Nitrogen Removal and N₂O Accumulation during Hydrogenotrophic Denitrification: Influence of Environmental Factors and Microbial Community Characteristics

Abstract

Hydrogenotrophic denitrification is regarded as an efficient alternative technology of removing nitrogen from nitrate-polluted water that has insufficient organics material. However, the biochemical process underlying this method has not been completely characterized, particularly with regard to the generation and reduction of nitrous oxide (NO). In this study, the effects of key environmental factors on hydrogenotrophic denitrification and NO accumulation were investigated in a series of batch tests. The results show that nitrogen removal was efficient with a specific denitrification rate of 0.66 kg N/(kg MLSS·d), and almost no NO accumulation was observed when the dissolved hydrogen (DH) concentration was approximately 0.40 mg/L, the temperature was 30 °C, and the pH was 7.0. The reduction of nitrate was significantly affected by the pH, temperature, inorganic carbon (IC) content, and DH concentration. A considerable accumulation of NO was only observed when the pH decreased to 6.0 and the temperature decreased to 15 °C, where little NO accumulated under various IC and DH concentrations. To determine the microbial community structure, the hydrogenotrophic denitrifying enrichment culture was analyzed by Illumina high-throughput sequencing, and the dominant species were found to belong to the genera Paracoccus (26.1%), Azoarcus (24.8%), Acetoanaerobium (11.4%), Labrenzia (7.4%), and Dysgonomonas (6.0%).

Modeling electron competition among nitrogen oxides reduction and N2O accumulation in hydrogenotrophic denitrification

“…Experimental data from Li et al () on N 2 O emission during hydrogenotrophic denitrification were used to calibrate and validate the model. Li et al () used a hydrogen gas‐ and nitrate‐fed denitrifying culture, acclimated and cultivated for 54 months continuously in three parallel 2‐L lab‐scale continuous‐flow reactors at pH 7.0 ± 0.5 at 30 ± 1 °C, with a cycle time of 12 hr, to study the N 2 O accumulation during hydrogenotrophic denitrification.…”

“…N 2 O, a highly undesirable significant intermediate, can thus accumulate and subsequently emit to the atmosphere during hydrogenotrophic denitrification, which has raised increasing concerns due to its potent greenhouse gas effect and ozone depleting ability (Liu et al, , ; Ravishankara, Daniel, & Portmann, ). It has been reported that the amount of N 2 O accumulation in hydrogenotrophic denitrification system ranged from 0.05% to 15.2% of the influent nitrogen load (Li et al, ). Therefore, understanding N 2 O accumulation in hydrogenotrophic denitrification is of great importance.…”

“…Increasing evidence has shown that these key enzymes acquire electrons from a common electron supply source in the electron transport chain (Pan et al, ; Richardson, Felgate, Watmough, Thomson, & Baggs, ), and the shortage of electron supply (i.e., the supply rate does not meet the demand for electron consumption rate by the four reduction steps) would induce the occurrence of the electron competition during hydrogenotrophic denitrification. Therefore, factors that could lower the hydrogen oxidation rate would lead to the accumulation of intermediates (e.g., N 2 O) during hydrogenotrophic denitrification, such as hydrogen/carbon dioxide supply rate (Li et al, ).…”

“…Mathematical models have been widely used to predict nitrate and nitrite dynamics during hydrogenotrophic denitrification (Martin, Picioreanu, & Nerenberg, ; Tang, Zhao, Marcus, Krajmalnik‐Brown, & Rittmann, ,b; Tang, Zhou, Ziv‐El, & Rittmann, ). In contrast, little effort has been dedicated to modeling the N 2 O dynamics during hydrogenotrophic denitrification despite of considerable amounts of N 2 O accumulation in this process and its detrimental impact on the atmosphere (Li et al, ). Current existing models have been proposed to describe hydrogenotrophic denitrification as one‐step or two‐step denitrification (Martin, Picioreanu, & Nerenberg, ; Rezania et al, ; Vasiliadou et al, ), without consideration of N 2 O production.…”

“…Current existing models have been proposed to describe hydrogenotrophic denitrification as one‐step or two‐step denitrification (Martin, Picioreanu, & Nerenberg, ; Rezania et al, ; Vasiliadou et al, ), without consideration of N 2 O production. Further, these models that couple the catabolic and anabolic processes do not consider electron competition among different steps of hydrogenotrophic denitrification as well as the effect of carbon dioxide on denitrifier metabolism, and thus would not be able to predict N 2 O accumulation under hydrogen‐ or carbon dioxide‐limiting conditions (Li et al, ).…”