Relationship of heme c, nitrogen loading capacity and temperature in anammox reactor

Effects of granular activated carbon and Fe-modified granular activated carbon on anammox process start-up

In this study, granular activated carbon (GAC) and Fe-modified granular activated carbon (FeGAC) prepared by ultrasonic impregnation method were added into respective up-flow anaerobic sludge blanket (UASB) reactors to explore their effects on the anammox process start-up. The results showed that the time of anammox system start-up could be reduced from 108 d in R1 (control group) to 94 d in R2 (GAC reactor) and to 83 d in R3 (FeGAC reactor). After 120 days of operation, the nitrogen removal rates (NRR) of all reactors could reach more than 0.8 kg-N m⁻³ d⁻¹. Extracellular polymeric substance (EPS) amount, heme c content and the anammox bacterial functional gene copy numbers gradually increased in all reactors with the passage of culture time, and manifested the superiority in R3 especially. High throughput sequencing revealed that Candidatus Kuenenia was the dominant species in all reactors in the end. It was also demonstrated that FeGAC markedly strengthened the growth and aggregation of anammox bacteria, which is promising for the practical application of the anammox process.

In this study, granular activated carbon (GAC) and Fe-modified granular activated carbon (FeGAC) prepared by ultrasonic impregnation method were added into respective up-flow anaerobic sludge blanket (UASB) reactors to explore their effects on the anammox process start-up.

Modeling of completely autotrophic nitrogen removal process with salt and glycine betaine addition

The susceptibility of the completely autotrophic nitrogen removal over nitrite (CANON) process to high salinity limits its widespread application. The addition of glycine betaine (GB), a type of compatible solutes that could resist osmotic stress, could be an effective strategy to enhance the salt tolerance ability of aerobic and anaerobic ammonium oxidizing bacteria (AOB and anammox bacteria) involved in the CANON process. This study aims to make use of mathematical modeling to systematically investigate the effects of salt and GB addition on the activities of AOB and anammox bacteria and the treatment performance of the CANON process. To this end, a series of dedicated batch tests and long-term experiments for the CANON process with salt and GB additions were conducted and the data was used to calibrate and validate the model established to consider the relationships between salt and GB concentrations and bacterial growth in the CANON process. The calibrated/validated CANON process model was then applied to simulate the long-term impacts of GB addition concentration and sludge retention time (SRT) on the CANON process. The results showed that 1 mM GB addition and a SRT of 50 days would be sufficient to protect AOB and anammox bacteria under the high salinity (30 g/L NaCl) conditions studied and therefore reduce the time needed to recover the treatment performance of the CANON process from exposure to salt inhibition by 35%-40%.

Effects of biotin on promoting anammox bacterial activity

Anaerobic ammonium oxidation (anammox) bacteria significantly improve the efficiency and reduce cost of nitrogen removal in wastewater treatment plants. However, their slow growth and vulnerable activity limit the application of anammox technology. In this paper, the enhancement of biotin on the nitrogen removal activity of anammox bacteria in short-term batch experiments was studied. We found that biotin played a significant role in promoting anammox activity within a biotin concentration range of 0.1-1.5 mg/L. At a biotin concentration of 1.0 mg/L, the total nitrogen removal rate (NRR) increased by 112%, extracellular polymeric substance (EPS) secretion and heme production significantly improved, and anammox bacterial biomass increased to maximum levels. Moreover, the predominant genus of anammox bacteria was Candidatus Brocadia.

Effects of Fe3+ on microbial communities shifts, functional genes expression and nitrogen transformation during the start-up of Anammox process

In this study, the effect of Fe³⁺ on the start-up of Anammox process was investigated. Four EGSB reactors were operated with the addition of 0 (R1), 0.04 (R2), 0.08 (R3) and 0.14 (R4) mmol/L Fe³⁺, respectively. The results showed that Fe³⁺ remarkably improved the nitrogen loading rate (NLR) and operation efficiency of the reactor. After 180 days, the influent NH₄⁺-N concentration in the four reactors was 201.4, 301.8, 343.2, 380.2 mg N/L, and the NLR was 589.3, 877.6, 993.0, 1105.8 mg N/(L·d), respectively. And the nitrogen removal rate (NRR) in R2, R3 and R4 was respectively 1.54, 1.73 and 1.94 times of that in R1. High throughput sequencing revealed that Fe³⁺ could promote the enrichment of Anammox bacteria Candidatus Brocadia. Moreover, the analysis by qPCR indicated that the abundance of Anammox 16S rRNA gene and the functional gene hzsB increased, which showed a positive correlation with the concentration of Fe³⁺.

