Agro-industrial wastewaters are characterized by the presence of multiple organic and inorganic contaminants of environmental concern. The high pollutant load, the large volumes produced, and the seasonal variability makes the treatment of these wastewaters an environmental challenge. A wide range of wastewater treatment processes are available, however the continuous search for cost-effective treatment methods is necessary to comply with the legal limits of release in sewer systems and/or in natural waters. This review presents a state-of-the-art of the application of advanced oxidation processes (AOPs) to some worldwide generated agro-industrial wastewaters, such as olive mill, winery and pulp mill wastewaters. Studies carried out just with AOPs or combined with physico-chemical or biological treatments were included in this review. The main remarks and factors affecting the treatment efficiency such as chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), total organic carbon (TOC), and total polyphenols removal are discussed. From all the studies, the combination of processes led to better treatment efficiencies, regardless the wastewater type or its physico-chemical characteristics.

In this work, the effect of the combined coagulation–flocculation–decantation (CFD) with the sulfate radical oxidation process on the treatment of two winery wastewaters (WW1 and WW2) was investigated. The oxidation process was optimized by the application of a Box–Behnken design of the Response Surface Methodology. Under the best CFD conditions: [potassium caseinate] = 0.4 g/L, [bentonite] = [PVPP] = 0.1 g/L, pH = 3.0, rapid mix (rpm/min) = 150/3, slow mix (rpm/min) = 20/20, sedimentation time = 12 h, and oxidation conditions: [sodium persulfate (SPS)] = 51.9 mM, [Fe²⁺] = 0.90 mM, pH = 3.0, radiation UV-A (365 nm), time = 300 min, a total organic carbon (TOC) and a chemical oxygen demand (COD) of 38.9 and 45.3%, respectively, were achieved for WW 1, and 51.2 and 73.3%, respectively, for WW2. The combined process shows a good potential for WW treatment.

In this study, the treatment of a winery wastewater (WW) by a photo-Fenton process, employing a combination of (S,S)-ethylenediamine-N,N’-disuccinic acid (EDDS) as a quelating agent and hydroxylamine (HA) to accelerate the Fe²⁺ recovery, was presented for the first time. The aim of this study was to improve the photo-Fenton process under UV-C, UV-A and solar radiation. The results show that under the best operational conditions—pH = 6.0, [Fe²⁺] = 5.0 mM, [H₂O₂] = 175 mM, [EDDS] = 1.0 mM, [HA] = 1.0 mM, agitation 350 rpm, time 240 min, temperature 298 K—a chemical oxygen demand (COD) removal of 93.2, 81.6 and 60.6% was achieved for UV-C, solar and UV-A radiation, respectively. EDDS-photo-Fenton is an excellent process for WW treatment.