Microbial community dynamics in replicate membrane bioreactors -- Natural reproducible fluctuations and the effect of toxins

Membrane bioreactors (MBRs) were used to examine microbial community dynamics within four replicates and in the presence and absence of the toxin 3-chloroaniline (3-CA). Three bench-scale studies were conducted to: (1) explore MBR reproducibility, (2) to determine the effects of 3-CA, and (3) to promote 3-CA biodegradation through bioaugmentation.;In the first study, no statistical difference was inferred for water quality among the 4 MBRs (COD load=400 mg l-1d-1). The 16S rRNA genes undergo natural reproducible fluctuations, whereas the amoA functional genes were well buffered against any discernable fluctuations or microbial shift(s).;The second study used two MBRs as controls, while the other two MBRs received treatment of 3-CA. In comparison with the controls, process performance was significantly disrupted by 3-CA addition. T-RFLP 16S rRNA results suggest no significant difference within either control or treatment duplicates (p-value>>0.12). However, one of the control MBRs was not significantly different from the other control or treatment MBRs (p-value>>0.12). The amoA functional genes were buffered against any discernable effect from 3-CA (p-value>>0.86). Besides the multivariate statistical analysis, a theoretical ecological model was employed that was in agreement with our T-RFLP statistical findings for both primer targets.;In the third study, all four MBRs were bioaugmented with Pseudomonas putida UWC3 (pWDL7::rfp) to remove 3-CA. The donor strain/plasmid was maintained throughout the study. The process performance is in agreement with the second study, where little or no 3-CA removal occurred. The T-RFLP 16S rRNA genes revealed a significant difference between the Control and Treatment MBRs (p-value=0.00). The amoA functional gene T-RFLP results were comparable to the first two studies with no significant disparity amongst MBRs (p-value>>0.21). The theoretical model employed was not in complete agreement with the multivariate statistical analysis.;The study illustrates that microbial communities evolve over time within MBRs according to controllable operational parameters, an outcome that may be useful in the future optimization of wastewater treatment processes. The findings emphasize the importance of acclimation and replicates during wastewater reactor experiments. Furthermore, the integration of a theoretical microbial ecology approach along with multivariate statistical analysis normalizes the results for comparative purposes among research groups.