Abstract
In a biological treatment process, hydraulic retention time (HRT) has a certain effect on the operation of the reactor. This study investigated the effect of HRT on carbon sequestration in a two-stage anaerobic ammonium oxidation (anammox) process using a partial nitrification reactor and anammox reactor to determine the optimal carbon sequestration operating conditions. Molecular biotechnology was used to analyze the sludge in the reactor in order to explore the denitrification performance and to determine the carbon sequestration pathway of the microorganisms. The results show that the partial nitrification stage had the highest carbon sequestration rate (0.319 mg/mg·N) when the nitrogen loading rate (NLR) was 0.44 kg·N/m3/d. The NLR of the anammox stage was 0.13 kg·N/m3/d. When the HRT was 33.4 h, the carbon sequestration of the anammox reaction was at its highest, reaching 0.183 mg/mg·N. The results of microbial analysis show that the carbon-fixing gene cbbLR1 was present in the sludge samples during the anammox and partial nitrification stages, and that there was a Calvin cycle carbon sequestration pathway during the growth process. However, the existence of a gene for reducing and immobilizing CO2 by the acetyl-CoA pathway was not detected; further research is thus needed.
Highlights
Anaerobic ammonia oxidation, a relatively new autotrophic denitrification method, is an efficient, economical, and environmentally friendly alternative to traditional denitrification processes [1]
In the biological treatment process of wastewater, the traditional biological nitrogen removal process consumes a large amount of energy, requires the addition of organic carbon sources, and produces the greenhouse gas CO2 ; it is difficult to treat wastewater with a low carbon–nitrogen ratio [2,3]
It has been confirmed that the anammox process has a certain carbon sequestration ability, which can be improved by adjusting the operating conditions
Summary
Anaerobic ammonia oxidation (anammox), a relatively new autotrophic denitrification method, is an efficient, economical, and environmentally friendly alternative to traditional denitrification processes [1]. In the biological treatment process of wastewater, the traditional biological nitrogen removal process consumes a large amount of energy, requires the addition of organic carbon sources, and produces the greenhouse gas CO2 ; it is difficult to treat wastewater with a low carbon–nitrogen ratio [2,3]. The application of the partial nitrification process as a nitrification reactor and the combination of anammox for nitrogen removal is increasing [6]. It has been confirmed that the anammox process has a certain carbon sequestration ability, which can be improved by adjusting the operating conditions
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