ABSTRACT
Partial nitritation-anammox was carried out successfully in a continuous fed Sequencing Batch Reactor (cf-SBR), composed of 3 compartments operated in continuous mode. The reactor was operated with floccular biomass (flocs) and biofilm to remove nitrogen from the anaerobic effluent from the potato industry at different nitrogen loading rates (0.16 g TN L-1 d-1 - 0.8 g TN L-1 d-1). At the maximum nitrogen loading rate (NLR) evaluated the nitrogen removal and ammonia oxidation achieved were 62% and 74% respectively. During the evaluation of the NLR, it was observed an improvement of the characteristics of the sludge, improving the Sludge Volumetric Index (SVI) from 228 to 63 mL g-1 MLSS. Moreover, molecular analysis (qPCR) confirmed the presence of anammox bacteria on the flocs and in the biofilm from the cf-SBR. The results showed the capability of the reactor to carry out the partial nitritation-anammox in the same reactor at pilot scale. The cf-SBR was presented as a suitable and feasible technology for advanced nitrogen removal under partial nitritation and anammox conditions.
Subject(s)
Ammonium Compounds , Solanum tuberosum , Bioreactors , Denitrification , Nitrogen , Oxidation-Reduction , Sewage , WastewaterABSTRACT
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.
Subject(s)
Bioreactors , Nitrogen/isolation & purification , Waste Disposal, Fluid/methods , Water Pollutants/isolation & purification , Bacteria, Anaerobic , Biomass , Nitrogen/chemistry , Nitrogen/metabolism , Oxidation-Reduction , Sewage/chemistry , Water Pollutants/metabolismABSTRACT
A lab-scale Rotating Biological Contactor (RBC) was operated with the purpose of oxygen-limited (autotrophic) nitrification-denitrification of an ammonium-rich synthetic wastewater without Chemical Oxygen Demand (COD). Based on the field observations that RBCs receiving anaerobic effluents come to anoxic ammonium removal, the RBC was inoculated with methanogenic sludge. Some 100 days after the addition of the anaerobic sludge to the reactor as a possible means of a rapid initiation of the nitrogen (N) removal process, a maximum ammonium removal of 1,550 mg N m(-2) d(-1) was achieved. Batch tests with 15N labeled ammonium and nitrite indicated that a large part of that N was removed via oxygen-limited oxidation of ammonium with nitrite as the electron acceptor. The other part was removed via conventional denitrification, presumably with COD released from lysis of cells. Species identification of the most abundant microorganisms revealed that Nitrosomonas spp. were the dominant ammonium-oxidizers in the sludge. Thus far, the molecular characterization of the sludge could not show the presence of Planctomycetes among the most dominant species. Overall this experiment confirms the property of the RBC system to remove ammonium to nitrogen gas without the use of heterotrophic carbon source.
Subject(s)
Bacteria, Anaerobic/physiology , Bioreactors , Nitrogen/metabolism , Quaternary Ammonium Compounds/chemistry , Waste Disposal, Fluid/methods , Biofilms , Carbon/metabolism , Nitrites/chemistryABSTRACT
The hypothesis is formulated that in case of oxygen limitation in the sediment, nitrifiers switch from nitrification to oxygen-limited autotrophic nitrification-denitrification (OLAND) in order to survive and maintain activity. During OLAND, ammonium is oxidised using nitrite as e-acceptor to form dinitrogen gas. As an additional advantage they benefit from the gaseous N(2) formed as a means of transport. In this way, the nitrifiers can move out of the sediment and rise through the water column towards more favourable conditions. At the surface, the bacteria could take up oxygen, and recommence nitrification. In order to test this hypothesis, nitrifying sediment with an overlaying water column was simulated in lab-scale columns. Nitrogen transformations and material transport through the water column were followed after addition of different forms of nitrogen under oxygen-limited conditions. (15)N-labelling experiments showed a large contribution of OLAND to the observed nitrogen deficits. Nitrifier enumerations, fluorescent in situ hybridisation and 16S rRNA gene analysis revealed increased populations of ammonia oxidising nitrifiers in the upper water layers. The results presented support the proposed hypothesis of transport using OLAND. Nitrifying activity in the sediment immediately recovered almost completely from prolonged oxygen-limited incubation when oxygen concentrations were increased.
