Efficiency and mechanism of micro zero-valent iron combined with pyrite in removing ofloxacin and nitrate in groundwater

A dual system comprising micro zero-valent iron (ZVI) and pyrite (FeS 2 ) was applied for the remediation of groundwater contaminated by nitrate and ofloxacin (OFL). The removal efficiency for nitrate, total nitrogen (TN), and OFL in the dual-material system with different ZVI-FeS 2 weight ratios, dosages, initial pH, and the co-existence ions and organic substances were investigated. Then, the synergetic effect between ZVI and FeS 2 and the possible OFL removal pathway in the ZVI/FeS 2 system was observed. And finally, the feasibility of reusing ZVI/FeS 2 particles was evaluated by recycling experiments. Results showed that the removal efficiency for nitrate and OFL reached up to 44.09 %–66.78 % and 49.67 %–69.29 %, respectively, at a pH range of 5.0–9.0 when the weight ratio and dosage of ZVI/FeS 2 were 2:1 and 16 g/L respectively, which were both considerably higher than those of the ZVI or FeS 2 system alone. In different co-solutes systems, the OFL and nitrate removal performance of the ZVI/FeS 2 material was differed. In addition, mechanism study revealed that FeS 2 could relieve the pH increase, accelerate the corrosion of ZVI surface, generate more Fe 2+ , and promote the generation of new S species (FeS and S 2 2− ) in the dual system. The possible OFL degradation pathway in the ZVI/FeS 2 system was established on the basis of the identified intermediate products. OFL degradation was successfully achieved through decarboxylation , demethylation, and piperazine epoxidation . And then, the degradation products were further degraded into smaller oxygen-containing compounds. Recycling experiments indicated that the ZVI/FeS 2 particles still showed satisfactory pollutant removal efficiency after five cycles. • The dual ZVI/FeS 2 materials exhibits satisfactory remediation performance for polluted groundwater. • Synergistic effect between ZVI and FeS 2 was revealed. • The mechanisms of OFL and nitrate removal and potential OFL degradation pathways in ZVI/FeS 2 system were proposed. • The presence of co-solutes, and the recyclability of the ZVI/FeS 2 material for removal OFL and nitrate were investigated.