Enhancement of biomass speciation in Step Sludge Recirculation activated sludge system by the use of submerged membranes

In this work the performances of the Step Sludge Recirculation (SSR) activated sludge process were improved by using submerged membranes. The SSR system used in the experiments consisted of an anoxic stage for the denitrification and four aerobic stages for the nitrification, followed by a sedimentation stage in order to separate the purified water from the biomass. This conventional SSR system was compared with an improved one by substituting the secondary clarifier with a submerged membrane module. Two different types of flat sheet membrane were fitted into the membrane module and checked on performances. The main objective of the work was to optimize the process in order to obtain a maximum in the removal of ammoniacal nitrogen. For all the tested systems, the activated sludge presented high microfauna density, and the system with submerged membranes presented highest efficiency in nitrogen removal. The use of membranes instead of a sedimentation tank has the additional advantage to selectively separate different microorganisms (among bacteria and protozoa) from the biomass, thus enhancing the overall efficiency of the biological process, with an increase equal up to 43%. (C) 2009 Elsevier B.V. All rights reserved.