Jar Testing

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Jar testing is a method we use to create a proportion. How much of a given chemical is needed to effect the change you want in a water sample? For example, how much of a given concentration of sodium hypochlorite would you have to put into a known volume of water to get a residual chlorine level of 0.5 parts per million? Or perhaps, how much soda ash would you need to put into your water to raise its pH from 6 to 7?

I originally suggested that sizing and selecting a chemical pump would be greatly simplified if some jar tests could be done. Then I realized that many people didn’t know how to do jar testing. Another problem was how to gather the necessary equipment and chemical, or if they were even available in their locale. Since making jar testing easy is to everyone’s advantage, I’ve put together an equipment kit (Table 3), a choice of testers (Table 4 and Table 5), and a way to do equivalent testing with chemicals you can pick up at your local grocery store.

JAR TEST FACTOIDS

  • One level teaspoon equals approximately 5 grams of dry powder, or 5 ml of a water-based solution. Two teaspoons are approximately equivalent to 10 ml.
  • If you count the number of drops from one of your pipets needed to put 1 ml into your 10 ml graduate cylinder, you can verify the number of drops per ml you’re actually dealing with.
  • A 5 % soda ash solution, by weight, is closely equivalent to ½ pound of soda ash dissolved in one gallon of water. You can make up solutions as strong as one pound per gallon, but it will require regular mixing to stay in solution, and you may run the risk of plugging up your pump and plumbing.

 

THE FIVE PERCENT SOLUTION

While my original suggestion regarding jar testing was to size and select a chlorinator, the concept applies equally well when pH adjustment for a water or wastewater sample is required. The same equipment kit is used, changing only the tester and sample chemical. Incidentally, doing several tests (at least three) will establish an average test result more reliable than from a single test. The formulas given in the How to Size a Chlorine Feed Pump section allow for feeding different concentrations of sodium hypochlorite. If your concern is pH adjustment, and it is not practical to test with the actual chemical solution you plan to use, you can use the sample solutions suggested below and then refer to the Relative pH Solution Strength table (Table 2) to determine the Correction Factor multiplier necessary for your application.

For chlorination, it is common to use a 5.25 % bleach solution of sodium hypochlorite. Some customers prefer to use this solution directly, without dilution. Some prefer to dilute this solution with water (preferably softened water), for ease in handling and longer solution life. Others, with greater flow volumes, will want to use commercial strength sodium hypochlorite at a 12.5 % concentration. For jar testing, you can buy a quart of the 5 % bleach at a grocery store. If possible, try to find a bleach with a minimum of additives (phosphates, perfume, etc.) to do the testing with – a generic brand might be best. You can tell by checking the label.

For pH adjustment, you may need to take the pH either up or down, according to your particular application. Domestic water treatment often requires the pH to be raised, most commonly by soda ash (sodium carbonate), since it is comparatively safe to handle. Sometimes a weak solution of sodium hydroxide is used. If so, both the sodium carbonate and sodium hydroxide are typically made up at a 5 % concentration by weight with water. Industrial applications can call for a 25 % or 50 % solution of sodium hydroxide. For our purposes, however, we can test with sodium bicarbonate, or baking soda, and get a relative measure of the amount of caustic solution needed to raise the pH as much as necessary. To do that, you can prepare a 5 % solution by weight in water of the baking soda. By the way, go out and buy a new box to work with – pulling an old one out of the refrigerator may give you marginal results.

When the sample water’s pH needs to be lowered, there are a number of different acids that can be used. Household applications might call for a relatively weak acetic acid (white vinegar). Industrial jobs could require a strong muriatic or hydrochloric acid, or even sulfuric acid. Your local grocery store will have a quart of white vinegar, which is typically a 5 % solution of acetic acid, and quite adequate for jar testing. You’ll use more for your tests than you would with a strong acid, but the results will get you into the right ballpark as far as pump sizing goes.

NOTE: Any chemical, even those of a household variety, can be dangerous. The most vulnerable part of your body is your eyes. Please wear safety glasses and use care when doing jar testing.

WHAT TO DO NEXT

Unless you already have the necessary equipment and test chemical, purchase the equipment kit and tester (Chlorine or pH) of your choice, and then go to a grocery store to get your test chemical – the smallest amount you can buy will be lots for your jar tests. We find a one liter water sample a convenient size to work with. A concentrated chemical or a bleach solution will generally require using an eyedropper (otherwise known as a pipet). You may prefer using a teaspoon (approximately 5 ml) or 10 ml graduate cylinder for the weaker solutions of baking soda or vinegar. You can overtreat with large additions, test, and then work backwards to the correct jar test result, or if you prefer put in small amounts, mix, and test after each step of the chemical addition. Be sure to draw at least two more water samples for testing to establish an average result.

While a one liter jar test sample is easy to work with, a 5.25 % hypochlorite solution represents 52,500 PPM, which is much too concentrated for us to use. We can, for example, understand just how big ONE MILLION DOLLARS is. Well, one part per million is equally small – literally one in a million. Since we generally want a pump feed rate of only 1 or 2 PPM, it will be necessary to dilute the 5.25 % solution a thousand times to use it for jar testing:

Prepare a 0.005 % solution of the hypochlorite by pouring some of the 5 % bleach into your first 100 ml beaker. Draw some of this solution into your pipet, and count the number of drops it takes to put 1 ml into your 10 ml graduate. Fill the graduate with water to the 10 ml mark and pour this solution into your second 100 ml beaker. Now fill this beaker to the 100 ml level with water and mix with your spoon. Next, use a second clean (uncontaminated) pipet to draw from this beaker, and count the drops needed to put 1 ml into the thoroughly rinsed graduate (a double check). Fill the graduate to the 10 ml level with water, then pour this solution into your third beaker and mix. This is the 0.005 % solution you’ll need for your jar tests. Use the third clean pipet to add this solution into your 1,000 ml water sample, along with your test kit for free chlorine.

