By Marianne R. Metzger
Water treatment dealers who have traditionally served the residential market are getting more involved in treating commercial and industrial water systems. The Water Quality Association (WQA) has recently developed educational resources and a certification program dedicated to this market, as it has seen a need to help dealers appropriately treat these water problems.
A simple mistake in a commercial or industrial application can be costly, especially to a smaller company. Appropriate testing is even more critical to ensure proper size and design of commercial systems.
In addition, there are regulatory requirements and agencies that must be dealt with for commercial or industrial applications. A well thought-out plan with water quality data will be helpful in establishing yourself as a knowledgeable resource for local regulatory agencies.
There are a variety of tests that can be conducted depending upon the application. But this article will focus on testing for pH and alkalinity adjustments, as they are widely used in pre-treatment for water conditioning, corrosion control and for wastewater being disposed of into sewers.
A variety of chemicals are used to treat commercial and industrial water for many reasons, including pH adjustment, disinfection, oxidation for precipitation and coagulation, to name a few. The water in these applications can be a municipal water supply needing further treatment, a groundwater source on the property, water that is being reclaimed from some industrial process or wastewater from some process, which requires treatment before it can be disposed of in a sewer.
If a business has a well on property that is being used for drinking water by its employees, it is considered a non-transient, non-community water supply and is subject to Federal and State regulations under the Safe Drinking Water Act. It is important to remember when designing a chemical feed system for a public water supply you must use chemicals that are NSF 60 approved to ensure safety for potable water supplies.
These chemicals are typically introduced into the water supply via a chemical feed pump. In order to properly size a feed pump, a little testing must be done to determine the correct amount of chemical to fully treat the water.
Jar testing is commonly used to simulate a full-scale water treatment process and is an excellent tool for sizing a chemical feed pump. It is important to keep in mind that water quality will vary depending on the source and how it is influenced by outside factors.
For example, water that is coming from a surface source can vary in quality based upon the amount of rain and potential sources of contamination within the water shed. With the potential of changes in water quality, it is common to oversize a chemical feed in order to make adjustments in treatment when needed.
Many commercial and industrial water treatment processes are dependent on pH level, so adjustment is very common. The pH of the water is often adjusted to help in preventing corrosion in the water distribution system where the pH is lower and can be aggressive in attacking plumbing fixtures and pipes, causing lead, copper or other metals to leach into the water.
In fact, whenever a public water supply fails and is contaminated by lead or copper, a corrosion control study must be done. This study not only includes pH but also takes into account alkalinity, which is directly related to the pH level.
The pH is adjusted using acids to lower the pH or bases in order to raise it. Some of the bases used include sodium bicarbonate, sodium carbonate, potassium carbonate and sodium hydroxide. Acids that can be used include acetic, citric, hydrochloric, nitric, phosphoric and sulfuric acid.
You can easily raise pH using sodium carbonate, more commonly known as soda ash, and lower pH using acetic acid, commonly known as white vinegar. Solution strength will be very important in determining the amount of chemical needed; the stronger the solution, the less you will need to use to adjust pH.
It is important when choosing your chemical feed pump that you take into account the materials of construction and if they are compatible with the chemical you are going to feed. For example, when feeding acids such as phosphoric or sulfuric, the pump you choose should not have stainless steel parts coming into contact with the chemical.
To perform jar testing you can use the above-mentioned common household chemicals, as these are easily obtainable, inexpensive and relatively safe. If you are planning to use a stronger chemical, there are conversion factors that can be used to extrapolate the results.
While working with household chemicals it is still important to protect yourself by wearing protective eyewear and gloves. Below is a list of some common equipment you should have to perform the testing needed.
- (two) 1,000 ml Beakers
- (two) 100 ml Beakers
- (one) Teaspoon sampler spoon
- (two) Transfer pipette
- Protective eyewear
- Latex gloves
- pH meter (probe style is easiest to work with)
- Magnetic stirrer (not necessary but helpful)
It is a good idea to have a complete understanding of the raw water chemistry, chlorides, bicarbonates, hardness and iron. This will help you better understand what is taking place when altering the pH of the water.
This information can be obtained through the Consumer Confidence Report for a public water system. If working for a specific project, ask the system owner or operator for a complete list of water chemistry. Also consider having a laboratory run some samples to get the most recent data.
