Wastewater Nitrogen Removal Research Articles

Enhancing nitrogen removal of carbon-limited municipal wastewater in step-feed biofilm batch reactor through integration of anammox

The biological nitrogen removal of municipal wastewater was successfully improved by integrating anammox in a step-feed sequencing biofilm batch reactor. Despite fluctuating influent carbon to nitrogen ratio (1.9–5.1) and decreasing temperature (24.1–16.3 ℃), nitrogen removal efficiency of 95.9 ± 1.4 % and nitrogen removal rate of 0.23 ± 0.02 kg N/(m3·d) were successfully maintained without requirement of external carbon sources. The advanced removal performance was mainly attributed to the enhanced anammox. Anammox bacteria presented a high relative abundance (42.9% in biofilms, 1.5% in flocs) and anammox activity was as high as 5.42 ± 0.12 mg N/(g volatile suspended solids·h). Further analysis suggested that flexible control of influent organic and ammonium through step-feeding could provide multiple substrate supply for anammox reaction, potentially resulting in stable combination of anammox with hybrid-nitrite-shunt processes. Overall, this study provides a promising anammox-related application with simple-control step-feed strategy for enhanced and stable nitrogen removal from carbon-limited municipal wastewater.

Phylogenetic and metabolic diversity of microbial communities performing anaerobic ammonium and methane oxidations under different nitrogen loadings

The microbial guild coupling anammox and nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) is an innovative process to achieve energy-efficient nitrogen removal with the beneficial use of methane in biogas or in anaerobically treated wastewater. Here, metagenomics and metatranscriptomics were used to reveal the microbial ecology of two biofilm systems, which incorporate anammox and n-DAMO for high-level nitrogen removal in low-strength domestic sewage and high-strength sidestream wastewater, respectively. We find that different nitrogen loadings (i.e., 0.1 vs. 1.0 kg N/m3/d) lead to different combinations of anammox bacteria and anaerobic methanotrophs (“Candidatus Methanoperedens” and “Candidatus Methylomirabilis”), which play primary roles for carbon and nitrogen transformations therein. Despite methane being the only exogenous organic carbon supplied, heterotrophic populations (e.g., Verrucomicrobiota and Bacteroidota) co-exist and actively perform partial denitrification or dissimilatory nitrate reduction to ammonium (DNRA), likely using organic intermediates from the breakdown of methane and biomass as carbon sources. More importantly, two novel genomes belonging to “Ca. Methylomirabilis” are recovered, while one surprisingly expresses nitrate reductases, which we designate as “Ca. Methylomirabilis nitratireducens” representing its inferred capability in performing nitrate-dependent anaerobic methane oxidation. This finding not only suggests a previously neglected possibility of “Ca. Methylomirabilis” bacteria in performing methane-dependent nitrate reduction, and also challenges the previous understanding that the methane-dependent complete denitrification from nitrate to dinitrogen gas is carried out by the consortium of bacteria and archaea.

Identification of a Strain Degrading Ammonia Nitrogen, Optimization of Ammonia Nitrogen Degradation Conditions, and Gene Expression of Key Degrading Enzyme Nitrite Reductase

In recent years, nitrogen pollutants have become one of the main causes of water pollution and eutrophication; thus, it is very important to increase the research on nitrogen removal in wastewater. In this study, a bacterium with outstanding ammonia nitrogen degradation capability was isolated from piggery wastewater and identified as Bacillus tequilensis (designated as A2). The ammonia nitrogen degradation rate of A2 reached the highest level (95%) when the incubation temperature was 42 °C, the initial pH was 7, the seed volume was 5%, the rotation speed was 160 r·min−1, the C/N was 10:1, and the carbon source was sodium citrate. A new nitrite reductase gene was successfully expressed in E. coli BL21 (DE3), and the result showed that the enzyme gene contained 2418 bp and 805 encoding amino acids, the recombinant enzyme was purified through an Ni2+ affinity chromatography column, it had a molecular weight of about 94 kDa, it displayed the maximum enzyme activity at 40 °C and pH 6.0, it exhibited good stability in the range of 25 °C to 35 °C, and it showed a pH of 6.0 to 7.0. A 1 mM concentration of Fe3+ promoted the enzyme activity, followed by a 1 mM concentration of Fe2+ and Mg2+. The kinetic parameters of Km, Kcat, and the Vmax of NiR-A2 were calculated to be 1.37 μmol·mL−1, 4.9 × 102 s−1, and 23.75 μmol·mg−1·min−1, respectively. This strain shows good prospects for wastewater treatment, especially in the treatment of high concentration ammonia nitrogen and nitrite degradation, because of its tolerance to and high degradation rate of high concentrations of ammonia nitrogen and high nitrite.

