Nitrate Removal Rate Research Articles

Assessing synchronous removal of nutrients and SMX based on novel Mn-C composites: Impact of different proportion of manganese dioxide

In this study, Mn-C composites using different MnO2 contents and solid carbon material were prepared to explore the synchronous removal performance of nutrients and SMX. Higher nitrate removal performance (97–98 %) with quickest nitrate removal rate (4.97 mg N L-1h−1) was obtained in Mn_20 systems. The increased Mn content and Mn-P compound were observed via surface characteristics, indicating the involvement of MnOx in pollutants removal, particularly for higher phosphorus removal (84–89 %) via Mn-P precipitation and BioMnOx adsorption. Nevertheless, compared to systems based on Mn_0 composites (74 %), systems with Mn-C composites presented lower SMX reduction efficiency (34–51 %), which might be attributed to the large Mn(II) accumulation, impairing certain microbes and lower the MnOx function. Higher abundance of genera affiliated to Bacteroidetes_vadinHA17 and Rhodocyclaceae was observed in the Mn-C composites, as well as the gathering of Geobacter and Desulfovibrio as keystone taxa, responsible for the removal of nitrate and SMX and microbial interactions. Besides, the increase of sulfonamide ARGs was closely related to the predominant microbes in the Mn-C composites, which acted as the hosts of ARGs. This study broadens the knowledge of Mn-C composites in synergetic removal of nutrients and organics, and supports the potential application of manganese oxide in wastewater treatment.

Improving accuracy of quantifying nitrate removal performance and enhancing understanding of processes in woodchip bioreactors using high-frequency data

Woodchip bioreactors have gained popularity in many countries as a conservation practice for reducing nitrate load to freshwater. However, current methods for assessing their performance may be inadequate when nitrate removal rates (RR) are determined from low-frequency (e.g., weekly) concurrent sampling at the inlet and outlet. We hypothesised that high-frequency monitoring data at multiple locations can help improve the accuracy of quantifying nitrate removal performance, enhance the understanding of processes occurring within a bioreactor, and therefore improve the design practice for bioreactors. Accordingly, the objectives of this study were to compare RRs calculated using high- and low-frequency sampling and assess the spatiotemporal variability of the nitrate removal within a bioreactor to unravel the processes occurring within a bioreactor. For two drainage seasons, we monitored nitrate concentrations at 21 locations on an hourly or two-hourly basis within a pilot-scale woodchip bioreactor in Tatuanui, New Zealand. A novel method was developed to account for the variable lag time between entry and exit of a parcel of sampled drainage water. Our results showed that this method not only enabled lag time to be accounted for but also helped quantify volumetric inefficiencies (e.g., dead zone) within the bioreactor. The average RR calculated using this method was significantly higher than the average RR calculated using conventional low-frequency methods. The average RRs of each of the quarter sections within the bioreactor were found to be different. 1-D transport modelling confirmed the effect of nitrate loading on the removal process as nitrate reduction followed Michaelis-Menten (MM) kinetics. These results demonstrate that high-frequency temporal and spatial monitoring of nitrate concentrations in the field allows improved description of bioreactor performance and better understanding of processes occurring within woodchip bioreactors. Thus, insights gained from this study can be used to optimise the design of future field bioreactors.

Influence of growth media and internal recycle rate on nitrogen removal from high-strength wastewater in a low footprint anoxic-upflow/aerobic process

