W. Edwards Demming
Each control test is linked to effluent quality, but because biological wastewater treatment is dealing with living organisms can have more variation and conflicting (at least on the surface) results.
For example, the normal first indication of a toxic shock to the system is an increase in effluent turbidity and deflocculation causing solids carryover in the secondary clarifier. If operating one of the newer membrane systems (MBR), you don't get this key indicator of effluent TSS carryover. So what should operators do to close this gap in information? In the case of MBR systems, operators should pay closer attention to turbidity in the SV30 supernatant and combined with a more through exam of the bacterial floc - with special attention paid to free bacteria and floc density. This means that we look beyond counting protozoa or metazoa and develop a process for looking at the floc on a daily basis.
Each system has some variation from the ideal wastewater unit used in training and engineering manuals. For operations, we need break treatment down according to simple monitoring tests that can be related by correlation or regression analysis to effluent quality. The ideal is too have a model that can predict effluent quality by daily tests done in the unit. We know BOD is not going to be in the model, so we often substitute COD, TOC or filtered TOC.
While I went through this topic quickly in this post, I am going to break out more information on each test and how what is observed can relate to microbial health over the next several posts. With tools to related test results to microbial health, you can construct the model that predicts your effluent quality.