• Energy Research
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Abstract Progressive replacement of petroleum chemicals with biomass derived products is an essential research goal toward sustainability. However, the progress of the development of new generation biorefinery has been affected by many factors, i.e., prices of crude oil, food, and carbon. To quantify the environmental and social impacts of the technologies, this study constructed a sustainability index for calculating two new bio-butanediol production processes with oil palm empty fruit bunches as example feedstock. The performance of organosolv pretreatment using butanediol was compared with the whole slurry conversion process using sulfite pretreated biomass, over the petroleum refinery and first generation biorefinery with food crop feedstock. The organosolv biorefinery process successfully converted the biomass into 77.3 ± 1.63 g/L of bio-butanediol (0.45 g/g yield), which is slightly higher (5.5%) than that of the sulfite-based process. The integration of biorefinery techniques, with oil palm farming shall result in 6.8 kg-CO2 and 0.5 kg-food benefits per kg butanediol produced, yielding a sustainability index of 7.30. The food index for first generation biorefinery is −1.04 kg food per kg butanediol produced. Using empty fruit bunches for butanediol production could save 1.54 kg food crop consumption, which turns the “food vs. fuel competition” into a “food plus fuel nexus”.

Bioenergy and biochemicals can be sustainably produced through fermentation and anaerobic digestion (AD). However, this bioconversion processes could be more economical if the hydrolysis rates of substrates in bioreactors can be accelerated. In this review, the feasibilities of including enzymatic hydrolysis (EH) in various bioconversion systems were studied to facilitate the biological synergy. The reaction kinetics of EH in bioconversion systems comparing pretreated lignocellulosic biomass (LCB) and food waste (FW) substrates were reviewed. Possible strategies to improve the hydrolysis efficiency were explored, including co-cultivation during enzyme production and replacement of pure enzyme with on-site produced fungal mash during EH. Key insights into improvement of current AD and fermentation technologies were summarized and further formed into suggestions of future directions in techno-economic feasibility of biorefinery using mixture of the first-generation food crop feedstock with FW; and/or co-digestion of FW with LCB.

Effective utilization of cellulose and hemicelluloses is essential to sustainable bioconversion of lignocellulose. A newly isolated xylose-utilizing strain, Klebsiella pneumoniae PM2, was introduced to convert the biomass "whole sugars" into high value 2,3-butanediol (2,3-BDO) in a biorefinery process. The fermentation conditions were optimized (30°C, pH 7, and 150 rpm agitation) using glucose for maximum 2,3-BDO production in batch systems. A sulfite pretreated oil palm empty fruit bunches (EFB) whole slurry (substrate hydrolysate 119.5 g/L total glucose mixed with pretreatment spent liquor 80 g/L xylose) was fed to strain PM2 for fermentation. The optimized biorefinery process resulted in 75.03 ± 3.17 g/L of 2,3-BDO with 0.78 ± 0.33 g/L/h productivity and 0.43 g/g yield (87% of theoretical value) via a modified staged separate hydrolysis and fermentation process. This result is equivalent to approximately 135 kg 2,3-BDO and 14.5 kg acetoin precursors from 1 ton of EFB biomass without any wastage of both C6 and C5 sugars.