The performance of UV/TiO2 (100 mg/L TiO2) process for Orange II degrdation was emphatically compared at pH 2.3, 6.9 and 11.5 by means of UV-Visible spectra, ionic chromatography, TOC, and HPLC analyses. The results revealed that the reaction intermediates were produced in different contents with the increasing reaction time due to the different pH conditions. The dye was oxidized more completely at pH 2.3 while the highest color removal percentage was achieved at pH 11.5. It was proved that active electrons, which is photo-generated along with positive holes on TiO2, not only contribute to the discoloration and mineralization of the dye due to the producing of oxidative species such as O2•- and •OOH, but also contribute to the discoloration of Orange II as reductive species. The most possible mechanism was put forward to explain the key roles of active electrons in dye degradation by UV/TiO2 process at pH 2.3 and 11.5.
The experiments of ultrafiltration of Taihu Lake water with sand filter and water- dropping aeration biological contact oxidation combinations were evaluated. The experiment results showed that under the conditions of the average water temperature was 19.8°C and the HRT of the biological contact oxidation was 1.5h, the removal rates of turbidity, ammonia nitrogen, CODMn and algae by technological purification process were 99.1%, 85.2%, 53.6% and 98.7% respectively. As a comparison, the removal rates of turbidity, ammonia nitrogen, CODMn, algae, UV254 by routine purification process respectively were 96.6%, 16.3%, 35.8% and 95.5% separately in Wuxi Chongshan waterworks at the same water temperature. Under the conditions of approximately equivalent in investment and running expenditure by technological and economical analyses, the efficiency of technological purification process was higher than that of routine purification process.
The feasibility of saving energy for A2/O processes was studied in a wastewater treament plant located in beijing by means of field investigation and lab-scale experiment. The results indicate that there are two operable ways to save energy in A2/O processes. One is to control the DO strictly within 2~3 mg/L in aeration tank and to aviod over-aeration,the other is to shift the forepart of the aerated tank into anoxic tank,by which 17.1% of aration could be reduced and about 13.6% of TN removal rate could be increased.
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