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<p>An integrated biotrickling filter (BTF)-Anammox bioreactor system was established
for the complete treatment of ammonia. Shortcut nitrification process was successfully
achieved in the biotrickling filter through free ammonia and free nitrous acid inhibition
of nitrite oxidizing bacteria. During transients, while increasing nitrogen loading,
free ammonia was the main factor that inhibited the activity of ammonia oxidizing
bacteria (AOB) and nitrite oxidizing bacteria (NOB). During steady state operation,
free nitrous acid was mainly responsible for inhibition of NOB due to the accumulation
of nitrite at relatively low pH. Ammonia removal by the BTF reached up to 50 gN m-3
h-1 with 100% removal at an inlet concentration of 403 ppm and a gas residence time
of 20.8 s. Average removal of ammonia during stable operation was 95%. The anammox
bioreactor could remove 75% of total nitrogen discharged by the BTF when the two reactors
were connected. The possibility of operating in complete closed loop mode for the
liquid was investigated. However, due to the limited activity of the Anammox bioreactor
or the fact that this reactor was undersized, recycling the Anammox effluent back
to BTF caused accumulation of nitrite in the system which further inhibited activity
of Anammox and progressively caused failure of the system.</p><p>A conceptual model
of both bioreactors was also developed to optimize the integrated system. The model
was developed by including mass balances of nitrogen in the system and inhibition
factors in microbial kinetics. Parameters such as hydraulic residence time (HRT),
empty bed residence time (EBRT) and pH had significant impact on the partial nitritation
process in the BTF. Model simulations also indicated that implementing a recycle for
the Anammox bioreactor was needed to reduce the inhibitory effect of nitrite on the
performance of the system.</p>
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