A membrane filtration process includes pretreating an influent solution to remove suspended solids, to produce a pretreated solution. pH of the pretreated solution is adjusted to at least 8.3 or lower by injecting CO2 into the pretreated solution, to produce a conditioned solution. Injecting CO2 also serves to supplement bicarbonate in the conditioned solution. The conditioned solution is flowed through a membrane filtration unit, to produce a permeate solution and a retentate solution. The membrane filtration unit comprises reverse osmosis membranes or nanofiltration membranes, or both. The retentate solution is then treated to cause precipitation, to produce a supernatant solution and a reject solution. At least a portion of the supernatant solution is recirculated by combining it with the influent solution prior to the step of pretreating.