Measuring in situ bacterial specific growth rates and population dynamics in wastewater

Reliable design and operation of biological wastewater treatment systems demands robust modelling of the degradation processes. However, methods to directly measure key bacterial growth parameters have not been available to the wastewater industry. Here, we directly measure bacterial specific growth rates without changing the treatment environment. Bacterial growth (with the thymidine assay) and biomass (by direct counts) measurements were used to compare the dynamics of the microbial community in the different compartments of an activated sludge process. The aerobic compartment specific growth rate μ was 0.5 d−1. In this work, we explain the concept of the thymidine growth assay, the traps for the novice and how to apply the method to biological nutrient removal processes. These methods now allow us to distinguish bacterial growth from metabolic activity and observe how the cell allocates its resources between the two. This represents the first application of a very powerful tool to directly measure population dynamics and kinetics of bacteria in wastewater treatment processes.