Anaerobic Ammonium-oxidizing Bacteria Research Articles

The Influence of Sulfate on Anaerobic Ammonium Oxidation in a Sequencing Batch Reactor

Anaerobic ammonia-oxidizing bacteria have a more comprehensive metabolism than expected - there may be other electron acceptors that oxidize ammonium nitrogen under anaerobic conditions, in addition to the well-known nitrite nitrogen, one of which is sulfate in the sulfammox process. Sulfate-containing compounds are part of the medium for the anammox process, but their concentrations are not particularly high (0.2 g MgSO4 ∙ 7H2O/dm3 and 0.00625 g FeSO4/dm3). They can react to some extent with influent ammonium nitrogen. In this work, tests were carried out in two sequencing batch reactors with granular sludge. The first reactor (R1) operated in a 6 h cycle, and the concentration of the inflowing sulfate was kept at 44 mg/dm3∙d. The second reactor (R2) was operated until the 36th day in a 6 h cycle; the influencing concentration was 180 mg SO42−/dm3∙d from the 37th to 64th day in a 3 h cycle, with an influencing concentration of 360 mg SO42−/dm3∙d; and from the 65th to 90th day, the reactor was operated again in a 6 h cycle with an influencing concentration of 180 mg SO42−/dm3∙d. Along with the increased share of sulfate, both the ammonium utilization rate and specific anammox activity showed an increasing trend. As soon as the sulfate dosage was reduced, the ammonium utilization rate and specific anammox activity values dropped. Therefore, it can be concluded that sulfate-containing compounds contribute to the efficiency and rate of the anammox process.

Autotrophic and mixotrophic metabolism of an anammox bacterium revealed by in vivo 13C and 2H metabolic network mapping

Anaerobic ammonium-oxidizing (anammox) bacteria mediate a key step in the biogeochemical nitrogen cycle and have been applied worldwide for the energy-efficient removal of nitrogen from wastewater. However, outside their core energy metabolism, little is known about the metabolic networks driving anammox bacterial anabolism and use of different carbon and energy substrates beyond genome-based predictions. Here, we experimentally resolved the central carbon metabolism of the anammox bacterium Candidatus ‘Kuenenia stuttgartiensis’ using time-series 13C and 2H isotope tracing, metabolomics, and isotopically nonstationary metabolic flux analysis. Our findings confirm predicted metabolic pathways used for CO2 fixation, central metabolism, and amino acid biosynthesis in K. stuttgartiensis, and reveal several instances where genomic predictions are not supported by in vivo metabolic fluxes. This includes the use of the oxidative branch of an incomplete tricarboxylic acid cycle for alpha-ketoglutarate biosynthesis, despite the genome not having an annotated citrate synthase. We also demonstrate that K. stuttgartiensis is able to directly assimilate extracellular formate via the Wood–Ljungdahl pathway instead of oxidizing it completely to CO2 followed by reassimilation. In contrast, our data suggest that K. stuttgartiensis is not capable of using acetate as a carbon or energy source in situ and that acetate oxidation occurred via the metabolic activity of a low-abundance microorganism in the bioreactor’s side population. Together, these findings provide a foundation for understanding the carbon metabolism of anammox bacteria at a systems-level and will inform future studies aimed at elucidating factors governing their function and niche differentiation in natural and engineered ecosystems.

