Wastes are categorized by their properties and level of hazard to human health and environment. The class of substances and waste determines how they must be used, stored, transported and disposed of.
The European waste hierarchy refers to the five steps included in the article 4 of the Waste Framework Directive.
- Prevention: preventing and reducing waste generation.
- Reuse and preparation for reuse: giving the products a second life before they become waste.
- Recycle: any recovery operation by which waste materials are reprocessed into products, materials or substances whether for the original or other purposes. It includes composting and it does not include incineration.
- Recovery: some waste incineration based on a political non-scientific formula that upgrades the less inefficient incinerators.
- Disposal: processes to dispose of waste be it landfilling, incineration, pyrolysis, gasification and other finalist solutions. Landfill is restricted in some EU-countries through Landfill Directives and there is a debate about Incineration E.g. original plastic which contains a lot of energy is just recovered in energy and not recycled. According to the Waste Framework Directive the European Waste Hierarchy is legally binding except in cases that may require specific waste streams to depart from the hierarchy. This should be justified on the basis of life-cycle thinking.
Substances which present a potential hazard for the environment and/or human health, are subject to special waste disposal regulations.
Special wastes are wastes from commercial or other economic enterprises or public bodies, which by their type, properties or quantity:
present a danger to health or environment, are explosive or flammable
can cause or contain carriers of transmissable disease
are listed in a waste ordinance as hazardous, e.g. the German Abfallverzeichnis Verordnung AVV ( PDF 128k)
are ruled by an Electronic Waste Law: e.g. German Electrical and Electronic Equipment Law: ElektroG (PDF 106k)
Liquid wastes usually need to be treated to some degree, such as to filter or otherwise remove harmful substances, or to chemically neutralize acids and alkalis. Chemical treatment is very expensive, so eliminating contaminants at source is the most cost-effective way to manage wastes.
Sewage and much industrial effluent is termed black water, and water with lesser degrees of contamination, such as sink water and road run-off, is grey water. Sewage passes through primary and secondary treatment phases before being used as fertiliser, incinerated, landfilled, or in some cases dumped at sea.
Many liquids used commercially contain hazardous substances, which must be treated separately. These include: solvents, acids, alkalis, paint sludge, pesticides, some categories of hospital waste, laboratory chemicals, and liquids containing heavy metal impurities or persistent organic pollutants.
Industrial and vehicle exhausts, and other gas emissions, need to be filtered and/or electrostatically 'scrubbed' to remove substances which may not be safely released into the ambient air.
Although not toxic in low concentrations, gases like methane and CO2 are subject to restrictions since they are greenhouse gases. CFCs (Chlorofluorocarbons) may not be released to the atmosphere, since they cause depletion of the ozone layer.
Vehicle exhausts and furnace flues emit NOx and SOx, which cause acid rain and photochemical pollutants. Other airborne pollutants common to the urban environment are ozone, CO, VOCs and particulate matter.