Removing Phosphorus from Municipal Waste Water before Its Discharge to Watercourse

Keywords: Eutrophication, phosphorus sources, municipal wastewater, phosphorus removal, chemical treatment, enhanced biological phosphorus removal, discharges, sludge, costs.

The phosphorus (P) sources to municipal wastewater are human excreta, kitchen waste and detergents and other cleansing agents. The phosphorus load on municipal wastewaters in Europe is estimated to vary between 0.65 and 0.95 kg P per capita per year. The variation is caused by differences in the consumption of detergent phosphorus. Removal of phosphorus in detergents and cleansing agents could reduce the phosphorus load to receiving waters by 25-40% in countries without special measures for phosphorus removal at the treatment plants. With such phosphorus removal, source control will have a negligible effect. Different methods for phosphorus removal using chemical precipitation and biological processes are reviewed. The pros and cons of the methods are briefly discussed. Both chemical and biological methods can provide effluents with phosphorus concentrations well below the requirements of the Urban Wastewater Directive of the European Union. Experiences from Finland and Sweden, countries where almost all treatment plants employ phosphorus removal, show that it on a national level is possible to achieve phosphorus discharges from municipal wastewater treatment plants below 0.05 kg phosphorus per capita per year. With phosphorus removal the amount of sludge dry solids will increase by between 10 to 20%, with the greater quantity resulting from the chemical methods, and the lesser increase from the biological. The investments for implementing phosphorus removal at existing plants is often low, as are the marginal operational costs. Examples of total operation cost at Scandinavian treatment plants with both phosphorus and nitrogen removal are given.

Dr Peter Balmér, VA-strategi, Östersnäsvägen 16, S-43136 Mölndal, Sweden.

16 pages, 2 figures, 1 table, 28 references.