Anammox-zeolite system acting as buffer to achieve stable effluent nitrogen values

For a successful nitrogen removal, Anammox process needs to be established in line with a stable partial nitritation pretreatment unit since wastewater influent is mostly unsuitable for direct treatment by Anammox. Partial nitritation is, however, a critical bottleneck for the nitrogen removal since it is often difficult to maintain the right proportions of NO₂-N and NH₄-N during long periods of time for Anammox process. This study investigated the potential of Anammox-zeolite biofilter to buffer inequalities in nitrite and ammonium nitrogen in the influent feed. Anammox-zeolite biofilter combines the ion-exchange property of zeolite with the biological removal by Anammox process. Continuous-flow biofilter was operated for 570 days to test the response of Anammox-zeolite system for irregular ammonium and nitrite nitrogen entries. The reactor demonstrated stable and high nitrogen removal efficiencies (approximately 95 %) even when the influent NO₂-N to NH₄-N ratios were far from the stoichiometric ratio for Anammox reaction (i.e. NO₂-N to NH₄-N ranging from 0 to infinity). This is achieved by the sorption of surplus NH₄-N by zeolite particles in case ammonium rich influent came in excess with respect to Anammox stoichiometry. Similarly, when ammonium-poor influent is fed to the reactor, ammonium desorption took place due to shifts in ion-exchange equilibrium and deficient amount were supplied by previously sorbed NH₄-N. Here, zeolite acted as a preserving reservoir of ammonium where both sorption and desorption took place when needed and this caused the Anammox-zeolite system to act as a buffer system to generate a stable effluent.     

Enrichment and granulation of Anammox biomass started up with methanogenic granular sludge

A sequencing batch reactor (SBR) seeded with methanogenic granular sludge was started up to enrich Anammox (Anaerobic Ammonium Oxidation) bacteria and to investigate the feasibility of granulation of Anammox biomass. Research results showed that hydraulic retention time (HRT) was an important factor to enrich Anammox bacteria. When the HRT was controlled at 30 days during the initial cultivation, the SBR reactor presented Anammox activity at t = 58 days. Simultaneously, the methanogenic granular sludge changed gradually from dust black to brown colour and its diameter became smaller. At t = 90 days, the Anammox activity was further improved. NH₄⁺-N and NO₂⁻N were removed simultaneously with higher speed and the maximum removal rates reached 14.6 g NH₄⁺-N /(m³ _reactor·day) and 6.67 g NO₂⁻-N /(m³ _reactor·day), respectively. Between t = 110 days and t = 161 days, the nitrogen load was increased to a HRT of 5 days (70 mg/l NH₄⁺ and 70 mg/l NO₂), the removal rates of ammonium and nitrite were 60.6% and 62.5% respectively. The sludge changed to red and formed Anammox granulation with high nitrogen removal activity.     

Effects of Environmental Factors on Anammox Bacterial Community Structure in Sediments of a Freshwater Aquaculture Farm,Yangcheng Lake

Previous studies have reported wide distribution of anaerobic ammonia oxidation (anammox) bacteria in various ecosystems. However, little is known about the distribution of anammox bacteria under varying environmental conditions in intensive aquaculture systems. In Yangcheng Lake, a famous crab farm situated in the Yangtze River Delta, sediment samples were collected in October (feeding period) and January (nonfeeding period) to analyze the distribution and diversity of anammox bacteria and their relationships with environmental factors. Based on the functional biomarker of Anammox bacteria, hzo gene, anammox bacterial clone libraries were constructed and their abundances were determined by quantitative PCR (qPCR). The Anammox bacteria were detected in the lake with the abundances ranging from 0.70 × 10⁵ to 6.05 × 10⁵ copies per gram of sediment. Sequences from eight clone libraries yielded seven unique operational taxonomic units (OTUs), distantly related to the Candidatus Jettenia genera with a similarity of about 91%. The Anammox bacterial community structures, diversities and abundances varied spatiotemporally with environmental conditions. In October, the level of the nitrogen compounds, the diversity, evenness and abundance of Anammox bacteria were higher than in January. The predominant OTU of samples changed from HZO-OTU-1 (34.25%) in January to HZO-OTU-2 (28.90%) in October. Moreover, the site (SW) nearing to sewage inlet was lack of HZO-OTU-7 in January. Canonical correspondence analysis (CCA) showed that the pore water NO₂^? concentration, ammonium to nitrogen oxides ratio (NH₄⁺/NO_x^?) and total organic carbon to total nitrogen ratio (TOC/TN) contributed most to Anammox bacterial community structures variances. Pearson correlations analysis revealed that the Anammox bacteria abundance had positive co-relationships with TN, NH₄⁺, NO₃^? concentrations, and negative correlation with TOC/TN in porewater.     