Cultivation of anaerobic ammonium oxidizing bacteria (AnAOB) using different sewage sludge inoculums: process performance and microbial community analysis

AbstractBACKGROUNDThis study explores the feasibility of three different inoculum sources (anaerobic, aerobic, and anoxic sludge from conventional sewage treatment plants) together with the potential of biomass carrier for Anaerobic ammonium oxidation bacteria (anammox) cultivation. Fed‐batch reactors were operated with synthetic medium at different temperatures.RESULTSThe reactor inoculated with anaerobic sludge and biomass carrier showed close to stoichiometric nitrite to ammonia utilization (1.2:1) and the highest ammonia removal (12.2 mg NH4+·g VS−1·day−1), followed by the reactor inoculated with activated sludge without carrier (4.3 mg NH4+·g VS−1·day−1), which also showed close to stoichiometric nitrite to ammonia utilization. Anammox development was recorded by higher nitrogen removal, gradually increasing gas production rate, and the presence of Brocadiaceae anammox family bacteria. All batch reactors revealed significant phosphorus removal (>80%), which was attributed to the co‐existence of anammox bacteria (Brocadiaceae) with denitrifying polyphosphate accumulating organisms (flavobacterium sp.).CONCLUSIONThe results of this study revealed that anaerobic sludge and activated sludge from sewage treatment plants with biomass carriers for microbial immobilization were suitable for anammox bacteria enrichment. The co‐existence of anammox bacteria with denitrifying polyphosphate accumulating microorganisms reveals new possibilities for simultaneous nitrogen and phosphate removal. © 2020 Society of Chemical Industry (SCI)

Sludge ratio affects the start-up performance and functional bacteria distribution of a hybrid CANON system

To investigate the effect of sludge ratio on the hybrid CANON system, autotrophic nitrogen removal sludge was inoculated with different granule/floc ratios to initiate the CANON system, and maintained the sludge ratio during the operation process. The start-up performances were compared, and the distribution characteristics of functional bacteria were investigated. The results show that the Equivalent system (granules:flocs = 1:1–1:1.5) successfully started-up on day 19, and the nitrogen removal rate (NRR) reached 0.299 kgN m−3·d−1 on day 63. At the same time, it was less affected by the load shock than High-granules and High-flocs systems. Therefore, the Equivalent system had the strongest start-up performance. The activities of the functional bacteria conformed to spatial heterogeneity, unlike the abundance. With the increased floc proportion, the difference in the activity and abundance of anaerobic ammonium-oxidizing bacteria (AAOB) between the granules and flocs increased, while there was a decrease in the difference in aerobic ammonium-oxidizing bacteria (AOB). However, the abundance of Nitrosomonas in the granules was higher than in the flocs when the proportion of flocs was higher than 50%. This study provides new ideas and insights for the fast start-up of the CANON system and can conform to the varying needs of engineering applications.

Spatial variability pattern of the anaerobic ammonia-oxidizing bacterial community across a salinity gradient from river to ocean

In natural habitats, the diversity of anaerobic ammonia-oxidizing (anammox) bacteria could be affected by multiple environmental variables. In this study, we investigated the distribution of the anammox bacterial community in surface sediment from the Dongjiang River (riverine sediment, DJ) to the Pearl River Estuary (estuarine sediment, PRE) and then to the South China Sea (coastal sediment, SCS). The results revealed evident differences in the structural diversity of anammox bacteria in three different habitats. Candidatus Brocadia accounted for approximately 90% of the total anammox bacteria in DJ, conversely, Ca. Scalindua dominated in the SCS. Nevertheless, Ca. Scalindua, Ca. Brocadia and Ca. Kuenenia coexisted in the PRE. The qPCR results indicated that anammox bacterial 16S rRNA gene abundance ranged from 2.23 × 105 to 1.19 × 107 copies g-1 of wet weight, but no significant correlation was found between the abundances and environmental variables (p > 0.05). The relative abundances of Ca. Brocadia gradually decreased with increasing salinity, and Ca. Scalindua showed the opposite trend, suggesting that salinity was a crucial factor in sculpturing the community composition of anammox bacteria in natural environments. Ca. Brocadia should be able to live in freshwater ecosystems, but it can also tolerate a certain level of salinity. Ca. Scalindua was halophilic anammox bacterium and exists only in saline environments. Ca. Kuenenia could adapt to a wide range of salinity and preferred to live in high DIN level conditions according to our search. The distribution pattern of anammox bacteria may be the result of microbial migration and long-term adaptation to salinity.

