Lag Phase in Wastewater Systems

Lag phase is where the biomass grows slowly with low respiration rates as they adjust to new environmental conditions or influent makeup. While we often think of this as an individual organisms that turns on or off various biochemical pathways, it is more often a general shift in microbial population makeup. Adding new waste streams, operating at different temperatures, D.O., or pH can be similar to starting up a system. The more change from existing operations, the greater the shift. How fast will a system return to stable or steady-state condition? It all depends on the changes and waste type.

Can the lag phase time be reduced? Yes. You can truck in sludge from a compatible plant with the same waste or in many cases it is easier to inoculate with a bioaugmentation product suited to the waste/system. By adding adapted cultures to the existing microbes, the adjustment time can be significantly reduced which can reduce holding back influent, adding extra polymers/antifoams, or having effluent permit issues.

Can you predict if adjustment will be an issue? Once again yes. You can do bench testing with oxygen uptake rates and various toxicity testing to determine if the new waste will be an issue. I have discussed both heterotrophic and nitrifier toxicity testing in previous posts.