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A Comparative Pilot-Scale Study of the Performance of Conventional Activated Sludge and Membrane Bioreactors under Limiting Operating Conditions

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The behavior of the conventional activated-sludge (CAS) process was compared to that of the membrane bioreactor (MBR) process under limiting operating conditions; that is, at a low solids retention time (SRT) and hydraulic residence time (HRT). The SRT was varied from 2 to 7 days, and the HRT ranged from 5 to 18 hours. The comparison was carried out in terms of nitrification and denitrification kinetics and in terms of the carbon and nitrogen removal performance of these processes. The study involved two pilot-scale units: a CAS unit with a 9-m3 aeration tank and a 225-L MBR. Both of these units were installed and run under real process conditions at a wastewater treatment plant in Evry, France. In the case of the MBR process, the specific nitrification rates, rN, and the specific denitrification rates, rDN, increased as SRT was reduced from 6.5 days to 2 days. This trend was reversed and the rN and rDN decreased only when the HRT was reduced to 5 hours. A similar behavior was observed in the case of the CAS process, although rN and rDN increased only when the SRT was reduced to as low as 4 days; below this value, the rates dropped considerably. It seems that the presence of the membrane renders the MBR more robust by preventing the washout of nitrifiers at low SRT and HRT. Besides the structure and size distribution of the MBR, flocs are more favorable to intraparticle mass trasfer than those of the CAS process and could explain the higher nitrification kinetics observed with the MBR process. In all cases, the carbon and nitrogen removal performance of the MBR process was better than that of the CAS system.


Document Type: Research Article


Publication date: May 1, 2003

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  • Water Environment Research® (WER®) publishes peer-reviewed research papers, research notes, state-of-the-art and critical reviews on original, fundamental and applied research in all scientific and technical areas related to water quality, pollution control, and management. An annual Literature Review provides a review of published books and articles on water quality topics from the previous year.

    Published as: Sewage Works Journal, 1928 - 1949; Sewage and Industrial Wastes, 1950 - 1959; Journal Water Pollution Control Federation, 1959 - Oct 1989; Research Journal Water Pollution Control Federation, Nov 1989 - 1991; Water Environment Research, 1992 - present.
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