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Wastewater disinfection

  • 1.  Wastewater disinfection

    SENIOR MEMBER
    Posted 08-08-2019 00:59
    Hi there,

    Just wanted to understand prechlorination and its impacts on the downstream equipment. Chlorine is added either in the flash mixer, i.e. prechlorination or after the filtration, i.e. postchlorination. However, I found in one of the facilities chlorination is done in a tank prior to activated carbon filter. The facility could not explain why chlorination is done there and not at the usual places.

    Could anyone please help me understand the benefits of chlorination just prior to ACF? Also, why it is not usually practiced.
    Also, would there be any risks/impacts especially on the adsorption capacity of the activated charcoal in ACF.

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    Ankush Jain

    ITC Limited
    India
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  • 2.  RE: Wastewater disinfection

    SENIOR MEMBER
    Posted 08-09-2019 03:31
    We design and sometimes construct industrial wastewater treatment plants. A semiconductor client with wastewater from electroplating had a problem meeting the statutory BOD limit of 50 mg/l (Philippine effluent standard for discharge into Class C or fisheries water bodies). Their effluent BOD ranged from 60 to 80 mg/l which is unusual for semiconductor electroplating wastewater which is typically 30 mg/l or less. Aerobic biological treatment (such as activated sludge) would have been very effective but would also be not cost-effective. We conducted treatability tests which showed that pre-chlorination followed by activated carbon filtration was effective and inexpensive in lowering the BOD to less than 50 mg/l (less than 20 mg/l was attainable, depending on chlorine dosage but would have used more chemicals so we targeted 30 mg/l).
    After a year of operation, it was still not necessary to replace the activated carbon media; hence, we suspect that the activated carbon functioned more like a catalyst than an adsorbent.

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    Manuel Gloria PE
    Principal Consultant
    Aquatreat Environmental Systems Inc
    Mandaluyong
    Philippines
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  • 3.  RE: Wastewater disinfection

    SENIOR MEMBER
    Posted 08-09-2019 04:32
    That is interesting!
    Though one year is still less, it is substantial enough to have signs of visible degradation. But do you think is it because there is no free chlorine (as BOD level is still 50 mg/l) in the stream entering the ACF and hence, micro-porous sites of activated carbon is not impacted.

    In my case, free chlorine is detected after the ACF.

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    Ankush Jain


    India
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  • 4.  RE: Wastewater disinfection

    SENIOR MEMBER
    Posted 08-09-2019 06:16
    No, we did not check for residual or free chlorine after the ACF.  It (residual or free chlorine) was not required by the regulations at that time nor even now, except in special circumstances.

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    Manuel Gloria PE
    Principal Consultant
    Aquatreat Environmental Systems Inc
    Mandaluyong
    Philippines
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