Removal of diclofenac sodium from simulated wastewater through an optimized plasma technology system synergized with activated carbon and persulfate

Diclofenac sodium (DCF) has received much attention due to the contaminations associated with its frequent usage. Current technologies for DCF removal from wastewater have presented higher energy consumption and lower cost efficiency, thus efficient removal of DCF without secondary pollution would be required. In this study, removal of DCF by plasma technology was modeled and optimized via the response surface methodology (RSM). The DCF removal rate could reach 66.3 % after a treatment of 60 min when the voltage was 12.7 kV, the discharge gap was 15 mm, and the number of discharge needles was 5. Subsequently, further addition of granular activated carbon (GAC) and persulfate (PS) enhanced the removal of DCF through the construction of an optimized plasma/GAC/PS system. The improved removal rate of DCF could rise to 90.4 %, when GAC was 2 g/L and PS was 2 mmol/L under the optimal conditions of RSM. Based upon the analysis of UPLC-QTOF-MS/MS and UV-vis and free radical quenching, the removal of DCF in the plasma/GAC/PS system mainly relied on the attack of center dot OH and SO4 center dot- on the benzene ring, involving the C-N breakage of DCF and the generation of by-products. Finally, residual toxicity and cost of the DCF treatment were evaluated.