Antiscalants in the Process of Reverse Osmosis: Antiscaling Mechanism and Modern Problems of Application

Despite the available long-term experience in the practical application of antiscalants for preventing the depositions on membranes during the reverse osmosis of sparingly soluble inorganic compounds of generally crystalline nature (scaling, inorganic fouling), the studies on the antiscaling mechanism, the development of express methods for estimating the optimal dose of antiscalants, and the creation of new efficient and environmentally friendly reagents still remain relevant. In this paper, the contemporary scientific studies concerning the mechanism of the action of scaling inhibitors and the topical problems of their practical application in reverse osmosis process are analyzed. The key role of the selective sorption of antiscalants on the surface of the particles of formed sparingly soluble compounds in their inhibiting efficiency at substoichiometric doses is described as exhibited in the change in nucleation and crystal growth kinetics, the morphological and structural transformation of crystals, and the change in the capability of particles for agglomeration and interaction with the surface of membranes. The relevance of the development of new efficient, non-toxic, non-bioaccumulated, and biodegradable antiscalants for avoiding the environmental risks upon the discharge of concentrates into the environment is shown, and the currently most promising types of "green" scaling inhibitors are considered. The results of studying the action of both traditional and "green" antiscalants by modern methods of analysis (scanning electron microscopy, X-ray diffraction, dynamic light scattering, fluorescent tagging) are given to confirm the "threshold effect" and the crystal deformation and dispersion effects in the process of scaling inhibition. The priority problems of fundamental and applied studies for improving the efficiency and environmental friendliness of the application of antiscalants in reverse osmosis processes are specified.