A comparison of energy use, water use and carbon footprint of cassava starch production in Thailand, Vietnam and Colombia

Energy use, water use and greenhouse gas (GHG) emissions were assessed for the transformation of cassava roots into starch by two small-scale (ST1, ST2: 1-2 t starch per day) and one large-scale (VLT: 100-200 t starch per day) technologies. The goal of the study was to identify hotspots of energy use and GHG emissions, as well as sustainable practices, with a view to uncover opportunities to improve the environmental performance of cassava starch production. VLT required 2527 MJ/t starch, mainly (77%) from biogas used to dry starch, but was the most efficient in terms of water use (10 m3/t starch) due to the practice of water recycling between unit operations. ST1 and ST2 were similar in terms of electricity use (212 MJ/t starch), and were able to rely on solar energy to dry starch, due to the small volumes of production. In contrast, water use varied from 21 to 62 m3/t starch due to differences in the design of the rasping and starch recovery (extraction) operations. GHG emissions were 149, 93 and 105 kg CO2eq/t starch for VLT, ST1 and ST2 respectively. For ST1 and ST2, methane emissions from untreated wastewater were the main contribution to GHG emissions. For VLT, methane was captured to produce biogas and to dry starch, and the main contribution to GHG emissions was the use of non-renewable grid electricity. Biogas technology was adopted in the past 12 years in the case of VLT. Previously fuel oil was used instead of biogas, which resulted in GHG emissions of 539 kg CO2eq/t starch. VLT used markedly more electricity than ST1 and ST2, which was necessary to ensure the high output and consistent starch quality. Strategies to reduce the impacts of cassava starch production could focus on (1) increasing the energy efficiency of the drying operation, in order to make more biogas available for other uses such as production of renewable electricity; (2) improving the design of some unit operations with regards to water and energy efficiency; and (3) promoting the trans