Biogas Production from Date Palm Wastes

       The 6th ENGII Conference——Saudi Arabia is one of the largest producers of date fruits in the world and hence huge quantities of date palm tree waste (DPTW) are produced. We used DPTW for the production of energy in the form of biogas through an anaerobic digestion (AD) process. Appropriate AD bioreactors were designed by the team and fabricated locally. These bioreactors included a simplified model in which the contents were shaken manually whereas a more sophisticated one was equipped with a mechanical stirrer. DPTW used contained 80-90% volatile solids,which makes it quite suitable for biogas production. A starter culture was developed from thermotolerant bacteria in cow dung from King Faisal University farm.Optimum operational parameters of AD were:40°C digestion temperature, 10%volatile solid concentration in digester slurry, 2-4 mm substrate particle size, initial pH of 7.0, 0.75% alkali pretreatment of feedstock, 30:1 C:N ratio and intermittent mixing/stirring. The best biogas yields (Liter biogas containing 50-70% methane per kg volatile solids) obtained from different parts of the tree were: Stem: 581, Leaf: 788, Fruit holder 778, Leaf stalk 867 and whole tree mixture 913. Reduction in the organic matter content of substrate after digestion was up to 58%. Reduction in the contents of cellulose, hemicellulose and soluble organic compounds after digestion was up to 68.7, 73.4 and 71.9%, respectively while lignin content was not affected. It was observed that there was minimal microbial growth during digestion which indicated that most of the organic matter consumed was converted into metabolic by products of which methane was the major component.