Membrane filtration process with high water recovery

A membrane filtration process, comprising:

• pretreating an influent solution to remove suspended solids, to produce a pretreated solution;
• reducing pH of the pretreated solution from above 8.3 to 8.3 or lower by injecting CO2 into the pretreated solution, to produce a conditioned solution containing an increased concentration of bicarbonate relative to the pretreated solution;
• flowing the conditioned solution through a reverse osmosis or nanofiltration membrane filtration unit, to produce a permeate solution and a retentate solution;
• collecting the permeate solution;
• treating the retentate solution to cause precipitation of solids, to produce a supernatant solution and a reject solution, wherein the treating comprises (i) a step to convert bicarbonate to carbonate selected from the group consisting of a) heating the retentate solution, (b) reducing pressure of the retentate solution, and (c) heating, and reducing pressure of, the retentate solution and (ii) adding an alkali to the retentate solution after step (i);
• and
• recirculating at least a portion of the supernatant solution by combining the portion of the supernatant solution with the influent solution prior to the step of pretreating.