Nitritation And Anammox Achieved In Continous Reactors Treating Sewage

Eutrophication is increasingly serious, making urban water environment systemdeterioration, and even making a break of drinking water supply. This phenomenonseriously affected industrial production and people’s daily life, and caused heavydirect and indirect economic losses. The main cause of eutrophication is nutrientover enrichment, so lots of wastewater treatment plants (WWTP) were built tocontrol eutrophication. Currently, the energy consumption of WWTP is too high, sohow to reduce energy consumption and operation cost is very important for thecontinuous development of wastewater treatment.Currently, organic matter is needed as carbon source of denitrification fornitrogen removal from wastewater, so lots of organic matter can’t be used toproduce methane. The discovery of anaerobic ammonium oxidation (anammox)bacteria makes it possible to achieve autotrophic nitrogen removal. Becauseanammox bacteria can directly convert nitrite and ammonium to nitrogen gaswithout organic carbon source. Now most studies about anammox were focused onammonium rich wastewater treatment under high temperature, the studies aboutsewage treatment via anammox were very limited.In order to apply anammox in sewage treatment, a novel nitritation anammox(autotrophic nitrogen removal) process was proposed in this study. Then thetechnical feasibility of two stage autotrophic nitrogen removal from real sewage wasinvestigated in continuous reactors. Bio-augmentation strategy was proposed toachieve stable nitritation in sewage treatment. Anammox granular sludge wasformed in an upflow anaerobic sludge blanket reactor treating low strengthwastewater. Meanwhile, nitrogen removal performance, microbial communitystructure and nitrous oxide (N2O) emission were also investigated.Based on the analysis of organic matter removal, nitritation and anammoxtechnology status, a novel autotrophic nitrogen removal process treating sewage wasproposed. In this process, organic matter was firstly concentrated into activatedsludge which was used to produce methane. After then, nitrogen removal fromsewage was achieved in the nitritation/anammox process. This process makes itpossible to make wastewater treatment energy-neural or even energy-generating.The technical feasibility of two-stage autotrophic nitrogen removal from sewagewas investigated, and the result indicated that total nitrogen (TN) removal efficiencywas up to88.38%when the influent TN concentration and chemical oxygen demand(COD) concentration were45.87mg/L and44.40mg/L, respectively. This resultindicated that autotrophic nitrogen removal from sewage was feasible. Bio-augmentation strategy was proposed to achieve stable nitritation in sewagetreatment system. Firstly, nitritation was achieved in the side-line system treatingN-rich wastewater (i.e. reject water), then nitritation sludge discharged from theside-line system was added into main stream system in order to achieve a faststart-up of nitritation and maintain a stable nitritation. The results indicated thatnitritation could be achieved in N-rich wastewater treatment system with over95%of nitrite accumulation rate (NAR), and ammonium oxidation rate was up to2.71kgN/m3/d through using micro-porous aeration. In the main stream systemnitritation could be repeatedly and reliably achieved by using bio-augmentationstrategy and controlling the dissolved oxygen (DO) at relative low level. After thedeterioration of nitritation, it can be reconstructed with an increased in NAR from1%to89%within15days.Anammox granular sludge was formed in an UASB reactor treating sewagethrough gradually increasing upflow rate under moderate temperature. The majorityof granules had a diameter of0.5-0.9mm, and interstice appeared in the granulesgive an advantage for improving substrate mass transfer. The anammox bacteria wasaccumulated by forming granular sludge, and it’s aboundance was observed at1.68±0.08×109copies/ml mixed liquor. The anammox sequences in granules weremost closely affiliated to Candidatus “Kuenenia stuttgartiensis”. When the inflowrate progressively increased, HRT decreased from1.26h to0.12h, and nitrogenremoval rate (NRR) increased from0.57kg N/m3/d to5.72kg N/m3. Ammoniumremoval efficiency of the was76.47-100.00%, and the average was92.81%. Nitriteremoval efficiency of the was78.75-99.65%, and the average was94.35%. Thisindicated that nitrogen could be efficiently removed via anammox granular sludgewith a high nitrogen removal rate. The N2O emission from the anammox reactor wasvery low, and the N2O emission rate was0.30×10-4kg N/m3/d which was below0.006%of NRR. The influent N2O-N concentration was0.08-0.13mg/L, while theN2O-N in the effluent was below0.02mg/L. This indicated that N2O in influentcould be removed in the anammox reactor.Autotrophic nitrogen removal performance and microbial community structurewere studied in anammox reactor treating sewage during the decrease of temperature.When the temperature decreased from30℃to16℃, the anammox granules wasmaintained, which made a good anammox bacteria retention in the UASB reactor.The anammox bacteria aboundance was1.93±0.41×109copies/ml mixed liquor at16℃. NRR of the UASB reactor decreased with the decrease of temperature, andmaintained at2.28kg N/m3/d at16℃, while nitrite and ammonium removalefficiency were92.31%and78.45%, respectively. A shift of community from singleCandidatus ‘‘Kuenenia stuttgartiensis’’ to a combination of Candidatus ‘Brocadia fulgida’ and Candidatus ‘‘Kuenenia stuttgartiensis’’ was observed.