The effect of mixed biological pretreatment and peg 4000 on reducing sugar production from coffee pulp waste

Biological methods using bacteria and fungi are regarded as more economically viable and environmentally friendly alternatives for improving lignocellulosic degradation. Coffee pulp waste (CPW) as a lignocellulosic biomass is abundant and has potential as a reducing sugar feedstock. However, it contains lignin as a matrix polymer, which associated with pectin and cover the cellulosic microfibrils and make it difficult to be digested during the bioprocess. In this study, the performance of biological pretreatment in reducing lignin and pectin using a co-culture of Bacillus subtilis (BS), Aspergillus niger (AN), or Trichoderma reesei (TR) has been investigated. The pretreatment of the CPW was made using various microbial ratios in an aerobic stirred-bioreactor and incubated at 30° C, pH 5 for 7 days. Removal of lignin and pectin was analyzed during the pretreatment process. PEG 4000 as a surfactant was used and its effect on the yield of reducing sugar production from pretreated CPW using a A. niger and T. viride (TV) co-culture with a surfactant to substrate ratio of 1:1 (w/w) was investigated. A culture without surfactant was used as a control. The results reveal that the best lignin and pectin removal was 99.9%, when using a co-culture of AN and TR with a ratio of 1:1 (v/v) and of BS and TR with a ratio of 2:1 (v/v). The cellulose content of CPW in these co-cultures was 86.99% (w/w) and 81.61% (w/w), respectively, and the reducing sugar concentration obtained was 12.5 g/L and 9.74 g/L respectively. In further hydrolysis of pretreated CPW using a AN:TV (2:1) co-culture with the addition of surfactant, the yield of reducing sugar obtained was higher than that of the control, at 20.69%. Use of PEG 4000 as a surfactant had a positive effect on enhancing the yield of reducing sugar from coffee pulp waste.