How do you estimate bacterial activity in a wastewater system? This is a question, we often ask and a number of methods have been used. I figured a list of common monitoring methods could be useful.
- Respiration Rate (Oxygen Uptake Rate)
This can be complex using respirometer equipment or simple using a BOD bottle/DO probe on the benchtop. Here you use oxygen consumption as a measurement of microbial activity. - Plate Counts
Using various plate count media, labs can evaluate numbers of microbes in wastewater plants. Most often used for coliforms, it can also be used for heterotrophic and specific organisms using selective media. Problems with plate counts include the number of organisms that don't grow on plates, plate development time, and expense/labor required to do pate counts. - ATP
Microbes store energy as ATP. Using a luminometer and various luciferase procedures, you can determine free ATP and cellular (bound) ATP. The more ATP present the more light produced in the reaction. A quick test, ATP can be used as a proxy for total plate count and a measure of non-specific microbial activity. - Flow Cytometry
Requring specialized equipment, flow cytometry uses fluorescent dyes and various techniques to quantify individual cells in the sample. Flow cytometry allows for evaluation of cell viability. - qPCR (molecular testing)
qPCR or real-time PCR is a rapid test method for quantifying DNA present in samples. As dead cellular DNA is rapidly degraded in wastewater, PCR favors viable cells. While total bacteria qPCR tests are similar to rich media plates counts in looking at all bacteria present. qPCR can be used to evaluate key organisms. For example, qPCR can look at specific DNA sequences such as those for nitrifiers, filaments, nocardia, or any other group of interest. qPCR is a relatively quick test (hours versus days) and is highly accurate.
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