The invention discloses an apparatus and method to uniformly disperse ozone gas bubbles into liquid phase water for the treatment thereof. The apparatus consists of a water inlet section connected with a section with structured packing or monolith having parallel flow channels. A portion of the influent water is withdrawn from the main water stream as a side stream, pressurized by a pump, mixed with ozone-containing gas, and then injected back into the main water flow. The side stream may be divided into multiple streams either before or after mixing with the ozone-containing gas, and then injected into the main flow section upstream of the packed section. In alternate embodiments, the ozone-containing gas can be injected directly through the gas diffusers just upstream of the packed section in order to achieve uniform concentration of gas and liquid in the fluid entering the monolith.