Nitrate Removal Efficiency Research Articles

Denitrification driven by additional ferrous (Fe2+) and manganous (Mn2+) and removal mechanism of tetracycline and cadmium (Cd2+) by biogenic Fe–Mn oxides

Zoogloea sp. MFQ7 achieved excellent denitrification of 91.71% at ferrous to manganous ratio (Fe/Mn) of 3:7, pH of 6.5, nitrate concentration of 25 mg L−1 and carbon to nitrogen ratio of 1.5. As the Fe/Mn ratio increasd, the efficiency of nitrate removal gradually decreased, indicating that strain MFQ7 had a higher affinity for Mn2+ than Fe2+. In situ generated biogenic Fe–Mn oxides (BFMO) contained many iron-manganese oxides (MnO2, Mn3O4, FeO(OH), Fe2O3, and Fe3O4) as well as reactive functional groups, which play an significant part in tetracycline (TC) and cadmium (Cd2+) adsorption. The adsorption of TC and Cd2+ by BFMO can better fit the pseudo-second-order and Langmuir models. In addition, multiple characterization results of before and after adsorption indicated that the removal mechanism of BFMO on TC and Cd2+ was probably surface complexation adsorption and redox reactions.

Management of biofilm by an innovative layer-structured membrane for membrane biofilm reactor (MBfR) to efficient methane oxidation coupled to denitrification (AME-D)

Aerobic methane oxidation coupled with denitrification (AME-D) has garnered significant attention as a promising technology for nitrogen removal from water. Effective biofilm management on the membrane surface is essential to enhance the efficiency of nitrate removal in AME-D systems. In this study, we introduce a novel and scalable layer-structured membrane (LSM) developed using a meticulously designed polyurethane sponge. The application of the LSM in advanced biofilm management for AME-D resulted in a substantial enhancement of denitrification performance. Our experimental results demonstrated remarkable improvements in nitrate-removal flux (92.8 mmol-N m−2 d−1) and methane-oxidation rate (325.6 mmol m−2 d−1) when using an LSM in a membrane biofilm reactor (L-MBfR) compared with a conventional membrane reactor (C-MBfR). The l-MBfR exhibited 12.4-, 6.8- and 3.4-fold increases in nitrate-removal rate, biomass-retention capacity, and methane-oxidation rate, respectively, relative to the control C-MBfR. Notably, the l-MBfR demonstrated a 3.5-fold higher abundance of denitrifying bacteria, including Xanthomonadaceae, Rhodocyclaceae, and Methylophilaceae. In addition, the denitrification-related enzyme activity was twice as high in the l-MBfR than in the C-MBfR. These findings underscore the LSM's ability to create anoxic/anaerobic microenvironments conducive to biofilm formation and denitrification. Furthermore, the LSM exhibited a unique advantage in shaping microbial community structures and facilitating cross-feeding interactions between denitrifying bacteria and aerobic methanotrophs. The results of this study hold great promise for advancing the application of MBfRs in achieving efficient and reliable nitrate removal through the AME-D pathway, facilitated by effective biofilm management.

Efficient photocatalytic reduction of nitrate byproducts during anammox process by novel extracellular polymeric substances-embedded NH2-MIL-101(Fe) photocatalysts

Anaerobic ammonium oxidation (anammox) is an efficient nitrogen removal process; however, nitrate byproducts hampered its development. In this study, extracellular polymeric substances (EPS) were embedded into NH2-MIL-101(Fe), creating NH2-MIL-101(Fe)@EPS to reduce nitrate. Results revealed that chemical nitrate reduction efficiency of NH2-MIL-101(Fe)@EPS surpassed that of NH2-MIL-101(Fe) by 17.3 %. After adding 0.5 g/L NH2-MIL-101(Fe)@EPS within the anammox process, nitrate removal efficiency reached63.9 %, consequently elevating the total nitrogen removal efficiency to 92.4 %. 16S rRNA sequencing results elucidated the predominant role of Candidatus Brocadia within NH2-MIL-101(Fe)@EPS-anammox system. Concurrently, sufficient photogenerated electrons were transferred to microorganisms, promoting the growth of Desnitratisoma and OLB17. Additionally, photogenerated electrons activated flavin and Complex III, thereby up-regulating crucial genes involved in intra/extracellular electron transfer. Subsequently, denitrification and dissimilatory nitrate reduction to ammonium were activated to reduce nitrate. In summary, this study achieved a notable rate of photocatalytic nitrate reduction within anammox process through the NH2-MIL-101(Fe)@EPS photocatalysts.

