The invention relates to a method for treating manure sludge comprising the steps of: providing manure sludge; subjecting the manure sludge to separation to provide a first dry fraction and a first liquid fraction; subjecting the first liquid fraction to a centrifugation step to provide a second dry fraction and a second liquid fraction; subjecting the second liquid fraction to one or more sequential reverse osmosis (RO) filtration steps to provide one or more RO retentates and one or more RO permeates, wherein the feed for each subsequent RO filtration step is an RO permeate obtained from theprevious RO filtration step.