How hot is too hot?  You’re not the only living thing that thinks the heat is overbearing. If you’re responsible for a biological wastewater treatment system, you may want to take an extra temperature reading or two during the warm season.

Temperature is a critical parameter to monitor for any biological wastewater treatment system.  Like humans and many other living organisms, bacteria in wastewater treatment systems function best within a certain temperature range – typically between 68 and 95 F (20 – 35 C).  The good thing about temperatures at the low end of this range is that bacteria can still function, they just do so much more slowly. However, at the upper end of this spectrum and beyond, bacteria slow down and eventually cease to function at all.  In the world of wastewater treatment, we would call this an upset (and not a minor one).

What are some of the major signs of high temperature-related bacterial stress?

Deflocculation and High Effluent TSS

At elevated temperatures, bacterial floc quality will begin to deteriorate.  In the microscope, you can observe floc that is already formed break apart and dispersed bacteria that are not yet within the floc structure stay dispersed.  On a large scale, deflocculation can be observed as elevated effluent TSS.

High Effluent BOD

At elevated temperatures, bacterial metabolism can become inhibited.  Inhibited metabolism can cause elevated effluent BOD via two different mechanisms: Bacterial metabolism reduction or failure
Elevated effluent TSS – bacteria are organic in nature and contribute oxygen demand to the BOD test

Filament Die-Off

Filaments aren’t immune to elevated temperatures.  If filaments are a mainstay in your treatment system, you’ll see them begin to deteriorate, die off, and disappear.  These dead filaments can also contribute to effluent TSS.

Low Dissolved Oxygen

At elevated temperatures, oxygen is less soluble in water.  Couple this with high BOD and At elevated temperatures, bacterial floc quality will begin to deteriorate.

High Dissolved Oxygen

That’s right.  Low or high DO can signify a high-temperature-related issue in your wastewater treatment system.  High DO observed at high temperatures can indicate a lack of oxygen uptake, which could be due to low BOD or inhibited bacteria.

Temperature is a difficult parameter to control and remediate within wastewater treatment systems.  However, with a good monitoring program in place, issues related to elevated temperatures can be identified and controlled.