Characterization of Sludges from Wastewater Coagulation with Polymeric Aluminium Salts

Abstract

The application of hydrolizing aluminium and iron salts in chemical water and wastewater treatment is continuously increasing. Dosage of these chemicals will result in a considerable reduction of phosphorus concentrations in the effluent of phosphorus elimination and sewage treatment plants and hence will satisfy stringent effluent requirements, e.g. in Germany of 1.0 mg P/l for larger sewage works (> 100000 p.e.) and of 0.3 mg P/l for discharges into protected rivers and lakes. In addition to precipitation reactions with dissolved pollutants the hydrolizing metal salts destabilize suspended and colloidal substances, bringing about their aggregation into larger flocs, which can be separated efficiently. If one takes into account that suspended and colloidal material in raw sewage contributes significantly to the total pollution load, measured for example as BOD or COD (Ødegaard, 1988) the application of these chemicals becomes attractive for mechanical sewage works with increasing effluent demands as well as for temporarily overloaded treatment plants. Furthermore, an extensive and specific elimination of pollutants already in the primary clarifier of a mechanical-biological wastewater treatment plant offers interesting aspects with regard to denitrification without additional tank volume (Karlsson, 1988; Henze and Harremoës, 1990).