A critical review on the effects of antibiotics on anammox process in wastewater

Anaerobic ammonium oxidation (anammox) has recently become of significant interest due to its capability for cost-effective nitrogen elimination from wastewater. However, anaerobic ammonia-oxidizing bacteria (AnAOB) are sensitive to environmental changes and toxic substances. In particular, the presence of antibiotics in wastewater, which is considered unfavorable to the anammox process, has become a growing concern. Therefore, it is necessary to evaluate the effects of these inhibitors to acquire information on the applicability of the anammox process. Hence, this review summarizes our knowledge of the effects of commonly detected antibiotics in water matrices, including fluoroquinolone, macrolide, β-lactam, chloramphenicol, tetracycline, sulfonamide, glycopeptide, and aminoglycoside, on the anammox process. According to the literature, the presence of antibiotics in wastewater could partially or completely inhibit anammox reactions, in which antibiotics targeting protein synthesis or DNA replication (excluding aminoglycoside) were the most effective against the AnAOB strains.

Insight into the benefits of anammox bacteria living as aggregates

This work tried understanding aggregation preference of anammox bacteria from benefit-driven perspective. Aggregated anammox sludge (AGS) gained benefits in specific anammox activity (SAA) (increased by 40.47 ± 12.64%) and in toxicity resistance (enhanced by 65.41%) than scattered anammox sludge (SCS), which were verified by kinetics. The increased heme c content by 35.67 ± 5.77% and enhanced relative abundance of anammox bacteria by 9.29% supported the benefits in biological activity and improved EPS content by 1097.59 ± 43.06% (622.16 ± 61.73% for protein (PN), 2403.47 ± 162.75% for humic acid (HA) and 1145.34 ± 97.33% for polysaccharide (PS)) justified the benefits in toxicity resistance. The diverse microbial communities and organized spatial structures owned by AGS promoted interactions between species, as the intrinsic justification for obtaining the benefits. We expect our findings to provide theoretical guidance for promotions and applications of the anammox process with excellent nitrogen removal capacity and stability.

Long-term effects of Fe3O4 NPs on the granule-based anaerobic ammonium oxidation process: Performance, sludge characteristics and microbial community

The performance of anaerobic ammonium oxidation (anammox) granules were studied under long-term exposure to Fe₃O₄ NPs. The Fe₃O₄ NPs had no negative impacts on nitrogen removal performance with the addition of 2-200 mg L^-1. The specific anammox activity (SAA) slightly decreased from 287.0 ± 13.2 to -253.0 ± 9.2 mg TN g^-1VSS d^-1 with the increase in Fe₃O₄ NPs level from 2 to 60 mg L^-1, and then significantly enhanced to 381.8 ± 15.7 mg TN g^-1VSS d^-1 at 200 mg L^-1 Fe₃O₄ NPs. And the change trends of the heme c content, extracellular polymeric substance amount and settling velocity were consistent with that of SAA. The Candidatus_Kuenenia was the dominant species during the entire experiment and its relative abundance was up to 33.4 % at the end the experiment. The results provide some useful information for comprehending the impact of Fe₃O₄ NPs on the performance of wastewater biological treatment systems.

Deciphering correlation between chromaticity and activity of anammox sludge

The red color is the most striking character of anaerobic ammonium-oxidizing bacteria (AnAOB) which has been used to estimate the anammox activity roughly. However, the quantitative relationship between the color and activity of anammox sludge still remains unknown. In this study, the chromaticity, activity and their correlation were systematically investigated at different steady-state nitrogen loading rates. The chromaticity of anammox sludge was digitalized by the CIE L*a*b* color space. The results revealed that the average chroma value was found to be significantly correlated with specific anammox activity (r = 0.940, p < 0.01) and the cluster centers of chromaticity coordinates (a*, b*) of anammox sludge were established to define the typical working states of anammox system. The visible spectra of anammox sludge were proved to originate from the cytochrome c. The correlation between chroma and heme c concentration of anammox sludge was consistent with the fully-reduced cytochrome c and the chroma was determined by both content and redox ratio of cytochrome c. The chromaticity of anammox sludge was able to be linked with the anammox activity via reduced cytochrome c content. The gene abundance of cytochrome c synthetase linked the chromaticity with AnAOB quantity via total cytochrome c content, while the enzyme activity of octaheme hydrazine dehydrogenase linked the chromaticity with AnAOB activity via reduced cytochrome c ratio. Moreover, the redundancy analysis proved that heme c, as the key component of cytochrome c, was the most important explanatory variable accounting for the maximum 69.6% of the total variation of the anammox community, which correlated positively with the relative abundance of dominant AnAOB (Candidatus Kuenenia). This work aimed at demonstrating the chromaticity of anammox sludge could be developed as an alternative intuitive anammox activity indicator which will promote the monitoring and optimization of anammox process.

