High Denitrification Efficiency Research Articles

Enhanced denitrification of biodegradable polymers using Bacillus pumilus in aerobic denitrification bioreactors: Performance and mechanism

Nitrate accumulation is an important issue that affects animal health and causes eutrophication. This study combined biodegradable polymers with degrading bacteria to lead to high denitrification efficiency. The results showed polycaprolactone had the highest degradation and carbon release rate (0.214 mg/g∙d) and nitrogen removal was greatest when the Bacillus pumilus and Halomonas venusta ratio was 1:2. When the hydraulic retention time was extended to 12 h, the nitrate removal rate for H. venusta with B. pumilus and polycaprolactone increased by 48 %. Furthermore, the group with B. pumilus contained more Proteobacteria (77.34 %) and denitrifying functional enzymes than the group without B. pumilus. These findings indicated B.pumilus can enhance the degradation of biodegradable polymers especially polycaprolactone to improve the denitrification of the aerobic denitrification bacteria H.venusta when treating maricultural wastewater.

The reaction characteristics and mechanism of polymer non-catalytic reduction (PNCR) for NOx removal

To overcome the defects of the traditional selective non-catalytic reduction (SNCR) process (e.g., low efficiency, narrow temperature range), a new modified SNCR technology based on the solid complex polymer reducing agents, also called polymer non-catalytic reduction (PNCR), was investigated both in the laboratory and pilot scale to reveal its reaction characteristics and mechanism. The PNCR process demonstrates excellent removal efficiency (about 90%) of NO in furnace in the wide temperature range (850–1150 °C), and possesses promising application feasibility with an average NOx emission concentration of 68.72 mg·m−3 even on unstable industrial operating conditions. The NO removal behaviors influenced by O2, temperature, or water steam illuminate the unique O2-independent and H2O-promoted reaction characteristics of PNCR in the wide temperature range. The thermogravimetric infrared spectra/mass spectrometry (TG-IR/MS) results further reveal a pyrolysis-assisted formation mechanism of active NH2/NH free radicals without the requirement of O2 and high temperature, which avoids the overoxidation of active radicals and accounts for the wide denitrification temperature window, low oxygen compliance and high denitrification efficiency of PNCR process. The excellent NO removal performance as well as the unique reaction characteristics/mechanism of PNCR forebode its broad industrial application prospect in the field of flue gas cleaning.

The Calculation of Both Electrostatic and Van der Waals Effects to Probe the Efficiency of Solvent Extraction of Heterocyclic Aromatics from Heavy Oil.

Due to the complex composition and similar structure, the extraction denitrification of aromatic rich oil is faced with the contradiction problem of denitrification efficiency and aromatic loss which cannot be efficiently solved by experiments. However, the complex interactions involved can be analyzed from the perspective of calculation, and the prediction criteria and methods are proposed. Based on rigorous density functional theory calculation data, Simple models based on electrostatic potential (ESP) and Van der Waals potential (VdWP)-based calculations were established and validated. The twofold model provided the best prediction for interactions between extractants and nitrogen compounds and between extractants and aromatics, which determines denitrification efficiency and aromatic loss, respectively, due to the most complete description of both electrostatic and VdW force. This provides a powerful tool for evaluating the non-covalent interactions and thence tuning the efficiency of the separation process. Thus, high denitrification efficiency (43.2~66.3 %) and moderate aromatic loss (1.7~4.4 %) were obtained using screened deep eutectic solvents (DESs). This ideal observation provided the potential for mild hydrodesulfurization and manufacture of high-grade carbon materials.

