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RE: High Chlorine Demand

zaffrulla — Wed, 09 Jan 2008 08:32:04 GMT

hai
Nitrites in the effluent is the main reason for increasing the chlorine demand as we know chlorine is a good oxidising agent when nitrite reacts with chlorine it prefers for oxidation that is conversion of NO2 to NO3 when oxidation is complete then it will will the breakpoint chlorination and finally go for residual chlorine
hence dosing more chlorine to nitrite rich effluent is a utter waste i would advice to see the upstream process and try to concentrate on the nitrification reaction
regards
zaffrulla
Manager -Operations & Process
WEIR ENGINEERING SERVICES
ABUDHABI

RE: High Chlorine Demand

The House — Fri, 14 Dec 2007 02:26:09 GMT

We are a plant that handles 25 MGD and are going through the same problems you are having. You may want to check with any industries that could be dumping large amounts of waste containing ammonia. Also any new industrila processes that containe polymers or discharges that may be binding up your available chlorine could be happening.

Rich in Kalamazoo.

RE: High Chlorine Demand

01780898 — Sat, 04 Aug 2007 04:55:48 GMT

Yes I agree it is almost likely to be nitrite in the effluent. This is occurring due to the warmer weather encouraging nitrification in your aeration tanks. The nitrite is caused by insufficient alkalinity in the aeration tank. Nitrification destroys alkalinity and denitrification recovers half that destroyed. The nitrite is caused by the unstable nitrification process in the aeration tank. Firstly nitrification is encouraged. Then the alkalinity drops to below 80 mg/L as CaCO3. You will see your mixed liquor pH drop to 6.2 or below. This then kills off the nitrifiers and their subsequent regrowth, when the pH recovers, is unstable and the nitrite is not converted to nitrate. You can see this under the microscope too.

Every mg/L of nitite-N will consume 5 mg/L of chlorine, so say 6 mg/L of nitrite-N uses 30 mg/L of chlorine. Ammonia forms chloramine in the chlorination process, and its presence will help to form stable residuals. If you have more ammonia-N in your effluent than nitrite-n, then the residual will probably form monochloramine and be stable. The more mixing at the chlorination point will help too.

Causes of low influent alkalinity include: large rising mains in your sewer system which ferment and produce VFAs which then neutralise alkalinity, ferric chloride dosing for odour control in the sewer network, acidic discharges (we have a 6.0 pH minimum limit on our trade waste),or too much nitrogen (from blood) from your poultry discharger (you should have an ammonia limit on them).

So what can you do to improve things: dose ammonia into the effluent before chlorination (although this does not resolve the problems in the aeration tank), reduce DO setpoint and SRT to reduce nitrification (however this depends on your ammonia permit limit), provide an anoxic zone to denitrify more, or dose alkalinity at the influent (lime, carbonate, etc.). I suggest that you seek engineering advice regarding you particular situation as some of these changes are significant.

Regards

Grant H

RE: High Chlorine Demand

01369073 — Sun, 08 Apr 2007 14:04:58 GMT

Are you nitrifying? If you are producing nitrite you will use about 5 times the amount of chlorine that you normally would. Test for nitrite and I am sure that will be the cause. Jeanette B

RE: High Chlorine Demand

Dean Falkner — Sat, 02 Dec 2006 15:31:16 GMT

A quick question....do you or have you had ammonia in your effluent? Ammonia in the effluent will react with the chlorine to form chloramines...a more effective disinfectant.

A common approach used in the water industry is to add ammonia prior to chlorination. For most wastewater plants....the amount added must be well regulated...but should not be a serious problem.

Contact your local water plant or chemical supplier for insights on how you might be able to pilot this concept. There's lots of money to be saved if this is your issue.

Please let us know what finally works for you!

Dean

RE: High Chlorine Demand

Tom C — Thu, 16 Nov 2006 10:19:55 GMT

Thanks for the replies. I will give all your suggestions a shot and let you know the outcome.

Tom

RE: High Chlorine Demand

thelorax — Thu, 09 Nov 2006 16:01:48 GMT

For what it is worth . . I seem to recall a plant having chlorine demand problems because of spent pickle liquor from steel plant (nitric acid I think). Good luck.

RE: High Chlorine Demand

Rob Baur — Thu, 09 Nov 2006 10:42:43 GMT

Run chlorine demand tests on your primary effluent daily for a week. If the demand spikes, then you know it is upstream of the plant. If you have access to a %UV transmission meter also check for %UVT. Organics that absorb UV usually have a high chlorine demand. If you can correlate the %UVT loss with increased chlorine demand then monitor your collection system for %UVT. We found a printed circuit board manufacturer that way.

RE: High Chlorine Demand

Jerry — Wed, 08 Nov 2006 17:47:11 GMT

My first choice would be to look for "Nitrites". What is your Disolved Oxygen averaging in your aeration basin?

High Chlorine Demand

Tom C — Wed, 08 Nov 2006 15:45:29 GMT

I am looking for recommendations on identifying a source in our WWTP which is periodically depleting our residual chlorine. Our WWTP usually adds around 200-300 lbs./day of chlorine. However, over the past several months on Wednesday/Thursday of each week, we add chlorine at a rate of 1,800 lbs./day in order to maintain a proper residual level. We have seen this spike for several months now but have not been able to identify the root cause.

I welcome anyone's suggestions on what chemicals could be causing this problem. We have several chemical plants, steel mill, poultry processors and metal finishers on our system.

thanks

Tom C.