Nitrate Removal Efficiency Research Articles

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.

Characterizing the role of hydraulic retention time on nitrate removal indices in denitrifying bioreactors by nonlinear models

Denitrifying bioreactors (DNBRs) are a sustainable and cost-effective practice commonly used at the edge of fields to reduce nitrate from agricultural runoff. The hydraulic retention time (HRT) is a crucial variable that affects nitrate removal rate (NRR, g N m−3 d−1), nitrate removal efficiency (NRE, %), and nitrate concentration reduction per length (Nrd, mg N L−1 m−1). In this study, two nonlinear models, the developed Michaelis-Menten (MM) model and the Mitscherlich (MT) model, were developed to characterize the relationship between nitrate removal indices (NRR, NRE, and Nrd) and HRT. This study first utilizes nonlinear models to quantitatively understand the relationship between NRR, NRE, Nrd, and HRT. To verify the models, eight experiments were conducted under different conditions, including different scales (laboratory and field), media (woodchip, woodchip+biochar, woodchip+silage leachate, woodchip+biochar+silage leachate), and influent nitrate concentrations (6.8–70 mg N L−1). The results showed that the MT model outperformed the MM model and MT could accurately characterize the nitrate removal changes with HRT and provide the optimal HRT (HRTO). Overall, the model could be beneficial for designers and practitioners to optimize nitrate removal.

Optimization bio-nest coupled microbial fuel cell performance using Taguchi and response surface method on purifying eutrophic water.

The bio-nest coupled microbial fuel cell is designed to transform chemical energy into electricity serving to purify river water pollutants. In this study, we utilized the river water adjusted to 15 mg/l for TIN, 7.5 mg/l for NO3-N, 7.5 mg/l for NH4-N, and 150 mg/l for COD concentrations. Within the anode chamber, uniformly mixed poly3-hydroxybutyrate-co-3-hydroxy, activated carbon, pyrite, and sponge iron particles were used. Our study focuses on the optimization of parameters by employing Response Surface Methodology and the Taguchi methods. We examined the factors of pH, hydraulic retention time (HRT), and dissolved oxygen (DO) on the removal efficiency of the responses nitrate, nitrite, ammonium, total inorganic nitrogen (TIN), and COD. The selected desirability was 0.921 with removal efficiencies 71.2% for NO3-N, 100% for NO2-N, 95% for NH4-N, 99.6% for TIN, and 84.3% for COD while the factors were at 8 mg/l DO, at pH 8, and a 72-hour HRT. Furthermore, we achieved a maximum voltage output of 334 mV while the COD concentration was 225 mg/l. The model initiates nitrification and heterotrophic or autotrophic denitrification to mitigate the pollution. Notably, the developed system reduces construction, installation, and operational costs while enhancing both bioelectricity generation and pollutant removal efficiency.

Testing and Evaluation Performance of Borosilicate Glasses for Ammonia, Nitrate, and Total Nitrogen Removal from Industrial Wastewater

Several studies were conducted utilizing various adsorbents in an effort to remove NH3+, NO3, and total nitrogen (TN) by adsorption process. In this study, Borosilicate glass is used as an adsorbent material. The effectiveness of the adsorbent in removing NH3+, NO3, and TN was examined, that in relation to the effect of solution characteristics. Three different types of glass intermediate oxides (Al2O3, SnO, and Bi2O3) were used to synthesize three different samples of borosilicate glass (adsorbents), that to study their effect on the adsorption efficiency of borosilicate glass. Aluminum oxide Al2O3 was used to synthesize adsorbent (I), tin oxide SnO was used to synthesize adsorbent (J), and bismuth oxide Bi2O3 was used to synthesize adsorbent (K). Adsorbents (I, J, and K) achieved a clear improvement in the performance of the adsorption process. Despite the convergence of competencies, adsorbents J and K were superior to adsorbent I. With adsorbent K and an initial concentration of contaminants 28 mg NH3+/ L, 28 mg NO3/ L, and 60 mg TN / L, the removal efficiency of NH3+, NO3, and TN was 49.5%, 55%, and 40%, respectively. The removal efficiency increased with initial concentration of contaminants increasing, which became around 79% NH3+, 93% NO3, and 88% TN for adsorbent K. The best efficiency of ammonia removal achieved with pH value 8.9, it was 64.1%, 75.3%, and 77.1% for adsorbents I, J, and K, respectively. The highest efficiency of nitrate removal was in acidic case, reaching 90.1%, 95.2%, and 93.8% for adsorbents I, J, and K, respectively, at pH value 4.1. Adsorption data were fitted with Langmuir and Freundlich isotherm models to demonstrate the adsorption behavior of NH3+, NO3, and TN onto adsorbents (I, J, and K). It was found that the data were well fitted to both models. Overall, the findings demonstrated that borosilicate glass has the potential to be an effective adsorbent for the removal of ammonia, nitrate, and total nitrogen from industrial effluent.

