Elimination of Phosphorus from Waste Water by Crystallization

Abstract

Precipitation by Fe and Al salts or lime, which is the main process used in Germany for phosphorus removal, entails some problems, such as increasing the anion concentration of the water, and problems in recovering the phosphorus from the precipitation sludge. Therefore, a process for phosphorus removal from waste water was developed, which involves a direct precipitation of Calcium phosphate induced by Calcite as the seeding material. The pH was adjusted with lime, but some experiments were done with MgO as well. Basic investigations led to possible applications with both municipal waste waters with low phosphorus concentrations and industrial effluents with considerably higher phosphorus contents of up to 400 mg l−1 P. Continuous bench scale experiments with a stirred reactor to remove phosphorus from the waste water of a motorcar factory were completed. Based on the good results achieved, a full scale device for the treatment of 160 m3 per hour was commissioned in July 1996 and has been run successfully since this time. Furthermore, aspects of recycling the phosphorus are given.