This research investigated the use of integrated fixed-film media in comparison to suspended-growth in a low-footprint upflow biological nitrogen removal (BNR) process to find a robust solution for treatment of high-strength dairy farm wastewater (DFW). Using real DFW and synthetic wastewater (SWW), two juxtaposed anoxic upflow bioreactor/aerobic systems (UBR-A) were operated under different internal recycle ratios (R) of 3 and 4 in both modes. Performance of the UBR-A system was sensitive to R, particularly in suspended-growth. The denitrification efficiency (ηD) and nitrate removal rates in this mode were significantly lower (p < 0.05) at R= 4 compared to R= 3 with both real DFW and SWW. With DFW, this was observed despite a higher COD/NO3-N of 20–50. In integrated fixed-film, ηD at R= 4 significantly improved to ∼95 % with both feeds. Whereas a COD/NO3-N > 9 was required to offset the imbalance caused by increased NO3-N loading at R= 4. Modeling of the denitrification potential controlled by R (PD-IR) and COD availability (PD-COD) showed that denitrification reciprocated with PD-IR. From the multiple regression analysis, nitrate removal was linearly correlated with growth medium, R, and wastewater type (p < 0.00001) accounting for 43 % of the variation. Nitrification efficiency was consistently higher > 90 % under all conditions but specific nitrification rates nearly doubled in integrated fixed-film mode. Correspondingly, the total nitrogen removal increased from 67 % to 80 % in DFW-system and 59–84 % in SWW-system at R= 4 compared to suspended growth at the same R. The study results add to the understanding of integrated media in BNR processes for high-strength wastewater treatment.

Novel nitrogen removal process in marine aquaculture wastewater treatment using Enteromorpha ferment liquid as carbon

The process performance of partial denitrification of a novel anaerobic fermentation integrated fixed-film activated sludge (IFAS-AFPD) of Enteromorpha was studied. The response surface method was used to determine the optimal reaction conditions, and the operation experiment was carried out under the optimal conditions. The results showed that the nitrogen removal effect was the best when the salinity was 12.2 g•L−1, the Carbon-Nitrogen ratio (C/N) was 4, the pH was 8.5, and the Nitrite Accumulation Rate, Nitrate Removal Rate, Chemical Oxygen Demand Utilization Rate could reach 77%, 89% and 51%. Experimental results have shown that the NAR of the Enteromorpha ferment liquid system could be maintained at about 74%, which was noteworthy higher than that of the sodium acetate (CH3COONa) system at 42%; Microbial community analysis showed that Enteromorpha ferment liquid was more beneficial to the growth of Bacteroidetes than CH3COONa.

Microbial nitrate reduction in propane- or butane-based membrane biofilm reactors under oxygen-limiting conditions

Nitrate contamination has been commonly detected in water environments and poses serious hazards to human health. Previously methane was proposed as a promising electron donor to remove nitrate from contaminated water. Compared with pure methane, natural gas, which not only contains methane but also other short chain gaseous alkanes (SCGAs), is less expensive and more widely available, representing a more attractive electron source for removing oxidized contaminants. However, it remains unknown if these SCGAs can be utilized as electron donors for nitrate reduction. Here, two lab-scale membrane biofilm reactors (MBfRs) separately supplied with propane and butane were operated under oxygen-limiting conditions to test its feasibility of microbial nitrate reduction. Long-term performance suggested nitrate could be continuously removed at a rate of ∼40–50 mg N/L/d using propane/butane as electron donors. In the absence of propane/butane, nitrate removal rates significantly decreased both in the long-term operation (∼2–10 and ∼4–9 mg N/L/d for propane- and butane-based MBfRs, respectively) and batch tests, indicating nitrate bio-reduction was driven by propane/butane. The consumption rates of nitrate and propane/butane dramatically decreased under anaerobic conditions, but recovered after resupplying limited oxygen, suggesting oxygen was an essential triggering factor for propane/butane-based nitrate reduction. High-throughput sequencing targeting 16S rRNA, bmoX and narG genes indicated Mycobacterium/Rhodococcus/Thauera were the potential microorganisms oxidizing propane/butane, while various denitrifiers (e.g. Dechloromonas, Denitratisoma, Zoogloea, Acidovorax, Variovorax, Pseudogulbenkiania and Rhodanobacter) might perform nitrate reduction in the biofilms. Our findings provide evidence to link SCGA oxidation with nitrate reduction under oxygen-limiting conditions and may ultimately facilitate the design of cost-effective techniques for ex-situ groundwater remediation using natural gas.