Since pH can adjust quickly upon exposure to the atmosphere, it is important to use a fresh sample to get the most accurate results in your jar tests. It is easy to work with a sample size of one Liter or 1,000 mL to make the calculations easier.
Fill your 1,000 ml beaker with your water sample and perform this test a couple of times to take into account any natural variation in the water quality. Take a baseline reading of the pH and then keep the pH probe placed in the beaker to readily see the pH as it changes .
To increase pH, add the base using a transfer pipette. You may want to use a magnetic stirrer to make sure you are completely mixing the chemical; otherwise, manually stir the sample while adding your chemical.
Continue to add your chemical until you reach the desired pH level. Once the amount of chemical needed to change the pH to the desired level is determined, some simple calculations can be used to help in determining the size of the chemical feed pump.
In conducting calculations, use baking soda as the base since it is readily available. A simple conversion factor can be used if a stronger chemical is used, such as soda ash or soda hydroxide, commonly referred to as caustic.
In this example, use a five percent solution of baking soda. Mix one teaspoon of baking soda to 100 mL of water. Using a transfer pipette, add the baking soda solution into a 1,000 mL beaker of the sample water, until the desired pH level is reached.
Convert the number of mL of solution into parts per million by using Calculation 1.
Calculate how many gallons per day (gpd) are needed in order to size the selected chemical feed pump (Calculation 2).
Since alkalinity is so closely related to pH, an evaluation is often required whenever a corrosion control study is done. Even if an alkalinity evaluation is not required, it is still highly recommended that some samples be run in order to have a better understanding of water chemistry and potential issues that may arise. It is always easier to run bench evaluations as opposed to modifying a large commercial system.
Alkalinity refers to the ability of the solution to neutralize acids, thus it’s relationship with pH. It’s typically made up of carbonates, bicarbonate and hydroxides, but can also include phosphates and silicates. These compounds act as buffering agents and can help in maintaining a stable pH. Alkalinity and pH can be used to predict the amount of CO2 in the water, which can also contribute to corrosion. If alkalinity is too low, anything added to the water will immediately affect the pH, which can cause scaling or corrosion. If alkalinity is too high, it will cause a gradual upward drift in pH, which can cause scale to form.
Keep in mind the final use of the water, as certain industries have special requirements for alkalinity levels. For example, the optimum alkalinity for growing plants is 30-70 mg/L, but can differ based upon crops being grown.
Alkalinity is also measured in other industries such as microbrews, other beverages, aquariums, ponds and swimming pools. It is important to maintain a moderate alkalinity level of about 300-700 mg/L to help maintain pH and minimize corrosion in boiler applications.
Titration can also be performed to determine alkalinity, using a standard sulfuric acid solution to a specific pH endpoint. In order to measure total alkalinity, add the solution while continually measuring and mixing the pH of the sample water. It may be a good idea to use a magnetic stirrer to ensure a complete mixing of the sample.
Add the sulfuric acid solution until pH reaches an endpoint of 4.9, 4.6, 4.5 or 4.3, depending on the type of sample. The endpoint alkalinity (above 500 mg/L) should be run to a 4.3 pH. For routine monitoring, an endpoint of 4.5 pH should be used.
If the sample if expected to have low alkalinity (below 30 mL/L) use 4.9 as the endpoint; with expected high alkalinity, use an endpoint of 4.3. For general monitoring an endpoint of 4.5 is commonly used.
The amount of sulfuric acid added can be used to estimate the total alkalinity of the sample, depending on the strength of the sulfuric acid being used. There are several simple titration kits using a colorimetric method, which include color endpoint indicators such as bromocresol green-methyl red, which turns a pink color.
Quality assurance and control
In order to ensure the most accurate results, certain steps must be taken to maintain testing equipment. First, when using pipettes to transfer your chemical solution, make sure they are free from any previous chemical residual that could throw off results.
A good way to ensure this doesn’t happen is to use the same pipette for the same chemical every time or use a disposal pipette every time. It is important to choose the right cleaning agent to clean all beakers and other glassware.
You will need one that is effective at cleaning yet does not leave behind a residual. There are several such cleaning agents on the market and can usually be found by asking glassware suppliers.
