Anammox Process For Nitrogen Removal Research Articles

Two-stage partial nitrification-denitrification and anammox process for nitrogen removal in vacuum collected toilet wastewater at ambient temperature

Vacuum collected toilet wastewater (VCTW) contains high and fluctuating contents of organics and nitrogen, which exerts technological challenges to biological treatment processes. A partial nitrification–denitrification and anammox (PND-AMX) process was developed in sequencing batch reactor (SBR) and moving bed biofilm reactor (MBBR) to achieve effective nitrogen removal in VCTW at low ambient temperature. Stable PND was achieved, and nitrogen removal efficiency in SBR could be manipulated by adjusting influent COD/N ratios. As temperature ≥18 °C, 91.0% nitrogen was removed in PND-AMX process. In spite of the decreased anammox activity at 13–18 °C, more than 90% nitrogen removal could be obtained by adjusting SBR influent COD/N to 2.43 ± 0.32 with methanol. In MBBR reactor, Candidatus Kuenenia was the dominant anammox bacteria and contributed to more than 90% nitrogen removal capacity. Co-existing anammox and denitrifying bacteria synergistically contributed to the removal of ammonium, nitrite, nitrate, and COD in MBBR.

Metagenomic insights into microbial metabolic mechanisms of a combined solid-phase denitrification and anammox process for nitrogen removal in mainstream wastewater treatment

To overcome the significant challenges associated with nitrite supply and nitrate residues in mainstream anaerobic ammonium oxidation (anammox)-based processes, this study developed a combined solid-phase denitrification (SPD) and anammox process for low-strength nitrogen removal without the addition of nitrite. The SPD step was performed in a packed-bed reactor containing poly-3-hydroxybutyrate-co-3-hyroxyvelate (PHBV) prior to employing the anammox granular sludge reactor in the continuous-flow mode. The removal efficiency of total inorganic nitrogen reached 95.7 ± 1.2% under a nitrogen loading rate of 0.18 ± 0.01 kg N·m3·d−1, and it required 1.02 mol of nitrate to remove 1 mol of ammonium nitrogen. The PHBV particles not only served as biofilm carriers for the symbiosis of hydrolytic bacteria (HB) and denitrifying bacteria (DB), but also carbon sources that facilitated the coupling of partial denitrification and anammox in the granules. Metagenomic sequencing analysis indicated that Burkholderiales was the most abundant HB genus in SPD. The metabolic correlations between DB (Betaproteobacteria, Rhodocyclaceae, and Anaerolineae) and anammox bacteria (Candidatus Brocadiac and Kuenenia) in the granules were confirmed through microbial co-occurrence networks analysis and functional gene annotations. Additionally, the genes encoding nitrate reductase (Nap) and nitrite reductase (Nir) in DB primarily facilitated nitrate reduction, thereby supplying nitric oxide to anammox bacteria for subsequent nitrogen removal with hydrazine synthase (Hzs) and hydrazine dehydrogenase (Hdh). The findings provide insights into microbial metabolism within combined SPD and anammox processes, thus advancing the development of mainstream anammox-based processes in engineering applications.

Adaptation of anammox process for nitrogen removal from acidic nitritation effluent in a low pH moving bed biofilm reactor.

Acidic partial nitritation (PN) has emerged to be a promisingly stable process in wastewater treatment, which can simultaneously achieve nitrite accumulation and about half of ammonium reduction. However, directly applying anaerobic ammonium oxidation (anammox) process to treat the acidic PN effluent (pH 4-5) is susceptible to the inhibition of anammox bacteria. Here, this study demonstrated the adaptation of anammox process to acidic pH in a moving bed biofilm reactor (MBBR). By feeding the laboratory-scale MBBR with acidic PN effluent (pH=4.6±0.2), the pH of an anammox reactor was self-sustained in the range of pH 5-6. Yet, a high total nitrogen removal efficiency of over 80% at a practical loading rate of up to 149.7±3.9mg N/L/d was achieved. Comprehensive microbial assessment, including amplicon sequencing, metagenomics, cryosection-FISH, and qPCR, identified that Candidatus Brocadia, close to known neutrophilic members, was the dominant anammox bacteria. Anammox bacteria were found present in the inner layer of thick biofilms but barely present in the surface layer of thick biofilms and in thin biofilms. Results from batch tests also showed that the activity of anammox biofilms could be maintained when subjected to pH 5 at a nitrite concentration of 10mg N/L, whereas the activity was completely inhibited after disturbing the biofilm structure. These results collectively indicate that the anammox bacteria enriched in the present acidic MBBR could not be inherently acid-tolerant. Instead, the achieved stable anammox performance under the acidic condition is likely due to biofilm stratification and protection. This result highlights the biofilm configuration as a useful solution to address nitrogen removal from acidic PN effluent, and also suggests that biofilm may play a critical role in protecting anammox bacteria found in many acidic nature environments.

