Reusing a mixture of anaerobic digestion effluent and thin stillage for cassava ethanol production

•A novel cassava ethanol process was explored to treat the wastewater.•Energy and water consumption were reduced and “zero-wastewater” was achieved.•Ethanol production was enhanced.

In this study, a novel process was explored for cassava ethanol fermentation. In the process, a portion of thin stillage was mixed with the effluent from anaerobic digestion of residual thin stillage and was then reused as process water for the following ethanol fermentation. This process was evaluated at the lab and a pilot scale was performed for anaerobic digestion and ethanol fermentation performance. Ethanol production was enhanced in the recycling batch compared with the first batch (freshwater was used). Anaerobic digestion of the thin stillage also showed high efficiency and stability with a chemical oxygen demand (COD) removal rate above 97% and a methane yield of 300 mL/g COD removed at both the lab and pilot scale. In addition, the COD and conductivity of the thin stillage remained consistent after the 6th and 3rd batch, respectively. In conclusion, in this novel process, energy consumption was reduced, and wastewater was utilized for value-added products, thereby contributing to the sustainable development in the cassava ethanol industry.