Alkaline-assisted Microwave Pretreatment of Tetraselmis suecica Biomass for Fed-batch Enzymatic Hydrolysis

Abstract

A two-part study on pretreatment and fed-batch enzymatic hydrolysis of pretreated Tetraselmis suecica using a high initial biomass concentration was conducted. First, the effect of different pretreatment processes, i.e. microwave (MC), dilute alkaline (AK), and microwave-alkaline assisted (MAK) pretreatment, on enzymatic hydrolysis of T. suecica biomass was evaluated. Furthermore, high initial biomass concentration enzymatic hydrolysis improvement via a fed-batch strategy was performed. Among the pretreatments tested, the MAK pretreatment produced the highest sugar concentration at 9.83 ± 0.24 mg/mL, corresponding to a conversion yield of up to 85.58% of carbohydrate content available in the pretreated biomass. The solid fraction generated after pretreatment was characterized using Fourier transform infrared (FTIR) spectroscopy. The FTIR analysis revealed a significant change in the functional hydroxyl and acetyl groups of the biomass, which is favorable for enzymatic hydrolysis. Introducing an initial microalgal biomass concentration beyond 15% (w/v) exhibited a low enzymatic hydrolysis yield. The fed-batch enzymatic hydrolysis strategy of the MAK pretreated T. suecica was further investigated by adding the substrate at different time intervals. The findings indicate that the fed-batch operation system could enhance sugar production and enzymatic hydrolysis yield one-fold.

Effect of temperature and time on alkaline pretreatment and alkaline microwave-assisted pretreatment on banana stem composition

“…It is caused by microwavegenerated microwaves penetrating the lignocellulose wall and directly vibrating molecules, causing an increase in temperature and destroying the lignocellulose structure. These resulting vibrations break inter-and intra-molecular hydrogen bonds, which refers to an increase in the percentage of cellulose [8], [14]. Based on the results of the analysis, the optimum condition in alkaline microwave assisted pretreatment is heating at 95 o C with a contact time in the microwave for 50 minutes.…”

“…Under optimum conditions, alkaline pretreatment produces the highest cellulose content of 64.38% and the smallest lingnin content of 8.13%, while alkaline microwave-assisted pretreatment produces the highest cellulose content of 68.27% and the smallest lingnin content of 6.84%. In addition, according to Kassim et al [8], the delignification process using alkaline pretreatment requires a longer time than alkaline microwave pretreatmentassisted in producing the same cellulose concentration at a fixed alkaline concentration [8], [20].…”

“…Their study found that the highest sugar concentration was 9.81 mg/mL with the microwave-assisted alkaline (MAK) method and 9.98 mg/mL with the AK (alkaline) method, which was processed for 72 hours. Although the sugar concentrations obtained from MAK and AK were comparable, it was found that AK pretreatment took significantly longer (±120 minutes) to get conversion results similar to MAK pretreatment [8]. On the other hand, previous studies also examined the effect of temperature and alkaline pretreatment time on cellulose isolation of banana stem waste with temperature variations of 60, 70, and 80°C and variations in cooking time of 60, 90, and 120 min.…”

Optimization of microwave-assisted carbohydrate extraction from indigenous Scenedesmus sp. grown in brewery effluent using response surface methodology

“…Moreover, many studies have used RSM optimization for carbohydrate/reducing sugar/extraction from microalgal biomass using autoclaved pretreatment ( Dong et al., 2016 ; Kassim and Bhattacharya, 2016 ). However, MAE of carbohydrate/reducing sugar from microalgal biomass was performed without optimization ( Nur et al., 2016 ; Kassim et al., 2019 ). This indicated that optimization of MAE of carbohydrates using RSM should be employed from microalgal biomass to evaluate the extraction efficiency and subsequently used for bioethanol production.…”