N2O production in a single stage nitritation/anammox MBBR process

Appendix E Scientific Article
N2O production in a single stage nitritation/anammox MBBR process.
Sara Ekström
Water and Environmental Engineering Department of Chemical Engineering, Lund
University, Sweden.
Abstract. The nitrous oxide (N 2O) production from a laboratory nitritation/anammox MBBR reactor was
determined from N 2O measurements in the water phase with a Clark-type microsensor. The reactor was
operated at intermittent and continuous aeration to evaluate which operation mode that gives the highest
N 2O production. Different aeration rates were used during continuous operation to examine the influence
of dissolve oxygen (DO) on N 2O emissions. Measurements of N 2O production during prolonged unaerated
periods were performed to examine possible mechanisms of the N 2O production. The MBBR produces 6-
11% of removed inorganic nitrogen as N 2O during intermittent operation, whereas only 2-3% was
produced during continuous operation at low oxygen concentrations. Higher inorganic nitrogen removal
was achieved during continuous operation and better process performance is thought to be one
explanation of lower N 2O emissions during continuous operations of the laboratory MBBR.
Introduction
Nitrous oxide, a greenhouse gas with a global warming potential 320 times stronger
than that of CO2, is known to be produced during nitrification and denitrification
processes used to remove nitrogen from wastewaters (Jacob, 1999). Variable
temperature and loading rates of inorganic nitrogen compounds, low pH, alternating
aerobic and anaerobic conditions together with growth rate and microbial composition
are parameters that have great influence on N2O emissions from a wastewater treatment
plant (Kampschreur et al., 2008).
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) with nitrite as electron acceptor was discovered by research teams in
Holland, Germany and Switzerland (Mulder et al., 1995, Hippen et al., 1997, Siegrist et
al., 1998). Total stoichiometry of the anammox process has been estimated by Strous et
al., (1998):
1NH
1.32NO 0.066HCO
0.13H
1.02 N 0.26NO
0.066CH2O . N . 2.03 H O.
Anammox 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.
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