Impact of seawater reverse osmosis (SWRO) product remineralization on the corrosion rate of water distribution pipeline materials

Abstract

Remineralization of desalinated water as part of the post-treatment has attracted great attention lately because of the need for high quality water and for pipeline protection. This study was conducted to examine the effect of various remineralization options on the stabilities of pipeline materials (ductile iron, cast iron and cement lined ductile iron) under tropical conditions. Red dust was found deposited at the reactor bottom in which the iron coupons were suspended. For treatments with Ca2+ or CO32− additions, white CaCO3 sediment was observed. Remineralization of SWRO water with Ca2+ and alkalinity resulted in less corrosion than the other treatments. The lowest corrosion rate occurred with cement lined ductile iron (2.69–6.02mpy) and the highest with cast iron (5.44–8.38mpy) in all post-treatments. As results of cement dissolution in the water with cement lined ductile iron, the total alkalinity and total hardness increased from 0–100 to 55–250mg/L as CaCO3 and the calcium carbonate precipitation potential (CCPP) was raised from −10.5–4.6 to 38–427. Other water quality parameters such as pH, total dissolved solids, conductivity and Ca2+ concentration also increased significantly. XRD analysis indicated that corrosion products included FeO(OH), Fe(OH)3, FeO and other iron compounds. Calcium compounds were also detected in the water with Ca2+ ions.