Role Of Denitrification Research Articles

Mechanism of N2 formation over the FeO-MnO2/SiO2 (100) surface in low-temperature NH3-SCR process: Electronic analysis of reaction pathways and key intermediates

Density Functional Theory (DFT) was used to study the process and details of N2 formation on the FeO-MnO2/SiO2 (100) surface during selective catalytic reduction of NH3 (NH3-SCR). The Fe and Mn sites on the surface of the FeO-MnO2/SiO2 (100) play important roles in denitrification. NH3 forms stable chemical adsorption on its surface, especially with stronger adsorption capacity on the Fe sites than on the Mn sites. Furthermore, Fe sites demonstrate better performance in NH3 dehydrogenation reactions in comparison to Mn sites, but the key intermediate NH2NO tends to form on the Mn sites. NH2NO may generate N2 through a dehydrogenation reaction at the Fe sites on the catalyst surface, while it is more inclined to decompose and generate N2 through internal migration on the Mn sites. These results help to deepen the understanding of the micro-mechanism of catalysts in N2 generation, laying a theoretical foundation for improving the denitrification performance and N2 selectivity of catalysts.

Role of Denitrification in Selenite Reduction by Azospirillum brasilense with the Formation of Selenium Nanoparticles.

Many bacteria are capable of reducing selenium oxyanions, primarily selenite (SeO32-), in most cases forming selenium(0) nanostructures. The mechanisms of these transformations may vary for different bacterial species and have so far not yet been clarified in detail. Bacteria of the genus Azospirillum, including ubiquitous phytostimulating rhizobacteria, are widely studied and have potential for agricultural biotechnology and bioremediation of excessively seleniferous soils, as they are able to reduce selenite ions. Cultures of A.brasilense Sp7 and its derivatives (mutant strains) were grown on the modified liquid malate salt medium in the presence or absence of selenite. The following methods were used: spectrophotometric monitoring of bacterial growth; inhibition of glutathione (GSH) synthesis in bacteria by L-buthionine-sulfoximine (BSO); optical selenite and nitrite reduction assays; transmission electron microscopy of cells grown with and without BSO and/or selenite. In a set of separate comparative studies of nitrite and selenite reduction by the wild-type strain A.brasilense Sp7 and its three specially selected derivatives (mutant strains) with different rates of nitrite reduction, a direct correlation was found between their nitrite and selenite reduction rates for all the strains used in the study. Moreover, for BSO it has been shown that its presence does not block selenite reduction in A.brasilense Sp7. Evidence has been presented for the first time for bacteria of the genus Azospirillum that the denitrification pathway known to be inherent in these bacteria, including nitrite reductase, is likely to be involved in selenite reduction. The results using BSO also imply that detoxification of selenite through the GSH redox system (which is commonly considered as the primary mechanism of selenite reduction in many bacteria) does not play a significant role in A.brasilense. The acquired knowledge on the mechanisms underlying biogenic transformations of inorganic selenium in A.brasilense is a step forward both in understanding the biogeochemical selenium cycle and to a variety of potential nano- and biotechnological applications.

Impact of N loading on Microbial Community Structure and Nitrogen Removal of an Activated Sludge Process with Long SRT for municipal wastewater treatment

Biological nutrient removal process is pivotal in controlling nitrogen and phosphorus from municipal wastewater treatment and reclamation plants in the water environment. The efficiency of municipal wastewater treatment is affected by the fluctuation of influent quality. In this study, the impact of N loading on the removal efficiency and the microbial community structure of activated sludge with long sludge retention time were investigated. The results showed that the effluent NH4+-N and NO2--N concentration were lower than 0.5 mg/L, and the TN removal efficiencies were 79.77% and 65.80%, respectively. The dehydrogenase activity, specific oxygen uptake rate, specific nitrification rate, and specific denitrification rate increased as the N loading increasing. At the phylum level, the most dominant bacterial was affiliated with Proteobacteria in the two systems, accounting for 60.65% and 48.62%, respectively. At the genus level, Acinetobacter, Thauera, and Zoogloea played significant roles in denitrification. The ammonia oxidation bacteria and nitrite-oxidizing bacteria were of the genus Nitrosomonas (r-strategist) and Nitrospira (K-strategist).

