Characterization of zinc oxide nanoparticle (nZnO) alginate beads in reducing gaseous emission from swine manure

Abstract

Hydrogen sulfide (H₂S) and greenhouse gases' emission from livestock production facilities are of concern to human welfare and the environment. Application of nanoparticles (NPs) has emerged as a potential option for minimizing these gaseous emissions. Application of bare NPs, however, could have an adverse effect on plants, soil, human health, and the environment. To minimize NPs' exposure to the environment by recovering them, NPs were entrapped in polymeric beads for treating livestock manure. The objectives of the research were to understand the mechanism of gaseous reduction in swine manure treated for 33 days with zinc oxide nanoparticles (nZnO) or nZnO-entrapped alginate (alginate-nZnO) beads by different characterization techniques. Headspace gases from treated manure flasks were collected in 2-6-day intervals during the experimental period and were analyzed for methane (CH₄), carbon dioxide (CO₂), and H₂S concentrations. The microbial analysis of manure was carried out using bacterial plate counts and Real-Time Polymerase Chain Reaction methods. Morphology and chemical composition of alginate-nZnO beads were analyzed by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Photoelectron Spectroscopy (XPS). Alginate-nZnO beads or bare nZnO proved to be an effective NP in reducing H₂S (up to 99%), CH₄ (49-72%), and CO₂ (46-62%) from manure stored under anaerobic conditions and these reductions are likely due to the microbial inhibitory effect from nZnO, as well as chemical conversion. Both SEM-EDS and XPS analysis confirmed the presence of zinc sulfide (ZnS) in the beads, which is likely formed by reacting nZnO with H₂S.