Pulp and paper mill wastewaters are nutrient deficient, BOD5:N:P may be as low as 100:1:0.2. Now that purification requirements have been tightened, the activated sludge process seems to be most commonly used treatment method. The conventional activated sludge process requires BOD:P ratios of 100 to 0.6 resulting in a need for P addition and hence in a possible increase in the P-level of the effluent.

In Finland and also in some other areas phosphorus removal is of great importance in the prevention of eutrophication of watercourses. There are several methods to control phosphorus level, such as biological phosphorus removal, running of the process under starvation of phosphorus, tertiary (chemical) treatment and simultaneous precipitation of phosphorus. This paper lists possible treatment methods and presents more closely chemical treatment using simultaneous precipitation by ferrous sulphate. The results are based on both pilot and full-scale experiments in two kraft pulp mills.

The study showed that phosphorus concentration can be reduced to a level of 1.2 mg/l (tot.P) by adding ferrous sulphate to the aeration basin in activated sludge treatment of kraft pulp mill wastewaters. Ferrous sulphate has, also, a slight positive effect on the sludge properties e.g. sludge settleability.

Activated sludge treatment, pulp and paper, wastewater treatment, phosphorus removal, ferrous sulphate, chemical treatment, simultaneous precipitation
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© IWA Publishing 1988
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