High Nitrogen Removal Rate Research Articles

Gel beads prepared by polyvinyl alcohol cross-linking with phytic acid and Fe as novel microbial carriers for simultaneous partial nitrification, anammox and denitrification

Enhancing the stability of biomass and ensuring a stable activity of anaerobic ammonia oxidizing bacteria are crucial for successful operation of the simultaneous partial nitrification, Anammox, and denitrification (SNAD) process. In this study, gel beads of polyvinyl alcohol/phytic acid (PVA/PA) and polyvinyl alcohol/phytic acid/Fe (PVA/PA/Fe) were prepared as innovative bio-carriers. Theoretical simulations and analyses revealed that these carriers are predominantly connected via hydrogen and borate bonds, with PVA/PA/Fe also featuring metal coordination bonds. The total nitrogen removal efficiency of reactors with PVA/PA/Fe and PVA/PA increased by 13.5 % and 9.0 %, respectively, compared to reactor without carriers. The iron-enriched PVA/PA/Fe carriers significantly improve SNAD by promoting Anammox, Feammox, and nitrate-dependent Fe2+ oxidation reactions, leading to faster nitrogen conversion and higher nitrogen removal rate than reactor without carriers and with PVA/PA. Using of PVA/PA and PVA/PA/Fe gel beads as bio-carriers offers benefits to the SNAD process, including cost-effective and low carbon requirement.

Enhanced aerobic granular sludge by thermally-treated dredged sediment in wastewater treatment under low superficial gas velocity

The positive contributions of carriers to aerobic granulation have been wildly appreciated. In this study, as a way resource utilization, the dredged sediment was thermally-treated to prepared as carriers to promote aerobic granular sludge (AGS) formation and stability. The system was started under low superficial gas velocity (SGV, 0.6 cm/s)for a lower energy consumption. Two sequencing batch reactors (SBR) labeled R1 (no added carriers) and R2 (carriers added), were used in the experiment. R2 had excellent performance of granulation time (shortened nearly 43%). The maximum mean particle size at the maturity stage of AGS in R2 (0.545 mm) was larger compared to R1 (0.296 mm). The sludge settling performance in R2 was better. The reactors exhibited high chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) removal rates. The total phosphorus (TP) removal rate in R2 was higher than R1 (almost 15% higher) on stage II (93-175d). R2 had a higher microbial abundance and dominant bacteria content. The relative abundance of dominant species was mainly affected by the carrier. However, the enrichment of dominant microorganisms and the evolution of subdominant species were more influenced by the increase of SGV. The results indicated that the addition of carriers induced the secretion of extracellular polymeric substances (EPS) by microorganisms and accelerated the rapid formation of initial microbial aggregates. This work provided a low-cost method and condition to enhance aerobic granulation, which may be helpful in optimizing wastewater treatment processes.

Enhanced Denitrification in Constructed Wetlands with Low Carbon/Nitrogen Ratios: Insights into Reallocation of Carbon Metabolism Based on Electron Utilization

Constructed wetlands (CWs) are a promising method to treat effluent from wastewater treatment plants (WWTPs). However, low carbon/nitrogen (C/N) ratios of the influent inhibit denitrification in CWs, resulting in poor nitrogen removal efficiency. Herein, we compared traditional (control), biochar (BC), and β-cyclodextrin-functionalized biochar (BC@β-CD) CW systems to investigate nitrogen removal from influent with low C/N ratios, and the mechanisms that enhance this process. The highest nitrogen removal rates were observed in the BC@β-CD group, with rates 45.89% and 42.48% higher than those of the control, accompanied by a 70.57% and 85.45% decrease in nitrous oxide release, when the C/N ratio decreased from 4 to 2, respectively. Metagenomic and enzymatic analyses indicated that BC@β-CD enhances nitrogen removal by coordinately promoting carbon metabolism and increasing denitrification enzyme activities, without affecting microbial species diversity in CWs. Structural equation modeling confirmed that the foremost advantages of BC@β-CD were effective electron generation and transportation resulting from increased activities of nicotinamide adenine dinucleotide (NADH) dehydrogenase and the electron transfer system (ETS), thereby strategically reallocating more carbon metabolic flow to support denitrification. Our results show that the application of BC@β-CD in CWs to optimize the reallocation of electrons from carbon metabolism is a feasible strategy to enhance denitrification under low C/N conditions.

