Treatment of municipal wastewater reverse osmosis concentrate using UVC-LED/H2O2 with and without coagulation pre-treatment

Abstract

Abstract The potential of a prototype batch reactor using ultraviolet light emitting diodes (UVC-LEDs) which emit at 255 nm in conjunction with H 2 O 2 for the treatment of a highly saline (electrical conductivity ∼22 mS/cm; DOC 32–37.5 mg/L) municipal wastewater reverse osmosis concentrate was investigated. Mineralization of organic content (measured as DOC) was low (22%) due to the low fluence rate (0.14 mW/cm 2 ), however, a large reduction in colour (94%) and A 254 (75%) occurred after delivering a UV fluence of 48 × 10 3 mJ/cm 2 at the original pH of 8.3. Fairly similar results were obtained at pH 7, but the reduction of DOC increased at lower pH with 38% and 36% achieved at pH 4 and 5, respectively. Similar trends were observed for colour and A 254 reduction. These results, in conjunction with excitation–emission matrix spectra, biological dissolved organic carbon (BDOC) assay and apparent molecular size distribution, demonstrated that the prototype system led to the breakdown of the chromophore bonds and thus changes in the molecular structure, and degradation of high molecular weight (MW) compounds to low MW compounds. Coagulation (1.5 and 3 mmol L −1 Al 3+ at pH 5) led to a significant reduction of DOC (34–38%), colour (50–66%) and A 254 (47–54%), and subsequent UVC/H 2 O 2 treatment led to further reduction in these parameters. For a target DOC reduction of 15 mg/L, the EE/O was 15 kWh/m 3 when coagulation was used as pre-treatment to the UVC/H 2 O 2 treatment (UV fluence 36 × 10 3 mJ/cm 2 ) and it reduced to less than half after biological treatment (as BDOC assay). This study demonstrated the potential of UV-LEDs as an alternative UV source for degrading the organic matter in ROC using advanced oxidation.