Microbial driving mechanism for nitrogen removal performance of anammox with combined fillers addition: Microbial community dynamics, metabolic function and network analysis

Microbial community is vital for efficient nitrogen removal in an anaerobic ammonium oxidation (anammox) system. However, the mechanisms of microbially driven anammox denitrification are far from clear. The results showed that the nitrogen removal efficiency (especially the removal rate of NH4+-N, which reached 85.6 ± 3.1 %) significantly increased (p < 0.05) by combined fillers addition. Scanning electron microscope (SEM) images showed the microflora changed gradually from short rod-shaped to spherical aggregates, improving shock loading resistance in the system. The dominant microflora shifted from Proteobacteria and Bacteroidetes to Chloroflexi and Planctomycetes, in which Candidatus Jettenia reached a maximum abundance of 30.7 %. Meanwhile, the abundance of denitrifying bacteria (Denitratisoma and Thiobacillus) was significantly diminished. Significant enhancements in the energy metabolic capacity of microorganisms, especially nitrogen metabolism, were observed in the anammox process. Moreover, the increase in abundance of hzo gene suggested the enhancement of the anammox process. Co-occurrence network analysis demonstrated that the genera Longilinea, Thiobacillus, Candidatus Jettenia, Dokdonella, and Candidatus Brocadia were the keystones, and complex microbial interactions (stronger symbiotic than competitive relationships) enhanced the nitrogen removal capability. Overall, the results of this study provided more comprehensive information regarding community succession, coexistence and collaboration in anammox process for nitrogen removal.

Combined partial denitrification-anammox with urea hydrolysis (U-PD-Anammox) process: A novel economical low-carbon method for nitrate-containing wastewater treatment

For the sake of exploring a new economical and low-carbon alternative for real nitrate-containing wastewater treatment, a new combined partial denitrification-anammox with urea hydrolysis (U-PD-Anammox) process was developed. The nitrogen removal performance of this process was investigated through long-term operation in a sequencing batch reactor (SBR) and two submerged anaerobic biological filters (SABF). Results showed that the average NO3−-N to NO2–N transformation ratio improved to 82.6% with organic carbon source to NO3–N ratio of 1.8, and urea hydrolysis provided sufficient NH4+-N and inorganic carbon to anammox process for nitrogen removal. The influent NH4+-N/NO2−-N ratio for subsequent anammox reactor could be adjacent to the optimal ratio of 1.32 during the whole operation. The combined process showed efficient nitrogen removal performance with 85% NO3−-N removal, 93.8% total nitrogen removal and total nitrogen loading rate as 1.1 ± 0.5 kg N/(m3·d). High-throughput sequencing analysis results revealed that Genera Thauera, Hyphomicrobium and Candidatus Brocadia were the dominant species responsible for partial denitrification, urea hydrolysis and anammox, respectively. The proposed process was more economically and environmental-friendly than the traditional denitrification process with 51.7% operational cost reduction, 99.7% N2O and 60% CO2 emission decrement, facilitating the sustainable development of the nitrate-containing wastewater treatment industry in the future.

Sulfammox forwarding thiosulfate-driven denitrification and anammox process for nitrogen removal

