N2O production in a single stage nitritation/anammox MBBR process

7. Future research
Better understanding off which mechanisms and organisms that are responsible for N2O
production in the nitrifying/anammox MBBR system is needed. There is also a need for
better accuracy in the measurements of emitted N2O from the process.
• Measurement should be done where N2O is measured both in the water phase
and in the off-gas simultaneously, this would both help to better understand
when the N2O is produced in the system and it would give a much better accuracy
of how much N2O that is produced and emitted by the MBBR system.
• Since the biofilm creates a microenvironment with anoxic conditions which are
believed to enhance the N2O production by AOB the importance of biofilm
structure and thickness should be investigated.
• Disturbances are believed to cause higher N2O production from the
microorganisms. It should be examined whether intermittent aeration could be
considered a disturbance to the bacteria performing the nitrogen removal
causing higher N2O emissions from the process.
• To be able to operate the MBBR in a manner that gives as small amounts of
emitted N2O as possible it is of great importance to understand which
microorganisms within the system that are responsible for the N2O emissions.
Measurements of the N2O production during batch tests with inhibitors should be
performed to gain this kind of knowledge.
• Since substrate concentrations (NH4 + , NO2 − and NO3 − ) are known to influence the
amount of produced N2O, it would be interesting to evaluate their impact on
emitted N2O in both batch tests and with operation at different influent inorganic
nitrogen concentrations. Performing the tests in this manner could give answers
to whether it is the increased nitrogen concentrations /disturbance that causes
the increase in N2O production or the actual higher substrate concentration.
• As volume to surface ratios are of importance to emitted N2O from a wastewater
treatment process and since there are further differences between full scale and
laboratory systems the emitted N2O from full scale systems should be
determined.
• Measurement from a process operated with real wastewater is needed for
determination of N2O emissions during real conditions.
• Examine the influence of aeration rate on N2O emission by continuous aeration
with pure oxygen, (a much lower aeration rate can maintain a sufficient oxygen
concentration in the reactor if pure oxygen is used.)
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