Nitrate Removal Efficiency Research Articles

Enhancement of denitrification in biofilters by immobilized biochar under low-temperature stress

Efficient removal of nitrate under low temperature is challenging because of the reduction of the microbial activity. This study successfully explored the promotion on the performance of denitrification utilizing the immobilized biochar in biofilters under low temperature (6 ± 2 °C). The results showed that the immobilized biochar increased the denitrification rate by 76.8% and decreased the nitrous oxide emissions by 82.5%. Mechanistic studies revealed that the immobilized biochar increased the activities of the denitrifying enzymes and three enzymes involved in glycolysis. Furthermore, the immobilized biochar elevated the activity of the electron transport system by 31.8%. Finally, structural equation model explained that the increase of nitrate reductase activity was a crucial factor to enhance the total nitrogen removal efficiency in biofilters with immobilized biochar. Overall, the use of immobilized biochar can be a novel strategy to enhance nitrogen removal and reduce greenhouse gas emissions in biofilters under low temperature.

Impact of Sulfamethoxazole on Mixotrophic Denitrification Process: Nitrate Removal Efficiency and the Response of Functional Microbiota

Impact of Sulfamethoxazole on Mixotrophic Denitrification Process: Nitrate Removal Efficiency and the Response of Functional Microbiota

Optimization of the electrochemical reduction process and ORP effects in nitrate removal.

Nitrate contaminated water resources, a huge environmental problem for countries, including our own. This research aims to evaluate the efficiency of the electrochemical process for the removal of nitrate from the aqueous solution by direct and alternating current. Experiments were done by the Taguchi method, including electrode array, time exposure, voltage, pH, and the initial concentration of nitrate. Minitab 17 and SPSS 18 software were utilized to design and data analysis. In detail, the connection of the electrodes was monopolar, and the direct current (DC) has a greater efficiency as alternating current (AC) in the nitrate removal (p > 0.001). In AC, the nitrate initial concentration, voltage, electrodes material, contact time, and pH have the most effect on the nitrate removal. The optimized conditions for nitrate removal include Al-Al electrode, pH of 7, a voltage of 30 V, and nitrate initial concentration of 100 mg/L with the contact of time 150 min. Selection of appropriate materials for electrodes construction, adequate voltage, and removal of intervention agents from aqueous solution led to greater removal efficiencies. The optimized conditions that can reduce the aqueous solution ORP with high speed and the electrochemical reactor efficiency for nitrate removal were increased. PRACTITIONER POINTS: Electrochemichal (EC) process is evaluated for treatment of nitrate wastewater for the first time. High removal efficiency (over 95%) from nitrate wastewater was obtained. Minimizing energy consumption and maximizing nitrate removal were simultaneously achieved in the integrated single EC process.

Synergistic effect of a triethanolamine-modified carbon-based layered double hydroxide for efficient removal of nitrate from micro-polluted water.

Owing to the ubiquitous existence and low concentrations of detrimental nitrogen pollutants in micro-polluted water, simple adsorption-oriented approaches are becoming increasingly appealing for the effective removal of NO3- from wastewater. Triethanolamine (TDA) modified carbon-based layered double hydroxide (LDH) composites (TDA@LDH/CS) were synthesized by a supersaturated co-precipitation method for efficient NO3- adsorption. The characterization results showed that TDA@LDH/CS, formed by the stacking of irregular nanosheets and lamellar aggregates, has a mesoporous structure and a specific surface area of 67.15 m2 g-1. The Langmuir and pseudo-second-order kinetic models were well fitted with the adsorption of NO3- by TDA@LDH/CS, with the maximum adsorption capacity reaching 14.45 mg g-1, and the adsorption process was consistent with the spontaneous exothermic entropy increasement. Furthermore, the synergistic adsorption mechanism of NO3- by the TDA-modified materials was proposed using XPS analysis, which indicated that TDA modification greatly enriched the surface of TDA@LDH/CS with tertiary amine groups (R3N) and hydroxyl groups (-OH), providing more adsorption sites and active sites. After five cycles, the NO3- removal rate could still reach 64.2%, which exhibited its high potential to be utilized as an adsorbent for the removal of nitrogen pollutants from micro-polluted water.