Microalgae cultivation trials in a membrane bioreactor operated in heterotrophic, mixotrophic, and phototrophic modes using ammonium-rich wastewater: The study of fouling.

In this work, microalgae cultivation trials were carried out in a membrane bioreactor to investigate fouling when the cultures of Chlorellavulgaris were grown under mixotrophic, heterotrophic, and phototrophic cultivation regimes. The Chlorella cultures were cultivated in wastewater as a source of nutrients that contained a high concentration of ammonium. In mixotrophic cultivation trials, the results showed that the elevated contents of carbohydrates in the soluble microbial product and proteins in extracellular polymeric substances probably initiated membrane fouling. In this case, the highest protein content was also found in extracellular polymeric substances due to the high nitrogen removal rate. Consequently, transmembrane pressure significantly increased compared to the phototrophic and heterotrophic regimes. The data indicated that cake resistance was the main cause of fouling in all cultivations. Higher protein content in the cake layer made the membrane surface more hydrophobic, while carbohydrates had the opposite effect. Compared to a mixotrophic culture, a phototrophic culture had a larger cell size and higher hydrophobicity, leading to less membrane fouling. Based on our previous data, the highest ammonia removal rate was reached in the mixotrophic cultures; nevertheless, membrane fouling appeared to be the fundamental problem.

Insights into the effects of exogenous folate on the recovery of SPNA system after starvation: Performance, microbial community and metabolism

To investigate the effects of folate addition on the recovery process of the single-stage partial nitritation-anammox (SPNA) system, two continuous stirred tank reactors (CSTRs), named R1 (adding folate) and R2 (control group), were operated for 105 days at room temperatures. The highest nitrogen removal rate (NRR) observed in R1 was 0.47 kg N/(m3·d) with the addition of 3.0 mg/L folate. Additionally, the activities of HZO and HZS in R1 were higher than those in R2. The relative abundance of Candidatus Brocadia reached 23.7% in R1 and 18.2% in R2. Moreover, the relative abundance of nitrogen metabolism genes and carbon metabolism genes increased with folate addition. However, 3.0 mg/L folate addition reduced the relative abundance of nirK/S and the activity and growth of ammonia-oxidizing bacteria, which was not conducive to continually improving the NRR. This study provided a novel perspective on improving the activity and abundance of anammox bacteria during the restoration process.

Heating aluminum dross: Harmless process and utilization as cement admixture

Phosphogypsum (PG) and aluminum dross (AD) with harmful impurities seriously hinder its large-scale engineering utilization. In this paper, the properties of AD and PG as cement admixture were investigated with the aim of reducing the environmental pollution and landfill stockpiling pressure. The migration and transformation rules under crucial factors were analyzed by different characterization methods while AD was heated at different temperature. Then, the compressive strength, soluble phosphorus and fluorine concentration, hydration heat and expansion rate of specimens prepared with AD, PG, and Portland cement (PC) were evaluated to illustrate the hydration mechanism. Compared to the other experiment sets, the results indicated that AD treated at 900°C not only had a higher nitrogen removal rate, but also maintained hydration activity at a relatively high level. Moreover, Heating AD at 900℃ effectively accelerated the dissolution of gypsum and calcium silicate, resulting in increased formation of ettringite (AFt), calcium silicate hydrates (C-S-H) and calcium aluminium hydrates (C-A-H). When the binder consisted of 14% heated aluminium dross (HAD), 6% PG, and 80% PC, the specimen reached the highest compressive strength value at 25.87 MPa. This work provided a new strategy for synergistic utilization of PG and AD, promoting the development of environment-friendly industrial wastes-based cementitious materials effectively.

