A Primer on Chlorination Applications

Chlorination of domestic, public and private water supplies has been carried on for many years as a
safeguard against waterborne diseases. In recent years, chlorination of industrial water has become a
common practice in food processing plants as a means of improving plant sanitation.

THE CONTROLLED APPLICATION OF CHLORINE
When used in a food plant, chlorine must be applied under controlled conditions if the desired
germicidal effects are to be obtained without adverse results.

SURVEY OF WATER TO BE CHLORINATED
To use chlorine effectively, the chemical and physical nature of the water must be known. The
following facts should be obtained: the average pH of the water, the temperature range, the chlorine
demand, the concentration of organic matter, the volume to be chlorinated and the presence of
contaminants which might lead to malodorous compounds.

SELECTION OF THE CHLORINE COMPOUND TO USE
The selection of a chlorine compound to use will depend to a great extent on the volume of water to be
chlorinated, the level desired and especially the use that will be made of the water.

CHLORINE GAS
Chlorine gas is generally considered the best source for in-plant chlorination where large volumes of
water are to be chlorinated to high levels (4-5 ppm) because:
1. It is pure substance, and no other materials are added.
2. It lowers the pH slightly
3. It is easy to control and apply.
4. It is the least costly source on the basis of pounds of available chlorine

The main objection to chlorine gas is the cost of chlorination equipment; however, this cost is eventually
balanced by the lower cost of the chlorine.

Hypochlorites are the second choice for in-plant chlorination for the following reasons:
1. When they are added, other chemicals such as CaCl2 and NaCl are produced which may have an adverse effect on the quality of the product.
2. The amount added is difficult to control.
3. The raise the pH of the water, and in hard water, this may contribute to deposits on equipment and cans.
4. They are more sensitive to organic matter in the water and so lose their germicidal potency faster.
5. Being unstable, they are difficult to store and deterioration results from storage.
6. Their cost is high in terms of available chlorine content.
Hypochlorites are a good source when only small amounts of chlorine are needed, such as in can
cooling systems, in a localized germicidal application for cleanup purposes and in prevention of slime
formation on belts and other equipment.

When a calcium hypochlorite is used, only the amount needed should be made into a solution because
it deteriorates on standing.

Salts of heavy metals, even in small amounts, catalyze the disintegration of hypochlorites.

CHLORAMINES
Chloramines are not suited for in-plant chlorination due to their slow action. However, because of their
stability, they are well suited for use when a long contact time is possible. For example, they may be
used in wood holding tanks held full of water during the off-season.

IN-PLANT CHLORINATION
In-plant chlorination provides a continuous application of germicidal chlorine to the food preparation
equipment, with the result that bacterial counts are reduced, slime formation is prevented, odors are
avoided, and the time required to accomplish a satisfactory cleanup is shortened. In addition, if the
water is used in can coolers, chlorination helps to prevent spoilage from re-contamination.

RECOMMENDED CHLORINE LEVELS
Free chlorine residuals of 4-7 ppm at the point of water application to equipment are recommended. If
the operations are light, with only one shift, satisfactory control may be maintained by the lower
concentrations, whereas during heavy or continuous operation, 5 ppm may be required.

An increase to chlorine residuals of 10-20 ppm is recommended for cleanup purposes. This serves to
give an effective germicidal treatment to all equipment in the plant.

EFFECT OF IN-PLANT CHLORINATION ON FOOD QUALITY
Of the products tested, it is evident that apples, pears, cling peaches, figs, strawberries and yams are
he most susceptible to absorption of a chlorine flavor.

However, when nonchlorinated water was not used for syrups and brines, off flavors did not develop
with the chlorine concentration. Tests on these products showed that a chlorine concentration of 5
ppm has no effect on the color or ascorbic acid content.

EFFECT OF IN-PLANT CHLORINATION ON CANS AND EQUIPMENT
Chlorine is corrosive to the common metals. However, in low concentrations such as are used in in-
plant chlorination (2-5 ppm), it does not noticeably corrode either cans or equipment under ordinary
conditions.

