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The City of Barrie wastewater treatment plant (WWTP) is a high purity oxygen activated sludge system that includes primary treatment, tertiary fixed film nitrification, effluent filtration and ultraviolet light disinfection. A dual digestion system is used for sludge treatment (Gemmell et. al, 1999). System operation has been successful in providing the degree of stabilization required, however, thermophilic temperatures have not always been achieved. Kinetic and thermodynamic evaluation of the full scale operating results showed that separate waste activated sludge (WAS) thickening was required to achieve a feed solids concentration between 5 and 6% dry solids (ds) necessary to achieve thermophilic temperatures. Site specific dual digestion aerobic and anaerobic hydraulic retention times of 3 days and between 12 and 15 days respectively are proposed. Side-by-side pilot testing was conducted to compare gravity belt thickeners (GBTs) and rotary drum thickeners (RDTs). Tests showed the GBTs and the RDTs achieved average thickened sludge concentrations of 6.2% ds and 7.4% ds, respectively. Polymer consumption for the GBT and the RDT averaged 6.2 and 8.3 kg/t ds, respectively. RDTs were selected for implementation because their performance and enclosed design minimizes operator exposure to processed solids and affords an effective means for ventilation design. Limited full scale operating results for the full scale dual digestion system with RDTs are also reported.

Document Type: Research Article


Publication date: 2000-01-01

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