Use of simulated evaporation to assessthe 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 potential for scale formation the 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 potential of a given input water to form scale the 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 scaleforming 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 evaporationof input water can be used as a technique to quantitatively assessthe potential for scaleformation in RO desalination systems.The useof 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-formingsolids. The techniquewas demonstratedby simulating the increasein soluteconcentrations, represented by CF values,requiredto form calcite, gypsum, and amorphoussilica scalesat 25°C and 40°C from 23 desalinationinput waterstaken from the literature. The resulting simulated CF values could be usedto quantitatively assess potenthe tial 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 scalewill form owing to the effectsof potentially stablesupersaturated solutions,solutionvelocity, andresidencetime inside RO systems.However, thesimulatedscale-formingpotentialof proposed input waters could be compared with the simulated scale-forming potential and actual scale-formingpropertiesof input waters having documented operationalhistoriesin RO systems. This may provide a technique to estimate the actual performance of proposed input waters during RO desalinationunder a specified set of conditions.If validatedby experimentaldata,the techniquedescribedin this studycould provide a reasonable systematicmethod for assessing and the suitability of proposedinput waters for RO desalination.