Bioenergy Potential Assessment of Distillery Stillage and Sugarcane Industry By-Products through Anaerobic Digestion

Abstract

Abstract Anaerobic digestion (AD) of waste streams has gained attention nowadays for both waste treatment and renewable energy generation. Agro-industrial activities generate huge amounts of solid wastes and effluents and sugarcane industry is one of them. Bagasse, press mud, combined sugar effluent and distillery stillage (spent wash), are wastes having high organic load, derived from sugarcane industry. Thus, the aim of this research was to evaluate the bioenergy potential assessment of distillery stillage and sugarcane industry by-products through anaerobic digestion. For this prospect, lab scale batch experiments were carried out. In the first phase of this study, characteristics of all substrates in terms of TS, VS, TKN, TOC, COD, BOD and C/N ratio were analyzed. Mono-digestion of bagasse, press mud (PM), combined sugar effluent (CSE) and spent wash (SW) substrates were assessed at organic loading, inoculum to substrate ratio, hydraulic retention time (HRT) and temperature of 10 gVS/L, I : l , 45 days and 35 o c respectively. Buffering capacity and reactors stability were analyzed in terms of initial and final pH, volatile fatty acids (VFA), total alkalinity (TA) and VFA/TA ratio. To assess the efficiency of all substrate reactors, volatile solids removal was also performed. Highest biogas yield of 533 Nml/gVS was observed from reactor having SW substrate and lowest of 123 Nml/gVS from reactor digesting CSE. In second phase, co-digestion often different combinations of substrates by keeping C/N ratio 25 and maintaining other parameters constant as described in mono-digestion, were carried out. Highest biogas yield of 607 Nml/gVS was observed from reactor having bagasse and SW with mixing ratio and lowest of 199 Nml/gVS from combination 3 reactor, having bagasse and CSE with mixing ratio 1:49. During co-digestion, process stability parameters affirmed better buffering capacity and reactors stability of all combinations as compared to mono-digestion. Bioenergy potential assessment and avoided emissions from sugar industry wastes were assessed in phase three of this study. Highest bioenergy potential was obtained from bagasse 1.88 TWh/year and avoided emissions from the same use was I .02 MtC02eq/year. Total theoretical bioenergy potential from all wastes was 2.6 TWh/year and their avoided emissions was I .41 MtC02eq/year. It can be concluded that agro-industrial wastes of sugarcane industry are enormous resource and by tapping resource recovery from these wastes into bio-energy, Pakistan can easily get rid of energy shortage. Key Words: Bioenergy potential, Anaerobic digestion, Co-digestion, distillery stillage, sugarcane industry by-products