Characterization and Genomic Analysis of Affinirhizobium gouqiense sp. nov. Isolated from Seawater of Gouqi Island Located in the East China Sea and Reclassification of Rhizobium lemnae to the Genus Affinirhizobium as Affinirhizobium lemnae comb. nov.

A novel bacterium designated as SSA5.23T was isolated from seawater. Cells of SSA5.23T are Gram-stain-negative, short, rod-shaped, and exhibit motility via numerous peritrichous flagella. The strain could grow at temperatures ranging from 15 to 35 °C (optimum at 25 °C), in a salinity range of 0-5.0% (w/v) NaCl, and within a pH range of 6.0-9.0 (optimum at pH 7.0). The predominant cellular fatty acid of SSA5.23T was C18:1 ω7c/C18:1 ω6c, and the major respiratory quinones were Q-9 and Q-10. Diphosphatidylglycerol, phosphatidylethanolamine, and phosphatidylglycerol were identified as the primary polar lipids. The complete genome (5.47 Mb) of SSA5.23T comprises of a circular chromosome of 3.64 Mb and three plasmids, specifically sized at 59.73 kb, 227.82 kb, and 1.54 Mb, respectively. Certain genes located on the plasmids play roles in denitrification, oxidative stress resistance, and osmotic tolerance, which likely contribute to the adaptability of this strain in marine conditions. Core-proteome average amino acid identity analysis effectively identified the strain's affiliation with the genus Affinirhizobium, showing the highest value (89.9%) with Affinirhizobium pseudoryzae DSM 19479T. This classification was further supported by the phylogenetic analysis of concatenated alignment of 170 single-copy orthologous proteins. When compared to related reference strains, SSA5.23T displayed an average nucleotide identity ranging from 74.9 to 80.3% and digital DNA-DNA hybridization values ranging from 19.9 to 23.9%. Our findings confirmed that strain SSA5.23T represents a novel species of the genus Affinirhizobium, for which the name Affinirhizobium gouqiense sp. nov. (type strain SSA5.23T = LMG 32560T = MCCC 1K07165T) was suggested.

Hematite enhances microbial autotrophic nitrate removal in carbonate and phosphate-rich environments by increasing Fe(II) activity

Groundwater contamination by nitrates presents significant risks to both human health and the environment. In groundwater characterized as oligotrophic—low in organic carbon, but abundant in carbonate and phosphate—chemolithoautotrophic bacteria, including nitrate-reducing Fe(II)-oxidizing bacteria (NRFeOB), play a vital role in denitrification. The chemoautotrophic nitrate reduction is sensitive to environmental factors, including widespread iron oxides like hematite in nature. However, the specific mechanisms of this influence remain unclear. We examined the mechanism of how hematite impacts autotrophic nitrate reduction in a model NRFeOB community known as culture KS. We found that hematite enhances the rate of autotrophic nitrate reduction by promoting Fe(II) oxidation. Mössbauer spectroscopy detected a significant amount of adsorbed Fe(II) when hematite was present, leading to a reduction in dissolved ferrous iron. In conjunction with XRD data, it can be inferred that the formation of vivianite decreased, thereby increasing the Fe(II) activity in the reaction system. Within the culture KS bacterial consortium, hematite fosters the proliferation of autotrophic microorganisms, specifically Gallionellaceae, and amplifies the presence of denitrifying microbes, notably Rhodanobacter. This dual enhancement improves Fe(II) utilization and nitrate reduction capabilities. Our findings highlight intricate interactions between hematite and a model NRFeOB community, offering insights into groundwater nitrate removal mechanisms and the ecological strategies of autotrophic bacteria in mineral-rich environments.

Transcriptomic profiling of haloarchaeal denitrification through RNA-Seq analysis.

