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Investigating the Fundamental Basis for Selectors to Improve Activated Sludge Settling
Author(s) -
GrayGabb Donald M.D.,
De Lange Vincent P.,
Chien Mark H.,
Esquer Mark A.,
Shao Y.J.
Publication year - 2010
Publication title -
water environment research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.356
H-Index - 73
eISSN - 1554-7531
pISSN - 1061-4303
DOI - 10.2175/106143009x12529484815791
Subject(s) - activated sludge , settling , environmental science , environmental engineering , waste management , biochemical engineering , sewage treatment , chemistry , engineering
Aerobic, anoxic, and anaerobic selectors have become popular for controlling filamentous bulking in activated sludge systems; however, selectors are not always successful. Regression analyses of data collected from 48 full‐scale wastewater treatment plants, with operating selectors, provided a method for ranking the importance of selector operating and design parameters (with respect to their influence on activated sludge settleability) and suggests optimum numerical ranges for these parameters for best selector performance. Selectors do not appear to control filamentous bulking in long mean cell residence time (MCRT) plants. Further, the elimination of all selector zones may help to control bulking in these plants. However, other design/operating parameters were shown to influence activated sludge settleability in long‐MCRT plants. Aerobic selectors in short‐MCRT plants can control filamentous bulking, if they are small enough to produce a biochemical oxygen demand (BOD) concentration gradient. Anoxic and anaerobic selectors can control filamentous bulking in short‐MCRT plants, if the selector volume is large enough and/or the selector mixed‐liquor suspended solids concentration is high enough. These unaerated selector systems do not appear to benefit from a BOD concentration gradient as the aerobic selectors in short‐MCRT plants do. Although anaerobic/anoxic selector compartmentalization in these plants appears to improve settleability, this presumably is because of reduced selector short‐circuiting.