Analysis and Comparison of the Bacterial Community in Membrane Bioreactors and Other Treatment Systems

Polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analysis and DNA sequencing was conducted to compare the bacterial communities that thrive in various wastewater treatment systems treating municipal wastewater. This study compares the microbial community structure from bench, pilot, and full-scale membrane bioreactors (MBRs), conventional activated sludge (CAS), and trickling filter solids-contact (TF/SC) systems. DGGE fingerprints obtained were examined by GelCompar II cluster analysis for community similarity. Bench and pilot-scale MBRs that treated the same wastewater had the highest similarity (73%) among all sites. Samples from a full-scale MBR treating a similar wastewater yielded a lower but still fairly high level of similarity (44%) to the bench and pilot-scale MBRs. Bacteria populations in CAS systems were more similar to each other (64%) than to the TF/SC systems (43%). The similarity between the MBR grouping and CAS plus TF/ SC grouping was in the significant low level (less than 5%) indicating that the dominant species in MBRs are very different than other forms of activated sludge treatment. Seventy-three percent of the excised DGGE bands were successfully identified by DNA sequencing which found four bacterial species that were present in more than one biological wastewater treatment system: uncultured Paracoccus sp. clone 3-3, uncultured Bacterium clone SB3-6, uncultured Clostridium sp., and uncultured Klebsiella sp. The results suggest that microbial community structure found in bench and pilot-scale MBRs may not be a good model for studying performance of full-scale MBRs due to non-identical operational conditions and internal hydrodynamic regime.