Evaluation of Calcium Alginate Entrapped Nano Zinc Oxide to Reduce Gaseous Emissions from Liquid Dairy Manure

Abstract

<abstract> <b><sc>Abstract. </sc></b>Direct application of nanoscale zinc oxide (nZnO) particles has shown promising results in controlling gaseous emissions (hydrogen sulfide-H₂S, methane-CH₄, and carbon dioxide-CO₂) from livestock liquid manure under anaerobic storage conditions. However, application of bare (unmodified) nanoparticles (NPs) could raise environmental concerns as their fate and transport are not well documented. Keeping this in mind, an innovative method has been adopted where NPs were entrapped in biopolymer beads that ensured that NPs were not released to the environment and can be recovered. The objective of this research was to evaluate the performance of calcium (Ca)-alginate entrapped nZnO (alginate-nZnO beads) and associated mechanisms involved in controlling gaseous emission from liquid dairy manure. Experiments were conducted in 1 L Erlenmeyer flasks with a working volume of 500 mL, where alginate-nZnO beads containing 3 g L^-1 of NPs were applied freely, as well as loosely contained in mosquito net bags. Headspace gas was collected every 2 to 5 days during the 33-day experiment and analyzed for H₂S, CH₄, and CO₂ concentration. Bacterial growth analysis and sorption test were also carried out to see the effect of NPs on microbial survivability and gaseous sorption capability, respectively. The concentration of H₂S, CH₄, CO_2, and total gas production was significantly reduced by 99%, 51%, 27%, and 43%, respectively, when beads were applied freely; while these reductions were 96%, 18%, 14%, and 20%, respectively, when beads were applied loosely in bags (P<0.05). Though both methods performed well, free beads application method outperformed the other application method.