Assessment of nitrate contamination of domestic wells and remedial treatment by electrocoagulation

Natural water contaminated with nitrates can pose serious problems for human health and aquatic ecosystems. Thus, effective, and low-cost treatment systems that can be implemented on both large and small scales are needed. The main goals of this work were to quantify nitrate pollution of groundwater (i.e., underground well water used for drinking purposes), to identify its causes, to evaluate the performance of the electrocoagulation (EC) process in nitrate removal, optimizing the treatment procedure using synthetic water, and to estimate the process cost. A total of thirty domestic wells, located in Sidi Bel Abbes city in North-West Algeria, used for drinking water were subject to sampling. Results indicated that most of the wells had nitrate contents that exceeded the World Health Organization (WHO) guideline value as well as the Algerian permissible limit of 50 mg.L−1, with a maximum NO3- concentration of 162 mg.L−1. The pollution was presumed to be due to agricultural activity, human and animal waste, and the nature of the soil. The EC treatment tests with aluminum electrodes exhibited a high nitrate removal efficiency of 90% at a current density of 5.12 mA.cm−2, electrolysis time 15 min, pH 8.8, agitation speed 400 rpm and at an initial nitrate concentration of 50 mg.L−1. Under optimum operating conditions, nitrate removal was 88% for an initial [NO3-] of 87 mg.L−1 in groundwater. The operating cost was estimated at 0.27 US $/m3 or 0.12 US $/Kg nitrate removed. The findings from this study showed that EC is an economically viable technique for dealing with nitrate contamination for small-scale water treatment applications.

Efficient nitrite accumulation in partial sulfide autotrophic denitrification (PSAD) system: insights of S/N ratio, pH and temperature

ABSTRACT To provide the necessary nitrite for the Anaerobic Ammonium Oxidation (ANAMMOX) process, the effect of nitrite accumulation in the partial sulfide autotrophic denitrification (PSAD) process was investigated using an SBR reactor. The results revealed that the effectiveness of nitrate removal was unsatisfactory when the S/N ratio (mol/mol) fell below 0.6. The optimal conditions for nitrate removal and nitrite accumulation were achieved within the S/N ratio range of 0.7-0.8, resulting in an average Nitrate Removal Efficiency (NRE) of 95.84%±4.89% and a Nitrite Accumulation Rate (NAR) of 75.31%±6.61%, respectively. It was observed that the nitrate reduction rate was three times faster than that of nitrite reduction during a typical cycle test. Furthermore, batch tests were conducted to assess the influence of pH and temperature conditions. In the pH tests, it became evident that the PSAD process performed more effectively in alkaline environment. The highest levels of nitrate removal and nitrite accumulation were achieved at an initial pH of 8.5, resulting in a NRE of 98.30%±1.93% and a NAR of 85.83%±0.47%, respectively. In the temperature tests, the most favourable outcomes for nitrate removal and nitrite accumulation were observed at 22±1 ℃, with a NRE of 100.00% and a NAR of 81.03%±1.64%, respectively. Moreover, a comparative analysis of 16S rRNA sequencing results between the raw sludge and the sulfide-enriched culture sludge sample showed that Proteobacteria (49.51%) remained the dominant phylum, with Thiobacillus (24.72%), Prosthecobacter (2.55%), Brevundimonas (2.31%) and Ignavibacterium (2.04%) emerging as the dominant genera, assuming the good nitrogen performance of the system.

Assembling fixed-biofilm reactor with modified basalt fiber and modified wild jujube seed biochar for concurrent removal of nitrate, tetracycline and cadmium: Performance and microflora response

Mixed pollution of nitrate, tetracycline (TC) and cadmium (Cd2+) induced by improper discharge of various wastewater from industry and agriculture has attracted extensive attention. A novel biocarrier (MBF@FMJSB) assembled with modified basalt fiber and modified wild jujube seed biochar (FMJSB) was used to construct fixed-biofilm reactor (FBR) for concurrent removal of nitrate, TC, and Cd2+. The removal efficiencies of nitrate, TC, and Cd2+ of the bioreactor were 79.34%, 85.45%, and 88.02%, respectively, when HRT was 6.0 h, C/N ratio was 1.5, influent nitrate concentration was 25 mg L−1, pH was 6.5, and TC and Cd2+ concentrations was 0.6 and 1 mg L−1. The addition of FMJSB was not only beneficial for bacteria to resist the stress of TC and Cd2+, but also contributed to the removal of TC and Cd2+ pollutants. In addition, microbial metabolism was a key pathway for pollutant removal in FBR. Microflora with Zoogloea as a core genus can dynamically regulate the community structure and expression of microbial metabolism related genes to adapt to TC and Cd2+ stresses. This study was valuable for the treatment of wastewater containing mixed pollutants.

