Compact exhaust gas treatment system and method of operating the same

Directing exhaust gas around a catalyst may pre-heat the catalyst and may thereby bring the catalyst quickly in its operating temperature range. An exhaust gas treatment system (2) for treating the exhaust gas may comprise a first flow path (38), a second flow path (40), and a control system (4). The first flow path may include a catalyst (41). The second flow path (40) may be arranged in heat exchange relation with respect to the first flow path (38). The control system (4) may be configured to control the flow of exhaust gas through the first flow path (38) or the second flow path (40) in dependency of the catalyst temperature.