A Rhode Island water treatment facility installed a new process chlorine analyzer using colorimetric measurement technology and is pleased with the results. Since the installation the facility has experienced an improvement in performance and saved time in calibration and maintenance procedures.
Until early last year, the Cumberland Water Treatment Department was using a potentiometric analyzer to monitor chlorine levels with output to a chart recorder. Staff reported that they analyzer was unreliable, wouldnt stay calibrated and the calibration and maintenance procedures were time consuming and complicated.
"The measurements were constantly way off and eventually the operators no longer even looked at the continuously monitored readings," said Herb Costa, plant foreman.
The Cumberland Water Treatment Plant was founded in the early 1950s. It produces 1.5 to 1.75 mgd in the winter and 4-5 mgd in the summer for 7,500 homes and businesses. Operators treat the raw water with sodium hypochlorite both before and after the filtering process. The chlorine level is kept at 1.2 ppm during the summer and 1.0 ppm during the winter, depending on conditions. Operators perform on-site tests with handheld instruments every two hours and manually record the chlorine residual data.
"The manual tests allowed them to keep track of chlorine levels, but with 700 gallons per minute going through the system they definitely needed to have real time data at a glance as well as automatically graphed for analysis and reporting," said Michael Bogolawski, technical services manager at Hanna Instruments.
Hanna Instruments, manufacturer of the PCA 300 analyzer, worked with Cumberland plant officials to solve the problem.
Bogolawski suggested installation of a continuous analyzer that uses colorimetric technology, which requires less maintenance and does not require complex calibration. The PCA 300 is the first in-line chlorine analyzer equipped with an LED light source. The green LEDs maintain a stable emission for the entire life of the instrument. The principle of operation is based on an adaptation of the EPA recommended DPD 330.5 method. The resulting chemical reaction is measured photometrically and converted to chlorine concentration, in mg/L (ppm), which appears on a large display and is graphed on a chart recorder in the operations center.
The unit took two hours to install. The project involved hanging the analyzer in the control cabinet, installing the sampling tubing and connecting it to a water supply line, and connecting the current loop for the chart recorder. The short install time was important as the water line had to be shut down and the installation needed to be completed as quickly as possible to keep the water flowing to Cumberland. As the unit does not have an in-line ion specific probe, the line will not have to be shut down again during maintenance procedures.
"The PCA 300 allows us to keep a continuous indisputable record using our chart recorder," Costa said. "The charts concur almost exactly with our handwritten record."
The accuracy of the new system has allowed staff to lower chemical usage. The colorimetric instrument rarely needs to be calibrated as it zeros each sample before the measured reaction takes place. Costa said maintenance costs have been reduced to approximately $400 from approximately $2,000 per year. The initial cost of the unit also was a consideration, with the colorimetric unit priced from $2,000-$2,200.
