Unwanted mainstream nitritation-denitritation causing massive N2O emissions in a continuous activated sludge process.

Nitrous oxide emissions can contribute significantly to the carbon footprint of municipal wastewater treatment plants even though emissions from conventional nitrogen removal processes are assumed to be moderate. An increased risk for high emissions can occur in connection with process disturbances and nitrite (NO2-) accumulation. This work describes the findings at a large municipal wastewater treatment plant where the levels of NO2- in the activated sludge process effluent were spontaneously and strongly increased on several activated sludge lines which was suspected to be due to shortcut nitrogen removal that stabilized for several months. The high NO2- levels were linked to a dramatic increase in nitrous oxide (N2O) emissions. As much as over 20% of the daily influent nitrogen load was emitted as N2O. These observations indicate that highly increased NO2- levels can occur in conventional activated sludge processes and result in high nitrous oxide emissions. They also raise questions concerning the risk of increased greenhouse gas (GHG) emissions of the nitritation-denitritation processes - although the uncontrolled nature of the event described here must be taken into consideration - and underline the importance of continuous monitoring and control of N2O emissions.

Performance and microbial community structure of a full-scale ANITATMMox bioreactor for treating reject water located in Finland.

The aim of this work was to study the operational performance and the microbial community dynamics during the start-up of ANITATMMox technology implemented at full-scale wastewater treatment plant in Finland to treat reject water from anaerobic digesters. The average ammonium removal in the studied setup reached around 90%, withstanding ammonium loads up to 0.13 g N m-2h-1. The nitrite concentration in the effluent did not exceed 10 mg L-1, and there was a slight accumulation of NO3--N during the operation which was controlled. Thus, the result showed a robust success to high ammonium loading in presence of organic matter. The sequencing showed a heterogeneous microbial population where Methanosaeta, WCHA1-57 genus, Sphingobacteriia, Chlorobia and diverse unknown fungi were found as dominant phylotypes. Moreover, members of the Brocadiaceae family were dominant in the adhered biomass, mostly represented by Candidatus Scalindua, rarely reported in WWTPs. Overall, the results demonstrated a drastic effect of region-specific operational conditions on carrier biofilm microbial communities as it was demonstrated by the microbial studies.

Environmental sustainability assessment from planetary boundaries perspective - A case study of an organic sheep farm in Finland.

Food production processes may have both positive and negative environmental sustainability impacts. This makes decision-making challenging in the transition towards more sustainable food production systems. In this paper, a new method for presenting environmental impacts in the context of planetary boundaries is demonstrated. This will help food and agricultural producers compare the magnitudes of various environmental impacts. The environmental sustainability impacts of an organic sheep farm in the boreal climate zone in Finland are studied herein first using a life cycle assessment method. The results are then normalized and presented in a planetary boundary framework to ascertain the extent of different environmental impacts. The results show that in the planetary boundary context, there are positive impacts of sheep grazing on biosphere integrity (genetic diversity) and biogeochemical flows and negative impacts on climate change, land use or freshwater use. Magnitudes of the impacts greatly dependent on the assumptions made especially regarding biosphere integrity impacts. In the future, it is crucial that decision-making be based on the evaluation of various environmental impacts and that the focus be more on complex sustainability thinking, rather than on one single environmental impact. This research demonstrates that results from a life cycle assessment can be modified and presented in a planetary boundaries context. A planetary boundary framework approach similar to that proposed herein could be further used to identify different environmental sustainability perspectives and to help one better recognize the multifunctional aspects of the ecosystem processes.