Management of biological nutrient removal plant sludges - Change the paradigms?

Experience with the management of BNR sludges in Johannesburg has shown tha t accumulated N and P can readily be released from these sludges during slu dge thickening, dewatering and digestion. Therefore, primary and waste acti vated sludges should be treated in as aerobic a state as possible in separa te process streams. All sludge dewatering liquors should be pretreated for P; suspended solids and N removal before recycle to the liquid phase. Compo sting provides a viable alternative to anaerobic digestion for the stabiliz ation of BNR sludges, as use of the latter leads to the maximum solubilizat ion of N and P. (C) 1999 Elsevier Science Ltd. All rights reserved.