CHLORINATION FOR ALGAE & SLIME CONTROL

 

GENERAL

 

One of the most important uses for chlorine, gas chlorine, and gas chlorinators is in the destruction or control of algae and slime. Algae and slime cause numerous difficulties in the various systems where they are found and although there are many different types of chemical agents used to combat them, chlorine is the most widely used because of its effectiveness and low cost.

 

Gas chlorine (liquid chlorine) and gas chlorinators have usually been used for treatment of the medium and large systems, but many of the smaller systems were not able to take advantage of the low cost of liquid chlorine in the past due to the high cost of equipment and installation. Direct cylinder mounted and ton container mounted gas chlorinators have provided the answer to low equipment and installation cost, simplicity of operation and minimum maintenance.

 

ALGAE AND SLIME

 

The general terms of algae and slime cover a multitude of microscopic organisms of both the plant and animal types. Algae are a group of plant organisms having many thousands of species in a wide variety of colors.  These organisms produce their own food through the use of light energy and water (photosynthesis). Since sunlight is required for their growth, they are found in almost all surface water supplies such as lakes, ponds, swimming pools, etc., where control methods have not been applied or have been ineffective. Long filaments or large clumps of algae colonies are not only unsightly, but can reduce flow in pipes, plug up valves and small orifices  and can induce corrosion. Although they do not live in enclosed systems, dead colonies still can create a considerable problem.

 

Slime is a general term widely used for clusters or long filaments caused by bacteria or fungi. These microorganisms do not produce their own food and therefore do not require sunlight.

Many strains grow best in dark areas and not only produce a problem due to their reproduction, but aggravate the problem by collecting inorganics, dead algae and other debris in their colonies. The most common types that cause difficulties are air-borne and, therefore, systems with open tanks, cooling towers and open water supplies are most susceptible. Slime not only presents the problem of system plugging, but also retards heat exchange in cooling water systems and promotes corrosion.

 

AFFECTED AREAS

 

Algae and slime affect many types of systems in municipal and industrial use and three of the most important ones are:

 

1. Water supply systems
2. Swimming pools
3. Cooling water systems

 

TREATMENT – WATER SUPPLIES

 

Chlorination of water supplies is a subject in itself since it includes treatment for disinfecting, taste, odor, color removal, etc.  The method and amount of chlorination may be dictated by one of these, rather than the need to eliminate algae and slime. In filtration plant systems for drinking water, algae can be carried into and through the filter system and into other sections of the treatment plant causing considerable difficulty. Strong chlorination of the water entering the plant is often recommended to kill the organisms, which can then more easily be filtered out. This also eliminates after affects of taste and odor caused by reactions with or decomposition of algae and slime.

Chlorination of deep well supplies usually required only a free chlorine residual of 0.5 to 1.0 PPM to destroy organisms as crenothrix.

 

Since this bacterium exists in iron and manganese-bearing waters, it may also be necessary to add a Tramfloc sequestering agent prior to the addition of chlorination in order to keep dissolved iron and manganese compounds in solution where chlorination alone would normal precipitate them. Chlorination of well systems usually is very effective in eliminating the source of troublesome bacteria, but in some cases periodic shock treatment of the system may be necessary to destroy bacteria growth that has already been established. Shock treatment may require residuals of 50 to 150 PPM, which are sealed into the section of the system being treated and allowed to stand for 12 to 24 hours, if possible.

 

SWIMMING POOLS

 

Swimming pool systems could receive shock treatment once a day, which would adequately eliminate algae and slime growths. Because of the need to eliminate disease-causing bacteria, it is recommended that continuous treatment be used and that a residual of 0.5 to 1.0 PPM exist in the pool at all times. This should adequately eliminate algae and slime problems, although in some systems in is also necessary to over-chlorinate to 5 to 10 PPM every week or two weeks and thoroughly brush the walls and bottom to bring the strong solution into contact with the organisms.

 

COOLING WATER

 

Cooling water treatment is most effective by continuous chlorination maintaining a free chlorine residual of about 0.5 to 1.0 PPM. This, however, is the most costly method of chlorination and is not always technically sound. Where cooling water is obtained from a river, stream or other surface supply and merely passed through the system once, it has often been found adequate to use shock treatment once every four, eight or twenty-four hours to eliminate organisms which have begun to collect in the system. The frequency and amount of both dosage and contact time will depend on the source. Many have found that shock treatment at a rate of 5 PPM every four or eight hours for duration of 15 to 30 minutes is adequate to give a residual of 0.5 to 1.0 PPM in the water leaving the system. Here again, it may be occasionally necessary to shock treat at higher values and for a longer contact period in order to keep the system clean.