Radical-based advanced oxidation for trichlorfon degradation and phosphorus recovery: Process feasibility and reaction mechanism

Trichlorfon is an organophosphate insecticide that has been widely used to protect crops and livestock from pest infestations all over the world. Due to its high phosphorus content, high chemical oxygen demand and low biodegradability, wastewater produced from trichlorfon manufacturing process has caused a series of health and environmental problems. To date, various physical, chemical and biological processes have been tested for trichlorfon degradation. However, their high capital cost, long processing time and lack of considerations to reuse the embedded phosphorus in trichlorfon make them unsustainable for a circular economy. By using potassium persulfate as a new oxidant for trichlorfon degradation, this research combines advanced oxidation and K-struvite precipitation for nutrient recovery for the first time. Experimental results showed that temperature and persulfate (PS) dosage could significantly improve trichlorfon degradation efficiency. The highest trichlorfon degradation efficiency achieved was 91.74%, with a PS dosage of 3.05 g/L at 80 °C under ultraviolet irradiation (UV) assistance. Further mechanism analysis proved that such degradation follows the frontier molecular orbital (FMO) theory. 92.96% degraded phosphorus could be recovered through K-struvite precipitation at pH 11.5, with a Mg:P molar ratio at 1.8.