Dechlorination
General
When chlorinated water is discharged in a flow test, it can drain into lakes, rivers and streams and harm aquatic life. According to AWWA, “Water released into the environment shall meet the applicable federal, state, provincial or local regulatory agency’s residual chlorine limit.” Your authority having jurisdiction provides dechlorination requirements.
Where do I find more information on dechlorination?
How does it work?
A portion of the water flowing through the Dechlor Demon™ is diverted through the bypass into a mixing tank, where it is combined with a concentrated dechlorinating agent. The bypass flow is controlled by a precision indicating valve. The concentrate is reintroduced into the Dechlor Demon and hose, where it continues to mix with the flowing water. The chlorine is neutralized by the time it exits the hose.
What equipment do I need?
1. Dechlor Demon assembly (DD2H, DD4, DD4H) — Flow from the hydrant nozzle (21⁄2" NH) or pumper port (4" or 41⁄2" NH). It includes:
- Dechlor Demon body — 21⁄2", 4" or 41⁄2"
- 1-gallon or 10-gallon mixing tank
- Two pickup tubes with ball valves
- Two 3⁄4" x 6' hoses with quick-connect couplings
- Indicating bypass valve
2. Dechlorinating agent (VDC#, DDVC500, BN#, BIOMAX) — An agent should be chosen on the basis of the chlorine concentration of your water system and the total amount of water to be flowed. We offer VC Mini Tabs and Vita-D-ChlorTM (both vitamin C) and Bio Neutralizer (sodium bisulphate). Other agents may be used, but check with us first.
3. Residual chlorine measurement — The chlorine measurement product will depend on the chlorine level to be expected. Take chlorine measurements before and during your flow test to make sure the correct amount of dechlorinating agent is being used.
- Test strips — Measure free and total chlorine by comparing test strip to a color scale
- Chlorimeter — An electronic device that does a comparative scan of discharge water samples
- Swimming pool test kits — A specified amount of reagents are put in and mixed with sample water in a test fixture; the resulting color is compared to a scale built into the fixture test kits — A specified amount of reagents are put in and mixed with sample water in a test fixture; the resulting color is compared to a scale built into the fixture
4. Test Hose (Hose) — At least 5' of hose is needed on the discharge end of the Dechlor Demon™ to enable mixing of dechlorinating agent with the water.
Fire flow test equipment
5. Hose Monster® (HML, HM2H)
6. 2" Pitotless NozzleTM (PN2GRV, PN2THD)
7. Discharge Flow-Rate Gauge (Gauges 4" dial)
8. Remote Reader (Remote Readers)
9. Test Hose (Hose)
10. Hydrant Gate Valve (HGV25, HGV4, HGV45)
11. Gauge Cap (GCSW)
12. Static/Residual Pressure Gauges (Gauges 4" dial)
13. Hydrant Wrench (HW107)
14. Spanner Wrench (WSPA101, WSPA104)
Determining quantity of dechlorinating agent
There are three variables in determining how much agent to put in the tank:
- Chlorine content in water main
- Flow-rate through hydrant or pump
- Concentration of agent in mixing tank
All of these variables change during the flow test or flushing operation. Monitor chlorine levels as required to maintain desired level.
Determine the quantity of dechlorinating agent by using our online calculator at www.hosemonster.com/dechlor.html. Enter in the total estimated gallons to be flowed and the chlorine PPM. The calculator will give you the quantity of tablets needed for each type of dechlorinating agent as well as the estimated cost.
Procedure
Put predetermined amount of dechlorinating agent in the tank and fill it with water. Open both ball valves fully. Open indicating ball-valve halfway. Open slow-close gate valve as would normally be done for flow testing or flushing. Check the discharge for chlorine level. If the chlorine level is too high, add tabs to the tank or open the intake ball valve more. If the chlorine is completely neutralized, it could be the result of using too much dechlorinating agent. Too much ascorbic acid or sodium sulfite is not known to damage the environment, but it is costly in terms of dechlorinating agent. Adjust the indicating bypass valve one half-turn, and check the chlorine level again. Open or close the bypass valve until the desired chlorine level is achieved. Note that the tabs are dissolving as water flows through the bypass. The chlorine level will need to be monitored and the indicating bypass valve adjusted accordingly.
US regulations
Most states use the EPA’s criterion for permissible residual chlorine concentration in receiving waters. It says that chlorine discharge in water releases into streams and wetlands shall not exceed 0.01 mg/L (or a more stringent limit depending on the state.) It also says that the total residual chlorine level for receiving streams should not exceed 0.019 mg/L for a one-hour average or 0.011 mg/L for a four-day average during any three-year period (ANSI/AWWA C655- 09, viii-ix, 2010).
