Optimization of hybrid treatment of olive mill wastewaters through impregnation onto raw cypress sawdust and electrocoagulation

This research investigation proposes a new method for sustainable olive mill wastewater (OMW) treatment and handling. It is based on the combination of its impregnation onto raw cypress sawdust (RCS) followed by electrocoagulation. The retention of OMW compounds onto various RCS doses show an important decrease of its chemical oxygen demand (COD) and its main cation and anion content. The maximum retention efficiencies of COD, Na+, K+, Ca2+, Mg2+, Cl−, $$ {PO}_4^{3-} $$ , and $$ {SO}_4^{2-} $$ were about 51.0%, 75.3%, 28.7%, 77.9%, 84.7%, 41.1%, 98.3%, and 90.9%, respectively, for the highest RCS dose (200 g L−1). This organic matter- and nutrient-loaded biomass could be thermochemically converted through pyrolysis into biofuel and biochar for energetic and agronomic purposes, respectively. The treatment by electrocoagulation of the pre-treated OMW using mild steel electrodes could be considered an attractive treatment method since 75.6% of COD removal efficiency was achieved. Besides, this approach permits a significant energy consumption reduction by 46% as compared with the electrocoagulation process alone. It allows also a significant improvement of the treated effluent quality in terms of both organic and mineral contents that could be reused for the irrigation of olive trees in the context of circular economy.