Nitrous oxide emissions in a biofilm loaded with different mixtures of concentrated household wastewater

Abstract

Aerobic biofilm systems are increasingly used for household wastewater treatment, but little is known about their potential to emit nitrous oxide in response to different loading conditions. We studied nitrification and nitrous oxide production in a biofilm reactor that was continuously fed with three different mixtures of household wastewater. Higher proportions of blackwater increased nitrification activity, which resulted in enhanced nitrite accumulation and nitrous oxide emissions. Applying a conceptual biofilm model together with the results of ancillary batch incubations suggested that this was caused by a higher proportion of slowly degradable compounds in blackwater. Increasing amounts of blackwater would result in less oxygen depletion by heterotrophic degradation in outer biofilm layers, leading to nitrite accumulation by enhanced ammonia oxidation as well as electron limitation of denitrification in anoxic biofilm layers. Under such conditions, nitrifier denitrification and incomplete heterotrophic denitrification would be the prevailing sources of nitrous oxide emission. These assumptions are supported by an exponential increase in the determined emission factor (nitrous oxide relative to oxidized ammonia), which accounted for 0.7 with 20 % blackwater, 1.1 with 50 % blackwater, and 8.5 with 100 % blackwater in the wastewater load.

Nitrous oxide from moving bed based integrated fixed film activated sludge membrane bioreactors

“…Todt and D€ orsch (2015) found an emission factor ranging between 0.7% and 8.5% in a pure MBBR system; Kong et al (2013) reported a mean emission factor equal to 2.7% in an MBBR operated with intermittent aeration; Lo et al (2010) found an emission factor equal to 21% of nitrogen load in an IFAS system operated with intermittent aeration. However, Fig.…”

“…Only a couple of studies have been carried so far (among others Lo et al, 2010;Ma et al, 2015;Todt and D€ orsch, 2015), indicating that significant knowledge gaps still exist. As far as the present authors are aware of, no studies are available on N 2 O emission from IFAS system coupled to MBR and more knowledge is therefore needed.…”

The influence of solid retention time on IFAS-MBR systems: Assessment of nitrous oxide emission

“…The latter configuration is usually referred to as MB-MBR (Di Trapani et al, 2014) or IFAS-MBR. Regarding the biofilm influence on N 2 O production, literature shows a very limited knowledge (Todt and D€ orsch, 2015). Indeed, to author's knowledge, there are only few modelling studies that compare the relative effects of the biofilm and the suspended sludge on N and P removal efficiencies and N 2 O emission in a hybrid BNPR system.…”

“…The combination of both heterotrophic non-PAOs and PAOs growth inside the anoxic reactors. However, the study of Mannina et al (2017b) Mannina et al (2017b), knowledge on biofilm system is still immature (Todt and D€ orsch, 2015). Therefore, the investigation of different operational conditions for a better understanding of the mechanisms involved in N 2 O production from hybrid systems aimed at nutrient removal is imperative.…”

Gaseous Emissions from Wastewater Facilities

“…Smith (2015) Nitrification and N2O production in a biofilm reactor fed with three different mixtures of household wastewater were studied (Todt et al, 2015). The results showed enhanced nitrite accumulation and N2O emissions with higher proportions of blackwater.…”