Microalgae digestive pretreatment for increasing biogas production

Microalgae have many advantages for the production of biogas by anaerobic digestion process. However, the anaerobic digestion process has been reported to be limited in the hydrolytic stage due to the specific characteristics of the cell wall components thus resulting in an inefficient conversion of biomass to biogas. Pre-treatments aim to achieve an increase in the biogas production by increasing solubilization. Enzymatic pretreatment is described as an environmentally-friendly process, due to the low energy consumption, great yield of freed, fermentable sugars from the biomass under light operational conditions, the absence of corrosive problems, and few derivatives produced. Within the category of enzymatic pretreatments, it might identify two types, which are related to the origin of the enzymes and which may be classified as endogenous enzymes, and commercial exogenous enzymes. It should also be considered that enzyme production costs for commercial enzymes might be a negative factor in the process. The objective of the present review is to analyze and discuss the application of digestive pretreatments on the solubilization of microalgae, with a focus on the cell wall, and its relation to biogas production increase.