Impact of Silver Nanoparticles on Wastewater Treatment
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Silver nanoparticles (AgNPs, nanosilver) are used as an excellent antimicrobial agent in many consumer products. These nanoparticles are often released during washing and eventually enter wastewater treatment plants. The objective of this study was to evaluate how silver nanoparticles would affect wastewater treatment systems for organic and nutrient removal. The results demonstrated that nitrifying bacteria are especiall susceptible to inhibition by silver nanoparticles. At a concentration of 0.4 mg/L total AG, a mixture of silver ions and AgNPs (50:50 mass ratio, average size 15-21 nm) inhibited nitrification by 11.5 percent. During a nanosilber shock loading event lasting for 12 hours, a peak concentration of 0.5 mg/L Ag in the activated sludge basin (more than 95% assocated with biomass) was detected, resulted in a prolonged period (>1 month) of nitrification inhibition reaching a maximum of 50%, as evidenced by accumulations of ammonia and nitrite in the wastewater effluetn. In batch anaerobic digestion studies, AgNPs at the concentration of 19 mg/L (19,000 ppb) started to reduce cumulative biogas production, although the inhibition could be due to the accompanied nitrate in the nanosilver suspension. Results from the aerobic and anaerobic treatment studies suggest that accumulation of silver in acivated sludge may have a detrimental effect on nitrification and nutrient removal, if the concentration reaches theshold levels. The suggested threshold concentration of total silver including nanosilver in wastewater influent is 0.1 mg/L.
KeywordsSilver Nanoparticles Wastewater Toxicity Nitrification Anaerobic digestion
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