Inorganic nitrogen uptake kinetics of sugarcane (Saccharum spp.) varieties under in vitro conditions with varying N supply

An in vitro system was established for the characterisation of inorganic nitrogen uptake by sugarcane plantlets of variety NCo376. After multiplication and rooting, plantlets (0.27–0.3 g fresh mass) were placed on N-free medium for 4 days, and then supplied with 2–20 mM N as NO₃ ^?-N only, NH₄ ⁺-N only or NO₃ ^?-N + NH₄ ⁺-N (as 1:1). With few exceptions, on all the tested N media, the in vitro plants always had a higher V_max for NH₄ ⁺-N (28.69–66.51 μmol g^?1 h^?1) than for NO₃ ^?-N uptake (10.24–30.19 μmol g^?1 h^?1) and the K_m indicated a higher affinity for NO₃ ^?-N (0.02–7.38 mM) than for NH₄ ⁺-N (0.06–9.15 mM). When N was applied as 4 and 20 mM to varieties N12, N19 and N36, the interaction between variety, N form and concentration resulted in differences in the V_max and K_m. The high N-use efficient varieties (N12 and N19), as determined in previous pot and field trials, behaved similarly under all tested conditions and displayed a lower V_max and K_m than the low N-use efficient ones (NCo376 and N36). Based on this finding, it was suggested that the N-use efficient designation (from pot and field trials) may not be ascribed solely to N uptake. Assessment of the relative preference index (RPI) for NO₃ ^?-N and NH₄ ⁺-N uptake revealed that, at present, the RPI has no application in sugarcane due to its preferential uptake of NH₄ ⁺-N.     

Influence of Agapanthus africanus on nitrification in a vertical subsurface flow constructed wetland

The aim of this study is to evaluate the influence of Agapanthus africanus (A. africanus) on nitrification in a vertical subsurface flow constructed wetlands (VSSFs) system. Two lab-scale VSSFs were operated: a) one was planted with A. africanus (vertical flow planted, VFP), and b) the other was unplanted (vertical flow control, VFC). The operation strategy was divided into three phases and consisted of increasing the ammoniacal nitrogen loading rate (ALR) (Phase I: 1.4; Phase II: 2.4; Phase III: 4.4 g NH₄⁺-N·m^?2·d^?1). Nitrification was evaluated in the system at two different depths in the VSSFs (30.5 cm and 60.3 cm, from the top of the system).

The removal efficiencies of COD, BOD₅, TP, and PO₄^?3-P were above 40% in the VFP and VFC during all operation. The mean removal efficiencies of NH₄⁺-N were above 70%. Nitrification was the principal NH₄⁺-N removal mechanism in both systems and transformed more than 50% of the NH₄⁺-N to NO₃^?-N. In terms of the effect of A. africanus on NH₄⁺-N removal during the three operational phases, nonsignificant differences between the two VSSFs were noted (p > 0.05). Thus, A. africanus did not influence nitrification. Finally, the analysis at different depths showed that nitrification occurred in the upper 30.5 cm.     

