Effects of Metal Nanoparticles on Methane Production from Waste-Activated Sludge and Microorganism Community Shift in Anaerobic Granular Sludge.

Tao Wang,Lingling Dai,Yinguang Chen,Xiaohu Dai,Dong Zhang

doi:10.1038/srep25857

Abstract

Extensive use of nanoparticles (NPs) in consumer and industrial products has led to concerns about their potential environmental impacts; however, the influences of different NPs (e.g., nZVI (nano zero-valent iron), Ag NPs, Fe2O3 NPs and MgO NPs) on the anaerobic digestion of sludge have not yet been studied in depth. Additionally, a new guideline or the use of different NPs in the anaerobic digestion of sludge should be established to improve the anaerobic digestion of sludge and avoid inhibitory effects. This study investigated the effects of four representative NPs (i.e., nZVI, Ag NPs, Fe2O3 NPs and MgO NPs) on methane production during the anaerobic digestion of waste activated sludge (WAS). The presence of 10 mg/g total suspended solids (TSS) nZVI and 100 mg/g TSS Fe2O3 NPs increased methane production to 120% and 117% of the control, respectively, whereas 500 mg/g TSS Ag NPs and 500 mg/g TSS MgO NPs generated lower levels of methane production (73.52% and 1.08% that of the control, respectively). These results showed that low concentrations of nZVI and Fe2O3 NPs promoted the amount of microbes (Bacteria and Archaea) and activities of key enzymes but that higher concentrations of Ag NPs and MgO NPs inhibited them.

Highlights

Studies have demonstrated that many NPs could induce strong inhibitory effects in biological treatment processes
The presence of 0.1 mM sodium dodecylbenzene sulfonate (SDBS), which was added as the dispersing reagent, in the waste activated sludge (WAS) anaerobic digestion experiments had no significant effect on methane production, which is consistent with other studies[21]
These results were nearly identical to those observed in the blank test (i.e., 181.72 mL/g volatile suspended solids (VSS)), which suggests that 1 mg/g total suspended solids (TSS) nZVI, Ag NPs, Fe2O3 NPs or MgO NPs had no measurable effect on methane generation (p > 0.05)

Summary

Introduction

Studies have demonstrated that many NPs could induce strong inhibitory effects in biological treatment processes. Exposure to Fe NPs effectively reduced H2S in biogas and significantly promoted methane production in certain cases[18] These results indicated that different types of NPs might show dissimilar behaviors in biological treatment processes; new guidelines for the use of different NPs (e.g., nZVI, Ag NPs, Fe2O3 NPs and MgO NPs) in the anaerobic digestion of sludge should be established to improve the anaerobic digestion of sludge and mitigate inhibitory effects. Li et al indicated that Fe2+ released from Fe NPs (nZVI) could combine with S2− during the anaerobic digestion process to relieve the inhibitory effects of S2− on microbial communities[20]. This study aimed to determine the effects of four types of NPs (nZVI, Ag NPs, Fe2O3 NPs and MgO NPs) on methane production during the anaerobic digestion of sludge. The activities of certain key enzymes that are associated with the anaerobic digestion process, such as protease, acetate kinase (AK) and coenzyme F420, were considered

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