Concept development of a mainstream deammonification and comparison with conventional process in terms of energy, performance and economical construction perspectives.

Deammonification for nitrogen removal in municipal wastewater in temperate and cold climate zones is currently limited to the side stream of municipal wastewater treatment plants (MWWTP). This study developed a conceptual model of a mainstream deammonification plant, designed for 30,000 P.E., considering possible solutions corresponding to the challenging mainstream conditions in Germany. In addition, the energy-saving potential, nitrogen elimination performance and construction-related costs of mainstream deammonification were compared to a conventional plant model, having a single-stage activated sludge process with upstream denitrification. The results revealed that an additional treatment step by combining chemical precipitation and ultra-fine screening is advantageous prior the mainstream deammonification. Hereby chemical oxygen demand (COD) can be reduced by 80% so that the COD:N ratio can be reduced from 12 to 2.5. Laboratory experiments testing mainstream conditions of temperature (8-20°C), pH (6-9) and COD:N ratio (1-6) showed an achievable volumetric nitrogen removal rate (VNRR) of at least 50 gN/(m3∙d) for various deammonifying sludges from side stream deammonification systems in the state of North Rhine-Westphalia, Germany, where m3 denotes reactor volume. Assuming a retained Norganic content of 0.0035 kgNorg./(P.E.∙d) from the daily loads of N at carbon removal stage and a VNRR of 50 gN/(m3∙d) under mainstream conditions, a resident-specific reactor volume of 0.115 m3/(P.E.) is required for mainstream deammonification. This is in the same order of magnitude as the conventional activated sludge process, i.e., 0.173 m3/(P.E.) for an MWWTP of size class of 4. The conventional plant model yielded a total specific electricity demand of 35 kWh/(P.E.∙a) for the operation of the whole MWWTP and an energy recovery potential of 15.8 kWh/(P.E.∙a) through anaerobic digestion. In contrast, the developed mainstream deammonification model plant would require only a 21.5 kWh/(P.E.∙a) energy demand and result in 24 kWh/(P.E.∙a) energy recovery potential, enabling the mainstream deammonification model plant to be self-sufficient. The retrofitting costs for the implementation of mainstream deammonification in existing conventional MWWTPs are nearly negligible as the existing units like activated sludge reactors, aerators and monitoring technology are reusable. However, the mainstream deammonification must meet the performance requirement of VNRR of about 50 gN/(m3∙d) in this case.

Partial nitritation and nitrogen removal of vacuum toilet wastewater from high-speed trains in a sequential batch reactor

Owing to the high contents of organics and nitrogen in vacuum toilet wastewater (VTW) generated from high-speed trains, onsite pretreatment is usually required before VTW can be discharged into municipal sewers. In this study, a partial nitritation process was stably established in a sequential batch reactor to efficiently utilize the organics in synthetic and real VTWs for nitrogen removal and to produce an effluent suitable for anaerobic ammonia oxidation. In spite of the high fluctuations of COD and nitrogen in VTW, the organics used for nitrogen removal stabilized at 1.97 ± 0.18 mg COD mg N−1 removed, and the effluent NO2−-N/NH4+-N ratios were maintained at 1.26 ± 0.13. The removal efficiencies of nitrogen and COD were 31.8 ± 3.5% and 65.2 ± 5.3% under the volumetric loading rates of 1.14 ± 0.15 kg N m−3 d−1 and 1.03 ± 0.26 kg COD m−3 d−1 for real VTW, respectively. Microbial community analysis revealed that Nitrosomonas (0.95%–1.71%) was the dominant autotrophic ammonium-oxidizing bacterial genus, but nitrite-oxidizing bacteria, Nitrolancea, was severely inhibited, with a relative abundance less than 0.05%. The relative abundance of denitrifying bacteria increased by 7.34% when the influent was switched to real VTW. Functional profile predictions of the biomass showed that the decrease in the COD/N ratio and the switch of reactor influent from synthetic to real VTW increased the relative abundance of enzymes and modules involved in carbon and nitrogen metabolisms.

