The relationship between the sorption of organic contaminants and the structure of activated sludge floc material

grantor: University of TorontoThe objective of this study was to examine the fate of organic contaminants in activated sludge processes. Two issues were addressed: (1) the sorption of selected hydrophobic contaminants to fresh floc material and (2) the influences of floc properties on contaminant sorption to biomass. Four organics of varying hydrophobicities were studied. They were pyrene, phenanthrene, 1,1,2-trichloroethane and 1,2-dichloroethane. Floc material was characterized by measuring the concentration of extracellular polymeric substances (EPS), extracted from the floc matrix by an ion exchange method. Protein, carbohydrate, DNA and acidic polysaccharide concentrations were measured. Floc settling and size were also measured, and statistically compared between samples. Correlative microscopy was used to observe floc structure. Sorption of contaminants to floc material occurred, without causing any significant changes in floc properties. Two methods were used to alter floc properties. A polyvalent metal, chromium(III), was added to activated sludge, which decreased the sorption of ruthenium red. Chromium(III) concentrations as low as 1.1 x 10$\sp{-3}$ mg/mg VSS corresponded to increased sorption of contaminants. Sludge age was also varied and EPS content and settling velocity changed with sludge age. At a sludge age of 6 days, no significant sorption of 1,2-trichloroethane occurred while at a 16 day sludge age, 24 $\pm$ 11 mg/L of 1,2-trichloroethane was sorbed, demonstrating that sorption increased with increasing sludge age. The results showed that floc properties influence the sorption of contaminants.M.A.Sc