Fungi-assisted bio-flocculation of Picochlorum sp.: A novel bio-assisted treatment system for municipal wastewater

Integration of microalgal cultivation with wastewater reclamations are sustainable valorizations approach to nutrients removal and lipid-rich biomass production. Lower growth rates and higher harvesting costs are the major bottlenecks of algal-based wastewater treatment process. Therefore, this study was carried-out to investigate lipid-rich biomass production using wastewater and demonstrate the low-cost biomass harvesting method. Picochlorum sp. BDUG 100241 (PC) was explored in various combinations of untreated raw municipal wastewater (UTMWW) and secondary treated municipal wastewater (STMWW) with a conventional ASN-III medium. The day-night cycles, pH, and aeration were optimized to improve PC biomass production. For harvesting of PC biomass, different concentrations of filamentous fungi Aspergillus niger MTCC 281 (A. niger) and Stropharia sp. ITCC-8422 assisted bioflocculation approach was investigated. In the first phase of optimization, PC showed maximum nutrient removal efficiency and growth in 50 % STMWW +50 % ASN-III. The present results indicated that a 12:12 h day-night cycle and a pH of 7.0 with aeration resulted in the highest nutrient removal efficiency of COD (90.92 %), phosphate (92.26 %) and nitrate (87.20 %). This optimized conditions also improved the biomass production (2.66 g/L), lipid content (44.04 %), photosynthetic and carotenoids (astaxanthin and β-carotene) production. Further, 10 % Stropharia sp. and A. niger granulated pellets signified the bioharvesting of PC biomass with maximum bioflocculation efficiency of 90.15 % and 92.48 %, respectively. The incorporation of bioflocculants, namely Stropharia sp. and A. niger for the harvesting of microalga biomass facilitated the removal of nutrients, enhanced biomass production (4.21 and 4.01 g/L), and augmented lipid content (43.0 % and 47.33 %) respectively.

A novel combined system for efficient nitrate removal using a continuous flow electrocoagulation and sand filtration (FECF) reactor: Statistical analysis by Taguchi design.

In this study, a new hybrid bench-scale electrocoagulation-sand filtration (FECF) reactor was developed for purifying nitrate-contaminated samples. Before and after electrochemical treatment, two sand filters were included in this continuous system to facilitate the purification procedure, and the contaminated water flows horizontally through the entire system according to a specific hydraulic gradient within the reactor, resulting in water purification. Significant improvement in treatment performance was observed due to the presence of metal hydroxides in the second filter media that were not fully involved in the electrocoagulation treatment. Energy dispersive X-ray (EDX) analysis was performed to detect metal hydroxide species in the sand media, and the need for filter regeneration was evaluated by monitoring changes in the system flow rate. Moreover, an evaluation of the effects of different factors including operating time, current intensity, initial pH, type of anode and cathode, initial nitrate concentration, hydraulic head level inside the reactor, number of electrodes, and NaCl electrolyte concentration on the performance of nitrate removal was conducted through the Taguchi design. Further, ANOVA analysis verified the accuracy of the predicted model, and the variables were classified based on their relative importance in the FECF process. According to the regression model, 97% of nitrates were removed with Al electrodes as anode and Fe as cathode, 70 min purification time, current intensity of 3 A, 100 mg/l initial nitrate concentration, pH 8, electrolyte concentration of 1 g/l, electrode number of 6, and 1.5 cm head level.