Impact of aeration on/off duration on the performance of an intermittently aerated MBR treating real textile wastewater

Uncontrolled discharge of textile industry wastewater, defined by its highly toxic content, causes serious problems in receiving environment. Especially nitrogen-derived pollutants in wastewater threaten the ecosystem and aquatic life. Separate or simultaneous nitrification/denitrification is the preferred biological processes for removing nitrogen-based pollutants from wastewater. This study aimed to evaluate the impact of aeration on/off cycle durations on organic matter, color, and nitrogen removal performances in an intermittently aerated membrane bioreactor (MBR) receiving real textile wastewater. For this purpose, the MBR was operated under different dissolved oxygen concentrations (6 and 3 mg/L) and the aeration on/off cycle durations (from 2 min/2 min to 90 min/360 min) at a constant flux of 10 L/(m2.h). While the chemical oxygen demand (COD) removal performance ranged from 84 to 91 %, the color removal efficiencies were highly variable. Nitrification performance of ≥89 % was achieved with a minimum of 30 min aeration cycles. The highest denitrification efficiency was obtained in the cycle with 360 min aeration-off duration. Intermittent aeration provided higher TN removal, less sludge generation, and lower energy requirements for aeration. The impacts of aeration cycle duration on membrane filtration performance and foulant characterization were also investigated by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), gel-permeation chromatography (GPC), SEM coupled with energy dispersive spectroscopy (SEM-EDS), particle size distribution (PSD) analyses.

Biochar enhanced the stability and microbial metabolic activity of aerobic denitrification system under long-term oxytetracycline stress

Reactors were established to study the feasibility of the direct addition of modified biochar to alleviate the long-term stress of oxytetracycline (OTC) on aerobic denitrification (AD) and improve the stability of the system. The results showed that OTC stimulated at μg/L, and inhibited at mg/L. The higher the concentration of OTC, the longer the system was affected. The addition of biochar, without immobilization, improved the tolerance of community, alleviated the irreversible inhibition effect of OTC, and maintained a high denitrification efficiency. Overall, the main mechanisms of AD enhancement by biochar under OTC stress were: enhancing the bacteria metabolic activity, strengthening sludge structure and substrate transport, and improving the community stability and diversity. This study confirmed that direct addition of biochar could effectively alleviate the negative effect of antibiotics on the microorganisms, strengthen the AD, which provided a new idea to broaden the application of AD technology in livestock wastewater.

Impact of instrumentation reliability on mainstream suspended Partial denitrification anammox (PdNA).

This study successfully revealed the importance of probe reliability and sensitivity with ion sensitive electrode (ISE) probes on achieving high partial denitrification (PdN) efficiency; and decreasing carbon overdosing events that cause the decline of microbial populations and performance of partial denitrification-anammox (PdNA). In a mainstream integrated hybrid granule-floc system, an average PdN efficiency of 76% was achieved with acetate as the carbon source. Thauera was identified as the dominant PdN species; Its presence in the system was analogous to instrumentation reliability and PdN selection and wasn't a consequence of bioaugmentation. Up to 27-121 mg TIN/L/d, an equivalent of 18 - 48% of the overall TIN removed, was achieved through the PdNA pathway. Candidatus Brocadia was the main anoxic ammonium oxidizing bacteria (AnAOB) species that was seeded from sidestream, and enriched and retained in the mainstream system with observed growth rates of 0.04 - 0.13 d-1 . Moreover, there was no direct negative impact of methanol's use for post-polishing on AnAOB activity and growth.

Simultaneous removal of nitrogen and arsenite by heterotrophic nitrification and aerobic denitrification bacterium Hydrogenophaga sp. H7.

Nitrogen and arsenic contaminants often coexist in groundwater, and microbes show the potential for simultaneous removal of nitrogen and arsenic. Here, we reported that Hydrogenophaga sp. H7 was heterotrophic nitrification and aerobic denitrification (HNAD) and arsenite [As(III)] oxidation bacterium. The appearance of nitrogen removal and As(III) oxidation of Hydrogenophaga sp. H7 in liquid culture medium was studied. The effect of carbon source, C/N ratio, temperature, pH values, and shaking speeds were analyzed. The impact of strains H7 treatment with FeCl3 on nitrogen and As(III) in wastewater was assessed. The key pathways that participate in simultaneous nitrogen removal and As(III) oxidation was analyzed by genome and proteomic analysis. Strain H7 presented efficient capacities for simultaneous NH4 +-N, NO3 --N, or NO2 --N removal with As(III) oxidation during aerobic cultivation. Strikingly, the bacterial ability to remove nitrogen and oxidize As(III) has remained high across a wide range of pH values, and shaking speeds, exceeding that of the most commonly reported HNAD bacteria. Additionally, the previous HNAD strains exhibited a high denitrification efficiency, but a suboptimal concentration of nitrogen remained in the wastewater. Here, strain H7 combined with FeCl3 efficiently removed 96.14% of NH4 +-N, 99.08% of NO3 --N, and 94.68% of total nitrogen (TN), and it oxidized 100% of As(III), even at a low nitrogen concentration (35 mg/L). The residues in the wastewater still met the V of Surface Water Environmental Quality Standard of China after five continuous wastewater treatment cycles. Furthermore, genome and proteomic analyses led us to propose that the shortcut nitrification-denitrification pathway and As(III) oxidase AioBA are the key pathways that participate in simultaneous nitrogen removal and As(III) oxidation.