Text taken from "The Chlorination of Water," and reprinted courtesy of National Canners Association.

This conclusion is based on years of experience by many canners using in-plant chlorination. Some
packers have reported that less corrosion takes place when chlorine is used because corrosion is most
severe under slime deposits and the chlorine provides slime formation. Even the high concentrations
(10-20 ppm) used for cleanup do not generally produce significant corrosion because the contact time
is too short. However, while corrosion attributable to chlorination is not normally a problem, its
possibility should not be completely ignored, and chlorination must be used with care. If the canned
cooling water contains sulfates or chlorides, the addition of chlorine increases the tendency toward can
corrosion, and the addition of a corrosion inhibitor such as sodium phosphate may be necessary to
counteract this.

INSTALLATION FOR IN-PLANT CHLORINATION
For reasons explained previously, chlorine gas is preferred to hypochlorites for in-plant chlorination;
however, both may be used. Various types of chlorinators are employed, depending on the source of
chlorine. Gaseous chlorine is ordinarily added to water by means of equipment, which mixes the gas
with water and then injects this water back into the supply line. "Homemade" gas chlorinators are not
advisable where accurate control is necessary. Cylinders of chlorine should preferably stand on
platform scales while being discharged. This provides a means for measuring the rate of discharge and
indicates when the cylinders are empty. Hypochlorites are added by pumping or aspirating a solution
of the material into the water line.

Pump hypochlorinators can be used for chlorinating either closed or open water systems. In closed
systems, the solution is pumped directly into the line. Pump chlorinators are made of corrosion
resistant material and may be equipped to add hypochlorite solution in proportion to the water flow. A
simple method for chlorinating well water is to connect the feed
pump motor to the same switch as the well pump motor in such a way that the chlorinator operates
when the well pump is on. Aspirator type hypochlorinators are available which add the solution in
proportion to the flow of water through the line. These have been employed successfully for in-plant
chlorination with sodium hypochlorite solutions. Regardless of the source of chlorine, only automatic
equipment that feeds the chlorine in proportion to the water flow should be used. This is necessary to
avoid fluctuations in the chlorine level which, which if too low, would be ineffective, or if too high, might
produce off-flavors and corrosion.

For in-plant chlorination to be most effective, there should be a continuous application of chlorinated
water to all surfaces where bacteria are likely to grow and form slime. This may involve additional
piping. For belts, bucket elevators, reel washers and similar equipment, the chlorine may be applied by
installing sprays of chlorinated water in such a way that they will constantly bathe in the moving
surfaces. Best results are obtained on belts when the chlorinated water is sprayed on both sides of the
belt.

For equipment (such as filters, dicers, peelers, etc.) where a continuous application of chlorinated
water is not possible, water lines with short hoses should be installed near each machine to be used for
washing the equipment each time operation ceases. As a precaution against off flavors, and to avoid
any employee objection, it is advisable to install lines of nonchlorinated water for syrup or brine
making, for boiler water and for drinking purposes.

PRECAUTIONS WHEN IN-PLANT CHLORINATION IS USED
After the installation has been made, the chlorine should be run for at least a week before canning
operations are commenced to "burn out" all organic matter in the lines. This helps to assure safety
from off flavor and will reduce the chances of objections from employees, because the flavor of the
water is usually unpleasant until the lines are clean. If there has been no previous experience with the
products being canned, an experiment pack using chlorinated water should be made prior to the start
of operations to determine the possibilities of off flavor. In the tests, chlorine is added directly to the
canned product in the approximate concentrations of 2, 5, 10 and 25 ppm, and the level at which any
flavor change occurs noted. All cresols, phenols or phenolic compounds should be removed from the
plant, because chlorine in combination with such materials produces compounds which have a very
strong flavor even when present in minimum quantities. Material which may contain phenols and
cresols are marking inks, paints, fly sprays, special wood sealers, hand lotions and the like.

When using chlorine gas, every precaution should be taken to avoid personal injury, because chlorine
gas, even in low concentrations, will cause skin irritations, serious injury to the lungs and throat, and in
high concentrations is poisonous. Chlorine cylinders should be handled carefully, never dropped or
rolled, and should be stored in upright position, in a well-ventilated area readily accessible for
inspection.