Denitrification, a crucial biochemical pathway prevalent among haloarchaea in hypersaline ecosystems, has garnered considerable attention in recent years due to its ecological implications. Nevertheless, the underlying molecular mechanisms and genetic regulation governing this respiration/detoxification process in haloarchaea remain largely unexplored. In this study, RNA-sequencing was used to compare the transcriptomes of the haloarchaeon Haloferax mediterranei under oxic and denitrifying conditions, shedding light on the intricate metabolic alterations occurring within the cell, such as the accurate control of the metal homeostasis. Furthermore, the investigation identifies several genes encoding transcriptional regulators and potential accessory proteins with putative roles in denitrification. Among these are bacterioopsin-like transcriptional activators, proteins harboring a domain of unknown function (DUF2249), and cyanoglobin. In addition, the study delves into the genetic regulation of denitrification, finding a regulatory motif within promoter regions that activates numerous denitrification-related genes. This research serves as a starting point for future molecular biology studies in haloarchaea, offering a promising avenue to unravel the intricate mechanisms governing haloarchaeal denitrification, a pathway of paramount ecological importance.IMPORTANCEDenitrification, a fundamental process within the nitrogen cycle, has been subject to extensive investigation due to its close association with anthropogenic activities, and its contribution to the global warming issue, mainly through the release of N2O emissions. Although our comprehension of denitrification and its implications is generally well established, most studies have been conducted in non-extreme environments with mesophilic microorganisms. Consequently, there is a significant knowledge gap concerning extremophilic denitrifiers, particularly those inhabiting hypersaline environments. The significance of this research was to delve into the process of haloarchaeal denitrification, utilizing the complete denitrifier haloarchaeon Haloferax mediterranei as a model organism. This research led to the analysis of the metabolic state of this microorganism under denitrifying conditions and the identification of regulatory signals and genes encoding proteins potentially involved in this pathway, serving as a valuable resource for future molecular studies.

Phylogenetics and environmental distribution of nitric oxide-forming nitrite reductases reveal their distinct functional and ecological roles.

The two evolutionarily unrelated nitric oxide-producing nitrite reductases, NirK and NirS, are best known for their redundant role in denitrification. They are also often found in organisms that do not perform denitrification. To assess the functional roles of the two enzymes and to address the sequence and structural variation within each, we reconstructed robust phylogenies of both proteins with sequences recovered from 6973 isolate and metagenome-assembled genomes and identified 32 well-supported clades of structurally distinct protein lineages. We then inferred the potential niche of each clade by considering other functional genes of the organisms carrying them as well as the relative abundances of each nir gene in 4082 environmental metagenomes across diverse aquatic, terrestrial, host-associated, and engineered biomes. We demonstrate that Nir phylogenies recapitulate ecology distinctly from the corresponding organismal phylogeny. While some clades of the nitrite reductase were equally prevalent across biomes, others had more restricted ranges. Nitrifiers make up a sizeable proportion of the nitrite-reducing community, especially for NirK in marine waters and dry soils. Furthermore, the two reductases showed distinct associations with genes involved in oxidizing and reducing other compounds, indicating that the NirS and NirK activities may be linked to different elemental cycles. Accordingly, the relative abundance and diversity of NirS versus NirK vary between biomes. Our results show the divergent ecological roles NirK and NirS-encoding organisms may play in the environment and provide a phylogenetic framework to distinguish the traits associated with organisms encoding the different lineages of nitrite reductases.

Analysis Of Silicon Crystal Materials: Meeting Growing Demands Across Industries

The demand for silicon crystal materials is poised for continued growth across diverse sectors in the upcoming years. In the realm of computers and communication, silicon single crystal wafers and chips are in high demand, fueled by the increasing adoption of communication equipment and the essential requirement for memory and control chips in information processing systems. Beyond the electronics domain, silicon crystals find applications in various industries, including environmental protection, new energy, and construction. In the field of environmental protection, silicon crystals play a vital role in denitrification and dust removal devices. In the new energy sector, they contribute to solar photovoltaic power generation systems and geothermal power generation systems. In construction, silicon crystals find their place in the production of building glass and semiconductor building materials. As China's economy continues to evolve and environmental concerns gain prominence, the demand for semiconductor materials, including silicon crystal materials, is anticipated to rise. This underscores a bright market outlook for silicon crystal materials in the foreseeable future.

