Strategies for the improvement of VFAs recovery in the nanofiltration process within the circular economy framework

Over the past decades, the anaerobic digestion (AD) process has been employed as a potential medium to produce valuable resources from the waste-based feedstock. Moreover, the use of AD technology can generate not only resources, but it also creates an avenue for useful chemicals recovery to further use in commercial purpose, which is a part of the circular economy consortium. Volatile fatty acids (VFAs) are one of the most precious chemical feedstock that can be recovered from anaerobically digested effluent through the use of a pressure-driven membrane filtration process. In an effort to improve the recovery percentages of VFAs from anaerobically digested effluent, this study proposed a sustainable pathway by reusing the permeate effluent in the nanofiltration process. For this purpose, particles free feed solution was produced using the ultrafiltration process and sequentially subjected to the nanofiltration process in the presence of a 200-300 Da nanofiltration membrane. Each permeate was mixed with a known amount of fresh feed and continues up to 3 cycles to be improved the recovery percentages of total VFAs concentrations. Results indicated that recycling strategies could be a potential way to modulate the concentration of VFAs compounds.