Deciphering the response of heterotrophic, autotrophic and mixotrophic denitrification to enrofloxacin stress: Performance, denitrifying community and antibiotic resistance genes

Antibiotics frequently coexist with nitrate (NO3−-N) in wastewater. This study systematically explored the negative effects of enrofloxacin (ENR) on the microbial performance of autotrophic, heterotrophic and mixotrophic denitrification processes under parallel conditions. The ENR concentration was set at 0, 0.1, 1 and 10 mg/L for four phases in sequence. As the influent ENR concentration increased, the nitrate removal efficiency (NrE) in the pyrite-based autotrophic denitrification (PAD) system declined gradually to 11.08% (minimum) and the expressed narG/H/I and napA/B genes decreased. However, the NrE in the polycaprolactone-based heterotrophic denitrification (PHD) and mixotrophic denitrification systems declined slightly (the lowest NrE: 88.10% and 85.28%, respectively), and the expressed narG/H/I (0–1 mg/L) and napA/B genes increased gradually in the PHD system. The removal pathway of ENR was mainly through adsorption by substrates and/or biofilms rather than through biodegradation. Increasing the concentration of ENR (0–10 mg/L) reduced the relative abundance of functional genera (Syntrophomonas, Lentimicrobiaceae_unclassified, Bacteroidetes_vadinHA17_unclassified, and Clostridium) capable of degrading polymers in the PHD system, but elevated the relative abundance of the dominant genus Thiobacillus in the PAD system. Network analyses showed that Thiobacillus in the PAD system as well as Anaerolineaceae_unclassified and Simplicispira in the PHD system were resistant to ENR stress.

Rapid and effective removal of copper, nitrate and trichloromethane from aqueous media by aluminium alloys

Zero-valent iron (ZVI) has been extensively studied for its efficacy in removing heavy metals, nitrate, and chlorinated organic compounds from contaminated water. However, its limited effectiveness due to rapid passivation and poor selectivity is prompting for alternative solutions, such as the use of aluminium alloys. In this study, the efficacy of five distinct aluminium alloys, namely Al–Mg, Al–Fe, Al–Cu, and Al–Ni, each comprising 50 % Al by mass at a concentration of 10 g/L, was assessed using copper, nitrate and trichloromethane (TCM) as model contaminants. Results show that chemical pollutants reacted immediately with Al–Mg. On the contrary, the remaining three alloys exhibited a delay of 24 h before demonstrating significant reactivity. Remarkably, Al–Mg alloy reduced nitrate exclusively to ammonium, indicating minimal preference for nitrate reduction to N2. In contrast, the Al–Cu, Al–Ni, and Al–Fe alloys exhibited N2 selectivity of 3 %, 5 %, and 19 %, respectively. The removal efficiency of copper, nitrate and TCM reached 99 % within 24 h, 95 % within 48h and 48 % within 48h, respectively. Noteworthy findings included the correlation between Fe concentration within the Al–Fe alloy and an increased N2 selectivity from 9.3 % to 24.1 %. This resulted in an increase of Fe concentration from 10 % to 58 % albeit with a concurrent reduction in reactivity. Cu2+ removal by Al–Fe alloy occurred via direct electron transfer, while the removal of nitrate and TCM was facilitated by atomic hydrogen generated by the alloy's hydrolysis. Intriguingly, nitrate and TCM suppressed Cu2+ reduction, whereas Cu2+ improved nitrate reduction and TCM degradation. These findings demonstrate the great potential of Al–Mg and Al–Fe alloys as highly efficient agents for water remediation.

Optimizing waste molasses utilization to enhance electron transfer via micromagnetic carriers: Mechanisms and high-nitrate wastewater denitrification performance

The biological denitrification of high-nitrate wastewater (HNW) is primarily hindered by insufficient carbon sources and excessive nitrite accumulation. In this study, micromagnetic carriers with varying micromagnetic field (MMF) strengths (0.0, 0.3, 0.6, 0.9 mT) were employed to enhance the denitrification of HNW using waste molasses (WMs) as a carbon source. The results revealed that 0.6 mT MMF significantly improved the total nitrogen removal (TN) efficiency at 96.3%. A high nitrate (NO3−-N) removal efficiency at 99.3% with a low nitrite (NO2−-N) accumulation at 25.5 mg/L was achieved at 0.6 mT MMF. The application of MMF facilitated the synthesis of adenosine triphosphate (ATP) and stimulated denitrifying enzymes (e.g., nitrate reductase (NAR), nitrite reductase (NIR), and nitric oxide reductase (NOR)), which thereby promoting denitrification. Moreover, the effluent chemical oxygen demand (COD), tryptophan and fulvic-like substances exhibited their lowest levels at 0.6 mT MMF. Analysis through 16S ribosomal ribonucleic acid gene sequencing indicated a significant enrichment of denitrifying bacteria including Castellaniella Klebsiella under the influence of MMF. Besides, the proliferation of Acholeplasma, Klebsiella and Proteiniphilum at 0.6 mT MMF promoted the hydrolysis and acidification of WMs. This study offers new insights into the enhanced utilization of WMs and the denitrification of HNW through the application of MMF.

