Method for monitoring the degree of fouling of a filter

A method of filtering a fluid, the method comprising the steps of:

• a) filtering a contaminated fluid to remove contaminants, which are deposited on a filter in the form of a filter cake;
• b) subsequently feeding through the filter a substantially non-fouling fluid at:
• I. a varying flux, and measuring the driving force;
• or
• II. a varying driving force, and measuring the flux;
• c) comparing using at least one standard set of data:
• I. the measured values of the driving force with the respective flux;
• or
• II. the measured value of the flux with the respective driving force;
• and
• d) on the basis of the comparison in step c) characterizing a fouling status of the fluid to be filtered or of the filter;
• and
• wherein during successive periods of time the steps a) to d) are repeated, and the values obtained in step d) during successive periods of time are compared with each other in step d) in order to obtain a change in the status characteristic.