Elliott, A. and Mahmood, T., Paprican, Canada
(free)With sludge management costs as high as 60% of the total wastewater treatment plant operating costs, it is economically advantageous for industrial applications such as with the pulp and paper sector, as well as the municipal sector to reduce their biosolids production. A reduction of excess biological sludge generated can substantially reduce these operating costs. Through the manipulation of the aeration stages for activated sludge systems, a scenario has been developed to reduce the generation aerobic sludge. This process is known as the low sludge production (LSP) process. In this process the return activated sludge by-passes the first (dispersed growth) stage to be received only by the second (predatory) stage. The resulting once-through operation of the first stage makes it potentially susceptible to bacterial washout under hydraulic shock conditions, which is an important consideration in full-scale implementation of this process. We have performed a sensitivity analysis of the first stage operation by varying its HRT time. The experimental data revealed that the optimal first stage hydraulic residence is between three to five hours with bacterial washout likely to be initiated below two hours. A dual-train activated sludge pilot treatment system was installed at pulp and paper mill site to evaluate the potential benefits of the LSP process. The treatment performance, including aeration demand and sludge dewatering, of the LSP train was compared with that of a conventional activated sludge (CAS) train. The LSP system produced 31% less sludge. The LSP system required 19% more aeration. Treatment performance in terms of BOD and COD removals remained unchanged compared to the CAS system. Ammonia release in the predatory stage was exhibited. The LSP system consistently exhibited lower settling indexes than those from the CAS system. A 40% reduction in dewatering cost was calculated for the mill if an LSP system were to be implemented. Based on these findings, as well as data from other researchers, the process has been implemented at several pulp and paper installations in Canada. There is potential for the transferability of this process to the municipal sector but several factors must be considered. KEY WORDS Low Sludge Process, LSP, Sludge Reduction, Dispersed Growth, RAS, Pulp and Paper
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