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 concentrate by pressure driven processes, such as UF and NF, to recover and fractionate valuable biophenols was also proven.