Reuse of olive mill wastewater as a bioflocculant for water treatment processes

Abstract

This study investigates the reuse potential of olive mill wastewater (OMW) high in tannin content and whose complete treatment requires the use of complex and expensive processes. Tannins from OMW could serve as bioflocculant compounds according to the literature. The defatted OMW is tested in a coagulation-flocculation process on synthetic water, and the best turbidity removal rate derived is: 92% ± 1% at pH 11 for 100 mg L−1. Water-solubilized material at pH 11 precipitates after acidification at pH 6. This precipitate fraction (PP), solubilized at pH 11, is found to contain more active constituents with a turbidity removal rate of 82% ± 2% for a 60 mg L−1 dose yet reveals an increase in absorbance at 254 nm. This increase in absorbance can be corrected by using lime for a pH adjustment to 11 with an absorbance removal at 254 nm of 50% ± 1%. The bioflocculant material is characterized by means of physicochemical methods. Acid-base titration, enzymatic treatment and colorimetric dosage all confirm that tannins and/or flavonoids and cellulose constitute the active groups involved in the coagulation-flocculation process.