Successful start-up of the anammox process: Influence of the seeding strategy on performance and granule properties

Insight into the short-term effect of fulvic acid on nitrogen removal performance and N-acylated-L-homoserine lactones (AHLs) release in the anammox system

Fulvic acid (FA) can serve as electron shuttles between bacteria and electron acceptors. It explored the short-term effect of FA dose on nitrogen removal performance and N-acylated-_L-homoserine lactones (AHLs) release change in the anaerobic ammonium oxidation (anammox) system. The results demonstrated that the total inorganic nitrogen removal efficiency increased with the FA dosages from 0.5 mM to 1 mM. FA addition improved anammox bacteria activity, together with extracellular polymeric substances production. FA addition from 0.5 mM to 1 mM stimulated AHLs release in both water and biomass phases, which indicated that the quorum sensing could be improved. These findings revealed that the addition of FA could improve quorum sensing and then enhance nitrogen removal performance.

Soil pH is the primary factor driving the distribution and function of microorganisms in farmland soils in northeastern China

Purpose

To understand which environmental factors influence the distribution and ecological functions of bacteria in agricultural soil.

Method

A broad range of farmland soils was sampled from 206 locations in Jilin province, China. We used 16S rRNA gene-based Illumina HiSeq sequencing to estimated soil bacterial community structure and functions.

Result

The dominant taxa in terms of abundance were found to be, Actinobacteria, Acidobacteria, Gemmatimonadetes, Chloroflexi, and Proteobacteria. Bacterial communities were dominantly affected by soil pH, whereas soil organic carbon did not have a significant influence on bacterial communities. Soil pH was significantly positively correlated with bacterial operational taxonomic unit abundance and soil bacterial α-diversity (P<0.05) spatially rather than with soil nutrients. Bacterial functions were estimated using FAPROTAX, and the relative abundance of anaerobic and aerobic chemoheterotrophs, and nitrifying bacteria was 27.66%, 26.14%, and 6.87%, respectively, of the total bacterial community. Generally, the results indicate that soil pH is more important than nutrients in shaping bacterial communities in agricultural soils, including their ecological functions and biogeographic distribution.

Metagenomic insights into functional traits variation and coupling effects on the anammox community during reactor start-up

Anammox technology is an energy-efficient wastewater treatment process and anammox community structure has gained extensive attention. However, the dynamics of community functional traits are still elusive. Here, we combined the long-term reactor operation and metagenomic, multiple bioinformatic and network analyses to reveal the succession of anammox community and function traits during reactor start-up. We found the cooperation of denitrifiers that affiliated to the phylum Proteobacteria could reduce nitrite to dinitrogen gas. These organisms and genes had higher abundance after the inhibition phase, which could contribute to nitrite consuming and reactor performance recovery. Importantly, the Terrimonas and Anaerolinea organisms had ability of extracellular polymers secretion or aggregate formation. They had the highest abundance at the end of the lag phase, which could benefit for promoting the nitrogen removal rate (NRR). Meanwhile, Terrimonas and Anaerolinea bacteria could cooperate with methanogenic and nitrite-denitrifying methanotrophic organisms based on H₂ and CH₄, respectively. Since these organisms also had higher abundance after the inhibition phase, their cooperation could prevent anammox bacteria from nitrite inhibiting when the influent nitrite concentration was higher. The analysis of community and function shift is expected to emphasize the importance of functional bacteria in anammox process and provides a potential control strategy for nitrogen-containing wastewater treatment process.

Strategy of rapid start-up and the mechanism of de-nitrogen in landfill bioreactor