Pyrrhotite-sulfur-limestone composite for high rate nitrogen and phosphorus removal from wastewater: Column study

Pyrrhotite-sulfur-limestone composite (PSLC) was prepared and PSLC autotrophic denitrification biofilter (PSLCAD) was constructed with PSLC particle (2–4.75 mm) in this study. During treating synthetic, municipal and industrial secondary effluent, PSLCAD showed good NO3−-N and PO43--P removal, and the highest TON (Total oxidized nitrogen) removal rate of PSLCAD was up to 1749.91 mg/L/d. At HRT 0.5 h, and influent NO3−-N 21.09 mg/L, TON removal rate was up to 1005.12 mg/L with effluent NO3−-N 0.10 mg/L. PSLCAD achieved effluent PO43--P below 0.2 mg/L when influent PO43--P was around 0.5 mg/L. HRT down to 0.5 h had no negative impacts on N removal. Effluent pH below 7 was harmful to denitrification performance of PSLCAD. TON removal rate increased with influent NO3−-N increasing, but influent NO3−-N over 103.55 mg/L decreased NO3−-N removal rate. In PSLCAD biofilter, the most dominant bacteria were Thiobacillus and Sulfurimonas, and they played the most important role in denitrification, but the abundance of heterotrophic denitrifiers was also quite high. PO43− was mainly removed through precipitate of Fe–P in PSLCAD. The synergistic effects between pyrrhotite and sulfur autotrophic denitrification were much enhanced, and that caused PSLCAD to achieve high rate N and P removal.

Performance and mechanism of chromium reduction in denitrification biofilm system with different carbon sources

In the process of biological reduction of Cr(VI), the type of carbon sources affects the rate and effect of Cr(VI) reduction, but its specific performance and influencing mechanism have not yet been explored. In this study, four denitrification biofilm reactors were operated under four common carbon sources (C6H12O6, CH3COONa, CH3OH, CH3COONa:C6H12O6 1:1) to reveal the impact of carbon sources on Cr(VI) reduction. Through preliminary experimental concentration research, 75 mg/L Cr(VI) was selected as the dosing concentration. In long-term operation, the composite carbon sources of CH3COONa and C6H12O6 demonstrated excellent stability and achieved an impressive Cr(VI) removal efficiency of 99.5 %. The following sequence was C6H12O6, CH3COONa, and CH3OH. Among them, CH3OH was less competitive and the system was severely unbalanced with lowest Cr(VI) reduction efficiency. The toxicity reactions, changes in EPS and its functional groups, and electron transfer revealed the reduction and fixation mechanism of chromium on denitrification biofilm. The changes in microbial communities indicated that microbial communities in composite carbon sources can quickly adapt to the high toxic environment. The proportion of Trichococcus reached 43.6 %, which played an important role in denitrification and Cr(VI) reduction. Meanwhile, the prediction of microbial COG function reflected its excellent metabolic ability and defense mechanism.

Low-carbon and high-ammonia nitrogen dispersed wastewater treatment: From “normal-sludge” to “low-sludge” to “no-sludge” modes

Several biological enhancements were implemented in the aerobic tank to address the challenges of treating expressway service sewage (ESS) with low-carbon and high-ammonia nitrogen using A/O-MBR technology, aiming to improve TN removal efficiency and reduce excessive sludge production. A novel moving bed biofilm reactor (MBBR) inoculated with heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria was developed for ESS, and the results showed that HN-AD bacteria significantly improved TN removal efficiency, with an increase of 65% compared to the traditional activated sludge system. High-throughput sequencing revealed that Bacteroidotas contributed significantly to MBBR denitrification, and the genes nirK and nosZ played a significant role in denitrification. The HN-AD biofilm-forming MBBR achieved the transition of ESS treatment from “normal-sludge” mode to the more environmentally-friendly “low-sludge” and “no-sludge” modes by reducing the sludge concentration.

A biofilm reactor based on slow-release carbon source effectively improved the continuous denitrification capacity of slightly polluted surface water at low carbon to nitrogen ratio

A biofilm reactor was exploited using Burkholderia sp. CF6. Polymers were attached to alkali-modified corn stover (CS) to prepare a novel slow-release carbon source. The slow-release carbon source not only released carbon into the nutrient-poor water in a stable manner to ensure denitrification, but also the microporous structure of the slow-release carbon source promoted the degradation of cellulose. Box-Behnken design was used to study the effects of hydraulic retention time (HRT), pH, and carbon to nitrogen ratio (C/N) on the nitrate removal efficiency. Under the HRT of 4 h, pH of 7.0, and C/N of 1.0, the nitrate removal efficiency reached 98.03%. Three-dimensional excitation emission matrix (3D-EEM) results showed that soluble microbial products (SMP) play a dominant role in denitrification. The PCR amplification technique showed that Burkholderia sp. CF6 assumed the main denitrification role in the reactor. This study provides a theoretical basis for the effective management of micro-polluted water bodies.

