N2O production in a single stage nitritation/anammox MBBR process

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The bacteria performing the microbial conversion of nitrite into dinitrogen gas are strict anaerobe autotrophs and the process has the potential to replace conventional nitrification/denitrification of recirculated high strength ammonium streams within the wastewater treatment plant (Strous et al., 1997). No additional carbon source is needed, the oxygen demand is reduced by 50-60% in the nitrifying step and the aeration can thereby be strongly reduced (Jetten et al., 2001, Fux et al., 2002). This means that the process offers an opportunity to decrease the carbon footprint of the wastewater treatment plant in terms of saving possibilities of both additional carbon source and power consumption (Jetten et al., 2004). Further advantages with the anammox process is that the production of surplus sludge is minimized and that high volumetric loading rates can be obtained resulting in reduced operational and investment costs (Abma et al., 2007). Indications that the process may produce significant amounts of N2O gas with negative environmental impacts detracting the process advantages. The aim of this study was to determine the amount of N2O produced in a nitritation/ anammox MBBR process during different operation modes. Materials and methods MBBR system A 7.5 litre laboratory MBBR (see Figure 1) fed with a synthetic medium was used to determine the N2O emissions from a single stage nitritation/anammox system. The reactor was originally started up in October 2008 with a carrier material with already established biofilm taken from Himmerfjärdsverkets full scale DeAmmon ® reactor. The used carrier was AnoxKaldnes carrier media type K1 with a protected surface area of 500 m 2 /m 3 . The total volume of carriers in the reactor was 3.5 litres which corresponds to a total protected area of 1.7 m 2 and a filling degree of 46.7%. Figure 1. The left part of the figure shows a photograph of the MBBR system, the schematic drawing to the right shows the main features of the MBBR system. 88
Cycle studies To examine what operation conditions that seem to produce the largest amounts of N2O gas, the reactor was operated at different DO concentrations during intermittent and constant aeration. A study where the anoxic phase was prolonged to two hours was made to observe how the N2O production was influenced. Parameters monitored every minute on-line in the reactor were; DO, pH, N2O and NO2-N. To examine the concentration changes of NH4-N, NO2-N and NO3-N grab samples were taken in both influent and effluent water. Analytical methods N2O concentrations were measured in the water phase with a Clark-type microelectrode sensor developed by Unisense, Århus, Denmark. Concentrations of NH4-N, NO2-N and NO3-N were determined with Dr Lange spectrophotometry kit after filtration through Munktel 1.6 µm glass fibre filters. During cycle studies NO2-N and N-tot were analyzed directly with Dr Lange’s method. Samples were frozen and flow-injection analysis was used to determine NH4-N and NOx, the sum of NO2-N and NO3-N. The NO3-N content was calculated by subtraction of NO2-N from the sum of the two NOx species. Dissolved oxygen and pH was measured with a portable meter HQ40d with mounted oxygen and pH probe. Parameters analysed and method used are summarised in Table 15. Table 15 Analysed parameters and methods. Analysed parameter Method N2O Unisense N2O microsensor NH4-N LCK 303/FIA NO2-N LCK 342/341/biosensor NO3-N LCK 339 NOx FIA N-tot LCK 238 DO HQ40d pH HQ40d Results and discussion Intermittent aeration The reactor was operated at a DO concentration of ~3 mg/l during the aeration phase. One reactor cycle lasted for one hour with 40 minutes of aeration and 20 minutes of mechanical mixing. Grab samples in the effluent were taken every 6 th minute. Only three measurements of the influent medium was taken in one cycle ( 0, 36 and 66 minutes) since it was considered that the variation of the influent medium during one hour should not be significant. 89
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Water and Environmental Engineering
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Summary Wastewaters contain abundan
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Acknowledgements I would like to ex
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Table of content Chapter 1 ........
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Chapter 1 1. Introduction Nitrogen
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1.3 Objectives The aim with this ma
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Chapter 2 2. Background 2.1 Biologi
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are intermediates in the chemical r
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minimum concentration of 2 mg/l sho
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2.3 Biofilm reactors Biofilm reacto
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2.3.4 Moving bed reactor Another wa
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To enable efficient nutrient remova
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The Canon process is often implemen
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2.5.1 Nitrification as a source of
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Table 3. N 2O emission from differe
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The microsensor is connected to a p
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Chapter 3 3. Material and Methods 3
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3.3 Analytical methods Concentratio
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Figure 11. Calibration setup for mi
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Chapter 4 4. Results 4.1 Process pe
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10 8 DO concentration, pH & tempera
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concentration), while the maximum p
Page 49 and 50: of N2O during aeration was slightly
Page 51 and 52: Table 13. Average N 2O concentratio
Page 53 and 54: 12 NO₂-N (mg/l) 10 8 6 4 2 NO₂-
Page 55 and 56: Aeration 1.6 (l/min) with carriers
Page 57 and 58: % produced N₂O 12 10 8 6 4 2 Prod
Page 59 and 60: laboratory system might be underest
Page 63: 6. Conclusions The following conclu
Page 67 and 68: 8. References Abma W.R., Schultz C.
Page 69 and 70: Hippen A., Rosenwinkel K-H., Baumga
Page 71 and 72: Metcalf & Eddy I. (2003). Wastewate
Page 73: van Niftrik L.A., Fuerst J.A., Sinn
Page 79 and 80: Appendix B Calculations of N2O emis
Page 81 and 82: The rN value is calculated with the
Page 83 and 84: Appendix C Microsensor measurements
Page 85 and 86: 12 090927 Prolonged unaerated perio
Page 87: 12 091016 Continuously operation, D
Page 90 and 91: 350 090921 NH₄-N 350 090922 NH₄
Page 92 and 93: 300 090926 Prolonged unaerated peri
Page 94 and 95: 091010 NOx-N 091013 NOx-N NOx-N (mg
Page 96 and 97: 35 091015 NO₃-N 70 091016 NOx-N 3
Page 98 and 99: 350 091018 NH₄-N 35 091018NO₃-N
Page 102 and 103: Typical profiles of how N2O and DO
Page 104 and 105: 12 10 091014 Continously operation,
Page 106: Mulder A.V.A, Robertson L.A., Kuene
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N2O production in a single stage nitritation/anammox MBBR process

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