Nitrate and perchlorate contamination assessment using water samples for bioremediation behavior of nitrate ion with denitrifying bacteria and hypothyroidism of perchlorate ion in rat studies

Perchlorate and nitrate ions are ubiquitous contaminants in the environment released from various activities which is increasingly affected the water quality and consequently the public health and agriculture. The denitrifying bacterial communities are potential drivers of water quality, soil fertility and agriculture productivity. The present study mainly assessed the contamination level of nitrate ion along with perchlorate ions in various water samples collected from fireworks, safety matches manufacturing industry areas around Pullalakkottai, Virudhunagar District, India. Nitrate, perchlorate, calcium, magnesium, sodium, potassium ions in water samples were qualitative and quantitatively analyzed by using various Physico-chemical analytical techniques. The observed maximum contamination values of nitrate and perchlorate ions were found to be 61 mg/L (VP-5), 85.5 mg/L (VP-11) respectively. The highly contaminated five water samples were subjected into bioremediation behavior of nitrate ion using the Pseudomonas sp., Bacillus sp. and Corynebacterium sp. bacterial cultures. The highest nitrate removal efficiency (E) 93.4 % was obtained with Corynebacterium sp. than the Bacillus sp. (83.6 %) and Pseudomonas sp. (80.3 %) cultured in contaminated water sample VP-3. Maximum perchlorate ions contaminated water samples (VP-11) used to examine the hypothyroidism in rat by intravenousinjection of observed days by measuring the T4 hormones level in the blood plasma. It was reduced to nearly half (296 µg/dl) in compared with control (620 µg/dl) for ten days exposure and notable decreasing trend was observed. Disruption of the thyroid can result in developmental disabilities and impair development especially among infants and children.

Adsorption of nitrate from aqueous solution with ZSM-5/Fe nanosorbent based on optimizing of the isotherms conditions before determination by UV-Vis Spectrophotometry

The life-threatening nature of high nitrate concentrations in various water resources motivated the present study to investigate the nitrate adsorption by ZSM-5 nanozeolite and the feasibility of increasing nitrate removal efficiency using iron-doped ZSM-5 (ZSM-5/Fe) nanosorbent. Energy dispersive X-ray diffraction analysis was employed to determine the physical properties of the adsorbent and the presence of iron particles in the nanosorbent structure and BET analysis to measure the specific surface area of the nanosorbent. The optimal adsorption conditions were determined first by modeling the central composite design (CCD) using Design Expert.7 software based on four influential factors . Then, the isotherms of nitrate adsorption under optimized conditions were investigated using the degree of fit of experimental data with Langmuir and Freundlich models for mathematical modeling of the nitrate adsorption process. Based on the test design results, the highest nitrate removal efficiency (%93.1) was reported at the contact time of 150 min, pH value of 3, adsorbent dosage of 4 g/l and initial concentration of 40 mg/l. Analysis of adsorption isotherms also confirmed the greater fit of the experimental data with the Freundlich equation, so that the correction factor of the Freundlich equation was greater than the Langmuir equation.

On-Demand Atomic Hydrogen Provision by Exposing Electron-Rich Cobalt Sites in an Open-Framework Structure toward Superior Electrocatalytic Nitrate Conversion to Dinitrogen.