Biomass-sulfur-based mixotrophic denitrification (BSMD) process for synthetic and real wastewater treatment: Engineering application, applicable scope, and operational strategy

Elemental-sulfur-driven autotrophic denitrification (ESDAD) process is widely used in sewage treatment, while its low denitrification capacity has become the bottleneck of this technology. The biomass-sulfur-based mixotrophic denitrification (BSMD) process is a promising denitrification pathway to improve nitrate removal of sewage. Based on previous research, a comparative analysis of the ESDAD and BSMD processes was adopted in this study. Then, three lab-scale reactors were constructed with various BSMD filters to investigate the characteristics of the BSMD process, and the optimal BSMD filter (F3) with the nitrate removal rate (NRR) of 556 ± 13.6 mg NO3–-N·L−1·d−1 was 3:1:1 by weight ratio of sulfur powder to rice straw powder to shell powder. Additionally, a pilot-scale reactor (volume: 1000 L) filled with filter F3 was designed and operated to treat the effluent of a municipal secondary tank. The feasibility of the BSMD process in engineering application was demonstrated, accompanied by a desirable treatment capacity (hydraulic retention time (HRT) ≤ 1 h) under varying conditions. Moreover, autotrophs and heterotrophs co-existed along the pilot-scale reactor, and the autotrophs remained dominant at seasonal temperatures. In general, the prospect of the BSMD is attractive, and the outcomes of this study could provide guidance for the operation of the BSMD process.

Application of Chlorella vulgaris for nutrient removal from synthetic wastewater and MBR-treated bio-park secondary effluent: growth kinetics, effects of carbon and phosphate concentrations

Application of Chlorella vulgaris for polishing secondary effluent of a wastewater treatment (containing C, N and P) was investigated. As a first step, batch experiments were conducted in Bold's Basal Media (BBM) to quantify the effects of orthophosphates (0.1-107mg/L), organic carbon (0-500mg/L as acetate) and N/P ratio on the growth of Chlorella vulgaris. The results revealed that the orthophosphate concentration was found to control the removal rates of nitrates and phosphates; however, both were effectively removed (> 90%) when the initial orthophosphate concentration was 4-12mg/L. The maximum nitrate and orthophosphate removals were observed at an N:P ratio of ~ 11. However, the specific growth rate (µ) was significantly increased (from 0.226 to 0.336g/g/day) when the initial orthophosphate concentration was 0.1-4.3mg/L. On the other hand, the presence of acetate had significantly improved the specific growth and specific nitrate removal rates of Chlorella vulgaris. The specific growth rate increased from 0.34g/g/day in a purely autotrophic culture to 0.70g/g/day in the presence of acetate. Subsequently, the Chlorella vulgaris (grown in BBM) was acclimated and grown in the membrane bioreactor (MBR)-treated real-time secondary effluent. Under the optimised conditions, 92% nitrate and 98% phosphate removals (with a growth rate of 0.192g/g/day) were observed in the bio-park MBR effluent. Overall, the results indicate that coupling Chlorella vulgaris as a polishing treatment in existing wastewater treatment units could be beneficial for highest level of water reuse and energy recovery goals.

Application of Membrane Processes for Nitrate (NO3-) Removal

Background: The primary sources of nitrate contamination in groundwater resources are excessive fertilizer use and unregulated land discharges of treated wastewater. Due to its harmful nature to human health and its contribution to eutrophication, the removal of nitrate from water has been of great interest in the last decades. Various techniques, such as adsorption, ion exchange, catalytic and biological denitrification, and membrane processes, have been applied for NO3 - removal. Objective: In this review study, the removal of NO3 - by membrane processes, including electrodialysis (ED), electrodeionization (EDI), reverse osmosis (RO), and ultrafiltration, has been reviewed. Method: The pressure-driven membrane and electro-membrane processes applications to NO3 - removal have been reviewed. Results: The effects of process parameters, interferences, and limitations of membrane processes have been summarized. Conclusion: Membrane processes could be a promising alternative for NO3 - removal. After suitable membrane preparation/modification, the nitrate removal rate could reach &gt;99%.

