Decomposition of humic acid by ozone: oxidation properties and water-matrix constituents

Wastewater often contains humic acid (HA) and inorganic anions together. We studied the oxidation properties of high concentration HA in an ozone system and effects of different mass concentrations of CO32-, HCO3-, SO42-, Cl-, NO2-and NO3-on the ozonation of HA were investigated. After 30 min, the color number, HA, chemical oxygen demand (COD) and total organic carbon were considerably eliminated, the ozone use decreased significantly and the biodegradability ratio of biochemical oxygen demand (BOD5)/COD increased from an influent 0.23 to 0.52. Also, the UV-visible spectrum and three-dimensional excitation and emission matrix fluorescence spectrum tests demonstrated that the HA was significantly decomposed into small molecular matters. Also, common inorganic anions had significant influences during the ozonation process. For a 30 min reaction, and water samples with mass concentrations of CO32-, HCO3-, Cl-and NO2-of 0.5–3.0, 5.0–20.0, 5.0–20.0 and 0.1–0.8 g L–1, respectively, the removal rates of HA were reduced by 8.36%–16.40%, 2.95%–8.85%, 0.66%–3.28% and 10.16%–16.06% respectively, compared with water samples without these anions, and the apparent kinetic constants kobswere 13.88–9.51, 14.59–11.31 and 16.67–14.20 min–1; for water samples with SO42-and NO3-mass concentrations of 0.5–2.0 and 2.0–8.0 g L–1, the removal rates of HA increased by 2.30%–10.16% and 2.30%–7.54%, and kobswere 17.71–23.85 and 17.9–21.19 min–1. Ozonation could be inhibited by CO32-, HCO3-, Cl-and NO2-, and the depressions increased as the input increased, however, there is some facilitation when SO42-and NO3-exist, and the degradation could be accelerated as theinput increased.