Impact of metallic nanoparticles on anaerobic digestion

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Silver nanoparticles (AgNPs) have been applied in various consumer products while nano zero valent iron (NZVI) has been proposed for site remediation and industrial wastewater treatment. In batch anaerobic digestion systems, AgNPs at the concentration of 40 mg/L did not inhibit methane production, as more than 90% of AgNPs were removed from the liquid to the associated sludge while almost no silver ions were released from AgNPs under anaerobic sludge digestion conditions. In a bench-scale landfill bioreactor study, however, a one-time dose of AgNPs at the final concentration of 10 mg/kg solids resulted in inhibition of methanogenesis along with reduced biogas production, prolonged period of accumulation of VFAs, soluble COD, low pH, and decrease in methanogenic population. With the addition of the same amount of bulk silver ions (10 mg Ag/kg); however, there was no inhibition on methane production. In another anaerobic sludge digestion study, at the concentrations of 1 mM and above, NZVI reduced methane production. At the concentration of 30 mM, NZVI led to a significant hydrogen gas accumulation, significant increase in soluble COD, VFA accumulation and slow growth of methanogens. In contrast, ZVI powders at micrometer were beneficial to methanogenesis due to their slow release of hydrogen gas.