HYBRID OZONATION-MICROFILTRATION SYSTEM FOR THE TREATMENT OF SURFACE WATER

The aim of this work was the investigation of the performance efficiency of a hybrid treatment system integrating two processes, i.e. membrane filtration and ozone oxidation, as a potential method for contaminated surface water quality improvement and mitigation of the membrane fouling during the process. Ozone treatment is a well-known method applied for the effective oxidation and disinfection of water; however, coupling of this process with membrane filtration requires the utilization of ozone resistant membranes. Therefore, a bench scale unit was designed and constructed, where ceramic microfiltration membrane was used in a submerged configuration; ozone-oxygen gas mixture was added to the reactor by gas spargers located at the bottom of the experimental tank producing fine bubbles at various gas flow rates and ozone concentrations. Ozone oxygen gas flow rates ranged from 0.3 L/min to less than 0.05 L/min, while ozone concentrations in the gas mixture varied from 6.6 mg O-3/min to less than 1.1 mg O-3/min. The treatment of simulated surface water was studied in this unit, prepared by the addition of 25 mg/L humic acid and 25 mg/L kaolin in tap water, corresponding to TOC content of 7.5 mg/L, turbidity 25 NTU and pH 7.5, aiming to the identification of optimum performance conditions. Treated water samples were collected and analysed for the determination of the quality of the permeate, including the measurement of turbidity, pH, UV254 absorbance and Total Organic Carbon (TOC) content. Nevertheless, the operation of the membrane modules and the estimation of the membrane fouling rate were evaluated by monitoring the Trans Membrane Pressure (TMP), and by the calculation of the corresponding Fouling Indices. The addition of ozone resulted mainly in mitigation of the membrane fouling; for the single process of microfiltration, the TMP increased 0.86 times of the initial TMP during the 2 hours of membrane operation, while for the hybrid process using ozonation at a gas flow rate of 0.3 L/min and ozone concentration of 6.6 mg O-3/min, the TMP increased only 0.17 times after the same period of membrane operation. The hybrid process of membrane microfiltration ozonation resulted in a substantial reduction of the membrane fouling rate for all the concentrations and flow rates of ozone, while the quality of the permeate varied depending on the ozone concentration used.