The evaluation of a Jerusalem artichoke tuber based combined ethanol and biogas production system

The thesis evaluates the performance of a next generation ethanol production system and compares this system to the corn ethanol model that has been implemented in North America. There are three distinct differences present in the next generation ethanol production system being evaluated here. Jerusalem artichokes tubers are used as the input feed stock for the ethanol production process. The next generation system incorporates an anaerobic digestion process to digest the ethanol production residues into biogas, which is used to meet the energy requirements of the original ethanol production process. The residual matter that is produced by the anaerobic digestion process is then used as a fertilizer and put back on to the lands that produced the tubers used for the ethanol process, this effectively recycles the nutrients and significantly reduces energy costs and environmental impact. The third major difference is that the next generation system is evaluated at a small scale, which significantly reduces transportation energy costs and makes land applying the anaerobic digester output back on the original land a feasible practice.The results of this evaluation demonstrate that this next generation ethanol production system has an energy balance of 1 input energy unit produces 7.2 units of ethanol energy, which is a significant improvement over the widely accepted corn ethanol energy balance of 1input unit producing 1.34 units of ethanol energy. Using Jerusalem artichoke tubers as an input feedstock produces between 1600-4400 litres of ethanol per acre (Schorr-Galindo and Guiraud, 1996 Schittenhelm, 1999), this is a significant increase when comparing to the corn ethanol yield of 1300 litres per acre (Pimentel & Patzek, 2005). These results also demonstrate that this next generation ethanol production system significantly reduces the environmental foot print on a per litre of ethanol produced basis. These reductions are mainly due to the system being a closed loop carbon system (biogas providing energy instead of natural gas), efficient nutrient recycling, reduced water input, less arable land required.