Sewage sludge is the consequence of successful wastewater treatment. With the increasing number of wastewater treatment facilities and increasing intensity of treatment the amount of sludge produced will grow. The task of sludge treatment and disposal will therefore assume a significant place in environmental quality control. Sewage sludge is considered both a valuable resource possibly for agriculture, and a waste material which must be disposed of safely. Thus, regional solutions must be aimed for if available sites for agricultural application or a limited number of disposal sites are to be used wisely. Technically and economically feasible alternatives of treatment (and disposal) are numerous. The selection process to be discussed in this paper is a minimization of overall cost and/or an optimization of process reliability and cost. There exist proven mathematical tools for the solution of such optimization problems; in this instance dynamic programming routines have been utilized. The applicability of these methods, as well as their limits, are shown in a practical case study.

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