The coupled process of thiosulfate-driven denitrification (NO3−→NO2−) and Anammox (TDDA) was a promising process for the treatment of wastewater containing NH4+-N and NO3−-N. However, the high concentration of SO42− production limited its application, which needs to be alleviated by an economical and effective way to promote the application of TDDA process. In this study, TDDA process was started in a relatively short time by stepwise replacing nitrite with nitrate and operated continuously for 146 days. Results presented that the average total nitrogen removal efficiency of 82.18% can be acquired at a high loading rate of 1.98 kg N/(m3·d) with maximum nitrogen removal efficiency up to 87.04%. It was observed that the increase of S/N ratio improved the denitrification efficiency and slightly inhibit the Anammox process. Batch tests showed that Sulfammox process appeared in TDDA process under certain conditions, further contributing 2.59% nitrogen removal and 10.46% sulfur removal (14.42 mg/L NH4+-N and 37.68 mg/L SO42--S were removed). This finding was mainly attributed to the reduction of sulfate in TDDA system to elemental S0 or HS−, which subsequently was used as an electron donor to realize the recycling of sulfate (SO42--S) pollutants and promote the sulfur-nitrogen (S–N) cycle. High-throughput analysis displayed that Anammox bacteria (Candidatus_Kuenenia), Sulfur-oxidizing bacteria (Thiobacillus) with relatively high abundance of 5.37%, 7.74%, respectively, guaranteeing the excellent nitrogen and sulfate removal performance in the reactor. The enrichment of phyla Chloroflexi (31.79%), Proteobacteria (31.82%), class Ignavibacteriales (10.55%), genus Planctomycetes (13.57%) further verified the exitence of Sulfammox process in the TDDA reactor. This study provides a new perspective for the practical application of TDDA in terms of reducing the production of high concentration SO42− and saving operational cost and strengthening deeply nitrogen removal.

Sulfammox Forwarding Thiosulfate-Driven Denitrification and Anammox Process for Nitrogen Removal

Sulfammox Forwarding Thiosulfate-Driven Denitrification and Anammox Process for Nitrogen Removal

Deciphering the microbial community and functional genes response of anammox sludge to sulfide stress

Sulfide has attracted increasing attention due to its odor nuisance, toxicity and corrosion. Although variations in the nitrogen removal performance of anammox under sulfide stress have been reported previously, understanding the microorganisms at the molecular level is of greater significance. This study first deciphered the microbial community and functional gene response of anammox sludge to sulfide stress. Results showed that 20 mg L−1 sulfide could reduce specific anammox activity by 61.7%. The protein-like substances within extracellular polymeric substances were quenched at the end of the experiment. Moreover, the relative abundance of Candidatus Kuenenia significantly decreased from 28.7% to 6.4% while Thiobacillus increased from 0 to 7.2% due to sulfide stress. Furthermore, the abundances of functional genes (hzsA, hdh, nirK and nirS) significantly decreased when the sulfide concentration reached 20 mg L−1. These findings provide a further theoretical basis for the anammox process for nitrogen removal from wastewater containing sulfide.

Immobilizing partial denitrification biomass and redox mediators to integrate with the anammox process for nitrogen removal.

In this study, immobilizing partial denitrification biomass and redox mediators to integrate with the anammox process for nitrogen removal was investigated. Three redox mediators (RMs), namely, 2-methyl-1,4-naphthoquinone (ME), anthraquinone (AQ) and 1-dichloroanthraquinone (1-AQ) were catalyzed to reduce nitrate to only nitrite by denitrification to integrate with the anammox process for nitrogen removal. First, our experimental results showed that there were 35.8, 42.2 and 53.0 mg-N L−1 nitrite accumulation values with the addition of ME, AQ and 1-AQ, respectively, at the dose of 75 µM by the denitrification process at C/N = 2, which were 25.6%, 48.2% and 86.1% higher than that of the control without the addition of any RMs. Nitrate reductase activities were higher than that of nitrite reductase affected by RMs, which was the main reason for nitrite accumulation and further maintenance of the anammox process. Second, owing to the stable nitrite production by the partial denitrifying biomass with the addition of 1-AQ, the nitrogen removal rate of the reactor that integrated the partial denitrification and anammox process reached 1788.36 g-N m−3 d−1 only using ammonia and nitrate as the influent nitrogen resource in the long-term operation. Third, the 16S rDNA sequencing results demonstrated that Yersinia frederiksenii and Thauera were the primary groups of the denitrifying biomass, which were considered the dominant partial denitrification species.

An innovative U-shaped sludge bed anammox process for nitrogen removal

In this study, we proposed an innovative U-shaped sludge bed reactor which could be a cost effective and simplified approach for the operation of an anammox reactor. The performance for nitrogen removal and the composition of bacterial communities were investigated for about 500 days of operation. The nitrogen removal rate could be approximately 85% when the total nitrogen loading rate was about 0.54 kg N/m3/d. The 16S rRNA gene pyrosequencing analysis of the bacterial community determined that Betaproteobacteria (class level) of the ammonia-oxidizing bacteria (AOB) community, Nitrospira (genus level) of the nitrite-oxidizing bacteria (NOB) community, and Brocadia (genus level) of the anammox bacteria community simultaneously coexisted in the reactor sludge. These results demonstrated that simultaneous growth and coexistence of AOB, NOB, and anammox were capable within the reactor. Furthermore, a mathematical modeling system was developed to simulate the nitrification and anammox processes. The model simulation showed that the oxygen was rapidly depleted and that led to a drop in the activity of AOB and NOB, then the growth of anammox bacteria started under anaerobic conditions.

