Fire Department Draft Tank Treatment Design

[hynhvac]

My firm is doing a water treatment design for a fire dept's draft tank. This tank hold 10,000 gal of water to be used to test the water pumps on the fire trucks. Water is pumped out of the tank, through the truck and back into the tank. They do this about once or twice a month, maybe. The tank is pumped out and drained a couple times a year onto a grassy area.

The tank is covered with removable concrete covers and is located below grade inside a building. The fire dept requires this water to be treated because when they test the pumps, water flys all over the place and the firemen get wet, opening up the chances for them to get sick.

We have experience with water treatment, but those designs involved circulating systems, such as water wells and irrigation systems. This type of project is new to us and we were looking for input on how to go about the design.

The fire dept has told us that they dont want the treament system to run while the pumps are running and they didnt mention total dissolved solids as one of the criteria, they just told us that we need a biocide and an algaecide. The current rough draft of our design has a sensor module that would monitor the water quality and the chemical dispensers would be somewhere in the tank.

We are trying to avoid putting in a circulating system, as this tank is existing and it would increase the cost.

thanks.

 

[coloeng]

Why don't they just dump some chlorox in the tank every once in a while. 1 gallon of clorox will provide 5ppm in 10,000 gallons of water. That should be more than enough to kill any bios or algaes.

 

[bimr]

Tank water may become contaminated with micro-organisms (bacteria, etc) that can cause gastroenteritis and other diseases. The simplest and least option is to periodically disinfect the water with chlorine. Other forms of disinfection may include ultra violet light sterilizers.

Two common forms of chlorine compounds can be used, those disinfectants that contain Sodium Hypochlorite (household bleach) or Calcium Hypochlorite (swimming pool chlorine powder). It is very important to add the Chlorine at the correct dosage.

Start out with 2.5 mg/l of sodium hypochlorite. That would be about 1/2 gal of 5% household bleach. After a week, check the chlorine concentration and adjust the dosage. After a few weeks, you should be able to make a regular weekly chlorination schedule.

You do not want to add too much chlorine or you will stain clothing.

You can use the calcium hypochlorite tablets instead of bleach. It would take 0.3 lbs of Calcium Hypochlorite (granular or PPG Accu-Tabs) any brand that is similar instead of the liquid bleach.

The turbulence in the tank may cause granular chlorine material to be flushed out and/or plug the drain.

There is no point trying to control TDS. You best option regarding TDS is to periodically dilute the storage volume with raw water. You mat contact Chemtreat or another chemical supplier for biocides, but it will be more expensive than bleach and you will have issues with exposure to the chemicals.

 

[hydrae]

Treat it like a swimming pool
1/2 hp pump, sand filter, automatic chlorinator
backwash once a week or once a month depends on the dirt
refill the chlorinator at the same time, adjust the pH as needed

Hydrae