Single-cell Raman spectra reveals the cytochrome c-mediated electron transfer in nanoscale zero-valent iron coupled denitrification process

Nanoscale zero-valent iron (nZVI) coupled denitrification is considered the typical abiotic-biotic synergistic process, but its underlying electron transfer mechanism remains unclear. Herein, we performed a heavy water labeling single-cell Raman spectroscopy (D2O-SCRS) for in-situ and dynamic characterization of the Cytochrome c-mediated electron transfer process with coexisting nZVI and a model denitrifying bacterium. Interestingly, the nZVI resulted in a strong synergistic effect with a high denitrification efficiency of 99.8 % (∼100 mg/L NO3-N), approximately 18 and 12-fold than those of pure nZVI (5.4 %) and model bacterium (8.3 %), respectively. The D2O-SCRS approach revealed the reduced Cytochrome c (Cyt c) facilitated electron transfer to enzymes and is responsible for NO2–→NO, NO → N2O, and N2O → N2 reactions in the denitrification respiratory chain, thus accelerating the occurrence of synergistic effects. Furthermore, the decreased metabolic activity contributed to higher ATP availability for nitrate reduction, thereby favoring denitrification. The metatranscriptomic analysis confirmed that both up-regulated genes encoding Cyt c reductase and the down-regulated Cyt c oxidase promoted the generation of reduced Cyt c, corresponding well with the D2O-SCRS results. Additionally, the elevated complex I, complex III, and excess NAD+ ensured a large number of electrons participated in the respiratory chain. This study deepened the understanding of the biotic-abiotic synergistic mechanism and provided a new method to in-situ characterize the electron transfer process at a single-cell level.

Capturing influent organic substrate for endogenous denitrification to enhance nitrogen removal in low C/N ratio municipal wastewater

Intending to reduce aerobic oxidation of carbon sources and leave more carbon resources for denitrification to improve nitrogen removal in low C/N ratio wastewater, batch tests were conducted by allowing sludge to directly capture carbon sources from the influent for feeding denitrifier. The capture effect of three pretreatments and capture modes, i.e., (a) oxic famine (Ofam) pretreatment and then anoxic feast (Afea) mode (Ofam-Afea); (b) anoxic famine (Afam) pretreatment and then oxic feast (Ofea) mode (Afam-Ofea); (c) Afam pretreatment then aerobic feeding of treated sludge in continuous stirred tank reactor (CSTR) with side-stream push-flow reaction (PFR) zone (Afam with side-stream PFR), were investigated. The storage of organic substances and accumulation of intracellular polymers by the sludge in Ofam-Afea mode was compared with that of the sludge in Afam-Ofea mode. The results show that the total capture efficiency (TCE) of the sludge in the Ofam-Afea mode was around 60 %, the amount of glycogen (Gly) remained essentially unchanged, and the intracellular polyhydroxyalkanoates (PHA) accumulated significantly without apparent “stagnation” for carbon source switching. In Afam-Ofea mode, the TCE increased to 60 %–70 %. The amount of Gly increased by 31.2 %–50.0 %, PHA accumulated considerably, and high denitrification efficiency was achieved, whereas denitrification stopped dramatically with the stage of carbon sources switching. The Afam with side-stream PFR allowed high-speed denitrification and hydrolytic fermentation, eliminating the “stagnation” of switching carbon sources. The optimal VPFR/VCSTR values were 1–1.5. A shorter side-stream time was equivalent to CSTR, whereas a longer side-stream time caused the sludge to synthesize fewer intracellular polymers.

