2,4-D-degrading bacterial consortium. Isolation, kinetic characterization in batch and continuous culture and application for bioaugmenting an activated sludge microbial community

Soil samples collected from the central region of Mexico were used as a source of microorganisms able to degrade 2,4-dichlorophenoxyacetic acid. These microorganisms were enriched by successive transfer of microbial cells batch cultivated in basal medium to which 2,4-D was added as the sole carbon and energy source. Five bacterial strains able to grow on 2,4-D were isolated and identified by sequencing fragments of their bacterial 16S rDNA. Those were Comamonas sp., Pseudomonas putida, Acinetobacter sp, Acinetobacter lwoffii and Klebsiella oxytoca. The effect of herbicide concentration on consortium's growth and 2,4-D degradation kinetics was studied in batch culture. By differential analysis of cell growth and 2,4-D depletion curves, the influence of 2,4-D concentration on instantaneous cell growth yield was quantified. Low growth yields in the culture's early phase could be attributed to metabolic uncoupling caused by the herbicide. In chemostat culture, 2,4-D removal efficiency was higher than 97% and global cell growth yields were lesser than those obtained in batch. Finally, in order to prevent a toxic shock provoked by the herbicide present in synthetic wastewater, the bacterial consortium was inoculated in a bench-scale wastewater treatment plant (WTP). However, the system was only temporally protected from an upset caused by 2,4-D. Hence, it was designed a system for continuous bacterial inoculation, allowing an undisturbed operation of the bench scale WTP.