Nitrogen and Phosphorus Removal of Wastewater via Constructed Wetlands Approach

This study aimed to determine the efficiency of media pollutant removal from municipal wastewater with high concentrations of ammonia and phosphorus in constructed wetlands (CWs). The study utilized secondary data from previous studies that were published in credible sources. The removal efficiencies of the five media used in the constructed wetland, namely, peat-cattails, cattails, peat, Viteveria zizanioides, and Phragmite karka, were compared. The results showed that CWs with Viteveria zizaniode exhibited the best performance on average, removing 84% nitrogen and 86% phosphorus. Peat was also effective in attenuating pH. Humic and fulvic acids in peat moss can be released quickly in an aqueous environment under alkaline conditions, effectively lowering the pH value. The combination of Viteveria zizaniode and peat significantly improved pollutant removal efficiency in municipal wastewater with high concentrations of ammonia and phosphorus.

Advanced nitrogen removal from low carbon nitrogen ratio domestic sewage via continuous plug-flow anaerobic/oxic/anoxic system: Enhanced by endogenous denitrification

An anaerobic/oxic/anoxic continuous plug-flow biorereactor was established to derive stable advanced nitrogen removal of oligotrophic domestic wastewater by setting a sludge dual-reflux system and a mixed liquid cross-flow system, while extending the hydraulic retention time in anoxic section. The effluent total inorganic nitrogen was 7.9 ± 2.2 mg N/L, with removal efficiency of 84 ± 3.9%. Results of nitrogen balance calculations indicated that the contribution of simultaneous nitrification and denitrification to total inorganic nitrogen loss in oxic region was 15% during stable stage, and the total inorganic nitrogen removal by endogenous-denitrification and enhanced exogenous-denitrification in the anoxic region was 39.9%. Prolongation of hydraulic retention time in anoxic segment is the critical reason for enhancing endogenous-denitrification, and cross-flow system is an important measure to improve exogenous-denitrification. This study provides new insights into bridging the gap between energy-saving and high-level nitrogen removal from municipal wastewater with low carbon to nitrogen ratios.

Simultaneous removal of phosphate, calcium, and ammonia nitrogen in a hydrogel immobilized reactor with bentonite/lanthanum/PVA based on microbial induced calcium precipitation

In recent years, it is urgent to solve nitrogen and phosphorus pollution in domestic wastewater. The target strain Pseudomonas sp. Y1 was immobilized using polyvinyl alcohol (PVA) matrix coupled with bentonite and lanthanum (La), respectively, to fabricate four hydrogel materials that used to construct bioreactors. The optimal operating parameters and dephosphorization mechanism were discussed, and the effects of hydrogel materials and different loads on the performance of the bioreactor were contrastively analyzed. The results manifested that when the hydraulic retention time (HRT) was 6.0 h, the C/N was 6.0, and the Ca2+ concentration was 100.0 mg L−1, the bioreactors had the best heterotrophic nitrification-aerobic denitrification (HNAD) and biomineralization capacity, and the maximum removal efficiencies of Ca2+, PO43–-P, and NH4+-N were 82.57, 99.17, and 89.08%, respectively. The operation data indicated that the addition of bentonite significantly promoted HNAD, and the bioreactor had stronger dephosphorization ability in the presence of La. The main phosphorous removal mechanisms were confirmed to be adsorption and co-precipitation. Finally, high-throughput sequencing results indicated that Pseudomonas accounted for the paramount proportion in the bioreactor, and the prediction of functional genes indicated that the C/N of 6.0 is more favorable for the expression of nitrogen removal-related functional genes in the bioreactor system. This study highlights the superiority of microbial induced calcium precipitation (MICP) combined with PVA hydrogel, and provides a theoretical basis for simultaneous nitrogen and phosphate removal of wastewater.

