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Cooper Harris YaBB Newbies Offline I love Water and Wastewater.com Posts: 33 Gender: Company or Organization: SEEN	pH raise due to increasing aeration? Apr 10^th, 2012, 9:24am is there any possibility that when we increase the aeration level, the pH of the aerobic tank also raises?
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The sludge judge God Member Offline Posts: 649 Wisconsin Gender: Company or Organization: private	Re: pH raise due to increasing aeration? Reply #1 - Apr 10^th, 2012, 10:10am It's fairly common to see a slight raise with the oxidation of organic acids. pH levels up to nearly 9 won't hurt anything.
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Geoff God Member Offline Posts: 1006 Gender: Company or Organization: Retired. :-)	Re: pH raise due to increasing aeration? Reply #2 - Apr 10^th, 2012, 9:25pm However if you start to oxidise ammonia then there is a risk of a significant reduction in pH unless you also denitrify. I have see the pH drop to 5.5 once nitrification takes off in alkalinity limited plants. Cheers
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Cooper Harris YaBB Newbies Offline I love Water and Wastewater.com Posts: 33 Gender: Company or Organization: SEEN	Re: pH raise due to increasing aeration? Reply #3 - Apr 11^th, 2012, 8:24pm is there a significant reduction in pH when using poly aluminium chloride for coagulation/flocculation?
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Geoff God Member Offline Posts: 1006 Gender: Company or Organization: Retired. :-)	Re: pH raise due to increasing aeration? Reply #4 - Apr 11^th, 2012, 8:29pm The polyaluminium coagulants in general consume considerably less alkalinity than say alum. But if your alkalinity is low to start with you'll need pH correction. You should have at least 50mg/L of alkalinity in your effluent at all times. Some folks suggest it should be 70mg/L. Cheers
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Cooper Harris YaBB Newbies Offline I love Water and Wastewater.com Posts: 33 Gender: Company or Organization: SEEN	Re: pH raise due to increasing aeration? Reply #5 - Apr 16^th, 2012, 10:12am Dear Thesludgefather, According to your explanation, the slight raise in pH is related to the oxidation of some organic acids. However the oxidation of organic matters by microorganisms also produces CO2 which results in the decrease of pH. Just my piece.
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The sludge judge God Member Offline Posts: 649 Wisconsin Gender: Company or Organization: private	Re: pH raise due to increasing aeration? Reply #6 - Apr 16^th, 2012, 11:16am oxidation of VFAs can cause increase of pH because these are stronger acids than CO2. (CO2 is a weak acid). You'll produce CO2, but you'll remove stronger acids. Another possibility is over-aeration stripping the CO2 from the water.
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DS God Member Offline sapere aude Posts: 1583 Company or Organization: Indept. Freelance Consultant	Re: pH raise due to increasing aeration? Reply #7 - Apr 16^th, 2012, 12:11pm The sludgefather (amen) is right: stripping of CO2 due to aeration makes the pH go up, and this ends somewhere below 8 à 8.5 max (difficult to predict...)
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Cooper Harris YaBB Newbies Offline I love Water and Wastewater.com Posts: 33 Gender: Company or Organization: SEEN	Re: pH raise due to increasing aeration? Reply #8 - Apr 16^th, 2012, 12:30pm Got it. Thanks guys
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argfin Full Member Offline I love Water and Wastewater.com Posts: 145 Company or Organization: None	Re: pH raise due to increasing aeration? Reply #9 - Apr 20^th, 2012, 4:08am Hi All, Can over-aeration and CO2 stripping have an effect on nitrification rates? I'm thinking in term of carbon source for nitrifiers, which I believe are chemolithotrophs... Regards, argfin
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The sludge judge God Member Offline Posts: 649 Wisconsin Gender: Company or Organization: private	Re: pH raise due to increasing aeration? Reply #10 - Apr 20^th, 2012, 12:06pm nitrifiers are autotrophs. They don't use organic carbon as a food source, they use alkalinity. They prefer pH closer to 8 a slight increase doesn't hurt them and may actually help.
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DS

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Re: pH raise due to increasing aeration?
Reply #11 - Apr 20^th, 2012, 1:16pm

Hi Guys,

bicarbonate (HCO3-) indeed stimulates their growth in terms of C-source (like plants do), but they get their energy from the oxidation of ammonium with O2. So adding bicarbonate may be beneficial in some cases.
I am however not sure if stripping of CO2 upon heavy aeration poses a real problem to them? I mean, they are after all slow growers... and kinetics & affinity aspects may play a role in this...

Best regards,

DS

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argfin

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Re: pH raise due to increasing aeration?
Reply #12 - Apr 23^rd, 2012, 1:21am

Hi,

Thanks for the replies...

It's just that I'm sure I read somewhere that carbon from CO2 can be used by nitrifyers? Maybe as part of the carbonate dissociation equilibrium?

Infact I just did a search and Wikipedia had the following:
"Both steps are producing energy to be coupled to ATP synthesis. Nitrifying organisms are chemoautotrophs, and use carbon dioxide as their carbon source for growth. "

Note specifically CO2 is mentioned... Is this correct?

In addition, would the removal of CO2 eventually use up more bicarbonate too? From Le Chatelier's Principle the carbonate equilibrium would move to make more CO2 as it is stripped?

Thanks,
argfin

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