Nitrogen removal from sludge reject water by a two-stage oxygen-limited autotrophic nitrification denitrification process.
Nitrogen removal from sludge reject water was obtained by oxygen-limited partial nitritation resulting in nitrite accumulation in a first stage, followed by autotrophic denitrification of nitrite with ammonium as electron donor (similar to anaerobic ammonium oxidation) in a second stage. Two membrane-assisted bioreactors (MBRs) were used in series to operate with high sludge ages and subsequent high volumetric loading rates, achieving 1.45 kg N m(-3) day(-1) for the partial nitritation MBR and 1.1 kg N m(-3) day(-1) for the anaerobic ammonium oxidation MBR. Biomass retention in the nitritation stage ensured flexibility towards loading rate and operating temperature. Nitrite oxidisers were out-competed at low oxygen and high free ammonia concentration. Biomass retention in the second MBR prevented wash-out of the slowly growing bacteria. Nitrite and ammonium were converted to dinitrogen gas in a reaction ratio of 1.05, thereby maintaining nitrite limitation to assure process stability. The anoxic consortium catalysing the autotrophic denitrification process consisted of Nitrosomonas-like aerobic ammonium oxidizers and anaerobic ammonium oxidizing bacteria closely related to Kuenenia stuttgartiensis. The overall removal efficiency of the combined process was 82% of the incoming ammonium according to a total nitrogen removal rate of 0.55 kg N m(-3) day(-1), without adding extra carbon source.
Wyffels
S
S
Laboratory for Applied Physical Chemistry, Ghent University, Coupure Links 653, B-9000 Gent, Belgium. stijn.wyffels@rug.ac.be
Boeckx
P
P
Pynaert
K
K
Zhang
D
D
Van Cleemput
O
O
Chen
G
G
Verstraete
W
W
D001421:Bacteria, Anaerobic; D018533:Biomass; D019149:Bioreactors; D009584:Nitrogen / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D010084:Oxidation-Reduction; D012722:Sewage / Q000737:chemistry; D014865:Waste Disposal, Fluid / Q000379:methods*; D014873:Water Pollutants / Q000302:isolation & purification* / Q000378:metabolism
D012722:Sewage; D014873:Water Pollutants; D009584:Nitrogen