Wastewater MLSS or MLVSS is often call the “microbes” or amount of working biomass in a treatment system. However, MLVSS is just the weight of volatile solids in the system rather than any direct measure of living/working biomass. MLVSS consists of living and dead microbes, insoluble organics, extracellular polymers (EPS), and other byproducts of microbial metabolism. So how do you get direct measures of microbial activity?
Oxygen Uptake Rate
OUR tests measures biomass respiration rates with results expressed in mg O2/L/hr. In aerobic systems, OUR gives a measure of metabolic activity which helps estimate both organic loadings and microbial activity. The test takes less than 10 minutes and doesn’t require any unique equipment other than a DO meter and BOD bottle. OUR procedure – https://asterbio.com/oxygen-uptake-rate-procedure/
ATP – Free and Total
Organisms store energy in the form of Adenosine Triphosphate ATP. Measuring ATP in wastewater gives you an idea of how much energy is generated by metabolic activity. To make measurement more useful, we look at Free ATP which is water phase ATP released by dividing or lysing cells versus Total ATP which is used to calculate Cellular ATP. The Cellular ATP is the ATP found inside living cells.
Total ATP = Free ATP + Cellular ATP
The ratio of Free to Cellular ATP gives information on cell division rates which helps determine where your biomass is on the growth curve.