If you have a biological wastewater treatment facility, you are running a "Bug Factory”.
Do you have good bugs or bad bugs? Based on the condition of the plant, certain types of condition will promote different microbiology. Change the environmental conditions and you change the quality of the bacteria in your system.
Learning how to interpret what type of bacteria you have in your system, and how to correlate that to lab testing and plant operations is key to running a smooth system.