Lignin and Extractive Tracing an Alternative approach to Assess and Predict Biogas Yields and Production Rates among Tropical Biomass Feedstocks

Abstract

Predicting biogas yields from the composition of biomass feedstocks has been difficult primarily due to the variations found in their chemical composition and structure of lignocellulosics. This study aims at understanding, assessing and predicting biogas yields from the chemical composition cutting across different types of biomass feedstocks: fruit peels and rinds, cereal straws, crop stalks, husks, leaves and conifers. A wide range of substrates were chosen to account for the variation in composition by choosing these feedstocks with large variations in the lignin (range, type and steric arrangement). This research answers a few fundamental questions pertaining to predicting biogas yields, the role played by extractives and lignin and also the arrangement of the constituents. A classical Biochemical Methane Potential (BMP) approach was taken up to understand the fermentation behavior of various feedstocks and understand the issues/ problems in a systematic manner. The first part of this study deals with predicting the pattern of biogas production. The results show that the biogas yield is a strong function of extractive , i.e., pectins, soluble carbohydrates that leach out into the water during the hot water extraction, content in the biomass species. The feedstocks with high concentration of extractives produced higher amount of biogas and at higher rates. As the lignin concentration rises the extent and rates of gas production falls down. Based on the preliminary results and prior understanding, a new methodology was developed where the gas production can be ascribed to sequential/ semi-sequential degradation of biomass components. The sequential decomposition leading to biogas production can be explained by a two-component fit, wherein the first stage of gas production is ascribed predominantly to the breakdown of the easily accessible extractives and hemicellulose (unbound). In the second stage the gas production is slower and can be ascribed to the conversion of difficult to degrade hemicellulose...