The transformation from anammox granules to deammonification granules in micro-aerobic system by facilitating indigenous ammonia oxidizing bacteria

Determination and risk assessment of total petroleum hydrocarbon (TPH) in fish (Cynoglossus senegalensis), water and sediment in Araromi Beach

The presence of Total Petroleum Hydrocarbons (TPH) in seawater and sediments raises concerns about aquatic ecosystems and human health. This study assessed TPH levels in water, fish (Cynoglossus senegalensis), and sediment from Araromi Beach, Nigeria. Gas chromatography-mass spectrometry identified 23 TPH congeners across all samples. TPH concentrations were highest in water (16.95 mg L-1), followed by fish (2.02 mg kg-1) and sediment (4.22 mg kg-1), suggesting recent contamination or continuous hydrocarbon input. Estimated risk values exceeded cancer and non-cancer benchmark thresholds, with Hazard Index (HI) values surpassing 1.0 for some TPH compounds, indicating potential health risks. Children's non-carcinogenic risk showed HI values from 1.10 × 10-2 to 7.47 × 10-2 (water) and 6.30 × 10-5 to 9.16 × 10-5 (sediment). Despite this, ecological risks were minimal, as bioaccumulation factors (BAF) remained below 1.0, except for undecane (1.13) in fish-water comparisons. While human exposure risks exist, particularly for children, overall ecological danger from TPH exposure at Araromi Beach appears low.

Impact of chemical oxygen demand to nitrogen ratio on ANAMMOX bacterial growth in an up-flow anaerobic sludge blanket reactor

While several studies have investigated the effect of varying carbon-to-nitrogen (C/N) ratios on the ANAMMOX performance, there is still a research gap in illustrating the shift in 16S rRNA gene copy number and functional microbial population during operation. Hence, this study focuses on utilizing a reference gene and target functional genes to demonstrate the synergetic interaction between ANAMMOX, ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB), using an up-flow anaerobic sludge blanket (UASB) under different C/N conditions. It was demonstrated that elevating the C/N ratio from 1.0 to 2.0 reduced the COD and NH4+-N removal efficiencies from 80.12 to 48.62% and from 88.99 to 72.59%, respectively. Based on the qPCR evaluation, at the C/N ratio of 1.5, the abundance of ANAMMOX, AOB, Nitrobacter, and Nitrospira was 2.52 × 106, 82, 5.39 × 103, and 12.98 × 103 copies/μL, respectively. However, with the further increase of C/N ratio to 2.0, their abundance was reduced to 1.09 × 106, 46, 0.98 × 103, and 3.47 × 103 copies/μL, respectively. The expression of hzo gene encoding for hydrazine dehydrogenase was 169-folds at C/N = 1 and almost inhibited at C/N = 2. The results of microbial population structure using 16S rRNA reverse transcriptase (RT)-qPCR technique depicted a competition between ANAMMOX and heterotrophic bacteria for the available substrate at higher C/N ratios.

Metabolic evolution and bottleneck insights into simultaneous autotroph-heterotroph anammox system for real municipal wastewater nitrogen removal

When biological nitrogen removal (BNR) systems shifted from treating simulated wastewater to real wastewater, a microbial succession occurred, often resulting in a decline in efficacy. Notably, despite their high nitrogen removal efficiency for real wastewater, anammox coupled systems operating without or with minimal carbon sources also exhibited a certain degree of performance reduction. The underlying reasons and metabolic shifts within these systems remained elusive. In this study, the simultaneous autotrophic/heterotrophic anammox system demonstrated remarkable metabolic resilience upon exposure to real municipal wastewater, achieving a nitrogen removal efficiency (NRE) of 82.83 ± 2.29 %. This resilience was attributed to the successful microbial succession and the complementary metabolic functions of heterotrophic microorganisms, which fostered a resilient microbial community. The system's ability to harness multiple electron sources, including NADH oxidation, the TCA cycle, and organics metabolism, allowed it to establish a stable and efficient electron transfer chain, ensuring effective nitrogen removal. Despite the denitrification channel's nitrite supply capability, the analysis of the interspecies correlation network revealed that the synergistic metabolism between AOB and AnAOB was not fully restored, resulting in selective functional bacterial and genetic interactions and the system's PN/A performance declined. Additionally, the enhanced electron affinity of PD increased interconversion of NO3--N and NO2--N, limiting the efficient utilization of electrons and thereby constraining nitrogen removal performance. This study elucidated the metabolic mechanism of nitrogen removal limitations in anammox-based systems treating real municipal wastewater, enhancing our understanding of the metabolic functions and electron transfer within the symbiotic bacterial community.

