N2O production in a single stage nitritation/anammox MBBR process

Chapter 1
1. Introduction
Nitrogen is one of the main building blocks in proteins and is therefore a vital element
for all living organisms. The elemental form of nitrogen is made available to the
biosphere through microbial fixation of dinitrogen gas which constitutes 79% of the
atmosphere. Combustion of fossil fuels, the use of nitrogen in industry and fertilizers,
waste and wastewater streams results in large amounts of anthropogenic nitrogen lost
to nature. The human contribution to nitrogen cycling impacts the environment
negatively through eutrophication of aquatic environments and emissions of
nitrogenous compounds to the atmosphere. Release of binary nitrogenous gases
contributes to the greenhouse effect and depletion of ozone layer with consequences on
a global scale lasting for centuries.
Since the start of the industrialisation human activity has increased the emissions of
greenhouse gases (carbon dioxide, chlorofluorocarbons, methane, ozone and nitrous
oxide), to the atmosphere with about 30%, with global warming as a result (Liljenström
& Kvarnbäck, 2007). In 2004 the global amount of anthropogenic emitted greenhouse
gases corresponded to 49 billion tons carbon dioxide equivalents, (a measurement
standard where the weight of a greenhouse gas released in to the atmosphere is
converted into the weight of carbon dioxide that would cause the same temperature rise
in Earths ecosystem). Carbon dioxide stands for the greatest proportion of the emissions
with 79% followed by methane and nitrous oxide contributing with 14% and 8%
respectively, (Naturvårdsverket, 2009).
Wastewater treatment plants produces greenhouse gases through; (i) burning of fossil
fuels for coverage of the energy demand, (ii) transportation of chemicals for on-site
usage and final disposal of solids, (iii) biologic treatment processes where nutrients,
(organic matter, nitrogen and phosphorus) are removed through microbial processes.
Biologic wastewater treatment processes are known to produce three of the major
greenhouse gases carbon dioxide(CO2), methane (CH4) and nitrous oxide (N2O) (Bani
Shahabadi et al., 2009). Nitrous oxide which is the strongest of these greenhouse gases is
known to be produced during nitrification and denitrification, processes used to remove
nitrogen from the wastewater. The global warming potential of N2O is 320 times
stronger than that of CO2. Release in to the atmosphere not only amplifies the warming
of Earth’s surface temperature it also contributes to depletion of the ozone layer (Jacob,
1999). During a thirty year period from 1990 to 2020 the N2O emissions associated with
microbial nitrogen degradation of both treated and untreated wastewaters are
estimated to increase with 25% from 80 to 100 megaton carbon dioxide equivalents.
Emissions from the post-consumer waste sector are approximately 1300 megaton
carbon dioxide equivalents which corresponds to