In vitro evaluation of nano zinc oxide (nZnO) on mitigation of gaseous emissions

Abstract

Background: Enteric methane (CH 4 ) accounts for about 70% of total CH 4 emissions from the ruminant animals. Researchers are exploring ways to mitigate enteric CH 4 emissions from ruminants. Recently, nano zinc oxide (nZnO) has shown potential in reducing CH 4 and hydrogen sulfide (H 2 S) production from the liquid manure under anaerobic storage conditions. Four different levels of nZnO and two types of feed were mixed with rumen fluid to investigate the efficacy of nZnO in mitigating gaseous production. Methods: All experiments with four replicates were conducted in batches in 250 mL glass bottles paired with the ANKOM RF wireless gas production monitoring system. Gas production was monitored continuously for 72 h at a constant temperature of 39 ± 1 °C in a water bath. Headspace gas samples were collected using gas-tight syringes from the Tedlar bags connected to the glass bottles and analyzed for greenhouse gases (CH 4 and carbon dioxide-CO 2 ) and H 2 S concentrations. CH 4 and CO 2 gas concentrations were analyzed using an SRI-8610 Gas Chromatograph and H 2 S concentrations were measured using a Jerome 631X meter. At the same time, substrate (i.e. mixed rumen fluid+ NP treatment+ feed composite) samples were collected from the glass bottles at the beginning and at the end of an experiment for bacterial counts, and volatile fatty acids (VFAs) analysis. Results: Compared to the control treatment the H 2 S and GHGs concentration reduction after 72 h of the tested nZnO levels varied between 4.89 to 53.65%. Additionally, 0.47 to 22.21% microbial population reduction was observed from the applied nZnO treatments. Application of nZnO at a rate of 1000 μg g − 1 have exhibited the highest amount of concentration reductions for all three gases and microbial population. Conclusion: Results suggest that both 500 and 1000 μg g − 1 nZnO application levels have the potential to reduce GHG and H 2 S concentrations.