Nitrogen management in landfill leachate using single-stage anammox process-illustrating key nitrogen pathways under an ecogenomics framework

Simultaneous functional gene expressions using mRNA, rate measurements, and biochemical analysis proved the consistent contribution of ammonia oxidizers, heterotrophic denitrifiers, and anammox bacteria in a single-stage attached growth partial nitritation/anammox system for nitrogen management in landfill leachate. Average removal efficiencies of ammonia-nitrogen, total inorganic nitrogen, and COD were 94%, 88%, and 26%, respectively, in the reactor. Off-gas N₂O fluxes increased at relatively higher dissolved oxygen. Batch activity tests revealed the occurrence of significant anammox activity even in the presence of high concentrations of organic carbon in the influent. mRNA based functional expressions of nitrite reductase (nirK and nirS) and hydrazine synthase (hzsA) suggested simultaneous active heterotrophic denitrification and anammox, respectively. 16S rRNA amplicon sequencing revealed Proteobacteria (36-56%), Planctomycetes (10-31%), and Bacteroidetes (6-39%) as dominant phyla in the reactor. Candidatus brocadia was observed as the most abundant genus representing anammox community.

Bulking and floatation of the anammox-HAP granule caused by low phosphate concentration in the anammox reactor of expanded granular sludge bed (EGSB)

The effect of phosphate concentration on the anammox-HAP process was investigated in this work. A high total nitrogen removal efficiency (>82.6%) and a stable total phosphate removal efficiency (>56.2%) was achieved in reactor with the phosphate concentration over 11.4 mg L^-1. However, a phosphate concentration below to 5.7 mg L^-1, a floatation of sludge occurred caused the deterioration of process. A new understanding for the floatation was divided into three stages: the stable stage, bulking stage and floating stage. First, anammox biofilm coupled with HAP for granulation in the stable stage. Second, the aggregation of bulking sludge resulted in changes in viscoelastic properties of the sludge. Third, the floatation resulted from unreleasable gas bubbles in the granules wrapped a high concentrations of slime layer proteins. Overall, this paper suggests that a control strategy was a sufficient supply of phosphate for the stable operation.

A self-assembled nanocompartment in anammox bacteria for resisting intracelluar hydroxylamine stress

Anammox bacteria play an important role in the global nitrogen cycle, but research on anammoxosome structure is still in its initial stages. In particular, the anammox bacteria genome contains nanocompartments gene loci. However, the function and structure of the nanocompartments in anammox bacteria is poorly understood. We apply genetic engineering to demonstrate the self-assembled nanocompartments of anammox bacteria. The encapsulin shell protein (cEnc) and cargo protein hydroxylamine oxidoreductase (HAO) can self-assemble to form regular nanocompartments (about 128 nm in diameter) in vitro. Cell growth curve tests show that nanocompartments help model bacteria resist hydroxylamine (NH₂OH) stress. Batch test results and transcriptional data show that cEnc and HAO are highly expressed in response to the negative effects of NH₂OH on anammox efficiency, predicting a potential role of nanocompartments in helping anammox bacteria resist NH₂OH stress. These findings improve our understanding of the mechanisms by which anammox bacteria respond to harmful environmental metabolites.