Performance of simultaneous carbon and nitrogen removal of high-salinity wastewater in heterotrophic nitrification-aerobic denitrification mode

In this work, heterotrophic nitrification-aerobic denitrification (HN-AD) mode was successfully established after a 105-day acclimation in a sequencing batch reactor (SBR) system using mustard tuber wastewater (MTWW) as substrate. The performance of simultaneous carbon and nitrogen removal (SCNR) was investigated using manual wastewater within the salinity from 1% to 6%. Results indicate that high salinity caused little effect on carbon removal, while it brought a significant influence on nitrogen removal. At the salinity of 1% and 3%, the heterotrophic nitrification rates were 2.83 and 3.96-fold of those of the autotrophic nitrification, respectively. As the salinity was up to 6%, the autotrophic nitrification was significantly inhibited, while the anoxic denitrification was slightly affected and the aerobic denitrification became dominant. The analysis on microbial community structure of the acclimated wastewater sludge reveals that the genera with autotrophic nitrification were gradually eliminated with an increasing salinity during the acclimation. Paracoccus, Pseudomonas, Alcaligenes and Bacillus were the dominant genera related to HN-AD process. The optimal operation parameters for SCNR were investigated, including C/N ratio (25), DO concentration (6 mg/L) and temperature (35 °C). This work provides an insight into the migration of nitrogen removal pathway and the succession of HN-AD microbial community in the process of high-salt wastewater biotreatment.

Nitrogen removal from high-saline municipal wastewater via anammox-based process driven by both nitritation and denitratation

Nitrogen removal from saline municipal wastewater has recently attracted attention; thus, developing energy-efficient technology such as anaerobic ammonium oxidation (anammox) for advanced nitrogen removal of hypersaline wastewater is significant. In this study, the long-term salt adaptation and evolution mechanisms of an anammox-based process driven by both nitritation (NH4+→NO2—, PN) and denitratation (NO3—→NO2—, PD) were investigated under salinities ranging from 1.0% to 3.0% (10–30 g NaCl/L). At 1.0% salinity, PN evolved into the major nitrite production pathway with thorough suppression of nitrite oxidation. At 1.5% salinity, nitrite reduction was inhibited along with suspended sludge loss due to poor sludge settleability. Under 2.0% salinity with only-biofilm, the highest nitrogen removal efficiency (81.2%) was observed with influent and effluent total inorganic nitrogen concentrations of 44.5 and 8.2 mg N/L, respectively. Notably, results showed that anammox bacteria occupied up to 1.07% of the microbial community (qPCR: 1.14×1011 copies/(g dry sludge)) and has strong adaptability to salinity. With salinity increases, anammox contribution kept over 85% and Ca. Kuenenia (0.57%→0.22%) was more tolerant than Ca. Brocadia (0.46%→0.02%). Metagenomic sequencing revealed that the multiple nitrite substrates production by Nitrosomonas (amoA-enriched), Denitratisoma and Denitromonas (narG-enriched) guaranteed the high anammox contribution. This study provides a multifaceted understanding of the anammox-based process, which can enable improved application in real saline wastewater treatment.

A Comprehensive Review on Wastewater Nitrogen Removal and Its Recovery Processes

Discharging large amounts of domestic and industrial wastewater drastically increases the reactive nitrogen content in aquatic ecosystems, which causes severe ecological stress and biodiversity loss. This paper reviews three common types of denitrification processes, including physical, chemical, and biological processes, and mainly focuses on the membrane technology for nitrogen recovery. The applicable conditions and effects of various treatment methods, as well as the advantages, disadvantages, and influencing factors of membrane technologies, are summarized. Finally, it is proposed that developing effective combinations of different treatment methods and researching new processes with high efficiency, economy, and energy savings, such as microbial fuel cells and anaerobic osmotic membrane bioreactors, are the research and development directions of wastewater treatment processes.

Performance characteristics and bacterial community analysis of a novel two-step-feed three-stage A/O-MBBR system for nitrogen removal in municipal wastewater