Nitrogen removal from landfill leachate via anaerobic ammonium oxidation (Anammox) process has been considered as an innovative and sustainable approach to the traditional nitrification and denitrification process. However, the various technologies for rapid start-up of Anammox are still being explored. In this study, two strategies (inoculating anaerobic sludge and without inoculation) were applied to treat landfill leachate based on biological nitrogen removal processes. The start-up and mechanism of de-nitrogen process in landfill bioreactor was explored using 15N stable isotopic tracing, quantitative polymerase chain reaction (qPCR) and high-throughput sequencing methods. Results showed that inoculating anaerobic sludge was beneficial to enhance the nitrogen removal at the initial stage (from day 10 to day 25), but no significant increase was found during days 25-55 (p > 0.05). 15N stable isotopic tracing demonstrated that the inoculation of sludge accelerated by denitrification other than Anammox. Inoculation of sludge was conducive to increase of ammonia-oxidizing bacteria (AOB)- amoA and niK genes. Thauera was the dominant genus for nitrogen removal due to inoculation of sludge in landfill bioreactor, whereas the abundance of Candidatus Kuenenia did not increase by inoculating the sludge. Moreover, seeding anaerobic sludge could not provide Anammox's ecological niches. The results will provide a scientific basis for the selection of suitable operational condition for the rapid start-up in the landfill bioreactor.

Start-up and operational performance of Anammox process in an anaerobic baffled biofilm reactor (ABBR) at a moderate temperature

A lab-scale anaerobic baffled biofilm reactor (ABBR) was used as a novel reactor to start up Anammox process at a moderate temperature around 20 °C and an innovative filling module was adopted as support material. Quick start-up of Anammox process from the aerobic activated sludge was achieved after 47 days operation. The max nitrogen loading rate and nitrogen removing rate attained 1.00 kg N m^-3 d^-1 and 0.90 kg N m^-3 d^-1 after 161 days operation. Scanning electron microscope photographs showed that the structure as well as the states of the micro-aggregates (micro-aggregates sticking on a non-woven fiber, entangling non-woven fibers and enwrapped by non-woven fibers) enhanced biomass retention for Anammox bacteria. Microbial community analysis showed that Anammox bacteria were effectively enriched with Candidatus Brocadia, Candidatus Jettenia and Candidatus Kuenenia being the main Anammox species in the mature biofilms. This contributed to the excellent Anammox operation performance at the moderate temperature.

Abundance and diversity of nitrogen-removing microorganisms in the UASB-anammox reactor

Anaerobic ammonium oxidation is considered to be the most economical and low-energy biological nitrogen removal process. So far, anammox bacteria have not yet been purified from cultures. Some nitrogen-removing microorganisms cooperate to perform the anammox process. The objective of this research was to analyze the abundance and diversity of nitrogen-removing microorganisms in an anammox reactor started up with bulking sludge at room temperature. In this study, the ammonia-oxidizing archaea phylum Crenarchaeota was enriched from 9.2 to 53.0%. Nitrosomonas, Nitrosococcus, and Nitrosospira, which are ammonia-oxidizing bacteria, increased from 3.2, 1.7, and 0.1% to 12.8, 20.4, and 3.3%, respectively. Ca. Brocadia, Ca. Kuenenia, and Ca. Scalindua, which are anammox bacteria, were detected in the seeding sludge, accounting for 77.1, 11.5, and 10.6%. After cultivation, the dominant genus changed to Ca. Kuenenia, accounting for 82.0%. Nitrospirae, nitrite oxidation bacteria, decreased from 2.2 to 0.1%, while denitrifying genera decreased from 12.9 to 2.1%. The results of this study contribute to the understanding of nitrogen-removing microorganisms in an anammox reactor, thereby facilitating the improvement of such reactors. However, the physiological and metabolic functions of the ammonia-oxidizing archaea community in the anammox reactor need to be investigated in further studies.

Recent advances in nitrogen removal from landfill leachate using biological treatments - A review

Landfill leachate, generated from the wastes in a landfill, is a type of wastewater with high concentrations of ammonia and organics, causing a serious environmental pollution. Because of its complex and changing characteristics, it is difficult to remove nitrogen from landfill leachate economically and effectively. Hence, nitrogen removal is a significant research priority of landfill leachate treatment in recent years. Biological processes are known to be effective in nitrogen removal. In this work, the biological nitrogen removal treatments were divided into the following processes: conventional nitrification-denitrification process, nitritation-denitritation process, endogenous denitritation process, and anaerobic ammonium oxidation (Anammox) process. This manuscript summarized the theories and applications of these approaches in detail, and concluded that appropriate processes should be selected in accordance with different characteristics of landfill leachate, in order to effectively remove nitrogen from all stages of landfill leachate and reduce disposal costs. Finally, perspective on the challenges and opportunities of biological nitrogen removal from landfill leachate was also presented.

