Integration of traditional systems and advanced oxidation process technologies for the industrial treatment of olive mill wastewaters.

A complete industrial treatment system (involving the integration of coagulation/flocculation and Fenton processes) to depurate real wastewaters coming from two-phase olive oil production mills has been studied. The experimental results indicated that at the end of this combined strategy, involving a primary physical separation stage followed by Fenton's chemical oxidation, chemical oxygen demand (COD) is reduced up to 90% and total polyphenols' concentration is decreased up to 92%. The treated stream biodegradability (BOD5/COD) reached 0.52 and the Total Suspended Solids (TSSs) and Total Dissolved Solids (TDSs) decreased up to 95% and 69%, respectively. Fenton's procedure was optimized bearing in mind the pH adjustment step, different procedures for hydrogen peroxide addition and the use of coagulants instead of the chemical precipitation (by raising pH) to promote iron sludge settling. Our results demonstrated that pH (3.0 ± 0.1) control during the oxidation reaction improves the oxidation efficiency. Moreover, the final NaOH addition is essential to a better sludge formation and consequent precipitation of the residual iron removing also some organic matter.