ATP Assay on activated sludge

Most undesirable situations in a wastewater treatment plant (WWTP), e.g., sludge bulking, toxic effects, high operating costs, poor performance, etc. can be prevented in time, by determining the exact quantity and quality of biomass in the biological reactors. The usual practice of estimating biomass concentration through the determination of suspended solids in mixed liquor samples (MLSS) is considered inadequate, because this parameter also includes dead microorganisms and inert solids and, at the same time, does not provide any information on the quality of the living biomass. This limitation may lead to delayed or, even, no diagnosis concerning the biological treatment process, with a subsequent risk of disturbing the performance of a WWTP.

A useful tool in this challenge is the accurate and real-time microbiological testing that can provide critical information on biomass quality and act proactively to address operational risks. ATP (adenosine triphosphate) is the main energy carrier for all life forms: bacteria, algae, plants, animal cells, all contain ATP. Therefore, determining the ATP concentration in an activated sludge sample provides a direct measurement of the living biomass concentration and an evaluation of the biomass health.

ATP is quantified by measuring the light produced through its reaction with the naturally occurring enzyme luciferase using a luminometer. The amount of light produced is directly proportional to the amount of ATP present in the sample. The following chemical equation shows the reaction that takes place for the conversion of ATP in the presence of the enzyme luciferase:

The knowledge of biomass health allows us to organize preventive measures in order to avoid operational disturbances in the treatment process. In addition, it helps us to identify possible toxic effects and take appropriate remedial action in a timely manner.

Parameters that can be quantified by the ATP analysis:

Active biomass via the cellular ATP (cATP) parameter without interferences from dead biomass and inert solids

Percentage of living biomass cells in total suspended solids through the “Active Biomass Ratio (ABR)” index

Biomass health through the “Biomass Stress Index (BSI)”

Detection of sludge bulking problems by determining the flock bulking ATP (fb-ATP)