Enhanced removal of fluoroquinolone antibiotics by peroxydisulfate activated with N-doped sludge biochar: Performance, mechanism and toxicity evaluation

N-modified sludge-derived biochar (N-SDBC) was prepared and then used for activation of peroxydisulfate (PDS) to degrade fluoroquinolone antibiotics (FQs). Seven commonly used FQs were degraded by N-SDBC/PDS effectively, with the rate constants from 0.131 min−1 to 0.505 min−1. Scavenging experiments combined with electron paramagnetic resonance (EPR) confirmed that 1O2 was the dominated reactive species, and the radicals SO4•− and •OH played minor roles. In-depth study revealed that the graphite-N and Fe0 on the surface of N-SDBC were the main active sites for PDS activation. The elevated N precursors and calcination temperature enhanced the yields of graphite-N and Fe0. Products analysis indicated enrofloxacin (ENR) degradation by 1O2 with the fragmentation of the piperazine ring, the disconnection of the quinolone ring, decarboxylation, and defluorination. The toxicity assessment by Escherichia coli and ECOSAR showed that the biological toxicity of ENR could be reduced after treating by N-SDBC/PDS. The application in surface water and wastewater samples demonstrates the efficiency of FQs removal by N-SDBC/PDS.