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Bulking sludge in biological nutrient removal systems
Author(s) -
Martins Antönio M. P.,
Heijnen Joseph J.,
van Loosdrecht Mark C. M.
Publication year - 2004
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.20029
Subject(s) - anoxic waters , anaerobic exercise , activated sludge , bioreactor , segmented filamentous bacteria , microaerophile , settling , chemistry , pulp and paper industry , enhanced biological phosphorus removal , bacteria , biology , environmental chemistry , environmental engineering , wastewater , environmental science , botany , physiology , genetics , engineering
Bulking sludge problems are commonly reported in biological nutrient removal (BNR) systems. This has led to the general belief that intrinsic BNR conditions favor the growth of undesirable and excessive filamentous bacteria. The present study shows that other factors have a major role in bulking, and not the BNR conditions. These factors have been verified in well‐controlled, strictly anoxic–aerobic and strictly anaerobic–aerobic sequencing batch reactor systems. The experimental results show that conditions known to be responsible for bulking sludge in aerobic systems (i.e., low concentration of electron donor and/or electron acceptor) did not lead to bulking. Even when acetate was present at very low concentrations in the aerobic stage of an anaerobic–aerobic bio‐P system, the sludge settleability remained very good. This clearly demonstrates that good bio‐P activity can stabilize and improve sludge settleability. The presence of microaerophilic conditions in the anoxic stage of the anoxic–aerobic system was the only factor leading to worsening sludge settling characteristics. The results are discussed in light of our previous hypothesis about the importance of diffusion‐limited substrate uptake for the development of filamentous structures in biological flocs. The hypothesis is extended to anaerobic–aerobic and anoxic–aerobic conditions, typical of BNR‐activated sludge systems. Taking into account the effect of feeding patterns on biochemical rates and on the development of filamentous bacterial structures, we recommend the adoption of plug‐flow selector configurations, with strictly anaerobic and/or strictly anoxic conditions, wherein microaerophilic conditions are excluded, in order to maintain reliable and robust BNR performance. © 2004 Wiley Periodicals, Inc.