Scottish Power has been burning dried sewage sludge pellets with coal at its massive Longannet plant since 2000. The sludge is provided by Scottish Water and dried at Daldowie near Glasgow (ENDS Report 279, pp 17-20 ).
Around 52,000 tonnes of fuel is created from 48% of Scotland's sludge at Daldowie. The fuel contributes around 2% of Longannet's 2400MW output.
Scottish Power has been working on the assumption that dried sludge was categorised as a waste-derived fuel and not a waste. It believed that the activity would not fall under the scope of the EU incineration Directive (ENDS Report 306, pp 37-38 ). The Directive, agreed by EU governments in the same year that Longannet began to burn sludge, must be applied to existing co-incineration facilities by 28 December 2005.
Last November, however, the Scottish Environment Protection Agency decided that the sludge pellets are indeed "waste" and that they do not qualify for any of the various exemptions for burning biomass under the Directive. This would mean having to meet limits for both nitrogen oxides and sulphur dioxide of 200mg/m3 which Scottish Power says are "impossible".
"We will have to stop burning sludge without considerable expenditure that would render Longannet's function as a coal power station unviable," said Fred Dinning, Scottish Power's corporate environment director.
Longannet would have to be equipped with flue gas desulphurisation and selective catalytic reduction technology.
"It's nonsense, and doesn't make environmental sense," argues Mr Dinning. "This material has very similar burning characteristics to brown coal, but because it's seen as a waste we have to suffer the limits [of the incineration Directive]."
Scottish Power has applied for a judicial review of the decision which is to be heard on 25 May. Mr Dinning says it makes "moral and legal" sense to classify sludge pellets as a non-waste. SEPA called co-burning the "best environmental option" for the disposal of sludge when Scottish Power applied for original consent, he adds.
Scottish Power sees alternative options for the disposal of sludge as being unsuited to the Glasgow area. Using the sludge as a fertiliser would introduce transport impacts.
It would not be suited to landfill either, Mr Dinning claims, because of complexities arising from the EU landfill Directive. Other options include combustion in a dedicated plant or its use in land reclamation.
About 27% of Scotland's sludge is currently used in land reclamation, 23% goes to agricultural land and 2% to landfill.
SEPA and Scottish Water both declined to comment on the case, although the implications for Scottish Water are immense.
If the decision goes SEPA's way, a legal battle is likely to arise between Scottish Water and Scottish Power over who has responsibility for the sludge under the complex contractual arrangements behind the project.
Water companies in England are also paying close attention to the case. "[This decision could] prevent the start-up of sewage sludge co-combustion elsewhere," says Mike Rewcastle, Northumbrian Water's technical strategy manager for sludge.
"At the moment, many water companies are investing in, or considering investing in, drying plants. Once they have those, one of the key outlets for the dried sludge would be co-combustion. But if the ruling comes through, it will prevent the development of a sensible, environmentally sound industry."
The ruling will not directly affect any water company in England as none burns sludge in power stations. Thames Water undertook a feasibility study 18 months ago, but the company has long believed that the sludge would be considered a waste. However, some companies fear the ruling will force them to be overly reliant on farm land as an outlet, which already accounts for over 58% of sludge disposal, according to industry body Water UK.
The definition of waste is causing headaches elsewhere in the biomass sector. The classification of both olive solids and sawdust as wastes has, for example, led the likes of Powergen to complain about having to draw up waste transfer notes.
However, the Environment Agency appears to accept that such materials qualify for exemption from the Directive. With respect to biomass, exemptions include uncontaminated wood waste and vegetable waste from agriculture and forestry.
An Agency spokesman said he could not understand why SEPA did not tell Scottish Power it would have to comply with the Directive in the first place.