Cleaning method of a water-filtration system under operation

A method for cleaning a filtration system under operation, said filtration system comprising:

• a cross-flow filtration membrane having:
• a feed side fed with a feed stream,
• a permeate side wherein a permeate stream is recovered and
• a retentate side wherein a retentate stream is recovered,
• a hydraulic circuit Cp being provided with a valve connecting the permeate side of said cross-flow filtration membrane to the feed side of said cross-flow filtration membrane, said hydraulic circuit Cp allowing recycling of a proportion of the permeate stream to the feed side of said cross-flow filtration membrane,
• said method comprising:
• measuring a difference in pressure between the feed side and the permeate side of the membrane, ΔP membrane, and/or measuring a difference in pressure between the feed side and the retentate side of the membrane, ΔP longitudinal,
• injecting an amount of a chemical product into the filtration system which is under operation directly in the hydraulic circuit Cp when at least one of ΔP membrane and ΔP longitudinal reaches a predetermined value which is 10% higher than ΔP longitudinal initial or ΔP membrane initial,
• setting a proportion of permeate stream collected in the hydraulic circuit Cp that is recycled to the feed side of said cross-flow filtration membrane with the valve to enable recycling of a significant amount of unreacted chemical product passing through said cross-flow filtration membrane, the significant amount of unreacted chemical product meaning that said unreacted chemical product is present in the recycled permeate stream at a concentration of at least 70% of initial concentration of chemical product injected directly into the hydraulic circuit Cp.