Nano-α-Fe2 O3 for enhanced denitrification in a heterotrophic/biofilm-electrode autotrophic denitrification reactor.

In this study, a heterotrophic/biofilm-electrode autotrophic denitrification reactor (HAD-BER) was constructed and nano-ɑ-Fe2 O3 was coated on granular activated carbon (GAC) as a third electrode to enhance the nitrate removal performance. The introduction of nano-ɑ-Fe2 O3 could stimulate microorganisms to secrete more extracellular polymeric substances (EPS), accelerating the electron transfer. Moreover, more denitrification bacteria were enriched on the particle electrodes, especially Pseudomonas and Thermomonas, which played a significant role in denitrification. The denitrification performance at different COD/N ratios (0.65-3.23) and current intensities (0-150 mA) was investigated in depth. When the nitrate concentration of the influent was 60 mg/L, nitrate was almost completely removed at the optimal current intensity (60 mA) and COD/N ratio (1.29). At the same time, there was almost no nitrite (<0.10 mg/L) and ammonia nitrogen (0 mg/L) accumulation in the effluent. This study provided a new direction for the advancement of HAD-BER and accelerated its implementation. PRACTITIONER POINTS: By introducing nano-a-Fe2O3 into HAD-BER, more denitrification bacteria were enriched on the particle electrodes. The increased contents of polysaccharide and protein content could accelerate the electron transfer. Almost completely denitrification could be achieved at current = 60 mA and COD/N = 1.29. The study provided a new direction for the further development of HAD-BERs.

The synthetic composite materials using PHBV, nZVI and biochar enhanced denitrification performance in water treatment

Solid carbon source (SCS)-based denitrification is a promising technique for nitrogen removal from sewage. However, a sustainable and effective supply of carbon sources, crucial to denitrification performance, has always been challenging. This study developed four synthetic SCSs: biochar (BC), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), PHBV loaded on biochar (BCP), and PHBV loaded on biochar-supported nanoscale zero-valent iron (BCPF), to examine their denitrification efficiency enhancement. Insufficient carbon sources caused low nitrate removal (<45%) in the BC reactor during the entire experiment. At the biofilm formation stage (influent nitrate: 40 mg L-1), the relatively higher nitrate removal in biochar-based SCS reactors than in the P reactor in the first 4 h indicated that the biochar's rapid release of carbon sources played a priming role in denitrification. Then, the subsequent sharp decrease in nitrate removal revealed the biochar's unsustainable release of carbon sources for the denitrifiers. Similar to the P reactor, the nitrate removal in BCP and BCPF reactors gradually increased after 12 h until the 48 h mark, where the high nitrate removal efficiency was stabilized (P: 79.93%−93.74%, BCP: 86.90%−100%, and BCPF: 91.68%−100%), except in the BC reactor. Evidently, the decomposed products from PHBV provided sustainable carbon sources for the denitrifiers. Compared with the P reactor in the continuous running stage, BCP and (especially) BCPF reactors exhibited excellent resistance to load impact. Here, PHBV supplied sustainable carbon sources and electron donors for denitrification, while nZVI served as extra electron donors. The biochar dominantly provided habitats for denitrifiers and functioned as an electron mediator.

The effect of reservoir expansion from underground karst cave to surface reservoir on water quality in southwestern China.