The Behavior of Terbuthylazine, Tebuconazole, and Alachlor during Denitrification Process.

Pesticide compounds can influence denitrification processes in groundwater in many ways. This study observed behavior of three selected pesticides under denitrifying conditions. Alachlor, terbuthylazine, and tebuconazole, in a concentration of 0.1 mL L-1, were examined using two laboratory denitrifications assays: a "short" 7-day and a "long" 28-day test. During these tests, removal of pesticides via adsorption and biotic decomposition, as well as the efficiency of nitrate removal in the presence of the pesticides, were measured. No considerable inhibition of the denitrification process was observed for any of the pesticides. On the contrary, significant stimulation was observed after 21 days for alachlor (49%) and after seven days for terbuthylazine (40%) and tebuconazole (36%). Adsorption was in progress only during the first seven days in the case of all tested pesticides and increased only negligibly afterwards. Immediate adsorption of terbuthylazine was probably influenced by the mercuric chloride inhibitor. A biotic loss of 4% was measured only in the case of alachlor.

Efficient nitrate removal by nitrogen-doped carbon spheres electrodes with interconnected architecture in novel stirring capacitive deionization: Dual promoting effect of facile mass transfer and additional active centers

Efficient nitrate removal by nitrogen-doped carbon spheres electrodes with interconnected architecture in novel stirring capacitive deionization: Dual promoting effect of facile mass transfer and additional active centers

Effect of hydraulic regime on sulfur-packed bed performance: Denitrification and disproportionation

Sulfur-packed beds (SPBs) have been increasingly incorporated into constructed wetland systems to overcome limitations in achieving satisfactory nitrate removal efficiency. However, the underlying impact of hydraulic regimes on SPB performance remains understudied. This study investigated the performance of a pilot-scale SPB, encompassing sulfur autotrophic denitrification (SAD) and sulfur disproportionation (SDP) processes, under various horizontal flow (HF) and vertical flow (VF) regimes. The HF regime exhibited superior SAD efficiency, achieving 3.1–4.4 mg-N/L of nitrate removal compared to 0.9–2.8 mg-N/L under VF regimes. However, greater sulfide production of 3.8–5.6 mg/L was observed, in contrast to only 1.5–2.3 mg/L under VF regimes when SDP occurred. Employing current computational fluid dynamics simulations could predict general regimes but lacked precision in detailing sulfur layer dynamics. In contrast, determining the spatial distribution of SAD substrates and SDP products offered a viable solution, revealing stagnate, short-circuit, and back flows. Moreover, the feasibility of an aeration approach to reduce sulfide emissions below 0.5 mg/L in case of accidental SDP occurrence was confirmed. This study offers a method for assessing detailed hydraulic regimes within SPBs. Additionally, it provides guidance on optimizing the packing of sulfur-based materials when implementing SPBs in constructed wetland systems and presents a strategy for mitigating excessive sulfide emissions.

