Abstract: A system for treating a fluid used for cleaning exhaust gas from pollutants including particulate matter comprises a circulation tank for accommodating the fluid, the circulation tank comprising an outlet for bleeding off part of the fluid. A first device is provided for adding a first chemical to the part of the fluid, wherein the first chemical comprises a coagulant. A separation device receives a mixture comprising the part of the fluid and the first chemical, and separates the mixture into a first fraction and a second fraction, which first fraction contains more particulate matter than the second fraction. A flocculation arrangement comprising a first flocculator device is arranged between the separation device and the first device to retain the part of the fluid and the first chemical to promote agglomeration of particulate matter comprised in the part of the fluid before the mixture is received by the separation device.