Electrocatalytic nitrate (NO3-) reduction to N2 via atomic hydrogen (H*) is a promising approach for advanced water treatment. However, the reduction rate and N2 selectivity are hindered by slow mass transfer and H* provision-utilization mismatch, respectively. Herein, we report an open-framework cathode bearing electron-rich Co sites with extraordinary H* provision performance, which was validated by electron spin resonance (ESR) and cyclic voltammetry (CV) tests. Benefiting from its abundant channels, NO3- has a greater opportunity to be efficiently transferred to the vicinity of the Co active sites. Owing to the enhanced mass transfer and on-demand H* provision, the nitrate removal efficiency and N2 selectivity of the proposed cathode were 100 and 97.89%, respectively, superior to those of noble metal-based electrodes. In addition, in situ differential electrochemical mass spectrometry (DEMS) indicated that ultrafast *NO2- to *NO reduction and highly selective *NO to *N2O or *N transformation played crucial roles during the NO3- reduction process. Moreover, the proposed electrochemical system can achieve remarkable N2 selectivity without the additional Cl- supply, thus avoiding the formation of chlorinated byproducts, which are usually observed in conventional electrochemical nitrate reduction processes. Environmentally, energy conservation and negligible byproduct release ensure its practicability for use in nitrate remediation.

Certain Environmental Conditions Maximize Ammonium Accumulation and Minimize Nitrogen Loss During Nitrate Reduction Process by Pseudomonas putida Y-9.

Realizing the smallest nitrogen loss is a challenge in the nitrate reduction process. Dissimilatory nitrate reduction to ammonium (DNRA) and nitrate assimilation play crucial roles in nitrogen retention. In this study, the effects of the carbon source, C/N ratio, pH, and dissolved oxygen on the multiple nitrate reduction pathways conducted by Pseudomonas putida Y-9 are explored. Strain Y-9 efficiently removed nitrate (up to 89.79%) with glucose as the sole carbon source, and the nitrogen loss in this system was 15.43%. The total nitrogen decrease and ammonium accumulation at a C/N ratio of 9 were lower than that at 12 and higher than that at 15, respectively (P < 0.05). Besides, neutral and alkaline conditions (pH 7–9) favored nitrate reduction. Largest nitrate removal (81.78%) and minimum nitrogen loss (10.63%) were observed at pH 7. The nitrate removal and ammonium production efficiencies of strain Y-9 increased due to an increased shaking speed. The expression patterns of nirBD (the gene that controls nitrate assimilation and DNRA) in strain Y-9 were similar to ammonium patterns of the tested incubation conditions. In summary, the following conditions facilitated nitrate assimilation and DNRA by strain Y-9, while reducing the denitrification: glucose as the carbon source, a C/N ratio of 9, a pH of 7, and a shaking speed of 150 rpm. Under these conditions, nitrate removal was substantial, and nitrogen loss from the system was minimal.

Cornstalk biochar promoted the denitrification performance and cellulose degradation rate of Burkholderia sp. CF6

A strain Burkholderia sp. CF6 with denitrification and cellulose degradation ability was isolated. When sodium carboxymethyl cellulose (CMC-Na) dosage was 5 g L−1, the nitrate removal efficiency reached 96.48% after 48 h and the nitrite accumulation was only 0.07 mg L−1. The exponential decay equation was used to match the kinetics of denitrification and the correlation coefficient (R2) was higher than 0.940. The denitrification and cellulose degradation capabilities were promoted by cornstalk biochar. Through the comparison of nitrogen balance of different biochars, biochar of 400 ℃ (BC400) had the highest gaseous nitrogen conversion efficiency (83.31%). BC400 can accelerate the nitrate removal rate (from 0.08 to 0.32 mg L−1 h−1) and shorten the peak time of cellulase activity (from 48 to 24 h). The fourier transform infrared spectroscopy (FTIR) manifested that the BC400 assisted biological denitrification was achieved through phenolic and quinone groups. From the results of three-dimensional excitation-emission matrix (3D-EEM), it can be concluded that soluble microbial by-product and aromatic protein have a significant correlation with the effect of BC400 on the biological process of strain CF6. This research will provide new insights for agricultural waste utilization to treat low carbon to nitrogen (C/N) ratio wastewater.

