Minimal loading to a WWTP
Minimal loading to a WWTP
(OP)
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.
Thank you in advance for your answers!
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.
Thank you in advance for your answers!





RE: Minimal loading to a WWTP
The other issue is how quickly the load changes. If you were operating at 10% load for 3 months and then went straight to 100% load for a weekend then back to 10% this would also cause issues. Extended aeration is relatively robust though because of the large process volumes.
You have not mentioned anything regarding licence conditions or influent quality but i would suggest that in general terms provided you address the turn down issues then 40% load would be okay with many plants operating at 30% or less. Low load operation has its challenges though.
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
RE: Minimal loading to a WWTP
RE: Minimal loading to a WWTP
Definitely consider modular design with parallel units as bimr suggested.
Get as precise information about winter period as possible and design the smallest unit to the winter loading.