Application of nanoparticles for biogas production: Current status and perspectives

Biogas production via anaerobic digestion (AD) of waste is a very attractive and challenging task. A slow rate of biodegradation and the presence of impurities in biogas propose the whole process for several risks. However, the adoption of nanoparticles (NPs) to the AD process can influence its performance and stability. The present work has classified the NPs used in AD into three categories: metal oxide NPs, zero-valent metallic NPs, and carbon-based NPs. The addition of metal oxide NPs showed the mixed effects on biogas production as it is depending on the concentration, types, and size of NPs. Zero-valent metallic NPs could be regarded as the most promising for increasing biogas production especially the Ni and Co NPs. Carbon-based NPs showed an appositive effect on the concentration of ammonia. NP mixtures greatly decreased H2S production. Usage of the waste containing NPs generated by other industries and improve the methods to recover the NPs inside AD reactors could decrease the environmental risk of NPs. Decreasing NPs' price and use low concentrations for enhancing biogas production (by over 90%, compared to control) would be more economically justified.