Two ways to achieve an anammox influent from real reject water treatment at lab-scale: Partial SBR nitrification and SHARON process

A comparative study to produce the correct influent for Anammox process from anaerobic sludge reject water (700–800 mg NH₄⁺-N L⁻¹) was considered here. The influent for the Anammox process must be composed of NH₄⁺-N and NO₂⁻-N in a ratio 1:1 and therefore only a partial nitrification of ammonium to nitrite is required. The modifications of parameters (temperature, ammonium concentration, pH and solid retention time) allows to achieve this partial nitrification with a final effluent only composed by NH₄⁺-N and NO₂⁻-N at the right stoichiometric ratio. The equal ratio of HCO₃⁻/NH₄⁺ in reject water results in a natural pH decrease when approximately 50% of NH₄⁺ is oxidised. A Sequencing batch reactor (SBR) and a chemostat type of reactor (single-reactor high activity ammonia removal over nitrite (SHARON) process) were studied to obtain the required Anammox influent. At steady state conditions, both systems had a specific conversion rate around 40 mg NH₄⁺-N g⁻¹ volatile suspended solids (VSS) h⁻¹, but in terms of absolute nitrogen removal the SBR conversion was 1.1 kg N day⁻¹ m⁻³, whereas in the SHARON chemostat was 0.35 kg N day⁻¹ m⁻³ due to the different hydraulic retention time (HRT) used. Both systems are compared from operational (including starvation experiments) and kinetic point of view and their advantages/disadvantages are discussed.     

Start-up and stabilization of an Anammox process from a non-acclimatized sludge in CSTR

Development of an Anammox (anaerobic ammonium oxidation) process using non-acclimatized sludge requires a long start-up period owing to the very slow growth rate of Anammox bacteria. This article addresses the issue of achieving a shorter start-up period for Anammox activity in a well-mixed continuously stirred tank reactor (CSTR) using non-acclimatized anaerobic sludge. Proper selection of enrichment conditions and low stirring speed of 30 ± 5 rpm resulted in a shorter start-up period (82 days). Activity tests revealed the microbial community structure of Anammox micro-granules. Ammonia-oxidizing bacteria (AOB) were found on the surface and on the outer most layers of granules while nitrite-oxidizing bacteria (NOB) and Anammox bacteria were present inside. Fine-tuning of influent NO₂ ⁻/NH₄ ⁺ ratio allowed Anammox activity to be maintained when mixed microbial populations were present. The maximum nitrogen removal rate achieved in the system was 0.216 kg N/(m³ day) with a maximum specific nitrogen removal rate of 0.434 g N/(g VSS day). During the study period, Anammox activity was not inhibited by pH changes and free ammonia toxicity.     

Simultaneous nitrification and denitrification with different mixed nitrogen loads by a hypothermia aerobic bacterium

Microorganism with simultaneous nitrification and denitrification ability plays a significant role in nitrogen removal process, especially in the eutrophic waters with excessive nitrogen loads. The nitrogen removal capacity of microorganism may suffer from low temperature or nitrite nitrogen source. In this study, a hypothermia aerobic nitrite-denitrifying bacterium, Pseudomonas tolaasii strain Y-11, was selected to determine the simultaneous nitrification and denitrification ability with mixed nitrogen source at 15 °C. The sole nitrogen removal efficiencies of strain Y-11 in simulated wastewater were obtained. After 24 h of incubation at 15 °C, the ammonium nitrogen fell below the detection limit from an initial value of 10.99 mg/L. Approximately 88.0 ± 0.33% of nitrate nitrogen was removed with the initial concentration of 11.78 mg/L and the nitrite nitrogen was not detected with the initial concentration of 10.75 mg/L after 48 h of incubation at 15 °C. Additionally, the simultaneous nitrification and denitrification nitrogen removal ability of P. tolaasii strain Y-11 was evaluated using low concentration of mixed NH₄⁺-N and NO₃^?–N/NO₂^?–N (about 5 mg/L-N each) and high concentration of mixed NH₄⁺–N and NO₃^?–N/NO₂^?–N (about 100 mg/L-N each). There was no nitrite nitrogen accumulation at the time of evaluation. The results demonstrated that P. tolaasii strain Y-11 had higher simultaneous nitrification and denitrification capacity with low concentration of mixed inorganic nitrogen sources and may be applied in low temperature wastewater treatment.     

