By Rick Andrew
The most common contaminant reduction claim for activated carbon based filtration systems is chlorine reduction under NSF/ANSI Standard 42. Whether point of entry, faucet-mount or pour-through pitcher filters, almost any filter system that contains activated carbon includes a chlorine reduction claim. It is also the major claim for filtration systems utilizing metallic reduction-oxidation (redox) media.
As common as the claim is, there are many details about it that are not commonly known. How is the test conducted? How much chlorine is in the influent challenge and how much is allowed to be in the effluent? Is a chlorine reduction claim the same as a taste and odor reduction claim? The answer to this last question may surprise many.
These questions, and others, will be addressed in this column, so that hopefully knowledge about the most common claim for activated carbon filter systems will be as widespread as the claim itself.
How does a chlorine reduction test work?
First, we’ll look at testing of plumbed-in filters. Two filter systems are connected to the test stand initially. Prior to testing, the filters are flushed and conditioned according to the manufacturer’s instructions. This is important to ensure that the filters are properly wetted and ready to perform effectively, and it is required by the Standard.
Test water is then introduced into the filters at 60 psig initial dynamic pressure, with the flow rate controlled to the manufacturer’s rated service flow. The requirements for the test water are described in Table 1. Flow to the filters is cycled on and off according to one of two schedules as specified by the manufacturer—either a 50/50 or a 10/90 cycle. The 50/50 cycle includes flow being on for 10 minutes and then off for 10 minutes. The 10/90 cycle means that flow is on for two minutes, then off for 18 minutes.
After 10-unit volumes of water have flowed through the filters, samples are collected. The sample collection is conducted in the middle portion of the on cycle, with enough water collected for a free available chlorine analysis. This analysis must be conducted within one minute of sample collection, because the chlorine is highly reactive and unstable. Influent and effluent samples are collected so percent reduction of chlorine may be evaluated.
Immediate sample analysis offers some advantages in testing. Because the results are available as the samples are collected, decisions regarding the test can easily be made in real time. These decisions may include whether to continue the test beyond the initially expected capacity, terminate the test early or take some other course of action. For some other tests that involve complicated instrumental analysis, sample results take time, making it more difficult to alter the course of the test based on sample results.
The test then continues, with samples being collected based on the manufacturer’s rated capacity (unless the feedback from sample results points to a change in plans). The sampling schedule specified by the Standard is included in Table 2. As indicated by Table 2, the test is complete once 100 percent of the manufacturer’s rated capacity has been reached.
Testing of pour-through batch filter systems
In many respects, pour-through batch filter systems are tested similarly to plumbed-in systems. The test water chemistry is the same. The sample points are identical. Two systems are tested. However, there are obviously differences. Test pressure and cycling do not apply to pour-through batch systems. Instead, they are manually operated exactly as a consumer would operate them. A number of batches consistent with the manufacturer’s instructions is processed each day. Only full batches are processed, and each batch is allowed to fully process prior to filling the next batch. A random amount of time is allowed between batches in order to be consistent with consumer usage.
Samples are collected directly from the filtered water reservoir immediately after a batch has been filtered. As with the testing of plumbed-in filters, free available chlorine analysis must be conducted within one minute of collection.
The pass/fail criteria for chlorine reduction involve significant calculations. The filter systems must reduce free available chlorine throughout the course of the test by at least 50 percent. This means that at each sample point, the effluent samples must contain 50 percent or less of the free available chlorine concentration in the influent. The Standard allows that 10 percent of the effluent samples may exceed this allowance, although no exceedances are allowed in the last effluent samples of the test.
This criterion based on percent reduction has an interesting consequence. Many think of the pass/fail criterion being 1.0 mg/L free available chlorine in the effluent samples. This is correct if the influent is 2.0 mg/L. However, the influent may vary between 1.8 and 2.2 mg/L. If the influent concentration is 1.8 mg/L, effluent concentrations over 0.9 mg/L would exceed the allowable 50 percent of the influent. On the other hand, if the influent concentration is 2.2 mg/L, the effluent concentration could be as high as 1.1 mg/L and still be within the requirement.
Taste and odor reduction
The question was posed—is the taste and odor reduction claim the same thing as chlorine reduction? As I indicated, the answer may surprise you…sometimes.
NSF/ANSI 42 states that the taste and odor reduction claim is based on the reduction of free available chlorine for activated carbon systems only. This means that systems using only metallic redox media may not make a taste and odor reduction claim. And those filter systems that contain both activated carbon and metallic redox media must be specially configured for testing without the metallic redox media to make the taste and odor reduction claim.
Sometimes it’s the commonplace that we need to learn more about
Most of us own cars and we are faced with the task of changing the oil (or getting it changed, as the case may be) every so often. Do we just guess what grade of oil to use or use the grade we used in previous cars we’ve owned? Or, do we actually check the owner’s manual to see which grade is recommended by the manufacturer? We may find that the manufacturer recommends a grade of oil we never would have expected. Sometimes a little bit of extra research or information on commonplace, everyday subjects can reveal enlightening and useful information.
Although many of us are familiar with the chlorine reduction claim under Standard 42, I hope this column has served to enlighten you and provide some new insights and information. If so, maybe it’s time to break out your car’s owner’s manual.
About the author
Rick Andrew has been with NSF International for over six years, working with certification of residential drinking water products. He has been the Technical Manager of the Drinking Water Treatment Units Program for over three years. His previous experience was in the area of analytical and environmental chemistry consulting. Andrew has a bachelor’s degree in chemistry and an MBA from the University of Michigan. He can be reached at 1-800-NSF-MARK or email: [email protected]