Ferric chloride injection point at WWTP

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Hello all,

Does anyone have any experience with ferric chloride injection points to control Total Phosphorus?  

Our current point Is at the headworks, I would like to reconfigure and start injecting at the influent of the aeration basin.  (After AB’s flow goes into MBR system. ) 

any thoughts?  

Thanks!! 

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7 Answers

  2. The best method is to first remove Phosphorus with biological process (aeration and secondary sedimentation) and after to dose Ferric chloride. This process gives the highest efficiency for Phosphorus removal, up to 95 %. Post precipitation will also give additional SS removal, which escape secondary sedimentation

  4. The aeration basin influent is a better location than headworks to inject iron salts.   Peter Naylor is correct about the competing reaction with sulfide formation.  You may be able to implement a cost saving option at this time.  Ferrous chloride is generally much cheaper than ferric chloride.  The oxygen of the aeration basin will oxidize the ferrous (2+) ion to ferric (+3) ion which will then react with phosphate (-3) ion.    Ferrous chloride can be stored and pumped with the same equipment as ferric chloride.  Safety considerations are the same.  

  5. I suggest you remove as much P as possible biologically and then trim with ferric downstream. If you dose ferric upstream at the headworks a significant proportion will react with sulphide and form insoluble iron sulphide, which may block your MBR. Any ferric consumed reacting with sulphide will be also be lost to phosphate removal and cost you more money. With a conventional SBR system I normally achieve 80% phosphate removal biologically.

    3 Comments

    2. I don't have a lot of experience in this area but we took this approach when implementing this in an SBR. The idea was that biological P removal was 'free' and that we didn't want to remove too much P too early on as we could run the risk of the biomass growth being limited by P.

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  7. Dear Fernando,

    Did you consider the chance of limiting the P for the biology? I would introduce it into the effluent stream of the aerated basin, after the internal recirculation (if there's any). 

    Sincerely, 

    László

    2 Comments

    1. Yes.  I have considered this.  Unfortunately, our flow scheme enters two stabilization ponds after headworks and I believe that this is decreasing chemical efficiency and costing a lot more money.  If you think otherwise, please share.  

      I will assess and monitor daily: pH, ferric dose and P conc.