Effect of ozone-UV pretreatment on coagulation of raw water with high organic matter

Humic acid as a model pollutant, this paper aims to evaluate the effect of ozonation, ultraviolet irradiation and ozone-UV (UltraViolet) pretreatment process on the coagulation performance of raw water with high organics. The results indicated that three kinds of pretreatment had obvious mineralization on soluble humic acid in the raw water, and UV and ozone-UV pretreatment had a strengthening effect on the later coagulation process. With the increase of adding ozone dose and extension of UV irradiation, a decline in both content of TOC and turbidity were observed. Under the ozonation pretreatment process, when the concentration of ozone dose (O₃/C) was 9.0 mg/mg, 47% of humic acid could be removed by pretreatment, the content of TOC and the turbidity of the filtrated water was 3.5 mg/L and 2.6 NTU, respectively. With the UV pretreatment process, after 3 h UV irradiation, 52% of soluble organic matter could be removed by pretreatment, and the content of TOC and the turbidity of the filtrated water were 2.0 mg/L and 1.0 NTU, respectively. Furthermore, the UV/O₃ combined system was better than separate system. The optimum in combined pretreatment process was that the concentration of ozone dose (O₃/C) was 1.0 mg/mg, the time of UV irradiation was 1 h, the TOC of the filtrated water was 2.6 mg/L and the turbidity of that was less than 1.0 NTU. The mineralization effect under various pretreatment processes was achieved by the oxidation of ·OH, and at the same time the construction of humic acid was changed by pre-oxidation. As a result, the stability of the Reunion construction of humic acid was reduced which promoted the removal of the organic matter during the coagulation process.