Green Extraction of Volatile Fatty Acids from Fermented Wastewater Using Hydrophobic Deep Eutectic Solvents

Volatile fatty acids (VFAs) are carboxylic acids mainly produced via the fermentation of organic waste streams. Being industrial platform chemicals, sustainable, green and economical recovery of VFAs is necessary. Herein, hydrophobic deep eutectic solvents (HDES), a new generation of water-immiscible designer solvents, were assessed for the recovery of VFAs via liquid-liquid extraction. The eutectic mixture of menthol-lauric acid exhibited the highest stability and hydrophobicity. The binary solubility of the pairs {VFA in water} and {VFA in HDES}-and the saturation of the HDES with water were measured. Furthermore, the influences of key parameters on the extraction efficiency were investigated. On multi-stage extraction, an efficiency of 88% was achieved in 4 stages, and the HDES was successfully regenerated using vacuum evaporation. The HDES performance was also compared to other reported relevant solvents. It was concluded that menthol-lauric acid HDES is a promising candidate for the green extraction of VFAs from fermented wastewater.

Automated summary

The study evaluated the use of hydrophobic deep eutectic solvents for the recovery of VFAs, finding that the menthol-lauric acid eutectic mixture performed the best in liquid-liquid extraction. An efficiency of 88% was achieved through multi-stage extraction, and the HDES could be successfully regenerated through vacuum evaporation.