A mechanical biological treatment (MBT) system is a type of waste processing facility that combines a sorting facility with a form of biological treatment such as

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 decomposing plant, food waste, recycling organic materials and manure. The resulting ...

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 manage waste or to produce fuels. Much of the ferm ...

. MBT plants are designed to process mixed household waste as well as

commercial Commercial may refer to: * a dose of advertising conveyed through media (such as - for example - radio or television) ** Radio advertisement ** Television advertisement * (adjective for:) commerce, a system of voluntary exchange of products and s ...

and

industrial waste Industrial waste is the waste produced by industrial activity which includes any material that is rendered useless during a manufacturing process such as that of factories, mills, and mining operations. Types of industrial waste include dirt an ...

Process

Mechanical biological treatment flowchart

The terms ''mechanical biological treatment'' or ''mechanical biological pre-treatment'' relate to a group of solid waste treatment systems. These systems enable the recovery of materials contained within the

mixed waste Waste (or wastes) are unwanted or unusable materials. Waste is any substance discarded after primary use, or is worthless, defective and of no use. A by-product, by contrast is a joint product of relatively minor economic value. A waste produ ...

and facilitate the stabilisation of the

biodegradable Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegrada ...

component of the material. Twenty two facilities in the UK have implemented MBT/BMT treatment processes. The sorting component of the plants typically resemble a materials recovery facility. This component is either configured to recover the individual elements of the waste or produce a refuse-derived fuel that can be used for the generation of power. The components of the mixed waste stream that can be recovered include: *

Ferrous metal In chemistry, the adjective Ferrous indicates a compound that contains iron(II), meaning iron in its +2 oxidation state, possibly as the divalent cation Fe2+. It is opposed to "ferric" or iron(III), meaning iron in its +3 oxidation state, suc ...

Non-ferrous metal In metallurgy, non-ferrous metals are metals or alloys that do not contain iron ( allotropes of iron, ferrite, and so on) in appreciable amounts. Generally more costly than ferrous metals, non-ferrous metals are used because of desirable prop ...

Plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adapta ...

Glass Glass is a non- crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenchin ...

Terminology

MBT is also sometimes termed biological mechanical treatment (BMT), however this simply refers to the order of processing (i.e., the biological phase of the system precedes the mechanical sorting). MBT should not be confused with

mechanical heat treatment 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 facilit ...

(MHT).

Mechanical sorting

The "mechanical" element is usually an automated mechanical

sorting Sorting refers to ordering data in an increasing or decreasing manner according to some linear relationship among the data items. # ordering: arranging items in a sequence ordered by some criterion; # categorizing: grouping items with similar pro ...

stage. This either removes

recyclable Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...

elements from a mixed waste stream (such as metals, plastics, glass, and paper) or processes them. It typically involves factory style

conveyor A conveyor system is a common piece of mechanical handling equipment that moves materials from one location to another. Conveyors are especially useful in applications involving the transport of heavy or bulky materials. Conveyor systems allow ...

s, industrial

magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nicke ...

s, eddy current separators,

trommel A trommel screen, also known as a rotary screen, is a mechanical screening machine used to separate materials, mainly in the mineral and solid-waste processing industries.Stessel et al. 1996, pp. 558-568. It consists of a perforated cylindrical dr ...

s, shredders, and other tailor made systems, or the sorting is done manually at hand picking stations. The mechanical element has a number of similarities to a materials recovery facility (MRF). Some systems integrate a wet MRF to separate by density and flotation and to recover and wash the recyclable elements of the waste in a form that can be sent for recycling. MBT can alternatively process the waste to produce a high calorific fuel termed

refuse derived fuel Refuse-derived fuel (RDF) is a fuel produced from various types of waste such as municipal solid waste (MSW), industrial waste or commercial waste. The World Business Council for Sustainable Development provides a definition: ''"Selected waste ...

(RDF). RDF can be used in

cement kiln Cement kilns are used for the pyroprocessing stage of manufacture of portland and other types of hydraulic cement, in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates. Over a billion tonnes of ...

s or thermal

combustion power plant A thermal power station is a type of power station in which heat energy is converted to electrical energy. In a steam-generating cycle heat is used to boil water in a large pressure vessel to produce high-pressure steam, which drives a steam ...

s and is generally made up from plastics and biodegradable organic waste. Systems which are configured to produce RDF include the Herhof and Ecodeco processes. It is a common misconception that all MBT processes produce RDF; this is not the case, and depends strictly on system configuration and suitable local markets for MBT outputs.

Biological processing

The "biological" element refers to either: *

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 manage waste or to produce fuels. Much of the ferm ...

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 decomposing plant, food waste, recycling organic materials and manure. The resulting ...

* Biodrying Anaerobic digestion harnesses anaerobic microorganisms to break down the

component of the waste to produce

biogas Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. It is a ...

and soil improver. The biogas can be used to generate

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describe ...

and

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

. Biological can also refer to a composting stage. Here the organic component is broken down by naturally occurring aerobic microorganisms. They break down the waste into carbon dioxide and compost. There is no green energy produced by systems employing only composting treatment for the biodegradable waste. In the case of biodrying, the waste material undergoes a period of rapid heating through the action of aerobic microbes. During this partial composting stage the heat generated by the microbes result in rapid drying of the waste. These systems are often configured to produce a refuse-derived fuel where a dry, light material is advantageous for later transport and combustion. Some systems incorporate both anaerobic digestion and composting. This may either take the form of a full anaerobic digestion phase, followed by the maturation (composting) of the digestate. Alternatively a partial anaerobic digestion phase can be induced on water that is percolated through the raw waste, dissolving the readily available sugars, with the remaining material being sent to a windrow composting facility. By processing the biodegradable waste either by anaerobic digestion or by

compost 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 decomposing plant, food waste, recycling organic materials and manure. The resulting ...

ing MBT technologies help to reduce the contribution of

greenhouse gas A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxide (), methane ...

es to

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

. Usable wastes for this system: *

Municipal solid waste Municipal solid waste (MSW), commonly known as trash or garbage in the United States and rubbish in Britain, is a waste type consisting of everyday items that are discarded by the public. "Garbage" can also refer specifically to food waste ...

