Disinfection - Wastewater Operators - page 350

at the end of the contact tank to the final effluent. Sulfur dioxide gas,
sodium sulfate, sodium metabisulfate, and sodium bisulfates are the
chemicals used to dechlorinate. No matter which chemical is used to
dechlorinate, its reaction with chlorine is instantaneous.
9.2.7 Chlorination environmental hazards and safety
Chlorine is an extremely toxic substance that can cause severe
damage when released to the environment. For this reason, most state
regulatory agencies have established chlorine water quality standards;
for example, in Virginia, the standard is 0.011 mg/L in freshwaters for
total chlorine residual and 0.0075 mg/L for chlorine produced oxidants
in saline waters. Studies have indicated that above these levels chlorine
can reduce shellfish growth and destroy sensitive aquatic organisms.
Such standards have forced many treatment facilities to add an additional
process to remove the chlorine prior to discharge. The process, known
as dechlorination , uses chemicals that react quickly with chlorine to
convert it to a less harmful form. Elemental chlorine is a chemical with
potentially fatal hazards associated with it. For this reason many differ-
ent state and federal agencies regulate the transport, storage, and use of
chlorine. All operators required to work with chlorine should be trained
in proper handling techniques. They should also be trained to ensure
that all procedures for storage transport, handling, and use of chlorine
are in compliance with appropriate state and federal regulations.
9.2.7.1 Safe Work Practices for Chlorine
Because of the inherent dangers involved with handling chlorine,
each facility using chlorine (for any reason) should be sure to have a
written safe work practice in place and followed by plant operators. A
sample safe work practice for handling chlorine is provided below:
1. Plant personnel must be trained and instructed on the use and han-
dling of chlorine, chlorine equipment, chlorine emergency repair
kits, and other chlorine emergency procedures.
2. Use extreme care and caution when handling chlorine.
3. Lift chlorine cylinders only with an approved and load-tested
device.
4. Secure chlorine cylinders into position immediately. never leave a
cylinder suspended.
5. Avoid dropping chlorine cylinders.
6. Avoid banging chlorine cylinders into other objects.
7. Store 1-ton chlorine cylinders in a cool dry place away from direct
sunlight or heating units. Railroad tank cars compensate for direct
sunlight.
8. Store 1-ton chlorine cylinders on their sides only (horizontally).
9. Do not stack unused or used chlorine cylinders.