Enhanced nitrate removal from groundwater using a conductive spacer in flow-electrode capacitive deionization

Flow-electrode capacitive deionization (FCDI) represents a promising approach for ion separation from aqueous solutions. However, the optimization of spacer, particularly for nitrate-contaminated groundwater systems, has often been overlooked. This research comprehensively investigates the influence of using a conductive (carbon cloth, CC) spacer on nitrate removal performance within FCDI system, comparing it to a non-conductive (nylon net, NN) spacer. In both CC and NN FCDI systems, it is unsurprisingly that nitrate removal efficiency improved notably with the increasing current density and hydraulic retention time (HRT). Interestingly, the specific energy consumption (SEC) for nitrate removal did not show obvious fluctuations when the current density and HRT varied in both systems. Under the auspiciously optimized process parameters, CC-FCDI attained a 20% superior nitrate removal efficiency relative to NN-FCDI, accompanied by a notably diminished SEC for CC-FCDI, registering at a mere 28% of NN-FCDI. This great improvement can be primarily attributed to the decrement in FCDI internal resistance after using conductive spacer, which further confirmed by electrochemical tests such as linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Upon prolonged continuous nitrate removal at the optimized conditions, the CC-FCDI system achieved a consistent 90% nitrate removal efficiency with a low SEC of 2.7–7.8 kWh/kg NO3-N, underscoring its steady performance. Overall, this study highlights the pivotal importance of careful spacer design and optimization in realizing energy-efficient groundwater treatment via FCDI.

Simultaneous and efficient removal of ammonium and nitrate by a novel isolated Agrobacterium tumefaciens M

A novel nitrogen removal strain M, was isolated and identified as Agrobacterium tumefaciens M. Strain M could remove 100% and 99% of 100 mg/L ammonium and nitrate mainly through assimilation, with elimination rates of 8.61 and 4.60 mg/L/h, respectively. The optimal growth and nitrogen elimination conditions were obtained by a single-factor experiment, including a shaking speed of 150 rpm, pH of 7, C/N ratio of 15, and carbon supply of sucrose (ammonium) and sodium citrate (nitrate). Key genes involved in nitrogen metabolism, including napAB, nirK, norBC, nosZ, nirBD, glnA, and nasAB, were identified in strain M. Moreover, strain M exhibited excellent nitrogen removal efficiencies higher than 90% when ammonium and nitrate coexisted. All results indicated that strain M shows great nitrogen removal potential.

Effects of salinity on sulfur-dominated autotrophic denitrification microorganisms: Microbial community succession, key microorganisms and response mechanisms

This study investigated the performance of sulfur-dominated autotrophic denitrification (SAD) process under four different salinities of 0 %, 0.5 %, 3 %, and 6 %, simulating groundwater, sewage, seawater, and industrial wastewater scenarios, respectively. In terms of removal efficiency, the nitrate removal rates at 0.5 % and 3 % salinities decreased by 5.8 % and 16.8 %, respectively, compared to 0 % salinity. At 6 % salinity, the efficiency fluctuated during long-term operation, ranging from 56.0 % to 89.9 % of the value at 0 % salinity. According to the succession of microbial communities across time and salinity gradients, the dominant denitrification functional microorganisms were ranked by their salinity-tolerance ability as low-tolerant bacteria (0 %–0.5 %: Simplicispira, Herpetosipin, and Thermomonas), medium-tolerant bacteria (0 %–3 %: Thiobacillus and Sulfurimonas), high-tolerant bacteria (3 %–6 %: Thiogranum, Xanthomarina, and Vicingus), and halophilic bacteria (6 %: Aequorivita). Additionally, Aequorivita and Thiogranum, as the top 2 genera under 6 % salinity, presented positive and negative correlations with nitrate removal efficiency. The molecular ecological network revealed that increased positive interactions of 58.7 % among dominant genera occurred at 6 % salinity, confirming an effective cooperation coping with the high-salinity stress. In addition, the microbial responses to high-salinity primarily exhibited 22 %–45 % decrease in protein content, a 15 % decrease in live cells proportion, and a comparable level of individual functional gene expression. The results indicate that the efficiency of SAD by high salinity is determined by biomass amount and individual microbial capacity. This study offered new sights for understanding microbial succession and relationships in response to saltwater with diverse origins and varying water qualities in SAD systems.

