Reducing Sludge Disposal Costs at an Integrated Fine Paper Mill, 2002 Environmental Conference Proceedings

A. C. Lo and T. Mahmood

An integrated fine paper mill land-spreads its combined sludge comprised of primary clarifier rejects (primary sludge), recycled fiber rejects (RFR), and waste activated sludge (WAS). A comprehensive analysis of long-term mill data showed that the flocculant usage was highly dependent on variations in composition of the combined sludge. Of the three constituents, the RFR had the most positive impact on dewatering efficiency. Despite that, through improved fiber recovery, the reduced RFR discharge led to significantly increased flocculant requirements and, thus, sludge dewatering and hauling costs. The mill wanted to optimize the sludge dewatering process for reducing sludge management cost. In order to optimize sludge conditioning, side-by-side evaluations were performed on three chemical conditioning programs in the laboratory and compared to full-scale trials at the mill. Based on laboratory and pilot studies, the most economical and optimal sludge-conditioning program was implemented at the mill saving $150,000 per year.

Although high sludge dewatering chemical costs have been frequently emphasized in the literature, sludge-hauling costs have received relatively less attention. In this study, an economic analysis was performed by considering dewatering chemical and sludge-hauling costs. The combined cost (dewatering chemical plus sludge-hauling cost) showed a minimum or a leveling-off trend when plotted against press cake solids, implying that the overall lowest cost of sludge disposal does not necessarily correspond to the highest cake consistency.