Recently I have been participating in an online discussion about Food/Microorganism (F/M) targets for a dairy wastewater treatment plant. The engineer wanted to know the target F/M ratio for dairy wastewater. Often I get this question with little supporting information such as: original system design and treatment targets.
When asked about F/M most consultants and engineers open a standard engineering text and give an answer from standard design numbers. I often will give a number from Metccalf & Eddy but indicate that this is just a starting point and influent makeup, temperature, pH, treatment targets, and a big "other factors" can require modifications on the number. For your reference here are a few of the target numbers:
In the dairy case that I first mentioned, I suggested that they look at their current F/M and check SV30, microscopic exam, and oxygen uptake rates to get a full picture of the system's biological state.
The easiest to interpret may be the microscopic exam. Use the following chart to determine how indicator protozoa, floc formation, and F/M relate. Note extended aeration operated at the far right side of the ideal F/M ratio section - this uses a lower F/M and higher mean cell residence time (MCRT) to both reduce solids yield and nutrient (N,P) control in systems with nutrient permits.
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
Click to set custom HTML