The agro-industry has increased over the years as a necessity to supply the needs of the population in regard to food and drink. This increase has led to the significant production of agro-industrial wastewaters characterized by a high content of organic matter, polyphenols, suspended solids, and turbidity, making these wastewaters dangerous if released into the environment without proper treatment. In this work, recent findings concerning the feasibility of coagulation–flocculation–decantation (CFD) and advanced oxidation processes (AOPs) for the treatment of agro-industrial wastewaters were collected and reviewed. More specifically, the mechanisms, limitations, operational conditions, and relevance of the different treatment processes for wastewater treatment and reuse are discussed. As a result, it was concluded that CFD processes and AOPs could be performed either separately or combined to achieve high efficiency in agro-industrial wastewater treatment.

In this work, the efficiency of ultrasound, Fenton, and ultrasound-Fenton (US-Fenton) processes were evaluated separately for the treatment of municipal activated sludge (MAS). Additionally, the effects of operational parameters such as pH, hydrogen peroxide and ferrous iron concentrations, and cavitation time were studied. During the experiments, the chemical oxygen demand (COD) reduction and the volatile solids (VS)/total solids (TS) ratio were evaluated. Under the best operational conditions, ultrasound and Fenton processes achieved 17.3 and 25.9% COD removal, respectively, while the combined US-Fenton process was more efficient with a 94.8% COD reduction. Regarding the VS/TS ratio, the process that showed better results was US-Fenton, reducing the original value of 0.59 to 0.16. The ultrasound and Fenton processes showed a lower VS/TS ratio reduction to 0.26 and 0.22, respectively. In conclusion, the combination of US-Fenton achieves high COD removal and a significant VS/TS ratio reduction of the municipal activated sludge, showing better efficiencies than both processes separately.