Optimization of nitrogen and carbon removal with simultaneous partial nitrification, anammox and denitrification in membrane bioreactor.

In this study, a membrane bioreactor (MBR) was used to achieve both nitrogen and carbon removal by a simultaneous partial nitrification, anammox and denitrification (SNAD) process. During the entire experiment, the intermittent aeration (non-aerobic time : aeration time, min min−1) cycle was controlled by a time-controlled switch, and the aeration rate was controlled by a gas flowmeter, and the optimal operating parameters as determined by response surface methodology (RSM) were a C/N value of 1.16, a DO value of 0.84 mg l−1 and an aerobic time (Tae) of 15.75 min. Under these conditions, the SNAD process achieved efficient and stable nitrogen and carbon removal; the total inorganic nitrogen removal efficiency and chemical oxygen demand removal efficiency were 92.31% and 95.67%, respectively. With the formation of granular sludge, the membrane fouling rate decreased significantly from 35.0 Pa h−1 at SNAD start-up to 19.9 Pa h−1 during stable operation. Fluorescence in situ hybrid analyses confirmed the structural characteristics and the relative ratio of aerobic ammonia-oxidizing bacteria, anaerobic ammonia-oxidizing bacteria and denitrifying bacteria in the SNAD system.

Spontaneous formation and mechanism of anaerobic ammonium oxidation (anammox) bacteria in swine wastewater treatment system

The anaerobic ammonium oxidation (anammox) process is a new and cost-effective green technology for inorganic nitrogen removal in wastewater treatment plants (WWTPs). Red activated sludge granules were found in a swine wastewater treatment system of Guangdong Province using two-stage A/O processes. In order to test the anammox process in the wastewater treatment system, both practical and simulation experiments were conducted, including water quality determination, nitrogen balance, 15N isotope tracing and 16S rRNA sequencing. The results showed that inorganic nitrogen and NH4+-N were removed from the first-stage aerobic tank by 94% and 99.99%, respectively. Anammox granules formed under a DO of 0.19–0.54 mg/L, C/N of 0.60, and COD <300 mg/L. In the laboratory experiment, the removal rates of NH4+-N and NO2−-N by the red granules (50 g) were 18.14 mgN·L−1·h−1 and 18.99 mgN·L−1·h−1, respectively, confirming that the anammox process was involved. Candidatus Brocadia was the main anammox bacteria, accounting for 16.5% of the relative abundance among nitrogen removal bacteria in the red granules, cooperating with denitrifying bacteria (DNB) and ammonia oxidizing bacteria (AOB) in removing nitrogen. Anammox bacteria occur naturally in swine wastewater treatment systems and provide promising evidence for future direct application of this technology in treating swine wastewater at full scale.

Nutrient Limitation Causes Differential Expression of Transport- and Metabolism Genes in the Compartmentalized Anammox Bacterium Kuenenia stuttgartiensis.

Anaerobic ammonium-oxidizing (anammox) bacteria, members of the “Candidatus Brocadiaceae” family, play an important role in the nitrogen cycle and are estimated to be responsible for about half of the oceanic nitrogen loss to the atmosphere. Anammox bacteria combine ammonium with nitrite and produce dinitrogen gas via the intermediates nitric oxide and hydrazine (anammox reaction) while nitrate is formed as a by-product. These reactions take place in a specialized, membrane-enclosed compartment called the anammoxosome. Therefore, the substrates ammonium, nitrite and product nitrate have to cross the outer-, cytoplasmic-, and anammoxosome membranes to enter or exit the anammoxosome. The genomes of all anammox species harbor multiple copies of ammonium-, nitrite-, and nitrate transporter genes. Here we investigated how the distinct genes for ammonium-, nitrite-, and nitrate- transport were expressed during substrate limitation in membrane bioreactors. Transcriptome analysis of Kuenenia stuttgartiensis planktonic cells showed that four of the seven ammonium transporter homologs and two of the nine nitrite transporter homologs were significantly upregulated during ammonium-limited growth, while another ammonium transporter- and four nitrite transporter homologs were upregulated in nitrite limited growth conditions. The two nitrate transporters were expressed to similar levels in both conditions. In addition, genes encoding enzymes involved in the anammox reaction were differentially expressed, with those using nitrite as a substrate being upregulated under nitrite limited growth and those using ammonium as a substrate being upregulated during ammonium limitation. Taken together, these results give a first insight in the potential role of the multiple nutrient transporters in regulating transport of substrates and products in and out of the compartmentalized anammox cell.

