Process and facility to treat contaminated process water

Process and facility for treating an aqueous solution containing substantial concentrations of a variety of contaminants, including solids, semi-solids, colloids, complexes, oligomers, polyvalents, organics and monovalents, and which tend to form gels and scale precipitates when their concentration levels are increased during treatment of the aqueous solution, the process comprising the steps of: a) feeding the aqueous solution to an ultrafiltration (UF) plant and recovering therefrom an UF permeate reduced in such suspended solids, semi-solids and colloids; b) feeding the UF permeate obtained from step (a) to a nanofiltration (NF) plant and recovering therefrom an NF permeate reduced in such complexes, oligomers, polyvalents and organics; and feeding the NF permeate obtained from step (b) to a first reverse osmosis (RO) plant and recovering therefrom an RO permeate reduced in such monovalents. The process and facility may be used for treating process water from wet process phosphate acid production.