Setbacks for co-composting

A project to co-compost sewage sludge with municipal waste has been abandoned following the withdrawal of support by its main sponsor, South West Water. Another proposal to co-compost Severn Trent Water's sludge with green waste is unlikely to get off the ground because of poor economics. But there is some good news for co-composting - trials began in January at Thames Water.

A project to co-compost sewage sludge with municipal waste in Plymouth began in August 1992, with support from the Department of Trade and Industry under the DEMOS scheme. The composting process proved successful, but South West Water decided last autumn not to build a commercial plant because markets for the finished products were uncertain (ENDS Report 226, p 15 ).

The company has now disbanded the composting team - and intends to stick to traditional methods of sludge disposal such as land spreading and landfilling. Its move was condemned as "short-sighted" by a former composting employee.

But it is not all bad news for the team. South West Water has donated the composting facilities for general research and development because of its commitments under DEMOS. Composting work, in particular market applications, will resume in a few months when the National Composting Development Association (NCDA) - an off-shoot of the DEMOS programme - is set up. EcoSci, a private company set up by former South West Water employees, will provide the support for NCDA.

Finding markets is certainly the principal obstacle to the development of co-composting of sewage sludge. Even the co-compost being produced by Thames Water with green waste supplied by Wycombe District Council is not being sold until a decision is taken whether to sterilise the material to enhance its acceptability to consumers.

Colin Highgate of the Waste Company believes that co-composting should only be promoted as a waste treatment method. The NCDA's work in promoting sewage sludge composts as a product, he says, "may destroy the very tentative marketplace" for other composts.

But co-composting as a treatment method alone has its own obstacles to overcome. A proposal prompted by Mr Highgate to co-compost 4,000 tonnes of Severn Trent's sewage sludge by International Process Systems is unlikely to come to anything. "Severn Trent is not positive - commercially it does not make a lot of sense." This may change, he says, if rules on sewage sludge spreading on land are tightened. In the meantime, capital intensive systems remain uneconomic.

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