No Perfect Chlorination

While there are many forms of disinfection, by far the predominant one is chlorination. When dealing with chlorination, there are five (5) common alternatives: Gas, Sodium Hypochlorite (Bleach), Calcium Hypochlorite (powder or tablets), Trichloro-s-triazinetrione (commonly called TriChlor) (tablets), and On-Site Generation of bleach and/or mixed oxidants. Each of these methods of chlorination has advantages and disadvantages. Unfortunately, this means that there is no perfect form of chlorination. At Chemical Feeding Technologies, Inc., we handle all of the above methods of chlorination. With 36 years of experience, we are able to explain the advantages and disadvantages of each form of chlorination to allow a customer to decide which method of chlorination is the best for them.

When chlorine is mixed with water, it produces hydrochloric (HCl) and hypochlorous (HOCl) acids. The rate of formation of HCl and HOCl is pH dependent and the HOCl is the stronger disinfectant.

When selecting a chlorination method, a key item to consider is if you have hard water (Calcium carbonate in your water). When you raise the pH of hard water, calcium carbonate will precipitate, or fall out of solution. This calcium carbonate is a white floc that starts out as a soft sludge but will eventually harden like concrete.

Gas Chlorination

Chlorine gas is 100% pure chlorine and does not degrade over time. It is supplied to users as a compressed liquefied gas. Since mixing chlorine gas with water produces an acidic solution, there is no effect on calcium carbonate in the water. For this reason, gas chlorination systems tend to be very low maintenance.

Because of the potential for chlorine gas leaks, a gas chlorination system should be supplied with a variety of safety devices, such as chlorine gas leak detectors and automatic chlorine cylinder shut-off systems. Because of this, gas chlorination systems will have a high capital cost. In most situations, the low chemical cost per pound of chlorine gas provides the lowest operating cost.

Bleach

Bleach is produced by bubbling chlorine gas through 50% sodium hydroxide (caustic soda). While chlorine gas does not like to be in solution, more can be dissolved into solutions with higher pH values. Since caustic soda is pH 14, it will hold up to 17% chlorine concentration. However, this bleach solution is very unstable and chlorine gas will come out of solution over time, depending on temperature and agitation. While the bleach is produced at 17% concentration, it is sold as 12.5% concentration. If you get a fresh batch of bleach, you might actually have 15+% chlorine. However, since the bleach manufacturers do not know how long it will be before the bleach will be delivered to you, they sell it as 12.5% concentration. The degradation of the bleach will continue after you have received it and you need to make sure that you do not order too much bleach at one time. The chlorine gas that comes out of solution is disinfection that you paid for that you will not be able to use.

If you are chlorinating a small well, the 12.5% bleach will be too strong to pump reliably and you will need to dilute it to 1% or 2% concentration.

Because of the high pH of bleach, calcium carbonate will precipitate from hard water where the bleach contacts the water. If you are pumping 12.5% bleach, this will be at the point of injection. If you are diluting the bleach with hard water, the calcium carbonate will start forming in the dilution tank and carry through your metering pump and to the point of injection. Bleach systems on small wells tend to be very high maintenance.

The capital cost for a bleach system is low, a pump and a tank. The operating cost of a bleach system will be 2 – 3 times the cost of a gas system.

Calcium Hypochlorite Tablets

Cal Hypo is produced by mixing chlorine gas with binding agents which are then dried into a powder. The powder is then compressed into a tablet. The cal hypo tablet will typically be 65% chlorine and 35% binding agents. When you dissolve the cal hypo tablet, it produces a chlorine solution typically less than 1% in concentration and at a high pH.

With the high pH, calcium carbonate will start precipitating in the tablet dissolving tank. Also, not all of the binding agents will dissolve, so you will also have a sludge being produced from the undissolved binding agents. This creates a very high maintenance system.

Cal hypo systems can have a low capital cost (depending on brand of tablet feeders) but have a high operating cost, 3 – 4 times the cost of a gas system.

TriChlor

TriChlor is produced by mixing chlorine gas with isocyanurates which is dried into a powder and then compressed into tablets. The tablets are 90% chlorine. When you dissolve the TriChlor tablet it produces a chlorine solution less than 1% in concentration with a low pH (acidic). The 10% binders all dissolve and the acidic solution does not cause calcium carbonate to precipitate. This creates a very low maintenance system.

TriChlor systems have a low capital cost with a high operating cost, about 2 – 3 times the cost of a gas system.

On-Site Generators

On-site generators (OSG) produce 0.8% concentration bleach, or 0.4% concentration bleach with mixed oxidants, from salt solution (Salt + electricity -> bleach + caustic soda). The water used in the OSG system is first softened so there is no calcium carbonate in the bleach solution. The production of caustic soda is minimized and produces a solution pH of approximately 9, so there is minimal effect on the calcium carbonate where the solution is injected into the well water.

