Use of simulated evaporation to assess the potential for scale formation during reverse osmosis desalination

The tendency of solutes in input water to precipitate efficiency lowering scale deposits on the membranes of reverse osmosis (RO) desalination systems is an important factor in determining the suitability of input water for desalination. Simulated input water evaporation can be used as a technique to quantitatively assess the potential for scale formation in RO desalination systems. The technique was demonstrated by simulating the increase in solute concentrations required to form calcite, gypsum, and amorphous silica scales at 25°C and 40°C from 23 desalination input waters taken from the literature. Simulation results could be used to quantitatively assess the potential of a given input water to form scale or to compare the potential of a number of input waters to form scale during RO desalination. Simulated evaporation of input waters cannot accurately predict the conditions under which scale will form owing to the effects of potentially stable supersaturated solutions, solution velocity, and residence time inside RO systems. However, the simulated scale-forming potential of proposed input waters could be compared with the simulated scale-forming potentials and actual scale-forming properties of input waters having documented operational histories in RO systems. This may provide a technique to estimate the actual performance and suitability of proposed input waters during RO.

Simulated evaporation of input water can be used as a technique to quantitatively assess the potential for scale formation in RO desalination systems. The use of PHREEQC to simulate input water evaporation allows quantification of changes in solution composition during precipitation of scale-forming solids and allows simulation of the effects of these changes on precipitation of subsequent scale-forming solids. The technique was demonstrated by simulating the increase in solute concentrations, represented by CF values, required to form calcite, gypsum, and amorphous silica scales at 25°C and 40°C from 23 desalination input waters taken from the literature. The resulting simulated CF values could be used to quantitatively assess the potential of a given input water to form scale or to compare the potential of a number of input waters to form scale during RO desalination. Simulated evaporation of input waters cannot accurately predict the conditions under which scale will form owing to the effects of potentially stable supersaturated solutions, solution velocity, and residence time inside RO systems. However, the simulated scale-forming potential of proposed input waters could be compared with the simulated scale-forming potential and actual scale-forming properties of input waters having documented operational histories in RO systems. This may provide a technique to estimate the actual performance of proposed input waters during RO desalination under a specified set of conditions. If validated by experimental data, the technique described in this study could provide a reasonable and systematic method for assessing the suitability of proposed input waters for RO desalination.