ORGANIC-CARBON BIODEGRADABILITY AND HETEROTROPHIC BACTERIA ALONG A COMBINED SEWER CATCHMENT DURING RAIN EVENTS

The aim of this study was the evaluation of fluxes of organic carbon a nd biodegradability of waste waters during rain events in order to bet ter predict the impacts of combined sewer overflows (CSO). The combine d sewer system studied was located in a densely populated urban catchm ent adjacent to Paris. Five subcatchments of different size, have been monitored during several rain events for suspended solids, conductivi ty, ammonium, chemical and biological oxygen demand. In addition, two of these subcathments have been evaluated for dissolved and particulat e organic carbon, their biodegradable fractions, and the total bacteri al biomass. Several indexes, indicate a lower degradability of waste w ater during dry weather at the downstream stations, accompanied by an increase of bacterial size and bacterial biomass. A further decrease o f biodegradable organic carbon related to rain intensity can be seen a t all stations. Our results show a higher proportion of refractory org anic carbon during rain events than during dry weather with a possible contribution of the in-sewer sediments to the bacterial wet weather f lux. (C) 1998 IAWQ. Published by Elsevier Science Ltd.