Water quality deterioration of reclaimed water produced by reverse osmosis process in large pilot-scale distribution systems of different pipe materials

Abstract

This work reports the effects of five pipe materials on reverse osmosis (RO)-reclaimed water quality in a large pilot-scale distribution system. These materials includes cast iron (CI), cast iron with cement-mortar lining (CML), stainless steel (SS), PVC, and PE. Long-term running tests for 96 hours are conducted with water quality parameters monitored online and analyzed offline. The results showed that red water appeared in CI pipe due to iron corrosion. The pH and TDS increased during the long-term test. Alkali–silica reaction in CML pipe led to a high increase of pH from 6.3 to 11.4, and TDS from 51 to 230 mg/L. Water quality deterioration was not observed in SS, PVC, and PE pipes. Residual chlorine decay occurred in all the five material pipes with the decay rate order of CI ≫ CML > SS ≈ PVC ≈ PE. Ion concentration variation was also followed during the tests. Fe and Mn ions were detected in CI pipe and Ca, Si, Al, and S were detected in CML pipe. No detectable ion release was found in SS, PVC, and PE pipes. A kinetic model was postulated for the detected ion release with the mechanisms discussed in-depth.