Abstract: In a nanofiltration system for removing sulfate impurity from an aqueous brine stream and for recovering the brine, introducing a dilution stream upstream of the feed stream inlet of a nanofiltration module in the system dilutes the feed stream. This increases the amount of brine salt and water obtained in the permeate stream without substantially diluting the concentration of sulfate in the pass stream and hence results in enhanced recovery of brine while efficiently removing sulfate impurity. The system and process is especially suitable for recovering brine and removing sulfate impurity from a brine stream in a brine electrolysis plant. In a conventional system, the heat exchanger typically used to cool the feed stream can be omitted if the dilution stream is provided at a temperature suitably lower than that of the feed stream.