Gas treatment system (10, 200, 300) capable of operating alternately in a treatment mode and in a regeneration mode, comprising: - an inlet and an outlet, and a main path connecting the inlet to the outlet and comprising a treatment portion so as to enable the circulation of a main gas stream from the inlet to the outlet, passing via the treatment portion, in the treatment mode; - at least one secondary path having two opposite ends (42, 44) connected to the main path, respectively upstream and downstream of the treatment portion, so that the secondary path and at least the treatment portion of the main path form a recirculation loop enabling closed-loop circulation of a recirculation gas stream in the treatment portion of the main path, in the regeneration mode; - a fan disposed in the recirculation loop and configured at least to propel the recirculation gas stream within the recirculation loop in a predetermined circulation direction, in the regeneration mode; - a first adsorption device disposed in the treatment portion of the main path, downstream of the fan with respect to the predetermined circulation direction, and capable of adsorbing predefined substances potentially present in the main gas stream, in the treatment mode; - an ozone generator disposed in the treatment portion of the main path, downstream of the fan with respect to the predetermined circulation direction, and capable of generating ozone in the regeneration mode; and - a switching device configured to keep the inlet and the outlet open, prevent the circulation of the main gas stream via the secondary path or each secondary path (40, 202, 302), and keep the ozone generator stopped, in the treatment mode, and to keep the inlet and the outlet closed, allow the circulation of the recirculation gas stream in the secondary path or in each secondary path (40, 202, 302), and keep the ozone generator in operation, in the regeneration mode; characterised in that it further comprises a second adsorption device capable of adsorbing the predefined substances, disposed in the treatment portion of the main path, downstream of the fan with respect to the predetermined circulation direction, and such that the first and second adsorption devices (60, 80) are respectively disposed upstream and downstream of the ozone generator with respect to the predetermined direction of circulation. - an inlet and an outlet, and a main path connecting the inlet to the outlet and comprising a treatment portion so as to enable the circulation of a main gas stream from the inlet to the outlet, passing via the treatment portion, in the treatment mode; - at least one secondary path having two opposite ends (42, 44) connected to the main path, respectively upstream and downstream of the treatment portion, so that the secondary path and at least the treatment portion of the main path form a recirculation loop enabling closed-loop circulation of a recirculation gas stream in the treatment portion of the main path, in the regeneration mode; - a fan disposed in the recirculation loop and configured at least to propel the recirculation gas stream within the recirculation loop in a predetermined circulation direction, in the regeneration mode; - a first adsorption device disposed in the treatment portion of the main path, downstream of the fan with respect to the predetermined circulation direction, and capable of adsorbing predefined substances potentially present in the main gas stream, in the treatment mode; - an ozone generator disposed in the treatment portion of the main path, downstream of the fan with respect to the predetermined circulation direction, and capable of generating ozone in the regeneration mode; and - a switching device configured to keep the inlet and the outlet open, prevent the circulation of the main gas stream via the secondary path or each secondary path (40, 202, 302), and keep the ozone generator stopped, in the treatment mode, and to keep the inlet and the outlet closed, allow the circulation of the recirculation gas stream in the secondary path or in each secondary path (40, 202, 302), and keep the ozone generator in operation, in the regeneration mode;