N2O production in a single stage nitritation/anammox MBBR process

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stricter it might lead to elevated emissions of nitrous oxide from the biological removal processes. It is therefore of great importance to design and operate these processes to minimise the emissions of nitrous oxide to the atmosphere. Wastewater treatment plants using biologic treatment processes for nutrient removal are producing excessive sludge giving rise to ammonium rich effluent from the anaerobic sludge digestion. This internal wastewater stream is recombined with the influent of the treatment plant and corresponds to 15-20% of the total nitrogen load of the wastewater treatment plant (Fux et al., 2003). In the early 1990s a new biological treatment process for nitrogen removal through anaerobic ammonium oxidation (anammox) was discovered by research teams in Holland, Germany and Switzerland (Mulder et al., 1995, Hippen et al., 1997, Siegrist et al., 1998). The technology has turned out to be suitable for treatment of reject waters and other problematic wastewaters with a low COD/N ratio and high ammonium concentrations. 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% 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). However there are doubts that the process could produce significant amounts of N2O gas with negative environmental impacts detracting the process advantages. 2
1.3 Objectives The aim with this master thesis was to estimate the N2O emissions from a partial nitritation/anammox laboratory moving bed biofilm reactor (MBBR) treating ammonium-rich synthetic wastewater. Measurements were carried out with a microsensor recording the N2O concentration online in the water phase, main objectives were: • To determine the N2O emission from the system under initial operation conditions which were intermittent aeration at a dissolved oxygen, (DO), concentration of ~3 mg/l. • To evaluate N2O production when changing the operation mode into continuous aeration to a lower DO concentration. Continuous operation at two different DO concentrations were tested ~1.5 mg/l and ~1.0 mg/l. • Determine how the N2O production was influenced during a longer period of anoxic conditions. • Investigate whether the N2O accumulation observed in the water phase as aeration is turned off was due to termination of N2O stripping or if the N2O production actually increases during the anoxic period. • To examine if a biosensor for online measurements of NO2-N concentrations can replace traditional analyse methods for determination of NO2-N during this master thesis work. 1.4 Accomplishment and scope The master thesis was based on both experimental work and a literature study. Laboratory studies were performed on an existing partial laboratory nitritation/anammox MBBR at AnoxKaldnes in Lund. The study took it’s start with a definition of the existing system and setting up the equipment for the microsensors used during online measurements. The laboratory work proceeded with measurement sessions where the N2O concentration was registered in the water phase at different operational conditions of the MBBR. Since no equipment for measurement of N2O in the off-gas were available experiments to estimate how much N2O that was stripped off from the water phase by diffusion and aeration were made. The collected data was analysed and the N2O production from the MBBR could be estimated with mass balance calculations of the system. The evaluation of the estimated N2O emission from the nitritation/anammox MBBR laboratory system was based on a literature study of N2O emissions in wastewater treatment. No calculations were made to estimate whether the anammox process is reducing or increasing the carbon footprint in comparison to common nitrogen removal processes. 3
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: Chapter 1 1. Introduction Nitrogen
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 and 46: 10 8 DO concentration, pH & tempera
Page 47 and 48: 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
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Metcalf & Eddy I. (2003). Wastewate
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van Niftrik L.A., Fuerst J.A., Sinn
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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
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12 090927 Prolonged unaerated perio
Page 87:
12 091016 Continuously operation, D
Page 90 and 91:
350 090921 NH₄-N 350 090922 NH₄
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300 090926 Prolonged unaerated peri
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091010 NOx-N 091013 NOx-N NOx-N (mg
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35 091015 NO₃-N 70 091016 NOx-N 3
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350 091018 NH₄-N 35 091018NO₃-N
Page 100 and 101:
The bacteria performing the microbi
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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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