Effect of Cathode Material and Its Size on the Abundance of Nitrogen Removal Functional Genes in Microcosms of Integrated Bioelectrochemical-Wetland Systems

Constructed wetland-microbial electrochemical snorkel (CW-MES) systems, which are short-circuited microbial fuel cells (MFC), have emerged as a novel tool for wastewater management, although the system mechanisms are insufficiently studied in process-based or environmental contexts. Based on quantitative polymerase chain reaction assays, we assessed the prevalence of different nitrogen removal processes for treating nitrate-rich waters with varying cathode materials (stainless steel, graphite felt, and copper) and sizes in the CW-MES systems and correlated them to the changes of N2O emissions. The nitrate and nitrite removal efficiencies were in range of 40% to 75% and over 98%, respectively. In response to the electrochemical manipulation, the abundances of most of the nitrogen-transforming microbial groups decreased in general. Graphite felt cathodes supported nitrifiers, but nirK-type denitrifiers were inhibited. Anaerobic ammonium oxidation (ANAMMOX) bacteria were less abundant in the electrochemically manipulated treatments compared to the controls. ANAMMOX and denitrification are the main nitrogen reducers in CW-MES systems. The treatments with 1:1 graphite felt, copper, plastic, and stainless-steel cathodes showed higher N2O emissions. nirS- and nosZI-type denitrifiers are mainly responsible for producing and reducing N2O emissions, respectively. Hence, electrochemical manipulation supported dissimilatory nitrate reduction to ammonium (DNRA) microbes may play a crucial role in producing N2O in CW-MES systems.

Analyzing the effect of organic carbon on partial nitrification-anammox process based on metagenomics and quorum sensing.

The effects of adding organic carbon on the performance of different partial nitrification-anammox (PNA) process (the activated sludge process and biofilm process) were studied, especially nitrogen removal, functional microbial activity, and microbial community structure. The potential influences of quorum sensing (QS) on the nitrogen metabolism were also analyzed. The results showed that the addition of organic carbon in biofilm systems could reduce total nitrogen (TN) removal percentages, while in activated systems it could increase TN removal percentages. The TN removal percentages in SBBR-CN (the biofilm system with addition of organic carbon) and SBR-CN (the activated sludge system with addition of organic carbon) were 15% and 45%, respectively, and those in SBBR-N (the biofilm system without addition of organic carbon) and SBR-N (the activated sludge system without addition of organic carbon) were 75% and 21%, respectively. Batch experiments have proved that organic carbon inhibited the activities of nitrite-oxidizing bacteria (NOB) and anaerobic ammonia oxidation (anammox) bacteria, and organic carbon could promote the activity of denitrifying bacteria in activated sludge systems. Compared with activated sludge systems, biofilm systems could protect the activity of anammox bacteria. The relative abundances of ammonia oxidizing bacteria (AOB) and anammox bacteria were decreased, while the relative abundances of denitrifying bacteria (Thauera) were increased with the addition of organic carbon. The biofilm systems were more conducive to the growth of anammox bacteria. Metagenomics revealed that the same bacteria might be involved in different nitrogen metabolism, and nitrogen metabolism was achieved through the complex cooperation among functional bacteria. Besides, functional bacteria involving in the nitrogen metabolism had genes related to QS, indicating that QS might affect the nitrogen metabolism by regulating the functional bacteria activity. PRACTITIONER POINTS: PNA was achieved through SBBR and complete nitrification was achieved through SBR under the low ammonia nitrogen concentration condition. The effect of organic carbon on biofilm and activated sludge PNA process was different under the low ammonia nitrogen concentration condition. QS and QQ may affect the nitrogen removal performance by regulating the expression of nitrogen metabolism-related genes.

