Light-emitting diodes as an emerging UV source for UV/chlorine oxidation: Carbamazepine degradation and toxicity changes

Carbamazepine (CBZ) is a ubiquitous micropollutant in wastewater and reclaimed water. In this study, we evaluated CBZ degradation by light-emitting diode (LED)-driven UV/chlorine oxidation. Under LED irradiation of 280   nm (LED280) and 310   nm (LED310), UV/chlorine could efficiently degrade CBZ. Compared with LED UV/H 2 O 2 treatment, LED UV/chlorine oxidation achieved a CBZ degradation rate that was one order of magnitude higher. The CBZ degradation followed pseudo-first-order kinetics, and the rate constants ( k obs,CBZ ) for LED280 UV/chlorine and LED310 UV/chlorine increased from 0.072 to 0.91   min −1 and 0.044 to 0.65   min −1 , respectively, when chlorine dosage increased from 0.07 to 0.14   mM. Under neutral conditions, the generated OH and Cl accounted for over 80% of the CBZ degraded by LED UV/chlorine. The maximum k obs,CBZ for LED UV/chlorine was observed at pH 8.5; k obs,CBZ decreased when solution pH increased to 9.5 or decreased to 5.5. This is because the main UV-absorbing chlorine species in the LED280 and LED310 systems is OCl − , which is different from those in low-pressure mercury lamp/chlorine systems. The acute toxicity for CBZ solution treated by LED UV/chlorine increased at lower fluence (<752   mJ/cm 2 ) and decreased at higher fluence (>1233   mJ/cm 2 ). However, the cytotoxicity to Chinese hamster ovary cells and adsorbable organic halide content of CBZ solution both increased after chlorination and LED UV/chlorine. The lowest electrical cost for the degradation of CBZ by LED UV/chlorine occurred under neutral conditions with a chlorine dosage of 0.4–0.7   mM (28.4–49.7   mg/L).