Relationship between silver inhibition and feeding of activated sludge

Silver is one of the heavy metals which is widely used in industrial, electronics and medical applications. Increase in the demand of silver and silver containing products cause accumulation of silver in sewer systems. Since silver ions are highly toxic on microorganisms, they affect biological wastewater treatment systems. The objective of this study is to examine the effect of silver ion on different types of activated sludge. Activated sludge was fed with synthetic wastewaters which had different C/N (COD/Nitrogen) ratios and inhibitory effect of silver ion was examined by using a respirometer. The result of the study shows that the C/N ratio in wastewater has a crucial role because it determines the relative ratio between heterotrophs and autotrophs in activated sludge. The inhibitory effect of silver ion changes with the C/N ratio in a wastewater. An activated sludge enriched in terms of autotrophs (C/N ratio = 0) is more sensitive to silver ion than other sludge types. On the other hand, with the increase in C/N ratio heterotrophs dominate in activated sludge and they can tolerate higher concentrations of silver ion.