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Orbit Chlorine and pH Analyzer
Teledyne Isco |
Description Residual chlorine is one of the most sensitive and useful indicator parameters in water distribution system monitoring. All water distribution systems monitor for residual chlorine concentrations as part of their Safe Drinking Water Act (SDWA) requirements, and procedures for monitoring chlorine concentrations are well established and accurate. Chlorine monitoring assures proper residual at all points in the system, helps pace re-chlorination when needed, and quickly and reliably signals any unexpected increase in disinfectant demand. A significant decline or loss of residual chlorine could be an indication of potential threats to the system.
Several key points regarding residual chlorine monitoring for security purposes are provided below:
- Chlorine residuals can be measured using continuous on-line monitors at fixed points in the system, or by taking grab samples at any point in the system and using chlorine test kits or portable sensors to determine chlorine concentrations.
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Correct placement of residual chlorine monitoring points within a system is crucial to early detection of potential threats. For example, while dead ends and low-pressure zones are common trouble spots that can show low residual chlorine concentrations, these zones are generally not of great concern for water security purposes because system hydraulics will limit the circulation of any contaminants present in these areas of the system.
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Monitoring points and monitoring procedures for SDWA compliance vs. system security purposes may be different, and utilities must determine the best use of on-line, fixed monitoring systems vs. portable sensors/test kits to balance their SDWA compliance and security needs.
Attributes and Features A variety of different portable and on-line chlorine monitors are commercially available. These range from sophisticated on-line chlorine monitoring systems to portable electrode sensors to colorimetric test kits. On-line systems can be equipped with control, signal, and alarm systems that notify the operator of low chlorine concentrations, and some may be tied into feedback loops that automatically adjust chlorine concentrations in the system. In contrast, use of portable sensors or colorimetric test kits requires technicians to take a sample and read the results. The technician then initiates required actions based on the results of the test.
RC-24P Chlorine Sensor
Courtesy of Analyticon |
Measurement Method There are several measurement methods currently available to measure chlorine in water samples. These include:
- N,N-diethyl-p-phenylenediamine (DPD) colorimetric method;
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Iodometric method;
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Amperometric electrodes; and
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Polarographic membrane sensors.
The chlorine measurement devices here use either the amperometric, DPD, or polarographic membrane sensor methods. It should be noted that there can be differences in the specific type of analyte, the range, and the accuracy of these different measurement methods. In addition, these different methods have different operations and maintenance requirements. For example, DPD systems require periodic replenishment of buffers, whereas polarographic systems do not. Users may want to consider these requirements when choosing the appropriate sensor for their system. Sensitivity and Detection Limit Both colorimetric and electrode technologies can detect free or total chlorine to hundredths of a milligram per liter. Linearity of response in the range of 0.5 percent with repeatability of 0.05 mg/L can be expected. Operation and Maintenance To operate reliably, the on-line monitoring instruments require regular inspection and frequent maintenance. In many cases, consumables such as compressed gases, reagents, solutions, and calibration standards must be refreshed on a regular basis. Colorimetric monitoring generally requires periodic replenishment of consumable test strips or reagents. Electrode monitors require maintenance, which may include membrane and electrolyte replacement as the cell performance degrades. Power requirements typically are line power with signal output as either milli-volts or milli-amps.
Table 1 provides a list of portable chlorine analyzers. The sensor technology used in these commercial products is readily available for setting up online chlorine measurement in water distribution systems. Table 1: Comparison of Chlorine Measurement Systems | Product | Chlorine Measurement Method | Sensitivity/ Detection Limit | Response Time | Reliability/Ease of Use | | ----- On-Line Monitoring Systems ----- | | CL17 On-line Chlorine Analyzer (HACH) | DPD | 0.035 mg/L | 2.5 min/ cycle | Strong and corrosion-resistant | | AccuChlor2 Residual Chlorine Measurement System (HACH [formerly GLI]) | Amperometric | 0.01 mg/L | 2 min/ cycle | Intermediate; stable and repeatable measurements | | CLF 110/111 Reagent-less Free Chlorine Analyzer (Analyticon) | Polarographic | 0.05 mg/L | 2 min/ cycle for 90% response | Easy to use; method requires no reagents | | Multi-parameter Probe (CENSAR) | Amperometric | 0.01 mg/L | No data | Sits on a robust ceramic chip, designed for durability | | Orbit Chlorine and pH Analyzer (Teledyne Isco) | Polarographic | 0.01 mg/L | 2 min/ cycle | Easy to use | | B20 Recording Chlorine Analyzer (ATI) | Polarographic | 0.01 mg/L | 1 minute | Easy to use | | ----- Portable Monitoring Devices ----- | | VR Water Analysis System (CHEMetrics) | DPD | Better than 1% | 4 seconds | Intermediate | | RC-24P Residual Chlorine Meter (Analyticon) | Polarographic | 0.05 mg/L | 90 seconds | Easy to use; does not require external reagents | | ----- Field Test Kits ----- | | AquaCheck Test Strips (HACH) | DPD | Low (semi-quantitative) | Very fast | Easy to use but semi-quantitative | | Color Disc (HACH) | DPD | 0.1 mg/L | Fast | Easy to use |
Cost Costs for chlorine monitoring systems can vary greatly depending on the level of system sophistication. On-line chlorine analyzers/sensors typically range from $2,700 to $3,100. Chlorine measurement systems that include automatic controls will be more expensive. Portable chlorine measurement systems typically cost around $600. However, multiple-parameter portable chlorine analyzers may cost $8,000 to $10,000 per unit. In comparison, disposable test kits for chlorine analysis costs about $115 for a pack of 250. The color disc for chlorine cost about $40 for a pack of 50. Vendors
Disclaimer: The information provided in this guide does not constitute an endorsement by the Environmental Protection Agency of any non-Federal entity, its products or its services. In addition, EPA does not endorse the vendors and products listed on this site. EPA is publishing lists of vendors on this site in an effort to further public awareness of vendors identified as possible contacts for further information and possible purchase of the different types of security equipment. The Agency has selected the listed vendors on that basis. The list of vendors is not a complete list, and EPA does not endorse the products or services of these vendors. Hach Company / GLI International / Hydrolab
P.O. Box 389
Loveland, Colorado 80539-0389
(800) 227-4224
www.hach.com
| Analyticon
P.O. Box 92, 99 Morris Avenue
Springfield, New Jersey 07081
(973) 379-6771
www.analyticon.com
| Analytical Technology Inc. (ATI)
6 Iron Bridge Drive
Collegeville, Pennsylvania 19426
(800) 959-0299
www.analyticaltechnology.com
| CHEMetrics, Inc.
4295 Catlett Rd.,
Calverton, Virginia 20138
(800) 356-3072
www.chemetrics.com
| Teledyne Isco
4700 Superior St.
Lincoln, Nebraska 68504
(800) 228-4373
www.isco.com
| CENSAR Technologies
US Representative - Water Security & Technology, Inc.
1738 Creekview Drive
Foglesville, Pennsylvania 18051
(610) 285-2738
www.censar.com
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