Insights into integration of polyhydroxyalkanoates (PHAs) production into wastewater treatment: Comparison of different electron acceptors on system function and PHA-producer enrichment

Mixed microbial culture polyhydroxyalkanoates (MMC PHA) process combined with mainstream wastewater treatment is a competitive resource recovery integrated process in which economical non-oxygen electron acceptors can be used to enrich PHA-producer and reduce operating costs. Oxygen and three non-oxygen electron acceptors (endogenous nitrate, exogenous nitrate, and nitrite) were used and comprehensively compared in terms of PHA production ability and microbial community ecophysiology in this study. The results showed that the PHA production ability with exogenous nitrate was comparable to that of oxygen, which had a maximum PHA content of 64.0 wt% (versus 62.3% of oxygen), qPHA of 0.7 mg COD/mg Xa/h, as well as 99.1% denitrification efficiency. The non-oxygen acceptors delayed the time for Arcobacter to occupy the dominant niche in the community, and the environmental selection pressure produced was slightly lower than that of oxygen. The symbiotic community between denitrifying bacteria and PHA-producers ensured the high PHA production potential and denitrification efficiency of the non-oxygen system. An economic assessment showed that the integrated PHA production and nitrate removal process with the mainstream wastewater treatment process proposed in this study could reduce aeration energy by 64%, and PHA recovery yield was 0.1 kg CODPHA/kg CODWAS from waste activated sludge (WAS).

Introducing PHBV and controlling the pyrite sizes achieved the pyrite-based mixotrophic denitrification under natural aerobic conditions: Low sulfate production and functional microbe interaction

The pyrite-based autotrophic denitrification usually focused on the anaerobic/anoxic environment with high sulfate production and low denitrification efficiency. In this study, the oxygen limitation was broken and high-rate mixotrophic denitrification was realized via introducing poly-3-hydroxybutyrate-hydroxyvalerate (PHBV) and controlling the pyrite grain sizes compared with PHBV-heterotrophic and pyrite-autotrophic denitrification under natural aerobic conditions. Results showed that the optimal pyrite grain size was 30 meshes (0.45–0.55 mm) with the highest denitrification rate of 0.65 mg NO3−−N/(L•h) and sulfate production of <5 mg/L in pyrite-PHBV system. Its removal efficiency of nitrogen and phosphorus was 96% and 25%, respectively. According to functional genes and Raman analysis, the low SO42− production were attributed to the S reduction and polysulfide formation in the mixotrophic systems, which also enhanced denitrification efficiency by improving bioavailability and multi-stage utilization of sulfur matrix (i.e., S2−, poly-S and SO42−) in these mixotrophic systems. Thiobacillus and Acidovorax have been enriched on the pyrite and PHBV surface, respectively, which highlighted that the autotrophic-heterotrophic synergy was achieved via different functional microbes domesticated by substrates. The differential analysis among functional genes suggested that PHBV surface promoted the NO2− reduction and S oxidation, and pyrite surface enhanced the N2O reduction and S reduction. A closer connection between C degradation and N cycle indicated their copiotrophic nutritional patterns based on the network analysis. The key taxa co-occurrence revealed rare species involved in Fe cycle metabolism were the hidden drivers in the mixotrophic denitrification process. These findings provide an in-depth understanding on the multiple interactions among N, S, and Fe cycling, and improve the practical application of pyrite-PHBV mixotrophic systems.

Pseudomonas oligotrophica sp. nov., a Novel Denitrifying Bacterium Possessing Nitrogen Removal Capability Under Low Carbon-Nitrogen Ratio Condition.

