Determining Factors for Nitrite Accumulation in an Acidic Nitrifying System: Influent Ammonium Concentration, Operational pH, and Ammonia-Oxidizing Community

Abstract

Acidic nitrification is attracting wide attention because it can enable robust suppression of nitrite-oxidizing bacteria (NOB) in wastewater treatment. This study reports a comprehensive assessment of the novel acidic nitrification process to identify the key factors that govern stable nitrite accumulation. A laboratory-scale moving-bed biofilm reactor receiving low-alkalinity wastewater was continuously operated under acidic conditions (pH < 6) for around two years, including nine stages varying influent and operational conditions. The results revealed that nitrite accumulation was related to three factors, i.e., influent ammonium concentration, operating pH, and ammonia-oxidizing microbial community. These three factors impact nitrite accumulation by altering the in situ concentration of free nitrous acid (FNA), which is a potent inhibitor of NOB. The critical FNA concentration is approximately one part per million (ppm, ∼1 mg HNO2-N/L), above which nitrite accumulation is stably maintained in an acidic nitrifying system. The findings of this study suggest that stable nitrite accumulation via acidic ammonia oxidation can be maintained under a range of influent and operational conditions, as long as a ppm-level of FNA is established. Taking low-strength mainstream wastewater (40–50 mg NH4 +-N/L) with limited alkalinity as an example, stable nitrite accumulation was experimentally demonstrated at a pH of 4.35, under which an in situ FNA of 2.3 ± 0.6 mg HNO2-N/L was attained. Under these conditions, Candidatus Nitrosoglobus became the only ammonia oxidizer detectable by 16S rRNA gene sequencing. The results of this study deepen our understanding of acidic nitrifying systems, informing further development of novel wastewater treatment technologies.

Nitrification kinetics, N2O emission, and energy use in intermittently aerated hybrid reactor under different organic loading rates

“…FNA is considered a universal NOB inhibitor, but its concentration determines to what extent it will affect individual types of nitrifying bacteria differing in terms of resistance (Meng et al 2022 ). According to Pedrouso et al ( 2017 ), Nitrospira (belonging to NOB) completely inhibits FNA concentration at a level of 0.02 mgFNA/L, while in the case of Nitrobacter (belonging to AOB), it is 20 times higher, i.e.…”

One-year stable pilot-scale operation demonstrates high flexibility of mainstream anammox application

“…The NOB control strategies developed to date can be divided into two major categories: in-situ NOB suppression and ex-situ NOB inactivation. The in-situ control comprises the use of low dissolved oxygen (DO) ( Blackburne et al., 2008 ), real-time controlled intermittent aeration ( Ma et al., 2017b ; Miao et al., 2022 ; Regmi et al., 2014 ), step feed ( Duan et al., 2022 ), short sludge retention time (SRT) ( Laureni et al., 2019 ), residual NH 4 + control ( Poot et al., 2016 ), or creating acidic conditions ( Meng et al., 2022 ; Wang et al., 2021b ). The ex-situ control includes the use of harsh physical/chemical treatments such as free nitrous acid (FNA) ( Wang et al., 2014 ), free ammonia (FA) ( Wang et al., 2017 ), sulfide ( Seuntjens et al., 2018 ), heat/ultrasonic shock ( Chen et al., 2016 ), and light irradiation ( Yang et al., 2022 ; Zheng et al., 2019 ), among others.…”

Toward Energy Neutrality: Novel Wastewater Treatment Incorporating Acidophilic Ammonia Oxidation

“…The aerobic MBBR was operated at acidic conditions (average pH of 4.3 ± 0.1), leading to the successful formation of high FNA concentration (3.0 ± 0.7 mg HNO 2 -N/L) under the condition of low NO 2 – -N concentration (about 30 mg N/L), which results in the stable inhibition of NOB (Figure c). The FNA concentration (i.e., 3.0 ± 0.7 mg HNO 2 -N/L) sustained in this aerobic MBBR was much higher than the reported threshold value (i.e., above 1 mg of HNO 2 -N/L) for NOB suppression . In the aerobic MBBR, TCOD of 36.0 ± 18.9 mg/L was removed (Figure S3), showing that heterotrophic bacteria survived in this acidic reactor and removed organic carbon to a certain extent.…”

“…The acidic PN is a novel concept, which was recently discovered by Li et al 26 in treating diluted real urine that contained NH 4 + -N at about 200 mg N/L, followed by Wang et al 27 and Meng et al, 28 proposed an integrated treatment process, using the acidic PN process to tactfully solve the issues of upfront CEPT (i.e., acidified wastewater by iron hydrolysis) and downstream autotrophic nitrogen removal via anammox (i.e., NOB suppression). This integrated system was comprehensively evaluated by treating real domestic sewage for 360 days at varying temperatures, during which satisfactory effluent quality was well maintained, with an average effluent TCOD concentration of 41.9 ± 11.2 mg/L, TN concentration of 5.1 ± 1.8 mg N/L, and phosphate concentration of 0.3 ± 0.2 mg/ L (Table S2).…”