One way for the reuse of reverse osmosis (RO) concentrates and thus increasing the water recovery is to recycle part of the brine concentrate to the feed, after precipitating the scaling salts such as CaSO4/CaCO3 held in solution by antiscalants. However, antiscalants impart considerable stability to the super-saturated solution. In the present study, desupersaturation of RO CaSO4 concentrate in the presence of antiscalants was studied by addition of coagulant polyaluminum chloride (PACI) and surfactant sodium dodecyl sulfate (SDS). Simulated experiments for testing the changes in antiscalant concentration were also conducted. The results indicated that under certain conditions, the above methods were effective for desupersaturation of RO concentrate. After the removal precipitation reactions, the calculated super-saturation ratio of the test solution deceased to about 1.0, which demonstrated that the test solution reached thermodynamic equilibrium. With respect to the removal of scaling salt, it was found to follow the second order kinetics. The removal of scaling salt was always accompanied by the adsorption precipitation of antiscalants. The ecomonic analyses show the proposed methods were feasible.
- Reverse osmosis