Insights into the transport and bio-degradation of dissolved inorganic nitrogen in the biochar-pyrite amended stormwater biofilter using dynamic modeling

The stormwater biofilter is a prevailing green infrastructure for urban stormwater management, but it is less effective in dissolved nitrogen removal, especially for nitrate. The mechanism that governs the nitrate leaching and performance stability of stormwater biofilters is poorly understood. In this study, a water quality model was developed to predict the ammonium and nitrate dynamics in a biochar-pyrite amended stormwater biofilter. The transport of dissolved nitrogen species was described by advection-dispersion models. The kinetics of adsorption and pyrite-based autotrophic denitrification are included in the model and simulated with a steady-state saturated flow. The model was calibrated and validated using eleven storm events. The modeling results reveal that the contribution of pyrite-based autotrophic denitrification to nitrate leaching alleviation improves with the increased drying duration. The nitrate removal efficiency was affected by a series of design parameters. Pyrite filling rate has a minor effect on nitrate removal promotion. Service area ratio and submerged zone depth are the key parameters to prevent nitrate leaching, as they influence the emergence and discharge time of nitrate breakthrough. The high inflow volume (high service area ratio) and small submerged zone can lead to earlier and increased discharge of peak nitrate otherwise the peak nitrate could be retained in the submerged zone and denitrified during the drying period. The developed mechanistic model provides a useful tool to evaluate the treatment ability of stormwater biofilters under varying conditions and offers a guideline for biofilter design optimization.

Effects of released organic components of solid carbon sources on denitrification performance and the related mechanism

Here, a hybrid scaffold of polyvinyl alcohol/sodium alginate (PVA/SA) was used to prepare solid carbon sources (SCSs) for treating low carbon/nitrogen wastewater. The four SCSs were divided into two groups, biodegradable polymers group (including polyvinyl alcohol-sodium alginate (PS) and PS-PHBV (PP), and blended SCSs (PS-PHBV-wood chips (PPW) and PS-PHBV-wheat straw (PPS)). After the leaching experiments, no changes occurred in elemental composition and functional groups of the SCSs, and the released dissolved organic matter showed a lower degree of humification and higher content of labile molecules in the blended SCSs groups using EEM and FT-ICR-MS. The denitrification performance of the blended SCSs was higher, with nitrate removal efficiency over 84%. High-throughput sequencing confirmed PPW had the highest alpha-diversity, and the microbial community structure significantly varied among SCSs. Results of functional enzymes and genes show the released carbon components directly affect the NADH level and electron transfer efficiency, ultimately influencing denitrification performance.

Nitrate removal for drinking water by FeCl3-oxidated polypyrrole- grafted activated carbon: Adsorption property and mechanism

Developing efficient nitrate removal technologies is crucial for ensuring the safety of drinking water, a polypyrrole-grafted activated carbon (PPy-AC) was synthesized via in situ chemical oxidative polymerization to enhance nitrate adsorption from water. It was showed that the PPy-AC composite featured a maximum adsorption capacity of 13.36 mg NO3−-N/g and exhibited high selectivity toward nitrate in the presence of co-existing anions. The PPy-AC composite exhibited a considerable capacity for adsorbing nitrate over a wide pH range of 3.0–9.0. The absorption performances were well-fitted by the Redlich-Peterson isotherm model, and the adsorption kinetics were well-described by the pseudo-second-order equation. Furthermore, the mass and charge balance calculations showed that 8.4% of the nitrogen atoms in the PPy-AC facilitated the adsorption of nitrate. The mechanisms of nitrate removal by the PPy-AC composite were determined through the electrostatic attraction and ion-exchange process, in which the nitrate ions are replaced by doped chloride ions, and the other N+ sites in PPy were occupied by nitrate ions. The PPy-AC is a promising material for the nitrate removal from wastewater.

A Promising Process to Remove Nitrate from Solar Panel Production Wastewater and Meanwhile Generating Electricity

For traditional heterotrophic denitrification technology, organics are usually added as the electron donor for nitrate removal, which increases the operation cost for wastewater treatment. Solar panel production wastewater contains a large amount of nitrate. To decrease the operation cost and reduce CO2 emissions, an iron anode microbial fuel cell (Fe-MFC) was constructed to treat solar panel production wastewater by sequencing batch operation. The results showed that the maximum nitrate removal efficiency reached 99.98% and the maximum removal rate was 0.049 kg·m−3·d−1. The output voltages rose rapidly to 560 ± 10 mV within 2 h and then stabilized at 520 ± 50 mV for about 40 h. Combining the detection of coulombic efficiency, CV curve, q* value and internal resistance; the decrease in denitrification efficiency and electricity generation efficiency probably resulted from the passivation of iron anode and the aging of the cathode biofilm resulted in the efficiency decrease. From the microbial analysis, Chryseobacterium, Thermomonas and Thauera predominated at the end of Fe-MFC operation. Microorganisms that cannot adapt to the autotrophic environment in Fe-MFC died out finally. Periodic replacement of the iron anode and domestication of the bio-cathode were essential to maintain the Fe-MFC efficiency. The Fe-MFC technology was feasible to be used to remove nitrate and generate electricity from solar panel production wastewater. Without organics addition, the Fe-MFC technology was cost-efficient and environmentally friendly, endowing itself with a broad prospect of application.