Effective inhibition prevention strategy for the enrichment of anammox bacteria with low concentrations of substrates at 25 °C

This work aimed to enrich anaerobic ammonia oxidation (anammox) bacteria, which can be potentially used in mainstream wastewater treatment systems for enhancing economical autotrophic nitrogen removal. Anammox bacteria were enriched in a sequencing batch reactor (SBR) with continuous feeding of ammonia and nitrite at 25 ± 2 °C. The results indicated that the concentrations of ammonia and nitrite at each moment ranged from 0 mg/L to 30 mg/L and 0 mg/L to 10 mg/L respectively, by adjusting the feed stream supply rate based on the reaction rate. Furthermore, the free ammonia (FA) and free nitrous acid (FNA) concentrations were controlled systematically at desired low levels of 0–1.96 mg/L and 0–2.94 μg/L respectively, to prevent substrate inhibition on anammox bacteria. Candidatus Kuenenia-anammox bacteria were highly enriched for approximately 4 months, as demonstrated by the proportion increased from a negligible value to 17.60 %. This promising operational mode proposed an available choice to enrich various microorganisms of expected functions, to accelerate reactor start-up and enhance biological efficiency.

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.

Fast Start-Up ANAMMOX Operation Strategy and Flora Characteristics of a Biofilter

To achieve the rapid start-up of anaerobic ammonia oxidation (ANAMMOX) reaction at room temperature and sludge granulation, a small amount of ANAMMOX sludge was inoculated by an upflow biological filter reactor, and ANAMMOX was started by stage variable load and shortening hydraulic residence time (HRT) operation strategy. The reaction was evaluated, and the nitrogen removal characteristics of the biofilter were evaluated. The results showed that the biofilter started the ANAMMOX reaction in a medium-temperature (25-29℃) environment for 22 days. After 97 days of culture, the total nitrogen volume removal rate (NRR) reached 5.64 kg·(m3·d)-1, the total nitrogen (TN) removal rate was close to 80%, and the average particle size of the granular sludge was 4.5 mm. High-throughput sequencing analysis showed that the biofilter formed a layered structure of nitrifying bacteria-heterotrophic bacteria, anaerobic ammonium oxidation bacteria (AAOB), and AAOB-heterotrophic bacteria from bottom to top. The various microflora synergistically denitrified, creating a low dissolved oxygen (DO) stable environment for AAOB, and the dominant population Candidatus Kuenenia (AF375995.1) was enriched. In addition, the removal process of pollutants along the path and the characteristics of sludge along the process were analyzed, and it was verified that the sludge in the reaction zone had good ANAMMOX activity. An ANAMMOX-biofilter reactor achieves rapid start-up of the ANAMMOX reaction, sludge granulation, and efficient operation by effectively maintaining the amount of bacteria and stabilizing the reaction conditions.

