Jar Test Dosages
Now that we have made up the stock solutions from the polymers, we need to determine how much we need to add to the jars. The following calculation is the only one needed for determining the dosage:
1 mL of a 1% stock solution added to 1,000 mL of sample adds 10 ppm of product
From this one formula, any dosage can be calculated by adjusting the ratio. The chart below is a summary of typical dosages. To use the chart:
- Locate the sample size in the beaker
- Find the % of the stock solution you are adding
- Note the ppm of product contributed from each mL of stock solution that is added
- With a 1,000 mL sample…
- Using a 1% stock solution…
- Each mL of stock solution added to the 1,000 mL jar adds 10 ppm of product as shown in the table below
Jar Test Mixing Protocol
The purpose of jar testing is to determine which approach yields the desired results and is the most cost effective. To accomplish this, jar testing should be conducted with a protocol that best represents the system dynamics. If, for instance, your plant does not have a static or flash mixer, starting the test at high rpm would provide misleading results. This rule applies to flocculator speed, length of settling time, and floc development.
Variables to consider when designing your jar testing procedure are:
- Mixing energy
- Time for the chemical reaction to occur
- Changing water conditions
- Chemical feed locations—current vs. optimal
- Chemical fed through a static mixer or a flash mixer
- pH adjustments
- Water temperature
The following procedure is only a guideline for jar testing. Modify the jar test procedure to simulate conditions in YOUR plant:
- Obtain sample for testing.
- Fill all one-liter beakers to either 500 or 1,000 mL mark. Test volume is dependent on amount of sample available and volume required for water quality analysis.
- Place beakers on mixer and begin mixing at maximum speed (120 rpm).
- Dose beakers with coagulant at various dosages. (1 – 10% polymer solutions are recommended for testing purposes with coagulants.)
- Mix on high speed (120 rpm) for 1 minute. Typical coagulant mixing is 2 – 5 minutes at
80 – 100% for rapid mixing.
- Reduce stirrer speed to slow mix (20 rpm) for 1-minute minimum. (Mix times can be varied to more closely duplicate actual operating conditions.)
- Dose beakers with flocculant at various dosages. (0.1 – 1.0% polymer solutions are recommended for testing purposes with flocculants.)
- Mix on low speed (20 rpm) for 1 minute. Typical flocculant mixing is 0.5 – 2 minutes at
10 – 20% for low mixing.
- Turn mixer off. Observe beakers for settling. Settling time is dependent on system and rate of contaminant removal (5 – 30 minutes should prove adequate).
- Wipe paddles clean with a paper towel or rag in preparation for the next test.
- Repeat steps 2 – 9 until the desired treatment program has been determined.
- After the predetermined settling time has lapsed, save beakers for appropriate water quality analysis, if required.
On a jar test data sheet, record floc size, settling rate, and supernatant clarity on a scale of 1 to 10. The best is represented by 10. Supernatant clarity is best determined with a turbidity meter, if available.
- Size of floc
- Speed of formation
- Settling or rising rate of floc
- Clarity of supernatant
- Density of resulting sludge
In some cases you may also be interested in the volume of sludge produced and how this volume may vary depending upon the treatment. This can easily be done using graduated jar test beakers after a given period of settling time.
Test Procedure and Work Plan
Because of water quality variations and unknown factors influencing coagulation and flocculation, it is impossible to predict the types and amounts of polymers necessary to achieve the desired result economically. Therefore, trial and error experimentation via the jar test procedure must be carried out, preferably with fresh water samples at the job site.
The important thing is to plan the work to permit reaching a logical, definite conclusion with a minimum of time and effort. In laying out your plan, you will want to ask yourself several questions and then seek answers to these questions from jar test data.
Generally, the questions are as follows. They are listed in logical order and are generally answered in the same order.
- Does the sample require coagulation, remembering that coagulation means charge neutralization?
- What pH is required to currently maximize coagulation?
- Is the plant willing to consider pH adjustment?
- Which product, or family of products, yields the optimum results?
- What is the optimal dosage (generally between 1 – 40 ppm)?
- Does pH have an effect on the organic coagulant? (If not, how does this affect the economics of your proposed program?).
- Can you totally replace inorganic coagulant with organic coagulant? If not, what combination of inorganic and organic coagulant is most economical, remembering that inorganic coagulant can be adding significantly to the amount of solids produced?
- What combination of inorganic and organic coagulant gives the most economical result?
- Remember that an inorganic can act simultaneously as a coagulant and a flocculant. Can a total replacement of inorganic be economically achieved with organic coagulant followed by organic flocculant?
- In many instances good clarification and settling can be attained with an organic coagulant, alone, no flocculant being required.
- Using either your best organic coagulant dosage alone, or your best-combined dosage of inorganic and organic coagulant, can better clarification and settling be attained with the additional use of organic flocculant?
- If it has been determined that an inorganic coagulant will have to be used or recommended at your account, is an ACH, a PAC, or an iron salt product the best choice? Perhaps another inorganic or an inorganic/organic coagulant blend will work as well or better. Perhaps the procurement situation at your account makes a particular inorganic coagulant less expensive than others.
- What is the flocculant of choice?
- What flocculant dosage is required? (Generally between 0.25 and 3.0 ppm).
- When it appears that very little or no inorganic or organic coagulant is necessary, in other words, that very little if any charge neutralization is required, and then it may be possible to achieve clarification with a flocculant alone. Without prior knowledge, it may take a cationic, nonionic, or anionic high molecular weight, low charge density, flocculant to give the desired economic effect.
Again, determine the following in jar tests:
- With each charge variety of flocculant, determine the best result.
- Determine the particular product that gives the best performance.
- Determine the most cost effective dosage.