Pretreatment of Sugar Beet Bagasse for Enhance Biogas Production

Abstract

World energy consumption is increasing depending on the rise in demand which threatens humanity with a soon shortage of fossil fuels. Therefore, the research is focused on alternative sources of energy such as the renewable ones. Biogas production is regarded as an alternative source of energy from various kinds‟ biomass feedstock or wastes which can also have negative effects on the environment if not properly disposed. Gradually, biogas has been gaining a new pace in the market due to the efficiency and the lack of technology modification, when compared with the other renewable energy sources. The problems encountered in anaerobic digestion degradation are caused by the complex and tough structure of lignocellulosic biomass. Its efficient disruption is required to increase the hydrolysis rate and biogas production. One way of enhancing biogas production from lignocellulosic biomass is implementing pretreatments to the substrate before the anaerobic digestion process for increasing the biodegradability. The physical, chemical and biological pretreatments are widely studied to improve the biomethane yield. The biomethane production can be enhanced by 25% and >100% with various pretreatment applications. Combinations of pretreatments are also applied. The selection of pretreatment method is always related to application procedure, time, energy and chemical costs. Besides, the effectiveness of chemical reagents, possible corrosion or degradation is also considered due to the concentrations used. In this study, the effects of physical and chemical pretreatments, and their combination were investigated on the degradation of lignocellulosic structure of sugar beet pulp, and (ii) the effect of pretreatment methods on the methane production by performing batch Biochemical Methane Production tests (BMP). By considering the previous facts in the present investigation, raw sugar beet (RSB) and exhausted sugar beet (ESB) were studied. Sugar beet pulp has 22-30% cellulose, 22-30 hemicellulose, 24-32% pectin and 1-3% lignin content. Acid pretreatment with dilute H2SO4 and alkaline pretreatment with dilute NaOH were used as the chemical pretreatment methods. The physical pretreatments were done under microwave and autoclave. Under the scope of the physical pretreatment the specific methane production potential (SMP) resulted in 328.90 mL CH4/gVSfeed, which increased by 40% with microwave radiation (300 Watts) for 2 minutes. The alkaline pretreatment with 2% NaOH (at 25°C, 48 hours) achieved 286.96 mL CH4/gVSfeed, which represents an increase by 45%. Furthermore, physicochemical pretreatment elevated the biomethane production potential by 65% when the sugar beet was exposed to 2% acid at 120°C during 30 minutes in autoclave as 387.82 mL CH4/gVSfeed. Besides, a mixed substrate (70 pretreated and 30 un-pretreated) could enhance SMP by 60% as 376.11 mL CH4/gVSfeed (RSB + Acid 2% + MW 300Watts for 2 min) or 280 mL CH4/gVSfeed (ESB + Alkaline 2% + Autoclave 120°C, 30 min). The applied pretreatment methods increased the biogas production from raw sugar beet (RSB) and exhausted sugar beet (ESB) by 40 – 65%. Also, it opened a new approach to investigate with the mixed substrate combination, which can reduce the cost implementation of the pretreatments in the industrial scale.