Evaluation of the olive mill wastewater treatment based on advanced oxidation processes (AOPs), flocculation, and filtration

Different eco-friendly processes are under study to treat olive mill wastewater in the line with European 2024 zero-waste plan. This study is focused on the application of advanced oxidation processes, flocculation, and filtration to determine the best operational condition to obtain high-quality regenerated water in a simple and fast process. In this sense, after photo-Fenton high organic matter removal percentages were obtained: turbidity = 78.3 ± 6.4 %, chemical oxygen demand = 82.9 ± 0.1 %, total organic carbon = 68.9 ± 8.2 %, total phenolic compound = 20.8 ± 9.1 %, and total nitrogen = 64.1 ± 2.1 %. However, the total iron was increased to 792 ± 71 mg/L generating toxicity in the wastewater (100 % mortality in D. magna toxicity test). The subsequent flocculation and filtration steps, refine the water quality. In this sense, different flocculants have been studied to optimize regenerated treated water and the operations time, determining the sedimentation rate in a typical Kynch curve. In quality terms, adjusting the oxidized water to pH = 6 showed the best option to determine lowest values of COD = 131 mg O2/L, TPCs = 0.110 mg/L, and total iron = 0.380 mg/L but with high values for sodium = 1320 mg/L and chloride ions = 473 mg/L. However, with a minimum amount of Nalco 9913 (10 mg/L) and Nalco GR-204 (50 mg/L) highest sedimentation rate was achieved. After three filtration steps, regenerated water for irrigation purposes with the following quality parameters pH = 7.0, electric conductivity = 6.04 mS/cm, turbidity = 0.66 FTU, COD = 451 mg O2/L, TOC = 142 mg/L, TPCs = 0.13 mg/L; sodium ions = 1.50 mg/L, chloride ions = 221 mg/L, total iron = 0.247 mg/L, and no toxicity was obtained.