Development of a fixed-bed anammox reactor with high treatment potential

A plug-flow type anaerobic ammonium oxidation (anammox) reactor was developed using malt ceramics (MC) produced from carbonized spent grains as the biomass carriers for anammox sludge. Partial nitrified effluent of the filtrate from the sludge dehydrator of a brewery company was used as influent to a 20 L anammox reactor using MC. An average volumetric nitrogen removal rate (VNR) of 8.78 kg-N/m³/day was maintained stably for 76 days with 1 h of HRT. In a larger anammox reactor (400 L), an average VNR of 4.84 kg-N/m³/day could be maintained for 86 days during the treatment of low strength synthetic inorganic wastewater. As a result of bacterial community analysis for the 20 L anammox reactor, Asahi BRW1, probably originating from the wastewater collected at Asahi Breweries, was detected as the dominant anammox bacterium. These anammox reactors were characterized by a high NH₄-N removal capacity for low strength wastewater with a short hydraulic retention time.     

Further Analysis of Anammox Bacterial Community Structures Along an Anthropogenic Nitrogen-Input Gradient from the Riparian Sediments of the Pearl River Delta to the Deep-Ocean Sediments of the South China Sea

The community structures of anammox bacteria in sediments along an anthropogenic inorganic nitrogen input gradient were further delineated with the newly available information incorporated. Anammox bacterial 16S rRNA gene-amplified sequences retrieved from riparian sediments of the Pearl River, Mai Po coastal wetland, and the South China Sea (SCS) sediments were compiled, compared and analyzed. Results indicated that the community structures of anammox bacteria varied from the upstream of the Pearl River to deep-ocean sediment of the SCS along the anthropogenic input grandient. Mai Po wetland had the most diverse anammox bacteria, followed by the shallow SCS, deep SCS and the Pearl River. Genera of the anammox bacteria Kuenenia and Brocadia showed higher proportion in the riparian sediments of the Pearl River, while those of Kuenenia and Scalindua dominated the Mai Po coastal wetland. The Scalindua subclusters showed apparent segregation in coastal wetland (S. zhenghei-III and S. wagneri), shallow SCS (S. zhenghei-I and S3) and deep SCS (S. zhenghei-I, S2 and S. arabica). Pearson correlation analysis indicated nitrogen species [NH₄⁺ and ∑(NO₂^?+NO₃^? )] negatively correlated with the diversity indices of anammox bacteria. Canonical correspondence analysis (CCA) showed that salinity, inorganic nitrogen [NH₄+, ∑(NO₂^?+NO₃^?)], and ratio of NH₄⁺/∑(NO₂^? +NO₃^?) significantly affected the bacterial community compositions. Results collectively support that the community composition of anammox bacteria can serve as a bio-indicator to the anthropogenic terrestrial N input or pollution.     

High-rate nitrogen removal by the Anammox process at ambient temperature

The purpose of this study is to investigate the nitrogen removal performance of the anaerobic ammonium oxidation (Anammox) process and the microbial community that enables the Anammox system to function well at ambient temperatures. A reactor with a novel spiral structure was used as the gas-solid separator. The reactor was fed with synthetic inorganic wastewater composed mainly of NH₄⁺-N and NO₂⁻-N, and operated for 92 days. Stable nitrogen removal rates (NRR) of 16.3 and 17.5 kg-N m⁻³ d⁻¹ were obtained at operating temperatures of 33 ± 1 and 23 ± 2 °C, respectively. To our knowledge, such a high NRR at ambient temperatures has not been reported previously. In addition, the experiments presented herein confirm that high influent NO₂⁻-N concentration of 460 mg L⁻¹ did not noticeably inhibit the Anammox activity. Furthermore, the freshwater Anammox bacterium KU2, which was identified as the dominant bacterial species in the consortium by 16S rRNA gene analysis, is considered to be responsible for the stable nitrogen removal performance at ambient temperatures.     