Enhanced nitrogen removal from micro-polluted water by Fe (II)/Fe (III) cycling under intermittent aeration

The potential of iron-carbon materials (FeC) as inorganic electron donors for aerobic denitrification of micro-polluted source water was explored. For this purpose, a raw water denitrification experiment was conducted using FeC under intermittent aeration condition. Then, magnetite was added as a biological carrier to construct another system, FeC and magnetite intermittent aeration reaction system, (FCMI). The findings revealed that FCMI notably removed the pollutants with the removal efficiencies of nitrate, total nitrogen, total phosphorus, and chemical oxygen demand reaching 95.63%, 88.62%, 90.48%, and 61.46%, respectively. Cycling between aerobic and anaerobic environments facilitated the formation of Fe (II)/Fe (III) cycle within FeC materials. Microbial profiling revealed that Proteobacteria and Actinobacteria comprised 97.14% of the total abundance in FCMI. Iron-reducing bacteria and aerobic denitrifying bacteria were found to thrive on the surface of magnetite materials. The abundance of enzymes related to denitrification under intermittent aeration exceeded those under continuous aeration levels by 8–19%. This study verifies the ability of iron electrons to cycle under intermittent aeration condition and proposes a novel strategy for in-situ denitrification of micro-polluted source water.

Simultaneous removal of phosphorus, zinc, and lead from oligotrophic ecosystem by iron-driven denitrification: Performance and mechanisms

Based on the current situation of complex pollution caused in surface water by oligotrophic condition and heavy metal release from river and lake bottom sediments. This study aimed to achieve the simultaneous removal of nitrate, phosphorus, Zn2+ and Pb2+ through microbial approach. At nitrate concentration of 4.82 mg L−1, carbon to nitrogen ratio of 1.5, pH of 6.0, and Fe2+ concentration of 5.0 mg L−1, the nitrate removal efficiency of Zoogloea sp. FY-6 reached 95.17%. The addition of pollutants under these conditions resulted in 88.76% removal of total phosphorus at 18 h, and 85.46 and 78.59% removal of Zn2+ and Pb2+ respectively, and there was competition for adsorption between Zn2+ and Pb2+. Extracellular polymers and fluorescence excitation-emission substrates confirmed that Fe2+ reduced heavy metal toxicity through promoting bacterial production of secretions and promotes denitrification as a carbon source. Meanwhile, contaminant removal curves and Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy demonstrated the synchronous removal of Zn2+ and Pb2+ mainly through biological action and the formation of nanoscale iron oxides. Biological-iron precipitation also provided adsorption sites for phosphorus. This research provides the theoretical foundation for applying microorganisms to restore oligotrophic source water (rivers and lakes) containing complex pollutants.

The competition between heterotrophic denitrification and DNRA pathways in hyporheic zone and its impact on the fate of nitrate

