Effects of the herbicide atrazine on the activated sludge process: microbiology and functional views

Two pilot laboratory plants were used in order to assess the impact of atrazine on the activated sludge process. At the steady state (15 days), one pilot received continuously, either 1 ppm of atrazine for 6 days, or 20 ppm for 7 days. At 20 ppm, atrazine had an immediate effect on COD which increased after 22 hours. After the 4th day, it reduced MLVSS and bacterial concentration. Metabolic activities of the sludge in oxidation of sewage (dehydrogenation), in proteolysis, as well as in the nitrogen cycle, were not affected. Atrazine had no effect on different genera of protists present in the mixed liquor and was not biotransformed Among 6 bacterial strains isolated from sludges, none degraded this pesticide but the growth of Flavobacterirem indologenes was inhibited by 100 ppm. This therefore suggests that the decrease of biomass in sludge at 20 ppm of atrazine was due to the inhibition of some bacteria.