Microbial Diversity of Biological Filters in Recirculating Aquaculture Systems for Sand Lobster (Panulirus homarus) Rearing

The recirculating aquaculture system (RAS) is a technology that reuses water (often less than 5%) in land-based production for farming aquatic organisms’ water treatment. This technology uses filters, either mechanical or biological, for any aquaculture species rearing. In lobster rearing using RAS, one of the most important factors is the quality of rearing water, which depends primarily on the biochemical activities of the microbial communities in the biofilter. There is a significant correlation between the abundance of nitrifying microbial communities and high total ammonia nitrogen (TAN) removal rate. These organisms can convert ammonia accumulates in the system into nitrate. The application of molecular tools (Metagenome 16S Full-Length Barcoding using Oxford Nanopore Platform) to characterize microbial community diversity has been conducted for this study. The diversity of microbes in RAS biofilter for sand lobster rearing is summarized as follows: Nitrification Bacteria group (β-Proteobacteria, g-Proteobacteria, Nitrospirae); Denitrification/Nitrate Reducing Bacteria (α-Proteobacteria, δ-Proteobacteria, Bacteroidetes/Chlorobi, Firmicutes), Sulfide Oxidation Bacteria (ε-Proteobacteria), Probiotic Bacteria (Bacillus subtilis, Pseudomonas sp., Roseobacter sp.). This study’s results indicate a potential for RAS in sand lobster-intensive aquaculture applications and also discuss future studies’ directions.

Hydraulic retention time optimization achieved unexpectedly high nitrogen removal rate in pilot-scale anaerobic/aerobic/anoxic system for low-strength municipal wastewater treatment

Applications of post-denitrification processes are subjected to low reaction rates caused by a lack of carbon resources. To offer a solution for reaction rate promotion, this research found a pilot-scale anaerobic/aerobic/anoxic bioreactor treating 55–120 m3/d low-strength municipal wastewater for 273 days. A short hydraulic retention time (HRT, 5–6 h) and a high nitrogen removal rate (63.2 ± 9.3 g-N/m3·d) were achieved using HRT optimization. The effluent total nitrogen concentration was maintained at 5.8 ± 1.4 mg/L while operating at a high nitrogen loading rate of 86.2 ± 12.8 g-N/m3·d. The short aeration (1.25–1.5 h) minimized the Glycogen loss. The endogenous denitrification rate increased to above 1.0 mg/(g-VSS·h). The functional genus Ca. Competibacter enriched to 2.3 %, guaranteeing the efficient post-denitrification process. Dechloromonas rose to 1.1 %, aiding in the synchronous phosphorus removal. These findings offered fresh insights into AOA processes to achieve energy/cost-saving wastewater treatment.

High-rate nitrogen removal by partial nitritation/anammox with a single-stage membrane-aerated biofilm reactor

In this study, a membrane aerated biofilm reactor (MABR) coupled partial nitritation/anammox (PN/A) system was established for high-rate nitrogen removal. Results showed that the nitrogen removal efficiency of 90.34% was finally obtained when influent ammonia increased from 150 mg L−1 to 300 mg L−1. Based on the fluorescence spectroscopy technology, the raised hydrophobicity tryptophan in extracellular polymeric substances (EPS) promoted biofilm formation and bacteria aggregation. 16S rRNA gene amplicon sequencing revealed that the relative abundance of AOB and AnAOB was also enhanced by ammonia (Nitrosomonas and Candidatus Brocadia increased by 6.02 % and 10.06 % in biofilm, respectively), which further facilitated nitrogen removal efficiency. Furthermore, the key functional genes involved in partial nitritation and anammox, especially hao and nirK, up-regulated by 1.31 and 1.26 times, respectively, accelerating the electron generation and consumption. Therefore, raising influent ammonia content intensified microbial electron transfer behavior and high-rate nitrogen metabolism.

Effect of exogenous folate addition on the start-up process of single-stage partial nitritation-anammox system

In this study, two lab-scale reactors were operated to evaluate the impact of exogenous folate on the start-up process of single-stage partial nitritation-anammox (SPNA). Folate at a dose of 0.5, 1.0, and 1.5 mg/L was continuously added into the experimental reactor (RI) at different operation stages. The highest nitrogen removal rate was 0.26 kg N/(m3•d) in RI with a nitrogen loading rate of 0.45 kg N/(m3•d), which was higher than that in the control reactor (RII) of 0.20 kg N/(m3•d). Moreover, the extracellular polymeric substances production in RI with 1.5 mg/L folate dosage was 264.24 ± 6.74 mg/gVSS, enhancing by 0.5-fold that of the RII, and the activity of hydrazine oxidase increased to the highest level of 0.37 ± 0.01 μmol cyt-c/(gVSS•s). Meanwhile, the activity of dehydrogenase in RI was enhanced from 796.39 ± 2.19 μg/(gVSS•min) to 819.17 ± 24.47 μg/(min•gVSS). The relative abundance of Candidatus Brocadia was 0.64 % at the end of phase 5 in RI whereas it remained at 0.25 % in RII. Function prediction showed that the nitrogen-related genes highly increased with the folate addition.

