Olive oil processing is a fledgling industry in Florida; however, treatment of olive mill wastewater (OMW) is a significant barrier to commercialization. This study assessed combining high-power-ultrasound (HPU) and electro-Fenton (EF) process in reducing contaminants in OMW; thereby allowing byproduct utilization without adversely affecting beneficial components such as phenolic compounds. Direct and indirect HPU treatments were conducted using a 20 kHz/1500 W ultrasonic processor. In both treatments, typical OMW samples were treated at constant ultrasound power (750 W) for 30, 60 or 90 min. For electro-Fenton method, OMW samples were treated for 4 h. After both treatments eight chemical procedures (COD, BOD, total phenol content, TA, FFA, ortho-PO4, Total-P and total Kjeldahl nitrogen) were performed. Treating OMW with HPU before EF improved the EF method. Direct HPU for 90 min followed by EF for 4 h achieved a reduction of 75.5% COD and 70.8% BOO, with other marker analytes reduced as well. The results indicate that combining HPU and EF is more effective compared to previous studies on OMW treatment. These results could encourage industrial scale application of HPU and EF processes as treatment steps for OMW, thus preserving by-product recovery while reducing the environmental impact of OMW disposal.