Effect of Micropollutants (Organic Xenobiotics and Heavy Metals) on the Activated Sludge Process

Abstract

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.

Technical Performance and Environmental Effects of the Treated Effluent of Wastewater Treatment Plants in the Shenzhen Bay Catchment, China

“…Biological treatments are designed to remove the organic matter and nutrients in wastewater and not necessarily to remove heavy metals; only a side benefit can be observed in the treatment of heavy-metal-bearing streams [41]. In this study, removal of Cr, Hg, and Pb was observed in all WWTPs, with the removal efficiency of 55.95%-92.5%, 37.87%-88.03%, and 8.7%-63.11%, while the removal of As and Cd was only achieved in some WWTPs, unsteadily.…”

Potential and Limits of Biodegradation Processes for the Removal of Organic Xenobiotics from Wastewaters

“…1 and 2, xenobiotics concentration is in the mg L −1 range in industrial wastewaters and in the μg L −1 in municipal ones. The different xenobiotics concentration in industrial and municipal wastewaters poses different challenges to biodegradation processes: very low concentrations of xenobiotics will cause a very slow microbial growth or might not be able to sustain growth at all; higher concentrations should give higher biodegradation rates and should be able to sustain microbial growth but inhibitory effects, e.g., on nitrification 21, might be possible.…”

Application of sequencing batch reactor (SBR) for treatment of refinery wastewater containing nickel

“…Discharge of untreated petroleum refinery wastewater containing nickel into water bodies results in environmental and human health problems [5]. Accumulation of nickel in the body can cause lung fibrosis, cardiovascular, kidney diseases and act as carcinogenic agent [8][9][10]. Excessive concentrations of nickel in water affect the living organism's growth such as algae [10].…”