Integrated Economic and Environmental Assessment of Biogas and Bioethanol Production from Cassava Cellulosic Waste

Cassava cellulosic waste, or cassava bagasse or pulp, is a solid waste generated from both the coarse and fine extraction processes used for producing starch. Current disposal alternatives, such as selling the wet or dried pulp for animal feed, do not provide a high economic value. Furthermore, when stored at the factory the resulting microbial fermentation of the waste causes environmental pollution and a strong odor. The pulp still has a high starch content and so is suitable for other utilization purposes. The aim of this research was to use a direct economic and environment cost model to assess three potential high value-added renewable energy utilization alternatives for cassava pulp utilization to help define appropriate option(s) for on-site pulp management. The selected utilization options were the production of (i) biogas for heat generation, (ii) biogas for electricity generation and (iii) bioethanol. Primary and secondary data were collected from the literature, surveys and field data. The boundaries of data collection were set as gate-to-gate of a new unit in an existing starch factory with a receiving capacity of 500 t/d of pulp (equivalent to the pulp produced from a 200-t starch factory). The total production cost of each cassava pulp utilization option was calculated from both the economic and environmental cost. The most economically attractive scenario was the production of biogas for heat generation since it gave the highest net present value (NPV), net cash flow and return on sale. The biogas for heat generation option has the highest NPV sensitivity value in all case studies.