Enhanced nitrogen removal and microbial community of the mainstream deammonification treating fluctuating influent C/N wastewater by the novel functional carriers

The plug-flow fixed bed reactors with zeolite/tourmaline-modified polyurethane carriers (PFBRZTP) and polyurethane carriers (PFBRPU) were operated to assess the fluctuating influent C/N impact on the system performance and the carrier effect on the enhancing the system operation. Result suggested that fluctuations in influent C/N and variations in operational temperature reduced the removal performance and system stability within PFBRPU. The negative impact of C/N fluctuation could be effectively mitigated by effluent reflux. In contrast, PFBRZTP performance and operational stability of maintained at high level with a greater nitrogen removal rate (0.18 kg N·(m³·d)-1). Redundancy analyses showed that the fluctuations in influent C/N dramatically affected the microbiome structure in PFBRPU, and the leading influencing factor was shifted to the fluctuating amount of influent C/N, which in turn reduced the system performance and stability. ZTP carriers could maintain the balance of main functional bacterial activity and abundance and promote the partial denitrification process with a higher Thauera abundance of 0.48%.

Efficient nitrogen removal from mature landfill leachate by single-stage partial-nitritation anammox using expanded granular sludge bed

The effective retention of anaerobic ammonia oxidizing (anammox) bacteria and its high sensitivity to toxic substances and oxygen posed a major challenge to the application of partial nitrification combined with anammox (PN/A) in mature landfill leachate treatment, although it is a promising and efficient nitrogen removal process. In this study, a single-stage PN/A process based on expanded granular sludge bed was proposed to treat the mature landfill leachate. During the last phase, when the NH+ 4-N concentration of mature landfill leachate in influent was 1150.0 mg/L, the nitrogen removal efficiency (NRE) was 83.64% with 1.07 kg N/(m3·d) nitrogen removal rate (NRR). The activity of anammox bacteria (AnAOB) and ammonia oxidizing bacteria (AOB) was 9.21 ± 0.22 mg N/(gVSS·h) and 14.34 ± 0.65 mg N/(gVSS·h), respectively. The bacteria produced a high amount of tightly bound extracellular polymeric substance (TB-EPS) i.e., 4071.79 mg/(g·VSS). This helped to create granular sludge and provided favorable spatial conditions for the distribution of functional bacteria that were adapted to different environments. Due to the efficient retention of functional bacteria by the granular sludge, the relative abundance of Ca.Brocadia and Ca.Kuneneia was 1.71% and 0.31%, respectively. Redundancy analysis (RDA) and microbial correlation network diagram showed that the relative abundance of Ca. Kuenenia, Nitrosomonas and Truepera had a stronger positive correlation with the increase of the proportion of mature landfill leachate added to the influent. Overall, the PN/A process based on granular sludge provides an effective method for autotrophic biological nitrogen removal from mature landfill leachate.

Mainstream deammonification at ambient temperature treating real sewage by a plug-flow fixed-bed reactor based on zeolite/tourmaline-modified polyurethane carriers

A plug-flow fixed-bed reactor (PFBR) with zeolite/tourmaline-modified polyurethane (ZTP) carriers (PFBR_ZTP) was constructed to realize mainstream deammonification for real domestic sewage treatment. The PFBR_ZTP and PFBR were operated for 111 days treating aerobically pretreated sewage in parallel. A higher nitrogen removal rate of 0.12 kg N·(m³·d)^-1 was achieved in PFBR_ZTP despite lowering the temperature (16.8-19.7 ℃) and fluctuating water quality. Meanwhile, it was indicated that anaerobic ammonium oxidation dominated (64.0 ±13.2%) in PFBR_ZTP, by nitrogen removal pathway analysis and high anaerobic ammonium-oxidizing bacteria (AnAOB) activity (2.89 mg N·(g VSS·h)^-1). And, the lower protein/polysaccharides (PS) ratio further indicated a better biofilm structure in PFBR_ZTP owing to a higher abundance of microorganisms relevant to PS and cryoprotective EPS secretion. Furthermore, partial denitrification was an important nitrite supply process in PFBR_ZTP based on low AOB activity/AnAOB activity ratio, higher Thauera abundance and a remarkably positive correlation between Thauera abundance and AnAOB activity.

