A theory of the lifecycle of bacteria
Aims: The principal objective of this study was to investigate viability kinetics in aerobic AS (Activated Sludge).
Methods and Results: A kinetic model was developed in order to predict viable cells, non-degraded dead cells and inert VSS (Volatile Suspended Solids) in a reactor – usually conventional models only predict active biomass and inert VSS. The following processes were considered in the derivation of the model: the death rate of viable cells, and the hydrolysis rate of dead cells. Equations development led to a decay coefficient (b) – previously considered constant – function of death rate, hydrolysis rate and solid retention time. Cell growth on soluble COD (Chemical Oxygen Demand) resulting from lysis/hydrolysis has been introduced in the model. Simulation methods of viability in AS, and OUR (Oxygen Uptake Rate) tests of AS in batch under starvation were developed in order to validate the approach, and to estimate model parameters. This result has been refined introducing the lysis process.
Conclusions: The results of this study indicate that the proposed models are consistent with experimental data, and provide strong evidence that there are regulatory processes controlling bacterial death and lysis.
Significance and Impact of the Study: Finally, the approach of this study provides some insights for the variability of AS decay coefficients obtained previously; and offers a better comprehension of viability processes in biological reactors.