Partial nitrification and denitrification (PDN) is a biological
nitrogen removal (BNR) process via nitrite pathway. The PND process
is a promising technology as it has been reported to be a lowcost
nitrogen removal technology [1]. Compared to conventional
nitrification and denitrification via nitrate, PDN process requires
less oxygen to oxidize ammonium to nitrite, less organic carbon
for the denitrification of nitrite and achieves a lower sludge production
[2]. For PND process, the successful and stable nitrite accumulation
is a critical procedure, and the further oxidation of nitrite
to nitrate should be prevented. Therefore, main characteristic of
the process is the enrichment of ammonium-oxidizing bacteria
(AOB) and inhibition of nitrite-oxidizing bacteria (NOB) [1]. In
order to inhibit the activity of NOB, some operation conditions
have been used, including high temperature, appropriate pH, low
dissolved oxygen (DO) concentration, appropriate sludge retention
time (SRT), high substrate concentration, high free ammonia (FA)
concentration and aeration pattern [3–6]. Temperature and DO