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

The characteristic carmine red color due to heme proteins is always observed in enriched anammox biomass. Heme c is a very important co-factor participating the main metabolic reactions with catalytic and electron-transfer potential in the anammox bacteria, and is possible for use as an indicator to evaluate anammox performance. Knowledge of the relationship between the heme c concentration and the anammox reactor performance is, however, very limited available information is constrained at an operation temperature of 35 °C. In this study, we report the heme c concentration change along with nitrogen removal rate (NRR) in three anammox expanded granular sludge bed reactors operated at different temperatures (15, 25, 35 °C). The response of specific anammox activity (SAA) to temperature was revealed for biomass originating from three reactors. The results indicate a strong relationship between heme c concentration and NRR at different culture temperatures. The possibility of evaluating the anammox performance by combining heme c quantification and the temperature is revealed.

Roles and correlations of functional bacteria and genes in the start-up of simultaneous anammox and denitrification system for enhanced nitrogen removal

Simultaneous anammox and denitrification (SAD) is a newly developed wastewater treatment process efficient in nitrogen removal, but its underlying microbiological mechanisms during start-up remains unknown. This study investigated the changing patterns of functional bacteria and genes, as well as their correlation during the start-up (260 d) of the SAD systems in two lab-scale up-flow anaerobic sludge blanket bioreactors separately inoculated with anaerobic granular sludge (R1) and aerobic floccular sludge (R2). Results showed that high total nitrogen removal was achieved in the SAD systems of both R1 (88.25%) and R2 (89.42%). High-throughput sequencing of 16S rRNA gene amplicons revealed that Armatimonadetes phylum had a high abundance (44.34%) in R2, while was not detectable in R1 during the anammox stage. However, the SAD bioreactors retained inherent microbial community and the inoculation with different sludge showed less notable effects on their microbial composition. In the SAD systems, Candidatus Brocadia had high abundance in R1 (2.93%) and R2 (4.64%) and played important role in anammox. Network analysis indicated that Denitratisoma and Dokdonella were positively correlated with nitrite reductase genes nirS and nirK (p < 0.05), while Thermomonas and Pseudomonas showing a positive correlation with nitrate reductase gene narG (p < 0.05) were mainly responsible for the nitrate reduction in the SAD systems. Moreover, the overwhelming dominance of narG v.s. napA revealed the crucial roles of respiratory nitrate reduction in the bioreactors. The results extend our knowledge regarding the microbial ecology of the SAD system, which might be practically helpful for application of the process in wastewater treatment.

Anammox granule as new inoculum for start-up of anaerobic sulfide oxidation (ASO) process and its reverse start-up

The feasibility of implementing anaerobic ammonium oxidation (anammox) granules to start up high-loading anaerobic sulfide oxidation (ASO) in an upflow anaerobic sludge bed (UASB) reactor was investigated. An innovation method of the reverse start-up of anammox was also validated. Firstly, the reactor was operated to treat sulfide-rich wastewaters into which nitrite was introduced as an electron acceptor. An high-rate performance with sulfide and nitrate removal rates of 105.5 ± 0.11 kg S m^-3 d^-1 and 28.45 ± 3.40 kg N m^-3 d^-1, respectively, was accomplished. Sulfurovum were enriched with the increase of the substrate load and then conquered Candidatus Kuenenia to be the predominant bacteria. Excitation-emission matrix (EEM) spectroscopy showed that the intensities of fluorescence decreased and protein-like substrates were the main components associated with the process of start-up. FT-IR analysis found that the main functional groups indicator were O-H groups. Secondly, the reverse start-up of anammox (achieving 90% TN removal) was achieved immediately when the substrate changed. 16S rRNA analysis indicated the successfully enrichment of anammox bacteria (Candidatus Kuenenia). These results suggest that anammox granules can act as inoculum of high-loading ASO process and the reverse start-up provides a new perspective for the fast initiation of anammox process.