Due to the excessive exploitation of traditional energy sources, the attention paid to water energy has increased in recent years. As an important means to effectively utilize water energy, reservoirs play an important role in drinking water, irrigation, flood control, and drought resistance. However, utilizing reservoirs often led to water quality issues resulting from the interaction of nutrients and hydrological conditions, especially due to the special structure of karst areas. Because of the change of hydrological conditions by the effect of dam construction, the dynamic of water quality will be more obvious in karst areas with a fast exchange of water and contaminants between underground and surface streams. In the present study, the change in water quality of a karst reservoir, the Muzhu Reservoir in the Houzhai Catchment, was studied. Long-term monitored datasets (1981-2002) and water quality datasets of more recent years were used to assess the effect on the water quality of reservoir expansion from the underground reservoir to the surface reservoir in a karst area. Long-term series datasets had shown that the hydro-chemistry type had been changed from HCO3-·SO42--Ca2+·Mg2+ type to HCO3--Ca2+ type in the short term after the reservoir's expansion. The chemical components of water originating from a rock background reduced markedly after the reservoir's expansion, whereas the content of the anthropogenic contribution in the water decreased after the expansion, except in April and May. Isotopic characteristics showed that δ15N-NO3- and δ18O-NO3- values were positively correlated before and after the reservoir expansion, but the slope of the linear regression before the expansion was 0.34, while the slope of the linear regression before the expansion was close to 0.7. This indicated that although denitrification and assimilation may occur simultaneously after the reservoir's expansion, the role of denitrification on nitrate removal decreased, which resulted in nitrate accumulation in the karst reservoir. The results highlighted that nitrate accumulation in karst reservoirs should be monitored to decrease nitrate concentration in the future.

A novel two-stage anoxic/oxic-moving bed biofilm reactor process for biological nitrogen removal in a full-scale municipal WWTP: Performance and bacterial community analysis

The application of a novel two-stage anoxic/oxic-moving bed biofilm reactor (TS-A/O-MBBR) was validated in a full-scale municipal wastewater treatment plant (WWTP), and its working mechanism was analysed for biological nitrogen removal in this study. Over one year, at a hydraulic residence time of only 9.8 h, the effluent chemical oxygen demand, ammonia nitrogen and total nitrogen (TN) concentrations remained below 40, 2 and 15 mg/L, which met strict emission standards. The seven compartments in this unit performed different functions, and together accomplished organics and nitrogen removal. TN removal could be controlled by the external carbon sources dosage added to the postanoxic compartments to cost effectively meet the standard with the lowest cost. The maximum TN removal efficiency and minimum effluent TN concentration reached 91.76 % and 4.12 mg/L, respectively. The bacterial communities differed in the suspended solids and preoxic, postanoxic and oxic biofilms (r = 0.87 and P = 0.001). The top 30 most abundant identified bacterial genera in biofilms included 24 denitrifying genera and 2 nitrifying genera. The most abundant biofilm genus was Methylotenera, which played important roles in denitrification in the anoxic compartments. 1 and 24 denitrifying genera were only abundant in the postanoxic and preanoxic compartments, respectively. Nitrosomonas and Nitrospira were abundant in the oxic compartments, and played roles in nitrification. This study verified the feasibility of the TS-A/O-MBBR process in a full-scale WWTP, and investigated its working mechanism.

Biofilm stratification in counter-diffused membrane biofilm bioreactors (MBfRs) for aerobic methane oxidation coupled to aerobic/anoxic denitrification: Effect of oxygen pressure

Aerobic methane oxidation coupled with denitrification (AME-D) executed in membrane biofilm bioreactors (MBfRs) provides a high promise for simultaneously mitigating methane (CH4) emissions and removing nitrate in wastewater. However, systematically experimental investigation on how oxygen partial pressure affects the development and characteristics of counter-diffusional biofilm, as well as its spatial stratification profiles, and the cooperative interaction of the biofilm microbes, is still absent. In this study, we combined Optical Coherence Tomography (OCT) with Confocal Laser Scanning Microscopy (CLSM) to in-situ characterize the development of counter-diffusion biofilm in the MBfR for the first time. It was revealed that oxygen partial pressure onto the MBfR was capable of manipulating biofilm thickness and spatial stratification, and then managing the distribution of functional microbes. With the optimized oxygen partial pressure of 5.5 psig (25% oxygen content), the manipulated counter-diffusional biofilm in the AME-D process obtained the highest denitrification efficiency, due mainly to that this biofilm had the proper dynamic balance between the aerobic-layer and anoxic-layer where suitable O2 gradient and sufficient aerobic methanotrophs were achieved in aerobic-layer to favor methane oxidation, and complete O2 depletion and accessible organic sources were kept to avoid constraining denitrification activity in anoxic-layer. By using metagenome analysis and Fluorescence in situ hybridization (FISH) staining, the spatial distribution of the functional microbes within counter-diffused biofilm was successfully evidenced, and Rhodocyclaceae, one typical aerobic denitrifier, was found to survive and gradually enriched in the aerobic layer and played a key role in denitrification aerobically. This in-situ biofilm visualization and characterization evidenced directly for the first time the cooperative path of denitrification for AME-D in the counter-diffused biofilm, which involved aerobic methanotrophs, heterotrophic aerobic denitrifiers, and heterotrophic anoxic denitrifiers.

