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Afshin

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Mixing of two different COD waste water
Apr 09^th, 2012, 9:15am

Dear Members,

Actually I am new in waste water treatment, I am working in project we need to mix two different High COD (15000-30000 mg/lit) and low COD (100-500 mg/lit) in an equalization tank.Low COD waste water is continiuos but high COD waste water is supplied with a storage tank through a centrifugal pump.We need to control high COD w.w. by installation of Flow Control Valve in discharge of pump, the flowrate of that stream should be calculated based on TOC analayzer installed in two inlet stream and mixed stream in outlet of tank, so mixed COD be lower than 1000 mg/l.My first question is which formula can be used to estimated High COD flowrate? Is TOC analyzer is appropriate measurement for such a application.Can we directly measure COD instead of TOC.

I am waiting to hearing from you soon.

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Mort YaBB Newbies Offline I love Water and Wastewater.com Posts: 6 Minnesota Gender: Company or Organization: Aire-O2	Re: Mixing of two different COD waste water Reply #1 - Apr 9^th, 2012, 11:36am C1xQ1 + C2xQ2 ... = CtotalxQtotal where C = concentration, Q = flowrate It may be possible to establish TOC correlation to your COD for your specific plant if the quality of the waste is consistent. Special note that this will be specific to your wastewater.
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The sludge judge

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Re: Mixing of two different COD waste water
Reply #2 - Apr 9^th, 2012, 12:02pm

You'll probably have to do this through trial and error. I wouldn't automate anything until you have a good feel for it. You can estimate the volume in the EQ tank and the COD along with the flow of the high strength COD to get an estimate of what the combined COD will end up being.

Since you already have the ability to control the flow rate of the high strength waste (you have a storagte tank) you may find that it's easier to tap into the effluent line of the EQ tank and feed at a desired % of your EQ effluent flow. This may also help prevent odors and septicity in the EQ tank.

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Afshin

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Re: Mixing of two different COD waste water
Reply #3 - Apr 9^th, 2012, 6:43pm

Mort,

Thank you for your reply.Can we do this offline?

Thanks

sludgefather

thank you for your reply, I am agree with you we can do this by trail and error,but remember the one inlet stream to Eq tank is continuous, and mixing process in Eq tank need to continue till all of stored high COD waste water will be finished.
Also I didn't get your point about in your below statement. "you may find that it's easier to tap into the effluent line of the EQ tank and feed at a desired % of your EQ effluent flow"
Could you please clarify probably by a sketch.

Thanks

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grrun

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Re: Mixing of two different COD waste water
Reply #4 - Apr 9^th, 2012, 9:10pm

I'm not sure if NH₃-N is of significant concentration; but I would think that you should measure the COD/TOC ratio from both streams. While the constant stream has the most variability; the concentrated stream has less variability. My thinking is that you only need one TOC controller on the discharge of the equalization tank to control the concentrated stream to keep the equalized mixture under 1,000 mg/L COD/(TOC) for the mixture. I'd be afraid that having TOC meters sensing the influent from both influent streams would only complicate the mixing of the streams. That being said; I would probably install a mixer on the equalization tank. Anyway, that would be my first approach to the problem.

grrun

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The sludge judge God Member Offline Posts: 649 Wisconsin Gender: Company or Organization: private	Re: Mixing of two different COD waste water Reply #5 - Apr 9^th, 2012, 10:16pm We need some idea of the volume of the high strength waste verse the normal influent. If this can be bled in slowly at a set rate that may be the best option and keep things simple. Do you have a flow meter and VFD on the high strength pump?
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Afshin

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Re: Mixing of two different COD waste water
Reply #6 - Apr 10^th, 2012, 12:55am

I attached a schematic diagram and proposed control system including size of tanks, maybe it can be helpful. The capacity of pump upstream of equlisation tank considerd as 10 m3/hr and most of flowrate will return to tank.

P.S. Sorry I can't attached any image because of warning any idea how I can attache file, the waring is about size of file but actually file size is not too much.

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« Last Edit: Apr 10^th, 2012, 9:27am by Afshin »

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The sludge judge God Member Offline Posts: 649 Wisconsin Gender: Company or Organization: private	Re: Mixing of two different COD waste water Reply #7 - Apr 10^th, 2012, 10:13am bleed it in slowly and make sure you have a pump that will account for the changes in head pressure due to the changing elevation of the liquid in the high strength storage tank, otherwise you'll never get a consistent flow.
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Afshin YaBB Newbies Offline I love Water and Wastewater.com Posts: 8 Company or Organization: MMC	Re: Mixing of two different COD waste water Reply #8 - Apr 10^th, 2012, 8:55pm Sludgefather, My pump selection is Horizental Centrifugal pump.As I know in this type of pump if suction pressure reduced discharge pressure will be reduced accordingly but total pressure increase is constant and then discharge flowrate doset change as pump working in it's constant operating point. Afshin
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