Microbial enzymatic activities in a pilot-scale MBR experimental plant under different working conditions M. Molina-Muñoz a,1 , J.M. Poyatos a,b, * ,1 , B. Rodelas a,c , C. Pozo a,c , M. Manzanera a , E. Hontoria a,b , J. Gonzalez-Lopez a,c a Institute of Water Research, University of Granada, Granada, Spain b Department of Civil Engineering, University of Granada, Granada, Spain c Department of Microbiology, University of Granada, Granada, Spain article info Article history: Received 27 May 2009 Received in revised form 17 August 2009 Accepted 18 August 2009 Available online 12 September 2009 Keywords: Membrane bioreactor Activated sludge Enzymatic activities Biomass activity abstract Phosphatases, glucosidase, protease, esterase and dehydrogenase activities in a MBR (membrane bioreac- tor) system equipped with ultrafiltration membranes for the treatment of real urban wastewater were measured at different volatile suspended solid (VSS) concentrations, total suspended solid (TSS) concen- trations, hydraulic retention times (HRT), temperatures and inflow rates. The results showed the capacity of the MBR system to remove COD and BOD 5 at TSS between 7200 and 13,300 mg/L; HRT values of 8.05 and 15.27 h; inflow rates of 14.67 and 27.81 L/h; and temperatures between 4 and 27 °C. The enzymatic activities are influenced by increases in VSS and TSS concentrations. These results suggest that the ability to get adapted to environmental changes of the bacterial populations and their microbial enzymatic activities is essential to understand the biological processes that occur in MBR systems and crucial for proper urban wastewater treatment when using MBR technologies. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Conventional activated sludge processes (CASPs) have estab- lished their efficiency in removing pollutants from sewage waters. Nevertheless technical developments require new technologies better adapted to the elimination of contaminants, thus enabling the effluent to reach an acceptable quality for the direct re-use of the treated wastewater. The adaptability of the submerged membrane bioreactor (MBR) systems enables the possibility of the latter to adjust to an acti- vated sludge previously present, thereby increasing the volume loading rate of the influent and/or the load that current treatment plants accommodate (Côté et al., 2004). The MBR technology is as suitable for the treatment of domestic wastewater as it is for industrial wastewater (Stephenson et al., 2000). Due to the high quality of the effluent and the exceptional compactness of the plants, MBR technology can be adapted for conditions where treatment of complex effluents need to operate with an aged activated sludge. CASPs cannot produce an effluent of high quality for re-use at reasonable cost in some specific appli- cations; and the spatial limitation of the area does not permit the size of a conventional process plant, or its amplification. One of the main benefits of MBR systems is the ability to work with high concentrations of mixed liquor volatile suspended solids (VSS) present in the sludge, regardless of the organic load in the wastewater (Witzig et al., 2002). Elevated concentrations of VSS enable to work with high cell retention times, favouring the devel- opment of slow-growing bacteria, such as ammonia oxidizers and nitrite oxidizers, which are crucial for the transformation of the toxic nitrogen compounds ammonia and nitrite (Witzig et al., 2002). Microbial communities developed in MBR-based treat- ments are exposed to completely different conditions that the mic- robiota developed in CASPs, mainly due to the biomass recycling occurring in MBR, which leads to changes in the biology of the sys- tem. Bacteria are subjected to a substrate-limited environment, which induces low growth rates and reduces the microbial respi- ratory potential. Consequently there is a marked influence in both the biological activities and species composition of the sludge community (Konopka, 2000; Konopka et al., 1996; Morgan et al., 2002). Measuring biomass concentration and enzymatic activities is essential to achieve the biological characterization of a complex microbial microcosm such as activated sludge (Liwarska-Bizukojc and Ledakowicz, 2003; Whiteley et al., 2002). During activated 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.08.071 * Corresponding author. Address: Instituto del Agua, Universidad de Granada, C/ Ramón Y Cajal No. 4, 18071 Granada, Spain. Tel.: +34 95826154; fax: +34 958246138. E-mail address: jpoyatos@ugr.es (J.M. Poyatos). 1 These authors have contributed equally to this work. Bioresource Technology 101 (2010) 696–704 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech