Comparative measurements of microbial activity in drinking water biofilters

Tetrazolium reduction assays, phospholipid analysis, and 16S rRNA (rDNA) se quence analysis were applied to assess the distribution, composition and ac tivity of microbial communities developing in biofilters treating non-ozona ted and ozonated drinking water, The response of media-attached biomass to both operating temperature (3 degrees C vs. > 12 degrees C) and ozone appli cation point was assessed. As judged by 2-(p-iodo-phenyl)-3-(p-nitrophenyl) -s-phenyl tetrazolium chloride (INT) reduction, the dehydrogenase activity in biofilter systems that were operated with non-ozonated water was 55% low er than in identical filters operating with ozonated water. There was no si gnificant difference between the microbiological activity measured in a bio filter series treating ozonated water and an identical series where ozonate d water was introduced at an intermediate point. The biomass levels in biof ilter systems that were operated with ozonated water were 47% higher on ave rage than identical systems operated with non-ozonated water. Operating tem perature had no significant impact on total biomass levels however, specifi c dehydrogenase activity was 70% higher in systems operated at ambient temp eratures ( > 12 degreesC) than in systems held at 3 degrees C. Phospholipid and rDNA analysis suggests that there was a community structure response t o ozone application and operating temperature, but no response to different ozone application points. (C) 2001 Elsevier Science Ltd. All rights reserv ed.