An Integrated Process of Olive Mill Wastewater Treatment

Abstract

Olive mill wastewater (OMWW) is considered as a challenge for environmental scientists. It is characterized by high values of total organics expressed by chemical oxygen demand (COD), biological oxygen demand (BOD5), and phenols. In this paper, an integrated process of OMWW treatment, which includes lime precipitation, filtration using a novel technology of a membrane filter press (a pilot scale) and a post‐treatment using activated carbon adsorption for the filtrate, was studied. Lime precipitation has removed ∼71% of phenols, ∼39% of COD, and ∼88% of BOD5 with a rise in the total suspended solids (TSS) from 31 kg/m3 (before precipitation) to 69 kg/m3 (after precipitation). The filtration and dewatering operation cycle is approximately 125–150 min. Filtration was examined at different feed pressure (3–5 bar), different slurry concentrations (23–69 kg/m3, dry weight), and filter aid pre‐coat with different additions of diatomite body feed. Specific cake resistance, α, was found to increase with the increase in feed pressure and to decrease with diatomite pre‐coating and slurry concentration increase. However, a further decrease in α values was obtained using diatomite body feed. Cake dewatering, via membrane squeezing, was applied using hot water (65°C) and cake moisture was dropped from ∼64% before squeezing to 35% after squeezing. Twenty minutes were found enough for that stage to be accomplished. With vacuum application, for 30 min, over the hot cakes, cake moisture decreased to ∼20% for cakes with an average thickness of 1 cm. The produced cakes lose more moisture by storing in open air (on the shelf), reaching an equilibrium value of 9% in 2–3 days. Calorific value of produced cake is 15.71 MJ/kg, suggesting strongly its use as an energy source. Activated carbon was used as an efficient sorbent for removing the remaining phenols and total organics from the filtrate as a post‐treatment showing promising results. Maximum removal of phenols and total organics, by lime precipitation and filtrate post‐treatment using activated carbon adsorption, reached ∼99.7% and ∼80%, respectively. A process flowsheet and preliminary cost estimates are presented and compared with other processes. The thermal energy produced by the burning of the produced cakes would be enough for the thermal needs of both the olive mill plant and the proposed treatment process.