Advanced Treatment Of Secondary Effluent By Ozonation

Advanced treatment of secondary effluent from a wastewater treatment plant by ozonation was discussed in this paper. Operational conditions for disinfection, removal of organic compounds, improvement of aesthetic parameters, removal of endocrine disrupting chemicals, transformation of nitrogen and control of by-product were examined.Specific ozone consumption defined as mg O3/mg DOC0 which is ozone consumption divided by initial DOC is adopted for the evaluation of the treatment performance. Three specific ozone consumptions such as 0.5,0.9 and 2.0 mg O3/mg DOC0 are proposed as important control points of ozonation of secondary effluent in this study. Dissolved ozone was not detected until 0.5 mg O3/mg DOC0 regardless of different original water qualities and different operational conditions. During this period, 95% of 7 kinds of estrogenic endocrine disrupting chemicals was removed at spiked concentrations of 1-6μg/L. 3-4 lg inactivation of fecal coliform was obtained and complete inactivation was achieved at 0.9 mg O3/mg DOC0. A 10-20% removal of CODCr and 70% removal of turbidity, UV400 and UV₂₅₄ were observed at consumed ozone of 2.0 mg O3/mg DOC0. No significant removal of theirs was observed after this period.UV₂₅₄ was proposed as a control parameter because of its easy monitoring. The removal rate of UV₂₅₄ had good relationships with not only ozone consumption but also the removal rate of UV400, turbidity, the accumulation of carboxylic acids and disinfection. The removal rate of UV₂₅₄ of 30%, 40% and 70% corresponded to the ozone consumption of 0.5, 0.9 and 2.0 mg O3/mg DOC0.In order to distinguish the effect of molecule ozone and hydroxyl radical, tert-butanol (t-BuOH) was added as a radical scavenger in an experiment. We concluded that molecule ozone was a main oxidant rather than hydroxyl radical in ozonation of secondary effluent.Ozonation is a promising technology for water reuse. UV₂₅₄ was proposed as a control parameter in ozonation of secondary effluent because of its easy monitoring and good relationships with ozone consumption and other water quality parameters.