[Effects of UV radiation on the aggregation performance of small molecular organic acids].

This study systematically investigated the effects of UV radiation on the aggregation of small molecular aliphatic carboxylic acids and phenolic acids by jar test. Experimental results show that solution pH has little effect on the coagulation of small molecular aliphatic carboxylic acids including citric acid, oxalic acid, tartaric acid, and succinic acid. For the solutions pretreated with UV light, the removal rates of the selected aliphatic carboxylic acids in coagulation are higher than that without UV radiation. Further study shows that photochemical reactions occur during UV radiation which decreases the negative charge in aliphatic carboxylic acids, and thereby increases their aggregation properties. Different from aliphatic carboxylic acids, phenol, salicylic acid, and benzoic acid have poor coagulation properties, and UV radiation does not have notable effects on their aggregation in the coagulation process. The coagulation performance of tannic acid is better than the other phenolic acids. At pH = 6, its removal rate is above 90%, which may be contributed to the aliphatic carboxylic acid structure in its molecular. Meanwhile, the large molecular of tannic acid is also easier to be adsorbed by the hydrolysis products of PAC1.

[Study on the stability variation mechanism of humic acid water solution after radiated by the UV light].

Humic acid widely presents in various surface waters. Molecular structure has significant impacts on its physical and chemical properties. To explore the stability variation of humic acid before and after the UV light radiation, spectroscopic and electrochemical analysis were applied in this paper. Structural parameters selected in the experiments include reactive sites, such as phenolic hydroxyl and carboxyl contents, Zeta potential, and colloidal size. It was found that there was little humic acid being removed in the solution without UV radiation pretreatment; while its remove ratio increased notably with radiation time. After 3 h pretreatment, humic acid removal ratio was above 80% in coagulation. Spectroscopy analysis results showed that partial of the groups with fluorescent effects might be shed or rearranged after the radiation; while its aromatic structure was not destroyed. Both the Zeta potential and average colloidal size decreased with the radiation time, which was not conducive to the aggregation of humic acid. However, -OH content decreased slightly after the UV radiation, and new carboxyl and carbonyl groups formed simultaneously. The increasing of the reactive sites and the improvement of the reaction effectiveness were the major reasons leading to humic acid stability decrease in PAC! coagulation.

[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.