Why does Organic Load Fluctuate?

[CivilEngineer401]

I usually work on wastewater treatment plants around 1 or 2 MGD and have noticed the BOD5 concentration entering these plants fluctuate significantly from day to day. The influent concentrations can be anywhere from 150 mg/l to 400 mg/l and I do not see a pattern. These systems are mostly residential with no industrial waste. We all know that flows into a plant can double (or more) due to Inflow and Infiltration but why would Organic Loading change from day to day? For Example at one plant:

Tuesday, January 8th 2019 (no rain) recorded 1.45 MGD flow with a BOD5 concentration of 325 mg/l resulting in an organic load of 3,900 pounds
Wednesday, January 9th 2019 (no rain) recorded 1.35 MGD flow with a BOD5 concentration of 169 mg/l resulting in an organic load of 1,900 pounds

Like I said, I see this occurring at multiple plants and not just one but it does not make sense to me. Does anyone know why it would?

 

[ashtree]

Sewerage is very changeable, but we are also creatures of habit.
Some days tend to be wash day or sleep in day or whatever.
Likewise you may get flow from different parts from dvarious pumpstations , so the flow that you get at some point in time will vary as different pumpstations contribute more or less to the flow or the blend. But probably if you tracked flows , times and BOD over years you would find patterns whereby the flow and the BOD at a certain time of the day would normally fall within certain values and it would be rare to be outside that.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[GeoEnvGuy]

From my understanding BOD5 in sewage is generated by the organic content entering the system. So you are asking how can a population have such a variation in the generation of the inputs, the answer is a mixture of daily and holiday diets, weekly food specials/routines, and potentially septic tank disposals into the system.