Comparison of the efficiencies of pyrite and zero-valent iron activated peroxydisulfate systems to degrade methomyl in water

The high leachability and solubility of methomyl (MET; C 5 H 10 N 2 O 2 S) result in water pollution; while, the polluted water channels can be depolluted by environmentally-friendly and highly-effective degradation technique. Therefore, MET degradation in water by peroxydisulfate (PDS) oxidation was investigated in this study employing the two most naturally-abundant iron species i.e. pyrite (PyR) and zero-valent iron (ZVI) as activators for PDS activation. The experiments were conducted at different activators’ dosage, pollutant concentration, oxidant concentration, initial pH and initial temperature for comparative assessment of degradation-efficiencies of PyR/PDS and ZVI/PDS systems. Using 0.25 g/L PyR/ZVI and 1.0 mmol/L PDS, PyR/PDS and ZVI/PDS systems respectively led to 98.8 % and 97.5 % degradation of 20.0 mg/L MET in 20 min, which became rapid by increasing the activators’ dosage and oxidant concentration in both systems. Further, the degradation has been more than 90.0 % at initial pH 3.0 to 11.0, which slowed with increasing the MET concentration in two systems. The free-radicals quenching analysis showed that degradation by PyR/PDS system was mainly executed by sulfate (SO 4 •− ) and hydroxyl ( • OH) radicals; while, SO 4 •− and super oxide radical anion (O 2 •− ) were dominant during degradation by ZVI/PDS system. PyR/PDS system had low stability and applicability, which supports the employment of ZVI/PDS system for efficient degradation of MET in water.