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Clarifying the roles of kinetics and diffusion in activated sludge filamentous bulking
Author(s) -
Lou In Chio,
de los Reyes Francis L.
Publication year - 2008
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.21886
Subject(s) - diffusion , activated sludge , substrate (aquarium) , segmented filamentous bacteria , chemistry , kinetics , chemical engineering , competition (biology) , process (computing) , biophysics , pulp and paper industry , environmental engineering , biology , sewage treatment , environmental science , thermodynamics , ecology , physics , quantum mechanics , computer science , engineering , operating system
We hypothesized that the growth rates of filaments and floc formers in activated sludge are affected by the combination of kinetic selection (Lou and de los Reyes, Biotechnol Bioeng 92(6): 729–739, 2005b) and substrate diffusion limitation (Martins et al., Water Res 37:2555–2570, 2003). To clarify the influence of these factors in explaining filamentous bulking, a conceptual framework was developed in this study. The framework suggests the existence of three different regions corresponding to bulking, non‐bulking, and intermediate regions, based on substrate concentration. In the bulking and non‐bulking regions, kinetic growth differences control the competition process, and filaments or floc formers dominate, respectively. In the intermediate region, substrate diffusion limitation, determined by the floc size, plays the major role in causing bulking. To test this framework, sequencing batch reactors (SBRs) were operated with influent COD of 100, 300, 600, and 1,000 mg/L, and the sludge settleability was measured at various floc size distributions that were developed using different mixing strengths. The experimental data in the bulking and intermediate regions supported the proposed framework. A model integrating the two factors was developed to simulate the substrate concentrations at different depths and floc sizes under intermittently feeding conditions. The modeling results confirmed that substrate diffusion limitation occurs inside the flocs at a certain range of activated sludge floc sizes over the operation cycle, and provided additional support for the proposed framework. Biotechnol. Bioeng. 2008;101: 327–336. © 2008 Wiley Periodicals, Inc.