The Relationship Between Delta Form and Nitrate Retention Revealed by Numerical Modeling Experiments

AbstractRiver deltas display a wide range of morphologic patterns that influence how nutrients interact in channels and wetlands on their way to the coast. To quantify the role of delta morphology on nitrate fate, we simulated reactive nitrate transport over steady base flow conditions for six synthetic, morphologically unique river‐dominated deltas created in Delft3D by varying incoming grain size distributions. We parameterized nitrate removal kinetics using an observed relationship with elevation from Wax Lake Delta (Louisiana, USA). Total nitrate retention across the six synthetic deltas and Wax Lake Delta ranged from 1.3%‐13%, suggesting that these river‐dominated deltas have limited ability to remove nitrate from incoming river water. Nitrate removal is constrained by limited hydrologic connectivity with the areas of greatest nitrate demand, which are found at higher elevation. In these synthetic numerical experiments, the efficiency of nitrate removal is greatest for deltas with more topologic complexity and greater proportions of the delta plain at higher elevation, which are both common characteristics of coarser‐grained deltas. The positive relationship between grain size and nitrate removal may help guide land reclamation projects if project goals include minimizing nitrate export to the sea.

Climate and Seasonal Temperature Controls on Biogeochemical Transformations in Unconfined Coastal Aquifers

AbstractCoastal aquifers are host to a range of biogeochemical reactions that alter groundwater‐derived nutrient, metal, and other chemical loads to coastal ecosystems. Temperature is a strong control on microbially mediated reactions; thus, chemical reactivity in coastal aquifers may vary spatially and temporally with changes to groundwater temperature. In this study, we investigated the influence of global groundwater and sea surface temperature controls and seasonal temperature variability on biogeochemical processing in coastal aquifers using variable‐density groundwater flow, heat transport, and reactive transport models. The coupled models showed that nitrate removal efficiency in coastal aquifers increased from 5% to 88% as fresh groundwater temperature increased from 5°C to 35°C, while ocean temperature had a negligible effect on removal efficiency. Transient simulations based on monthly groundwater and ocean temperature measurements showed that denitrification and ammonification hotspots migrated seaward seasonally within warm fresh groundwater masses. The reaction hotspots were separated by colder groundwater emplaced during winter months. The reaction hotspots and nitrate plumes oscillated vertically along horizontal flow paths due to buoyancy effects between warm and cold groundwater. Comparison between transient and temperature‐equivalent steady‐state models suggests that steady‐state models adequately capture mean annual NO3− removal, but neglect local reactive transience and changes to plume geometry. The sensitivity analysis provides a first‐order estimate of the reactive potential of coastal aquifers considering globally diverse thermal regimes. The findings have implications for regional‐scale estimates of groundwater nutrient fluxes and for predicting coastal aquifer reactivity in a warming climate.

Performance and enhancement mechanism of redox mediator for nitrate removal in immobilized bioreactor with preponderant microbes

The acceleration of nitrate removal in wastewater treatment by redox mediator (RM) is greatly weakened due to wash-out loss and mass transfer resistance (low hydrophilia) of RM during operation. In this study, an RM reactor with the fixed 1-Amino-4-hydroxyanthraquinone (AHAQ) and three core strains was established and achieved high nitrate removal efficiency (NRE) under low carbon to nitrogen ratio (C/N) and short hydraulic retention time (HRT) conditions, with the maximum efficiency of 99.41% (14.00 mg L−1 h−1) and average improvement by 11.97% (1.41 mg L−1 h−1). This acceleration led to more proportion of carbon consumption by denitrifying bacteria and improved their competitiveness against others in carbon deficiency, although resulting in nitrite accumulation (NIA) in lower C/N. The RM reactor induced the decorrelation tendencies between NRE and active extracellular organics and more sensitive denitrification toward C/N, which favored the stability of effluent organics and biological activities. The increase of oxidative phosphorylation and ubiquinone and other terpenoid-quinone biosynthesis pathway suggested electron transport activity was potentially enhanced by AHAQ. Although the lower C/N deteriorated the reactor NRE, the abundances of amino acids-, fatty acids- and carbohydrate-related metabolisms (45% of the total up-regulating pathways) were enhanced to utilize carbon source effectively. Meanwhile, the enhanced phosphotransferase system facilitated the balance between carbon and nitrogen metabolism. These indicated the changes in biological strategy to grow better and resist the adverse condition. This study highlighted the superior NRE by AHAQ in an immobilized reactor with core strains and more importantly, extended the RM application in wastewater treatment.

