Column gas-liquid contacting apparatus and its use thereof

1. Field of the Invention A gas-liquid contacting apparatus of a column system, comprising a column having an inlet for introducing a liquid to be treated and an outlet for a discharged gas in an upper part thereof, and an inlet for introducing a gas and an outlet for a treated liquid after gas-liquid contact in a lower part thereof, and at least two units comprising a packing material or a wetted wall structure, said units being separated by a gas back mixing preventer plate between the upper and lower parts, wherein the liquid introduced and the gas introduced are brought into countercurrent contact while keeping the gas phase as a continuous phase; and a process for producing an ozone liquid, a process for oxidizing an organic substance in a liquid, a process for removing a gas dissolved in a liquid, a process for treating a volatile substance in a liquid, a process for dissolving a gas into a liquid, each using the same.