Nutrient uptake and biomass productivity performance comparison among freshwater filamentous algae species on mesocosm-scale FANS under ambient summer and winter conditions

Filamentous algae nutrient scrubbers (FANS) have demonstrated potential for cost-effective and sustainable nutrient bioremediation of a wide range of polluted waters. Their performance depends on the rate at which the algae can assimilate nutrients from the water and produce biomass. This study investigated the growth rates and nutrient uptake rates of four locally isolated filamentous algae species (Cladophora sp., Oedogonium sp., Rhizoclonium sp., and Spirogyra sp.) cultivated with nutrient enriched freshwater with a concentration of 2 mg L−1 of nitrate and 0.2 mg L−1 of phosphate under ambient summer and winter conditions to identify target species for use on FANS. Variation in environmental conditions had a large effect on the performance of each species. Biomass productivity of the four species ranged from 1.2 to 4.5 g DW m−2.d in summer and 0.7 to 1.6 g DW m−2.d in winter. Nutrient removal rates ranged from 0.39 to 0.51 g NO3 m−2.d and 0.16 to 0.18 g PO4 m−2.d in summer and 0.32 to 0.51 g NO3 m−2.d and 0.08 to 0.09 g PO4 m−2.d in winter. Overall, Oedogonium sp. was the best performer of the four species tested, with the highest biomass productivity (mean 4.5 g DW m−2.d in summer; 1.6 g DW m−2.d in winter) and the highest nitrate removal rates under summer (mean 0.51 g NO3 m−2.d) and winter (mean 0.51 g NO3 m−2.d) conditions. Furthermore, Oedogonium sp. FANS had the lowest contamination in terms of percentage cover of non-target species compared to the other three species under both summer and winter conditions. These results demonstrate that Oedogonium sp. has higher tolerance than the other three species to summer and winter ambient temperature and light variation, allowing Oedogonium sp. to maintain dominance on the floway for a longer period. For these reasons, Oedogonium sp. is identified as a promising target for year-round cultivation on FANS.

Efficient nitrogen removal through coupling biochar with zero-valent iron by different packing modes in bioretention system

Three kinds of bioretention were designed to explore the effects of zero-valent iron (ZVI) and biochar on the nitrogen removal performance and to seek a more reasonable packing method in this study. The results showed that the effluent removal rates of nitrate, ammonium and total nitrogen were 53.30 ± 12.68%, 98.41 ± 0.38% and 64.03 ± 8.72% respectively in Bioretention-3 during the rainfall events, while the nitrate concentration decreased gradually with the increase of drying time. According to the batch experiment, it was found that zero-valent iron could release continuously and stably in Bioretention-3 and Bioretention-1 due to the interception effect of biochar on dissolved oxygen. In addition, biochar in soil layer could protect zero-valent iron from excessive oxidation while biochar in the substrate layer could release organic matter to promote heterotrophic denitrification. Microbial community analysis showed that the dominant phyla were Proteobacteria (20.92–40.81%) and Actinobacteriota (9.89–24.54%). The dominant nitrifying genera was Nitrospira while there were also aerobic denitrifying bacteria (Sphingomonas, Bradyrhizobium and Chryseolinea, etc.) in soil layer. In the substrate layer, there was more ferrous iron-mediated autotrophic denitrification process (Thiobacillus, Geobacter and Denitratisoma, etc.) in Bioretention-1 and Bioretention-3 while a larger proportion of Dissimilatory Nitrate Reduction to Ammonium process (DNRA) (Bacillus, Desulfovibrio and Pseudomonas, etc.) in Bioretention-2. In general, this study showed that biochar addition in soil coupled with mixing zero-valent iron and biochar as substrate layer was a more stable and efficient design through various aspects of evidence. It provides a new way for how to use zero-valent iron and biochar to improve nitrogen removal capacity in stormwater management.

