Effect of co-substrate concentration on dual-species population distribution, permeability reduction and trichloroethylene (TCE) biodegradation in porous media

Dual-species microbial interactions have been extensively reported for batch and continuous culture environments but very little research has been performed on dual-species interaction in a biofilm on the surface of a well-mixed reactor and even less research has been performed on porous media biofilms. The fundamental motive for this research was to gain a better understanding of the interaction between two microbial species when grown together in an engineered biofilm. Two organisms were combined together in planktonic, rotating disk, and porous media reactors to determine which variables controlled population distribution. The feasibility of using planktonic and biofilm growth kinetic data to predict dual-species porous media interactions was addressed. In addition, the ability to control the activities of each organism in a dual-species porous media environment was examined. The two bacterial species used in this research were Burkholderia cepacia PR1-pTOM_31c, an aerobic organism capable of constitutively mineralizing trichloroethylene (TCE), and Klebsiella oxytoca, a highly mucoid, facultative organism capable of reducing porous media permeability.; This research demonstrated the importance of growth rate and substrate concentration to predict dual-species interactions in batch, rotating disk and porous media reactors. The substrate concentrations used were different dilutions of LBG media resulting in dissolved organic carbon (DOC) concentrations of 30, 70 and 700 mg/L. In batch reactors, planktonic growth rates predicted the dual-species planktonic population distribution, with the faster growing organism (K. oxytoca) “outcompeting” the slower growing organism (B. cepacia). In the rotating disk and porous media reactors, however, biofilm growth rates did not correlate with the dual-species biofilm population distribution. The biofilm population distribution did correlate with substrate concentration, with B. cepacia having a greater dual-species population density than K. oxytoca at a low (30 mg/L DOC) substrate concentration and K. oxytoca having a greater dual-species population density at a high (700 mg/L DOC) substrate concentration. In addition, an increase in substrate concentration resulted in a decrease in TCE degradation and an increase in permeability reduction. This research demonstrated the effectiveness of using substrate concentration to control population density, TCE degradation and permeability reduction in a dual-species porous media bioreactor.