Kinetic Modeling for Simultaneous Organic Carbon Oxidation,Nitrification, and Denitrification of Abattoir Wastewater in Sequencing Batch Reactor

A laboratory-scale study was conducted in a 20.0-L sequencing batch reactor (SBR) to explore the feasibility of simultaneous removal of organic carbon and nitrogen from abattoir wastewater. The reactor was operated under three different combinations of aerobic-anoxic sequence, viz., (4+4), (5+3), and (5+4) h of total react period, with influent soluble chemical oxygen demand (SCOD) and ammonia nitrogen (NH₄⁺-N) level of 2200 ± 50 and 125 ± 5 mg L^?1, respectively. In (5+4) h cycle, a maximum 90.27% of ammonia reduction corresponding to initial NH₄⁺-N value of 122.25 mg L^?1 and 91.36% of organic carbon removal corresponding to initial SCOD value of 2215.25 mg L^?1 have been achieved, respectively. The biokinetic parameters such as yield coefficient (Y), endogenous decay constant (k_d), and half-velocity constant (K_s) were also determined to improve the design and operation of package effluent treatment plants comprising SBR units. The specific denitrification rate (q_DN) during anoxic condition was estimated as 6.135 mg N/g mixed liquor volatile suspended solid (MLVSS)·h on 4-h average contact period. The value of Y, k_d and K_s for carbon oxidation and nitrification were found to be in the range of 0.6225–0.6952 mg VSS/mg SCOD, 0.0481–0.0588 day^?1, and 306.56–320.51 mg L^?1, and 0.2461–0.2541 mg VSS/mg NH₄⁺-N, 0.0324–0.0565 day^?1, and 38.28–50.08 mg L^?1, respectively, for different combinations of react periods.     

The effect of nutrient concentrations,nutrient ratios and temperature on photosynthesis and nutrient uptake by Ulva prolifera: implications for the explosion in green tides

The green-tide macroalga, Ulva prolifera, was tested in the laboratory to determine its nutrient uptake and photosynthesis under different conditions. In the nutrient concentration experiments U. prolifera showed a saturated uptake for nitrate but an escalating uptake in the tested range for phosphorus. Both N/P and NO₃ ^?/NH₄ ⁺ ratios influenced nutrient uptake significantly (p?<?0.05) while the PSII quantum yield [Y(II)] (p?>?0.05) remained unaffected. The maximum N uptake rate (33.9?±?0.8 μmol g^?1 DW h^?1) and P uptake rate (11.1?±?4.7) was detected at N/P ratios of 7.5 and 2.2, respectively. U. prolifera preferred NH₄ ⁺-N to NO₃ ^?-N when the NO₃ ^?-N/NH₄ ⁺-N ratio was less than 2.2 (p?<?0.05). But between ratios of 2.2 and 12.9, the uptake of NO₃ ^?-N surpassed that of NH₄ ⁺-N. In the temperature experiments, the highest N uptake rate and [Y(II)] were observed at 20 °C, while the lowest rates were detected at 5 °C. P uptake rates were correlated with increasing temperature.     

Removal of nitrogen by heterotrophic nitrification–aerobic denitrification of a novel halotolerant bacterium Pseudomonas mendocina TJPU04

