BACTERIAL STRUCTURE OF BIOFILMS IN WASTE-WATER INFILTRATION SYSTEMS

The objective of the present study was to use a test system for cluste ring and characterizing the bacterial populations in five wastewater i nfiltration systems ranging in size from 12 m(2) to 1960 m(2) (corresp onding to the demand for 4-500 population equivalents). From each syst em two sand samples were taken and from each sample 88 bacterial isola tes were collected. Every isolate was exposed to 52 physiological and biochemical tests. The resulting 880 objects x 52 variable data matrix was subjected to principal components analysis (PCA). After a variabl e reduction the PCA model revealed a scattered bacteria pattern (score plot) in parts of the sand filters expected to have high loading rate s of wastewater, e.g. at the inlet of the filters. This indicates that a diverse bacterial population had developed in response to the carbo n and energy source in the wastewater. In contrast to this pattern a m ore narrow bacteria pattern had developed in low loaded parts of the s and filter. The most important variables explaining the structure of t he microbial biofilm at high wastewater load were the ability to ferme nt sugars and the capacity to sustain different pH levels. The potenti al to ammonify and grow on nutrient broth was also an important featur e. In conclusion, the bacterial test system together with PCA seems to be a useful tool to evaluate the function of a bacterial sand-filter ecosystem. (C) 1998 IAWQ. Published by Elsevier Science Ltd.