Dissimilatory nitrate reduction to ammonium (DNRA) and heterotrophic denitrification (DEN) are recognized as two key nitrate reduction pathways competing for both nitrate and dissolved organic carbon (DOC). However, the mechanisms and influencing factors governing this competition in the dynamic hyporheic system remain unclear. In this study, a numerical model that coupled flow, reactive solute transport and microbial activities was developed to investigate the competition between DEN and DNRA in the hyporheic zone. The modeling results indicate that DNRA hotspots are distributed along the hyporheic flow path. The greater the flow velocity, the farther the DNRA hotspots are from the water-sediment interface. In the simulation scenario involving river stage fluctuations, the relative contribution of DNRA resulting from these fluctuations under a small initial hydraulic gradient (0.001) of the hyporheic zone increased by 60% compared to the range observed under a large initial hydraulic gradient (0.01). The C/N ratio in river water does not dictate the prevailing microbial group at specific locations within the hyporheic zone. Instead, the river C/N ratio governs the competition outcomes across the entire hyporheic system, demonstrating a three-phase pattern. The nitrate removal efficiency in the hyporheic system approaches 100% at C/N = 3. As the stream C/N ratio increases, the contribution of DNRA gradually rises and can reach 80% (C/N = 10). At this point, the contribution of the heterotrophic denitrifying bacteria and their corresponding nitrate removal efficiency decreases to only about 20%. Disregarding the DNRA reaction might lead to an underestimation of nitrate removal efficiency of a hyporheic zone. Our investigation improves the understanding of nitrate fate in hyporheic zones and provides a scientific foundation for watershed management and pollution control.

Clarification of the phosphorus release mechanism for recovering phosphorus from biofilm sludge in alternating aerobic/anaerobic biofilm system

A novel wastewater treatment plant process was constructed to overcome the challenge of simultaneous nitrate removal and phosphorus (P) recovery. The results revealed that the P and nitrate removal efficiency rose from 39.0 % and 48.4 % to 92.8 % and 93.6 % after 136 days of operation, and the total P content in the biofilm (TPbiofilm) rose from 15.8 mg/g SS to 57.8 mg/g SS. Moreover, the increase of TPbiofilm changed the metabolic mode of denitrifying polyphosphate accumulating organisms (DPAOs), increasing the P concentration of the enriched stream to 172.5 mg/L. Furthermore, the acid/alkaline fermentation led to the rupture of the cell membrane, which released poly-phosphate and ortho-phosphate of cell/EPS in DPAOs and released metal‑phosphorus (CaP and MgP). In addition, high-throughput sequencing analysis demonstrated that the relative abundance of DPAOs involved in P storage increased, wherein the abundance of Acinetobacter and Saprospiraceae rose from 8.0 % and 4.1 % to 16.1 % and 14.0 %. What's more, the highest P recovery efficiency (98.3 ± 1.1 %) could be obtained at optimal conditions for struvite precipitation (pH = 7.56 and P: N: Mg = 1.87:3.66:1) through the response surface method (RSM) simulation, and the precipitates test analysis indicated that P recovery from biofilm sludge was potentially operable. This research was of great essentiality for exploring the recovery of P from biofilm sludge.

Coeffect of Co-Mn in bimetallic oxide catalyst for ultrafast electrochemical reduction of nitrate: Insight into ion interaction

Co3O4 has been considered as promising catalysts for electroreduction of nitrate (ERN), which is an emerging tactic to close the nitrogen cycle on earth. However, the nitrate reduction efficiency of Co3O4 is less than satisfactory, which could be enhanced by assistance of Mn element. Herein, we synthesized Co3O4, Mn2O3 and Mn1.5Co1.5O4 nanoparticles for electrodes via a simple sol–gel method using metal nitrates. Moreover, a special electrode 3-Mn/Co was fabricated by physical mixed Co3O4 and Mn2O3. Mn1.5Co1.5O4 and 3-Mn/Co electrodes presented 78.6 % and 64.09 % nitrate removal efficiency after 3 h, 115.46 % and 75.68 % higher than that of Co3O4, proving the existence of Co-Mn coeffect. The optimum Mn1.5Co1.5O4 endures operating parameters experiments of applied potential, level of NO3– concentration, pH value and Cl- concentration and maintains solid stability through ten batches of reaction. Eventually, the ion valence changes of electrodes before and after electrocatalysis verifies that both Co and Mn function in the reaction. The ERN performance variation between electrodes, doped and physically mixed with Mn, and Co3O4 further elucidates that Mn3+ takes major effect in ERN process, while Mn4+ would blocks the electrons transferred to NO3–. In general, a novel process of Co3+/Mn3+- Co2+/Mn4+ reaction cycle in Co and Mn bimetallic and monometallic oxides for ERN performance is proposed as a clue for electrode fabrication.