Minimal Organic Loading to a WWTP

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Hi everybody! 

I am ​designing a ​1000 PE WWTP ​for a Sea ​Resort. I ​assumed ​extended ​aeration ​process and ​volumetric ​loading of 0.25 ​kgBOD/m3.d and ​got the needed ​volume of ​aeration basin ​of 240 m3. ​
My question ​is: What is the ​minimal ​volumetric ​loading or F/M ​ratio necessary ​for the process ​to work, i.e. ​what is the ​minimal number ​of people that ​need to be in ​resort ​throughout the ​year in order ​for the process ​to be ​maintained? ​
M&E book ​states that the ​typical design ​values for ​extended ​aeration are 0.​1-0.3 kgBOD/m3.​d. When I apply ​the lowest ​value of 0.1 to ​my 240 m3 basin ​I end up with ​the load from ​400 PE, which ​is quite high, ​because I guess ​the Resort will ​not be 40% full ​in winter ​months. ​
I assume the ​values given in ​M&E are given ​for the highest ​loading. Same ​case in other ​books and ​standards that ​I use, they all ​make recommendations ​for the highest ​loading, and I ​haven't yet ​come across the ​data about the ​lowest possible ​loading needed ​for the biomass ​to survive and ​do its work. ​

I guess the ​best solution ​is to make ​multiple trains ​and shut down ​one of the ​trains in off-​season. ​

Thank you in ​advance for ​your answers! ​

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7 Answers

  1. Dear MIrko,

    Supposing a maximum of 80 m3/d, you can use the same 240 tank with some baffles and our bioreactor that generates and release good microorganism to treat the wastewater and to digest the organic sludge at the same time.

    This is a bioreactor submerged in the tank, and it help to find the equilibrium in both seasons without manipulation of the system.

    You just need turn it on, forget it and  and let the biocleaner do the work.
    The total power is near to 2,5 kw to treat the system all the year in all the seasons.

    You can contact to me to my contact data or by inbox.

    Regards,
     

  3. My experiences with small plants and fluctuating loads has shown best and most consistent process performance with attached growth systems rather than activated sludge, or suspended growth, exactly for this reason of fluctuating F/M ratio, since the operating responsibility usually lies with the resort or hotel that has little skill in applying process control to respond to changing load. Across Africa and the India Ocean Islands, I have had lots of success in applying rotating biological contactors (RBC) as a process that seems to be very resilient to fluctuating F/M ratio due to the nature of the installed process. MBBR should give similar consistent performance. Another key attraction of RBC is the low sludge yield, again reducing the skilled operational input required.

    I will gladly assist if you require additional support, since effluent qualities and utilisation needs to be understood - i hope that at a resort effluent re-use/recycle is being applied.

    Good luck

    Gary

    gary@dikubu.co.za

  4. Thank you all for your answers! A combination of loading of 0.05 kgBOD/m3.d and 2 trains would mean that the WWTP can work with only 10% of its maximum capacity, which is great.

    Thank you once again for your help!

  5. Hello in your post and in the answers made, one realizes that it is not done describing the function of the process of prolonged aeration.

    It is therefore necessary to differentiate between the aeration function and the volume of effleutn to Aerate.

    The more the volume of effluent is therefore and the longer the aeration process must be important. This makes it clear that this aeration process has a real effect on the effluent. 

    What is it? Aeration removes and kills the anaerobic digestion of the medium, making the effluent inert.

    Long before this aeration tank is put in place, the material is fissuraited under the effect of a strong digestion. 

    Conclusion: The prolonged aeration that it is maximum for a large volume or for a small volume of effluent, does not change anything. 

     

  7. In my experience, extended aeration can be applied at lower loadings (0.05 KgBOD/m3/d).   If the load is seasonal, it makes sense to use multiple trains to maintain optimum loading and minimise operational costs.

    1 Comment

    1. F/M is the key parameter for operating any biological treatment. Hence if the F (food as kg/d BOD or COD) drops then also the M (micro-organisms as kg VS in bioreactor) shall be lowered by wasting more biosludge and vice versa.

      The minimum F/M depends largely on the operating temperature and can be very low in winter conditions down to about 0.01 kg BOD/d / kg VS at 5°C.