A dual-probe approach for evaluation of gypsum crystallization in response to antiscalant treatment

An experimental system was developed to assess and rank the performance of commercial antiscalants designed to inhibit mineral scale formation on reverse osmosis membrane surfaces. The study focused on calcium sulfate dihydrate (gypsum) precipitation to illustrate an approach to antiscalant ranking based on its ability to retard the observed onset (i.e., induction time) of gypsum crystallization from supersaturated solutions. The experimental method consisted of on-line monitoring solution turbidity rise and calcium ion concentration decline to signal the onset of gypsum crystallization. Significant differences were found among commercial antiscalants with respect to achievable levels of induction time retardation. Moreover, antiscalant effectiveness with respect to dosage also varied significantly among antiscalants. The present approach enables a relatively simple and robust initial screening of candidate antiscalants based on their induction time as a function of the applied dose.

An experimental approach to ranking antiscalant effectiveness in retarding mineral salt crystallization was demonstrated based on the dual use of turbidity and calcium potential measurement. The observed crystallization induction times identified from either calcium potential or turbidity measurements were found to be consistent. The results demonstrate a significant difference in retardation of crystallization induction depending on the type of antiscalant, as well as marked differences in AS effectiveness with The present study was supported in part by the California Department of Water Resources, Metropolitan Water District of Southern California, the California Energy Commission and by an International Desalination Association (IDA) Research Fellowship to Ms. Wen-Yi Shih.