Simultaneous dairy wastewater treatment and bioelectricity production in a new microbial fuel cell using photosynthetic Synechococcus.

Photosynthetic microbial fuel cell (PMFC) is a novel technology, which employs organic pollutants and organisms to produce electrons and biomass and capture CO2 by bio-reactions. In this study, a new PMFC was developed based on Synechococcus sp. as a biocathode, and dairy wastewater was used in the anode chamber. Different experiments including batch feed mode, semi-continuous feed mode, Synechococcus feedstock to the anode chamber, Synechococcus-Chlorella mixed system, the feedstock of treated wastewater to the cathode chamber, and use of extra nutrients in the anodic chamber were performed to investigate the behavior of the PMFC system. The results indicated that the PMFC with a semi-continuous feed mode is more effective than a batch mode for electricity generation and pollutant removal. Herein, maximum power density, chemical oxygen demand removal, and Coulombic efficiency were 6.95 mW/m2 (450 Ω internal resistance), 62.94, and 43.16%, respectively, through mixing Synechococcus sp. and Chlorella algae in the batch-fed mode. The maximum nitrate and orthophosphate removal rates were 98.83 and 68.5%, respectively, wherein treated wastewater in the anode was added to the cathode. No significant difference in Synechococcus growth rate was found between the cathodic chamber of PMFC and the control cultivation cell. The heating value of the biocathode biomass at maximum Synechococcus growth rate (adding glucose into the anode chamber) was 0.2235MJ/Kg, indicating the cell's high ability for carbon dioxide recovery. This study investigated not only simultaneous bioelectricity production and dairy wastewater in a new PMFC using Synechococcus sp. but also studied several operational parameters and presented useful information about their effect on PMFC performance.

Electrochemical Mechanisms and Optimization System of Nitrate Removal from Groundwater by Polymetallic Nanoelectrodes.

Zn-Cu-TiO2 polymetallic nanoelectrodes were developed using Ti electrodes as the substrate. The reaction performance and pollutant removal mechanism of the electrodes were studied for different technological conditions by analyzing the electrochemical properties of the electrodes in the electrochemical system, using Ti, TiO2, Cu-TiO2, and Zn-Cu-TiO2 electrodes as cathodes and Pt as the anode. The Tafel curve was used for measuring the corrosion rate of the electrode. The Tafel curve resistance of the Zn-Cu-TiO2 polymetallic nanoelectrode was the smallest, so the Zn-Cu-TiO2 nanoelectrode was the least prone to corrosion. The electrode reaction parameters were determined using cyclic voltammetry (CV). Zn-Cu-TiO2 polymetallic nanoelectrodes have the lowest peak position and the highest electrochemical activity. The surface area of the electrode was determined by the time-current (CA) method, and it was found that the Zn-Cu-TiO2 polymetallic nanoelectrode had a larger surface area and the highest removal rate of nitrate. The Ti, TiO2, Cu-TiO2, and Zn-Cu-TiO2 electrodes also had higher removal rates for real groundwater, and the differences between the removal rates of nitrates for deionized water and real groundwater decreased as removal time increased. The Zn-Cu-TiO2 polymetallic nanoelectrode exhibited the highest removal rate for real groundwater. This study reveals the reaction mechanism of the cathode reduction of nitrate, which provides the basis for constructing electrochemical reactors and its application in treating nitrate-contaminated groundwater. A mathematical model of optimized working conditions was created by the response surface method, and optimum time, NaCl concentration, and current density were 93.39 min, 0.22 g/L, and 38.34 mA/cm2, respectively. Under these optimal conditions, the nitration removal rate and ammonium nitrogen generation in the process solution were 100% and 0.00 mg/L, respectively.