Early OSG systems required significant operator maintenance. If maintenance was not performed it had negative effects on the operation of the OSG systems. Current OSG systems are much more automated and require very little operator intervention. Because the solutions that are being produced are less than 1% concentration, the solutions are considered non-hazardous.

OSG systems have a high capital cost with an operating cost about the same as chlorine gas.

Summary:

As you evaluate various forms of chlorination, you need to think about the variables and which ones are most important to you: Capital cost, Operating cost, Maintenance, Safety? As mentioned earlier, chlorine gas is perceived as being dangerous. However, throughout the years it has been shown that 60 – 70% of all reported chlorine accidents are actually caused by bleach and cal hypo.

Pro’s Con’s of Chlorination Methods

Summary of Pros and Cons of various chlorination methods

Notes:

1. Even though chlorine gas is perceived to be unsafe, 60 – 70% of all reported chlorine accidents involve either bleach or calcium hypochlorite.
   
   
2. Relative operating costs, low to high: Cl2 gas/OSG, Bleach, TriChlor, Cal Hypo

Importance of water, are you drinking enough?

We all know that water is important but I've never seen it written down like this before.

• 75% of Americans are chronically dehydrated.
• In 37% of Americans, the thirst mechanism is so weak that it is often mistaken for hunger. Even MILD dehydration will slow down one's metabolism as much as 3%.
• One glass of water shuts down midnight hunger pangs for almost 100% of the dieters studied in a U-Washington study.
• Lack of water is the #1 trigger of daytime fatigue.
• Preliminary research indicates that 8-10 glasses of water a day could significantly ease back and joint pain for up to 80% of sufferers.
• A mere 2% drop in body water can trigger fuzzy short-term memory, trouble with basic math, and difficulty focusing on the computer screen or on a printed page.
• Drinking 5 glasses of water daily decreases the risk of colon cancer by 45%, plus it can slash the risk of breast cancer by 79%, and one is 50% less likely to develop bladder cancer.

Are you drinking the amount of water you should every day?

More Water Facts You Should Know...

While water covers 70% of the earth's surface only 3% is freshwater, most of which is locked away in glaciers, icebergs, and snow, leaving just 1% of accessible freshwater for the entire planet's population.

• One trip through a car wash uses 150 gallons of drinking water
• Fixing a leaky faucet saves 20 gallons of water per day
  If your faucet is dripping at the rate of one drop per second, you can expect to waste 2,700 gallons per year which will add to the cost of water and sewer utilities, or strain your septic system.
• Collecting water for gardening from the faucet while waiting for hot water saves about 250 gallons of water a month
• Using a broom to clean the sidewalk instead of a hose saves 150 gallons of water
• Using a pool cover prevents about 1,000 gallons per month from evaporating

Are you doing your part to help protect this precious resources?

It wasn’t too many years ago that measuring things in the parts per million range was the limit of our capabilities. Now, we routinely see data presented in the parts per billion range and they are moving to the parts per trillion range. Where will it end and what does it mean? Just because we can measure it, does that mean it is important?

One of the issues is relating to parts per billion. Following are some examples that you may be able to relate to:

• One minute in 2000 years
• One heartbeat in 36 years
• One thin mint in 25,000,000 boxes of Girl Scout cookies
• One inch in 16,000 miles
• One dimple on 2,600,000 golf balls
• One M&M in 1,000 tons of M&Ms
• One sheet in 3,600 miles of toilet paper
• One shot of vermouth in 7,500,000 gallons of gin (a very dry martini)

Operator Job Description

Mr. Operator....It is now up to you to make this Treatment Plant perform!!!

1. The owner needed it.
2. The regulatory agencies oversee it.
3. The engineer designed it.
4. The equipment manufacturer and contractor furnished and installed it.

Do You know what an operator really is?

1. Superintendent, full or part-time.
2. Licensed operator, or qualified person.
3. Sometimes laborer, plumber, electrician, carpenter, brick mason, mechanic, grounds keeper, lab technician, purchasing agent, record-keeper, secretary, and maybe inventor and possibly a magician.
4. Of course, you need a background in: Law--to meet the various regulations, Psychology--to meet the neighborhood problems, Biology--to understand the treatment principles, Chemistry--to handle the disinfection and tests, Mathematics, Hydraulics, English and Metrics--to handle the rest of the duties.
5. It goes without saying that you must be: Courteous, Trustworthy, etc... Calm, Dependable, and physically and mentally in top condition.

Now that you know how to be an operator -- GOOD LUCK!!!

Author Unknown