Fast start-up of anammox process with mixed activated sludge and settling option

In this study, successful start-up of the anaerobic ammonium oxidation (anammox) process in a sequencing batch reactor (SBR) was achieved by seeding mixed activated sludge which included aerobic sludge, anaerobic sludge, simultaneous partial nitrification, anammox and denitrification (SNAD) sludge, and anammox sludge with low activity at a 2200:2100:5:2 volume ratio. On day 15, the effective anammox activity was attained in SBR, with the specific total nitrogen removal rate (SRR) of 0.214 gNg^-1 VSSd^-1. The total nitrogen removal rate (NRR) increased to 230 gNm^-3 d^-1 by gradually reducing the setting time to 10 min. With the nitrogen loading rate (NLR) up to 506 gNm^-3 d^-1, the total NRR of the SBR reached 433 gNm^-3 d^-1 during stationary phase. Candidatus Brocadia was detected as predominant functional microbes in the anammox SBR. The results demonstrated the feasibility of seeding mixed activated sludge to start-up an anammox SBR by settling option.

Influence of temperature on an Anammox sequencing batch reactor (SBR) system under lower nitrogen load

The nitrogen removal performance and microbial communities of an Anammox sequencing batch reactor (SBR) was studied under varied temperatures with a lower nitrogen loading rate (NLR) about 0.28 kgN/m³/d. Results showed that the temperature could influence the nitrogen removal performance and the community structure in the Anammox SBR system. Under lower temperatures, both the nitrogen removal efficiencies and Anammox activity were in lower levels. When temperature was raised again, the Anammox activity recovered accordingly. When the temperature dropped from 33 ± 1 °C to15 °C, the dominant Anammox bacteria shifted from Ca. Brocadia to Ca. Kuenenia in the sludge. When the temperature returned over, the abundance of Ca. Brocadia recovered, while the Ca. Kuenenia was still the dominant Anammox bacteria. This indicated that Ca. Kuenenia is more adaptable to low temperature environment than Ca. Brocadia under low NLR with temperature variation.

Selection of seeding strategy for fast start-up of Anammox process with low concentration of Anammox sludge inoculum

The long start-up time and large demand of Anammox seed sludge limit the practical application of Anammox process. In this study, the seeding strategy of fast start-up of Anammox process using 2.0 g VSS L^-1 of anaerobic granular sludge (AGS) or activated sludge (AS) with various low concentration of Anammox sludge as inoculum was investigated. In laboratory scale, the start-up (achieving 70% TN removal) was shortened from 21 days to 5 days when Anammox sludge concentration increased from 0.02 g VSS L^-1 to 0.2 g VSS L^-1 with 2 g VSS L^-1 AS as inoculum, and 16S rDNA analysis indicated the enrichment of Anammox bacteria, while the start-up failed with AGS. In pilot scale, the start-up was achieved in 10 days using 0.02 g VSS L^-1 of Anammox sludge and 2.0 g VSS L^-1 of AS, confirming the fast start-up of Anammox process with low concentration of Anammox sludge.

Genome-Centered Metagenomics Analysis Reveals the Symbiotic Organisms Possessing Ability to Cross-Feed with Anammox Bacteria in Anammox Consortia

Although using anammox communities for efficient wastewater treatment has attracted much attention, the pure anammox bacteria are difficult to obtain, and the potential roles of symbiotic bacteria in anammox performance are still elusive. Here, we combined long-term reactor operation, genome-centered metagenomics, community functional structure, and metabolic pathway reconstruction to reveal multiple potential cross-feedings during anammox reactor start-up according to the 37 recovered metagenome-assembled genomes (MAGs). We found Armatimonadetes and Proteobacteria could contribute the secondary metabolites molybdopterin cofactor and folate for anammox bacteria to benefit their activity and growth. Chloroflexi-affiliated bacteria encoded the function of biosynthesizing exopolysaccharides for anammox consortium aggregation, based on the partial nucleotide sugars produced by anammox bacteria. Chlorobi-affiliated bacteria had the ability to degrade extracellular proteins produced by anammox bacteria to amino acids to affect consortium aggregation. Additionally, the Chloroflexi-affiliated bacteria harbored genes for a nitrite loop and could have a dual role in anammox performance during reactor start-up. Cross-feeding in anammox community adds a different dimension for understanding microbial interactions and emphasizes the importance of symbiotic bacteria in the anammox process for wastewater treatment.