Quaternary ammonium-functionalized UiO-66-Sal as an efficient and fast adsorbent for nitrate removal from water

UiO-66-Sal as modified form of UiO-66-NH2 was prepared by post-synthesis procedure and functionalized by dimethyl dodecyl[3-(trimethoxysilyl)propyl] ammonium chloride (DMDAC) as the quaternium agent prepared by the reaction between (3-chloropropyl) trimethoxysilane and N, N -dimethyl dodecyl amine. The sample was characterized by BET, XRD, FT-IR, SEM, EDS, TEM, and TGA/DTA equipments and applied as the adsorbent for nitrate removal from aqueous solution. Batch experiments were carried out in different conditions to study adsorption efficiency and rate of nitrate removal. The quaternized UiO-66-Sal demonstrated high efficiency and fast rate for nitrate removal. Maximum efficiency using 1 g/l of the adsorbent was 96% in neutral pH after 60 min. Based on the results of characterization techniques, it was found high amount of loading quaternium agent on the surface of UiO-66-Sal as the efficient factor for nitrate removal and also the synergetic effects between the modified MOF and quaternized agent. It was found that anion exchange through quaternized ammonium agent as non-specific adsorption and inner-sphere complexation in aqueous solution as specific adsorption were two mechanisms of nitrate uptake in quaternized UiO-66-Sal. It was also observed that the anion with the lower hydration energy exhibits more adsorption during the competition with the nitrate anion.

Experimental and economic evaluation of nitrate removal by a nanofiltration membrane.

Membrane nanofiltration (NF) process was employed to remove nitrate from synthetic and natural waters. The optimum technical and economic ranges of governing parameters for the water treatment process were determined using central composite design method and Verbernen's economic model. The results of nitrate removal from synthesized water showed the minimum and maximum rates of permeation were 16.5 and 84.3 L/m2h (LMH), respectively. The minimum and maximum nitrate rejection were 44.1% and 78.4%, respectively. Increasing pH had no significant effect on permeation flux but increased the nitrate removal rate. Additionally, as pressure was increased, the nitrate rejection and permeation flux both increased; but, as temperature was increased, the permeation flux increased while the nitrate removal decreased. In the case of natural water, the minimum and the maximum flow rate were 7.7 and 68.1 LMH. Furthermore, the minimum and maximum rejection rates of nitrate were 22.1% and 74.8%. The effects of variables on the permeation flux and nitrate removal for natural water were similar to those for synthetic water. However, by increasing pH, the amount of water passing through the membrane decreased. In all experiments, natural water had less permeation flux and less nitrate rejection than synthesized water. The presence of other anions and cations in the natural water decreases the amount of the nitrate removed. The total investment cost reduced as the pressure increased. The cost per m3 of treated water decreased from 3 to 7 bars, then increased as the pressure increased.

Can Woodchip Bioreactors Be Used at a Catchment Scale? Nitrate Performance and Sediment Considerations

Highlights Novel three-bed, cascading-inlet bioreactor treated agricultural drainage from a 249-ha catchment. Nitrate removal rates and load reduction efficiencies were similar to those of traditional single-field bioreactors. Sedimentation problems reduced bed life; a sediment sensing and exclusion system solved them. This scale provides opportunities for centralized management and nutrient reduction verification. Abstract. Denitrifying bioreactors, a structural practice deployed at the field scale to meet water quality goals, have been underutilized and require additional evaluation at the small catchment scale. The objective of this study was to quantify the performance of a large, multi-bed denitrifying bioreactor system sized to treat agricultural drainage runoff (combined drainage discharge and surface runoff) from a 249-ha catchment. Three woodchip bioreactor beds, 7.6 m wide by 41 m long by 1.5 m deep, with cascading inlets, were constructed in 2016 in southern Minnesota, U.S. The beds received runoff for one water year from a catchment area that is 91% tile-drained row crops, primarily maize and soybeans. Initial woodchip quality differed among the three beds, affecting flow and nitrate removal rates. Bioreactor flow was unimpeded by sediment for twelve events from September 2016 to July 2017, during which time 55% of the discharge from the catchment was treated in the bioreactor beds. Average daily nitrate removal rates ranged from 2.5 to 6.5 g-N m-3 d-1 for the three bioreactor beds, with nitrate-N load removal of flow through the beds between 19% and 27%. When accounting for untreated by-pass flow, the overall nitrate-N removal of the multi-bed system was 12.5% (713 kg N). During high-flow events, incoming sediment clogged the reactor beds, decreasing their performance. There was 4,520 kg of sediment trapped in one bed, and evidence suggests the other two trapped a similar load. To solve this problem and prolong the bioreactor’s lifespan, we installed a shutoff gate that activated when inflow turbidity exceeded a threshold value. Finally, the findings indicate that catchment-scale denitrifying bioreactors can successfully remove nitrate load from agricultural runoff, but sediment-prevention measures may be required to extend the bioreactor's lifespan. Keywords: Bioreactor, Denitrification, Nitrate removal, Sedimentation, Subsurface drainage.