Impacts of Chosen Parameters on Fe-Dependent Nitrate Reduction in Anammox Consortia: Performance and Bioactivity

Fe-dependent nitrate reduction by anammox consortia could serve as a valuable autotrophic denitrification process for wastewater treatment. However, influences of temperature, pH, and Fe/NO3-N ratio on this biochemical process have not been studied. The present study investigated individual and interactive effects of aforementioned parameters on nitrate removal performance and bioactivity of anammox consortia via a series of batch assays. Enzymes activity of nitrate reductase (NAR) and hydrazine dehydrogenase (HDH) of anammox consortia had high consistency with nitrogen removal performance and significantly depended on temperature and Fe/NO3-N ratio, while the narG and hdh genes expression were drastically depressed by extreme temperature. Models developed by response surface methodology (RSM) showed the significance of individual parameter followed by Fe/NO3-N ratio > temperature > pH, while combined effects of temperature versus Fe/NO3-N ratio exerted the most significant impacts. The pH in range of 4.0–8.0 had less influence. The optimum condition for nitrate removal efficiency (NRE) > 90% and total nitrogen removal efficiency (TNRE) > 75% was 4.0–7.4 for pH, 25.5–30.0 °C for temperature, and 31–48 for Fe/NO3-N molar ratio. The maximum NRE and TNRE could be 98.68% and 79.42%, respectively, under the condition of pH = 4.00, temperature = 28.5 °C and Fe/NO3-N ratio = 37.4. The models showed good dependability for simulation nitrogen removal performance by anammox in the real semiconductor wastewater.

What's the variation in anammox reactor performance after single and joint temperature based shocks?

A laboratory-scale up-flow anaerobic sludge blanket reactor was used to investigate the effects of temperature-based (single and combined with loading) shocks on the performance of anaerobic ammonium oxidation (anammox) reactor. The reactor was tolerant to 15 °C and 25 °C shocks; however, temperature shock of 55 °C led to severe accumulation of effluent NO₂^--N (>100 mg L^-1), which induced substrate inhibition. Although the shock experiments achieved a maximum effluent NO₂^--N concentration of 205.4 mg L^-1 after a hydraulic retention time-substrate concentration shock at 25 °C, the inhibition was still reversible. During the experiments, the content of extracellular polymeric substances (EPS) increased significantly after each shock to protect the anammox bacteria, and the value decreased correspondingly at the end of the recovery phase. The specific anammox activity showed the opposite tendency compared with that of the EPS. The performance of anammox reactor under a series of short-term temperature shocks was investigated, and the results can provide new ideas for future research.

Simultaneous nitrogen removal and phosphorus recovery using an anammox expanded reactor operated at 25 °C

While anammox is a cost-effective nitrogen treatment process for wastewater with high nutrient strength, phosphorus remains untouched during this process and needs further treatment. In this study, the nitrogen removal and phosphorus recovery were achieved simultaneously at 25 °C using an anammox expanded bed. A stable high nitrogen removal efficiency of 83.7 ± 4.8% at a 1500 mgN/L influent total nitrogen concentration and a phosphorus removal efficiency of 94.2 ± 1.2% at 100 mg P/L influent total phosphorus were obtained during continuous operation. The effects of the nitrogen loading rate, hydraulic retention time (HRT), pH, Ca²⁺ and PO₄^3- concentration on the phosphorus removal was verified in the long-term operation of the reactor. The sludge produced contained a high content of phosphorus mainly in the form of hydroxyapatite (HAP), and the sludge composition strongly reflected the nitrogen and phosphorus loading. The structure of the anammox-HAP composite granules was illustrated by the use of fluorescence in situ hybridization (FISH) and Raman spectroscopic mapping analysis. The results in this study indicate that by controlling the operation parameters, it is possible to integrate a high efficiency phosphorus recovery with the anammox process, and significantly reduce the nutrient loading for further wastewater treatment.

Effect of storage conditions on maintaining anammox cell viability during starvation and recovery

Anammox bacteria can easily undergo starvation due to fluctuations in feed flowrate and concentration in wastewater treatment plants. In this study, we analyzed the effects of different types of storage conditions (presence of ammonium (R_a), nitrite (R_n), hydrazine (R_h), and no substrate (R_c)) in aiding the viability of anammox bacteria during starvation and recovery. After starvation, the bacteria were subjected to a 15-week recovery period. Anammox bacteria showed better results during starvation and recovery in R_h as compared to other conditions. Decay rate values obtained after starvation in R_a, R_n, R_h, and R_c were 0.032/day, 0.042/day, 0.019/day, and 0.037/day, respectively. Meanwhile, µ_max values obtained in R_h, R_a, R_n, and R_c on the 15th week of recovery were 0.092, 0.075, 0.011, and 0.067 d^-1, respectively. This indicated that the availability of hydrazine helps to reduce the mortality rate of anammox bacteria during starvation and enhances the recovery of anammox process.