Effect of Hydroxylamine on Community of ANAMMOX Sludge

At present, the anaerobic ammonium oxidation (ANAMMOX) process has the advantages of high efficiency, low energy consumption, and low sludge quantity, and it therefore has broad application prospects in sewage nitrogen removal. Hydroxylamine is not only an intermediate product of ANAMMOX metabolism but also an inhibitor. However, the effect of hydroxylamine on the activity of ANAMMOX is not clear. Therefore, we investigated the ANAMMOX activity under the condition of adding different concentrations of hydroxylamine (40-80 mg·L-1) through a hydroxylamine batch experiment. It was found that hydroxylamine can inhibit ANAMMOX activity. However, it was impossible to determine the threshold of ANAMMOX bacteria to hydroxylamine. Next, the mRNA levels of hydrazine oxidase (HZO) in different reactors were detected by real-time fluorescent quantitative polymerase chain reaction (RT-qPCR), and it was found that the expression levels of HZO peak and then decrease with an increase of hydroxylamine concentration. It was suggested that the tolerated hydroxylamine concentration was within 60-70 mg·L-1 for 3.12 g·L-1 ANAMMOX granular sludge. Moreover, a 16S rRNA high-throughput sequencing method was used to analyze the structure and function of ANAMMOX granules in microbial communities in the reactor. It was found that the addition of an appropriate concentration of hydroxylamine (50 mg·L-1) helped to enhance the cellular motility of bacteria and promoted the composition of ANAMMOX bacteria, providing a better ecological balance.

Diversity, enrichment, and genomic potential of anaerobic methane- and ammonium-oxidizing microorganisms from a brewery wastewater treatment plant

Anaerobic wastewater treatment offers several advantages; however, the effluent of anaerobic digesters still contains high levels of ammonium and dissolved methane that need to be removed before these effluents can be discharged to surface waters. The simultaneous anaerobic removal of methane and ammonium by denitrifying (N-damo) methanotrophs in combination with anaerobic ammonium-oxidizing (anammox) bacteria could be a potential solution to this challenge. After a molecular survey of a wastewater plant treating brewery effluent, indicating the presence of both N-damo and anammox bacteria, we started an anaerobic bioreactor with a continuous supply of methane, ammonium, and nitrite to enrich these anaerobic microorganisms. After 14 months of operation, a stable enrichment culture containing two types of ‘Candidatus Methylomirabilis oxyfera’ bacteria and two strains of ‘Ca. Brocadia’-like anammox bacteria was achieved. In this community, anammox bacteria converted 80% of the nitrite with ammonium, while ‘Ca. Methylomirabilis’ contributed to 20% of the nitrite consumption. The analysis of metagenomic 16S rRNA reads and fluorescence in situ hybridization (FISH) correlated well and showed that, after 14 months, ‘Ca. Methylomirabilis’ and anammox bacteria constituted approximately 30 and 20% of the total microbial community. In addition, a substantial part (10%) of the community consisted of Phycisphaera-related planctomycetes. Assembly and binning of the metagenomic sequences resulted in high-quality draft genome of two ‘Ca. Methylomirabilis’ species containing the marker genes pmoCAB, xoxF, and nirS and putative NO dismutase genes. The anammox draft genomes most closely related to ‘Ca. Brocadia fulgida’ included the marker genes hzsABC, hao, and hdh. Whole-reactor and batch anaerobic activity measurements with methane, ammonium, nitrite, and nitrate revealed an average anaerobic methane oxidation rate of 0.12 mmol h−1 L−1 and ammonium oxidation rate of 0.5 mmol h−1 L−1. Together, this study describes the enrichment and draft genomes of anaerobic methanotrophs from a brewery wastewater treatment plant, where these organisms together with anammox bacteria can contribute significantly to the removal of methane and ammonium in a more sustainable way.Key points• An enrichment culture containing both N-damo and anammox bacteria was obtained.• Simultaneous consumption of ammonia, nitrite, and methane under anoxic conditions.• In-depth metagenomic biodiversity analysis of inoculum and enrichment culture.

