In-situ prevention of hydrogen sulfide formation during anaerobic digestion using zinc oxide nanowires

The utilization of Anaerobic Digestion (AD) technology for biogas and energy generation is often hindered by high concentration of sulfur-containing compounds in wastewater and consequential hydrogen sulfide (H2S) in biogas. In this work, we demonstrated a process, where independent mechanisms of anaerobic microorganisms and an inorganic reactive adsorbent (zinc oxide nanowires) worked synergistically to remove soluble sulfide (HS−) and prevent H2S formation during AD. Using a model aqueous sodium sulfide (Na2S) system, the nanowires (dosage 1 g/L) effectively removed sulfides from the Na2S solution to a maximum of 625 mg S2−/L per gram of ZnO. During 24 h and 3-day long (involving three consecutive sulfate feeding cycles) AD studies using anaerobic microbial medium (2 g/L SO42− and 1 g/L ZnO), no decrease in methanogenic activity and biogas production were observed using the ZnO nanowires, indicating that the nanowires can reduce the sulfide toxicity during AD. The post-process analysis of the recovered nanomaterial using energy-dispersive X-ray spectroscopy and X-ray diffraction showed the presence of sulfur and zinc sulfide (ZnS), respectively, validating HS− removal by the nanowires. This process intensification approach of combining AD and H2S removal into a single process step will help extend AD technology to high sulfate containing wastewaters.