Sludge: a resource

Åse Dragland

Dr.ing.-student John Bollingmo and prof. Hallvard Ødegaard.

Grey, unpleasant, sewage sludge, containing organic materials, bacteria, viruses and heavy metals could turn out to be a resource.

As a soil improver, a source of energy or a methanol substitute capable of removing nitrogen from waste water. Norwegian sewage treatment plants produce 450,000 tons of sludge a year, and quantities of this form of concentrated contamination will grow in the future. Problems associated with sludge include hygiene and heavy metal. Now the authorities have decided that sludge cannot be deposited on rubbish tips in the future.

This might easily have turned sludge into a major environmental problem, but research and innovative ways of thinking have led us to just the opposite point of view: sludge is in the process of becoming an environmental resources.

"Using sludge as a soil improver gives us the most complete recovery of its useful components. This has therefore become the general strategy of the Norwegian authorities," says Professor Hallvard Ødegaard of NTH's Dept. of Hydraulic and Environmental Engineering.

Until recently, agriculture has taken up about 45% of the sludge produced. This has been done with a certain amount of scepticism, since there has been some doubt as to its content of environmental toxins. But now, the State Pollution Control Authority (SFT) has a declared aim of putting 75% of the sewage sludge that is produced on the fields, on the basis of more effective sludge treatment and checking of the composition of the sludge before it is used. Farmers who accept sludge will be given documentation of its content.

The "water purification group," which consists of researchers from SINTEF NHL and the Dept. of Hydraulic and Environmental Engineering, has taken an interest in alternative uses of sewage sludge. The scientists have been working for a number of years on "hydrolysing" sludge, i.e. transforming particulate organic material that is difficult to break down into easily degradable organic compounds that may be reused within the wastewater treatment process for nitrogen removal.