To obtain a high nitrogen removal efficiency and fully use the carbon sources in raw wastewater, a novel two-step-feed three-stage anoxic/oxic (A/O)-moving bed biofilm reactor (MBBR) system with ten chambers was established for municipal wastewater treatment. The designed ten chambers in the 2F-3S-A/O-MBBR system played different roles in nitrogen and organic removals, and they accomplished the task of achieving stable high nitrogen removal efficiency at different temperatures together. Concretely, the average total inorganic nitrogen (TIN) removal efficiency was improved to 72.88 % from 61.55 % without any external carbon sources by the second-stage A/O-MBBR subsystem due to the two-step-feed configuration, and it was further improved to 91.42 % by the third-stage A/O-MBBR subsystem due to the use of the external carbon sources. Specific functional biofilms with different bacterial communities (r = 0.85, P ≤ 0.001) and functional genes of denitrification and nitrification (r = 0.63, P ≤ 0.001) were formed in 4 groups of functional zones, including the first-stage anoxic, second-stage anoxic, third-stage anoxic and oxic chambers. This study developed an efficient 2F-3S-A/O-MBBR biological nitrogen removal process and investigated the performance characteristics and bacterial community to provide fundamental support for the application of this process.

Effect of streptomycin sulphate on the nitrification system in activated sludge: insight into nitrification characteristic, antibiotic resistance gene and microbial community

ABSTRACT Wastewater with residual streptomycin sulphate usually contains high content of ammonia-nitrogen. However, the biological removal process of ammonia-nitrogen under streptomycin sulphate circumstance was unclear. In this study, short-term and long-term effects of streptomycin sulphate on biological nitrification systems, including AOB, NOB, SAOR, SNOR and SNPR, were evaluated comprehensively. The results indicated IC50 for AOB and NOB were 7.5 and 6.6 mg/L. SAOR and SNPR could be decreased to 3.43 ± 0.52 mg N/(g MLSS·h) and 0.24 ± 0.03 mg N/(g MLSS·h) while the addition of streptomycin sulphate was 10 mg/L. When streptomycin sulphate addition was stopped, nitrification ability recovered slightly, SAOR and SNPR increased to 9.37 ± 0.36 mg N/(g MLSS·h) and 1.66 ± 0.49 mg N/(g MLSS·h), respectively. The protein of EPS increased gradually during the acclimatization process, and the maximal protein value was 68.24 mg/g MLSS on the 100th day, however, no significant change of polysaccharose was observed during the acclimatization process. High abundance of ARGs and intI1 was detected in effluent and sludge of the biological treatment system. The maximal relative abundance of aadA1 in the sludge appeared on the 140th day, and increased by 0.99 orders of magnitude. Biological diversity decreased significantly during the acclimatization process, relative abundance of nitrosomonas was changed from 9.07% to 38.68% on the 61st day, while relative abundance of nitrobacter was changed from 1.30% to 0.64%. It should be noted that relative abundances of nitrosomonas and nitrobacter were reduced to 16.17% and 0.25% on the 140th day. This study would be helpful for nitrogen removal in wastewater with antibiotic.

NITROGEN REMOVAL FROM WASTEWATER TREATMENT

The methodologies for genetic nitrogen removal and improvement through the dirtywater
 have been précised in this study. Although there are some low energy options, like as denitritation
 and the proficient partial Ammonium that has been displayed in a well manner for sidewatercourse
 treatment and is growing towards the normal applications, and the usually usedtechnology of BNR is one of the energy exhaustive. Cell absorption with photographs may get betternitrogen, but bottleneck having solids division and space needs maximum applicability to the tertiarymanagement. Bacteriological cell, alternatively, is the power proficient at improving nitrogen by theside stream but not at obtaining low waste matter levels. And by the low usage of energy, nitrogenrecovery, to minimize waste matter nitrogen and the joint power of the growing techniques will getbetter wastewater nitrogen removal.

The coupling system of magnetite-enhanced thermophilic hydrolysis-acidification and denitrification for refractory organics removal from anaerobic digestate food waste effluent (ADFE)

The aim of this study was to remove the refractory organics from high-temperature anaerobic digestate food waste effluent by the coupling system of hydrolysis-acidification and denitrification. Iron-based materials (magnetite, zero-valent iron, and iron-carbon) were used to enhance the performance of thermophilic hydrolysis-acidification. Compared with the control group, magnetite had the best strengthening effect, increasing volatile fatty acids concentration and fluorescence intensity of easily biodegradable organics in the effluent by 47.6 % and 108.4 %, respectively. The coupling system of magnetite-enhanced thermophilic hydrolysis-acidification and denitrification achieved a nitrate removal efficiency of 91.2 % (influent NO3−-N was 150 mg L−1), and reduced the fluorescence intensity of refractory organics by 33.8 %, compared with influent. Microbiological analysis indicated that magnetite increased the relative abundance of thermophilic hydrolytic acidifying bacteria, and coupling system enriched some genera simultaneously removing nitrate and refractory organics. This study provided fresh information on refractory organics and nitrogen removal of thermophilic wastewater biologically.

