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.

This study aims to determine the maximum specific biomass growth rates of Nannochloropsis gaditana and Tetraselmis chuii grown in sequential batch reactors. The maximum specific growth rates of N. gaditana and T. chuii were found to be 0.23 ± 0.04 gVSS/gVSS·d and 0.22 ± 0.05 gVSS/gVSS·d respectively. Optical density measured at 550 nm (OD 550 ) accurately predict volatile suspended solids (VSS) concentration in N. gaditana growth media but not in T. chuii growth media. We observed decoupling of nitrate uptake from cell growth for both microalgae as growth continued well beyond the point where concentrations of nitrate in the growth media fell below the detection limit. This nitrate decoupling highlights the challenges in current microalgae growth models as growth was independent of the extracellular dissolved nitrogen in the system.

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