Accepted ManuscriptTitle: Biodegradation of the Endogenous Residue of Activated SludgeAuthors: Abdellah Ramdani, Peter Dold, Stéphane Déléris, Daniel Lamarre, AlainGadbois, Yves ComeauPII: S0043-1354(09)00849-5DOI: 10.1016/j.watres.2009.12.037Reference: WR 7819To appear in:Water ResearchReceived Date: 29 July 2009Revised Date: 23 November 2009Accepted Date: 22 December 2009Please cite this article as: Ramdani, A., Dold, P., Déléris, S., Lamarre, D., Gadbois, A., Comeau, Y.Biodegradation of the Endogenous Residue of Activated Sludge, Water Research (2009), doi: 10.1016/j.watres.2009.12.037This is a PDF file of an unedited manuscript that has been accepted for publication. As a service toour customers we are providing this early version of the manuscript. The manuscript will undergocopyediting, typesetting, and review of the resulting proof before it is published in its final form. Pleasenote that during the production process errors may be discovered which could affect the content, and alllegal disclaimers that apply to the journal pertain.MANUS CRIP T ACCEP TEDACCEPTED MANUSCRIPT Biodegradation of the Endogenous Residue of Activated Sludge 1 Abdellah Ramdania,*, Peter Doldb, Stéphane Délérisc, Daniel Lamarred, Alain Gadboisd, Yves 2 Comeaua 3 4 a Department of Civil, Geological and Mining Engineering, Ecole Polytechnique of Montreal, 5 P.O. Box 6079, Station centre-ville, Montreal (Quebec) H3C 3A7, Canada 6 b EnviroSim Associates Ltd., 7 Innovation Drive Suite 205, Flamborough (Ontario) L9H 7H9, 7 Canada 8 c Anjou Recherche, Veolia Environment, BP79, Chemin de la Digue, 76 400, Maisons-Laffitte, 9 France 10 d John Meunier Inc., 4105, Sartelon Street, Saint-Laurent (Quebec) H4S 2B3, Canada 11 *Corresponding author. Tel.: +1 514 340 4711 (ext. 3966); Fax: +1 514 340 5918. 12 E-mail address: [email protected] 13 14 Abstract 15 This study evaluated the potential biodegradability of the endogenous residue in activated sludge 16 subjected to batch digestion under either non-aerated or alternating aerated and non-aerated 17 conditions. Mixed liquor for the tests was generated in a 200 L pilot-scale aerobic membrane 18 bioreactor (MBR) operated at a 5.2 days SRT. The MBR system was fed a soluble and 19 completely biodegradable synthetic influent composed of sodium acetate as the sole carbon 20 source. This influent, which contained no influent unbiodegradable organic or inorganic 21MANUS CRIP T ACCEP TEDACCEPTED MANUSCRIPT materials, allowed to generate sludge composed of essentially two fractions: a heterotrophic 22 biomass XH and an endogenous residue XE, the nitrifying biomass being negligible (less than 23 2%). The endogenous decay rate and the active biomass fraction of the MBR sludge were 24 determined in 21-day aerobic digestion batch tests by monitoring the VSS and OUR responses. 25 Fractions of XH and XE: 68% and 32% were obtained, respectively, at a 5.2 days SRT. To assess 26 the biodegradability of XE, two batch digestion units operated at 35°C were run for 90 days using 27 thickened sludge from the MBR system. In the first unit, anaerobic conditions were maintained 28 while in the second unit, alternating aerated and non aerated conditions were applied. Data for 29 both units showed apparent partial biodegradation of the endogenous residue. Modeling the 30 batch tests indicated endogenous residue decay rates of 0.005 d-1 and 0.012 d-1 for the anaerobic 31 unit and the alternating aerated and non-aerated conditions, respectively. 32 Keywords: Activated sludge; endogenous residue; aerobic digestion; anaerobic digestion; 33 biodegradation; modeling. 34 1. Introduction 35 The activated sludge process is the most commonly used method for biological wastewater 36 treatment of both municipal and industrial effluents. In this process, organic and inorganic 37 pollutants are transformed into acceptable end-products and treated water can be discharged to 38 the receiving environment. A significant amount of excess activated sludge (containing more 39 than 99% water) is generated in this process, however. The treatment and disposal of this sludge 40 is expensive and accounts for up to 60% of the total operating costs of wastewater treatment 41 plants (Canales et al., 1994; Low and Chase, 1999; Wei et al., 2003). Reducing sludge 42 production in wastewater treatment plants thus presents an obvious economic interest. 43MANUS CRIP T ACCEP TEDACCEPTED MANUSCRIPT Earlier studies dealing with aerobic and anaerobic digestion of activated sludge studied ways to 44 design and optimize processes aimed at stabilizing the active heterotrophic biomass (XH) fraction 45 of the activated sludge. Solids degradation usually was the most important parameter used to 46 evaluate the efficiency of aerobic and anaerobic digestion processes. The effect of these 47 processes on the degradation of each organic fraction of the activated sludge, however, was 48 rarely investigated. Furthermore, it is generally considered that the inactive organic fractions of 49 sludge (unbiodegradable influent organic matter XU,Inf and endogenous residue XE) do not 50 undergo transformation in such digestion processes. 51 The objective of this work was to study the potential biodegradation of endogenous residue XE 52 under either anaerobic conditions or under alternating aerated and non-aerated conditions. To 53 target XE in this investigation, a biological sludge was developed in an activated sludge system 54 fed with synthetic and completely soluble and biodegradable influent. 55 A concise review is first presented about the endogenous residue in activated sludge systems, the 56 mathematical models describing its generation, the composition of the mixed liquor in activated 57 sludge systems fed with municipal influent and with soluble and completely biodegradable 58 synthetic influent, the theoretical considerations for the active fraction determination in activated 59 sludge systems, and a summary of earlier studies dealing with the biodegradation of XE. 60 1.1. Endogenous residue in activated sludge systems 61 Ordinary heterotrophic biomass (XH) utilizes readily biodegradable substrate SS for growth 62 according to Monod kinetics in an activated sludge system, not limiting in oxygen (Grady et