Starting-up performances and microbial community shifts in the coupling process (SAPD-A) with sulfide autotrophic partial denitrification (SAPD) and anammox treating nitrate and ammonium contained wastewater

A novel coupling process (SAPD-A) with sulfide autotrophic partial denitrification (SAPD) (NO₃^--N→NO₂^--N) and anaerobic ammonium oxidation (Anammox) was developed using anaerobic sequencing batch reactor (ASBR) in this work. The integrated process comprised two stages. Firstly, the starting-up of SAPD process succeeded by gradually increasing the influent nitrate and sulfide in 95 days. The average nitrate removal efficiency (NRE) and NO₂^--N accumulation rates were 71.24% ± 0.21% and 46.44% ± 0.53% at SAPD process (days 75-95). Then, successful coupling process (SAPD-A) was implemented in two stages (stage I and stage II of SAPD-A). In stage I, it is feasible to promote the successful construction of SAPD-A process by elevating influent ammonium only based on SAPD system, making the NRE increased from 44.45% ± 0.46% (day 95) to 64.62% ± 0.12% at the end of stage I in SAPD-A system (day 126). Meanwhile, the ammonium nitrogen removal efficiency (ARE) and total nitrogen removal efficiency (TN-RE) also rose up to 42.46% ± 2.02% and 63.28% ± 0.54% respectively. Furthermore, the average ARE, NRE and TN-RE during the stage II in the bioreactor could reach 65.17% ± 1.45%, 74.50% ± 0.81% and 77.81% ± 0.37% by loading some biofilters (with of approximate 10% of the volume of the bioreactor) attached anaerobic ammonium oxidation bacteria (AnAOB). High-throughput sequencing results showed that the dominant genera concerning nitrogen removal were norank_f_norank_o_Fimbriimonadates (with the abundance of 2.88-8.54%), norank_ o_ norank _ c_ OM190 (2.48-4.41%), norank_f_norank_o_norank_c_WWE3 (11.01-17.69%), subgroup_10 (1.97-3.81%), Limnobacter（2.17-3.49%）, norank_f_n orank_ o_norank_ c_OLB14 (2.03-5.23%), norank-f-PHOS-HE36 (2.18-5.5%), Ellin6067 (1.34-2.24%) and Candidatus_ Brocadia (1.95-2.42%) during the whole starting-up period of coupling SAPD-A process. Batch experiments revealed that the sulfide was fully oxidized within 2 h, with the maximum reaction rate of 38.30 ± 1.53 mg (L h)^-1 in the first 1 h. Simultaneously, the concentration of nitrate sharply decreased from 53.08 ± 0.23 mg L^-1 to 24.16 ± 0.42 mg L^-1 with the reaction rate of 66.41 ± 2.12 mg (L h)^-1 in 0.5 h. Also, the ammonium concentration significantly declined from 47.88 ± 0.34 mg L^-1 to 10.98 ± 0.39 mg L^-1 in 8 h. Anammox process was responsible for the dominant nitrogen removal in the coupling SAPD-A system.

Long-term adaptation of two anammox granules with different ratios of Candidatus Brocadia and Candidatus Jettenia under increasing salinity and their application to treat saline wastewater

Nitrogen removal in saline wastewater is a challenge of the anaerobic ammonium oxidation (anammox) process, which is dominated by freshwater anammox bacteria (FAB). Candidatus Brocadia and Candidatus Jettenia, the most widely used FABs, have been separately applied and evaluated for their ability to treat saline wastewater. To understand the effect of salinity on nitrogen removal capability when they present together in an anammox granule, we compared two anammox granules: GRN1 was evenly dominated by Ca. Brocadia (42 %) and Ca. Jettenia (43 %), while GRN2 was dominated with mostly Ca. Brocadia (90 %) and a small amount of Ca. Jettenia (1 %). Each granule was inoculated into a continuous column reactor to treat artificial wastewater containing 150 mg NH₄⁺-N/L and 150 mg NO₂^--N/L under increasing saline conditions for 250 days. GRN1 showed superior and more stable nitrogen removal than GRN2 under saline conditions of up to 15 g NaCl/L. Under high-saline conditions, both the granules' sizes decreased (larger GRN1 than GRN2 in initial). The mass percent of Na salt increased (more in GRN2) and mineral contents decreased more in GRN1. High-throughput sequencing for microbial community analysis showed that Planctomycetes in GRN1 (85 %) and GRN2 (92 %) decreased to 14 % and 12 %, respectively. The ratio of Ca. Brocadia and Ca. Jettenia in GRN1 changed to 37 % and 63 %, respectively, whereas the ratio in GRN2 (99 % and 1 %, respectively) did not change. Both salt-adapted granules were applied to the two-stage partial nitritation and anammox (PN/A) process to treat high strength ammonium (400 mg/L) wastewater under high saline condition (15 g NaCl/L). The PN/A process containing GRN1 showed more stable nitrogen removal performance during approximately 100 days of operation. These results suggest that the anammox granules evenly dominated by two FABs, Ca. Brocadia and Ca. Jettenia, would be advantageous to treat high-strength NH₄⁺ wastewater under high-saline conditions.