Fast start-up of the single-stage nitrogen removal using anammox and partial nitritation (SNAP) from conventional activated sludge in a membrane-aerated biofilm reactor

The single-stage nitrogen removal using anammox and partial nitritation (SNAP) is a promising alternative for low-cost ammonium removal from wastewaters. This study aimed to evaluate the anammox biomass enrichment and SNAP process start-up in a laboratory-scale membrane-aerated biofilm reactor (MABR) at nitrogen loading rates of 50 g N.m^-3.d^-1 (period 1) and 100 g N.m^-3.d^-1 (period 2). Anammox activity was observed after 48 days, and the SNAP process was stable after 80 days. In period 1, the average total nitrogen (TN) removal was 78 ± 6%, and the maximum removal was 84%. In period 2, the average TN removal was 61 ± 5%, and the maximum was 69%. Higher dissolved oxygen levels may have caused imbalances in the microbial community in period 2, decreasing the reactor performance. These results demonstrated the potential of the MABR for the fast implementation of the single-stage partial nitritation and anammox processes.

Roles of MnO2 on performance, sludge characteristics and microbial community in anammox system

The long-term impacts of MnO₂ on performance, sludge characteristics and microbial community of biogranule-based anaerobic ammonium oxidation (anammox) process were evaluated in an up-flow anaerobic sludge blanket reactor. It was found that the total nitrogen removal efficiency of reactor was fluctuated between 90%-93% at 1-200mgL^-1 MnO₂. Notably, the specific anammox activity was increased to maximum value of 657.3±10.6mgTNg^-1VSSd^-1 at 50mgL^-1 MnO₂ and then slightly decreased, but still higher than that achieved at 0-15mgL^-1 MnO₂, which had similar variation trends to the content of heme c and extracellular polymeric substances in anammox granules. High throughput sequencing indicated that MnO₂ could improve the microbial richness and diversity of anammox granules and Candidatus Kuenenia was always the dominant species, and its abundance continued to increase to 21.3% at the end of operational experiment. Therefore, MnO₂ could be applied to enhance the anammox process and the optimal influent MnO₂ concentration was lower than 50mgL^-1 in view of the reactor performance and cost issues.

Metagenomic approaches to understanding bacterial communication during the anammox reactor start-up

Increasing attention has been paid to the anammox community for its significant function in high-efficiency wastewater treatment. However, bacterial interaction in terms of bacterial communication is still elusive. This study firstly explored the intra- and interspecific communication of bacteria in the anammox community using metagenomic sequence data obtained during bioreactor operation. We verified the existence of multiple bacterial communication gene (BCG) subtypes by alignment with the constructed BCG database containing 11 identified gene subtypes. Bacterial communication was more active at the initial start-up than in the high loading-rate phase, and was correlated with the gradually decreasing bacterial diversity. Hdts, one of the key genes that produced the intraspecific signaling molecule AHL, and RpfF, the key gene that produced the intra- and interspecific signaling molecule DSF, were the primary communication engines in the anammox community because of their high abundance. Anammox bacteria mainly used Hdts genes to communicate with others, while RpfF gene played a core role characterized by their multiple correlations with other BCG subtypes. Interestingly, bacteria with abundant BCGs were more inclined to interact with the bacteria with the same functional traits, indicating the potential communication-related interaction among these bacteria in addition to the frequently reported substrate co-utilization. This highlights the primary importance of AHL and DSF for the anammox community, and thereby hints at a potential strategy for the target regulation of the signals to improve anammox viability and competitive capacity in wastewater treatment.

