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Abstract
Nitrogen and carbon components in domestic modified wastewater were completely removed
by simultaneous nitrification and denitrification using a membrane-aerated biofilm
reactor where biofilm was fixed on a hollow-fiber membrane. To measure the spatial
distribution of pH, ammonium and nitrate ions and to observe microbes inside the biofilm
fixed on the membrane, microelectrodes and the fluorescence in situ hybridization
(FISH) method were applied. Due to plug flow in the vertical direction (from the bottom
to the top of the reactor), ammonium nitrogen was gradually removed and negligible
nitrate nitrogen was detected throughout the reactor. FISH revealed that ammonia-oxidizing
bacteria were mainly distributed inside the biofilm and other bacteria, which included
denitrifying bacteria, were mainly distributed outside the biofilm and over the suspended
sludge. In order to characterize bacterial activity in the vertical direction of the
reactor, nitrification rates at lower, central and upper points were calculated using
microelectrode data. The nitrification rate at the lower point was 7 and 125 times
higher than those at the central and upper points, respectively. These results show
that the removal of carbon and nitrogen compounds was accomplished efficiently by
using various kinds of bacteria distributed vertically and horizontally in a single
reactor.