Pseudomonas is a large and diverse genus within the Gammaproteobacteria known for its important ecological role in the environment. These bacteria exhibit versatile features of which the ability of heterotrophic nitrification and aerobic denitrification can be applied for nitrogen removal from the wastewater. A novel denitrifying bacterium, designated JM10B5aT, was isolated from the pond water for juvenile Litopenaeus vannamei. The phylogenetic, genomic, physiological, and biochemical analyses illustrated that strain JM10B5aT represented a novel species of the genus Pseudomonas, for which the name Pseudomonas oligotrophica sp. nov. was proposed. The effects of carbon sources and C/N ratios on denitrification performance of strain JM10B5aT were investigated. In addition, the results revealed that sodium acetate was selected as the optimum carbon source for denitrification of this strain. Besides, strain JM10B5aT could exhibit complete nitrate removal at the low C/N ratio of 3. Genomic analyses revealed that JM10B5aT possessed the functional genes including napA, narG, nirS, norB, and nosZ, which might participate in the complete denitrification process. Comparative genomic analyses indicated that many genes related to aggregation, utilization of alkylphosphonate and tricarballylate, biosynthesis of cofactors, and vitamins were contained in the genome of strain JM10B5aT. These genomic features were indicative of its adaption to various niches. Moreover, strain JM10B5aT harbored the complete operons required for the biosynthesis of vibrioferrin, a siderophore, which might be conducive to the high denitrification efficiency of denitrifying bacterium at low C/N ratio. Our findings demonstrated that the strain JM10B5aT could be a promising candidate for treating wastewater with a low C/N ratio.

High efficient bio-denitrification of nitrate contaminated water with low ammonium and sulfate production by a sulfur/pyrite-based bioreactor

Sulfur-based autotrophic denitrification (SAD) and pyrite-based autotrophic denitrification (PAD) are important technologies that address nitrate pollution, but high sulfate production and low denitrification efficiency, respectively, limit their application in engineering. A bio-denitrification reactor with sulfur and pyrite as filler materials was studied to remove NO3–-N from nitrate contaminated water. At an influent NO3–-N concentration of 50 mg/L, NO3–-N removal efficiency of the sulfur/pyrite-based bioreactor was 99.2%, producing less NH4+-N and SO42- than the sulfur-based bioreactor, even after long-term operation. Denitrification performance was significantly related to environmental variable, especially dissolved oxygen. Proteobacteria and Epsilonbacteraeota were the predominant phyla in the sulfur/pyrite-based bioreactor, and fewer dissimilatory nitrate reductions to ammonia process-related bacteria were enriched compared to those in the sulfur-based bioreactor. Sulfur-pyrite bio-denitrification provides an efficient alternative method for treatment of nitrate contaminated water.

Insights into the mechanism of Mn(II)-based autotrophic denitrification: Performance, genomic, and metabonomics

The technologies for groundwater nitrate pollution treatment have drawn increasing global attention. As for autotrophic denitrification (AD), most researches aimed to the mixed microbial culture bioreactors, the mechanism of AD by purely cultured bacteria has not been fully investigated yet. Here, denitrification ability, bacterial activity, and dissolved organic matter evolution of Cupriavidus sp. HY129 in both AD and heterotrophic denitrification (HD) were studied. Genomic analysis and microbial metabolomic analysis were applied to explore the mechanism of AD and the difference and intrinsic factors in AD and HD. The results revealed that HD resulted in higher denitrification efficiency and biomass compared to AD and the bacteria preferred to synthesize humic-like proteins to maintain the progress of AD. Bacteria carry out Mn oxidation outside the bacteria cell and transfer electrons into the cell for AD. Cupriavidus sp. HY129 genome has critical metabolic pathways in both autotrophic and heterotrophic conditions, as well as the MCO gene for mediating the Mn oxidation. Energy metabolism pathways were the most significantly differences between AD and HD. Moreover, sphingolipid metabolism and mineral absorption metabolism were the most essential pathways in the autotrophic process to maintain the normal physiological activities and Mn transfer. The results explored the differences between AD and HD pathways in the same bacteria for the first time and provided new insight into understanding the metabolic characteristics of different denitrification, which provide useful information to the global nitrogen cycle and nitrate pollution treatment.

