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RE: Chemical Phosphorus removal

cochise55 — Fri, 01 Feb 2008 01:58:08 GMT

hi all,
i'm new to this forum but have had experience using PAC (polyaluminate chloride) for phosphorus removal with small wastewater plant in southern rockies. have used it for over 6 years and feed it into our first (of five) basin(s) which has been converted to an anoxic basin with a submersible mixer. our influent is introduced at the front of the 1st basin along with our RAS from our clarifiers, and the selector return from our 4th basin. we drip the PAC into the RAS and INF zone and achieve < 0.1 mg/l consistently in our effluent. it is a bit more costly than ferric but not a pH depressant, most permits are 6-9 and most PAC has pH over 6.5 we feed soda ash to our first basin as alkalinity boost for nitrogen removal. a simple jar test can determine dosing rates.
good luck

RE: Chemical Phosphorus removal

01780898 — Thu, 24 Jan 2008 07:59:14 GMT

You can expect a 35% increase in sludge production if you are adding the optimum dose of iron.

Regards

Grant H , Australia

RE: Chemical Phosphorus removal

Wiff P — Fri, 04 Jan 2008 12:29:11 GMT

Andy, just picking up on discussion and would agree with last comment that sodium aluminate, which add's alkalinity, can be very useful if pH depression is a problem for you (but will likely be more expensive than ferric alone). To my experience ferric depresses pH the most, alum second most, ferrous third most (only works for P removal if aerated to ferric in the aeration tanks or aerated grit chamber), and then polyaluminum chloride (PAC). There's your range of typical P removing chemicals.

Assume your influent P levels are not up in summer (not mentioned to date) and that you don't run higher TSS in summer (as P in TSS will add to total P in effluent of course). To my experience most plants do better in the summer not worse.

Another thing you can try if your effluent limit is very low (say 0.3 mg/l or less) is dual point addition with one metal salt added at the aerated grit chamber ahead of primary treatment (not sure from your description if you have primary sed) followed by second smaller dosage to mixed liquor ahead of secondary. Or if you don't have primary tanks, since it appears you have filters you can add ferric as you're doing, possibly augmented by polymer, or substituing PAC for ferric which has elements of both metal salt and polymer coagulant properties, then if needed add a small PAC dose ahead of filters for additional reduction. At the end of the day combination of effectiveness and cost by trial and error will tell you what's best.

Once again if you haver a very low standard looking at where you're missing target- effluent soluble P or total P, will help guide you in best corrective action ie. mix of chemicals and/strategies to get to you to target P level at the end of the day. Chemical vendors may help you with some testing and contacting them for help is always a good idea.

Wiff Peterson

RE: Chemical Phosphorus removal

John Sansalone — Mon, 31 Dec 2007 10:36:00 GMT

In areas with soft water, both ferric and alum have a tendency to drop the pH to levels that can cause other problems. They basically chew up the alkalinity pretty much. If you have to then nitrify, this can be a problem, and you may have to add another chemical to suceed. Some of the operators I know have gone to sodium aluminate, which is expensive, but actually adds alkalinity to the system. Alldepends upon your effluent limits, background characteristics of the water, and relative costs of chemicals in your area.

RE: Chemical Phosphorus removal

John Walton — Sat, 29 Dec 2007 14:26:55 GMT

Given the seasonality of your observation (and my current research), I suspect that what you’re seeing is a background demand (from e.g., sulfide) that reduces ferric to ferrous. Per Snoeyink & Jenkins, the respective solubility products for FeS, Fe3(PO4)2, and FePO4 are 17.3, 17.9, and 33. Depending on the influent sulfide levels, you may end up with FeS or Fe2+. Either way, PO4 removal will suffer.

To confirm, test your influent for Total Sulfide and (after FeCl3 addition) for Total Iron and Ferrous Iron. If you find that much of the iron is ferrous, then you might improve the situation somewhat by adding your FeCl3 before the aerated grit basins - to catalytically air oxidize the sulfide. However, this may just remove the sulfide and leave mostly ferrous. If your influent sulfide levels are relatively low (<1 mg/L), then perhaps you can try adding only a portion of the FeCl3 to the influent and save the rest until after the sulfide is removed. Otherwise, you’ll probably find it cheaper to add an oxidant such as H2O2 15-30 minutes before adding FeCl3. The key measure here is testing for Total Iron and Ferrous Iron after the FeCl3 is added. Regards, John.

RE: Chemical Phosphorus removal

TerryF — Thu, 27 Dec 2007 19:44:07 GMT

Andy,

There will be significant sludge increases perhaps as much as 75% increase but it will depend on dose rates and the make up of your wastewater and your plant operating parameters. I would think that a 50% increase would be a reasonable starting point for planning.

pH will be lowered and is once again dose dependent. At the dose rates typically used for P removal (about 50mg/l) this will not be a major factor unless your pH is already fairly low or you have low levels of buffering alkalinity(unusual in wastewater). Ferric works best for P removal at around 6.8 pH .

Regards

TerryF

RE: Chemical Phosphorus removal

67239 — Thu, 27 Dec 2007 15:25:31 GMT

From my research, it appears that the use of ferric chloride will have a negative affect on the pH. Have your found this to be true? Trying to plan for the possibilities.

The ferric is also supposed to increase sludge production, can we expect a significant increase in production or minor? (rough percentages 5% 20% 50%??) The existing plant has good sludge handling, but it can't handle a significant amount more than what it already produces.

RE: Chemical Phosphorus removal

67239 — Thu, 27 Dec 2007 15:09:06 GMT

Thanks much for the input!

Andy

RE: Chemical Phosphorus removal

rocsmith — Thu, 27 Dec 2007 14:04:57 GMT

The conditions required for P release are very low DO and nitrates and ample supply of readily biodegradable carbon, e.g. acetate. I wouldn't be surprised if there is more rbCOD in the influent in the summer due to biological activity in the sewer.

Additional P may be released from recycle streams in warmer temperatures and may be overlooked if your influent sampling point is upstream from the point where recycle is returned.

roc

RE: Chemical Phosphorus removal

TerryF — Thu, 27 Dec 2007 02:44:38 GMT

Andy,

Just to clarify my last post. Dosing into the aeration should give the most P removal for a given amount of Ferric dosed. That may not mean that it is absolutely the best spot to achieve your effluent limit.

Regards

TerryF

RE: Chemical Phosphorus removal

TerryF — Thu, 27 Dec 2007 02:41:30 GMT

Andy,

Ferric theoretically works best for P removal in the presence of oxygen. That would mean it would be best for it to be dosed into the splitter prior to the aeration.

Regards

TerryF

RE: Chemical Phosphorus removal

67239 — Wed, 26 Dec 2007 16:35:31 GMT

Rob,

Where would you recommend the Ferric Chloride be added at?

Simple 40kgpd aeration plant... trash trap -> AFE -> Splitter -> Aeration chamber -> Settling -> Splitter -> fixed media clarifier -> Sand Filter -> Chlorination/Dechlorination -> Discharge

RE: Chemical Phosphorus removal

Rob Baur — Wed, 21 Jun 2006 10:43:30 GMT

Where are you applying it? Primaries, aeration basin, secondaries, or tertiaries? What is your P limit?

Chemical Phosphorus removal

dguell — Wed, 21 Jun 2006 08:42:59 GMT

Hi

we remove phosphorus with ferric cloride. In general there are no problem whith it and we remove almost all P dosing 50-80 ppm of comercial product (40%).
In summer we have to increase the dose to remove the same concentration. Do you know why ? Is it possible that if there are any anaerobic zone could increase Phosphorus in the water ?