Role of quorum sensing-based regulation in development of anaerobic ammonium oxidation process

Shortage of anaerobic ammonium oxidation (anammox) sludge greatly limits the extensive full-scale application of anammox-based processes. Although numerous start-up strategies have been proposed, the interaction among microbial consortia and corresponding mechanism during the process development remain unknown. In this study, three reactors were established based on different seed sludges. After 27 days, the anammox process inoculated with anammox granules and activated sludge (1:5) was firstly achieved, and the highest nitrogen removal rate was 1.17 kg N m^-3 d^-1. Correspondingly, the anammox activity and abundances of related functional genes increased. Notably, the dominant anammox bacteria shifted from Candidatus Kuenenia to Candidatus Brocadia. Metagenomic analysis indicated that quorum sensing-based regulation mainly contributed to the proliferation and accumulation of anammox bacteria. This work provides an insight into the quorum sensing (QS)-regulated microbial interactions in the anammox and activated sludge consortia during the process development.

Effect of exogenous hydrazine on metabolic process of anammox bacteria

The effect of N₂H₄ (hydrazine) on AnAOB (anaerobic ammonia oxidizing bacteria) metabolic pattern is unknown. Therefore, the main purpose of this paper was to explore the effects of exogenous N₂H₄ on the SAA (specific anammox activity), characteristics and metabolic pathway of AnAOB. The results showed that low N₂H₄ concentration (1-5 mg/L) continuous dosing can promote SAA. The promoting effect was found to be more obvious within the dosage of 3-5 mg/L N₂H₄. It was also indicated that high N₂H₄ concentration dosing (5-10 mg/L) can trigger the self-protection mechanism of AnAOB granular sludge by secreting a large amount of B-PN (binding polymeric protein). Intermittent addition of N₂H₄ at low concentration is conducive to the long-term stable operation of anammox process. Exogenous N₂H₄ can be directly oxidized by AnAOB to promote the consumption of NO₂^--N and NH₄⁺-N. In addition, excess electrons can also drive the process of NO₃^--N reduction and NO₂^--N disproportionation. Theoretically, these reaction processes need two and ten extra electrons respectively, which is not easy to occur compared with the anammox process.

Achieving rapid mainstream deammonification through inoculating long-term refrigerated sidestream sludge in plug-flow fixed-bed biofilm reactor

The start-up of a stable mainstream deammonification requires sufficient anaerobic ammonia-oxidizing bacteria (AnAOB). This study used a plug-flow fixed-bed reactor (PFBR) to verify the feasibility of establishing the mainstream deammonification system by inoculating the sidestream sludge after long-term refrigeration. A rapid resuscitation of the mainstream deammonification system was accomplished by controlling the front-end aeration rate of the PFBR. Results showed that the system was rapidly resuscitated in 44 days eventually with the nitrogen removal rate and nitrogen removal efficiency of 0.1 kg N·(m³·d)^-1 and 79.1%, respectively. Also, the efficient performance was secured by the proportionate approaching equilibrium of AnAOB and ammonia-oxidizing bacteria (AOB) activity of 2.35 ± 0.40 and 2.60 ± 0.29 mg N·(g VSS·h)^-1, respectively. In addition, Pearson correlation analysis revealed that AnAOB abundance (detected Candidatus Kuenenia) negatively correlated with the AOB (mainly Nitrosomonas)/AnAOB abundance ratio, while correlated positively with the residual ammonium concentration of a region. Furthermore, long-term refrigeration probably reduced the cross-feed relationship between AnAOB and other symbiotic organisms (Armatimonadetes and Chloroflexi) to maintain the basic metabolism. Meanwhile, extracellular polymeric substances produced by other genera (order Xanthomonadales and Pseudomonadales) decreased the mass transfer, protecting AnAOB from unfavorable conditions, thereby facilitating high AnAOB abundance during refrigeration. Thus, this study provides a promising perspective towards the practical applications of mainstream process.

Potential microbial functions and quorum sensing systems in partial nitritation and anammox processes

