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This study investigated the factor that affect enzymatic hydrolysis of dilute alkaline pretreated Chlorella sp. biomass and its potential as a bioethanol feedstock. The enzymatic hydrolysis optimization of dilute alkaline pretreated Chlorella sp. biomass was carried out prior to fermentation process. The enzymatic hydrolysis was performed using cellulase cocktail from Trichoderma longibrachiatum. The enzymatic hydrolysis parameters such as pH, temperature, enzyme and biomass concentrations that affect hydrolysis performance were also investigated. The optimization of enzymatic hydrolysis was carried out using the central composite design (CCD) approach. The study indicated that the highest reducing sugar 413.42 ± 7.62 mg gbiomass-1, which corresponding to 84.33% hydrolysis yield was achieved when the hydrolysis was performed using 12.5 g L-1 biomass at 45 °C and initial pH 5.0 for 96 h of incubation. The enzymatic hydrolysis kinetic parameters (Vmax and Km) of the pretreated biomass were also been determined. The analysis indicated that Vmax and Km values for enzymatic hydrolysis of the biomass were 0.18 mgmL-1min-1 and 26.34 mg mL-1 respectively. The hydrolysate generated from the enzymatic hydrolysis was further fermented for bioethanol production using Saccharomyces cerevisiae in batch and fed-batch fermentation modes. The fed-batch fermentation resulted slightly higher bioethanol concentration of 1008.48 mg L-1, corresponding to bioethanol yield of 0.43 ggsugar-1 and 0.081 ggbiomass-1 compared to batch fermentation. The results revealed that optimization of enzymatic hydrolysis process could enhance reducing sugar production from dilute alkaline pretreated Chlorella sp. biomass. The results obtained also demonstrated that fed-batch fermentation of alkaline pretreated Chlorella sp. hydrolysate from enzymatic hydrolysis process improve the efficiency of ethanolic fermentation in term of ethanol concentration production and yield.
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