Economic and environmental assessments of a novel integrated process for biomethane production and ammonia recovery from pot ale

Abstract

The necessity to decarbonise the whiskey distillery industry and minimize environmental pollution has triggered interest in the conversion of co-products such as pot ale into green fuels and chemicals. The disposal of pot ale to the environment creates severe environmental challenges due to its harmful composition. This study assesses the economic and environmental impacts of a novel integrated process for biomethane production and ammonia recovery from pot ale. Two scenarios were comprehensively studied. Scenario 1 includes the alkali pre-treatment, anaerobic digestion (AD) unit and biomethane purification unit. In contrast, scenario 2 introduces an additional gas–liquid stripping unit for efficient ammonia recovery from pot ale. Both scenarios were profitable from an economic standpoint. Scenarios 1 and 2 had a biomethane minimum selling price (MSP) of 142 U.S.$/ MWh and 148.9 U.S.$/MWh respectively. Ammonia produced from scenario 2 is estimated at a minimum selling price of 720 U.S.$/tons. The undiscounted net present value (NPV) of scenario 1 (10.4 million U.S.$) is greater than scenario 2 (6.7 million U.S.$). Also, Scenario 1 had a shorter payback period (PBP) (12.8 years) compared to scenario 2 (14.1 years). A local sensitivity analysis shows that factors such as raw material cost and fixed capital investment influenced the biomethane MSP. The environmental impact assessment of the two scenarios using the waste reduction algorithm confirms the environmental benign nature of the process. The total potential environmental impacts (PEI)/y for scenario 1 with coal as an energy source inside the system is 8494 PEI/y while the use of oil as an energy source produces a lower PEI of 8488 PEI/y.