Comparative Performance of Tetraphosphonate and Diphosphonate as Reverse Osmosis Scale Inhibitors

Abstract

Reverse osmosis (RO) technologies are widely used throughout the world for drinking, industrial and waste water treatment purposes. Proper and economically attractive operation of RO installations should be provided by the correct maintenance of all technical process parameters. One of the significant operational problems is precipitation and deposition of sparingly-soluble salts on the membrane surface, which can be prevented by dosing special chemical additives into the feed solution. The aim of the present work is to reveal the structure/function relationship of phosphonate scale inhibitors, which possess systematic structural similarities and differences. Specifically, two classes of tetraphosphonate (5 additives) and diphosphonate (6 additives) have been tested as calcium carbonate scale inhibitors on the lab membrane unit. It was found that among the family of tetraphosphonates and diphosphonates the inhibitor efficiency increases with elongation –(CH2)– chain, but the longest additives have a sharp drop in inhibition efficiency.