Chapter II
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Chapter II
Nitrifying Bacteria
in Various Types
Biofilms and an Effective Method for
Tailoring of Nitrifying Biofilm
SUMMARY
The microbial ecology of nitrifying bacteria in various types of wastewater treatment
processes and the dynamic response of the microbial ecology in biofilms were investigated
using fluorescence in situ hybridization (FISH) with 16S rRNA-targeted oligonucleotide
probes. Nitrifying bacteria were found to exhibit various organizational forms under
different conditions of substrate composition and concentration. Ammonia-oxidizing
bacteria were dominant in ammonia-rich inorganic wastewater, while heterotrophic
bacteria and ammonia-oxidizing bacteria were localized at different positions in the
biofilm in organic wastewater. The dynamics of the microbial ecology in the biofilm with
regard to the spatial distribution of ammonia-oxidizing bacteria and heterotrophic
bacteria caused by a gradual change in substrate composition was successfully monitored
by FISH analysis.
Microbial Ecology and Tailoring Method of Nitrifying Biofilm
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2.1 INTRODUCTION
Biological removal of nitrogen from wastewater involves nitrification of ammonia to
nitrite and nitrate followed by denitrification of nitrite and nitrate to nitrogen gas which is
released into the atmosphere. Nitrification is carried out by two phylogenetically unrelated
groups of autotrophic bacteria. First, oxidation of ammonia to nitrite is carried out by
ammonia-oxidizing bacteria. This is followed by oxidation of nitrite to nitrate by
nitrite-oxidizing bacteria. Although nitrification is a key process in wastewater treatment,
maintaining large amounts of nitrifying bacteria in a reactor for stable nitrification is
difficult. This is due to the extremely low growth rate of lithoautotrophic nitrifying
bacteria and their sensitivity to toxic shock, pH and temperature fluctuation, or unknown
factors unique to a complex microbial community (1). Thus, nitrification is a
r