Persistence and competition of denitrifying bacteria in a dual-strain biofilm subjected to a natural wastewater flora
Bioaugmentation for enhanced wastewater treatment performance depends on survival, maintained activity and retention of the inoculated microorganisms in the reactor. Biofilms could be suitable mediators of bioaugmentation due to the retention of the immobilized cells and the protection offered by the biofilm matrix. The overall objective of this study was to investigate the potential of biofilm-mediated bioaugmentation for enhanced denitrification in the presence of a natural wastewater flora. In order to select a suitable inoculum, single and mixed strain biofilms were investigated in sterile wastewater with respect to biofilm formation, denitrification activity and bacterial interactions. The dual strain biofilm formed by the denitrifying organisms Comamonas denitrificans and Brachymonas denitrificans displayed good biofilm formation and high denitrification activity and was thus further investigated. When exposed to a natural wastewater flora, the relative number of C. denitrificans and B. denitrificans cells in the biofilm decreased over time until it was stabilized at just below 20 % of the total population after 4 weeks. The selected strains were thereby shown to persist in the competition with natural wastewater flora, highlighting the potential of biofilm mediated bioaugmentation.