Enrichment of high activity nitrifers to enhance partial nitrification process

Partial nitrification (PN) process is an essential pre-treatment to Anammox process for nitrogen removal from ammonium-rich wastewaters. High activity nitrifiers (HANs) are considered as the key to high-rate PN process. The HANs could be successfully enriched at free ammonia (FA) concentrations of 10–20 mg NH 3–N L −1, which differed significantly from those enriched at FA concentrations of 1–3 mg NH 3–N L −1. The maximum specific ammonium conversion rate, half saturation constant, half inhibition constant, cell yield and decay rate were 2.87 g N g −1 VSS d −1, 5.82 mg N L −1, 8218.8 mg N L −1, 0.15 g VSS g −1 NH 4 + –N and 0.09 d −1 for HANs at 30 °C, respectively, which endowed the PN process a volumetric conversion rate (VCR) as high as 2.22 ± 0.33 kg N m −3 d −1. The cultivation mode of HANs was workable and the HANs were promising as inoculum for the PN process.

Partial Nitritation of Raw Anaerobic Sludge Digester Liquor by Swim-Bed and Swim-Bed Activated Sludge Processes and Comparison of Their Sludge Characteristics

This study evaluated performance of swim-bed (SB) reactors packed with a novel acrylic fiber carrier (BF) and swim-bed activated sludge (SBAS) reactor for partial nitritation of anaerobic sludge digester liquor from a municipal wastewater treatment plant. Comparison of characteristics of sludge obtained from both the reactors was also made. The average conversion rates of ammonium to nitrite were 52.3% and 40.0% under relatively high nitrogen loading rates over 3.0 kg-N/m(3)/d, respectively in two reactors. The average BOD(5) removal efficiencies were 74.3% and 64.4%, respectively in the two reactors. The size of the sludge pellets taken from SB and SBAS reactors was found to be approximately three times (229 mum versus 88 mum) of that of the seed sludge. This sludge also had relatively high extracellular proteins levels indicating better sludge settling capability as compared to the sludge taken from SBAS reactor. Although the effluent nitrite/ammonium ratios had fluctuated in both reactor in some extent, the low dissolved oxygen concentration (average of 2.5 versus 0.35 mg/l), low suspended solids (average of 33.3 versus 33.5 mg/l), and about 50% ammonium conversion to nitrite demonstrated the application potential of anammox process for nitrogen removal.

Anammox process for nitrogen removal from anaerobically digested fish canning effluents

The Anammox process was used to treat the effluent generated in an anaerobic digester which treated the wastewater from a fish cannery once previously processed in a Sharon reactor. The effluents generated from the anaerobic digestion are characterised by their high ammonium content (700-1000 g NH4+ -Nm(-3)), organic carbon content (1000-1300 g TOCm(-3)) and salinity up to 8,000-10,000 g NaCl m(-3). In the Sharon reactor, approximately 50% of the NH4+ -N was oxidised to NO2- -N via partial nitrification. The effluent of the Sharon step was fed to the Anammox reactor which treated an averaged nitrogen loading rate of 500 g N m(-3) x d(-1). The system reached an averaged nitrogen removal efficiency of 68%, mainly limited due to the nonstoichiometric relation, for the Anammox process, between the ammonium and nitrite added in the feeding. The Anammox reactor bacterial population distribution, followed by FISH analysis and batch activity assays, did not change significantly despite the continuous entrance to the system of aerobic ammonium oxidisers coming from the Sharon reactor. Most of the bacteria corresponded to the Anammox population and the rest with slight variable shares to the ammonia oxidisers. The Anammox reactor showed an unexpected robustness despite the continuous variations in the influent composition regarding ammonium and nitrite concentrations. Only in the period when NO2- -N concentration was higher than the NH4+ -N concentration did the process destabilise and it took 14 days until the nitrogen removal percentage decreased to 34% with concentrations in the effluent of 340g NH4+ -N m(-3) and 440 g NO2- -N m(-3), respectively. Based on these results, it seems that the Sharon-Anammox system can be applied for the treatment of industrial wastewaters with high nitrogen load and salt concentration with an appropriate control of the NO2- -N/NH4+ -N ratio.