The effect of micropollutants (organic xenobiotics and heavy metals) in the activated sludge process

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Removal of organic xenobiotics in activated sludges under aerobic conditions and anaerobic digestion of the adsorbed species

none6The abiotic and biotic fate in activated sludge plants of a mixture of aromatic pollutants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlorinated and non-chlorinated benzenes, phenols and surfactants was studied. To this aim, an activated sludge collected from a municipal plant was artificially spiked with the target compounds. Under aerobic conditions, adsorption, and biodegradation were distinguished as possible mechanisms of target compound removal through comparison of tests with and without oxygen. With the exception of phenol, which was completely biodegraded (at an average rate of 2.6 mg phenol/gVSS/h), the pollutants were completely or significantly removed from the liquid phase through adsorption. In the tested conditions the amount of substance removed through adsorption ranges from 75-80% for 4-dodecylbenzenesulfonic acid and pentachlorophenol to more than 90% for the other compounds. Kinetic and equilibrium parameters describing the adsorption of the different xenobiotics to the sludge were also determinedThe role of anaerobic digestion in the final decontamination of the xenobiotic-containing sludge was evaluated under mesophilic and termophilic condition. A significant average depletion of the chlorinated pollutants was observed in mesophilic conditions (24.6%). The addiction of yeast extract stimulated the process by allowing an higher chlorinated pollutant average depletion (49.7%) and a complete disinfection of the sludge.mixedD. Dionisi; L. Bertin; L. Bornaroni; S. Capodicasa; M. Petrangeli Papini; F. FavaD. Dionisi; L. Bertin; L. Bornaroni; S. Capodicasa; M. Petrangeli Papini; F. Fav

Effect of micropollutants (organic xenobiotics and heavy metals) in the activated sludge process

Four experiments were performed in sequencing batch reactors, two by two in parallel, to study the effect of micropollutants (organic xenobiotics and heavy metals) on the performance of activated sludge processes. The reactors were operated for long times (at least 11 months each) and in a wide range of sludge ages (5-30 days). It was observed that production of biological solids, COD removal, and settling properties were not affected by the presence of micropollutants significantly. On the other hand, ammonia removal was much lower in the reactors fed with micropollutants (29-37% removal) than in the reactor without micropollutants (82% removal). Batch tests allowed the measurement of maximal activities of heterotrophic and autotrophic biomass. The activity of nitrifying microorganisms grown without micropollutants was greatly reduced (about 50%) by the addition of the micropollutants, but the residual micropollutants after treatment did not exert any inhibiting effect. Nitrate balances on the four runs confirmed that the fraction of nitrifying microorganisms was much higher in the reactor without micropollutants (4.5% of overall VSS) than in the reactors fed with micropollutants (maximum 0.5% of VSS). In spite of the fact that in the reactors fed with micropollutants the fraction of nitrifying microorganisms increased at increasing sludge age, a satisfactory nitrogen removal was not achieved in the whole tested range of experimental conditions, even after the 11-month acclimation. With regard to nitrogen removal in processes operated with micropollutants, the results obtained in this study seem to indicate the effectiveness both of processes with separate nitrification after a first treatment stage and of single-sludge processes carried out at very high sludge ages, as acheivable, e.g., by the use of membranes or of attached growth systems