The effect of the COD: N ratio on mainstream deammonification in an integrated fixed-film activated sludge sequencing batch reactor

For eight months, a sequencing batch reactor (SBR) with integrated fixed-film activated sludge (IFAS) was operated in ambient temperature to study engineering and practical aspects of application of deammonification for mainstream conditions. For biofilm formation, K3 Kaldnes carriers were used, where the anaerobic ammonium oxidation (anammox) process can occur in deep layers of biofilm, while partial nitritation occurs in oxygen-rich outer layers. After the initial running phase of the reactor (Phase 1) to provide time for microorganisms to adapt, the COD: N ratio increased to around 2.6 in Phase 2 through reducing the ammonium concentration and increasing COD in synthetic wastewater to get closer to mainstream conditions. The total reaction time in each half-day batch cycle was kept 625 min throughout various phases, but the duration of intermittent aeration was regulated at 4 ± 1 min. While final nitrogen removal efficiency (NRE) for Phase 1 was 43%, at the end of Phase 2, it decreased to 37%. However, a maximum NRE at 90% was achieved during Phase 2. The identification of the responsible microorganisms was made through Fluorescence in situ hybridization (FISH), while Mixed Liquor Suspended Solid (MLSS) and Mixed Liquor Volatile Suspended Solid (MLVSS) was used to estimate the physical presence of bacteria. Ammonium oxidizing bacteria (AOB) and anaerobic ammonia-oxidizing bacteria (AnAOB) were dominant bacteria, respectively. The adverse effects of a gradual increase of COD: N ratio from 0.17 to more than 2.0 caused a decline in NRE to around 15%.

The interaction of dissolved organic nitrogen removal and microbial abundance in iron-filings based green environmental media for stormwater treatment

Nonpoint sources pollution from agricultural crop fields and urbanized regions oftentimes have elevated concentrations of dissolved organic nitrogen (DON) in stormwater runoff, which are difficult for microbial communities to decompose. The impact of elevated DON can be circumvented through the use of green sorption media, such as Biosorption Activated Media (BAM) and Iron-Filing Green Environmental Media (IFGEM), which, as integral parts of microbial ecology, can contribute to the decomposition of DON. To compare the fate, transport, and transformation of DON in green sorption media relative to natural soil (control), a series of fixed-bed columns, which contain natural soil, BAM, and two types of IFGEM, respectively, were constructed to compare nutrient removal efficiency under three distinct stormwater influent conditions containing nitrogen and phosphorus. The interactions among six microbial species, including ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, complete ammonia oxidation (comammox) bacteria, anaerobic ammonium oxidation (anammox) bacteria, dissimilatory nitrate reduction to ammonium bacteria, and iron-reducing bacteria, were further analyzed from microbial ecology perspectives to determine the DON impact on nutrient removal in BAM and IFGEM. Natural soil was only able to achieve adequate DON transformation at the influent condition of lower nutrient concentration. However, the two types of IFGEM showed satisfactory nutrient removals and achieved greater transformation of DON relative to BAM when treating stormwater in all three influent conditions.

Effect of Ni(Ⅱ) on Anaerobic Ammonium Oxidation and Changes in Kinetics

Anaerobic ammonium oxidation (ANAMMOX) is widely used for treatment of ammonium-rich wastewater because of its economic and environmental benefits. However, ANAMMOX bacteria are sensitive to environmental conditions, especially to heavy metals. The short-term and long-term effects of Ni(Ⅱ) on ANAMMOX were studied by batch and continuous flow experiments, respectively. Results showed that low concentrations of Ni(Ⅱ) had promoted nitrogen removal by ANAMMOX and high concentrations inhibited ANAMMOX performance during a short-term period. Compared with the specific anaerobic ammonium oxidation activity (SAA) without Ni(Ⅱ) addition, SAA with 1 mg·L-1 Ni(Ⅱ) addition increased by 11.14% and the SAA with 100 mg·L-1 Ni(Ⅱ) addition reduced by 49.55%. The IC50 of Ni(Ⅱ) for ANAMMOX was determined to be 83.86 mg·L-1. In contrast, long-term Ni(Ⅱ) addition significantly suppressed nitrogen removal of ANAMMOX, and the suppression threshold of Ni(Ⅱ) on ANAMMOX was 15 mg·L-1. The Monod model was applied to simulate the kinetics of ANAMMOX without Ni(Ⅱ) addition. The qmax0(TN/VSS) and KS0 values were 12.25 mg·(g·h)-1 and 405.36 mg·L-1, respectively. The modified Haldane model was suitable to describe the kinetics of ANAMMOX with 50 mg·L-1 Ni(Ⅱ) addition. The qmax(TN/VSS), KS, and Ki values were 6.78 mg·(g·h)-1, 313.2 mg·L-1, and 1.32, respectively. The inhibition of ANAMMOX by Ni(Ⅱ) is anticompetitive inhibition. In addition, the inhibition of Ni(Ⅱ) on ANAMMOX was mainly related to the content of intracellular Ni(Ⅱ). The IC50intracellular Ni(Ⅱ)(VSS) of intracellular Ni(Ⅱ) was 0.072 mg·g-1.

