Linking hydrolytic activities to variables influencing a submerged membrane bioreactor (MBR) treating urban wastewater under real operating conditions C. Go ´mez-Silva ´n a , J. Are ´valo b , J. Pe ´rez b , J. Gonza ´ lez-Lo ´pez a , B. Rodelas a, * a Departamento de Microbiologı´a, Facultad de Farmacia, Campus de Cartuja s/n, 18071 Granada, Spain b Departamento de Ingenierı´a Civil, Universidad de Granada, 18071 Granada, Spain article info Article history: Received 3 May 2012 Received in revised form 10 September 2012 Accepted 16 September 2012 Available online 4 October 2012 Keywords: Wastewater treatment Hydrolytic enzymes Phosphatase Glucosidase Protease Multivariate analysis abstract The seasonal variation of the hydrolytic activities acid and alkaline phosphatase, a- glucosidase and protease, was studied in both the aerated and anoxic phases of a full-scale membrane bioreactor (MBR) (total operational volume ¼ 28.2 m 3 ), operated in pre- denitrification mode and fed real urban wastewater. Non-metric multidimensional scaling (MDS) and BIO-ENV analysis were used to study the distribution of enzyme activ- ities in different seasons of the year (spring, summer and autumn) and unveil their rela- tionships with changes in variables influencing the system (composition of influent wastewater, activated sludge temperature and biomass concentration in the bioreactors). The activities of all the tested hydrolases were remarkably dynamic, and each enzyme showed complex and diverse patterns of variation. Except in the summer season, the variables included in this study gave a good explanation of those patterns and displayed high and consistent correlations with them; however, markedly different correlation trends were found in each season, indicating dissimilar adaptation responses of the community to the influence of changing conditions. A consistent and highly negative correlation between protease and a-glucosidase was revealed in all the experiments. The variables included in this study showed contrary influences on these activities, suggesting an alternation of the major groups of carbon-degrading hydrolases in connection to changes in temperature and the availability and composition of nutrients in the different seasons. Sampling over a long period of time was required to adequately lay down the links between hydrolytic activities and the variables influencing the MBR system. These results highlight the complexity of the regulation of substrate degradation by the mixed microbial sludge communities under real operating conditions. ª 2012 Elsevier Ltd. All rights reserved. 1. Introduction In biological wastewater treatment (WWT), the removal of organic matter relies on the activity of a mixed community of heterotrophic microorganisms (Burgess and Pletschke, 2008). The oxidative processes can utilize oxygen as the terminal electron acceptor or use nitrate under anoxic conditions, a step which is also of central importance to support nitrogen removal through nitrificationedenitrification (Galvez et al., 2003). Organic matter in wastewater is composed of a high fraction (40e60%) of particulate material, which requires an initial hydrolysis into low-molecular weight products prior to * Corresponding author. Tel.: þ34 958 241755; fax: þ34 958 246235. E-mail address: mrodelas@ugr.es (B. Rodelas). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 47 (2013) 66 e78 0043-1354/$ e see front matter ª 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.watres.2012.09.032