The effectiveness of bioaugmentation in nitrifying systems stressed by a washout condition and cold temperature

Bioaugmentation consists of adding selected strains of microorganisms with known capabilities to a biological process to improve performance. In this study, laboratory-scale completely stirred tank reactors were bioaugmented with nitrifying bacteria while operated under high-stress conditions for the nitrifiers: a 2-day solids retention time (SRT) at 22 degrees C or a 5-day SRT at 4 degrees C. Intensive sampling was carried out to document the effects of the bioaugmentation. To quantitatively interpret the effects of biomass addition on process performance, mathematical modeling was carried out. Experimental and modeling results indicate that the maximum effect of a one-time bioaugmentation depend on the dose and decays as bioaugmented nitrifiers are washed out. Daily maintenance dosing results in long-term good performance, provided that the dose is large enough. For severe stress, almost all of the biomass in the system must be added by bioaugmentation.