Nickel (ii) effects on Anammox reaction: reactor performance, dehydrogenase, sludge morphology and microbial community changes

ABSTRACT Nickel (ii) (Ni2+) is considered as one of the necessary trace elements in the process of Anammox culture, but it may have toxic effects at high concentration. This study explored the long-term influence of Ni2+ on the denitrification efficiency of Anammox bioreactors. The results showed that when the concentration of Ni2+ was 0.5 mg/L, the bioreactor had the highest denitrification efficiency, while the removal efficiency of ammonia nitrogen and nitrite nitrogen gradually decreased at concentrations higher than 2 mg/L, and the removal rates of ammonia nitrogen and nitrite nitrogen were 26% and 39.81% at the end of the experiment, respectively. The NRR was decreased from 7.47 kg N/m3 d to 3.28 kg N/m3 d during the whole process. The highest concentration of microbial dehydrogenase was attained in about 40 days; in the meantime, its ability to consume organic matter was also maximized. The sludge morphology was changed from granular cluster to loose flocculant with a small number of spherical and filamentous bacteria and bacilli distributed on the surface. At the end of the experiment, both species richness and community diversity were reduced, and the proportion of the dominant bacteria Candidatus Kuenenia was also decreased from 59.89% to 36.72%.

Efficient photochemical denitrification by UV/sulfite system: Mechanism and applications

Denitrification is an effective strategy to control eutrophication caused by excessive nitrate in water. However, the comparatively low efficiency of nitrate removal and N2 selectivity remains a challenge in the denitrification process. Herein, this study proposed a novel photochemical denitrification process by introducing hydrated electron (eaq-) to reduce nitrate in UV/sulfite system. The results indicated that the optimized UV/sulfite system could effectively reduce nitrate to N2 with a nearly 100% denitrification efficiency in 90 min. eaq- was identified as the mainly reactive species to achieve rapid removal of nitrate and nitrite, and the result was verified by quenching and laser flash photolysis tests. Benefiting from the high dispersion of eaq- in water and the rapid reaction rate between eaq- and the target, the generated N2O is susceptible to be reduced, leading to a high selectivity of N2 that was confirmed by 15N-isotopic. Besides, thermodynamic results based on the density functional theory (DFT) calculations suggested that the photochemical denitrification process was exothermic process and tend to transform to N2. Significantly, UV/sulfite system applied in the nickel-plating wastewater showed high denitrification efficiency, demonstrating that the novel photochemical denitrification process is promising for practical wastewater treatment.

Improving denitrification efficiency in constructed wetlands integrated with immobilized bacteria under high saline conditions

Constructed wetlands (CWs) inoculated with exogenous microbes have great potential for removing pollutants in adverse environments. The rapid loss of functional bacteria and the high cost of repeated additions of inoculum, however, limit the practical application of this technology. In this study, C–F2 immobilized bacteria (i.e., immobilized salt-tolerant bacterium Alishewanella sp. F2 incorporated with a carbon source) were developed and utilized in CWs for solving the above problems. A 60-day experiment demonstrated that bioaugmented CWs (Bio-CWs) with the addition of C–F2 immobilized bacteria into the bottom gravel layer of CW microcosms (B-CF2 treatment) exhibited high nitrogen removal efficiency under a saline condition (electrical conductivity of 15 mS/cm). We measured mean nitrate nitrogen (NO3−-N) and total nitrogen (TN) removal percentages of 97.8% and 88.1%, respectively, which were significantly (p < 0.05) higher than those in Bio-CWs with microbial inoculum (MI-F2 treatment, 63.5% and 78.2%) and unbioaugmented CWs (CK, 48.7% and 67.2%). The TN content of the entire plant was significantly (p < 0.05) increased in B-CF2 (636.06 mg/microcosm) compared with CK (372.06 mg/microcosm). The relative abundances of the genera Alishewanella (i.e., the exogenous bacterium, 5.5%), Clostridium-XlVa (8.8%) and Bacteroides (21.1%) in B-CF2 were significantly (p < 0.05) higher than in MI-F2 and CK, which improved the denitrification capacity of CWs. Overall, a high denitrification efficiency and durability were achieved in the newly developed Bio-CWs (i.e., B-CF2 treatment) with immobilized bacteria under saline conditions, which provides an alternative technology for the rapid removal of nitrogen from saline wastewater.

