Effects Of Nano-silver On The Recovery Performance Of Aerobic Nitrifying Granules After Storage

With the increasing utilization of nanomaterials, silver nanoparticles (Ag NPs) have been reported to induce adverse effects on human health and aquatic organisms. However, the potential impacts of Ag NPs on wastewater nitrogen removal with an aerobic granules process are unknown. In this paper, long-term exposure experiments were conducted to study the performance of physical characteristics and respirometric activities during reactivation of aerobic nitrifying granules after a3-month storage time in three sequencing batch reactors. Results showed that the color of the aerobic granules had completely become dark, the size and settleability did hardly change during the storage period. The color turned to be brownish-yellowish when the three reactors was restarted for7d,10d and30d, respectively. Compared with the absence of AgNPs, the presence of1mg/L and5mg/L of Ag NPs increased ammonia-nitrogen removal efficiencies to95%for15d and27d, respectively. It was found that the average COD removal efficiencies were almost90%at Ag NPs concentration of1mg/L, which were almost the same as those observed in the control test (90%), suggesting that1mg/L of Ag NPs showed no measurable effect on COD removal, but the COD removal efficiencies were from56%to90%at Ag NPs concentration of5mg/L in6days, suggesting that5mg/L of Ag NPs showed short-term effect on COD removal. The activity of ammonia-oxidizing bacteria at Ag NPs concentration of0,1and5mg/L resumed above90%within10d,16d,28d, respectively. It was found that the inhibition of ammonia-nitrogen removal induced by higher concentrations of Ag NPs was due to the release of silver ions from Ag NPs dissolution, which caused inhibitory effect on aerobic nitrifying granules.