A typical hypochlorination system will consist of:
* A solution tank holding bleach or an HTH solution
* A chemical feed pump, usually a diaphragm-type pump
* A tee into the well line as the point of application
The solution tank should hold at least a one-day supply of chlorine solution. If the solution is bleach, it will have between 5.25% and 12% available chlorine (1/3 to 1 lb/gallon respectively). If HTH is used, add 1.5 pounds of HTH per gallon of water to achieve a 1.0-lb/gallon chlorine solution. Using breakpoint chlorination, adjust the stroke on the pump to achieve the desired dosage. Small systems may need to dilute the solution further, since the low flows may require feed rates too low for most feed pumps. Dilution of 5.25 % bleach may be easier than HTH solutions.
The chemical feed pump consists of a diaphragm driven pump chamber, and two check valves. The check valves, that provide the one-way flow through the pump, can get clogged with lime deposits. This occurs because the HTH that is added to the solution tank is 30-35 % lime. The strainer on the pump suction line should be located several inches above the bottom of the solution tank to prevent lime and grit from being drawn into the pump and fouling the check valves.
If the check valves get fouled, the pump will not pump any solution. Flushing the line with clean water or a weak acid, like vinegar, may also correct the problem. In severe cases the valves may have to be disassembled and cleaned. Always make sure the pump is primed before putting it back into service. It may also be advantageous to locate the pump so that it has a positive suction head.
When chlorine systems are located in areas where a chlorine release might endanger the general public, the water system is responsible for developing an emergency response program.
The following steps should be followed when a leak poses immediate danger to employees or the public:
1. Evacuate, in an upwind direction, to high ground.
2. Once evacuation is complete, notify emergency medical units of casualties and begin administering First Aid to the injured.
3. Notify local fire and police departments. Include the following information:
a) Nature of the accident
b) Approximate amount of chlorine that may be released.
c) Location of chlorine facility
d) Current wind direction
4. Notify County and State health agencies.
Dechlorination is the physical or chemical removal of all traces of residual chlorine remaining after the disinfection process and prior to the discharge of the effluent to the receiving waters. This is commonly accomplished by the use of sulfur compounds such as sulfur dioxide, sodium sulfite or sodium metabisulfite.
Dechlorination may be achieved by the following treatment processes:
1. Long detention periods. Prolonged detention periods
provide sufficient time for dissipation of residual chlorine.
2. Aeration. Bubbling air through the water with a chlorine residual in the last portion of long narrow chlorine contact basins will remove a chlorine residual.
3. Sunlight. Chlorine may be destroyed by sunlight. This is accomplished by spreading the chlorinated effluent in a thin layer and exposing it to sunlight.
4. Activated carbon. Residual chlorine can be removed from water by adsorption on activated carbon.
5. Chemical reactions. Sulfur Dioxide (SO2) is frequently used because it reacts instantaneously with chlorine on approximately a one-to–one basis (1 mg/ l SO2 will react with and remove 1 mg/l chlorine residual). Other chemicals include sodium sulfite (Na2SO3), sodium bisulfite (NaHSO3), sodium metabisulfite (Na2S2O5), and sodium thiosulfate (Na2S2O3).