Phosphate Chemical Use for Sequestration, Scale Inhibition, and Corrosion Control

Abstract

Water utilities commonly dose phosphates to potable water to (1) reduce aesthetic problems by sequestration, (2) inhibit calcium carbonate scale formation via threshold inhibition, and (3) reduce corrosion of lead or copper plumbing materials by forming protective pipe scales. Despite widespread use and increasing importance of phosphates, significant gaps in fundamental understanding still exist. This is partly due to the proprietary nature of some phosphate chemicals, causing experimental data and acquired knowledge for public water supplies to be considered trade secrets. Here, we summarize the current state of the science, provide operational guidance, and identify knowledge gaps regarding the use of ortho-and polyphosphates. The goal is to empower water scientists to improve phosphate chemical performance and to avoid unintended adverse consequences.

Simultaneous Use of Polyphosphate for Sequestration and Antiscaling

“…Two proprietary phosphate chemicals (Chemicals A or B) used at these utilities were dosed during the experiments. The structure and length of the polyphosphates are unknown and they slowly revert to orthophosphate with age . Each phosphate chemical was stored at 6 °C, and fresh stock solution was prepared before experimentation to reduce the chance for reversion.…”

“…The structure and length of the polyphosphates are unknown and they slowly revert to orthophosphate with age. 13 Each phosphate chemical was stored at 6 °C, and fresh stock solution was prepared before experimentation to reduce the chance for reversion. Total P was measured using ICP-MS and orthophosphate was measured using HACH DR 3900 Spectrophotometer using Method 8048.…”

“…Fe and Mn sequestration occurs through the formation of strong polyphosphate–metal complexes. These complexes can slow or inhibit each step in the sequence that affects the formation of visible particles, including (1) oxidation of soluble Fe 2+ to Fe 3+ , or soluble Mn 2+ to Mn 4+ ; (2) precipitation of Fe 3+ and Mn 4+ solids; (3) particle growth (coagulation) to a visible size, and (4) hypothesized deagglomeration (i.e., growth reversal or dispersion) of large visible particles to invisible sizes . Sequestration effectiveness is dependent on water quality and type of phosphate. − Factors that are influential include Fe/Mn concentration, pH, hardness, natural organic matter (NOM), disinfectant type and concentration, alkalinity, and water age (i.e., reaction time).…”

Beyond Microbial Inactivation: Unveiling the Potential of Detachment-Promoting Agents in Water Distribution System Biofilm Control

“…However, significant biofilm dispersal by DPAs was observed in previous studies once used in combination with other antibiofilm agents. , The concentrations of DPAs (1–100 mM) in this study are higher than what may be allowable in the WDS, and thus their direct applicability in WDS biofilm dispersal would be challenging. For instance, polyphosphate used for corrosion inhibition, red water control, and scale inhibition in WDS usually does not exceed 1 mg/L as P (32.3 μM). − The concentration of STP needed for biofilm removal (1 to 100 mM or more) is likely much greater than would be possible for routine use in drinking water pipelines. However, the higher concentrations of DPAs could be acceptable for periodic WDS flushing operations and for use in industrial settings.…”

Improved Control of Lead Release from Boosting Orthophosphate and Removing Polyphosphate from a Blended Phosphate Corrosion Inhibitor

“…Polyphosphates are a class of polymeric compounds containing PO 4 structural units that can have linear or cyclic structures. Polyphosphates are effective sequestering agents for certain metals in water, especially calcium, iron, and manganese. , Polyphosphate interactions with those metals can prevent them from further reaction and precipitation, which in the case of iron and manganese could result in complaints of “colored water” from the presence of iron and manganese oxides in the tap water, and in the case of calcium, excessive scaling could occur in LSLs. , The use of blended phosphate as a corrosion inhibitor seeks to benefit from both its corrosion control property (orthophosphate) and its sequestering ability (polyphosphate).…”