FIELD EXPERIENCE WITH DIFFERENT SYSTEMS FOR BIOMASS ACCUMULATION IN ANAEROBIC REACTOR TECHNOLOGY

Thanks to undeniable advantages as recovery of energy aid a low sludge production, anaerobic wastewater treatment has received recognition i n the last decade. However due to the slow methanogenic growth, in-rea ctor biomass accumulation is essential to maintain high loading rates. Indeed wash-out of biomass is one of the main problems encountered in the anaerobic treatment of industrial effluents. A broad scoped overv iew of the different reactor technologies is given each with its prope r biomass accumulation system. All of them are founded on two basic me chanisms for biomass accumulation: separation and retention. Settling (Anaerobic Contact reactor), ultrafiltration and flotation (Flotamet(P )) are the techniques used to separate externally the biomass from the effluent after which the biomass can be recirculated to the anaerobic reactor. Concentration of biomass can also be achieved by attachment to a mobile (Fluidized Bed reactor) or a static carrier with possible entrapment in its macroporous structure (Anaerobic Filter reactor). Th e UASB-reactor incorporates retention as well as separation. By stimul ating granular growth, biomass is accumulated in the lower pan of the reactor. A three phase separator at the top of the reactor contributes to the final clarification of the effluent. Hybrid reactors eventuall y combine different biomass accumulation mechanisms: granulation, exte rnal biomass separation (Upflow Anaerobic Contact reactor) and fixatio n (Upflow Anaerobic Contact Filter reactor).