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| | | Forum Newbie
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| 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 ? |
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Supreme Being
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| | Where are you applying it? Primaries, aeration basin, secondaries, or tertiaries? What is your P limit? |
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| | | Forum Newbie
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| | 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
Andy |
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| | | Supreme Being
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| | 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 |
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| | | Supreme Being
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| | 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 |
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Junior Member
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| | 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
ttfn |
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| | Thanks much for the input! Andy
Andy |
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| | 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.
Andy |
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| | | Supreme Being
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| | 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 |
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| 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.
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