Enhancing biocathode denitrification performance with nano-Fe3O4 under polarity period reversal

The presence of excessive concentrations of nitrate poses a threat to both the environment and human health, and the bioelectrochemical systems (BESs) are attractive green technologies for nitrate removal. However, the denitrification efficiency in the BESs is still limited by slow biofilm formation and nitrate removal. In this work, we demonstrate the efficacy of novel combination of magnetite nanoparticles (nano-Fe3O4) with the anode-cathode polarity period reversal (PPR-Fe3O4) for improving the performance of BESs. After only two-week cultivation, the highest cathodic current density (7.71 ± 1.01 A m−2) and NO3−-N removal rate (8.19 ± 0.97 g m−2 d−1) reported to date were obtained in the PPR-Fe3O4 process (i.e., polarity period reversal with nano-Fe3O4 added) at applied working voltage of −0.2 and −0.5 V (vs Ag/AgCl) under bioanodic and biocathodic conditions, respectively. Compared with the polarity reversal once only process, the PPR process (i.e., polarity period reversal in the absence of nano-Fe3O4) enhanced bioelectroactivity through increasing biofilm biomass and altering microbial community structure. Nano-Fe3O4 could enhance extracellular electron transfer as a result of promoting the formation of extracellular polymers containing Fe3O4 and reducing charge transfer resistance of bioelectrodes. This work develops a novel biocathode denitrification strategy to achieve efficient nitrate removal after rapid cultivation.

A kinetic model for porosity evaluation in Fe(0) mixed material-based sequential groundwater remediation

In aquifer systems, particularly those characterized by homogeneity in the shallow layers, the even distribution of contaminants, such as solutes, solvents, and reductive agents or substrates is frequently impeded. Consequently, this complicates the accurate delineation homogeneity within the groundwater matrix, which is a crucial aspect for the effective subsurface treatment of contaminants. In this study, columnar assays were conducted using acid-activated zero-valent iron [Fe(0), ZVI] emulated in situ remediation across disparate iron-to-sand weight ratios. To decipher the interaction between porosity and solute migration, a mass transfer-centric model was developed to provide quantitative insights during heterogeneous groundwater interventions. The results revealed that nitrate attenuation by Fe(0) rigorously adheres to a first-order kinetic paradigm. The efficiency porosity (n̅) during non-equilibrium (rate-limited) conditions can be calculated under different NO3− concentrations and Fe(0)/sand ratios. This analysis predicts that large porosity and preferential flow will occur in the Fe(0)50/% and Fe(0)25/% columns. The optimal parameters were determined as a mixing ratio of Fe(0)/sand of 0.5/0.5 (volume) and an HRT of 7.3 h when the influent NO3−-N concentration ranged from 20 mg·L−1 to 100 mg·L−1, resulting in enhanced nitrate removal efficiency. A positive correlation was observed between K (a mass-transfer rate coefficient) and Fe(0)/sand ratio. Using a power-law function to fit A [the value of fitting parameter] and the Fe(0)/sand ratio, a positive correlation was calculated that closely resembles the trend observed in lab columns. This model subsequently facilitated the calibration of operational variables, optimizing the in situ amelioration of nitrate-laden groundwater.

Pd/Cu bimetallic nano-catalyst supported on anion exchange resin (A520E) for nitrate removal from water: High property and stability

High nitrate concentration in water can lead to eutrophication and the disruption of healthy aquatic ecosystems. Additionally, in the human digestive system, it has the potential to be reduced to nitrite, which can be damaging to people's physical health. Catalytic hydrogenation of nitrate is one of the strategies for removing nitrate from water. Using A520E resin as support, we prepared Pd/Cu nano-catalyst (Pd/Cu@A520E) according to a liquid phase reduction method. A520E could improve the transfer process of nitrate in the solution to the activity sites of Pd/Cu nanoparticles, thus increase the reaction rate of nitrate reduction. Pd/Cu bimetallic nano-particles were evenly distributed on/in the resin with a size range from 2 nm to 10 nm. The External Circulating System equipped with Venturi tube (ECSV) was designed to improve the utilization efficiency of H2 in both batch tests and long-term continuous-flow tests. Nearly 100% of nitrate removal efficiency and above 90% of N2 selectivity were achieved in both batch tests and continuous-flow tests. Coexisting Cl− and SO42− at 300 mg/L showed little impact on the property of Pd/Cu@A520E. Pd/Cu@A520E also showed high nitrate removal property and stability in continuous-flow tests of more than 800 h. NO3− was adsorbed onto the active sites (functional groups and Pd/Cu particle sites), meanwhile H2 was adsorbed onto the active sites of Pd/Cu@A520E to form Pd [H]. Then the adsorbed NO3− was reduced into N2 (main product) or NH4+ by Pd [H]. In addition, Pd/Cu@A520E showed high nitrate removal property from municipal waste water.

