INPUT OUTPUT ANALYSIS ALGAL BIOENERGY PRODUCTION CHAIN

Abstract

This study investigates the net energy balance of algal bioenergy production, using nutrients present in the dairy manure, as well as the acidification impact caused by the algal bioenergy - system. Algal bioenergy production system include, dairy waste treatment through anaerobic digestion, uses of solubilized nutrients for algal growth, uses of algal biomass for biodiesel production and then recovery of nutrients and energy from the residual biomass through anaerobic digestion. The useful energy outputs from the algal bioenergy production considered in this study are methane and biodiesel; methane produced from anaerobic digestion of organic solids, and biodiesel produced from transesterification of algal biomass. For optimization purpose, an energy input output function and an acidification input output functions were developed for the production of bioenergy through different processes as described before. The energy input output function and acidification input output function were minimized taking various parameters such as efficiencies of various processes, algal biomass produced in the algal pond, lipid accumulation in the biomass and nitrogen concentration in the algal pond as the constraints. The net energy of a process is defined as the difference of the sum of total energy required for the process from the useful energy output from the process. The simulation was carried out for 1 year taking residence time of completing one cycle of bioenergy production as 45 days. NER (Net Energy Ratio) value for different scenarios considered in our study varied from 1.91 to 2.39 whereas the acidification varied from 1998 to 3402 kg. Acidification showed decreases in value with increase in NER value of different scenarios. NEV (Net energy value) for 1 year of algal bioenergy production, of the highest NER value scenario, comes out to be 3184.861 GJ (Giga-Joule), where the total input is 3260.541 GJ and the output is 6445 .402 GJ. Drying of algal biomass, for the dry phase extraction, is the most energy intensive process in the algal processing unit, contributing about 40% to 60% of the total input, depending upon the scenario.