Long-term stability of reactor microbiome through bioaugmentation with Alcaligenes aquatilis AS1 promotes nitrogen removal of piggery wastewater

Bioaugmentation is considered as an attractive method for nitrogen removal in water treatment, but its effectiveness in actual high-strength piggery wastewater has not been adequately verified and the mechanism of bioaugmentation in actual wastewater treatment system is not very clear especially from the perspectives of microbial communities and functional genes. This study investigated the mechanisms of a heterotrophic nitrifying-aerobic denitrifying strain Alcaligenes aquatilis AS1 in the bioaugmentation of continuous biological nitrogen removal of actual piggery wastewater at laboratory scale. The addition of strain AS1 significantly improved the nitrogen removal efficiency (more than 95% of NH4+-N and 75% of TN were removed) and raised the activated sludge resistance to shock loading. AS1 addition also significantly shifted the microbiota structure and interactions among microbial networks were enhanced to obtain the stable bacterial communities. Moreover, strain AS1 achieved effective proliferation and long-term colonization in activated sludge with a relative abundance of genus Alcaligenes more than 70% during the whole operation process and played a dominant role in biological nitrogen removal, while different genera were respectively enriched and involved in pollutants removal at different stages in the control group. In addition, the abundances of most functional genes involved in carbon (C) degradation, carbon fixation and nitrogen (N), phosphorus (P), sulfur (S) cycling in activated sludge were significantly increased in reactor AS1, indicating that strain AS1 not only relied on its unique C and N metabolic activities, but also recruited microorganisms with diverse functions to jointly remove pollutants in wastewater, which could be a common bioaugmentation mechanism in open reactors. This study proves the promising application prospect of strain AS1 in the treatment of high-strength piggery wastewater and shows great importance for guiding bioaugmentation application of functional strains in practical wastewater treatment systems.

Low energy-consumed process of integrated anammox and in-situ fermentation-based denitrification for ultra-efficient nitrogen removal from mainstream domestic sewage

Anammox is a promising biotechnology for nitrogen removal and gaining popularity in mainstream wastewater treatment. The efficient and low energy-consumed elimination of the intrinsic byproduct nitrate in anammox-mediated process is still a tough barrier and urgently demands resolving. To explore a newly green alternative for advanced nitrogen removal from domestic sewage, this study proposed a novel Integrated Anammox, Fermentation and Denitrification (IAFD) process. After 215-day operation, total inorganic nitrogen (TIN) removal efficiency markedly increased from 72.6% to 94.1% and effluent TIN dropped from 7.9 mg L−1 to 1.8 mg L−1 with influent TIN of 56 mg L−1. Through in-situ activated sludge fermentation, 37.341 mg COD·L−1·d−1 organics was yielded, causing a COD/NO3−-N of 8.9, Soluble protein (63.8%), polysaccharide (10.6%) and acetic acid (13.9%) were primary components. Candidatus_Brocadia (0.8%) and Candidatus_Competibacter (4.6%) were dominant functional bacteria, which contributed 81.1% and 18.9% to nitrogen elimination, respectively. Robust anammox (3.37 mg N·g VSS−1·h−1), fermentation-assisted denitrification and denitritation synergistically boosted N removal. The novel process required no external carbon, reduced 59.5% aeration and 35.8% external sludge. The novel process showed significantly environmental and economical advantages of low operation expenses and energy cost with no external carbon requirement, 59.5% aeration and 35.8% external sludge reduction. This work provided an energy-neutral and sustainable scheme for the advanced nitrogen removal of municipal wastewater and sludge disposal in WWTPs.