Boosting light harvesting and charge separation over hollow double-shelled Ag@SrTiO3-TiO2 with Z-scheme heterostructure for highly efficient photocatalytic reduction of nitrate to N2

Hollow double-shelled Ag@SrTiO3-TiO2 with Z-scheme heterostructure was constructed for highly efficient photocatalytic reduction of nitrate to N2. The 3D finite-difference-time-domain analysis indicated that hollow double-shelled structure improved light harvesting due to multiple reflections. Photo-generated electrons transfer from SrTiO3 to Ag0 caused by electron sink effect were utilized to reduce nitrate, while photo-generated electrons of TiO2 migrated to SrTiO3 via transport bridge of Ti3+ defects for electron–hole recombination. Such charge carriers migration pathway facilitated the construction of Z-scheme heterostructure, which enhanced charge separation yet still retained high redox powers. Both photogenerated electrons and CO2− played important role in photocatalytic denitrification. Furthermore, Ag0 acted as co-catalyst which not only promoted photogenerated electrons transfer to nitrate but also enhanced nitrate conversion selectivity to N2. Combining the above advantages, nitrate removal rate and the nitrogen selectivity reached 97.2 % and 98.8 % within 60 min, respectively. Even after five cycles, it still remained satisfied photocatalytic activity and stability. In summary, this work proposed a feasible strategy to construct Z-scheme hollow double-shelled photocatalyst for efficient photocatalytic denitrification.

Nitrate removal rates, isotopic fractionation, and denitrifying bacteria in a woodchip-based permeable reactive barrier system: a long-term column experiment.

This study evaluated the effectiveness of using organic carbon materials (i.e., woodchips) to remove nitrate from groundwater. The results of our flow-through column experiment, which was conducted over 1.6years, suggested that denitrifying bacteria reduce nitrate by using it as an electron acceptor and woodchips as an electron donor. The nitrate removal rates were sufficiently high (0.39-1.04mmol L-1day-1) during the operation of the column. Denitrification process was supported by fractionation of nitrogen and oxygen isotopes (δ15N and δ18O), with the δ15N and δ18O values enriched from 7.4‰ and 22.3‰ to 21.2‰ and 30.4‰, respectively. Enrichment factors ([Formula: see text]) for 15N and 18O were calculated using the Rayleigh fractionation model, with values of - 13.2‰ for ε15N and - 7.1‰ for ε18O. The fractionation ratio of 15N to 18O was 1.9:1, confirming denitrification. The most abundant bacterial genera in the soil used for inoculation were Enterobacter (86.7%), Nitrospira (1.8%), and Arthrobacter (1.5%), while those in the column effluent were Macrococcus (37.1%), Escherichia (14.7%), and Shigella (14.6%), indicating that bacterial communities changed in response to geochemical conditions in the column. This study suggests that nitrate in groundwater can be effectively removed using woodchip-based passive treatment systems and that information on isotopic fractionation and denitrifying bacteria can be key tools to understand denitrification.

Iron Nanoparticles Protected by Chainmail-structured Graphene for Durable Electrocatalytic Nitrate Reduction to Nitrogen.

