Combining submerged membrane technology with anaerobic and ...

Chapter 4excellent COD removal performance. On average, the permeate COD was less than 15mg·L -1 with COD removals above 95%. The absence of suspended solids, the very low COD concentration and the levelof nutrients in the effluent allow reusing purified wastewater (e.g. in agriculture). The application of anoxic cycles in the first chamber of the MBR did notestimulate denitrification process as a consequence of the worsening on nitrificationcapacity. The proposed system showed flexibility to convert total nitrogen to NH 4+and/orNO 3- . Biogas production was detected during the whole operating period, with averagemethane content of 75-80%. Due to effective retention of biomass by the UASB reactorand membrane module, sludge concentration in the anaerobic bioreactor could be kept athigh values, reaching more than 30 g·L -1 . Moreover, granular sludge growth was observed. The employment of internal recirculation from aerobic biofilm chamber of the MBRto the UASB allowed diminishing biomass production, to values similar than thoseobserved for the anaerobic treatment. The membrane was operated at ambient temperature with fluxes of 15 L·m -2·h -1 ,lower than those achieved in aerobic MBRs treating municipal wastewater, but higher thanfluxes obtained in AnMBR. The only difference between the two proposed configurations was the bettermembrane performance observed during period II, when recirculation was turned off andthe system could be considered as a UASB reactor with an aerobic MBR post-treatment. In this kind of configurations is important to assure a minimum F/M ratio in theMBR in order to reach a suitable MLVSS concentration for membrane operation.4.6. ReferencesAPHA-AWWA-WPCF. 1998. Standard Methods for the Examination of Water and Wastewater, 20 thed., American Public Health Association, Washington, USA.Bouhabila, H., Ben Aïm, R., Buisson, H. 2001. Fouling characterisation in membrane bioreactors.Separation and Purification Technology 22-23, 123-132.Brepols, C. 2011. Operating large scale membrane bioreactors for municipal wastewater treatment,1 st ed., IWA publishing, London, UK.126