Multi-point monitoring of nitrous oxide emissions and aeration efficiency in a full-scale conventional activated sludge tank

In this work the biological tank of a WRRF in Italy was monitored placing five floating hoods on a plug-flow-like biological aerated tank surface in order to capture emission dynamics in both time and space domains. The five hoods report which location is more responsible for N2O production at a certain moment of the day. Moreover, with this experimental investigation, a spatial shift in N2O production towards the end of the biological tank could be detected. This provides important insights in the changes in biological dynamics especially with varying incoming load

Greenhouse Gas Emissions from Membrane Bioreactors

Nowadays, it is widely accepted that wastewater treatment plants (WWTPs) are significant sources of greenhouse gas (GHG) emission, contributing to the anthropogenic sources. Among the GHG emitted from WWTPs, nitrous oxide (N2O) has been identified of having the major interest/concern, since its high global warming potential (GWP), is 298 times higher than that of CO2 and also to its capability to react with stratospheric ozone causing the layer depletion. Up to now, most of the experimental investigations have been carried out on conventional activated sludge (CAS) processes. The knowledge of N2O emission from advanced technologies such membrane bioreactors (MBRs) is still very limited. The present paper is aimed at providing a picture of the GHG emissions from MBR systems. In particular, data of N2O acquired from pilot plant systems monitoring are here presented. The key aim of the study was to highlight the effect of wastewater features and operational conditions on N2O production/emission from MBRs

Effect of Temperature on N2O and NO Emission in a Partial Nitrification SBR Treating Reject Wastewater

Temperature is a very important parameter during nitritation, having a direct effect on ammonia oxidation rate (AOR) and enzymatic activities which relate to both N2O and NO emission. This study aims at investigating the effect of temperature on AOR, N2O and NO production in an enriched ammonia oxidizing bacteria (AOB) sequencing batch reactor (SBR) performing partial nitrification (PN) of synthetic reject wastewater. To achieve that, a SBR was subject to several shifts in temperature (in the range of 30 to 15 \ub0C, 5 \ub0C for each decrease). Cycle studies, which contain two aeration phases, were conducted under each temperature. The results showed that AOR specific exponentially correlates with the temperature during the temperature decreasing experiments. With the decrease of the temperature, N2O firstly increased and then dropped to very low levels along with the decrease of the AOR, unlike NO that did not show any apparent connection with the temperature

Comparison of Two Mathematical Models for Greenhouse Gas Emission from Membrane Bioreactors

In this study two mathematical models (Model I and Model II), able to predict the nitrous oxide (N2O) and carbon dioxide (CO2) emission from an University Cape Town (UCT) \u2013 membrane bioreactor (MBR) plant, have been compared. Model I considers the N2O production only during the denitrification. Model II takes into account the two ammonia-oxidizing bacteria (AOB) formation pathways for N2O. Both models were calibrated adopting real data. Results highlight that Model II had a better capability of reproducing the measured data especially in terms of N2O model outputs. Indeed, the average efficiency related to the N2O model outputs was equal to 0.3 and 0.38 for Model I and Model II respectively

Gender differences in the use of cardiovascular interventions in HIV-positive persons; the D:A:D Study

Peer reviewe

Genetic and Environmental Controls on Nitrous Oxide Accumulation in Lakes

We studied potential links between environmental factors, nitrous oxide (N2O) accumulation, and genetic indicators of nitrite and N2O reducing bacteria in 12 boreal lakes. Denitrifying bacteria were investigated by quantifying genes encoding nitrite and N2O reductases (nirS/nirK and nosZ, respectively, including the two phylogenetically distinct clades nosZ(I) and nosZ(II)) in lake sediments. Summertime N2O accumulation and hypolimnetic nitrate concentrations were positively correlated both at the inter-lake scale and within a depth transect of an individual lake (Lake Vanajavesi). The variability in the individual nirS, nirK, nosZ(I), and nosZ(II) gene abundances was high (up to tenfold) among the lakes, which allowed us to study the expected links between the ecosystem's nir-vs-nos gene inventories and N2O accumulation. Inter-lake variation in N2O accumulation was indeed connected to the relative abundance of nitrite versus N2O reductase genes, i.e. the (nirS+nirK)/nosZ(I) gene ratio. In addition, the ratios of (nirS+ nirK)/nosZ(I) at the inter-lake scale and (nirS+ nirK)/nosZ(I+II) within Lake Vanajavesi correlated positively with nitrate availability. The results suggest that ambient nitrate concentration can be an important modulator of the N2O accumulation in lake ecosystems, either directly by increasing the overall rate of denitrification or indirectly by controlling the balance of nitrite versus N2O reductase carrying organisms.Peer reviewe

Nitrogen Removal by a Nitritation-Anammox Bioreactor at Low Temperature

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