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A Case for Low Return Sludge Flow Rates

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A common problem encountered by traditional activated sludge systems involves failure to develop biomass that separates efficiently from the liquid, leaving behind a clear effluent that is low in BOD5 and suspended solids. Another problem is the bleed-through of ammonia due to low detention time in the aeration tank. Oftentimes, failure may be attributed to high return sludge flow rates (RSF) that affect not only clarifier hydraulics, but also the growth of bacteria in the system. In order to promote efficient separation and nitrification, system conditions should be maintained that favor the growth of flocforming bacteria and nitrifiers over nuisance microorganisms that may include filaments. Favorable conditions are encouraged by a regime of higher detention time and feast and famine experienced by the bacteria in the system. By viewing system operation through this lens, the following paper proposes that many activated sludge treatment systems can achieve significant operational improvement through reduction in RSF. This paper further provides a method for minimizing RSF and presents examples of successful application of this method
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Keywords: Activated sludge; bioreactor; feast/famine; microbiology; respiration rate; return sludge flow rate; sludge settleability; specific oxygen uptake rate; state-point analysis

Document Type: Research Article

Publication date: 2010-01-01

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