A novel pattern of coupling sulfur-based autotrophic disproportionation and denitrification processes for achieving high-rate and precisely adjustable nitrogen removal

Sulfur-based autotrophic disproportionation (SADP) has been accidentally discovered during employing sulfur-based autotrophic denitrification (SADN) bioreactor to treat low C/N ratio wastewater. The SADP products, including sulfide (SADP-S2−) and polysulfide (SADP-Sn2−), can supply additional electrons to improve the denitrification efficiency. However, the in-situ SADP process was challenging to control, resulting in the unstable enhancement efficiency and excessive sulfide emissions, thereby impeding its scalability in practical engineering. In this study, an independent SADP process was achieved in a sulfur-packed bed bioreactor, with a controllable sulfide production rate ranging from 0.24 ± 0.02 to 0.83 ± 0.03 kg-S/m3/d by adjusting the empty bed contact time between 1 and 5 h. Subsequently, the SADP bioreactor was connected upstream of a SADN bioreactor to create a sulfur-based autotrophic disproportionation-denitrification (SAD2) system. The SAD2 system realized an enhanced denitrification rate by up to 2.38 times, with flexibility to adjust between 0.65 ± 0.06–1.55 ± 0.20 kg-N/m3/d. One reason for this enhancement was that SADP-S2− provided additional electrons to the SADN process and exhibited higher biocompatibility than chemical-S2− (Na2S) at similar doses. Additionally, it stimulated the sulfur bioavailability by 1.66 times as a result of stoichiometry matrix calculation. SADP-Sn2− was only detected in the biofilm, as indicated by a linear increase in the Sn proportion from 8.1 % to 30.1 %, but with minimal releases (352 μg-S/L) into the water. Another reason for the enhancement was bioaugmentation, with increases in protein (30.0 %), ATP (6.9 %), live cells proportion (10.1 %) and total relative abundance of denitrificans (87.7 %). These findings imply that the novel SAD2 system facilitates adjustable and high-rate nitrogen removal without the risk of sulfide emission, surpassing the capabilities of the independent SADN system. This offers a new pattern for practical applications.

A modelling method for simulating nitrogen dynamics under the hydrodynamic context of river network

River network comprised by varieties of interconnected rivers is an essential form of lotic environments. Unravelling the biogeochemical processes are essential for promoting the water quality and ecological health of river networks. However, biogeochemical processes in river networks are difficult to be quantified, since they are controlled by multi-directional mass transport processes and transformation processes associated with varieties of microbial metabolic pathways. To address this gap, the present research combined turbulence model and gene-centric model to establish a systematic modelling method to quantitively describe the nitrogen dynamics in a river network. The proposed model can capture the mass transport and microbial metabolic processes, and can accurately simulate the distribution characteristics of chemical materials and functional genes. The relative errors between simulated results and in-site measured data were low than 40%. With the help of the modelling method, this study further investigated the nitrogen dynamics in the river network. The results illustrated sulfide oxidation and nitrate reduction pathway and anaerobic ammonium oxidation pathway, participated by genes hzo and nap respectively, were the main pathways of NO3– and NO2– reduction. Besides, these two pathways exhibited high rates in all of the six confluence hydrodynamic zones (CHZs) of the river network and further increased the nitrogen removal efficiency. Moreover, the high-rate nitrogen removal processes continued in the downstream areas after CHZs, and the scope of such continuous influences increased with the discharge ratio between tributary and main stream. The modelling method and results in this research can be useful for prediction of water environmental quality and design of river connection engineering.

