The Effect of Short-Term Exposure of Engineered Nanoparticles on Methane Production During Mesophilic Anaerobic Digestion of Primary Sludge

Nanoparticles have been used widely in industry and consumer products in recent years. Most of the engineered nanoparticles (NPs) eventually enter municipal wastewater treatment systems (WWTP) through sewers. In this experimental study, the impact of nano-TiO2, nano-ZnO, and nano-Ag on methanogenesis was investigated during mesophilic batch anaerobic digestion of primary sludge. The experimental sets consisted of 1, 10 mg NP/g TS, and a control group for TiO2 NP, ZnO NP, and Ag NP, separately. The results showed that neither of the NPs used remarkably changed methane production. Methane yields in the units of m(3) CH4/kg VS in were between 0.08 and 0.13 and showed no significant difference between the control groups and experimental sets for tested NPs. Soluble Ti concentrations were below 0.07 mg/L after the end of anaerobic digestion. Soluble Zn and soluble Ag concentrations were below 0.78 and 2.02 mg/L, respectively. Most of the NPs remained in the sludge rather than in aqueous supernatant. The authors suggest that the effects of the NPs, just above the sludge, or the NPs that adsorbed to sludge, on methanogenic activity at long-term exposure should be examined in the future studies.