Commercial Commercial may refer to: * a dose of advertising conveyed through media (such as - for example - radio or television) ** Radio advertisement ** Television advertisement * (adjective for:) commerce, a system of voluntary exchange of products and s ...

and

Sewage sludge Sewage sludge is the residual, semi-solid material that is produced as a by-product during sewage treatment of industrial or municipal wastewater. The term " septage" also refers to sludge from simple wastewater treatment but is connected to s ...

Possible products of this system: * Renewable fuel (biogas) leading to renewable power * Recovered recyclable materials such as metals, paper, plastics, glass etc. * Digestate - an organic fertiliser and soil improver *

Carbon credit A carbon credit is a generic term for any tradable certificate or permit representing the right to emit a set amount of carbon dioxide or the equivalent amount of a different greenhouse gas (tCO2e). Carbon credits and carbon markets are a compo ...

s – additional revenues * High calorific fraction

- renewable fuel content dependent upon biological component * Residual unusable materials prepared for their final safe treatment (e.g.,

incineration Incineration is a waste treatment process that involves the combustion of substances contained in waste materials. Industrial plants for waste incineration are commonly referred to as waste-to-energy facilities. Incineration and other high ...

gasification Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (). This is achieved by reacting ...

) and/or

landfill A landfill site, also known as a tip, dump, rubbish dump, garbage dump, or dumping ground, is a site for the disposal of waste materials. Landfill is the oldest and most common form of waste disposal, although the systematic burial of the wast ...

Further advantages: * Small fraction of inert residual waste * Reduction of the waste volume to be deposited to at least a half (density > 1.3 t/m³), thus the lifetime of the landfill is at least twice as long as usual * Utilisation of the

leachate A leachate is any liquid that, in the course of passing through matter, extracts soluble or suspended solids, or any other component of the material through which it has passed. Leachate is a widely used term in the environmental sciences wh ...

in the process *

Landfill gas Landfill gas is a mix of different gases created by the action of microorganisms within a landfill as they decompose organic waste, including for example, food waste and paper waste. Landfill gas is approximately forty to sixty percent methane ...

not problematic as biological component of waste has been stabilised * Daily covering of landfill not necessary

Consideration of applications

MBT systems can form an integral part of a region's waste treatment infrastructure. These systems are typically integrated with

kerbside collection Kerbside collection or curbside collection is a service provided to households, typically in urban and suburban areas, of collecting and disposing of household waste and recyclables. It is usually accomplished by personnel using specially built ...

schemes. In the event that a refuse-derived fuel is produced as a by-product then a combustion facility would be required. This could either be an incineration facility or a gasifier. Alternatively MBT solutions can diminish the need for home separation and kerbside collection of recyclable elements of waste. This gives the ability of local authorities, municipalities and councils to reduce the use of waste vehicles on the roads and keep recycling rates high.

Position of environmental groups

Friends of the Earth Friends of the Earth International (FoEI) is an international network of environmental organizations in 73 countries. The organization was founded in 1969 in San Francisco by David Brower, Donald Aitken and Gary Soucie after Brower's split wi ...

suggests that the best environmental route for residual waste is to firstly maximise removal of remaining recyclable materials from the waste stream (such as metals, plastics and paper). The amount of waste remaining should be composted or anaerobically digested and disposed of to

, unless sufficiently clean to be used as compost. A report by Eunomia undertook a detailed analysis of the climate impacts of different residual waste technologies. It found that an MBT process that extracts both the metals and plastics prior to landfilling is one of the best options for dealing with our residual waste, and has a lower impact than either MBT processes producing RDF for incineration or incineration of waste without MBT. Friends of the Earth does not support MBT plants that produce refuse derived fuel (RDF), and believes MBT processes should occur in small, localised treatment plants.

References

External links

Waste-to-Resources
World's largest conference on mechanical biological treatment (MBT) of municipal solid waste (MSW) and material recovery facilities (MRF)
Environment Agency Waste Technology Data Centre
An independent UK government review of advanced waste treatment technologies. * Kuehle-Weidemeier et al. (2007
Plants for Mechanical-Biological Waste Treatment
Summary of the evaluation of all German MBT plants in the introduction phase 2005-2006. By order of the German EPA (Umweltbundesamt)

An independent study of MBT technologies commissioned with the use of UK landfill tax credits.
SEPA MBT Planning Information Sheet
Fact Sheet for Scottish Planning Considerations
Compostinfo
An independent comprehensive bibliography and review web site focusing on "mixed waste" sources * GTZ (2003
Sector project mechanical-biological waste treatment. Final report

Mechanical-biological waste treatment concept of FABER-AMBRA
- Scientific results and videos {{Waste Biodegradable waste management Environmental engineering Industrial composting Bioenergy Sewerage