High Load Trickling Filters. Biofilm Accumulation and Sludge Production

A pilot–scale investigation was carried out to evaluate the parameters affecting biofilm accumulation and sludge production. The behaviour of a cross flow (CF) plastic medium filter (4.3 m of Plasdek B 27) was followed over an eight month period. Four hydraulic loadings, from 2.5 to 3.6 m³/m²h, (organic loadings from 1.5 to 6.2 Kg BOD₅/m³d) were experimented. Medium temperature, BOD₅ influent and hydraulic loading were determinants for biofilm accumulation and sludge production. The specific oxygen uptake rate (SOUR) of waste sludge was found related to inlet BOD₅. Furthermore a relationship between median retention time (MRT) and filter biomass was obtained; this relationship gave also a good capacity to interpret MRT for low–rate filters.