Critical design factors for polyvinyl alcohol hydrogel entrapping ammonia-oxidizing bacteria: biomass loading, distribution of dissolved oxygen, and bacterial liability

The single-stage configuration of the partial nitritation (PN)–anaerobic ammonium oxidation (AMX) process is preferred due to low pH fluctuation and the low concentration of inhibitory NO2-. The novel core-shell structure integrates ammonia-oxidizing reaction in the outer layer to protect AMX bacteria in the core gel bead from oxygen inhibition and provide NO2-. Here, the initial activity of ammonia-oxidizing bacteria (AOB) in the outer layer was assessed by the specific oxygen uptake rate (OUR). AOB activity was positively correlated with biomass loading in the outer layer. A maximum OUR of 10.5 mg-DO/L∙h was achieved with AOB loading of 0.23 mg-VSS per bead. During AOB enrichment, the NO2- production rate was linearly increased up to 0.65 kg-N/m3-d for 17 days (PVA hydrogel packing ratio=17%). The maximum oxygen penetration depth (OPD) was reduced from 966.7±52.3 μm before enrichment to 333.3±36.4 μm after the AOB enrichment. The liable bacteria were observed within a range of 165 μm of the outer layer using the live and dead cell staining. Based on the OPD and liable cell distribution results, a minimal outer layer thickness of approximately 350 μm was suggested to facilitate a successful PN–AMX process.

Simultaneous anammox and denitrification process shifted from the anammox process in response to C/N ratios: Performance, sludge granulation, and microbial community

An up-flow anaerobic sludge blanket (UASB) reactor was operated to investigate the performance, sludge granulation, and microbial community dynamics of the simultaneous anammox and denitrification (SAD) process at different C/N ratios by inducing a shift from the anammox process. The nitrogen removal efficiency (NRE) increased with an increase in the C/N ratio at lower C/N ratios (≤ 0.5). The NRE and nitrogen removal rate (NRR) were 90.81% and 1.75 kgN m-3d-1, respectively, at a C/N ratio of 0.5. The contribution of the anammox process to nitrogen removal (Eanammox) decreased sharply to 51% from 81% as a result of the decreased activity of the anaerobic ammonia-oxidizing bacteria (AnAOB) at a C/N ratio of 0.9. The EPS production and the ratio of the protein fraction of EPS (EPSp) to the carbohydrate fraction of EPS (EPSc) increased with the increase in the C/N ratio (0.0-0.9), which induced sludge aggregation and resulted in larger particle size. The enrichment of denitrifying bacteria (DNB) on the surface of the AnAOB due to EPS bridging further enhanced sludge granulation. The Illumina sequencing results showed that the dominant genus of AnAOB (Candidatus Jettenia) initially increased with an increase in the C/N ratio at lower levels and then decreased sharply at a C/N ratio of 0.9. The relative abundance of Candidatus Jettenia was promoted by decreasing the C/N ratio, which supported the recovery of the AnAOB activity. Denitratisoma, Bacillus, Acinetobacter, and Pseudomonas were responsible for denitrification throughout the entire operational period.