Pertraction of volatile fatty acids through biodiesel-based liquid membranes

Volatile fatty acids (VFAs) are ideal substrates for mixed microbial cultures to synthesize polyhydroxyalkanoates. Therefore, VFA pertraction from anaerobic diluted fermentation broths to slightly alkaline aerobic medium becomes a crucial step to develop a closed loop concept in which VFAs are used for polyhydroxyalkanoate production. New liquid membranes (LMs) based on lipophilic amines and biodiesel were proposed for this purpose. The performance of each LM was tested through a VFA distribution coefficient test and pertraction kinetic experiments. The transfer of VFAs from LM to receiving solution was the main limiting step of the process, with flux rates of 0.001–0.04 cm3 cm−2 h−1 (best LM with 10 wt% of trioctylamine). The biocompatibility of trioctylamine -biodiesel LM towards anaerobic bacteria was confirmed through a 15-d acidogenic fermentation test. Trioctylamine-biodiesel LM was finally tested in a specifically designed continuous pertraction module, where VFA transfer rates of 1–3 h−1 were achieved.