Membrane applications for biogas production processes and purification: an overview on a smart alternative for process intensification

Biogas is the result of a complex process of onversion that takes place because of the metabolic activity of various kinds of bacteria. The anaerobic digestion (AD) plants are characterized by many different criticisms, which risk producing a failure condition; one of this is the washout phenomena that imply a premature removal of the active biomass, owing to a vigorous adduction of organic matter. There is also the possibility of generating an excess of digestate with high nitrogen and phosphorous content that can induce water eutrophication if freely left in nature. In this sense, the use of membrane can be useful; with their high separation power, they can be employed both for the stabilization of the exhausted digestate and the enhancement of the solid retention time (SRT). Membranes are promising even in the field of biogas final separation for biomethane production. Various kinds of setup have been tested so far for CO2 capture and the results push to think in a possible stable application for anaerobic digestion plants. Therefore, membranes are a good choice for the development of advanced processes optimized for both the gas and semiliquid phase handling.