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. The process is made up of an anoxic stage for the denitrification and four aerobic stages for the nitrification. The conventional system was compared with system where the secondary clarifier was substituted by a submerged membrane module. Two different types of flat sheet membrane were fitted into the membrane module. The performances were measured by means of a microscopic observation of the microfauna and other physical-chemical analysis. The main objective of the work was to optimize the process in order to obtain a maximum in the removal of ammoniacal nitrogen. For the all tested systems, the activated sludge presented high microfauna density although the system with submerged membranes presented a higher efficiency in nitrogen removal. These results were however affected by the inhibition of nitrification provoked by free ammonia. No significant fouling was observed for the membranes.