Denitrification performance of nitrate–dependent ferrous (Fe2+) oxidizing Aquabacterium sp. XL4: Adsorption mechanisms of bio–precipitation of phenol and estradiol

In this study, a nitrate–dependent ferrous (Fe2+) oxidizing strain under anaerobic conditions was selected and identified as XL4, which belongs to Aquabacterium. The Box–Behnken design (BBD) was used to optimize the growth conditions of strain XL4, and the nitrate removal efficiency of strain XL4 (with 10% inoculation dosage, v/v) could reach 91.41% under the conditions of 30.34 ℃, pH of 6.91, and Fe2+ concentration of 19.69 mg L–1. The results of Fluorescence excitation–emission matrix spectra (EEM) revealed that the intensity of soluble microbial products (SMP), aromatic proteins and the fulvic–like materials were obvious difference under different Fe2+ concentration, pH, and temperature. X–ray diffraction (XRD) data confirmed that the main components of bio–precipitation were Fe3O4 and FeO(OH), which were believed to be responsible for the adsorption of phenol and estradiol. Furthermore, the maximum adsorption capacity of bio–precipitation for phenol and estradiol under the optimal conditions were 192.6 and 65.4 mg g–1, respectively. On the other hand, the adsorption process of phenol and estradiol by bio–precipitation confirmed to the pseudo–second–order and Langmuir model, which shows that the adsorption process is chemical adsorption and occurs on the uniform surface.

Denitrifying bacteria immobilized magnetic mycelium pellets bioreactor: A new technology for efficient removal of nitrate at a low carbon-to-nitrogen ratio

This study integrated spores and magnetite (Fe3O4) to form magnetic mycelium pellets (MMP) as bio-carriers immobilized with denitrifying bacteria in a bioreactor. Different carbon-to-nitrogen (C/N) ratios and hydraulic retention time (HRT) were established for investigating the performance of the bioreactor. The nitrate removal efficiency was 98.14% at C/N = 2.0 and HRT = 6 h. Gas chromatography (GC) results indicated that the main component of the produced gas was N2. Fe3O4 was well-integrated into MMP according to X-ray diffraction (XRD) results and infrared spectrometer (FTIR) analysis. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that bacteria were successfully immobilized on MMP. Fluorescence excitation-emission matrix (EEM) indicated that functional bacteria GF2 might enhance the metabolic activity of the microbial community in the bioreactor and microbial activity was highest at C/N = 2.0. Pseudomonas stutzeri sp. GF2 might be immobilized and had a major role in the bioreactor according to high throughput sequencing results.

Characteristics and mechanism of heterotrophic nitrification/aerobic denitrification in a novel Halomonas piezotolerans strain.

A strain was isolated from an activated sludge system and identified as Halomonas piezotolerans HN2 in this study, which is the first strain in H. piezotolerans with the capability of heterotrophic nitrification and aerobic denitrification. Strain HN2 showed the maximum nitrogen removal rate of 9.10 mg/L/h by utilizing ammonium at the salinity of 3.0%. Under saline environment, HN2 could remove nitrogen efficiently in neutral and slightly alkaline environments, with the carbon sources of sodium succinate and sodium citrate and the C/N ratio of 15-20, and the maximum removal efficiencies of ammonium, nitrite, and nitrate were 100%, 96.35%, and 99.7%, respectively. The genomic information revealed the presence of amoA, napA, and nosZ genes in strain HN2, and the target bands of nirS were obtained via a polymerase chain reaction. Therefore, we inferred that ammonium was mainly utilized for the growth of strain HN2 through assimilation, and another part of the initial ammonium was converted into nitrate through nitrification, and then into gaseous nitrogen through denitrification. This report indicated the potential application of strain HN2 and other nitrifying and denitrifying Halomonas strains in the removal of nitrogen pollution in marine-related environments and also implies the important role of Halomonas in the nitrogen cycle process of the ocean.

