The four methods of chlorination: gas, liquid, on-site generation, and granulated or tablet, have characteristics which should be considered when choosing a disinfection method. Suitability should be consistent with all the needs of the system. Although disinfection is the primary consideration; safety, handling, storage, rate of usage, availability of product and costs, are all factors which must be considered. Since no two systems are exactly alike, an objective analysis is necessary to insure the best possible method for any given facility.

• Safety, handling, storage, availability
• Chemical costs
• Equipment costs

By addressing some of the characteristics of the four methods, it will be easier to assess the one that most suits your specific needs.

CHLORINE
CATEGORY	GAS	SODIUM HYPOCHLORITE	CALCIUM HYPOCHLORITE	MIOX ON-SITE GENERATION
Chlorine Content	100%	12.5%	60 - 70%	<1%
Container	150# Cylinder., Ton cont.	Tanks of various capacitys, drums	Std. capacity drums (steel, fiber, plastic)	Owner's day tank
Aging	None (100%)	Degrades with time and conditions	Degrades with time and conditions	None - generated as needed
Relative Cost	Unit cost (base)	3 - 5 time cost of gas	3 - 7 times cost of gas	Equivalent to gas
Reactivity	Oxidizer	Reactive with chemicals, heat, organics, releases Cl2	Reactive with chemicals, moisture, impact, heat, releases Cl2	Minimial - considered non-hazardous by EPA
Effect on pH	Lowers	Raises	Raises	None
Container Disposal	No	Yes (consider local codes & restrictions)	Yes (consider local codes & restrictions)	Empty salt bags to trash
Added Chemicals	No	Yes (sodium)	Yes (calcium)	Yes (ozone, chlorine dioxide)
Increases Volumes	No	Yes	Minimal	Minimal
Safety	Partial Cylinder - No change	Partial container - Cl2 release	Partial container - Cl2 release	Safest of all methods

The preceeding chart was developed as a guideline to help you determine the most efficient, cost effective means of chlorination for your particular treatment system.

AVAILABLE CHLORINE

• Chlorine gas contains100% available chlorine.
• Calcium hypochlorite (dry granular) contains 60-70% available chlorine.
• Sodium hypochlorite (liquid) contains 12.5% available chlorine (average)
• On site generation (MIOX) solution contains <1% hypochlorus acid.

Based on the chlorine content, it is necessary to feed different amounts of each to achieve the same disinfection level.

The best way to understand the impact of savings to be realized is to equate the costs into a monthly figure. First, fill in the line representing your method of chlorination. Calculate the amount of chemical you use each month and apply it to the following chart. (Since prices vary by geographic location, contact your local supplier for prices of the other three methods.)

 

The selection of a gas chlorinator is dependent upon the flow rate of water to be treated, in Gallons Per Minute (GPM); and the chlorine demand of the water, in Parts Per Million (PPM). The feed rate of the chlorinator is expressed in Pounds Per Day (PPD).

Chlorine demand is the tendency of the water you are treating to consume the chlorine that you mix into the water. Chlorine demand in your water is effected by many different things. Some of them may be: algae, bacteria, iron, manganese, hydrogen sulfide, water temperature, and agitation, or aeration, of the water. While it is possible to test for chlorine demand, experience has shown the following values to be very reliable for estimating chlorine demand:

• Well Water - 1 to 2 PPM
• Surface water - 4 to 5 PPM
• Waste water - 8 to 10 PPM

Chlorine Gas Feeder Sizing
	Process flow rate (GPM) X				Dosage (PPM) X 1440 minutes/day X 8.32 #/gallon			=		ChlorineFeed Rate (PPD)
1,000,000 PPM Concentration
This formula will calculate the PPD feed rate for chlorine gas based on the GPM flow rate and the PPM dosage.

CHLORINE GAS

Chlorine gas is supplied in steel cylinders, as a compressed gas in a liquid state. The pressure in the cylinder is dependent upon the temperature of the cylinder. Cylinder pressures will range from 80 PSI at 32�F to 200 PSI at 122�F. As a safety feature, the cylinders are fitted with fusible plugs that will melt at about 165�F. This is done to prevent the cylinder from exploding if it is in a fire situation.

For smaller water systems, chlorine gas is typically supplied in "150 pound cylinders," while larger systems will use "ton ( 2000 pound ) containers". The weight refers to the weight of chlorine that is being supplied, not the weight of the full cylinder. Full 150 pound cylinders will weigh from 235 ponds to 290 pounds. Full ton containers will weigh from 3,300 pounds to 3,650 pounds.