The electrochemical nitrate reduction reaction (NO3 RR) is an appealing technology for regulating the nitrogen cycle. Metallic iron is one of the well-known electrocatalysts for NO3 RR, but it suffers from poor durability due to leaching and oxidation of iron during the electrocatalytic process. In this work, a graphene-nanochainmail-protected iron nanoparticle (Fe@Gnc) electrocatalyst is reported. It displays superior nitrate removal efficiency and high nitrogen selectivity. Notably, the catalyst delivers exceptional stability and durability, with the nitrate removal rate and nitrogen selectivity remained ≈96 % of that of the first time after up to 40 cycles (24 h for one cycle). As expected, the conductive graphene nanochainmail provides robust protection for the internal iron active sites, allowing Fe@Gnc to maintain its long-lasting electrochemical nitrate catalytic activity. This research proposes a workable solution for the scientific challenge of poor lasting ability of iron-based electrocatalysts in large-scale industrialization.

Iron Nanoparticles Protected by Chainmail‐structured Graphene for Durable Electrocatalytic Nitrate Reduction to Nitrogen

AbstractThe electrochemical nitrate reduction reaction (NO3RR) is an appealing technology for regulating the nitrogen cycle. Metallic iron is one of the well‐known electrocatalysts for NO3RR, but it suffers from poor durability due to leaching and oxidation of iron during the electrocatalytic process. In this work, a graphene‐nanochainmail‐protected iron nanoparticle (Fe@Gnc) electrocatalyst is reported. It displays superior nitrate removal efficiency and high nitrogen selectivity. Notably, the catalyst delivers exceptional stability and durability, with the nitrate removal rate and nitrogen selectivity remained ≈96 % of that of the first time after up to 40 cycles (24 h for one cycle). As expected, the conductive graphene nanochainmail provides robust protection for the internal iron active sites, allowing Fe@Gnc to maintain its long‐lasting electrochemical nitrate catalytic activity. This research proposes a workable solution for the scientific challenge of poor lasting ability of iron‐based electrocatalysts in large‐scale industrialization.

Solid-phase denitrification and denitritation of swine manure-contaminated waters: Bioreactor performance and microbial community profiles

Waste streams from livestock facilities contribute to water contamination by nitrogenous compounds and a feasible approach for their treatment is needed. In this work, a microbial culture, originally developed for anoxic biodegradation of naphthenic acids, was used in woodchip bioreactors to evaluate denitrification and denitritation in medium simulating livestock wastewaters. Effects of nitrate and nitrite concentrations (10–150 mg L−1), loading rate (0.8–2000.2 mg L−1 day−1), manure content (0–10%), and residence time (0.04–11.26 day) on the performance of bioreactors operated with nitrate, nitrite or their mixture were investigated. The highest nitrate removal rates for nitrate alone were achieved at loading rates of 1000–1500 mg L−1 day−1 and 9–10% manure (removal rate ≥ 400 mg L−1 day−1), and for nitrate in mixture at 775–1150 mg L−1 day−1 and 7–10% manure (removal rate ≥ 350 mg L−1 day−1). For nitrite alone, these were 1000–1500 mg L−1 day−1 and 0–2% manure (removal rate ≥500 mg L−1 day−1) and 600–850 mg L−1 day−1 and 5–10% manure (removal rate ≥ 300 mg L−1 day−1) for nitrite in mixture. High nitrite concentration (75–100 mg L−1) negatively impacted its removal rate in mixture with nitrate or alone. Bioreactors microbial profiles were different from each other and from the stock cultures. Cloacimonetes, Firmicutes, and Proteobacteria phyla were prevalent in all bioreactors, but Bacteroidetes was seen only in the nitrate and nitrite bioreactors. At the class level, Candidatus cloacamonas, Thiomicrospira and Pseudomonas were seen in all bioreactors but Acidovorax and Comamonas were significant only in the nitrite bioreactor.