A Synergistic Approach to Develop Sustainable Scale Inhibitors Combining Amino Acids and Polyphosphates

Abstract

Applying conventional antiscalants, e.g., polyphosphates, may bring about environmental and health concerns, warranting the application of green compounds. This work reports the application of amino acids such as glutamic acid and glycine, individually and in the presence of sodium tripolyphosphate (STPP) and sodium hexametaphosphate (SHMP), as antiscalants. At various dosages, these inhibitors were added to calcium sulfate supersaturated solutions, and the inhibition values were determined at 71 °C for 24 h, according to a standard jar test method. Moreover, in the jar environment, the changes in electrical conductivity and turbidity, and size and bulk volume of the deposit particles were measured and used to unveil the affected stages of scaling and the governing mechanisms. Statistical analyses revealed that some amino acid-containing inhibitors used at commercially acceptable dosages, 2 and 4 ppm, effectively inhibited the scale formation by approximately 90%, comparable to pure polyphosphates (p < 0.05). These mixtures also provided up to 70% reduction in the consumption of pure polyphosphates. Consequently, drawbacks associated with polyphosphates are mitigated, and the risk of biofouling linked to applying green molecules at high dosages is minimized. Furthermore, the amino acids and polyphosphates synergistically inhibited one or multiple stage(s) of scale formation. Notably, ion association in the prenucleation stage, and nucleation were selectively and remarkably prevented in the presence of 2 ppm glycine/STPP and 4 ppm glycine/SHMP, respectively. These findings hold great promise for developing sustainable, safe, and efficient inhibitors for various processes such as membrane-based water purification.