Fate of wastewater organic pollution during activated sludge treatment: Nature of residual organic matter

Activated sludge treatment is used to remove wastewater organic matter (OM) and residual OM is found at low levels in treated water. The molecular com position of OM of waters and sludge was determined In order to understand t he fate of the organic substances during biological treatment and the natur e of residual OM. Proteins, sugars, lipids and polyphenolic compounds were quantified in a municipal wastewater treatment plant via chromatographic an alysis after chemical hydrolysis. The concentration of OM was decreased by more than 90% by biological treatm ent. However, if 63% of the OM were characterized in activated sludge, mole cular analysis did not allow us to characterize all the OM in the water sam ples. Relatively higher amounts of total organic carbon (TOC) were identifi ed in wastewater (50%) than in treated water (20%). Likewise, for total nit rogen, 33% were identified as amino acid nitrogen in wastewater, and only 1 0% in treated water. Analytical pyrolysis suggested that some of the diffic ulties in identifying OM of treated water with common analytical methods ar e due to the presence of complex structures, refractory to hydrolysis. Thes e structures may also be refractory to microbial degradation since they are concentrated during the biological treatment of wastewater. Suggestions on the possible origin and structure of resistant OM were formulated accordin g to the analytical results. (C) 2000 Elsevier Science Ltd. All rights rese rved.