effective in taste and odor control, provided the
1. type of activated carbon used meets minimum standards,
2. dosage is correct,
3. carbon is mixed intimately with the water, and
4. carbon is in contact with the water for an adequate period.
Acceptable commercial preparations of activated carbon should meet the following minimum specifications:
1. It does not contain any soluble mineral injurious to health.
2. Moisture content is not over 8.0 percent.
3. It is powdered form that wets down and goes into suspension readily, does not settle too rapidly, and does not float on the surface when applied.
4. At least 99 percent of the carbon in water suspension passes a 100-mesh sieve and 95 percent passes a 200-mesh sieve.
5. It has enough adsorption capacity to reduce a concentration of 0.1 milligrams per liter (mg/l) phenol in distilled water to 0.01 ppm.
Because of the wide range in waters, no general rule can be given for activated-carbon dosage. The dose required at each water plant must be determined by periodic laboratory tests. The test is made by preparing a number of samples of raw water, adding the standard amount of treating chemicals and varying amounts of carbon to each sample, allowing plant contact time, filtering, and making odor tests. Numerical comparison can be made with the threshold odor test. A carbon dose of 3 ppm removes most tastes and odors from water. However, dosages can vary from 3 to 15 ppm, depending upon the odor of the water. Laboratory tests will determine the dosage.
Activated carbon is fed into the water by dry feeders. It must be handled more carefully than coagulant because it is a fine powder; therefore, the feeder must bean approved type and designed to prevent the spreading of the carbon dust and causing fires. In addition, inhaling of the dust by personnel, even in low concentration, can affect their lungs. The dry feeder room should have explosion proof electrical equipment. A spark or pilot flame can create an explosion. Dry carbon will float on the surface of the water for a long time. Therefore, it is important that the carbon be wetted thoroughly, mixed by agitation using a paddle wheel, swirling action, a spray, or so forth, in a small tank. Some dry feeders have a mixing chamber in which the carbon is wetted by the swirling action of the water.
Activated carbon may be applied to the water at one or several points, depending on the results desired. Carbon is added at one or more of the following points:
In the raw water, as early as possible after it enters the plant. This point of application is not recommended for extremely turbid waters.
In the mixing basin. When added before sedimentation, activated carbon not only removes foreign matter from the water, but the carbon that settles in the sedimentation basin continues to absorb products of sludge decomposition, thus preventing formation of secondary tastes and odors. Black alum is premixed activated carbon and coagulant that can be used in special situations both as a coagulant and for taste and odor control.
Should chemical or biological agents or nuclear weapons be employed during conflicts, the water supply of the area involved would, in all likelihood, become contaminated. A water source contaminated with a chemical, biological, or radiological agent can cause incapacitation or death to a consumer. Effective means for determining the presence of CBR agents, followed by proper decontamination procedures, can reduce or eliminate the hazards caused by these agents.
In the event that you are assigned to supervise or manage a field water supply point, you will be responsible for the detection and removal of CBR contaminants. The supervisor of a water point crew must be sure the crew is trained in the identification of CBR contamination byContinue Reading