PACKED-BED AND FLUIDIZED-BED BIOFILM REACTOR PERFORMANCE FOR ANAEROBIC WASTE-WATER TREATMENT

Anaerobic degradation performance of a laboratory-scale packed-bed reactor (PBR) was compared with two fluidized-bed biofilm reactors (FBRs) on molasses and whey feeds. The reactors were operated under constant pH (7) and temperature (35 degree C) conditions and were well mixed with high recirculation rates. The measured variables were chemical oxygen demand (COD), individual organic acids, gas composition, and gas rates. As carrier, sand of 0. 3-0. 5 mm diameter was used in the FBR, and porous clay spheres of 6 mm diameter were used in the PBR. The results of dynamic step change experiments, in which residence times and feed concentrations were changed at constant loading, demonstrated the rapid response of the reactors. Thus, the response times for an increase in gas rate or an increase in organic acids due to an increase in feed concentration were less than 1 day and could be explained by substrate limitation. The performance of the FBR with whey was comparable to its performance with molasses, and switching of molasses to whey feed resulted in immediate good performance without adaptation.