Wet scrubber systems for flue gas treatment, giving rise to a production of wastewater contaminated with heavy metals, are used at many coal-fired power stations in Europe, the USA and Japan.

In order to remove the heavy metals from the wastewater, chemical precipitation with hydroxide and sulphide is applied. Results from two full-scale plants are given.

Due to strict regulations for landfilling of waste contaminated with heavy metals, the amount of sludge must be minimised. Different techniques to meet this requirement are described.

Biological post-treatment to reduce the nitrogen content of the wastewater will apparently be a need in the future, and pilot-scale testing is presently being carried out to determine the basic operation rules for a full-scale plant.