30 June 1998
Sewage sludge ‘an important agricultural resource’

SEWAGE sludge could ultimately be regarded as an important national agricultural resource rather than an unpleasant material to be dumped as cheaply as possible.

Alan Frost, a soil scientist at the Scottish Agricultural College, at Bush End Estate, Penicuik, estimates that Scotland will produce about 3 million tonnes of sewage sludge each year by 2000.

Sewage sludge contains valuable plant nutrients, which make it a useful fertiliser. It consists mainly of organic matter valued by farmers as a soil conditioner which helps to improve soil structure.

Although the application of untreated liquid sludge directly to farmland as a fertiliser is currently allowed, it is accepted that this practice is environmentally undesirable.

Mr Frost said there were genuine concerns about traces of heavy metals in sewage sludge. These include lead, mercury, cadmium and zinc which, in sufficient quantities, can be toxic.

He said processing the sludge into a valuable humus-rich fertiliser would be the best way to utilise what seems, at first, an unlikely resource.

He claims that only by re-using the nutrients in the sludge to again produce crops of food can the current wasteful use of irreplaceable reserves of the phosphate-rich rocks, from which fertilisers are produced, be avoided.

The article is written in the context of the expectation that sludge dumping at sea will be banned. Mr Frost argues that turning the sludge into fertiliser would be the best way to deal with the problem.

  • The Scotsman 30/06/98 page 26