete bunkers in which air flow and temperature can be controlled, using the principles of a "

bioreactor A bioreactor is any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical reaction, chemical process is carried out which involves organisms or biochemistry, biochem ...

". Generally the air circulation is metered in via buried tubes that allow fresh air to be injected under pressure, with the exhaust being extracted through a

biofilter Biofiltration is a pollution control technique using a bioreactor containing living material to capture and biologically degrade pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, a ...

, with temperature and moisture conditions monitored using probes in the mass to allow maintenance of optimum

aerobic decomposition Decomposition is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is essen ...

conditions. This technique is generally used for municipal scale

organic waste Biodegradable waste includes any organic matter in waste which can be broken down into carbon dioxide, water, methane, compost, humus, and simple organic molecules by micro-organisms and other living things by composting, aerobic digestion, ana ...

processing, including final treatment of sewage

biosolids Biosolids are solid organic matter recovered from a sewage treatment process and used as fertilizer. In the past, it was common for farmers to use animal manure to improve their soil fertility. In the 1920s, the farming community began also to us ...

, to a stable state with safe pathogen levels, for reclamation as a soil amendment. In-vessel composting can also refer to aerated static pile composting with the addition of removable covers that enclose the piles, as with the system in extensive use by farmer groups in Thailand, supported by the National Science and Technology Development Agency there. In recent years, smaller scale in-vessel composting has been advanced. These can even use common roll-off waste dumpsters as the vessel. The advantage of using roll-off waste dumpsters is their relatively low cost, wide availability, they are highly mobile, often do not need building permits and can be obtained by renting or buying. Evaluation is ongoing with regard to the health risks associated with compost derived from sewage biosolids—including identifying safe levels of contaminants such as

PFAS Per- and polyfluoroalkyl substances (also PFAS, PFASs, and informally referred to as "forever chemicals") are a group of synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain; there are 7 millio ...

("forever chemicals"). Offensive

odor An odor (American English) or odour ( Commonwealth English; see spelling differences) is a smell or a scent caused by one or more volatilized chemical compounds generally found in low concentrations that humans and many animals can perceive ...

s are caused by putrefaction (

anaerobic decomposition Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the fermen ...

) of nitrogenous animal and vegetable matter gassing off as

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

. This is controlled with a higher carbon to nitrogen ratio, or increased aeration by ventilation, and use of a coarser grade of carbon material to allow better air circulation. Prevention and capture of any gases naturally occurring (

volatile organic compounds Volatile organic compounds (VOCs) are organic compounds that have a high vapor pressure at room temperature. They are common and exist in a variety of settings and products, not limited to house mold, upholstered furniture, arts and crafts sup ...

) during the hot aerobic composting involved is the objective of the biofilter, and as the filtering material saturates over time, it can be used in the composting process and replaced with fresh material. A more advanced systems design is able to limit the odor issues considerably, and it is also able to raise the total energy and resource output by integrating in-vessel composting with

anaerobic digestion Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to Waste management, manage waste or to produce fuels. Mu ...

. Through anaerobic decomposition it is also possible to reduce pathogen levels similarly to that of traditional aerated composting when the anaerobic bioreactors operate at thermophilic temperatures, between .§

Gallery

File:CVRD1loader.5bays.jpg, Biosolids composting facility – receiving and mixing bays and five reactor chambers File:CVRD2week1bay.jpg, Composting chamber material after one week File:CVRD3week2.bay.jpg, Composting chamber material after two weeks File:CVRD4chamber.air.jpg, Air supply and exhaust system for enclosed composting File:CVRD5biofilter.air.exhaust.jpg, Exhaust biofilter mound

References

{{Environmental technology Industrial composting Waste treatment technology

Gallery

See also

References