Phosphate Inhibitors and Red Water in Stagnant Iron Pipes

Abstract

This four-year study evaluated the effect of phosphate inhibitors on the corrosion of iron pipes under extended stagnant water conditions. Study parameters included pH and alkalinity, age of the pipe, water stagnation time, and inhibitor type. For iron release, addition of phosphate inhibitors had no statistically significant effect (at 95% confidence) in two-thirds of the experiments. In the remaining experiments, addition of orthophosphate or zinc orthophosphate always increased iron concentration. Polyphosphate addition decreased iron release at only one water quality and increased it at other conditions. For weight loss, polyphosphate inhibitor dosing did not decrease the extent of scale buildup or overall weight loss. Orthophosphate dosing reduced overall weight loss at only one water quality condition; at all other conditions, the addition of orthophosphate had a detrimental effect.

Distribution system water age can create premise plumbing corrosion hotspots

“…Orthophosphate can decrease copper and lead levels (Holm and Schock 1991;Dodrill and Edwards 1995;Schock et al 1996;Cantor et al 2000), but in some cases, the phosphate inhibitor can be consumed by prolonged contact with unlined iron pipe (McNeill and Edwards 2002;. Polyphosphate inhibitors, which tend to increase lead and copper solubility, can hydrolyze and revert to orthophosphate with higher water age (Goldberg 1995;Edwards et al 2001;U.S.…”

Control of corrosive water in advanced water treatment plant by manipulating calcium carbonate precipitation potential

“…1 Alkalinity mg/L as CaCO 3 Raw water; before pre-ozonation process Alk.2 BAC effluent; before 2nd control tank Alk. 3 Controlled water; after 2nd control tank Turb. 1 Turbidity NTU Settling tank effluent; before sand-filtration process Turb.…”

“…The corrosiveness of the tap water depends on chemical factors, such as pH, alkalinity, buffer intensity, dissolved oxygen and total dissolved solids (TDS), and physical properties, such as temperature, flow and velocity, as well as the nature of the pipe material [3][4][5]. In the water treatment process, pH, alkalinity and calcium hardness can be manipulated for the removal of color and corrosion control to prevent internal corrosion of a water distribution system [6,7].…”

“…There are several kinds of corrosion control methods, including corrosion indexes (e.g., Langelier Saturation Index (LSI), the Larson Index (LI), the Ryznar Index (RI), Aggressive Index (AI), Driving Force Index (DFI), Momentary Excess (ME) and Calcium Carbonate Precipitation Potential (CCPP)), corrosion control inhibitors (e.g., orthophosphates, molecularly dehydrated polyphosphates, and bimetallic (zinc-containing) phosphates) and water quality controls [1][2][3][4]8].…”

“…Therefore, corrosive water from water treatment plants can cause problems, such as health hazards, taste, color and higher utility pumping costs, due to the obstruction of water flow by the corrosion products deposited on the pipe surface in water pipelines and plumbing systems [2,12,13]. The most common symptom of corrosion problems within a water system is customer complaints with regard to "red water" and "discolored water" [3,14,15].…”