INFLUENCE OF DETACHMENT, SUBSTRATE LOADING AND REACTOR SCALE ON THE FORMATION OF BIOFILMS IN AIRLIFT REACTORS

For a stable and reliable operation of the biofilm airlift suspension reactor (BAS reactor) means to control biomass concentration, biofilm thickness and biofilm morphology are required. For this reason, the in fluence of applied detachment forces and surface substrate loading on the formation of heterotrophic biofilms in laboratory-scale BAS reacto rs was studied. Detachment forces were altered by variation of the ini tial bare carrier concentration or the superficial air velocity. In ad dition, the dynamics of biofilm formation during start-up of a full sc ale BAS reactor (300 m(3)) was monitored and compared with the laborat ory-scale start-up (31). This study shows that the biofilm morphology and strength were influenced to a large extent by the surface substrat e loading and applied detachment forces. A moderate surface substrate loading and a high detachment force yielded smooth and strong biofilms . The combination of a high surface substrate loading and low detachme nt forces did lead to rough biofilms, but did not lead to the expected high amount of biomass on the carrier, apparently because of the form ation of weaker biofilms. The strength of the biofilms appeared to be related to the detachment forces applied during biofilm formation, in combination with the surface substrate loading. The biofilm morphology and biomass on carrier in the BAS reactor can be controlled using the carrier concentration, substrate loading rate and the superficial air velocity as parameters. The dynamics of biofilm formation during the start-up of a full-scale BAS reactor proved to be similar to heterotro phic biofilm formation in laboratory-scale reactors. This indicates th at a model system on the laboratory scale can successfully be applied to predict dynamic phenomena in the full-scale reactor.