N2O production in a single stage nitritation/anammox MBBR process

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made the increase in N2O accumulation will then be equal to the N2O production rate, (see appendix B for calculation example). The N2O production is calculated as % of removed inorganic nitrogen. Two N2O production rates are estimated and referred to as initial and maximum production rates. The initial production rate is calculated from the increase of N2O that can be seen in the water phase immediately after switching of aeration. Maximum N2O production is estimated between the two measuring points where the increase in N2O has its maximum during the unaerated period. Mean N2O concentration in the water phase when the MBBR is aerated, calculated initial and maximum N2O production rates, mean O2 concentrations during the aerated period, mean nitrogen concentrations, reduction and removal rates for all measurements are summarised in Table 9 -Table 14. One figure of typical N2O and O2 profiles for each operation mode is shown in Figure 15 -Figure 20, N2O and O2 profiles for all measurements made are found in appendix C. 4.3.2 Intermittent aeration. Measurements of produced N2O at intermittent aeration, (DO ~3.0 mg/l) were performed at four different occasions. Typical profiles of how N2O and DO changed during the cycle are shown in Figure 15. The N2O concentration measured in the water phase varied with the aeration of the MBBR. When aeration started in the beginning of the cycle the airflow striped N2O out of the water phase and the concentration decreased to a constant minimum level. As soon as the aeration was shut off the N2O started to accumulate in the water phase until aeration was switched on again and the procedure started over as shown in Figure 15. N₂O (µmol/l) 12 10 8 6 4 2 0 4.5 3.75 2.25 1.5 0.75 0 0 20 40 60 80 Time (min) 3 DO (mg/l) N₂O (µmol/l) DO (mg/l) Figure 15. Concentration profiles of N 2O and O 2 during a cycle of intermittent aeration, DO ~3 mg/l in the aerated phase. The cycle study started in the beginning of the aerated period. N 2O gas was stripped from the water phase at the same time as the oxygen concentration rose. Initial N2O production varied between 5.6-11% of influent nitrogen concentration that was converted into dinitrogen gas (here after referred to as removed inorganic N- 34
concentration), while the maximum production ranged from 11-16% of removed inorganic nitrogen, see Table 9. Table 9. Average N 2O concentration in the water phase during aeration. Calculated initial and maximum N 2O production rates, mean O * 2 concentrations during the aerated period, mean nitrogen concentration, reduction and removal rates for studies of intermittent aeration at a DO concentration of ~3.0 mg/l. Date Average N 2O µmol/l Produced N 2O in % of removed inorganic N- concentration O 2 mean N-concentration mg/l initial max mg/l NH 4-N NO 3-N NO 2-N N-red. % Removal gN/m 2 d 090918 3.2 11.0 16.3 3.22 300 - - 54 1.1 090921 2.0 5.6 11.0 3.49 293 - - 56 1.1 090922 2.6 9.9 13.9 3.10 287 - - 56 1.1 *Mean O2 concentration from the moment when the DO level reaches its maximum concentration until aeration is shut off and oxygen starts to decrease again. 4.3.2 Prolonged unaerated period. Three studies of a prolonged unaerated period were made to examine for how long the accumulation of N2O proceeded. The measurement started in the beginning of a normal cycle when the airflow was switched on. Aeration lasted for forty minutes followed by an unaerated period of two hours and twenty minutes, typical profiles of how N2O and O2 changes during the cycle are illustrated in Figure 16. 12 10 4.5 3.75 N₂O (µmol/l) 8 6 4 2 3 2.25 1.5 0.75 DO (mg/l) N₂O (µmol/l) DO (mg/l) 0 0 0 50 100 150 200 Time (min) Figure 16. Concentration profiles of N 2O and O 2 during prolonged unaerated period, DO ~3 mg/l during aerated phase. (Only manually registered O 2 concentrations every sixth minute are available during the first fifty minutes, due to problems with overwriting of data in the DO meter). N2O decreased in the water phase as aeration was switched on and the oxygen concentration started to increase, the concentration profiles resembles the cycle profile shown in Figure 15 until the prolonged unaerated period started. At first N2O accumulation was rather linear, when DO decreases under 1 mg/l the accumulation rate of N2O was reduced until a maximum concentration was reached at DO concentrations 35
Page 1: Water and Environmental Engineering
Page 5 and 6: Summary Wastewaters contain abundan
Page 7: Acknowledgements I would like to ex
Page 11 and 12: Table of content Chapter 1 ........
Page 13 and 14: Chapter 1 1. Introduction Nitrogen
Page 15 and 16: 1.3 Objectives The aim with this ma
Page 17 and 18: Chapter 2 2. Background 2.1 Biologi
Page 19 and 20: are intermediates in the chemical r
Page 21 and 22: minimum concentration of 2 mg/l sho
Page 23 and 24: 2.3 Biofilm reactors Biofilm reacto
Page 25 and 26: 2.3.4 Moving bed reactor Another wa
Page 27 and 28: To enable efficient nutrient remova
Page 29 and 30: The Canon process is often implemen
Page 31 and 32: 2.5.1 Nitrification as a source of
Page 33 and 34: Table 3. N 2O emission from differe
Page 35 and 36: The microsensor is connected to a p
Page 37 and 38: Chapter 3 3. Material and Methods 3
Page 39 and 40: 3.3 Analytical methods Concentratio
Page 41 and 42: Figure 11. Calibration setup for mi
Page 43 and 44: Chapter 4 4. Results 4.1 Process pe
Page 45: 10 8 DO concentration, pH & tempera
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
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The bacteria performing the microbi
Page 102 and 103:
Typical profiles of how N2O and DO
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12 10 091014 Continously operation,
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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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