Utilization of nanoparticles for sustainable biogas production: process stability and effluent quality

One of the most important techniques for converting complex organic waste into renewable energy in the form of biogas and effluent is anaerobic digestion (AD). Several issues have been raised related to the effectiveness of the AD process in recent years. Hence nanoparticles (NPs) have been used widely in AD process for converting organic wastes into useful biogas and effluent in an effective way. This review addresses the knowledge gaps and summarizes recent researchers’ findings concentrating on the stability and effluent quality of the cattle manure AD process using various NPs (e.g., Fe, Ni, Co, and metal oxides). In summary, the utilization of NPs have beneficial effects on methane generation, process optimization, and effluent quality. Their function, as key nutrient providers, aid in the synthesis of key enzymes and co-enzymes, and thus stimulate anaerobic microorganism activities when present at an optimum concentration (e.g., Fe NPs 100 mg/L; Ni NPs 2 mg/L; Co NPs 1 mg/L). Furthermore, utilizing Fe NPs at concentrations higher than 100 mg/L is more effective at reducing hydrogen sulfide production than increasing methane, whereas Ni NPs and Co NPs at concentrations greater than 2 mg/L and 1 mg/L, respectively, reduce methane production. Effluent with Fe and Ni NPs showed stronger fertilizer values more than Co NPs.