Diverse microbial communities coexist in the partial nitritation-anaerobic ammonium oxidation (PNA) process, in which nitrogen metabolism and information exchange are two important microbial interactions. In the PNA process, the existence of diverse microorganisms including nitrifiers, anammox bacteria, and heterotrophs makes it challenging to achieve a balanced relationship between anaerobic ammonium oxidation bacteria and ammonia oxidizing bacteria. In this study, potential microbial functions in nitrogen conversion and acyl-homoserine lactones (AHLs)-based quorum sensing (QS) in PNA processes were examined. Candidatus_Kuenenia and Nitrosomonas were the key functional bacteria responsible for PNA, while Nitrospira was detected as the dominant nitrite oxidizing bacteria (NOB). Heterotrophs containing nxr might play a similar function to NOB. The AHLs-QS system was an important microbial communication pathway in PNA systems. N-octanoyl-L-homoserine lactone, N-decanoyl homoserine lactone, and N-dodecanoyl homoserine lactone were the main AHLs, which might be synthesized by nitrogen converting microorganisms and heterotrophs. However, only heterotrophs had the potential to sense and degrade AHLs, such as Saccharophagus (sensing) and Leptospira (degradation). These results provide comprehensive information about the possible microbial functions and interactions in the PNA system and clues for system optimization from a microbial perspective. PRACTITIONER POINTS: ●Potential functions of anammox bacteria, nitrifiers, and heterotrophs were revealed. ●Diverse nitrogen conversion and AHLs-quorum sensing related genes were detected. ●Anammox bacteria and AOB played important roles in the AHLs synthesis process. ●Heterotrophs could sense and degrade AHLs during information exchange.

Characteristics of anammox granular sludge using color differentiation, and nitrogen removal performance of its immobilized fillers based on microbial succession

The characteristics of anammox granular sludge (AnGS) based on color differentiation, and the regulation mechanism of immobilized fillers in the system were investigated. The results showed that biomass content, EPS and activity of red AnGS (R1) were higher than those of brown AnGS (R2). Moreover, R1 showed nitrification, while R2 showed denitrification. Filamentous bacteria constituted the granule skeleton of R1, while R2 mainly constituted inorganic nucleation and granulation. Additionally, immobilization improved the contribution rate of Anammox, and involved different regulatory mechanisms. High-throughput sequencing analysis showed that R1 encapsulation biomass eliminated miscellaneous bacteria and established specific flora, while mixed encapsulated biomass of R1 and R2 re-formed a functional bacterial network, which strengthened interspecies cooperation. The R2 encapsulated biomass and AnAOB copy numbers were inferior and the interspecific cooperation was weak, resulting in an unsatisfactory nitrogen removal performance. These results can strengthen the understanding and optimization of AnGS and its immobilization system.

Insights into two stable mainstream deammonification process and different microbial community dynamics at ambient temperature

How to achieve stable mainstream deammonification is still a huge challenge. In this work, satisfactory nitrogen removal were achieved in a deammonification granular sludge reactor (R1, 0.42 ± 0.03 kg N / (m³·d)) and a mixed flocculent with granular sludge reactor (R2, 0.39 ± 0.04 kg N / (m³·d)) at ambient temperature (21-28 ℃) . The good adaptability of anammox bacteria (Candidatus Jettenia) to ambient temperature ensured its efficient activity (0.84-1.54 mg N/(g VSS·h)). The overexpression ammonia monooxygenase gene abundances in ammonia oxidizing bacteria (Nitrosomonas) was also predicted. The inhibition of hydrazine and the competition of denitrifying bacteria (Denitratisoma) to nitrite nitrogen, leading to a low Nitrospira relative abundances (0.2%-2.1%) . It was also found that R1 was more resistant to the unfavorable condition. For R2, higher Denitratisoma abundances (9.2%-18.5%) and predicted metabolic pathway abundances related to carbon metabolism were observed.

Performances of simultaneous enhanced removal of nitrogen and phosphorus via biological aerated filter with biochar as fillers under low dissolved oxygen for digested swine wastewater treatment

This study aims to explore the feasibility of biochar as a carrier to improve the simultaneous removal of nitrogen and phosphorus in biological aerated filters (BAFs) for treating low C/N digested swine wastewater (DSW). Two similar BAFs (BAF-A with hydrophobic polypropylene resin as fillers and BAF-B with bamboo biochar as carrier) were developed for DSW treatment. Results showed that the NH₄⁺-N, TN, and TP removal performances in BAF-B were higher than those in BAF-A. Carrier type had an obvious influence on the structures and diversity of the microbial population. The biochar carrier in BAF-B was conducive to the enrichment of the functional microorganisms and the increase of microbial diversity under high NH₄⁺-N conditions. Microbial analysis showed that the genera Rhodanobacter (10.64%), JGI_0001001-h003 (14.24%), RBG-13-54-9 (8.87%), Chujaibacter (11.27%), and Ottowia were the predominant populations involved in nitrogen and phosphorus removal in the later stage of phase III in BAF-B. BAF with biochar as carrier was highly promising for TN and TP removal in low C/N and high NH₄⁺-N DSW treatment.