Maintenance & Storage
When using a meter to measure parameters such as pH, conductivity/TDS or oxidation reduction potential (ORP), it is important to properly maintain and calibrate the instrument to ensure results are highly accurate. Probes designed for pH measurement need to be stored in an appropriate storage solution.
In a pinch, a pH 4 buffer can be used. But this should not be used as a permanent solution as the color in this buffer can build up on the probe, causing off readings.
Make a salt-saturated solution by adding table salt to distilled, deionized (DI) or reverse osmosis (RO) water, but make sure not to use salt that contains iodine. This is a temporary solution only; use the proper storage solution whenever possible as recommended by the manufacturer.
Many meters currently on the market today contain a microprocessor. It is important to not store these types of meters in any extreme heat or cold. They should be treated with the same care given to a laptop.
Calibration allows the user of the meter to ensure the meter is reading accurately. When it comes to calibrating a pH meter, there are three standard buffers that are commonly used.
These buffers are solutions with a known pH value, with the common buffers being four, seven and 10. The pH electrode is extremely sensitive to changes so it should be calibrated on a more regular basis than most other electrodes. It is a good idea to calibrate a pH electrode every time prior to use to ensure the most accurate result.
Begin with the seven buffer, by placing the electrode in the solution and waiting a few moments for the meter to get a reading. The reading should be somewhat close to seven, but may need to be adjusted up or down to the 7.0 the meter is supposed to be reading.
You should then move to a four or 10 buffer and repeat the process, making adjustments when necessary. It is a good idea to use all three buffers. Although some manufacturers claim their meters can be calibrated using two points, using the three-point calibration will yield higher accuracy levels.
When a probe is going bad, the meter will drift further and further from the standard buffers. The pH electrode is replaced on a more frequent basis than other electrodes. Depending on the application it should be replaced once every six months to a year.
If the electrode is not calibrated and cared for properly, it can fail much quicker. A conductivity electrode does not need calibration as frequently as the pH electrode, but should be calibrated on a regular basis (about once a month).
Use a solution that has conductivity close to the anticipated measurement. Don’t use a 30-micron solution to calibrate when you are consistently measuring samples of high conductivity. Never reuse buffers or calibration solutions, always use a fresh solution.
Buffers and calibration solutions will go bad over time. For example, the pH 10 buffer will absorb carbon dioxide from the air and slowly drift down in pH.
Use a solution that has not expired, as the expiration dates will vary anywhere from a few months up to several years, depending upon the manufacturer. If you suspect solutions have gone bad, discard them. It is less costly to purchase these solutions than to purchase new electrodes.
When testing to properly size a commercial treatment system it is important to take more than one sample, as water quality can greatly fluctuate depending on the source. By taking the time to properly test, all elements will ensure the client receives a system that is designed to take into account these natural changes.
- Holmes-Farley, Randy. Reff Alchemy: A Comparison of pH Calibrations, Reef Keeping an Online Magazine, February 2005. http://www.reefkeeping.com/issues/2005-02/rhf/index.php
- Eaton, Andrew F., et al, Standard Methods for Examination of Water and Waste Water, 20th Edition, pages 2-26, 2-27.
- McGown, Wes. Harrison, Joseph E. Water Processing Residential, Commercial, Light Industrial, Third Edition, Water Quality Association, 2000.
- US EPA National Exposure Research Laboratory, EPA Method 150.1, pH Eletrometric Method, Issued 1971 and revised in 1978 and 1982.
- US EPA National Exposure Research Laboratory, EPA Method 310.1, Alkalinity by Titration, Issued 1971 and revised in 1978.
- Furrow Pumps, Inc. Jar Testing Made Easy, http://www.furrowpump.com/Applications/JarTesting/JarTest1.htm
About the author
Marianne R. Metzger resides in Douglassville, PA where she works as a Sales Engineer for Accent Control Systems. The company represents various manufacturers whose equipment represents various manufacturers whose equipment is geared toward the water treatment market, including chemical feed, process control and analytical. Metzger has a Bachelor’s Degree in environmental geology and political science from Case Western Reserve University of Cleveland, OH. She spent more than a decade working for National Testing Laboratories of Cleveland, holding a variety of positions including customer service, technical support and business group manager.