Fe-C wrapped in polyurethane sponge cubes tied in anoxic zones to enrich multiple denitrifying bacteria enhancing wastewater nitrogen removal

To enhance nitrogen removal in wastewater treatment, a novel method of wrapping waste iron shavings (Fe-C) in polyurethane sponge cubes tied in anoxic zones of a continuous reactor was proposed. Three types of denitrifying bacteria were enriched simultaneously in biofilms and activated sludge, including iron autotrophic denitrifying bacteria (7.83–8.71 %), heterotrophic denitrifying bacteria (10.60–11.95 %), and heterotrophic nitrification-aerobic denitrifying bacteria (23.47–40.06 %). Iron autotrophic denitrifying bacteria (Dechloromonas and Sphaerotilus) can remove NO3−-N using Fe2+ as electron donor produced by micro-electrolysis of iron shavings without organic carbon demand, and heterotrophic nitrification-aerobic denitrifying bacteria (Ferribacterium and Zoogloea) can simultaneously accomplish nitrification and denitrification under aerobic conditions. The enrichment of these two functional bacteria strengthened the nitrogen removal performance compared to conventional heterotrophic denitrifying process, which could achieve efficient and stable total nitrogen removal (87.4 %) even with low organic carbon. In addition, the synergy of biological and chemical processes through Fe-C micro-electrolysis also enhanced total phosphorus removal (86.0 %).

Long-term adaptation of two anammox granules with different ratios of Candidatus Brocadia and Candidatus Jettenia under increasing salinity and their application to treat saline wastewater

Nitrogen removal in saline wastewater is a challenge of the anaerobic ammonium oxidation (anammox) process, which is dominated by freshwater anammox bacteria (FAB). Candidatus Brocadia and Candidatus Jettenia, the most widely used FABs, have been separately applied and evaluated for their ability to treat saline wastewater. To understand the effect of salinity on nitrogen removal capability when they present together in an anammox granule, we compared two anammox granules: GRN1 was evenly dominated by Ca. Brocadia (42 %) and Ca. Jettenia (43 %), while GRN2 was dominated with mostly Ca. Brocadia (90 %) and a small amount of Ca. Jettenia (1 %). Each granule was inoculated into a continuous column reactor to treat artificial wastewater containing 150 mg NH4+-N/L and 150 mg NO2−-N/L under increasing saline conditions for 250 days. GRN1 showed superior and more stable nitrogen removal than GRN2 under saline conditions of up to 15 g NaCl/L. Under high-saline conditions, both the granules' sizes decreased (larger GRN1 than GRN2 in initial). The mass percent of Na salt increased (more in GRN2) and mineral contents decreased more in GRN1. High-throughput sequencing for microbial community analysis showed that Planctomycetes in GRN1 (85 %) and GRN2 (92 %) decreased to 14 % and 12 %, respectively. The ratio of Ca. Brocadia and Ca. Jettenia in GRN1 changed to 37 % and 63 %, respectively, whereas the ratio in GRN2 (99 % and 1 %, respectively) did not change. Both salt-adapted granules were applied to the two-stage partial nitritation and anammox (PN/A) process to treat high strength ammonium (400 mg/L) wastewater under high saline condition (15 g NaCl/L). The PN/A process containing GRN1 showed more stable nitrogen removal performance during approximately 100 days of operation. These results suggest that the anammox granules evenly dominated by two FABs, Ca. Brocadia and Ca. Jettenia, would be advantageous to treat high-strength NH4+ wastewater under high-saline conditions.

Bioaugmentation reconstructed nitrogen metabolism in full-scale simultaneous partial nitrification-denitrification, anammox and sulfur-dependent nitrite/nitrate reduction (SPAS)

To enhance nitrogen removal of fermentation pharmaceutical wastewater with high nitrogen load, a full-scale process based on simultaneous partial nitrification-denitrification/ anammox/ sulfur autotrophic denitrification (SPAS) was established via inoculating with bioaugmentation consortia in a modified two-stage AO. More than 93 % TN and 98 % NH4+-N removal were obtained at a rate of 0.8 kg-N/ m3/d in the first A/O stage, in which short-cut SND was involved with 96.05 % ESND when bioaugmented with SND, while S0-SAD could coordinate with anammox to exert further deep denitrification in the second A/O stage. KEGG analysis demonstrated that the SPAS process was synergism of HD, PN/PDN, SND, SAD and anammox metabolism, bioaugmentation could significantly up-regulate genes related to microbial metabolism (TCA cycle, Carbon metabolism, ABC transporters) and environmental adaptation (Two-component system, Quorum sensing) based on the FAPROTAX and Picrust2 functional prediction. This study provided a new perspective in engineering applications.