A new kinetic model to predict substrate inhibition and better efficiency in an airlift reactor on deammonification process

A collection of kinetic models to explore the bacteria pathway inhibition by high-ammonia during deammonification process was fitted. The main goal was to determine the substrate concentration to operate the deammonification with efficiency, performance and low impact to ANAMMOX and ammonia-oxidizing bacteria (AOB) by substrate. A new mathematical model was created to describe the deammonification behavior, since the empirical theoretical models showed inconsistent parameters to describe the process. The proposed model showed significant prediction to the estimable parameters and according to it, until 550 mg NH₃-N L^-1 no inhibitions by ammonia and nitrite were observed. However, concentrations higher than this promote the decrease on specific bacterial activity and nitrite accumulation, since it was not quickly consumed by the bacteria. The proposed model can be applied to predict microorganism affinity and inhibition by substrate over a wide range of ammonia concentrations (<900 mgNH₃-N L^-1) in reactors treating high-ammonia concentration swine wastewater.

Hydroxyapatite crystallization-based phosphorus recovery coupling with the nitrogen removal through partial nitritation/anammox in a single reactor

For digestion effluent treatment, while the anammox-based process has been successfully applied for nitrogen removal, in most cases, phosphorus (P) represents another major concern. In this study, a novel process, integrating the partial nitritation/anammox and hydroxyapatite crystallization (PNA-HAP) in a single airlift reactor, was developed for the simultaneous nitrogen removal and P recovery from synthetic digestion effluent. With a stable influent P concentration of 20.0 mg/L, an HRT of 6 h, and alternating increases of influent calcium and ammonium, the final achieved nitrogen removal rate was 1.2 kg/m³/d and the P removal efficiency was 83.0%. The settleability of sludge was desirably enhanced with the calcium addition and a high biomass concentration was achieved in reactor. Quantitative and qualitative analyses confirmed that HAP was the main inorganic content in sludge, which could be harvested for P recovery. According to the Scanning Electron Microscope observation and the Energy Dispersive X-ray spectrometry analysis, the microbes were mainly distributed on the outer layer of the sludge aggregate, while the HAP mainly in the interior. The relevant theoretical calculation also revealed that the sludge discharge manipulation has direct effect on the sludge composition and aggregate structure. In sum, the results are evidence of the feasibility of simultaneous nitrogen removal and P recovery through one-stage PNA-HAP process for digestion effluent.

Performance and microbial community analysis of two sludge type reactors in achieving mainstream deammonification with hydrazine addition

The deammonification process is a promising and energy efficient nitrogen removal technology. Since deammonification process has succeeded in high-strength ammonia nitrogen wastewater treatment (sidestream deammonification) but its application in treating low-strength ammonium nitrogen wastewater (mainstream deammonification) remains a great challenge. In this study, mainstream deammonification process in two reactors maintained stability with hydrazine (N₂H₄) addition. The two reactors consisted of a deammonification granular reactor and a mixed ammonia oxidizing bacteria (AOB) flocculent with anaerobic ammonia oxidizing bacteria (AnAOB) granular reactor. Deammonification granular reactor had a more efficient total nitrogen removal efficiency (TNRE, 80.5 ± 5.8%) and nitrogen removal rate (NRR, 0.33 ± 0.04 g/(L·day)). The advantage of retain biomass in granular sludge reactor lead to a more balanced ex-situ activity between AOB (0.37 mg N/(g VSS·h)) and AnAOB (0.43 mg N/(g VSS·h)). Candidatus Brocadia and Nitraspira were detected the dominant genus responsible for the observed AnAOB and nitrite oxidizing bacteria (NOB), respectively. The more obvious effect of N₂H₄ on enhancing AnAOB and suppressing NOB both in ex-situ activity and genus abundances in mixed sludge reactor were also founded may due to loose spatial distribution among species.

The occurrence and role of Nitrospira in nitrogen removal systems

Application of the modern microbial techniques changed the paradigm about the microorganisms performing nitrification. Numerous investigations recognized representatives of the genus Nitrospira as a key and predominant nitrite-oxidizing bacteria in biological nutrient removal systems, especially under low dissolved oxygen and substrate conditions. The recent discovery of Nitrospira capable of performing complete ammonia oxidation (comammox) raised a fundamental question about the actual role of Nitrospira in both nitrification steps. This review summarizes the current knowledge about morphological, physiological and genetic characteristics of the canonical and comammox Nitrospira. Potential implications of comammox for the functional aspects of nitrogen removal have been highlighted. The complex meta-analysis of literature data was applied to identify specific individual variables and their combined interactions on the Nitrospira abundance. In addition to dissolved oxygen and influent nitrogen concentrations, temperature and pH may play an important role in enhancing or suppressing the Nitrospira activity.

