Ozonation of dissolved organic matter in biologically treated wastewater effluents

Ozonation was evaluated for control of dissolved organic pollutants in biologically treated wastewater effluents. The non-purgeable dissolved organic carbon (NPDOC) concentration was 7 mg/L in the wastewater effluent, and the aqueous ozone dosage applied in the reactor was between 0.5 - 5 mg/L. Due to the presence of the unsettled activated sludge (similar to8 mg/L of suspended solids), the concentration of the dissolved organic compounds could be increased by more than 120% due to the decomposition of the microorganisms during the ozonation processes. An 80% reduction in NPDOC concentration was obtained in two hours contact time if the water was filtered before ozonation. A rapid removal Of UV254 was observed whether or not the water was filtered before the ozonation. Better oxidation efficiency was obtained when the water samples were adjusted to an acidic condition, and it was observed that the presence of the carbonate/bicarbonate ions inhibited the degradation of the organic compounds. However, the effects from various pH and alkalinity conditions were not pronounced. In addition, ammonia nitrogen was oxidized to nitrate nitrogen during the ozonation processes, causing a large increase in UV absorbance at wavelength lower than 240 nm.