Mechanical heat treatment

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Mechanical heat treatment (MHT) is an alternative waste treatment technology. This technology is also commonly termed autoclaving. MHT involves a mechanical sorting or pre-processing stage with technology often found in a material recovery facility. The mechanical sorting stage is followed by a form of thermal treatment. This might be in the form of a waste autoclave or processing stage to produce a refuse derived fuel pellet. MHT is sometimes grouped along with mechanical biological treatment. MHT does not however include a stage of biological degradation (anaerobic digestion or composting).

Thermal treatment is any waste treatment technology that involves high temperatures in the processing of the waste feedstock. Commonly this involves the combustion of waste materials.

A waste autoclave is a form of solid waste treatment that uses heat, steam and pressure of an industrial autoclave in the processing of waste. Waste autoclaves process waste either in batches or in continuous-flow processes. In batch processes, saturated steam is pumped into the autoclave at temperatures around 160 °C. The steam pressure in the vessel is maintained up to 6 bar (gauge) for a period of up to 45 minutes to allow the process to fully 'cook' the waste. The autoclave process gives a very high pathogen and virus kill rate, although the fibrous products which come from the process are susceptible to bacteria and fungus as they are high in starch, cellulose and amino acids.

A mechanical biological treatment system is a type of waste processing facility that combines a sorting facility with a form of biological treatment such as composting or anaerobic digestion. MBT plants are designed to process mixed household waste as well as commercial and industrial wastes.

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Configurations

Different MHT systems may be configured to meet various objectives with regard to the waste outputs from the process. The alternatives (depending on the system employed) may be one or more of the following: [1]

Biological processes are the processes vital for a living organism to live, and that shape its capacities for interacting with its environment. Biological processes are made up of many chemical reactions or other events that are involved in the persistence and transformation of life forms. Metabolism and homeostasis are examples.

Recycling process using materials into new products to prevent waste of potentially useful materials

Recycling is the process of converting waste materials into new materials and objects. It is an alternative to "conventional" waste disposal that can save material and help lower greenhouse gas emissions. Recycling can prevent the waste of potentially useful materials and reduce the consumption of fresh raw materials, thereby reducing: energy usage, air pollution, and water pollution.

Glass amorphous solid that exhibits a glass transition when heated towards the liquid state

Glass is a non-crystalline, amorphous solid that is often transparent and has widespread practical, technological, and decorative uses in, for example, window panes, tableware, and optoelectronics. The most familiar, and historically the oldest, types of manufactured glass are "silicate glasses" based on the chemical compound silica (silicon dioxide, or quartz), the primary constituent of sand. The term glass, in popular usage, is often used to refer only to this type of material, which is familiar from use as window glass and in glass bottles. Of the many silica-based glasses that exist, ordinary glazing and container glass is formed from a specific type called soda-lime glass, composed of approximately 75% silicon dioxide (SiO2), sodium oxide (Na2O) from sodium carbonate (Na2CO3), calcium oxide (CaO), also called lime, and several minor additives.

See also

Anaerobic digestion Processes by which microorganisms break down biodegradable material in the absence of oxygen

Anaerobic digestion is a collection 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 fermentation used industrially to produce food and drink products, as well as home fermentation, uses anaerobic digestion.

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Compost organic matter that has been decomposed

Compost is organic matter that has been decomposed in a process called composting. This process recycles various organic materials otherwise regarded as waste products and produces a soil conditioner.

Waste management activities and actions required to manage waste from its inception to its final disposal

Waste management are the activities and actions required to manage waste from its inception to its final disposal. This includes the collection, transport, treatment and disposal of waste, together with monitoring and regulation of the waste management process.

Landfill site for the disposal of waste materials by burial

A landfill site is a site for the disposal of waste materials by burial. It is the oldest form of waste treatment. Historically, landfills have been the most common method of organized waste disposal and remain so in many places around the world.

Materials recovery facility plant to process recyclates

A materials recovery facility, materials reclamation facility, materials recycling facility or Multi re-use facility is a specialized plant that receives, separates and prepares recyclable materials for marketing to end-user manufacturers. Generally, there are two different types: clean and dirty materials recovery facilities.

Articles related to waste management include:

Greater Manchester Waste Disposal Authority

The Greater Manchester Waste Disposal Authority (GMWDA) is England’s largest Waste Disposal Authority, responsible for the management and disposal of municipal waste from Greater Manchester. It deals with 1.1 million tonnes of waste produced each year, from approximately 1 million households and population of over 2.27 million in the metropolitan districts of Bolton, Bury, Manchester, Oldham, Rochdale, Salford, Stockport, Tameside and Trafford — though part of Greater Manchester, the Metropolitan Borough of Wigan administers its own waste disposal operations, however they are represented on the authority for administration purposes. The waste comes primarily from household waste collections and 20 Household Waste Recycling Centres (HWRCs) provided and serviced by the GMWDA. It handles around 4% of the nation's municipal waste.

