Comparative sustainability assessments for integrated cassava starch wastes biorefineries

Abstract

Abstract Sustainable development in cassava starch industries is hampered by high cost and environmental burdens associated with the business-as-usual (BAU) waste management strategies. In BAU, starch wastewater & bagasse wastes are anaerobically digested to produce biogas for starch drying with the digestate getting disposed into watercourses while the cassava stalks are burnt. Converting the wastes into high-value bio-products in an integrated cassava wastes biorefinery (CWB) could enhance the economic exploitation while reducing the environmental burdens of the wastes. Five simulated CWBs and the BAUhave been assessed and compared using simulations in SimaPro and a percentage sustainability index (PSI) estimation tool to identify product integration schemes that support the development of sustainable CWBs. The CWB scenarios included (I) combined heat & power, with (II) hexose-bioethanol, (III) pentose & hexose-bioethanol, (IV) pentose-bioethanol + glucose syrup, and (V) pentose-bioethanol + succinic acid. The environmental impacts generally increased with the number of product integrations within the biorefinery gate boundaries. However, accounting for avoided emissions from the corresponding fossil-products, the CWBs show higher emission savings than the BAU. The PSIs for the CWBs show that scenarios (I)-(II) favour the economic dimension over the environment dimension and vice versa for scenarios (III)-(V) and the BAU. Based on the substantial net power (∼148–363 kW h/1 t feedstock) and fossil emission reduction potentials, implementation of green power tariffs could enhance the economic dimension for near-term applications of the CWBs. Thus, the CWBs should be explored for their potential to enhance sustainable industrial developments in cassava starch industries.