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Estimation of Autotrophic Maximum Specific Growth Rate Constant—Experience from the Long-Term Operation of a Laboratory-Scale Sequencing Batch Reactor System

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The autotrophic maximum specific growth rate constant, μ A,max, is the critical parameter for design and performance of nitrifying activated sludge systems. In literature reviews (i.e., Henze et al., 1987; Metcalf and Eddy, 1991), a wide range of μ A,max values have been reported (0.25 to 3.0 days −1); however, recent data from several wastewater treatment plants across North America revealed that the estimated μ A,max values remained in the narrow range 0.85 to 1.05 days −1. In this study, long-term operation of a laboratory-scale sequencing batch reactor system was investigated for estimating this coefficient according to the low food-to-microorganism ratio bioassay and simulation methods, as recommended in the Water Environment Research Foundation (Alexandria, Virginia) report ( Melcer et al., 2003). The estimated μ A,max values using steady-state model calculations for four operating periods ranged from 0.83 to 0.99 day −1. The International Water Association (London, United Kingdom) Activated Sludge Model No. 1 (ASM1) dynamic model simulations revealed that a single value of μ A,max (1.2 days −1) could be used, despite variations in the measured specific nitrification rates. However, the average μ A,max was gradually decreasing during the activated sludge chlorination tests, until it reached the value of 0.48 day −1 at the dose of 5 mg chlorine/(g mixed liquor suspended solids · d). Significant discrepancies between the predicted X A/ Y A ratios were observed. In some cases, the ASM1 predictions were approximately two times higher than the steady-state model predictions. This implies that estimating this ratio from a complex activated sludge model and using it in simple steady-state model calculations should be accepted with great caution and requires further investigation.

Keywords: Activated Sludge Model No. 1; bioassay; modeling; nitrification; sequencing batch reactor

Document Type: Research Article


Publication date: April 1, 2008

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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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