Treatment of Olive Mill Wastewater by Forward Osmosis

Olive millings periodically release huge volumes of environmentally detrimental wastewater. In this work, Forward Osmosis (FO) is applied to de-hydrate Olive Mill Wastewater (OMWW) within the logic of Zero Liquid Discharge and by-products valorization. Single-step FO operated with 3.7 m MgCl2 draw solution and 6 cm/s crossflow velocity resulted in a volume reduction of 71%, complete decolorization of the permeate, and more than 98% rejection to OMWW components, including biophenols and ions. This makes FO more attractive than conventional multi-stage treatment processes that may include energy-intensive centrifugation and adsorbent utilization. Moreover, MBR-based pre-treatment prior to FO reduced pectins by 92.3%, thus resulting in 30% flux enhancement. Cleaning cycle based on osmotic back-flushing, after continuous OMWW dehydration tests carried out over 200 h, resulted in an almost complete removal of the foulant layer and permitted to restore up to 95% pure water permeability of cellulose triacetate (CTA) membranes. The possibility to process FO con-centrate by pressure driven processes, such as UF and NF, to recover and fractionate valuable biophenols was also proven.