Abstract: An apparatus and a method for an ozone-based treatment of polluted water are disclosed. The apparatus and the method generally comprise three stages. The first stage is an ozone treatment stage wherein the polluted water is treated with ozone gas. The second stage is a gas-liquid separation stage wherein excess non-dissolved gases, from the ozone treatment stage, are removed from the water whereby the water exiting the gas-liquid separation stage is substantially saturated with dissolved gases and substantially free of non-dissolved gases. The last stage is a membrane filtration stage wherein the gas-saturated water generally undergoes micro-filtration or ultra-filtration. Microbubbles formed during this final stage generally prevent the accumulation of particles and pollutants on the surface of the membranes and/or inside the openings or pores thereof; thereby acting as a self-cleaning mechanism for the membrane filter.