Closure to Discussions

The authors present a valuable contribution to a better understanding of membrane bioreactor (MBR) performance, especially related to biomass properties and process operation. We agree that there has been ‘‘little, if any, attention given to the behavior of membrane-derived sludges’’; hence, any new information is likely to be quickly absorbed by the professional community interested in the MBR process. For this reason, we would like to comment on the presented data and their interpretation and to ask the authors to provide some clarification. Biomass Production. From a practical point of view, the claim that ‘‘the amount of sludge produced as quantified by the observed yield was different’’ for MBR and activated sludge systems is very important and warrants additional examination. In a suspended growth biological system (such as activated sludge or MBR), the mean cell residence time (MCRT) is defined as follows: MCRT 1⁄4 XV Mx Where

[1]  Gary Amy,et al.  Role of soluble microbial products (SMP) in membrane fouling and flux decline. , 2006, Environmental science & technology.

[2]  Samer Adham,et al.  Are membrane bioreactors ready for widespread application? , 2005, Environmental science & technology.

[3]  S. Hermanowicz,et al.  Membrane bioreactor operation at short solids retention times: performance and biomass characteristics. , 2005, Water research.

[4]  Nancy G Love,et al.  Investigation of sorption behavior between pyrene and colloidal organic carbon from activated sludge processes. , 2004, Environmental science & technology.

[5]  J. Novak,et al.  Mechanisms of floc destruction during anaerobic and aerobic digestion and the effect on conditioning and dewatering of biosolids. , 2003, Water research.

[6]  H. Walker,et al.  Stability of particle flocs upon addition of natural organic matter under quiescent conditions. , 2001, Water research.

[7]  David C. Stuckey,et al.  A REVIEW OF SOLUBLE MICROBIAL PRODUCTS (SMP) IN WASTEWATER TREATMENT SYSTEMS , 1999 .

[8]  G. Phillips.  Effect of Solids Retention Time on Activated Sludge Properties and Effluent Quality , 1998 .

[9]  J. Novak,et al.  A Comparison of Membrane Bioreactor and Conventional‐Activated‐Sludge Mixed Liquor and Biosolids Characteristics , 2005, Water environment research : a research publication of the Water Environment Federation.

[10]  D. Jenkins,et al.  PHYSICAL, CHEMICAL AND BIOLOGICAL PROPERTIES OF SUBMERGED MEMBRANE BIOREACTOR AND CONVENTIONAL ACTIVATED SLUDGES , 2004 .

[11]  G. Daigger,et al.  Effect of Alum Addition on the Performance of Submerged Membranes for Wastewater Treatment , 2004, Water environment research : a research publication of the Water Environment Federation.

[12]  P. Ginestet,et al.  Transfer of organic matter between wastewater and activated sludge flocs. , 2001, Water research.

[13]  Nazim Cicek,et al.  Characterization and Comparison of a Membrane Bioreactor and a Conventional Activated‐Sludge System in the Treatment of Wastewater Containing High‐Molecular‐Weight Compounds , 1999 .

[14]  I. Droppo,et al.  Composition of extracellular polymeric substances in the activated sludge floc matrix , 1998 .

[15]  J. Chudoba.  Inhibitory effect of refractory organic compounds produced by activated sludge micro-organisms on microbial activity and flocculation , 1985 .