Process Integration in Sludge Management

Abstract

Complex interactions occur between individual sludge treatment processes and other sludge management processes. Sludge treatment processes also interact with wastewater treatment processes. Consideration of those interactions has been facilitated in this work by a computerized optimization scheme using models of process performance and cost based on fundamental design and operational variables. Illustrations of the type of results obtained are described. It is indicated that the mean cell residence time of activated sludge processes and the retention time of anaerobic digesters should, with current energy costs, be as short as possible while assuring satisfactory operation. The additional cost of larger gravity thickeners is often offset by savings in anaerobic digestion and other process costs. The method by which sludge is transported to a point of ultimate disposal has an important effect on identification of the lowest cost technique for sludge management. Based on available cost information, ocean disposal, where feasible, is nearly always cost effective and sludge combustion is not. The cost of energy significantly affects optimal design of sludge treatment processes.