Inhibitory effect of silver on activated sludge: effect of organic substrate and the carbon to nitrogen ratio

Abstract

BACKGROUND: Sensitivity of activated sludge to heavy metals may depend on the strength and type of organics in the feed. However, literature data are usually derived from systems with an unknown or variable composition. To fill this gap, this study examined whether in activated sludge systems the inhibitory effect of Ag + depended on the carbon to nitrogen (COD/TKN) ratio and the type of organic matter in the feed. RESULTS: Different activated sludges reactors were operated at steady-state conditions. Regularly, sludge samples taken from reactors were contacted with Ag + in a respirometer and the inhibitory effect was determined by the relative decreases in O 2 consumption and CO 2 generation. The inhibitory property of Ag + drastically increased as the COD/TKN ratio became lower. While sludges fed with acetate, glucose and peptone or glucose alone were equally inhibited when exposed to Ag + , the peptone-fed sludge proved to be much more resistant. It was also clarified whether indicated Ag + doses had an effect on nitrification, organic carbon removal or both processes. CONCLUSION: To date, comparative evaluations have rarely been made between different activated sludge systems in under-standing the response to silver input. Overall, this study pointed to the need to consider the characteristics of the feed to explain the discrepancies between different activated sludge systems.

Influence of growth media components on the antibacterial effect of silver ions on Bacillus subtilis in a liquid growth medium

“…Also in more complex systems, this phenomenon had been put forward in literature, for example in a study of Çeçen et al . which showed that the inhibitory effect of Ag + on active sludge systems depended the type of organic matter in the feed, and peptone was suggested to form complexes with the Ag + ions 36 . We believe that our stepwise approach by going from a defined minimal to an undefined complex medium was highly needed and can form a basis for further experiments.…”

Inhibitory Effect of Silver and Nanosilver on Activated Sludge Fed with Proteinaceous Feed

“…Then, it was also continuously dosed with AgNP. The details of operation and the composition of synthetic wastewater feed can ICEPR 121-2 be found in previous studies [7,8]. The inhibitory effect of Ag + on activated sludge in RP was studied in the range 0-5 mg/L Ag + .…”