A chlorinator installation should be located in an above ground room with good ventilation and never in
a basement, because if any leaks occur, chlorine, being heavier than air, will accumulate in a basement
room and toxic concentrations may develop. Since liquid chlorine expands very rapidly when heated,
the cylinders are equipped with fusible plugs which melt at about 158o F
and release the gas as a precaution against explosion. It is desirable therefore to have the chlorinator
room and the chlorine storage area of fire proof construction and to keep the cylinders away from heat
sources. In case of fire, chlorine cylinders should be removed from the building, or if this is not
possible, firemen should be informed of the gas's presence.

If a leak occurs in a chlorine cylinder, steps should be taken to correct the condition immediately
because chlorine leaks usually become worse. Never spray leaking cylinders with water because
chlorine reacts with water to produce heat, which increases the pressure, and in turn, increases the
escape of chlorine. Gas evolution from chlorine spilled on the floor or ground can be reduced by
spraying with cold water. Keep the windward side higher than the leak. If a chlorine container is
leaking and is in a position that would cause liquid chlorine to escape, the cylinder should be turned so
that the gas escapes from the leak as a gas. That leak would emit only about 7% as much as a liquid
leak of the same magnitude.

A bottle of ammonia should be kept in the chlorinator room for use in checking for gas leaks. The
open bottle of ammonia or a rag wrapped on a stick and soaked in ammonia is placed near places
which are likely to leak. A chlorine gas mask (U.S. Bureau of Mines approved; the common industrial
type is not satisfactory) should be provided for each employee who might be exposed to chlorine.

Chlorine may be absorbed in caustic soda, soda ash or hydrated lime solutions. Caustic soda is
recommended. The amount of alkali is recommended by The Chlorine Institute.

One man should be responsible for the repair and maintenance of chlorination equipment, and if a leak
is suspected, he should be notified while everyone else should leave the area.

It is desirable to post instructions near the chlorine. They are used to inform employees what to do in
case of an accident. Instructions may be obtained from the chlorine manufacturer.

LABORATORY CONTROL OF IN-PLANT CHLORINATION
Continuous laboratory control is essential for application of in-plant chlorination, and the following
schedule is recommended:

1. Check the chlorine residual every 2 hours for the first week using the orthotolidine test. This will help to establish what variations are likely to occur.
2. After the first week, check the chlorine residual at several points in the plant at least twice a day. Always sample at the same places each day.
3. If possible, take the sample from a tap that has been running for several minutes. A sample taken from a tank or flume may not give true values.
4. Keep a record of all residuals observed.
5. Taste the water (if it is potable) every time a residual is taken, as a check on possible off flavors.
6. Record the chlorinator setting each time the residual is taken. After a few days, it may be possible to correlate residuals with chlorinator settings, and recognize discrepancies which would indicate that something is wrong.
7. Weigh the chlorine cylinder each day at the same time, and record the loss in weight. This is a check on the accuracy of the chlorine feed setting and the results indicate when a new cylinder is needed.
8. Check the chlorinator operations, and at least once a day inspect for leaks using ammonia as previously described.
9. For hypochlorinators, check and record the volume of chlorine solution in the supply tank and each day calculate the gallons of solution that have been fed during the previous day.

CHLORINATION OF COOLING WATER
When cooling water is reused or has a high bacterial content, chlorination is advisable. When cans are
to be processed in retorts or continuous cookers, chlorination of cooling water should always be
accompanied by washing the cans after filling.

COOLING TOWERS
Water that is cooled for reuse by passing over a cooling tower may be highly contaminated with
microorganisms, and chlorination is usually necessary. Sufficient chlorine should be added as the water
leaves the tower for use in the plant to maintain a free residual of approximately 0.5 ppm in the water.
This treatment should be accompanied by filtration to remove suspended solids. The chlorine residual
after cooling should be increased from 0.5 to 4-5 ppm for a few hours every week to eliminate more
resistant microorganisms which gradually build up in towers.