Oxygenic denitrification for nitrogen removal with less greenhouse gas emissions: Microbiology and potential applications

Nitrogen pollution is a worldwide problem and has been extensively treated by canonical denitrification (CDN) process. However, the CDN process generates several issues such as intensive greenhouse gas (GHG) emissions. In the past years, a novel biological nitrogen removal (BNR) process of oxygenic denitrification (O2DN) has been proposed as a promising alternative to the CDN process. The classic denitrification four steps are simplified to three steps by O2DN bacteria without producing and releasing the intermediate nitrous oxide (N₂O), a potent GHG. In this article, we summarized the findings in previous literatures as well as our results, including involved microorganisms and metabolic mechanisms, functional genes and microbial detection, kinetics and influencing factors and their potential applications in wastewater treatment. Based on our knowledge and experience, the benefits and limitations of the current O2DN process were analyzed. Since O2DN is a new field in wastewater treatment, more research and application is required, especially the development of integrated processes and the quantitative assessment of the contribution of O2DN process in natural habitats and engineered systems.

Using low frequency and intensity ultrasound to enhance start-up and operation performance of Anammox process inoculated with the conventional sludge

A lab-scale ultrasound enhancing Anammox reactor (R1) was established and irradiated once a week by ultrasound with the optimal parameter (frequency of 25 kHz, intensity of 0.2 W cm^-2 and exposure time of 3 min) obtained by batch experiments. R1 and the controlled Anammox reactor (R2) without exposure to the ultrasound were operated in parallel. The start-up period of Anammox process (53 days) in R1 was shorter than that (61 days) in R2. The nitrogen loading-enhancing period (day 53-day 135) in R1 was also shorter than that (day 61-day 151) in R2. At the end of the nitrogen loading-enhancing period, NLR (0.76 kg N m^-3 d^-1) and NRR (0.68 kg N m^-3 d^-1) of R1 were both higher than NLR (0.66 kg N m^-3 d^-1) and NRR (0.56 kg N m^-3 d^-1) of R2. Moreover, The stability of Anammox process in R1 was better than that in R2. The results demonstrated that the periodical irradiation of ultrasound enhanced the start-up and operational performance of Anammox reactor. Microbial community analysis indicated that the ultrasound accelerated the microbial succession from some other bacteria to Anammox bacteria so that shorten the start-up period of Anammox process from the conventional activated sludge. It also indicated that the ultrasound strengthened the competitive advantage of Candidatus Kuenenia stuttgartiensis in Anammox bacteria of the mature sludge so as to enhance the nitrogen removal performance of the Anammox reactor under the operation condition of high nitrogen loading.

Bacterial community evolutions driven by organic matter and powder activated carbon in simultaneous anammox and denitrification (SAD) process

A distinct shift of bacterial community driven by organic matter (OM) and powder activated carbon (PAC) was discovered in the simultaneous anammox and denitrification (SAD) process which was operated in an anti-fouling submerged anaerobic membrane bio-reactor. Based on anammox performance, optimal OM dose (50 mg/L) was advised to start up SAD process successfully. The results of qPCR and high throughput sequencing analysis indicated that OM played a key role in microbial community evolutions, impelling denitrifiers to challenge anammox's dominance. The addition of PAC not only mitigated the membrane fouling, but also stimulated the enrichment of denitrifiers, accounting for the predominant phylum changing from Planctomycetes to Proteobacteria in SAD process. Functional genes forecasts based on KEGG database and COG database showed that the expressions of full denitrification functional genes were highly promoted in R_C, which demonstrated the enhanced full denitrification pathway driven by OM and PAC under low COD/N value (0.11).

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

Granular deammonification process is a good way to retain aerobic and anaerobic ammonia oxidizing bacteria (AOB and anammox bacteria) and exhaust flocculent nitrite oxidizing bacteria (NOB). In this study, to facilitate indigenous AOB growth on anammox granules, by stepwise reducing influent nitrite, anammox granules were effectively transformed into deammonification granules in a micro-aerobic EGSB in 100 days. Total nitrogen removal efficiency of 90% and nitrogen removal rate of 2.3 g N/L/d were reached at stable deammonification stage. High influent FA and limited oxygen supply contributed suppression for Nitrospira-like NOB. In transition stages, Proteobacteria and Chloroflexi were always dominated. Anammox abundance decreased, while AOB abundance grew fast. Anammox bacteria and AOB were dominated by Brocadia fulgida and Nitrosomonas europaea, respectively. Denitrification activity and bacteria existed although without influent organic. The final AOB abundance was about 4.55-13.8 times more than anammox bacteria abundance, with almost equal potential activities.

