Oxidation Effects of Different Levels of Ozone on Ammonia, Nitrite, Nitrate and Dissolved Organic Carbon in Seawater

Abstract

Ozone is applying to the recirculation aquaculture system (RAS) by the purpose to reducing bacteria and parasites. In stead of sterilization effects, it is known that ozone has oxidizing effects on some water quality parameters such as nitrogen compounds and organic carbon. Therefore, oxidizing effects of ozone on the total ammonia nitrogen (TAN), nitrite nitrogen (NO2-N), nitrate nitrogen (NO3-N), and dissolved organic carbon were tested. During the test, ozone effects on the pH, dissolved oxygen (DO) and bromide concentration were also monitored. Ozone treatment concentrations were originally set up to 0.05, 0.1, 0.15, 0.2 and 0.25 ppm, but actual treatment concentrations were maintained at 0.04, 0.11, 0.15, 0.19 and 0.23 ppm. The 5 ppm of TAN was oxidized within 12 hours in all concentrations of ozone treatments with the average oxidizing rate of 0.65±0.28 mg NH4-N/L per hour. The 5 ppm of NO2-N was oxidized within 1.5 hour in all concentration of ozone treatments and the oxidizing rate was 4.5 mg NO2-N/L per hour. One out of 5 ppm NO3-N was oxidized by all concentration of ozone treatment after 24 hours. Ozone also oxidizes dissolved organics carbon and maintains the concentration about 2.9±0.77 ppm from the 15 ppm of initial concentration. Average value of pH was increased from 8.1 to 8.6 in all ozone treatments within 20 minutes and stabilized there after. The DO were also increased from 5.9 ppm to 9.4 ppm within 30 minutes in all ozone treatment and stabilized there after. Bromate concentrations were increased sharply within the first 6 hours of ozone treatments at the rate of 7.3±2.4 mg/L per hour in all ozone treatments and the rate was decreased up to 2.5±0.15 mg/L per hour there after. However, bromate concentration was not increased until all TAN was oxidized. Therefore, further studies are needed to find out the relationship between TAN concentration and bromate formation in seawater.