Improved anaerobic digestion of agro-industrial waste by enhanced hydrolysis and operational design.

The anaerobic digestion of organic west in a process that has become a major focus of interest and competitive alternative biotechnological approach in waste management trough the world. The use of renewable energy sources is becoming increasingly necessary; to achieve the changes required addressing the impacts of global warming and pollutions due to use of conventional fossil fuel energy sources. Biogas is produced when organic matter is degraded by microorganisms under anaerobic conditions, the main constituents being energy-rich methane, a clean renewable fuel. However, greater knowledge of the theory and practice of anaerobic biotechnology is still needed both as the basis to improve it in many aspects and to assist in efficient waste management. This thesis provides important biotechnological information for the first time on the improved anaerobic digestion of agro-industrial waste. Anaerobic digestion of various kinds of waste has been shown to improve the digestibility of the materials and the biogas yield. A successful anaerobic co-digestion of sisal pulp and fish waste is reported for the first time. Co-digestion improved the accumulated methane production and increased the methane yield by 59-94% compared with digestion of sisal pulp and fish waste separately. Various pre treatment technologies are applied for enhancement of energy recovery from particulate organic fraction in anaerobic digestion. A new approach to solid substrate pre-treatment in biogas technologies is reported. A short aerobic pretreatment time (9 hours) of sisal pulp waste (SPW) using activated sludge mixed cultures as an inoculum demonstrated 26% higher methane yield compared to anaerobic digestion of (SPW) without pretreatment. Moreover in the two stage anaerobic digestion system the method was found to be promising for fast stabilization of SPW, while at the same time energy yield of 0.23 m3 kg volatile solids (VS)-1 added in the form of methane was recovered. Support materials were utilized to facilitate the retention of slow growing organisms in biofilms thereby stabilizing anaerobic digestion process. A novel support material; sisal fiber waste was successfully used as a biofilm carrier in high rate anaerobic filter, single stage anaerobic fixed bed and two bed anaerobic systems treating SPW without serious operational problems. A new single stage anaerobic digester employing sisal fiber waste fixed bed was successfully demonstrated for digestion of SPW. A high organic loading of 10 kg VS m-3 d 1 could be applied and methane yields in range of 0.13 – 0.48 m3 kg VS added were obtained. In this study it was concluded that high process efficiency and increased stability in anaerobic digestion of agro-industrial waste namely; sisal fiber, sisal pulp and potato waste could be improved by pre-treatment and maintaining ample microbial growth on support material. Anthony Manoni