Potable Water Chlorination 2

[coachk]

I am looking at possible disinfection systems for a 1 MGD potable water treatment facility for a resort. Would a hypochlorite dosing system be considered `typical' for this type/size facility?

 

[orenda1168]

CoachK:

You might want to consider a chlorine dioxide system as a better approach than sodium hypochlorite. Another option may be electrolytic chlorination.

Orenda

R. J. Kersey

http://www.orenda-tech.com

 

[bimr]

It depends. You need to know the availabity of hypochlorite.

The drive for getting rid of chlorine is the costs for complying with the UFC. If this is out of the US, building codes may be different.

You may be better of with chlorine. Hypochlorite has a shelf life and loses it strength depending on the temperature and storage time.

 

[sbush]

A hypochlorite system is very appropriate for your resort application because of the risks that chlorine gas can introduce to a close-knit population such as yours. And calcium hypochlorite is better than liquid bleach (sodium hypochlorite) because of storage and handling concerns.

A 1 MGD system targeting a 1 - 2 mg/L chlorine dosage requires roughly 8 - 17 pounds of 100% chlorine per day.

A calcium hypochlorite system uses dry tablets so there is no need to store poisonous gas or thousands of gallons of liquid bleach. Tablets are supplied in plastic 5-gallon pals containing 50 pounds of 65% chlorine. 50 pound pals can be stacked 3-high. These tablets are dissolved then pumped into the water supply using a special feeder system designed for precise tablet erosion.

A skid-mounted erosion system for this application would measure approximately 40" X 55" X 53" high and costs about $10,000 - $15,000 for a basic system with rotameter and manual throttling valve (without extras like a chlorine analyzer/recorder, automatic flow pacing, spare pump or weigh scale). A system of this size holds up to 75 pounds of dry chlorine tablets and is capable of delivering between 5 to 50 pounds of chlorine per day.

S. Bush

http://www.water-eg.com

 

[coachk]

All: Thanks for the help!

sbush: what would typical cost of calc hypo tablets on a $/lb basis, assuming usage is say 10 lb/day?

 

[sbush]

The cost for PPG AccuTab tablets with built-in scale inhibitor and NSF-61 listing is typically around $1.50 to $2.00 per pound. There are other brands of cal hypo tablets on the market that cost less but PPG's tablets are patented and dissolve accurately for precise dosage control.

S. Bush

http://www.water-eg.com

 

[bimr]

Not so fast, my friend. There are other factors that you should consider as well. For instance, the technical ability of the operating staff should be considered. Yesterday, I sat down with a village public works director and he said that the operators that he had were not capable of making the simple calculations to operate a hypochlorite system.

Also, the problems associated with pumping hypochlorite solutions are legendary.

Finally, you should give some thought to the variablity of the flow and how you will handle it. At a resort, Your seasonal peak demand in the summer (if you have one) versus the off-season will vary markedly and you chlorine system has to adjust to it.

I am not advocating either system, just giving some items to consider.