Recovery of acids from anaerobic acidification broth by liquid–liquid extraction

In this study, anaerobic acidification of sugar beet processing wastes and subsequent liquid–liquid extraction of produced fermentation metabolites were investigated. The aim of extraction experiments was to asses the influence of pH and extractant (trioctylphosphine oxide (TOPO) in kerosene) concentrations on the recovery of volatile fatty acids (VFAs) from fermentation broth. The effect of TOPO in kerosene concentration was as crucial as the effect of pH on the recovery of VFAs via extraction. Consequently, pH 2.5 was determined as optimum. At this pH, percent recoveries of VFAs were changed from 43% to 98%, depending on the type of the acid extracted (acetic, butyric, propionic and valeric acids) and the concentration of TOPO in kerosene (5–20%). As the concentration of TOPO in kerosene was increased, efficiency of extraction was increased. As a result, highest VFA recoveries (61–98%) were observed at 20% TOPO in kerosene with distribution ratio values ranging between 1.54 and 40.79. At pH 2.5, the increase in TOPO concentration directly increased the chemical oxygen demand (COD) removal efficiencies, as it does for total VFA recovery. Up to 72% COD removals were achieved, at 20% TOPO in kerosene at pH 2.5, while the removal efficiencies remained between 19% and 22% at pH 5.5.