A review of bioreactor technology used for enzymatic hydrolysis of cellulosic materials

Cellulases are costly, a principal challenge of enzymatic hydrolysis of cellulosic materials for bioethanol production. For an efficient cellulase production, fungi are preferred over bacteria due to their permeation capability and versatile substrate consumption. Some limitations in the enzymatic hydrolysis step prevent the process to be economically feasible. Different strategies have been investigated to overcome these limitations, including genetic engineering, enzyme recycling, high solid loadings, pretreatment technologies, supplementation of cellulases with additives and application of nanomaterials for improving the thermal and pH stability of cellulases. Several studies have been performed in various bioreactors with the target to procure higher yields of glucose in the enzymatic hydrolysis step. The key factors for designing a bioreactor include efficient mixing, sufficient mass transfer, low shear stress, low foaming problems and low consumption of water and energy. In this scenario, different bioreactor configurations, including stirred tank bioreactor, horizontal rotating tubular bioreactor, airlift bioreactor, membrane bioreactor, reciprocating plate bioreactor, solid-state fermentation bioreactors have been reviewed for cellulase production with the aim to investigate main factors for designing a bioreactor.