A techno-economic case for volatile fatty acid production for increased sustainability in the wastewater treatment industry†

Methane, the final product of methanogenesis during anaerobic digestion is a low value product (0.1 $ per m(3)). Concerns over fugitive emissions from methane coupled with recent reduction in costs of solar and wind energy raise questions over the long-term sustainability of the anaerobic digestion process as a technology to produce renewable energy. The production of short chain volatile fatty acids (VFAs), a by-product of acetogenesis, represents a high value product. The projected VFA market demand for 2020 is 18 500 kilotons, increasing at an annual rate of 3% per year. Here, we review the business case for wastewater treatment plants (WWTPs) to produce VFAs instead of biogas. Techno-economic and sensitivity studies are conducted to understand and compare economic feasibilities. Under favourable conditions, with positive government incentives, future WWTPs could produce high purity (>98%) propionic acid at 3.8 $ per kg, 35% less than the commercial selling value (6 $ per kg).