Approach enhancing nitrate removal from actual municipal wastewater by integrating electric-magnetic field with Fe0 in UMSR reactor

This study aimed to investigate the effectiveness of combining zero-valent iron (Fe0) with an electric-magnetic field (EMF) with an intensity of 48-mT generated by an alternating current (AC) of 6 V and 50 Hz applied deep within a reactor using actual wastewater obtained from a secondary stage of a wastewater treatment plant (WWTP). The lab-scale experiment was conducted using the UMSR reactor, maintaining a controlled temperature of 25 ± 2 °C and a hydraulic retention time (HRT) of 5-hour, with a dissolved oxygen (DO) level below 1.5 mg/L. Fine Fe0 particles with a size of ≤ 0.3 µm were added into the reactor at a concentration of 3 g/L. The actual wastewater had an approximate nitrate nitrogen (NO3–-N) concentration of 30 ± 2 mg/L, and the substrate mass ratio of carbon to nitrogen (C:N) was at 1:1. The results examined the performance of the EMF-Fe0 system in terms of nitrate removal efficiency and the enrichment of denitrifying bacteria, achieving a nitrate removal rate of 67 % with an effluent NO3–-N concentration of 10 mg/L and a chemical oxygen demand (COD) concentration of 11.8 mg/L at removal rate of 60 %. Illumina sequencing revealed various enriched denitrifying bacteria after coupling EMF with Fe0, including autotrophic Nitrospira (NOB) at 4 %, denitrification bacteria like Hydrogenophaga at 1.3 %, Hyphomicrobium at 1 %, and Sphingobium at 5 %, along with thermophilic bacteria Thermus at 1.1 % and Meiothermus at 3.5 %. PICRUSt predicted bacterial functions and analyzed interactions, while KEGG and GO analyses linked nitrogen removal pathways to specific species, genes, and enzymes in the EMF-Fe0 system.

Micron zero-valent iron chitosan hydrogel balls boosts nitrate removal in constructed wetlands for secondary effluent treatment

Reducing nitrate in the secondary effluent from municipal wastewater treatment plants can prevent eutrophication, which can be achieved by constructed wetlands. Zero-valent iron has been used as electron donors for nitrate removal in constructed wetlands to deal with the low carbon-to-nitrogen ratio (C/N) problem, but the effects are often limited by passivation. In this study, micron zero-valent iron chitosan hydrogel balls were prepared as part of the substrate. The total nitrogen removal efficiency maintained at 85 %-96 % in 70 days. The chelating ability of chitosan could reduce the formation of iron oxides on the surface of iron particles and microbial cells, thus eliminating the passivation. Denitrification microorganisms were enriched and the expressions of denitrification genes were increased. The study provides new understandings of further improving the nitrate removal efficiency of constructed wetlands under low C/N and efficient use of iron materials.

Highly efficient nitrate removal in sulfur-based constructed wetlands: Microbial mechanisms and environmental risks

Nitrate is widely distributed in groundwater, posing an increasing threat to both water resources and human health. In this study, the treatment performance, removal mechanisms and environmental risks of sulfur-based constructed wetlands (CWs) for purifying nitrate-contaminated groundwater were investigated. Results showed that sulfur-based CWs could achieve the highest nitrate removal (95%). However, sulfate was largely produced as a by-product in sulfur-based CWs, which declined the nitrogen and phosphorus assimilation by plants. Metagenomic analysis indicated that autotrophs denitrifiers (e.g., Thiobacillus) were enriched, and the abundance of nitrate removal genes was enhanced in sulfur-based CWs. Additionally, sulfur cycle was formed in sulfur-based CWs, which explained the highest nitrate removal reasonably. This study provides comprehensive insights into the nitrate removal mechanisms in sulfur-based CWs and the associated environmental risks in purifying the polluted groundwater.