Sidestream partial nitritation and deammonification (pN/A) of high-strength ammonia wastewater is a well-
established technology. Its expansion to the mainstream is, however mainly impeded by poor retention of
anaerobic ammonia oxidizing bacteria (AnAOB), insufficient repression of nitrite oxidizing bacteria (NOB) and
difficult control of soluble chemical oxygen demand and nitrite levels.
At the municipal wastewater treatment plant in Strass (Austria) the microbial consortium was exhaustively
monitored at full-scale over one and a half year with regular transfer of sidestream DEMON® biomass and further
retention and enrichment of granular anammox biomass via hydrocyclone operation.
Routine process parameters were surveyed and the response and evolution of the microbiota was followed by
molecular tools, ex-situ activity tests and further, AnAOB quantification through particle tracking and heme
measurement.
After eight months of operation, the first anaerobic, simultaneous depletion of ammonia and nitrite was
observed ex-situ, together with a direction to higher nitrite generation (68% of total NOx-N) as compared to
nitrate under aerobic conditions. Our dissolved oxygen (DO) scheme allowed for transient anoxic conditions and
had a strong influence on nitrite levels and the NOB community, where Nitrobacter eventually dominated
Nitrospira. The establishment of a minor but stable AnAOB biomass was accompanied by the rise of Chloroflexi
and distinct emergence of Chlorobi, a trend not seen in the sidestream system. Interestingly, the most pronounced
switch in the microbial community and noticeable NOB repression occurred during unfavorable conditions, i.e.
the cold winter season and high organic load. Further abatement of NOB was achieved through bioaugmentation
of aerobic ammonia oxidizing bacteria (AerAOB) from the sidestream-DEMON® tank. Performance of the
sidestream pN/A was not impaired by this operational scheme and the average volumetric nitrogen removal rate
of the mainstream even doubled in the second half of the monitoring campaign. We conclude that a combination
of both, regular sidestream-DEMON® biomass transfer and granular SRT increase via hydrocyclone operation
was crucial for AnAOB establishment within the mainstream.Ministerio de Economía, Industria y Competitividad | Ref. RYC-2016–2123