When it comes to jar testing, pH adjustment is somewhat simpler than chlorination. You’ll need to collect a one liter water sample for the initial pH testing. Use a pH test strip or your tester to determine your starting point. To raise your pH, you’ll need to prepare a 5 % baking soda solution (baking soda directly from the box is 100 % sodium bicarbonate). Half-fill one of your 100 ml beakers with water, add a level teaspoon of the baking soda, mix, fill the beaker to the 100 ml mark with some more water, and mix again. Depending upon how much you feel you need to bring your pH up, I’d add 5 or 10 ml at a time, mix, and test after each addition until I’d overshot the pH I wanted. Then I’d go back and test more carefully to zero in on the correct addition amount. To lower your pH, pour some of the white vinegar, or 5 % acetic acid, into a 100 ml beaker, and repeat the steps above until you have the pH change you want.

HOW TO INTERPRET YOUR JAR TEST RESULTS

The ratio between the amount of test solution used and the volume of the water sample can be converted to parts per million, which will help us to size a chemical pump. In the case of chlorination, you may have needed only a few drops from the pipet before your free chlorine test kit showed you a residual of 0.5 – 1.0 PPM. You can determine the milliliters of hypochlorite solution used from the formula below:

mL used = test drops/drops per mL

mL used/1,000 mL  =  PPM/1,000,000

PPM  =  mL used   X  1,000,000/1,000

Our jar testing allows us to use readily measured volumes at convenient test levels, while still using weak concentrations of test chemicals we’re able to easily locate. To actually size a pump, it will also be necessary to employ a Conversion Factor (CF) that converts the test chemical results so that they will be comparable to the strength of the chemical you choose to use in your application. For domestic water chlorination, I’d recommend using a 0.5 % hypochlorite solution. You can see from the following table that the CF we’d use in the calculation formula would be 0.01.

CHLORINATION CONVERSION FACTORS
CHLORINE % CF
5.25 0.001
0.5 0.01
0.05 0.1
0.005 1

The calculation formula we use to size a pump is a modified version of the rough sizing formulas given in HOW TO SIZE A CHLORINE FEED PUMP.

GPD  =  GPM  X  60 Minutes/Hour  X  24 Hours/Day  X  PPM  X  1/Cl%  X  CF

 

Example: You anticipate treating a maximum flow of 10 GPM. Your testing showed that your pipet delivered 25 drops per ml, and that it took 5 drops of the 0.005 % jar test solution to reach a residual of 0.5 PPM. You plan to actually chlorinate with a 0.5 % bleach solution. How many gallons of this solution would you need to pump in a 24 hour day?

mL used  =  5/25  =  0.2

PPM  =  0.2   X   1,000,000/1,000  =  200

 GPD  =  10   X   60   X   24   X    200/1,000,000   X    1/0.005    X    0.01  =  5.76

 

As noted previously, you’ll need to at least double this jar test result to select a pump that operates around midrange. In this case you’d select a pump with an output of 12 GPD or more, and enough pressure capability to overcome your system pressure by 20 PSI plus. The example result of 5.76 GPD represents the amount of chlorine that would be needed if virtually every fixture in your house was on all of the time. In reality, a pump is on considerably less than an hour each day, so your actual chlorine consumption will be much less.

If your concern is pH adjustment, the steps used to size a pump are much the same. Do the jar testing according to the previous instructions, and use the formulas above to calculate the PPM of test chemical needed for the pH change you want. If you used only a few drops of a strong chemical for the adjustment, you can do the calculations without adding to the water sample volume.

Caution: If you choose to dilute a strong acid, always put the acid slowly into water, stirring constantly. Putting water into a concentrated acid will result in an explosive reaction.

If, on the other hand, you did the pH adjustment with one of our suggested test chemicals, you may have added enough milliliters of test solution that you’ll need to add that volume to the 1,000 ml of the water sample to get a “treated” water sample volume. If, for example, you used 10 ml of a 5 % baking soda solution, your PPM ratio would be:

10 mL/1,010 mL  =  PPM/1,000,000

 PPM  =  10 X 1,000,000/1,010  =  9,901

These formulas would work if you used 10 ml of 5 % baking soda, or the same amount of 5 % white vinegar, to effect your pH change. In essence, for every 1,000,000 gallons of water to treat, you would need 9,901 gallons of these 5 % solutions to make the same pH change. If you plan to treat your water with a chemical stronger than one of our test solutions, we have created a RELATIVE pH SOLUTION STRENGTH table (TABLE 2) to provide a Conversion Factor (CF) for your pump sizing. Use the same formula given above for sizing a chlorine pump, substituting the 5 % baking soda concentration for the chlorine concentration, and the CF from TABLE 2 for the chlorine CF. For this example, if you choose to actually pump soda ash rather than baking soda, the CF would be 0.50.

GPD  =  10  X  60  X  24  X  9,901/1,000,000  X  1/5  X  0.50  =  14.26

 

Use the pump sizing information above to select a pump for your application.

Jar tests capture a few “frozen” moments in time as far as your ongoing water stream is concerned. The tests give you a starting point from which to select a pump and treatment system. Conditions vary. Things change. Fine tuning adjustments can be made in both pump output and chemical concentration to match the conditions called for by your application. Call or e-mail with questions.