CHARACTERIZATION OF DETACHMENT MODE OF BIOFILM DEVELOPED IN AN ATTACHED-GROWTH REACTOR

In this study the in situ behavior of biofilm development and detachme nt was continuously observed by a video camera. The model biofilms con sisting of denitrifiers were formed on the flat surfaces of polyvinylc hloride plates that were placed in a rectangular open-channel reactor. The effects of intrinsic biofilm properties on biofilm detachment, su ch as intrafilm gas-vacuoles formation, extracellular biopolymer (ECP) content biofilm density and cavity formation at the biofilm/substratu m interface were quantified using attached-biofilms onto flat substrat a. The result indicated that there were three phenotypes of massive bi ofilm detachment (see Fig. 4) under the conditions of low shear stress of now. The first type showed that a large fraction (approximately 1/ 4-1/3) of the biofilm was sloughed off as a whole layer from the subst ratum surface at a relatively early stage of biofilm formation. This t ype was primarily caused by the cavity formation and by the decrease o f ECP content. Succeeding to the first type, the second type occurred as fragmentary detachments. The second phenomenon was attributable to the increase in biofilm buoyancy due to the gas-vacuoles formation wit hin the biofilm. The third type took place as the combination of the f irst and the second types following the occurrence of the second type. In contrast at a higher flow shear stress only the second type of det achment became prevalent throughout the progression of biofilm formati on.