Optimisation of an anaerobic co-digestion process

Abstract

Anaerobic co-digestion, ACD, is regarded as a key environmental technology in industrial, agricultural and domestic sectors for integrated solid and liquid waste treatment and renewable energy production. The main objective of this thesis is to optimize the wet co-digestion process of canteen food waste by combined experimental and mathematical modeling approaches. Anaerobic co-digestion of canteen food waste with water hyacinth, Gliricidia and Rice straw was conducted in this study. Two batch experiments were performed to find out the best co-substrate for co-digestion and subsequently to investigate the effect of increasing co-substrate fractions. Concurrently, dynamic batch modeling results from ADM1 is used to validate the results from each experiment. Semicontinuously fed experiments were conducted to determine hydrolysis rate constants of best co- substrate mixtures by combining parameter estimation of ADM1. The highest total Chemical Oxygen Demand (TCOD) removal and the highest average biogas production were obtained when Gliricidia was used as co-substrate. Total biogas production increased with increasing co-substrate concentration. Hydrolysis parameters were estimated using simulated total gas flow rate and experimental gas flow rate. Estimated hydrolysis rate constant for carbohydrates is higher than for the protein and lipids. Increase of Gliricidia contents in co digestion feed mixtures did not influence hydrolysis rate constants. Keywords: Anaerobic Co-digestion, Optimization, ADM1, Mathematical Modeling, AQUASIM 2.1f, Canteen Food Waste, Gliricidia,