Environmental impacts and economic benefits of different wastewater management schemes for molasses-based ethanol production: A case study of Thailand

This research investigates the environmental impacts and economic benefits of six molasses-based ethanol production schemes using open lagoon or upflow anaerobic sludge blanket (UASB) waste-water management system in Thailand (schemes A-F). The aim is to determine the most environmentally and economically favorable scheme in terms of the environmental cost, payback period, and cost savings, using analytic hierarchy process (AHP). Schemes A and B use open lagoon for treating wastewater from ethanol production. The ethanol production of scheme A relies on steam and electricity from a sugar mill on the premises, and scheme B is a stand-alone ethanol plant that purchases steam and electricity from external sources. Schemes C - F use UASB technology. In scheme C, the ethanol plant acquire power from a sugar mill on the premises, and biogas from UASB is used for electricity generation. In scheme D, the stand-alone ethanol plant utilizes both biogas and natural gas in combined heat and power system, while in scheme E, biogas and natural gas are used for steam production while electricity is acquired from external sources. In scheme F, a stand-alone ethanol plant uses biogas for electricity generation and purchases steam. The results indicate that the overall environmental cost of open lagoon is greater than that of UASB. Scheme C has the lowest environmental impacts and environmental cost. The payback period of scheme E is the shortest (2.19 years), and the ethanol production costs after payback period decrease by 3.11, 0.24, and 2.92 Thai baht per liter ethanol under schemes C, E, and F. Scheme C is the most environmentally and economically favorable scheme, given the highest AHP weighted score of 0.354. Since the country's ethanol production is expected to increase to 9 million liters per day by 2021, scheme C should be adopted to make use of molasses and mitigate the environmental impacts. (C) 2019 Elsevier Ltd. All rights reserved.