Aerobic Digester Water & Low DO Issues

In the summer, when the water is warm, it’s natural to have low dissolved oxygen.  For every 5 degrees F warmer, the bacteria activity doubles.  When the bacterial activity rises, so does the oxygen demand. When this happens the plants can get low DO filaments that cause sludge bulking and poor settling.

Aerobic digesters can add to that problem.  When water from a digester, aka “funny water”, is brought back up to the head works, it can cause slight to major upsets.  The water and material in digesters are strong in ammonia and fatty acids.  When this water is brought back to the front, it sucks out the DO. Low D.O. can lead to filaments like Type 021N and excess Zoogloea. This typically will happen in the heat of summer. In the winter funny water can cause effluent ammonia levels to rise. It is easily fixed with the addition of VitaStim Dynamic Duo and VitaStim Rebuild.

Low DO Filament Type 021N

Excess Zoogloea causes bulking

The digester water contains organic matter and chemistry that has been broken down multiple of times. When this is given this food to activated sludge, it’s going to upset them.  For example, when you give a child an ice cream cone, he will get a small sugar rush 20 minutes later, but if you give a child the equivalent amount of straight sugar, he will get an instant sugar rush.  This is a similar situation, but in this case your mixed liquor cannot digest the broken down contaminants and typically die out.  This causes poor settling and ammonia spikes, as bacteria are roughly 10% ammonia.

How to combat low DO and aerobic digester funny water:

1. Treat the lift stations!  Treating lift stations helps catch and degrade materials that lowers the DO
2. Lower the amount of solids in the system.   The more bacteria in this system, the higher the oxygen demand, and higher the oxygen demand, the lower the DO. You can add VitaStim Rebuild to help the bacteria thrive.
3. Temporarily raise the DO and stimulate the bacteria with OxyPaks XL.  Ideally you would apply this every day and double it when  the digester water is returned.  This will help nurture the bacteria and raise the DO.