Chlorine gas is sold "by the pound". In addition to the price of the chlorine, a deposit will be charged for each cylinder. A typical deposit for a 150# cylinder is $200.00, while a typical ton container deposit is $1,500.00. The deposit on the 150# cylinder allows use for 180 days (six months), and the ton container deposit allows use for 30 - 90 days (depending on the supplier). If the cylinder is not returned within the designated time, a penalty will be assessed for each day over the allowed time.

HYDRAULIC REQUIREMENTS

To allow proper selection of a chlorinator injector, you need to know the specific "hydraulic conditions" at the site you want to chlorinate. This means that you need to know the pressure where the chlorine solution will be applied. Additionally, you will need to know the maximum capacity of the chlorinator, typically about twice the calculated feed rate.

If you are injecting the chlorine solution into a closed pipe, you need to know the pressure in the pipe. If you are injecting the chlorine solution into an open channel, or tank, you need to know how many feet of water will be above the point where the solution is injected.

With the above information, it is possible to select the proper nozzle for use in the injector. If the correct hydraulic information is not provided, the injector may not create enough vacuum to feed the gas into the water.

Most water well applications will use water from the well discharge to operate the chlorinator. In this application, you will need a booster pump to raise the pressure of the injector inlet water, so the injector will create a vacuum. Based on the information that you provide, Chemical Feeding Technologies, Inc. can recommend a correctly sized booster pump.

Copyright March 1992, Chemical Feeding Technologies, Inc. Revised 04/19/99 Brochure 910

 

METERING PUMP SIZING

The selection of a chlorine solution metering pump is dependent upon the flow rate of the water to be treated, in gallons per minute (GPM); the chlorine demand of the water, in parts per million (PPM); and the concentration of the chlorine (Cl2) solution, in percent (%). The feed rate of the metering pump is expressed in gallons per hour (GPH).

Chlorine demand is the tendency of the water you are treating to consume the chlorine that you inject into the water. Chlorine demand in your water is affected by many different things. Some of them may be: algae, bacteria, iron, manganese, hydrogen sulfide, water temperature, and agitation or aeration of the water. While it is possible to test for chlorine demand, experience has shown the following values to be very reliable for estimating chlorine demand:

• Well Water - 1 to 2 PPM
• Surface Water - 4 to 5 PPM
• Wastewater - 8 to 10 PPM
  

The formula to calculate hypochlorite feed rate is

 

Flow Rate (GPM) X Demand (PPM) X 0.006 = Cl2 Feed Rate (GPH)

Using a 2% Solution:

Flow Rate (GPM) X Demand (PPM) X 0.003 = Cl2 Feed Rate (GPH)

Once the feed rate of the metering pump is determined, then a metering pump with the proper capacity can be selected. It is good practice to try to select a metering pump that has about twice the calculated feed rate capacity. By doing this you can make significant changes in feed rates, if your flow rates or chlorine demand change, without having to buy a new metering pump.

50 GPM x 2 PPM x 0.006 = 0.6 GPH of 1% hypochlorite solution

This application could be handled very well with a metering pump rated at 1 GPH capacity. If the chlorine demand should climb to 5 PPM, then the required feed rate would climb to 1.5 GPH, which is more than the rated capacity of the metering pump. In this situation the concentration of the hypochlorite solution can be increased to 2%. This will result in a new calculated feed rate of 0.75 GPH, which is still within the rated capacity of the metering pump. By sizing your pump based on a 1% solution, you can effectively double its capacity by changing to a 2% solution. Or, you can cut the capacity in half by going to a 0.5% solution.

System Backpressure:

In addition to determining the metering pump feed rate, in GPH, you also need to know the system "backpressure." The backpressure. is the pressure at the point the metering pump will be injecting the chlorine solution. All metering pumps are rated to provide some maximum GPH at a maximum PSI backpressure. If you exceed the backpressure. rating of the pump it will either not pump as much as it is rated for, or it may not pump at all.

Calcium Carbonate:

If you are using hypochlorite for chlorination, and you have hard water, you will notice calcium carbonate buildup. If you use hard water to make your hypochlorite solution you will notice a white precipitate in the chlorine solution tank. If you are injecting hypochlorite into hard water you will find calcium carbonate accumulating on the injection diffuser, where it injects into the main line. This precipitation of calcium carbonate is caused by the high pH of the hypochlorite solution.

