Recovery optimization of RO concentrate from desert wells

Process design for a 15 mgd (2370 m3/h) reverse osmosis (RO) plant in El Paso, Texas, in the desert area of the US southwest presents many challenges. High recoveries in the pilot plant were limited by silica and barium sulfate scaling. Following testing at 85–90% recovery using a silica polymerization inhibitor and antiscalant, the disposal of a projected 2.1 mgd (332 m3/h) of an unstable supersaturated RO concentrate presents a significant problem. While deepwell and evaporative disposal alternatives are being considered, a pilot program towards a zero liquid discharge process to recover more water and perhaps useful by-products has progressed with very encouraging results. We report here our initial results, attaining a further recovery of 70% of water, and the production from a lime-softening step of sludge with high silica content, and promise as a useful road-base and embankment materials additive.