Treatment of sewage sludge in a continuous-flow radiofrequency-oxidation system

This study explored the applicability of a pilot-scale continuous-flow radiofrequency (RF) heating system to treat sewage sludge by the RF-oxidation process (RF/H₂O₂). Depending on temperature and hydrogen peroxide dosage, high amounts of soluble chemical oxygen demand and volatile fatty acid were produced, and phosphates, nitrogen, and metals were solubilized. A high temperature and/or a higher H₂O₂ dosage implemented in this system yielded high solubilization of organic matters. Orthophosphate increased with an increase in treatment temperature up to 60°C, its concentration decreased as temperature further increased. There was little effect on orthophosphate release by varying H₂O₂ dosage. The efficiency of the RF/H₂O₂ process was comparable to the microwave (MW) enhanced advanced oxidation process (MW/H₂O₂-AOP), in terms of solids disintegration and nutrient release; however, the solubilization rate was lower for RF/H₂O₂ process. The overall energy consumed by the RF/H₂O₂ process was higher than the MW/H₂O₂-AOP.