A novel control strategy for the partial nitrification and anammox process (PN/A) of immobilized particles: Using salinity as a factor

The impact of the addition of salinity on partial nitrification and anammox (PN/A) was investigated in this study. The sludge was immobilized by polyethylene glycol (PEG)-modified polyvinyl alcohol (PVA)-sodium alginate (SA) immobilization technology, and the effective diffusion coefficient (D_e) of the immobilized particles was measured to be 0.313 × 10^-9 m²·s^-1, indicating that the system has excellent mass transfer performance. An experiment was carried out by adding NaCl to create a salinity gradient. It was found that the initiation of partial nitrification was achieved at a concentration of 10 g·L^-1 NaCl and the nitrite accumulation rate (NAR) reached 81.03%, which could provide sufficient NO₂^--N for subsequent anammox. Additionally, an anammox reactor operating at the same salinity maintained a stable state after acclimation, and the removal rates of NH₄⁺-N and NO₂^--N reached 80%. The dominant population in the anammox system was Planctomycetes. Salinity is a feasible factor for controlling the PN/A process.

Towards more efficient nitrogen removal and phosphorus recovery from digestion effluent: Latest developments in the anammox-based process from the application perspective

Over the past forty years, anammox-based processes have been extensively researched and applied to some extent. However, some of the long-standing problems present serious impediments to wide application of these processes, and knowledge gap between lab-scale research and full-scale operations is still considerable. In recent years, anammox-based research has developed rapidly and some emerging concepts have been proposed. The focus of this review is on the critical problems facing actual application of anammox processes. The latest developments in anammox-based processes are summarized, and particular consideration is given to the following aspects: (1) the evolution of the chemical stoichiometry of anammox reaction; (2) the status of several main anammox-based processes; (3) the critical problems and countermeasures; (4) the emerging anammox-based processes; and (5) the suggested optimal process integrating partial nitritation, anammox, hydroxyapatite crystallization and denitratation for digestion effluent treatment towards more efficient nitrogen removal and phosphorus recovery in the future.

Impacts of salt shocking and the selection of a suitable reversal agent on anammox

In this study, an anaerobic ammonium oxidation (anammox) reactor, which was inhibited by a salinity of 50 g NaCl L^-1 during a long-term experiment, was rapidly restarted by decreasing the salinity to 20 g NaCl L^-1 and adding biomass. The effects of exposure time and shock concentrations on the anammox reactor indicate that anammox granular sludge has a high tolerance to salinity and strong ability for self-recovery. The nitrogen removal efficiency was higher than 50% after exposure to 50 g NaCl L^-1 for 66 h. To shorten the time taken for effluent nitrogen concentrations to attain national standards (GB18918-2002) after the anammox reactor was shocked with NaCl, reactor performance (i.e., recovery) after the addition of K⁺, glycine betaine, Fe²⁺, and hydroxylamine were compared after the reactor was inhibited by 80 g NaCl L^-1. The results indicate that hydroxylamine was the best reversal agent. The recovery time of the anammox reactor could be shortened by 50% following the addition of hydroxylamine. The most favorable NH₂OH-N/NO₂^--N concentration ratio for improving nitrogen removal of anammox was 1:11. The abundances of Planctomycetes and its genera Candidatus Kuenenia and Brocadiaceae_g_unclassified increased after repeated salinity shock-recovery phases, indicating that Candidatus Kuenenia and Brocadiaceae_g_unclassified are able to adapt to NaCl shocking and recovery.

Nitrogen-associated niche characteristics and bacterial community estimated by 15N-DNA-stable isotope probing in one-stage partial nitritation/anammox process with different ammonium loading

Anaerobic ammonium oxidation coupled with partial nitritation is critical for cleaner production in sewage treatment. The long-term effects of high- and low-strength influent ammonium (NH₄⁺-N) on the anammox activity, ecological niche characteristics and active microbial community were investigated in a one-stage partial nitritation/anammox (PN/A) process. The total nitrogen (TN) removal efficiency was up to 90% with influent NH₄⁺-N of 192 mg/L. The ¹⁵N-isotope pairing technique illustrated that the potential anammox rate could reach to 3507.8 nmoL/g-sludge/h, accounting for 73.2% of dinitrogen production. As the influent NH₄⁺-N decreased to 63 mg/L, the anammox population significantly decreased and the Nitrospira became the dominant specialized species in the PN/A system. The Nitrobacter had the smallest niche overlap value and the furthest ecological distance to the anammox bacteria among the seven investigated nitrogen conversion-related genes along the influent NH₄⁺-N concentration gradient, indicating different ecological similarities. The redundancy analysis showed that the rise of dissolved oxygen caused by low NH₄⁺-N might be the main cause of the excessive proliferation of the Nitrospira. The ¹⁵N-DNA-stable isotope probing illustrated that both the class Anaerolineae and Proteobacteria had closely symbiotic relations with the Planctomycetacia in this in situ surveys. This study provides a deep understanding of PN/A process treating low-ammonium mainstream wastewater from the viewpoint of microecology.