Excess inorganic nitrogen in water poses a severe threat to enviroment. Removal of inorganic nitrogen by heterotrophic nitrifying–aerobic denitrifying microorganism is supposed to be a promising and applicable technology only if the removal rate can be maintained sufficiently high in real wastewater under various conditions, such as high concentration of salt and wide range of different nitrogen concentrations. Here, a new heterotrophic nitrifying–aerobic denitrifying bacterium was isolated and named as Pseudomonas mendocina TJPU04, which removes NH₄⁺-N, NO₃⁻-N and NO₂⁻-N with average rate of 4.69, 5.60, 4.99 mg/L/h, respectively. It also maintains high nitrogen removal efficiency over a wide range of nitrogen concentrations. When concentration of NH₄⁺-N, NO₃⁻-N and NO₂⁻-N was up to 150, 150 and 50 mg/L, 98%, 93%, and 100% removal efficiency could be obtained, respectively, after 30-h incubation under sterile condition. When it was applied under non-sterile condition, the ammonia removal efficiency was slightly lower than that under sterile condition. However, the nitrate and nitrite removal efficiencies under non-sterile condition were significantly higher than those under sterile condition. Strain TJPU04 also showed efficient nitrogen removal performance in the presence of high concentration of salt and nitrogen. In addition, the removal efficiencies of NH₄⁺-N, NO₃⁻-N and TN in real wastewater were 91%, 52%, and 75%, respectively. These results suggest that strain TJPU04 is a promising candidate for efficient removal of inorganic nitrogen in wastewater treatment.

     

Effects of inorganic carbon limitation on anaerobic ammonium oxidation (anammox) activity

Anammox bacteria are chemoautotrophic bacteria that oxidize ammonium with nitrite as the electron acceptor and with CO₂ as the main carbon source. The effects of inorganic carbon (IC) limitation on anammox bacteria were investigated using continuous feeding tests. In this study, a gel carrier with entrapped anammox sludge was used. It was clearly shown that the anammox activity deteriorated with a decrease in the influent IC concentration. The relationship between the influent IC concentration and the anammox activity was analyzed using Michaelis-Menten kinetics, and the apparent K_m was determined to be 1.2 mg-C/L. The activity could be recovered by adding IC to the influent. The consumption ratio of IC to ammonium was not constant and mainly depended on the influent ratio of the IC to ammonium concentrations (inf.IC/inf.NH₄-N). The results indicated that an inf.IC/inf.NH₄-N ratio of 0.2 in the anammox reactor was ideal for the anammox process using gel cubes.     

Withanolide A production from Withania somnifera hairy root cultures with improved growth by altering the concentrations of macro elements and nitrogen source in the medium

Withania somnifera is an important medicinal plant that contains withanolides as bioactive compounds. We have investigated the effects of macroelements and nitrogen source in hairy roots of W. somnifera with the aim of optimizing the production of biomass and withanolide A content. The effects of the macroelements NH₄NO₃, KNO₃, CaCl₂, MgSO₄ and KH₂PO₄ at concentrations of 0, 0.5, 1.0, 1.5 and 2.0× strengths and of nitrogen source [NH₄ ⁺/NO₃ ^? (0.00/18.80, 7.19/18.80, 14.38/18.80, 21.57/18.80, 28.75/18.80, 14.38/0.00, 14.38/9.40, 14.38/18.80, 14.38/28.20 and 14.38/37.60 mM)] in Murashige and Skoog medium were evaluated for biomass and withanolide A production. The highest accumulation of biomass (139.42 g l^?1 FW and 13.11 g l^?1 DW) was recorded in the medium with 2.0× concentration of KH₂PO₄, and the highest production of withanolide A was recorded with 2.0× KNO₃ (15.27 mg g^?1 DW). The NH₄ ⁺/NO₃ ^? ratio also influenced root growth and withanolide A production, with both parameters being larger when the NO₃ ^? concentration was higher than that of NH₄ ⁺. Maximum biomass growth (148.17 g l^?1 FW and 14.79 g l^?1 DW) was achieved at NH₄ ⁺/NO₃ ^? ratio of 14.38/37.60 mM, while withanolide A production was greatest (14.68 mg g^?1 DW) when the NH₄ ⁺/NO₃ ^? ratio was 0.00/18.80 mM. The results are useful for the large scale cultivation of Withania hairy root culture for the production of withanolide A.     