SYSTEM ACCESSORIES

To make a complete chlorination system, you may need to add the following accessories to the metering pump that you select:
Chlorine Solution Tank:

Typically this is a 50 gallon polyethylene tank with a molded cover. The molded cover allows mounting of the metering pump and a mechanical mixer and also has openings for adding water and hypochlorite. Other sizes and materials are available on special request.
Mechanical Mixer:

When you are using calcium hypochlorite to make your chlorine solution, you need to have a mechanical mixer to provide agitation to dissolve the powder. For the typical 50 gallon solution tank this is done with a 1/20th H.P. 1750 RPM mechanical mixer. The mixer has a stainless steel impeller and shaft with a special epoxy coating to protect the stainless steel from the chlorine solution.
Chlorine Residual Test Kit:

Once you have your system installed and running, you need to take periodic chlorine residual tests to confirm that the pump is properly adjusting and also operating properly. A DPD chlorine residual test kit is the accepted test method for this procedure.

Follow this hyperlink to see a typical installation of a liquid system.

CHLORINE SOLUTIONS

There are two sources of chlorine solution available, sodium hypochlorite (bleach) and calcium hypochlorite (powdered chlorine).

You can purchase bleach at the corner market, with a typical concentration of 5%. You can purchase powdered chlorine at stores that sell pool supplies, with a typical concentration of 65%. You can also purchase both bleach and powdered chlorine from chemical suppliers in bulk. The bulk bleach is generally sold at 10 - 12% concentration, which is very unstable.

Chlorine solution concentrations greater than 5% have a tendency to be unstable. When this happens the concentration of the chlorine solution will decline over time. If the strength of your chlorine solution changes, then you will need to keep adjusting the metering pump feed rate to maintain a constant residual.

Mixing 1% Sodium Hypochlorite Chlorine Solution:

• Using 5% sodium hypochlorite (household bleach), mix 1 gallon of bleach with 4 gallons of water to make 5 gallons of 1% solution.

• Using 10% sodium hypochlorite (commercial bleach), mix 1 gallon of bleach with 9 gallons of water to make 10 gallons of 1% solution.

Mixing 1% Calcium Hypochlorite Chlorine Solution:

• Mix 1 pound of 65% calcium hypochlorite with 7.75 gallons of water.

OR

• Gallons of solution x 0.128 = Pounds of calcium hypochlorite

Copyright July 1990, Chemical Feeding Technologies, Inc. Revised 04/19/99 Brochure 450

 

Content 4

There are 3 primary types of chlorine residual:

• Free Residual - Strong disinfecting power, relatively unstable
• Combined Residual - Weak disinfecting power, relatively stable
• Total Residual - Free Residual + Combined Residual

Typically, well water will only create a free residual. Surface water may have free and/or some combined residuals. Wastewater will, typically, have combined and free residuals, depending on the treatment process.

The most common field test method for determining chlorine residual concentration is the DPD test. This is a colorimetric test that relies on comparison of a developed color in a water sample against a color standard.

Color standards that are made of plastic, liquid filled glass, or dye colored glass will fade with time. If the standard fades, then your test will not be valid. Only glass standards made with rare earth elements will not fade with time. Plastic color standards should be replaced every 6 -12 months, even if kept out of the light. Using a faded color standard will cause you to under-chlorinate and expose you to the liability of under-chlorination. The current technology offers a digital tester, also using the DPD test.

There are three common DPD reagents:

• DPD #1 is for free residual testing
• DPD #3 is for combined residual testing
• DPD #4 is for total residual testing (DPD #1 + DPD #3 = DPD #4)

There are four forms of DPD reagents available on the market:

• DPD Tablets, plastic/foil wrapped:
  The DPD tablets have a 3 year shelf life guarantee. If a DPD tablet is bad it will either change color or crumble, to indicate that it is bad. The plastic/foil wrapper can be opened with your fingers for ease of use.
• DPD Powder Pillows:
  The powder pillow has no shelf life guarantee and it is not possible to know if the powder has gone bad. The plastic pillow will pass moisture which destroys the DPD powder. The pillow must be cut open with a cutting instrument. The pillows can not be opened with your fingers.
• DPD Liquid, in a dropper bottle:
  The liquid has no shelf life guarantee and it is not possible to know if the liquid has gone bad. Also, the size of the drops can vary and affect the accuracy of the test.
• DPD Powder Pop Dispenser:
  The powder pop dispenser delivers one dose of reagent directly into the tester. It contains 500 doses. The dispenser should be used completely within one year. It is not possible to know if the powder has gone bad.

If the reagent that you are using for your chlorine residual test is no good, then your chlorine residual test is no good. Make sure that you are using fresh reagents, and your color standard is accurate, to ensure that your tests are valid.