Aerobic treatment of black ripe olive processing streams to reduce biological contamination

Abstract

A new aeration treatment of black ripe olive streams prior to their vacuum evaporation was studied. It was found that the aeration for two days of these solutions reduced the chemical oxygen demand (COD) of the distillate phase (>80%) generated during their vacuum evaporation; although the temperature (14–38 °C) and the air flow rate (10–50 L air/h/L) had a great influence on this reduction. Moreover, the COD in the distillate was mainly associated with the presence of acetic acid (~400 mg/L) and ethanol (~500 mg/L), the later substance being eliminated by strong aeration. Additionally, the growth of native aerobic microorganisms, mainly Acetobacter, increased the pH of the wastewater to 7–8 units, thus avoiding evaporation of the acetic acid salt formed. These results make the use of the distillate for plant irrigation viable and its discharge into municipal depuration plants possible, given the low COD (<500 mg/L) reached with this new method.