Olive Mill Wastewater Removal by H3PO4 Treated Olive Stones as an Efficient Adsorbent and Electrocoagulation Process

Olive mill wastewater (OMW) is the major problem from olive oil extraction, due to its polluting organic and mineral matter and acid pH. This study aims to electrochemically treat OMW in an Al electrode reactor, to oxidize the organic matter, discolor the margins and neutralize the pH, thus reducing the pollutants. Various low cost adsorbents have been studied for the treatment of different types of effluents. In this study, the potential of activated carbon (C) derived from olive stones (OS) was studied for OMW removal. H 3 PO 4 (phosphoric acid) treated OS (AOS), as a low-cost, natural and eco-friendly biosorbent, was investigated for OMW removal from aqueous solutions. This work found that the increase in electrolysis time and current intensity significantly improved the treatment, while energy consumption and electrodes were observed. The results showed thirty-fold diluted margins for effluents with an acid pH of 5.02 and a conductivity of 14.89. The physicochemical parameters evolution during the electrocoagulation (EC) treatment showed that, under the conditions of an electrolysis time of 3 h and a current intensity of 3 A (= 416 A/m -2 ), the margins discoloration diluted ten times (91%), the mass loss of the electrodes was 0.55 kg.m -3 and the chemical oxygen demand (COD) reduction was 50%. These optimal operational levels allowed a good degradation of the margins. Biosorption kinetic data were properly fitted with the pseudo-second-order kinetic model. The experimental isotherm data were analyzed using Langmuir’s and Freundlich’s isotherms equations. The best fit was obtained by the Langmuir’s model, with maximum OWM monolayer biosorption capacity of 189.83 mg/g. The biosorption was exothermic in nature (entalphy change:  H° = -13.11 kJ/mol). The reaction was accompanied by a decrease in entropy (  S° = -72.91 kJ/mol). The Gibbs energy (  G°) was higher when the temperature was increased from 303 to 318 K, indicating a decrease in the biosorption feasibility at higher temperatures. The results have established good potentiality for EC and ALS to be used for OMW removal.