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belonged to the order Burkholderiales of
-Proteobacteria,afewtoComamonadaceae,but
the majority to an undescribed family, and the related sequences belonged mainly to
uncultured bacteria. Among the less common
b
-Proteobacteria the genus Sphingo-
monas and the genera Afipia, Bosea,orBradyrhizobium of the Bradyrhizobiaceae family
were detected. The majority of cultured bacteria persisting in the BAC biofilter were
Burkholderiales, which according to ecological information are efficient in the miner-
alization of dissolved organic matter in BAC.
Other researchers have shown by phylogenetic analysis that Escherichia coli,
Shigella sp., E. fergusonii and Firmicutes bacteria predominated in the BAC reactors
that were fed with the effluent of a pilot-scale sand filter [90].
The effect of backwashing on the biofilm community was studied by means of
bacterial cell enumeration and terminal-restriction fragment length polymorph-
ism (T-RFLP) fingerprinting analysis of bacterial and eukaryotic ribosomal RNA
genes (rDNA) [140]. The BAC samples were taken from a plant employing coa-
gulation sedimentation, rapid sand filtration, ozonation, BAC treatment, chlor-
ination, and secondary rapid sand filtration. Additional chlorination is conducted
before coagulation (prechlorination) or after the secondary sand filtration (post-
chlorination), depending on the situation. The enumeration of bacterial cells
attached to the BAC revealed that 36% of the bacterial cells were lost after back-
washing. The T-RFLP analysis of bacterial and eukaryotic communities associated
with the BAC demonstrated that the relative abundances of some terminal-
restriction fragments (T-RFs) changed significantly after backwashing.
Using Polymerase Chain Reaction (PCR), a gene involved in microcystin
degradation, the mlrA gene, was detected in sand biofilters, providing supporting
evidence that the primary removal mechanism was biodegradation [85].
a
9.9.4.2
Nitrifying Biomass and Activity in BAC Filters
Although in BAC filters much attention is paid to heterotrophs, there is still a lack
of information on nitrifiers. Nitrifiers have mostly been investigated in biofilters
with nonadsorbing media. Moreover, the amount of nitrifying biomass has rarely
been estimated. A method developed by Kihn and co-workers aims at estimation of
fixed nitrifying biomass by using potential nitrifying activity measurement [141].
In a recent study, the occurrence and diversity of ammonia oxidizing bacteria
were investigated using 16S rDNA and amoA gene-based molecular techniques in
BAC filters in which organic carbon removal and nitrification were taking place
concurrently [6, 60]. Filters were fed with both raw and preozonated water. Details
about these filters can be found in the Examples 9.1 and 9.2.
In all BAC filters, ammonia was almost completely removed by nitrification, as
seen from Figure 9.8. Most of ammonia removal took place in the upper part of the
filters. This finding coincided with the results of real-time PCR analysis, which
showed that the amoA gene numbers were high at the top (28.7%) and decreased
toward the bottom (2.1%).
Ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) in bio-
filters were most closely related to Nitrosomonas sp. and Nitrospira sp. as determined
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