Integrated enzymatic pretreatment and hydrolysis of apple pomace in a bubble column bioreactor

Waste biomass from agro-food industry can be exploited to produce several products according to the sugar-based biorefinery concept. The success of the biomass exploitation stems from the equilibrium among several issues regarding the process costs, the environmental impact, and the energy efficiency. The present work is focused on the use of apple pomace as possible renewable feedstock for the production of biofuels and of bio-commodities. The aim of the present work was the optimization of the enzymatic pretreatment and hydrolysis of apple pomace in a bubble column bioreactor by using a recombinant laccase as biocatalyst for the delignification step and commercial cellulases for the hydrolysis step. Both the enzymatic processes were investigated to select the optimal operating conditions for the maximization of sugar yields. Optimal conditions for the sequential enzymatic delignification and hydrolysis process in the bubble column were: 15%w/v biomass concentration; 60 nL/h air flow rate, 30 U/g laccase activity; 20 FPU/g cellulase activity. Moreover, the selected operating conditions were applied to a long term test of the sequential pretreatment/hydrolysis in the bubble column that resulted in a maximum sugar yield of 0.34 g/g and 0.61 g/g from the raw apple pomace. Result discussion highlighted advantages and drawback of pneumatic mixing and sequential pretreatment/hydrolysis strategy applied to enzymatic delignification and cellulose hydrolysis.