Refuse-derived fuel (RDF) is a fuel produced from various types of waste such as municipal solid waste (MSW), industrial waste or commercial waste.

In-vessel composting generally describes a group of methods that confine the composting 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". 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, with temperature and moisture conditions monitored using probes in the mass to allow maintenance of optimum aerobic decomposition conditions.

Waste-to-energy process of generating energy from the primary treatment of waste, or the processing of waste into a fuel source

Waste-to-energy (WtE) or energy-from-waste (EfW) is the process of generating energy in the form of electricity and/or heat from the primary treatment of waste, or the processing of waste into a fuel source. WtE is a form of energy recovery. Most WtE processes generate electricity and/or heat directly through combustion, or produce a combustible fuel commodity, such as methane, methanol, ethanol or synthetic fuels.

Sewage sludge treatment Processes used to manage and dispose of sewage sludge produced during sewage treatment

Sewage sludge treatment describes the processes used to manage and dispose of sewage sludge produced during sewage treatment. Sludge is mostly water with lesser amounts of solid material removed from liquid sewage. Primary sludge includes settleable solids removed during primary treatment in primary clarifiers. Secondary sludge separated in secondary clarifiers includes treated sewage sludge from secondary treatment bioreactors.

Biodegradable waste includes any organic matter in waste which can be broken down into carbon dioxide, water, methane or simple organic molecules by micro-organisms and other living things by composting, aerobic digestion, anaerobic digestion or similar processes. In waste management, it also includes some inorganic materials which can be decomposed by bacteria. Such materials include gypsum and its products such as plasterboard and other simple organic sulfates which can decompose to yield hydrogen sulphide in anaerobic land-fill conditions.

Biodrying is the process by which biodegradable waste is rapidly heated through initial stages of composting to remove moisture from a waste stream and hence reduce its overall weight. In biodrying processes, the drying rates are augmented by biological heat in addition to forced aeration. The major portion of biological heat, naturally available through the aerobic degradation of organic matter, is utilized to evaporate surface and bound water associated with the mixed sludge. This heat generation assists in reducing the moisture content of the biomass without the need for supplementary fossil fuels, and with minimal electricity consumption. It can take as little as 8 days to dry waste in this manner. This enables reduced costs of disposal if landfill is charged on a cost per tonne basis. Biodrying may be used as part of the production process for refuse-derived fuels. Biodrying does not however greatly affect the biodegradability of the waste and hence is not stabilised. Biodried waste will still break down in a landfill to produce landfill gas and hence potentially contribute to climate change. In the UK this waste will still impact upon councils LATS allowances. Whilst biodrying is increasingly applied within commercial mechanical biological treatment (MBT) plants, it is also still subject to on-going research and development.

Aerobic digestion is a process in sewage treatment designed to reduce the volume of sewage sludge and make it suitable for subsequent use. More recently, technology has been developed that allows the treatment and reduction of other organic waste, such as food, cardboard and horticultural waste. It is a bacterial process occurring in the presence of oxygen. Bacteria rapidly consume organic matter and convert it into carbon dioxide, water and a range of lower molecular weight organic compounds. As there is no new supply of organic material from sewage, the activated sludge biota begin to die and are used as food by saprotrophic bacteria. This stage of the process is known as endogenous respiration and it is process that reduces the solid concentration in the sludge.

Waste converter machine used for the treatment and recycling of solid and liquid refuse material

A waste converter is a machine used for the treatment and recycling of solid and liquid refuse material. A converter is a self-contained system capable of performing the following functions: pasteurization of organic waste; sterilization of pathogenic or biohazard waste; grinding and pulverization of refuse into unrecognizable output; trash compaction; dehydration. Because of the wide variety of functions available on converters, this technology has found application in diverse waste-producing industrial segments. Hospitals, clinics, municipal waste facilities, farms, slaughterhouses, supermarkets, ports, sea vessels, and airports are the primary beneficiaries of on-site waste conversion.

The Jundiz recycling plant is located in the Basque Country, particularly in Vitoria-Gasteiz Jundiz Álava. This place is responsible for recycling the city garbage. The trash is converted by a physical-chemical or mechanical process to submit a substance or a product already used to a cycle of total or partial treatment for a commodity or a new product or raw materials from waste, introducing them back into life cycle. This occurs at the prospect of depletion of natural resources, macro economic and eliminate waste efficiently.

Resource recovery is using wastes as an input material to create valuable products as new outputs. The aim is to reduce the amount of waste generated, therefore reducing the need for landfill space and also extracting maximum value from waste. Resource recovery delays the need to use raw materials in the manufacturing process. Materials found in municipal solid waste can be used to make new products. Plastic, paper, aluminium, glass and metal are examples of where value can be found in waste.

References

  1. MHT & MBT Archived 2006-12-10 at the Wayback Machine . Mechanical Biological Treatment and Mechanical Heat Treatment of Municipal Solid Waste, Defra, Waste Implementation Programme, New Technologies