Effectiveness of advanced oxidation processes for the removal of manganese and organic compounds in membrane concentrate

• UV alone cannot remove of organic compounds from membrane concentrate stream.
• UV-ozonation can remove manganese completely at high initial ozone concentration.
• Oxidation with ozone alone was the most suitable method for manganese removal.
• Ozonation can lead to over-oxidation of manganese.

The effectiveness of batch UV, ozone, and UV/ozone induced oxidation processes in treatment of manganese and organics in reverse osmosis concentrate stream is evaluated. The most effective advanced oxidation techniques are identified and the optimum operating conditions are determined. Application of UV alone (wavelength of 254 nm, light intensity of 4400 μW/cm2, and lighted length of 2.13 in.) was found to be ineffective for removal of organic compounds while it led to a gradual decrease in manganese concentration. Although UV-ozonation could remove manganese completely at initial ozone concentration of 15.2 ppm, oxidation with ozone alone at initial concentration of 6.2 ppm is found to be the most suitable condition for manganese removal. At low initial ozone concentration of 6.2 ppm, the removal for manganese reached 97.2%. The only limitation of ozonation is that over-oxidation occurs when the initial ozone concentration exceeds 6.2 ppm, and therefore the efficiency of the treatment decreases due to the production of soluble permanganate. It was also found that the highest oxidation efficiency for the organic carbon is 89% which occurs in UV-ozonation treatment at the initial ozone concentration of 15.2 ppm.