Metagenomics insights into high-rate nitrogen removal from municipal wastewater by integrated nitrification, partial denitrification and Anammox at an extremely short hydraulic retention time

To achieve high-rate nitrogen removal in municipal wastewater treatment through anaerobic ammonia oxidation (Anammox), the nitrification, partial denitrification, and Anammox processes were integrated by a step-feed strategy. An exceptional nitrogen removal load of 0.224 kg N/(m3·d) was achieved by gradient-reducing the hydraulic retention time (HRT) to 5 h. Metagenomic analysis demonstrated that Nitrosospira could express all genes encoding ammonia oxidation under low nitrogen and dissolved oxygen conditions (less than 0.5 mg/L), enabling complete nitrification. With the short of HRT, the relative abundance of Thauera increased from 2.8 % to 6.4 %. Frequent substrate exchanges at such extremely short HRT facilitated enhanced synergistic interactions among Nitrosospira, Thauera, and Candidatus Brocadia. These findings provide a comprehensive understanding of the utilization of Anammox combined processes for high-speed nitrogen removal in municipal wastewater treatment and the microbial interactions involved.

The evolution of nitrogen transformation microorganism consortium under continued manganese domestication conditions

Manganese redox-stimulated bioremediation of nitrogen wastewater is receiving increasing attention. However, the nitrogen metabolic capacity and community evolution during manganese-mediated nitrogen transformation process under continued manganese domestication conditions are ambiguous. In this study, nitrogen- metabolizing microbial consortiums were incubated with synthesized Mn-humic acid complex (Mn-HA) for one month (M1), three months (M2) and six months (M3), respectively. During the Mn-HA incubation period, Bio-MnOx accompanying with bacterial consortiums (MnOB consortiums) with high TIN removal capacities were obtained. The TIN removal rates in M1, M2 and M3 were 0.220, 1.246 and 4.237 mg·L−1·h−1, respectively, which were 15.961, 90.006 and 1550.006 times higher than CK (Control Check group, no Mn-HA added group) (0.014 mg·L−1·h−1), respectively. Functional genes (amoA, AMX and narG) were most abundant in M3, which was associated with the highest nitrogen removal rate in M3. MnOB1 (bacterial consortium in M1), including Geobactor, Geothrix, Anaeromyxobacter and Bacillus, may be responsible for the Mnammox-NDMO (MnOx reduction coupled to ammonium oxidation – nitrate/nitrite-dependent low-valent Mn oxidation) process. MnOB3 (bacterial consortium in M2) enriched nitrifying bacteria Ellin6067, and denitrifying bacteria Denitratisoma, which dominated nitrogen transformation. MnOB6 (bacterial consortium in M3) enriched denitrifiers Denitratisoma, nitrifiers Ellin6067 and potential anammox bacteria SM1A02, Candidatus_Brocadia. Combined with the reduced abundance of Nitrospirae, a short-cut partial nitrification and denitrification (PND) or partial nitrification, denitrification and anammox (PNDA) could occurred in M2 and M3. It is suggested that community may have evolved into an energetically efficient short-cut nitrification, denitrification and anammox consortium to replace the full-range nitrification and denitrification community in M1 and CK under the continued manganese domestication conditions. Enhanced metabolic pathways of hydroxylamine oxidation and the nitric oxide reduction may confirm that PND or PNDA occurred in M2 and M3.

Metalloenzymes play major roles to achieve high-rate nitrogen removal in N-damo communities: Lessons from metaproteomics

Nitrite-driven anaerobic methane oxidation (N-damo) is a promising biological process to achieve carbon–neutral wastewater treatment solutions, aligned with the sustainable development goals. Here, the enzymatic activities in a membrane bioreactor highly enriched in N-damo bacteria operated at high nitrogen removal rates were investigated. Metaproteomic analyses, with a special focus on metalloenzymes, revealed the complete enzymatic route of N-damo including their unique nitric oxide dismutases. The relative protein abundance evidenced that “Ca. Methylomirabilis lanthanidiphila” was the predominant N-damo species, attributed to the induction of its lanthanide-binding methanol dehydrogenase in the presence of cerium. Metaproteomics also disclosed the activity of the accompanying taxa in denitrification, methylotrophy and methanotrophy. The most abundant functional metalloenzymes from this community require copper, iron, and cerium as cofactors which was correlated with the metal consumptions in the bioreactor. This study highlights the usefulness of metaproteomics for evaluating the enzymatic activities in engineering systems to optimize microbial management.

