Anaerobic Digestion

A biological process in which organic solids are decomposed into stable substances.  Digestion reduces the total mass of solids and destroys pathogens (disease-causing microbes).  The digested sludge should have the appearance and characteristics of a rich potting soil.  As the organic solids are broken down by anaerobic bacteria, carbon dioxide and methane gases are formed and the methane can be used as a fuel to produce electricity.

Biodegradable

Material capable of being broken down, usually by microbes into basic elements.  Most organic wastes are biodegradable.  ‘Organic’ means material produced from living or once-living organisms such as plant or animal matter.

Clinical waste

Waste material, generally from medical centres and hospitals that has been produced in connection with medical or surgical procedures.

Confidential waste

Waste material of a confidential nature, often comprising business or legal papers, private letters, etc.

Composting

The breakdown of organic matter such as leaves, paper, kitchen wastes, etc, by aerobic bacteria and other micro-organisms to produce a stable humus-like end product.  It can be carried out in open air ­ known as windrow composting ­ or in special vessels, containers or buildings ­ known as closed system composting.

Hazardous waste

Waste that is potentially hazardous or dangerous and that may require extra precautions during handling, storage, treatment or disposal.  Defined as ‘special waste’ if listed with a six digit code in the Special Waste Regulations 1996 (as amended) and containing substances at or above a threshold level, giving it one or more hazardous characteristics (e.g. explosive, oxidising, corrosive, ecotoxic, etc).

Gasification

A thermal process which partly breaks down waste (or other) material leaving an energy-rich gas product.  The conversion of coal to town gas is gasification.

Incineration

 The process of burning waste under controlled conditions to reduce its weight and volume and often to produce energy.

Landfill

Disposal of waste by burying it in a controlled manner, for natural decomposition. Modern landfills are fully lined and capped with inert materials so that the products of decomposition do not gain access to the environment, and so that the gas generated as a natural produce of the decomposition can be harnessed to produce 'green' electricity.

Landfill gas

Gas generated as a result of natural decomposition of waste within landfills ­ predominantly consisting of carbon dioxide and methane.

Leachate

Liquid produced as part of natural decomposition in landfills, which percolates down through the waste. This liquid, which is water-based, can be pumped up and fed back into landfills to further aid decomposition.

MBT

Mechanical Biological Treatment ­ a treatment process dealing with residual waste after most recyclable materials have been removed (at an MRF or through kerbside collection).  The residual waste is then mechanically sorted to produce three main fractions ­ recyclable materials (mainly metals), organic material suitable for composting and materials suitable for use as refuse-derived fuel (RDF).  The result is a major reduction in waste needing to be sent to landfill and energy recovery via the incineration of RDF.

MRF

Materials Reclamation Facility ­ an operational unit designed to sort and prepare waste materials (e.g. metals, paper, card, plastics, etc) in order to produce secondary materials that can be reprocessed or used for the manufacture of other new products.

Methane

A colourless, odourless flammable gas that is the main constituent of landfill gas. Chemical formula: CH4.

Pyrolysis

Heating material in a controlled atmosphere in which there is not enough oxygen to initiate burning.  The process produces gases that can be used as a fuel.

Renewable Power
('Green energy')

Electricity generated from a renewable resource such as methane in landfill gas. It is deemed 'green' because it is made as a result of recovering energy from wastes, rather than from non-renewable fossil fuels.

Sustainable Waste Management

A generic term used to describe waste management methods meeting the needs of society in the present day without compromising the ability of future generations to meet theirs.  Usually considered to involve a ‘portfolio’ of waste management solutions maximising resource efficiency and including recycling, recovery, energy recovery and safe and efficient final disposal.

Void

Holes in the ground that could, potentially, become available for use as landfills often comprising of disused quarries or open cast mines.

Consented void

Void space with planning consent for use as landfills.

Zero Waste Theory

The theory that a society, organisation or process can reduce, re-use or recycle all of its waste, thus producing zero waste of no economic value needing final disposal.