YSI XA00067 Technical Note
Technical Note
YSI Municipal Monitoring • XA00067
How Online Orthophosphate Analyzers Can
Help Control Pipe Corrosion in Drinking Water
Phosphorus (P) is a critical mineral in the water and wastewater
world, occurring mostly as a form of phosphate (PO
phosphorus is designed to be removed before discharging into our
natural waters, reducing eutrophication and the issues that arise with
it. On the contrary, phosphate is a common additive in the water
treatment process for drinking water, usually in the form of phosphoric
acid, orthophosphate, or condensed phosphate. Phosphate products
provide many benefits to the distribution system, such as helping to
improve color and taste and reduce scaling from hard water.
3-
). In wastewater,
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Perhaps the most crucial benefit to dosing phosphate in drinking water
is its ability to prevent corrosion of lead and copper from the piping,
reducing the risk of health concerns. When phosphate is introduced
into a lead or copper pipe, it binds with the metals on the interior
surface of the pipe, creating a coating that inhibits corrosion.
The EPA’s Lead and Copper Rule (LCR) provides the guidelines
for which drinking water plants must reduce the lead and copper
concentrations coming from their customers’ taps. If phosphate is not
dosed correctly, this can cause problems for the water treatment plant
and its customers. Online orthophosphate analyzers, such as YSI’s IQ
SensorNet Alyza PO4, play a significant role in maintaining the the
correct phosphate dosing rate and optimal phosphate residual for
appropriate treatment.
Phosphates are often dosed manually with a calculated mass balance.
Depending on current flow and water composition, this manual dosing
can be adjusted to maintain the desired phosphate residual, which
can be monitored by performing grab samples. Since flow and water
composition can change relatively quickly, manual dosing and grab
samples may prove to be problematic and cause over- or underfeeding
of the chemical.
P: Orthophosphate
A: Phosphate Dosing in Drinking Water
I: YSI Alyza PO4 Orthophosphate Analyzer
The most common issue with overfeeding chemicals is the excess cost.
Chemical additives are costly, and efficient dosing is the best practice.
Other risks associated with overfeeding phosphates are risking
exceeding NSF guidelines for maximum use and increased phosphorus
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runoff into the environment. Underfeeding phosphate chemicals is
also problematic, in which you can reduce the effectiveness of the
chemical. Unusual color or taste, scaling, and lead or copper corrosion
are all issues that may occur. Continuously monitoring orthophosphate
with the Alyza PO4 analyzer can help maintain the recommended
phosphate residual of 1 ppm PO4 and reduce these risks.
The YSI Alyza PO4 is an extremely effective tool for providing
continuous phosphate residual readings. With measurements
occurring as frequently as every 5 minutes, drinking water operators
can get the up-to-date information they need to make informed
decisions on phosphate dosing.
TECHNICAL NOTE XA00067
The Alyza PO4 also offers lower reagent consumption and reduced
maintenance with its newly designed Multi-Port Valve and “IVstyle” reagent bag features. Even further, this continuous online
measurement can be used to control phosphate dosing directly using
process control. By using a simple feedback control loop, a signal
from the Alyza PO4 can be used to automatically increase or decrease
phosphate dosing based upon the analyzer’s measurement and the
desired phosphate residual set point. Automated control of phosphate
dosing provides several benefits.
First, it ensures that the desired phosphate residual is maintained to
provide proper treatment to the water, reducing the risks associated
with overfeeding and underfeeding. Second, operators are alerted
when the phosphate residual is out of range, and the operator can then
investigate and fix the problem, whether that is a malfunctioning feed
pump or a process issue.
Lastly, operators save the time involved with monitoring and
controlling the phosphate feeding process manually, reducing the
need for performing grab samples and changing the feed rate
themselves. Utilizing the YSI Alyza PO4 analyzer for phosphate
residual monitoring can provide all of these benefits to drinking water
operators, along with high accuracy, reduced maintenance, and the
ease of use that the Alyza PO4 provides.
References:
Cantor, A.F. 2017. “Optimization of Phosphorus-Based Corrosion
Control Chemicals Using a Comprehensive Perspective of Water
Quality.” Water Research Foundation
Turner, R.C. “Utilizing A Phosphate Analyzer to Monitor and Control
Chemical Feed Reduces Operating Costs and Improves Reliability.”
Swan Analytical USA.
Discolored tap water due to pipe corrosion.
Replacing reagent bags in the Alyza PO4 is simple and easy.
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Yellow Springs, OH 45387
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