Spatiotemporal Assembly and Immigration of Heterotrophic and Anammox Bacteria Allow a Robust Synergy for High-Rate Nitrogen Removal.

The novel partial denitrification-driven anammox (PD/A) is an energy-efficient method for nitrogen removal from wastewater. However, its stability and efficiency are impeded by the competition between heterotrophic denitrifying bacteria and relatively slow-growing anammox bacteria. In this study, a PD/A granular sludge system was developed, which achieved a nitrogen removal efficiency of 94% with 98% anammox contribution, even as the temperature dropped to 9.6 °C. Analysis of bacterial activity in aggregates of different sizes revealed that the largest granules (>2.0 mm) exhibited the highest anammox activity, 2.8 times that of flocs (<0.2 mm), while the flocs showed significantly higher nitrite production rates of PD, more than six times that of the largest granules. Interestingly, fluorescent in situ hybridization (FISH) combined with confocal laser scanning microscopy (CLSM) revealed a nest-shaped structure of PD/A granules. The Thauera genus, a key contributor to PD, was highly enriched at the outer edge, providing substrate nitrite for anammox bacteria inside the granules. As temperature decreased, the flocs transformed into small granules to efficiently retain anammox bacteria. This study provides multidimensional insights into the spatiotemporal assembly and immigration of heterotrophic and autotrophic bacteria for stable and high-rate nitrogen removal.

ZVI-Mediated High-Rate Nitrogen Removal from Fulvic Acid (FA)-Containing Wastewater by Anammox: Revealing the Genomic and Molecular Level Mechanisms

The anammox-based technologies are generally inhibited by refractory dissolved organic matter (rDOM), which is ubiquitous in real wastewater. In this study, a novel cost-effective approach, namely, zero-valent iron (ZVI) treatment, was presented to alleviate such inhibitory effects. The results showed that ZVI mitigated the inhibition of fulvic acids (FA) to anammox. Due to the 2 g/L ZVI addition, the nitrogen removal efficiency (NRE) increased from 83.53 to 90.06% when the FA concentration increased from 0 to 160 mg/L in wastewater. Additionally, the co-occurrence network linking Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and 16S rRNA sequencing results revealed the mechanism of ZVI mitigating inhibition by promoting the reduction of nitro and nitroso groups of FA and reshaping the metabolic division of functional bacteria. Hydrolytic acidifying bacteria (e.g., Anaerolineaceae and Ignavibacterium) were enriched for FA degradation, which was ultimately beneficial for denitrifying bacteria and anaerobic ammonium oxidation bacteria (AnAOB). Furthermore, metagenomics revealed that ZVI stimulated multiple nitrogen removal formed by anammox, denitrification, and DNRA by accelerating extracellular electron transfer resorting to FA serving as an electron shuttle and upregulating functional genes encoding electron generation, transport, and consumption processes.

Nitrogen removal from mature landfill leachate through enhanced Partial Nitrification-Anammox process in an innovative multi-stage fixed biofilm reactor

In the current integrated PN/A method/process for mature landfill leachate treatment, microbial inhibition and low nitrogen removal capacity are the big barriers due to high ammonia concentration and low C/N. This study aimed to evaluate the performance of a high-rate nitrogen removal lab-scale reactor, which combines pre-denitrification and Partial Nitrification-Anammox (PN/A) in a multi-stage fixed biofilm reactor (MFBR), for mature landfill leachate treatment. A nitrogen removal efficiency (NRE) of 90.43 % and an average nitrogen removal rate (NRR) of 0.94 kg/m3·d were observed at an influent NH+ 4-N concentration of 2274.39 mg/L during the last operational phase. The nitrogen mass balance showed that the nitrogen concentration gradually decreases along the course, and nitrogen was mainly removed in the aerobic chambers, in which Anammox contributed to 86.4 % of the removed nitrogen, while the front anoxic chamber is mainly used to remove NO- 3-N from the recirculation. Redundancy analysis showed that the variation in NH+ 4-N concentration along the course was the main factor affecting microbial community succession, which shows that the reactor configuration enables efficient cooperation and distribution of different microorganisms. Moreover, economic analysis of MFBR process showed that the energy consumption and carbon addition were reduced by 58.9 % and 100 %, respectively. Therefore, the MFBR established in this study, with its new configuration, achieves efficient treatment of landfill leachate in a single reactor and is environmentally friendly, and could be considered as a reference for full-scale landfill leachate treatment.

