Abstract: A process for purification of waste water from dairy processing, which may include providing waste water from the dairy-processing industry that includes lactic acid and urea; adjusting the waste water to an alkaline pH value, while precipitating the lactic acid as a lactate; subjecting the waste water to a first reverse osmosis step, obtaining a lactate-containing first retentate and a lactate-free first permeate; adjusting the first permeate such obtained to an acid pH value; cooling the permeate that has been adjusted to an acid pH to a temperature within the range of 2 to 10° C.; subjecting the cooled first permeate to a second reverse osmosis step, obtaining a urea-containing second retentate and a second permeate that is practically completely free from organic loading; and, optionally, recycling the second permeate, reintroducing it into a dairy-processing procedure.