Electrochemical reduction of nitrate in a catalytic carbon membrane nano-reactor

Nitrate pollution is a critical environmental issue in need of urgent addressing. Electrochemical reduction is an attractive strategy for treating nitrate due to the environmental friendliness. However, it is still a challenge to achieve the simultaneous high activity and selectivity. Here we report the design of a porous tubular carbon membrane as the electrode deposited with catalysts, which provides a large triple-phase boundary area for nitrate removal reactions. The achieved nitrate removal rate is one order of magnitude higher than other literatures with high nitrate conversion and high selectivity of nitrogen. The carbon membrane itself had a limited catalytic property thus Cu-Pd bimetal catalysts were deposited inside the nano-pores to enhance the activity and selectivity. When Na2SO4 electrolyte was applied, the achieved single-pass removal of nitrate was increased from 55.15% (for blank membrane) to 97.12% by adding catalysts inside the membrane. In case of NaOH as the electrolyte, the single-pass nitrate removal efficiency, selectivity to nitrogen formation and nitrate removal rate was 90.66%, 96.40% and 1.47 × 10−3 mmol min−1 cm−2, respectively. Density functional theory studies demonstrate that the loading of bimetal catalysts compared with single metal catalysts enhances the adsorption of *NO3 on membrane surface favorable for N2 formation than NH3 on Cu-Pd surface. The application of catalytic carbon membrane nano-reactors can open new windows for nitrate removal due to the high reactor efficiency.

Nitrate removal from a nitrate-rich reverse osmosis concentrate: Superior efficiency using the bioaugmentation of an Acinetobacter biofilm

Highly effective nitrate removal from a nitrate-rich reverse osmosis (RO) concentrate was achieved by the bioaugmentation of a new Acinetobacter isolate. The anoxic denitrifying capabilities of the isolate were studied in a real RO concentrate solution (containing 230 mg/L nitrate, 14,120 mg/L total dissolved solids, and 18 mg/L biological oxygen demand) obtained from a brackish, nitrate-rich groundwater desalination facility. The treatment of the real RO concentrate with a biofilm afforded a nitrate removal efficiency up to four times greater than that of a bioaugmented bacterial suspension of the Acinetobacter isolate in both batch and continuous bioreactors (nitrate removal rates: 1.34 and 1.37 kg-N/m3•d, respectively). These values are the highest rates of groundwater and groundwater RO concentrate denitrification ever reported. Additionally, the developed method provides the highest denitrification ratio (C:N = 3:1) between biological nitrate assimilation and denitrification. Lastly, both the isolate suspension and the biofilm cultures were able to consume all the organic matter supplemented to the concentrate, which is important since that the organic matter must be removed prior to chlorination and release. This bacterium, therefore, has great potential for successful nitrate removal during RO concentrate treatment.

Amine-grafted walnut shell for efficient removal of phosphate and nitrate.

The presence of emerging pollutants such as PO43- and NO3- in water bodies has attracted worldwide concern about their severe effects on water bodies and the health of humankind in general. Therefore, to preserve the health of humankind and environmental safety, it is of the essence that industrial effluents are treated before they are discharged into water bodies. Amine functionalized walnut shells (ACWNS) were synthesized, characterized, and then tested as a novel adsorbent for PO43- and NO3- removal. The effects of pH, dosage, initial phosphate concentration, interference ions, and temperature on the removal of phosphate and nitrate were investigated. Notably, the adsorption of PO43- and NO3- was exothermic and spontaneous, with a maximum uptake capacity of phosphate and nitrate, at 293K, 82.2 and 35.7mgg-1, respectively. The mechanism by which these ions were adsorbed onto ACWNS could be electrostatic interactions and hydrogen bonding. Pseudo-second-order kinetic modelfitted the PO43- and NO3- adsorption, while Freundlich and Langmuir models best fitted the PO43- and NO3- adsorption, respectively. Furthermore, in the binary system, the uptake capacity of phosphate decreased by 14.4% while nitrate witnessed a reduction in its uptake capacity of 10.4%. ACWNS has a higher attraction towards both ions and this could be attributed to the existence of a variety of active areas on ACWNS that exhibit a degree of specificity for the individual ions. Results obtained from real water sample analysis confirmed ACWNS as highly efficient to be utilized for practical remediation processes.