Anaerobic ammonium oxidation process in an upflow anaerobic sludge blanket reactor with granular sludge selected from an anaerobic digestor

The purpose of this work was to evaluate the development of the anammox process by the use of granular sludge selected from a digestion reactor as a potential seed source in a lab-scale UASB (upflow anaerobic sludge blanket) reactor system. The reactor was operated for approximately 11 months and was fed by synthetic wastewater. After 200 days of feeding with NH₄ ⁺ and NO₂ ⁻ as the main substrates, the biomass showed steady signs of ammonium consumption, resulting in over 60% of ammonium nitrogen removal. This report aims to present the results and to more closely examine what occurs after the onset of anammox activity, while the previous work described the start-up experiment and the presence of anammox bacteria in the enriched community using the fluorescencein situ hybridization (FISH) technique. By the last month of operation, the consumed NO₂ ⁻N/NH₄ ⁺-N ratio in the UASB reactor was close to 1.32, the stoichiometric ratio of the anammox reaction. The obtained results from the influentshutdown test suggested that nitrite concentration would be one key parameter that promotes the anammox reaction during the start-up enrichment of anammox bacteria from granular sludge. During the study period, the sludge color gradually changed from black to red-brownish.     

Growth of Salvinia molesta as affected by water temperature and nutrition I. Effects of nitrogen level and nitrogen compounds

The growth of Salvinia molesta D.S. Mitchell was studied in a greenhouse using controlled-temperature water-baths at 16, 19 and 22°C and 4 different nitrogen compounds (NO₃^?, NH₄⁺, NH₄NO₃ and urea) at levels up to 60 mg N l^?1. Little growth occurred at 16°C even if 20 mg N l^?1 was supplied together with other nutrients including phosphorus (2 mg H₂PO₄-P l^?1). The highest relative growth rate and total dry matter production occurred at 22°C when plants were supplied with 20 mg NH₄-N l^?1. At this temperature, the NH₄⁺ ion was superior to the NO₃^? ion or urea as a nitrogen source (almost doubling the biomass), but was not significantly better than NH₄NO₃. Over a period of 19 days for plants receiving 0.02 mg NH₄-N l^?, biomass increased 4-fold at 16°C, 9-fold at 19°C and 10-fold at 22°C. In contrast, for plants receiving 20 mg NH₄-N l^?1, biomass increased 4-fold at 16°C, 18-fold at 19°C and 38-fold at 22°C.     

Taxonomical and functional microbial community dynamics in an Anammox-ASBR system under different Fe (III) supplementation

In the present study, we explored the metabolic versatility of anaerobic ammonium oxidation (anammox) bacteria in a variety of Fe (III) concentrations. Specifically, we investigated the impacts of Fe (III) on anammox growth rates, on nitrogen removal performance, and on microbial community dynamics. The results from our short-term experiments revealed that Fe (III) concentrations (0.04–0.10 mM) significantly promote the specific anammox growth rate from 0.1343 to 0.1709 d^?1. In the long-term experiments, the Anammox-anaerobic sequencing batch reactor (ASBR) was operated over 120 days and achieved maximum NH₄ ⁺-N, NO₂ ^?-N, and TN efficiencies of 90.98 ± 0.35, 93.78 ± 0.29, and 83.66 ± 0.46 %, respectively. Pearson’s correlation coefficients between anammox-(narG + napA), anammox-nrfA, and anammox-FeRB all exceeded r = 0.820 (p < 0.05), confirming an interaction and ecological association among the nitrogen and iron-cycling-related microbial communities. Illumina MiSeq sequencing indicated that Chloroflexi (34.39–39.31 %) was the most abundant phylum in an Anammox-ASBR system, followed by Planctomycetes (30.73–35.31 %), Proteobacteria (15.40–18.61 %), and Chlorobi (4.78–6.58 %). Furthermore, we found that higher Fe (III) supplementation (>0.06 mM) could result in the community succession of anammox species, in which Candidatus Brocadia and Candidatus Kuenenia were the dominant anammox bacteria species. Combined analyses indicated that the coupling of anammox, dissimilatory nitrogen reduction to ammonium, and iron reduction accounted for nitrogen loss in the Anammox-ASBR system. Overall, the knowledge gained in this study provides novel insights into the microbial community dynamics and metabolic potential of anammox bacteria under Fe (III) supplementation.