Abstract
The effect of pH and extraction temperature on flux, recovery, mass transfer coefficient and separation factor of volatile fatty acids (VFAs) and alcohols from synthetic solutions and cheese whey fermentate was investigated using a silicone membrane contactor with water as extractant. The silicone membrane allowed extraction of undissociated acids only, resulting in substantially higher recovery efficiencies at pH 3 than at pH 5. Furthermore, the non-porous silicone membrane favoured extraction of longer chain over shorter chain acids. Caproic acid was extracted with the highest flux of 1.30 (± 0.02) g m−2 h−1 in short time (32 h), with a 41.5 % recovery efficiency at pH 3 and 20 °C, indicating the feasibility of its selective separation from the VFA mixture. A similar trend was observed for alcohols, with butanol being extracted with a 39 % recovery efficiency at 40 °C, against 32 % and 19 % of propanol and ethanol, respectively, while the mass transfer coefficients were not affected by temperature. When applying the silicone membrane contactor to real cheese whey fermentate at pH 3, butyric and acetic acid were extracted with 21.5 % and 7% recovery efficiency, respectively, suggesting the feasibility of the contactor for VFA recovery from real fermentate.
Highlights
Waste valorisation plays a key role in circular economy that relies on the transformation of value chains from linear to closed loop (Maina et al, 2017)
In-line recovery of these products from biological processes would be advantageous as continuous harvesting of volatile fatty acids (VFAs) and alcohols would facilitate their efficient and stable operation (Trad et al, 2015)
The present study investigated the applicability of silicone membranes for VFA and alcohol separation from synthetic solutions and a model anaerobic fermentate, i.e. cheese whey, with water as the extractant
Summary
Waste valorisation plays a key role in circular economy that relies on the transformation of value chains from linear to closed loop (Maina et al, 2017). This is necessary to achieve EU’s longterm goal of a low carbon economy by 2050 (Scarlat et al, 2015). Biological processes such as dark and photo fermentation (Yuan et al, 2019) have the potential to partially replace fossil fuel-based refineries to produce platform chemicals such as volatile fatty acids (VFAs) and alcohols. In-line recovery of these products from biological processes would be advantageous as continuous harvesting of VFAs and alcohols would facilitate their efficient and stable operation (Trad et al, 2015)
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