Effect of ferric chloride coagulation, lime precipitation, electrocoagulation and the Fentons reagent on the particle size distribution of olive mill wastewater

Size fractionation of olive mill wastewater (COD:155000 mg/L; TOC:40000 mg/L; BOD₅:37700 mg/L; total phenols:4100 mg/L; absorbance at 395 nm:145 cm^-1) before and after FeCl₃ coagulation, Ca(OH)₂ precipitation, electrocoagulation and the Fenton process was investigated. Particulate organic compounds were the major components of COD (54%), TOC (43%), BOD5 (43%), absorbance (57%), followed by an appreciable soluble size fraction. For the total phenols parameter, a dominant fraction (54%) appeared in the colloidal (5-8 nm) size range besides significant particulate (22%) and soluble (24%) size fractions. FeCl₃ coagulation and Ca(OH)₂ precipitation appeared to be most efficient in organic matter removal, whereas electrocoagulation was superior in phenolics removal. No shift in the size distribution pattern was observed after chemical treatment since phase-transfer was the dominant removal mechanism of the selected processes. The highest inhibition of the Vibrio fischeri photobacteria was observed in the particulate size range and decreased in the solube size range due to the elimination of the phenolic content.