Autoclaved sludge as the ideal seed to culture anammox bacteria: Reactor performance and microbial community diversity

Reducing activity of commensal bacteria in inocula may enhance anammox bacteria proliferation and realization of anammox process. Fast start-up of anammox process in an UASB reactor was successfully achieved by using autoclaved sludge (anaerobic granular sludge pretreated by autoclaving) and 0.3% active anammox sludge as inoculum. Continuous experiments indicated that R2 (autoclaved sludge addition) could shorten the start-up period from 72days to 63days. The first 50days anammox population specific growth rates (μ) of R1 (the control) and R2 were determined to be 0.014d^-1 and 0.045d^-1 using q-PCR assays. Analysis of coefficient of variations of nitrogen removal performance during days 96-225 indicated that R2 was more stable than R1. The Illumina MiSeq sequencing showed that autoclaving could decrease microbial diversity of sludge and enhance the abundance of anammox bacteria. Furthermore, PICRUSt community functions forecast and c-di-GMP measure illuminated the result of higher stability in R2.

Mass transfer characteristics, rheological behavior and fractal dimension of anammox granules: The roles of upflow velocity and temperature

In this study, the mass transfer, rheological behavior and fractal dimension of anaerobic ammonium oxidation (anammox) granules in upflow anaerobic sludge blanket reactors at various temperatures (8.5-34.5°C) and upflow velocities (0.06, 0.18mh^-1) were investigated. The results demonstrated that a lower temperature increased the external mass transfer coefficient and apparent viscosity and impaired the performance of anammox granules. The external mass transfer coefficient was decreased, but efficient nitrogen removal of up to 96% was achieved under high upflow velocity, which also decreased the apparent viscosity. Furthermore, a fractal dimension of up to 2.93 achieved at low temperature was higher than the previously reported values for mesophilic anammox granules. A higher upflow velocity was associated with the lower fractal dimension. Because of the disturbance in granule flaking, the effectiveness factor was less suitable than the external mass transfer coefficient for characterization of mass transfer resistance.

A pilot-scale study on the start-up of partial nitrification-anammox process for anaerobic sludge digester liquor treatment

Treatment of sludge digester liquor was successfully accomplished using a pilot-scale partial nitrification-anammox (PN/A) reactor with a nitrogen removal rate (NRR) of 1.23kgN/m³/d. A stable and efficient PN process was attained by controlling the concentration of free ammonia (0.7-8.4mg/L) and free nitrous acid (0.02-1.0mg/L). The application of hydroxylamine played a vital role in the reactivation of anammox bacteria. The bacteria exhibited improved granule properties at a specific input power between 0.065 and 0.097kW/m³, and achieved a specific anammox activity (SAA) of 1.01kgN/kgVSS/d on day 148. From day 0 to 120, the heme c content in the granules increased from 0.42±0.1 to 5.77±1.0µmol/gVSS, with a corresponding increase in NRRs and SAAs. High-throughput sequencing techniques revealed that the dominant anammox bacterial genus was Candidatus Brocadia. These conclusions provide valuable information for the full-scale treatment of sludge digester liquor.

Microbial monitoring of ammonia removal in a UASB reactor treating pre-digested chicken manure with anaerobic granular inoculum

Performance and microbial community dynamics in an upflow anaerobic sludge bed (UASB) reactor coupled with anaerobic ammonium oxidizing (Anammox) treating diluted chicken manure digestate (Total ammonia nitrogen; TAN=123±10mg/L) were investigated for a 120-d operating period in the presence of anaerobic granular inoculum. Maximum TAN removal efficiency reached to above 80% with as low as 20mg/L TAN concentrations in the effluent. Moreover, total COD (tCOD) with 807±215mg/L in the influent was removed by 60-80%. High-throughput sequencing revealed that Proteobacteria, Actinobacteria, and Firmicutes were dominant phyla followed by Euryarchaeota and Bacteroidetes. The relative abundance of Planctomycetes significantly increased from 4% to 8-9% during the late days of the operation with decreased tCOD concentration, which indicated a more optimum condition to favor ammonia removal through anammox route. There was also significant association between the hzsA gene and ammonia removal in the UASB reactor.

