Water and Wastewater.com Help Forums - Alkalinity & Phosphate

argfin

Full Member

Offline

I love Water and
Wastewater.com

Posts: 145

Company or Organization: None

Alkalinity & Phosphate
Jul 04^th, 2012, 6:23am

Hi All,

I have a couple of questions, one about alkalinity, the other about phosphorus. I have searched already but nothing really answered my question directly, although there was a hint at it in one thread.

I want to understand the different roles of alkalinity and alkaline species, specifically with respect to nitrification.

My first question is:

Does nitrification specifically need carbonate to proceed, or will any alkali capable of mopping up H+ do?

For example, imagine if in theory you had a wastewater with no carbonate in it at all and very high ammonia, but you did have a sufficient caustic dosing system to maintain the pH at say 7.5, would the nitrification still occur, or do you specifically need carbonate for nitrification? Is it possible to have a situation where pH is fine, but carbonate is too low and dissolved CO2 negligable?

My second question is:

Phosphate requirements. If ever I do a search all I get is phosphate removal.

I assume nitrification uses phosphate as well as the heterotrophic stages?

Are there any equations to show the balance or at least give some iindication of its role.

Thanks,
argfin.

Back to top

IP Logged

DS

God Member

Offline

sapere aude

Posts: 1583

Company or Organization: Indept. Freelance Consultant

Re: Alkalinity & Phosphate
Reply #1 - Jul 4^th, 2012, 10:39am

Argfin,

nitrifiers do need bicarbonate to grow on; it is their main C-source, so if carbonate would be completely absent => no growth of nitrifiers... Since their growth rate is much lower compared to heterotrophs, not very much bicarbonate is required for growth.
Regarding the pH depencency of the nitrification reaction; any H+-absorbing species will do, but remember that the most important buffer in wastewater treatment (COD oxidation and CO2 absorption) is the bicarbonate buffer-system.. a good guideline for pH buffer consumption (at about pH = 7) is that 2 Mol H+ is formed for every mol nitrate formed..
Denitrification partially restores this buffer capacity (a rato of one mole per mole nitrate denitrified).

Nitrifiers also require phosphate for their metabolism but because of their low abundance in (most) activated sludges and their low growth rate, not very much (understatement) P is required for these guys..

hope this helps,

DS

Back to top

www.AquaICS.be

IP Logged

argfin Full Member Offline I love Water and Wastewater.com Posts: 145 Company or Organization: None	Re: Alkalinity & Phosphate Reply #2 - Jul 5^th, 2012, 9:21am Hi DS, Yes, that's great! You always come to my rescue! Do you have any rough guidelines for how much PO4 is required for heterotrophic consumption per Kg BOD and per Kg NH3 for nitrification? Or a stoichiometric equation? Thanks, argfin.
Back to top	IP Logged

The sludge judge God Member Offline Posts: 649 Wisconsin Gender: Company or Organization: private	Re: Alkalinity & Phosphate Reply #3 - Jul 5^th, 2012, 10:18am the normal ratio is around 100BOD:5TKN:1Phos taken up as a nutrient by the bacteria.
Back to top	IP Logged

DS

God Member

Offline

sapere aude

Posts: 1583

Company or Organization: Indept. Freelance Consultant

Re: Alkalinity & Phosphate
Reply #4 - Jul 5^th, 2012, 11:08am

Hi,

sludge judge gives a good rough guideline based on BOD ( Sad

). after applying this guideline, check the nutrients in the effluent in case you have to dose them. If I remember well, your influent is quite rich in nutrients, right?

The amount of P required for nitrifiers is much lower compared to the heterotrophic P-requirement (only for normal heterotrophic growth, so excluding bio-P uptake by specific Bio-P removal bacteria like Accumulibacter and the like). If you assume 3% viable Nitrifiers, compared to 60% alive heterotrophs (and the SRT being the same for both bacteria in a CSTR), then the P uptake for nitrifiers is only 5% of the total...
If the N/BOD ratio gets higher, the total heterotrophic p requirement also decreases.
Also; Nutrient requirements in general are less (if expressed per kg COD given) when the Sludge age (SRT) increases since the sludge production decreases.

Back to top

www.AquaICS.be

IP Logged

The sludge judge God Member Offline Posts: 649 Wisconsin Gender: Company or Organization: private	Re: Alkalinity & Phosphate Reply #5 - Jul 5^th, 2012, 11:36am DS explained this well
Back to top	IP Logged

argfin Full Member Offline I love Water and Wastewater.com Posts: 145 Company or Organization: None	Re: Alkalinity & Phosphate Reply #6 - Jul 6^th, 2012, 1:52am Thanks again! I have plenty of P in the system, I'm just interested to know! Regards, argfin.
Back to top	IP Logged

Luci YaBB Newbies Offline Give bugs a chance! Posts: 6 Company or Organization: UL	Re: Alkalinity & Phosphate Reply #7 - Jul 13^th, 2012, 3:09pm what's the compliant requirement of P in your system? argfin wrote on Jul 6^th, 2012, 1:52am: Thanks again! I have plenty of P in the system, I'm just interested to know! Regards, argfin.
Back to top	IP Logged

RoCSmith Junior Member Offline Posts: 68 Ohio Gender: Company or Organization: YSI	Re: Alkalinity & Phosphate Reply #8 - Jul 16^th, 2012, 10:21am argfin, At a pH < 8.3 any alkalinity present will be in the form of bicarbonate in a system open to the atmosphere. RS
Back to top	IP Logged