Abstract: A method for the supply of a constant-concentration ozonated water, employs a unit for producing ozonated water and a system for using the ozonated water at a place separated therefrom, interposing an ozonated water circulating line between the ozonated water producing unit and the place for using the ozonated water, causing the interior of the circulating line to circulate the ozonated water so that the flow rate may be constantly fixed at the outlet of the ozonated water producing unit, monitoring the ozone concentration of the ozonated water in the neighborhood of the outlet, adjusting the amount of an ozone gas supplied to the ozonated water producing unit based on the results of the monitoring, further monitoring the amount of the ozonated water used at the place for using the ozonated water, and controlling the amount of the ozonated water to be produced based on the results of this monitoring.

Abstract: An apparatus is provided which allows the ozonated water concentration to be retained and avoids being affected by the fluctuation of the amount of the ozonated water to be used.

Abstract: A method is provided forwarding ozonated water efficiently with the loss of ozone lowered. The method for forwarding ozonated water is from an ozonated water producing device to a use point separated from the device. This enables the use point to be supplied with ozonated water having a concentration adjusted as aimed at, by adding a diluting water to a raw material ozonated water in the neighborhood of the ozonated water producing device under a condition inhibiting exposure to an ambient air, adjusting the amount of the diluting water to be added thereby giving the ozonated water a target concentration at the use point, and subsequently guiding the ozonated water through a pipe to the use point.

Abstract: 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.