Comparing two hydrazine addition strategies to stabilize mainstream deammonification: Performance and microbial community analysis

In this study, an expanded granular sludge blanket reactor (EGSB) was proposed to achieve stable mainstream deammonification process by adding hydrazine (N₂H₄). Two N₂H₄ addition methods consisted of constant concentration (strategy A) and variable concentration (strategy B) both can inhibit nitrite oxidizing bacteria. A efficient performance was achieved with higher total nitrogen removal efficiency (82 ± 6%) and nitrogen removal rate (0.32 ± 0.02 kg N/(m³·d)) under strategy B. For strategy A, anaerobic ammonia oxidizing bacteria (AnAOB) in-situ activity was decreased from 2.76 to 0.68 mg N/(g VSS·h) at 42 mg/L NH₄⁺-N. Candidatus Brocadia abundance increase from 14.62% to 20.07% under the strategy may indicated the self-regulate mechanism of AnAOB. Aerobic ammonia oxidizing bacteria (AOB, mainly Nitrosomonas) and AnAOB (mainly Candidatus Brocadia) were always dominated under two strategies. Strategy B provided better environment for most microorganisms (mainly Chloroflexri, Planctomycetes, Proteobacteria and Chlorobi).

Achieving stable and efficient single-stage deammonification using plug flow reactor

The deammonification process is a promising technology, while achieving stable performance is still a challenge for domestic sewage treatment. To investigate the stability of deammonification in the plug flow system, which can be updated from A/O or A/A/O bioreactor, a plug flow fixed biofilm reactor was started-up and fed with synthetic low-strength wastewater. As a result, average ammonium removal efficiency of 90.0 ± 10.0% and total nitrogen removal efficiency of 79.4 ± 9.3% were achieved, while the nitrate production ratio (∆Nitrate/∆Ammonium) was at superior levels (9.5 ± 3.4%). Candidatus Jettenia and Candidatus Brocadia were the anammox bacteria in this reactor, and Candidatus Jettenia was the predominant anammox bacteria. Anammox bacteria were dominated in three of the four sampling points except the first one. Relative abundance of NOB increased along the reactor. The result of the present work implied that the plug flow system was able to maintain stable deammonification process, and NOB was suppressed by higher residual ammonium concentration in the front of reactor while the suppression weakened along the reactor.

Approaches and processes for ammonia removal from side-streams of municipal effluent treatment plants

The main objective of this review article is to provide a comprehensive view on various conventional and emerging side-stream ammonia removal treatment options for municipal wastewater treatment plants (WWTPs). Optimization of wastewater treatment facilities from an energy and emissions stand-point necessitates consideration of the impact of the various internal side-streams. Side-streams from anaerobic sludge digesters in particular have the potential to be a significant ammonium load to the mainstream treatment process. However, the literature suggests that managing side-streams through their treatment in the mainstream process is not the most energy efficient approach, nor does it allow for practical recovery of nutrients. Furthermore, as effluent criteria become more stringent in some jurisdictions and sludge hydrolysis pre-treatment for digesters more common, an understanding of treatment options for ammonia in digester supernatant becomes more important. Given these considerations, a variety of side-stream treatment processes described in the literature are reviewed.

The threshold of influent ammonium concentration for nitrate over-accumulation in a one-stage deammonification system with granular sludge without aeration

Low-strength ammonium is still a challenge for the mainstream deammonification because of nitrate over-accumulation. In this study, the threshold of influent ammonium concentration of one-stage deammonification system with granular sludge was investigated, by stepwise decreasing influent ammonium from high concentrations (280mg/L to 140mg/L) to the low concentration (70mg/L) in 108d at 32°C without aeration. Results showed that, under 70mg/L NH₄⁺-N, ΔNO₃^--N/ΔNH₄⁺-N ratio increased to 0.2, deviated from the theoretical value of 0.11, with ammonium and TN removal efficiencies of 91% and 71%, respectively. However, under both high ammonium concentrations (280mg/L and 140mg/L), nitrate production stabilized at only 13%. Chloroflexi, Planctomycetes and Proteobacteria contributed >70% of the communities under all three ammonium concentrations. As influent ammonium decreasing, the relative abundances of bacteria for anammox, aerobic oxidizing and denitrifying decreased, while NOB (nitrite oxidizing bacteria) abundance increased greatly. So 70mg/L was the threshold of influent ammonium concentration for stable deammonification without organic influent. It was the decrease of functional bacteria and overgrowth of NOB that worsen the deammonification performance under low-strength ammonium.