Treatment of olive mill wastewater by filtration through fly ash: an efficient and economic strategy for purification

Olive mill wastewaters (OMW) are known for their complexity, notably the high concentration of polyphenols and fats. These elements prevent the treatment of these effluents, for which all the treatments applied failed to meet the discharge standards. On the other hand, fly ash from thermal power plants is a severe environmental issue worldwide. The valorization of these wastes may be the best strategy to protect our environment. In this respect, the primary purpose of this work is to emphasize a promising technique for OMW treatment, using filtration through fly ash. A physical–chemical and microbiological characterization of the OMW was carried out beforehand. Then, the treatment was performed in the fixed-bed column adsorption process using fly ash as an adsorbent. This characterization revealed that the OMW have an acidic pH and is abundant in organic matter, as illustrated by the BOD₅ (20,650 mg O₂/L) and COD (99,864 mg O₂/L). They are equally characterized by a high concentration of phenolic compounds (6452 mg/L). Microbiological characterization revealed a total absence of pathogenic and fecal germs. The treatment of OMW by fly-ash filtration provided outstanding results as illustrated by the abatement rates obtained, which were 100%, 99.77%, 99.63%, and 99.96%, respectively for discoloration, BOD₅, COD, and polyphenols. In addition, the treated effluent perfectly fulfilled the Moroccan rejection standard. The fly ash support has shown a purifying performance for all toxic loads. Therefore, fly ash filtration could be an appealing and cost-effective technique for the treatment of both highly loaded and poisonous wastewater. Furthermore, fly ash could replace activated carbon in water treatment plants.