Serial ozone/peroxide/low pressure UV treatment for synergistic and effective organic micropollutant conversion

Serial ozone/peroxide/low pressure UV was tested for an advanced oxidation process (AOP) application on pre-treated surface water in a pilot plant. The pilot plant consisted of an ozone loop reactor followed by a low pressure UV (LP-UV) reactor. Fourteen model compounds and 6 or 10ppm hydrogen peroxide were dosed to the water. Ozone doses varied from 0.5 to 2.0g/m3 and UV doses varied, depending on the UV transmission (73–83%) of the water, between 700 and 950mJ/cm2. The treatment process was evaluated on bromate formation, compound conversion and energy demand. The bromate formation during the O3/H2O2 process was kept lower than 0.5μg/L by using a peroxide dose of 6ppm and an ozone dose of 1.5mg/L. With a 1.5mg/L ozone dose and 6ppm of peroxide, 8 out of 14 compounds were converted by more than 90% with an energy consumption of 0.027kWh/m3. During the subsequent UV/H2O2, the EEO for atrazine was 0.52kWh/m3; together with the O3/H2O2, the EEO for serial AOP was 0.55kWh/m3, which was 0.73kWh/m3 for UV/H2O2 only. During O3/H2O2 treatment, the DOC decreased with 0.2mg/L and the UV-T254 increased with almost 5%, illustrating the synergistic effect of serial AOP. When 3 UV reactors in series were used, with each reactor dosing 1/3 of the total dose, the total conversion increased 5–15%.