Impact of substrate concentration on anammox-UBF reactors start-up

Two up-flow blanket filter (UBF) reactors were employed to treat synthetic wastewater with different substrate concentrations and nitrogen load rates (NLR) for 178days. During days 0-60, higher influent NLR of R₂ (0.21-0.58kg·m³·d) slowed down the formation of anammox sludge compared with the lower NLR of R₁ (0.18-0.31kg·m³·d). Difference in sludge color and nitrogen conversion rate indicated greater anammox activity of R₂ than R₁. During days 61-178, R₁ and R₂ achieved the maximum nitrogen removal rates (NRR) of 1.213 and 1.684kg/(m³·d) under the NLRs of 1.924 and 2.502kg/(m³·d), respectively. Furthermore, high-throughput sequencing showed that R₂ (43.5%) had a higher proportion of anammox bacteria than R₁ (37.8%) and less species. These results showed that after going through a higher NLR acclimation process during start-up period, stronger resistant capability against high impact nitrogen load and greater anammox activity were obtained by R₂.

Nitrogen removal performance and loading capacity of a novel single-stage nitritation-anammox system with syntrophic micro-granules

The operation performance of a novel micro-granule based syntrophic system of nitritation and anammox was studied by controlling the oxygen concentration and maintaining a constant temperature of 25°C. With the oxygen concentration of around 0.11 (<0.15)mg/L, the single-stage nitritation-anammox system was startup successfully at a nitrogen loading rate (NLR) of 1.5kgN/m³/d. The reactor was successfully operated at volumetric N loadings ranging from 0.5 to 2.5kgN/m³/d with a high nitrogen removal of 82%. The microbial community was composed by ammonia oxidizing bacteria (AOB) and anammox bacteria forming micro-granules with an average diameter of 0.8mm and good settleability. Results from pyrosequencing analysis revealed that Ca. Kuenenia and Nitrosomonas were selected and enriched in the community over the startup period, and these were identified as the dominant anammox bacteria and AOB species, respectively.

Rapid start-up of the anammox process: Effects of five different sludge extracellular polymeric substances on the activity of anammox bacteria

This study investigated the rapid start-up of the anaerobic ammonium oxidation (anammox) strategy by inoculating different biomass ratios of denitrifying granular sludge and anammox bacteria. The results demonstrated that two reactors (R1 and R2) were rapidly and successfully started-up on days 25 and 28, respectively, with nitrogen removal rates (NRRs) of 0.70kg/(m(3)·d) and 0.72kg/(m(3)·d) at biomass ratios of 10:1 (R1) and 50:1 (R2). The explanation for rapid start-up was found by examining the effect of five different sludge extracellular polymeric substances (EPS) on the activity of anammox bacteria in the batch experiments. Batch experiments results first demonstrated that the denitrification sludge EPS (DS-EPS) enhanced the anammox bacteria activity the most, and NO2(-)-N, NH4(+)-N removal rates were 1.88- and 1.53-fold higher than the control with optimal DS-EPS volume of 10mL. The rapid start-up strategy makes possible the application of anammox to practical engineering.

The role of residual quantities of suspended sludge on nitrogen removal efficiency in a deammonifying moving bed biofilm reactor

In a moving bed biofilm reactor (MBBR) system, the vast majority of biomass is immobilized as biofilm besides small amounts of suspension. In this study, the influence of the individual biomass components of a deammonifying MBBR, the biofilm on carriers (BC), residual suspended biomass (SB) with a volatile suspended solids concentration of 0.09±0.03g/L, and its combination (BC+SB) on nitrogen removal efficiency was investigated. While the performance was highest for BC+SB (0.42kgN/(m(3)·d)), it was reduced by a factor of 3.5 for BC solely. SB itself was only capable of nitrite accumulation. This suggests a high abundance of AOBs within suspension besides the coexistence of AOBs and anammox bacteria in the biofilm, which could be supported by results using fluorescence in situ hybridization(FISH). Thus, small amounts of suspended microorganisms can positively influence the deammonification's efficiency. If this fraction is partially washed out, the system recovers nevertheless within hours.