Application of metallic nanoparticles for biogas enhancement using the biomethane potential test

Abstract

Owing to the continued global environmental crisis, wastewater treatment is seen with great potential to limit the demand on freshwater usage while contributing to depletion of global warming with alternative source of renewable energy. Thus, in the wastewater settings, anaerobic digestion (AD) reduces organic pollutants while generating green energy in the form of biogas. However, AD is a relatively slow microbial–based process, which has become a major challenge to produced methane–enriched biogas. Therefore, augmentation of AD was investigated via the addition of metallic–based nanoparticles (NPs) (Fe, Cu, and Ni) at a concentration of 1 g and 2 g. Scanning electron microscopy and energy dispersive X-ray (SEM/EDX) were used to track the NPs distribution and utilisation in the post-AD digestate. A biomethane potential (BMP) technique was employed with 1 L Duran schott bottles. This was operated at a working volume of 0.8 L (0.3 L inoculum and 0.5 L wastewater), hydraulic retention time of 10 days and mesophilic temperature 40 °C. The wastewater treatability performance showed over 65% removal of chemical oxygen demand (COD), turbidity and colour. The NP additives showed a synergetic effect on biogas production as it hinged on the NPs type and concentration (1 g Fe-NPs > 2 g FeNiCu-NPs > 1 g Cu-NPs > 2 g Cu-NPs > 1 g Ni-NPs > 2 g Ni-NPs > 2 g Fe-NPs). Usage of 1 g of Fe NPs balanced the nutrient supply of the microbes, which increased the biogas production (by 75% >3 mL/d of the control) with 100% methane composition. The prospects of Fe-based NPs seems very promising and industrially worthy for wastewater treatment and bioenergy production. This warrants future research into NPs recovery and reuse as a way of mitigating its economic viability and environmental risk.