Abstract
Large amounts of waste biomass are generated in sugar factories from the processing of sugar beets. After diffusion with hot water to draw the sugar from the beet pieces, a wet material remains called pulp. In this study, waste sugar beet pulp biomass was enzymatically depolymerized, and the obtained hydrolyzates were subjected to fermentation processes. Bioethanol, biomethane, and biohydrogen were produced directly from the substrate or in combined mode. Stillage, a distillery by-product, was used as a feedstock for anaerobic digestion. During biosynthesis of ethanol, most of the carbohydrates released from the sugar beet pulp were utilized by a co-culture of Saccharomyces cerevisiae Ethanol Red, and Scheffersomyces stipitis LOCK0047 giving 12.6 g/L of ethanol. Stillage containing unfermented sugars (mainly arabinose, galactose and raffinose) was found to be a good substrate for methane production (444 dm3 CH4/kg volatile solids (VS)). Better results were achieved with this medium than with enzymatic saccharified biomass. Thermal pre-treatment and adjusting the pH of the inoculum resulted in higher hydrogen production. The largest (p < 0.05) hydrogen yield (252 dm3 H2/kg VS) was achieved with sugar beet stillage (SBS). In contrast, without pre-treatment the same medium yielded 35 dm3 H2/kg VS. However, dark fermentation of biohydrogen was more efficient when sugar beet pulp hydrolyzate was used.
Highlights
Biomass is considered a potential substitute for fossil fuels, and has attracted a great interest from governments and industry
The smallest amount of reducing sugars was detected in the hydrolysate obtained from briquetted pulp, while the largest was found in the hydrolyzate from wet pulp (p < 0.05)
This article has presented a concept for the management of waste sugar beet pulp biomass, delivering three valuable bio-products: ethanol, methane, and hydrogen
Summary
Biomass is considered a potential substitute for fossil fuels, and has attracted a great interest from governments and industry. It is the fastest-growing renewable energy source in the European. Large amount of waste biomass are generated in sugar factories from the processing of sugar beet pulp. After diffusion with hot water to draw the sugar from the beet pieces, a wet material called pulp remains. Around 660 kg of sugar beets are required to produce 100 kg of sugar, with 330 kg of wet pulp and 25 kg of molasses generated as by-products [2]. The pulp mostly contains polymeric saccharides such as cellulose (22–30%), hemicelluloses (24–32%), lignin (1–2%) and pectin (38–62%), which constitute up to 75–85% of the dry matter [3]
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