The relationship between the structure of activated sludge flocs and the sorption of hydrophobic pollutants

The relationships between the structure of minimally perturbed activated sludge flocs and the sorption of organic contaminants were studied. Sorption, settling velocity, size distributions, floc structure and EPS composition were all examined. The results show significant removal of selected halogenated hydrocarbons and polycyclic aromatic hydrocarbons by biosorption to activated sludge flocs. However, statistically significant effects on the settling or size of the flocs caused by this sorption were not observed. The addition of chromium (Cr(III)) metal ions to the biomass caused observable changes in the floc structure and decreased ruthenium red binding to the acidic polysaccharides of the floc matrix. At low concentrations (0.6 mg/l), chromium caused an increase in the sorption of organic compounds to flocs, suggesting that changes in the floc structure can be induced, which can have an impact on the sorption of pollutants to the flocs.