Generation and treatment of sewage sludge
Assessment made on 01 Jan 2001
ClassificationWaste and material resources (Primary theme)
Policy issue: Are we disposing of the growing stream of sewage sludge in an environmentally friendly way?
The amount of sewage sludge for disposal in landfills is expected to increase by 50% by 2005.
Sewage sludge is the waste left over after wastewater treatment plants have done their work. Although it can be a valuable fertilizer, it is often contaminated by heavy metals, micro-organisms and a range of hazardous organic substances. As a result, in 1998 some 25% of sewage sludge was dumped in landfill sites.
The more stringent demands for treatment in the Directive on Urban Waste Water Treatment will result in many new treatment plants coming into operation by 2005. The total amount of sewage sludge is expected to increase from 7.2 million tonnes of dry matter in 1998 to at least 9.4 million tonnes in 2005.
In 2005, the proportion dumped in landfills is expected to fall to 19%, fertiliser use will rise slightly (54%), and disposal by incineration will grow significantly (24%).
Currently, the EU is considering tightening the limits on the contamination levels allowed in sewage sludge used for fertiliser, with some countries already adopting lower levels. Tighter limits will increase costs - it costs over five times more to incinerate sludge than to use it as a fertiliser - thereby possibly increasing the quantity of sludge sent to landfill instead.
Reducing the contamination levels in sludge, therefore, would both reduce landfilling, pollution, and costs in the sector.
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Sewage sludge - a future waste problem?