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.