Regulation of heavy metals accumulated by Acorus calamus L. in constructed wetland through different nitrogen forms

Improving accumulation of heavy metals (HMs) by plants is an important pathway for constructed wetland (CW) to alleviate the environmental risks caused by their release. This study aims to regulate HMs (Cr, Ni, Cu, Zn, and Cd) accumulated by Acorus calamus L. in the sandy substrate CW with different nitrogen forms, including ammonia (NH4+), nitrate (NO3‾), and NH4+/NO3‾ (1:1) in synthetic tailwaters. In general, the removal efficiency of HMs by CW could reach 92.4% under the initial concentrations below 500 μg/L. Accumulation percentages of HMs in the shoots and roots of plants in CW with NH4+ and NH4+/NO3‾ influents increased by 52–395% and 15–101%, respectively, when compared with that of NO3‾ treatment. Influents with NH4+ promoted plant growth of Acorus calamus L. and metabolic functions, such as carbohydrate metabolism/amino acid metabolism, related to HMs mobilization of rhizosphere bacterial communities, which might induce more organic acids and amino acids secreted by plants and microbes during their metabolic processes. These are the main reasons for the enhancive mobilization of HMs from their precipitation fractions and their uptake by plants in CW with NH4+ treatments. Moreover, the enhancement of organics secreted from plants and microbes also led to the high denitrification efficiency and nitrogen removal in CW. Overall, this study could provide a feasible method for the enhancive accumulation of HMs by wetland plants via the regulation water treatment process to appropriately increase NH4+ for CW.

Performance and mechanism of a novel woodchip embedded biofilm electrochemical reactor (WBER) for nitrate-contaminated wastewater treatment

In this study, a woodchip biofilm electrode reactor (WBER) with woodchips embedded anode and cathode was developed, and its denitrification mechanism was analyzed by investigating the denitrification performance, organic matter change, redox environment and microbial community. The results show that the WBER with a carbon rod as anode (C-WBER) had a higher denitrification efficiency (2.58 mg NO- 3-N/(L·h)) and lower energy consumption (0.012 kWh/g NO- 3-N) at 350 mA/m2. By reducing the hydroxyl radical and dissolved oxygen concentrations, anode embedding technology effectively decreased the inhibition on microorganisms. Lignin decomposition, nitrification and aerobic denitrification were carried out in anode. Additionally, hydrogen autotrophic denitrification and heterotrophic denitrification were occurred in cathode. The WBER effectively removed nitrate and reduced the cost, providing a theoretical basis and direction for further develop BERs.

High efficient photocatalytic reduction of nitrate to N2 by Core-shell Ag/SiO2@cTiO2 with synergistic effect of light scattering and surface plasmon resonance

Photocatalytic denitrification has attracted great attention owing to its high efficiency and environmentally friendly features. However, selectively photocatalytic reduction of high concentration nitrate to N2 is still a challenging problem due to the competition of photons between nitrate and photocatalysts. Herein, the Ag/SiO2 core encapsulated in the crystalline TiO2 shell (Ag/SiO2@cTiO2) was constructed for improvement of photocatalytic denitrification. Finite difference time domain (FDTD) simulation demonstrated that strong light scattering improved light harvesting via optical confinement. Meanwhile, surface plasmon resonance and electron sink effect of Ag not only enhanced the photogenerated electrons density but also promoted charge carriers separation of Ag/SiO2@cTiO2. More importantly, ecb− of TiO2-shell could be immediately transferred to Ag to keep the balance between Ag0 and Ag+, which contributed to the good stability of Ag/SiO2@cTiO2. 95.8% nitrate (C0 = 2000 mg/L) was removed by 5 wt%Ag/SiO2@cTiO2 with N2 selectivity of 93.6% within 4 h. Even after five cycles, 5 wt%Ag/SiO2@cTiO2 still remained high photocatalytic denitrification efficiency (92.2%). Notably, since TiO2-shell prevented the reaction between Ag and Cl−, more than 92% nitrate could be removed within 5.3 h in the presence of high concentration Cl−.