Biological and Ion Exchange Mining of Reverse Osmosis Concentrate: Enhancing Water and Mineral Extraction from Salinity-Impaired Surface Water

Generation of reverse osmosis concentrate (ROC) is a barrier for reverse osmosis (RO) process application due to challenges managing supersaturated brine. Biological concentrate management (BCM) is a novel utilization of microbes for phosphorus-based antiscalant inactivation contained within ROC, aerobically inducing precipitation. BCM bench-scale reactors treating agricultural drainage impacted ROC inactivated antiscalant by 88%, precipitating 41% and 10% of ROC calcium and sulfate, respectively. Testing indicated ROC precipitated gypsum and calcite, and thermodynamic modeling specified precipitate can be controlled for a pure gypsum recovery at a pH ≤7, producing ∼125 kg of gypsum per 1 million liters of water fed to the RO process. High calcium and sulfate concentrations in agricultural return waters originate as extensively used gypsum soil amendments that can be mined by BCM and resold locally, limiting salt importation and yielding increased crop production. The BCM induced reduction in ROC saturation theoretically increased overall recovery from 85% to 92% when treated with another RO stage. Alternatively, post-BCM mineral mining using cationic ion exchange increased calcium removal and water recovery while providing an opportunity for potassium (K), lithium (Li), magnesium (Mg), and rubidium (Rb) recovery from a volume ∼97% smaller than the original flow being treated, yielding 5.0, 0.026, 142, and 0.001 kg of K, Li, Mg, and Rb per 1 million L of RO influent, respectively.