Optimization, upscaling and kinetic study of famine technique in a microalgal biofilm-based photobioreactor for nutrient removal

Microalgal wastewater treatment systems are promoted as promising, while harvesting costs, low removal efficiency, and long process time are major obstacles. The present study aims to introduce a comprehensive solution to overcome the difficulties by combining two methods of depletion and biofilm in the culture of Scenedesmus sp. using synthetic wastewater. For this purpose, two factors of depletion periods (one, two, three, and five days) and types of depletion (nitrogen, phosphorus, and both) were optimized by Taguchi design for the wastewater nutrient removal rate in lab-scale. The analysis of factors showed that a five-day complete depletion of nitrogen and phosphorus had the most significant effect on the removal of nitrogen compounds and phosphate, respectively. Optimization of factors led to 35, 8, 28 percent increases in ammonium, nitrate, and phosphate removal efficiencies, respectively and about 50 percent decrease in the process time in flasks. Lab-scale results were validated in cylindrical photobioreactors with external recycling (CPBERs) that achieved 73.2, 76.6, and 65.3 percent in ammonium, nitrate, and phosphate removal efficiencies, respectively. Finally, the comparative kinetic study of starved and non-starved processes led to a remarkable change in concentration dependency from first- to second-order after depletion. The optimized system that was provided can be of benefit for further researches in this area.

Synergistically enhanced nitrate removal by capacitive deionization with activated carbon/PVDF/polyaniline/ZrO2 composite electrode

• Mixture design to optimize composite electrode toward nitrate removal in CDI cell. • 75.13% increase of Cs and 55.47% reduction in R ct for composite vs. AC electrode. • E3 as optimum electrode with ion electrosorption capacity of 6.01 mg g −1 at 2.0 V. • Maximum specific capacitance of 58.67F g −1 and Rct of 1.26 Ω for E3 electrode. • Highest water recovery of 72.94% and nitrate removal efficiency of 60.01% in the CDI. This work aims to introduce a novel ternary composite electrode to improve the performance of the capacitive deionization process toward nitrate removal from water through enhancing the specific capacitance of the carbon-based electrode. The mixture design methodology was utilized to find the optimum composite electrode containing activated carbon (AC), PVDF, ZrO2, and polyaniline as emeraldine salt (PANi-ES) with the highest specific capacitance. The morphology, specific surface area, functional groups and wettability, electrochemical behavior, specific capacitance, and charge transfer resistance of the electrode were evaluated by field emission scanning electron microscopy, Brunauer–Emmett–Teller analysis, Fourier-transform infrared spectroscopy, contact angle, cyclic voltammetry, and electrochemical impedance spectroscopy, respectively. The optimum E4 electrode containing 80 wt% AC, 6.0 wt% ZrO 2 , and 6.0 wt% PANi–ES and 8 wt% PVDF was compared to E1 (AC/PVDF), E2 (AC/PVDF/PANi-ES) and E3 (AC/PVDF/ZrO 2 ) electrode. The addition of ZrO 2 into AC as the E3 electrode could attain 19.43% increase in specific capacitance and 34.27 %decrease in charge transfer resistance. In comparison, incorporating both PANi-ES and ZrO 2 into AC led to 75.13% and 51% increase of specific capacitance and wettability, respectively, and 55.47% reduction in charge transfer resistance. This behavior was attributed to the synergistic improvement of specific capacitance by increasing its electrical conductivity and wettability (hydrophilic) and consequently improved the performance of nitrate ion separation by mesoporous structure. Based on the optimum applied voltage of 2.0 V on the E3 electrode, the electrosorption capacity, the maximum nitrate removal efficiency, the water recovery, and specific capacitance were calculated 6.01 mg g −1 , 60.01%, 72.94%, and 58.67F g −1 in the batch mode CDI cell, respectively.