Abstract
The anaerobic ammonium oxidation (anammox) process holds great promise for treating nitrogen-contaminated water; stable nitrite-nitrogen (NO2 --N) production is significant to anammox performance. In this study, partial hydrogenotrophic denitrification (PHD) was used to stably and efficiently produce NO2 --N from nitrate-nitrogen (NO3 --N). An investigation of the effects of initial pH on the PHD process revealed that a high NO2 --N production efficiency (77.9%) could be ensured by setting an initial pH of 10.5. A combined PHD-anammox process was run for more than three months with maximal ammonium-nitrogen (NH4 +-N), NO3 --N, and total dissolved inorganic nitrogen removal efficiencies of 93.4, 98.0, and 86.9%, respectively. The NO2 --N to NH4 +-N and NO3 --N to NH4 +-N ratios indicated that various bioprocesses were involved in nitrogen removal during the anammox stage, and a 16S rRNA gene amplicon sequencing was performed to further clarify the composition of microbial communities and mechanisms involved in the nitrogen removal process.
Highlights
IntroductionThe anaerobic ammonium oxidation (anammox) process, which simultaneously converts ammonium-nitrogen (NHþ4 -N) and nitrite-nitrogen (NOÀ2 -N) to nitrogen gas (van de Graaf et al ), has been studied intensively as a remarkably effective biological nitrogen removal process
The anaerobic ammonium oxidation process, which simultaneously converts ammonium-nitrogen (NHþ4 -N) and nitrite-nitrogen (NOÀ2 -N) to nitrogen gas, has been studied intensively as a remarkably effective biological nitrogen removal process.The anammox process is superior, in terms of both energy efficiency and cost-effectiveness, to conventional processes such as nitrification and denitrification (Siegrist et al.)
A considerable amount of attention has been given to NOÀ2 -N production by partial denitrification (PD), in which NOÀ3 -N is partially denitrified to NOÀ2 -N under anoxic conditions (Du et al, b; Cui et al ; Cao et al ; Shi et al )
Summary
The anaerobic ammonium oxidation (anammox) process, which simultaneously converts ammonium-nitrogen (NHþ4 -N) and nitrite-nitrogen (NOÀ2 -N) to nitrogen gas (van de Graaf et al ), has been studied intensively as a remarkably effective biological nitrogen removal process. The anammox process is superior, in terms of both energy efficiency and cost-effectiveness, to conventional processes such as nitrification and denitrification The NOÀ2 -N used in the anammox process is generally produced from NHþ4 -N or nitrate-nitrogen (NOÀ3 -N). Most research has focused on the production of NOÀ2 -N from NHþ4 -N sources through partial nitrification (Li et al ; Laureni et al ), the long-term stability of NOÀ2 -N production, especially when low-strength water is used, remains a significant concern (Shi et al ). Anammox activity is heavily inhibited by the presence of organic carbon (Jin et al ), making it preferable to minimize the addition of organic carbon
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