TANK, CANAL, AND ROTARY CONTINUOUS COOLERS
Bacterial counts may rapidly build up to high levels in water, tank, or continuous rotary coolers unless
the water is chlorinated. A free chlorine residual 0.5 to 1.0 ppm at the discharge end of the cooler is
recommended. When in-plant chlorination is practiced, the 5 ppm residual carried to the cooler inlet
water is often sufficient to maintain the necessary 0.5 ppm at the discharge end of the cooler without
additional chlorination.

CHLORINE COMPOUNDS AND CHLORINATOR EQUIPMENT
Chlorination of cooling water may be accomplished with either gaseous chlorine or hypochlorites.
Either automatic or manual feed equipment may be used, but it is sometimes more difficult to get
accurate control with manual feed. The same precautions apply for these installations as are described
under in-plant chlorination for using gaseous chlorine.

For cooling canals and open coolers, hypochlorites are generally used, and these may be fed by a
means of a chemical metering pump. Calcium hypochlorite solutions are best added with specialized
tablet chlorinators.

LABORATORY CONTROL
The following routine is recommended for cooling water chlorination.

1. Chlorine residuals and the operation of the chlorinator should be checked at least every two hours when chlorination first starts, and at least every four hours after the first week.
2. The solution tank should be calibrated so that the feed rate may be checked.

CHLORINATION OF WATER REUSED FOR PURPOSES OTHER THAN COOLING
When it is necessary to use water in food preparation departments, the best and safest method is the
counter flow of product through the lines. The fresh water is used for the final washing or fluming of the
product to canning. The second or third uses may be for fluming, washing or pumping the raw product
as it enters the preparation lines, after which the water is discarded or used for fluming waste. The
exact details of such a system must be worked out for each cannery because no two plants handle a
given product in exactly the same manner.

With the counter flow system, the water is collected in a separate tank after each use and
rechlorinated. A gaseous chlorinator other than the in-plant chlorinator is used for this purpose.
The concentrated chlorine solution is fed into a header with a valve controlled outlet for each tank.
Special rubber hoses from these outlets carry the chlorine solution to the collection tanks. Sufficient
concentrated chlorine solution is added to the water in the tank to give a trace of free residual at the
end of the next use. This completely satisfies the chlorine demand of the water and, because of the
organic matter present, results in a fairly high combined residual. Because of the long contact time, this
residual exerts enough germicidal power to prevent the proliferation of microorganisms. When water is
reused according the counter flow principal, the following considerations are important:

1. Water used for the first wash of the product as it enters the plant, or for the first wash of the product after blanching should be discarded.
2. The water which is being reused should be kept cool (below 85oF) by adding fresh cold water to the various collection tanks as the need indicates.
3. Reuse of water must be accompanied by effective daily clean up of the plant.
4. In addition of chlorination of the reused water, in-plant chlorination to a level of at least 5 ppm free residual is essential.
5. Only gaseous chlorine should be used, because successive rechlorination with hypochlorites would result in the accumulation of a large amount of chemicals other than chlorine compounds which might adversely affect the quality of the product.

The reuse of water four times by the counter flow system has resulted in a saving of 50% in water
consumption in pea canneries, without any spoilage hazard or lessening of plant sanitation.
(Mercer and York, 1953)

Reuse of water by circulation within one operation and with discharge only by overflow is not
recommended. The temperature tends to rise, and after recirculation over a long period of time, the
water becomes so filled with soluble and suspended organic matter that even with chlorination, it is
difficult to maintain bacterial population at a low level. The build-up in organic matter may also result in
contamination of the product. A canner has no way of making certain that fresh water will always be
added in the amount needed to keep the recirculated water from becoming foul.

We at Tramfloc, Inc. have endeavored to offer some thoughts on common practices of chlorination.
Each plant operator should have his own chlorination requirements individually evaluated for efficiency
and effectiveness in view of the unique characteristics at each plant. Tramfloc's engineers are available
for consultation on all aspects of disinfection chemistry and equipment systems.

Last Updated July, 2013

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