The influence of dilute acid pretreatment conditions on the enzymatic saccharification of Erica spp. for bioethanol production

Production of bioethanol from biomass is one way to reduce both consumption and depletion of fossil fuels and environmental pollution. The conversion of lignocellulosic biomass-to-ethanol comprehends three major steps: thermochemical pretreatment, enzymatic saccharification and fermentation. The aim of this work is to study the influence of dilute acid pretreatment conditions in sugars removal and in enzymatic saccharification of Erica spp. for bioethanol production as well as the influence of poly(ethylene)glycol addition to the enzymatic saccharification step. Pretreatment of Erica spp. with dilute sulfuric acid was studied at different conditions of reaction time, temperature and acid concentration. The influence of supplementation of enzymatic saccharification with poly(ethylene)glycol 4000 and concentration of polymer were tested, using as response the release of glucose and the adsorption of cellulase to biomass by protein content in supernatant and by SDS-PAGE. The addition of PEG 4000 affects the adsorption of cellulase and influences the yield of enzymatic saccharification, leading to an improvement of 13–74% depending on the pretreatment applied to biomass. A maximum of 440 mg glucose/g dry biomass was obtained by enzymatic saccharification when pretreated Erica spp. at 180 °C with 2.75% of sulfuric acid for 75 min, supplemented with 0.25 g/g dry biomass of PEG 4000, was used. The observation of biomass structure by scanning electron microscopy after pretreatment reveals visible breaks in the structure, which could be related to the improvement of enzymatic process.