Removal of nitrate nitrogen from wastewater by green synthetic hydrophilic activated carbon supported sulfide modified nanoscale zerovalent Iron: Characterization, performance and mechanism

In this study, A green reducing agent green tea extract is used instead of traditional sodium borohydride and porous activated carbon was supported to prepare nano-zero valent iron (nZVI) combined with sulfate (GT-PAC-nZVI/S) to remove Nitrate Nitrogen (NO3–-N) in wastewater. SEM-EDS, BET, XRD and FTIR characterization results confirmed that effective preparation of porous and high specific surface area and successful loading of sulfide nZVI on PAC. Batch experiments were conducted to measure the effects on the removal of nitrate nitrogen of different parameters including pH, temperature, dosage, interfering agents, carbon-iron ratio and iron-sulfur ratio. The experimental results demonstrate that GT-PAC-nZVI/S has a high nitrate nitrogen removal rate and reduction product gaseous nitrogen can reach 93.00% and 22.10%, respectively, at pH = 7, the dosage of GT-PAC-nZVI/S = 4 g/L, temperature of 60 ℃, iron-sulfur ratio = 1:0.3 and time of 95 min. And interfering ion HPO42- have the strong inhibition for NO3–-N degradation. The adsorption isotherm and kinetic data for GT-PAC-nZVI/S was fitted well with the Langmuir and pseudo-second order model, respectively, indicating that the adsorption process for nitrate was chemisorption. Furthermore, GT-PAC-nZVI/S enhanced the removal of nitrate nitrogen through complexation, redox, and adsorption co-precipitation. This work highlights the efficient remediation of nitrate-nitrogen water pollution by porous activated carbon loaded with sulfide nZVI.

Insight into the Cold Adaptation Mechanism of an Aerobic Denitrifying Bacterium: Bacillus simplex H-b.

Psychrophilic bacteria with aerobic denitrification ability have promising potential for application in nitrogen-contaminated wastewater treatment, especially under cold conditions. A better understanding of the cold adaptation mechanism during aerobic denitrification would be beneficial for the practical application of this type of functional bacterium. In this study, Bacillus simplex H-b with good denitrification performance at 5°C was used to investigate the corresponding cold tolerance mechanism. Transcriptomics and nitrogen removal characterization experiments were conducted at different temperatures (5°C, 20°C, and 30°C). At low temperatures, more nitrogen was utilized for assimilation, accompanied by the accumulation of ATP and extracellular polymeric substances (EPS), rather than transforming inorganic nitrogen in the dissimilation pathway. In addition, the proportion of unsaturated fatty acids was higher in strains cultured at low temperatures. At the molecular level, the adjustment of membrane transport, synthesis of cofactors and vitamins, and transcriptional regulators might contribute to the survival of the strain under cold conditions. Moreover, nucleotide precursor synthesis, translation, and oxidative and temperature stress response mechanisms also enhanced the resistance of strain H-b to low temperatures. The results suggest that combining multiple regulatory mechanisms and synergistic adaptation to cold stress enabled the growth and relatively high nitrogen removal rate (27.22%) of strain H-b at 5°C. By clarifying the mechanism of regulation and cold resistance of strain H-b, a theoretical foundation for enhancing the application potential of this functional bacterium for nitrogen-contaminated wastewater treatment was provided. IMPORTANCE The newly isolated aerobic denitrifying bacterium Bacillus simplex H-b removed various forms of inorganic nitrogen (nitrate, nitrite, and ammonium) from wastewater, even when the temperature was as low as 5°C. Although this environmentally functional bacterium has been suggested as a promising candidate for nitrogen-contaminated water treatment at low temperatures, understanding its cold adaptation mechanism during aerobic denitrification is limited. In this study, the cold tolerance mechanism of this strain was comprehensively explained. Furthermore, a theoretical basis for the practical application of this type of functional bacterium for nitrogen removal in cold regions is provided. The study expands our understanding of the survival strategy of psychrophilic bacteria and hence supports their further utilization in wastewater treatment applications.