Improving nitrogen and phosphorus removal and sludge reduction in new integrated sewage treatment facility by adjusting biomass concentration

Aiming at the practical problem of rural wastewater and excess sludge treatment difficulties, micro-pressure swirl reactor (MPSR) was employed to carry out the experiment on the treatment of sewage under five different biomass concentration (MLSS concentration) conditions (4.14, 6.05, 7.98, 11.45, 14.46 g/L). The results showed that the nitrogen removal and phosphorus removal and sludge reduction performance of the system showed an increase and then a decrease with increasing MLSS concentration, and 7.98–11.45 g/L was the optimal MLSS concentration range. In addition, parameters related to in situ sludge reduction were further examined, and the extracellular polymeric substance content and sludge dehydrogenase activity were negatively and positively correlated with sludge reduction, respectively. According to the microbial analysis, at suitable MLSS concentration, beneficial microorganisms (Tetrasphaera, Aeromonas, Candidatus_Competibacter) were enriched in the MPSR to facilitate the nitrogen and phosphorus removal and sludge reduction of the system. In addition, the potential gene(nirK, norB, nosZ) functions of the microorganisms were positively regulated. The increase in the expression abundance ratio of dissimilatory and anabolic nitrate reduction genes played a positive role in denitrification and sludge reduction of the system.

Potential of food waste-derived volatile fatty acids as alternative carbon source for denitrifying moving bed biofilm reactors

Fossil-based materials such as methanol are frequently used in the denitrification process of advanced biological wastewater treatment as external carbon source. Volatile fatty acids (VFAs) produced by anaerobic digestion of food waste, are sustainable compounds with the potential to act as carbon sources for denitrification, reducing carbon footprint and material costs. In this study, the effectiveness of food waste-derived VFAs (AD-VFA) was investigated in the post-denitrification process in comparison with synthetic VFA and methanol as carbon sources. Acetic acid had the highest rate of disappearance among single tested VFAs with a denitrification rate of 0.44 g NOx-N removed/m2/day, indicating a preferential utilization pattern. While AD-VFA had a denitrification rate of 0.61 mg NOx-N removed/m2/day, sVFA had a rate of 0.57 mg NOx-N removed/m2/day, indicating that impurities in AD-VFA did not play substantial role in denitrification. AD-VFA proved to be promising carbon source alternative for denitrification in wastewater treatment plants.

Nitrogen removal from low COD/N interflow using a hybrid activated sludge membrane-aerated biofilm reactor (H-MABR)

A hybrid activated sludge membrane-aerated biofilm reactor based on a two-stage simultaneous nitrification–denitrification (SND) process was built, and its utility for treating interflow with low chemical oxygen demand (COD)/total nitrogen (TN) (COD/N) was explored. The operating performance, functional microbial communities, and functional genes for nitrogen metabolism were evaluated at low COD/N (4–1.3). The reactor could achieve stable operation at COD/N = 4–1.5, and the removal efficiency of COD, TN, and ammonia nitrogen was stable at 90.30 ± 2.36 %, 85.69 ± 2.22 %, and 89.52 ± 6.06 %, respectively. The SND rates were 70.89 % and 50.75 % when influent COD/N was 2.0 and 1.7, respectively, indicating that SND makes an important contribution to nitrogen removal under these two COD/N conditions. Microbial analysis revealed that the sampling sites with a high abundance of denitrification genes in the outer ring experienced aerobic conditions, inferring that aerobic denitrification also plays an important role in denitrification.