Microbial Community Changes Do Not Change Biochemical Degradation of 2,4,6-Trichlorophenol in a Fluidized-Bed Reactor

摘要

A fluidized-bed bioreactor (FBBR) was operated for more than 1000 days to remove 2,4,6-Trichlorophenol (TCP) and phenol (Phe) from a synthetic wastewater, containing different concentrations of TCP and Phe and using different oxygen flowrates (0.0 or methanogenic M, and 2.13 NL/L.d) also named partially-aerated methanogenic M-A). The mesophilic lab scale FBBR consisted of a glass column loaded with 1 mm diameter granular activated carbon colonized by an anaerobic consortium. Sucrose (lg COD /L) was used as cosubstrate in all conditions. The hydraulic residence time was kept constant at 1 day. All conditions showed similar TCP and Phe removals (99.9~+%); nevertheless, in methanogenic conditions, accumulation of 4-chlorophenol (4CP) up to 16mg/L and phenol up to 4mg/L was observed. When oxygen was added, intermediates decreased and eventually complete removal was achieved. Specific methanogenic of bioparticles suggested a significant tolerance of the methanogenic archaea to oxygen exposure for nearly 500 days. Oxygen supply seemed to stimulate the degradation of less substituted chlorophenols.The microbial community harbored on bioparticles of the FBBR was followed using 16S rDNA-PCR-DGGE. The last sample of each condition was further analyzed by DGGE band sequencing and comparing the sequences reported in the international databases. Under M conditions, the microbial community remained relatively stable in spite of the accumulation of 4-CP; this fact was supported by the use of different similarity and diversity indices. In general, results indicate a greater stability of biofilms in our FBBR than that of biomass in different bioreactors from literature, both suspended and attached growth. Sequencing analysis of isolated clones indicated the presence of bacteria of the genus Propionibacterium, Dehalobacter, Methanosaeta, Methano-bacterium and Syntrophobacter. Under M-A conditions, the bacterial community showed great changes, likely due to the change in environmental conditions, although the removal of 2,4,6-Trichlorophenol was as high as that in methanogenic conditions. Microorganisms close related to genus Mycobacterium, Microcella, Syntrophobacter, Cellulo-monas, Dehalobacter, Beutenbergia, and Methanosaeta were detected in M-A conditions. Other identified microorganisms were similar to uncultured bacteria. The detection of Syntrophobacter, Methanosaeta, and Dehalobacter, strongly suggests the coexistance of aerobic and anaerobic microniches inside the bioparticles of the FBBR. Also, in spite of a great variation of bioreactor microbial community during M-A operation, the bioreactor could show a stable performance in relation to removals of TCP and intermediate chlorophenols.