Combined biological and chemical-physical process for olive mill wastewater treatment

The aim of the present study was to investigate on the combined biological and chemical-physical process for the olive mill wastewater treatment for its ultimate disposal into surface waters and/or reuse. The chemical-physical process was used as a pre-treatment to the biological step. Tests on precipitation were performed using three coagulants, such as lime, alum and iron chloride salts, and varying their dosages under predetermined optimum pH conditions. At optimal pH of about 12, lime achieved 51% COD removal efficiency. As far as the alum and iron chloride salts (FeCl3 × 6H2O) performances, the latter resulted in a 19% COD removal at a dosage of 3 g/l, while in the experiments using Al2(SO4)3 × 18H2O, 20% COD removal with a dose of 4 g/l was observed. From the results obtained, lime was chosen as the optimal reagent. It was also shown that it is suitable to be used as influent to a subsequent biological step. A lab-scale sequencing batch reactor (SBR) was used to carry the biological process. The plant was fed by the diluted OMWs as in the chemical coagulation tests. A final removal efficiency of about 60% was obtained at optimal operative conditions.