Addition Of Nitrate Research Articles

Nitrogen Addition Affects Ecosystem Carbon Exchange by Regulating Plant Community Assembly and Altering Soil Properties in an Alpine Meadow on the Qinghai-Tibetan Plateau.

Nitrogen (N) deposition can affect the global ecosystem carbon balance. However, how plant community assembly regulates the ecosystem carbon exchange in response to the N deposition remains largely unclear, especially in alpine meadows. In this study, we conducted a manipulative experiment to examine the impacts of N (ammonium nitrate) addition on ecosystem carbon dioxide (CO2) exchange by changing the plant community assembly and soil properties at an alpine meadow site on the Qinghai–Tibetan Plateau from 2014 to 2018. The N-addition treatments were N0, N7, N20, and N40 (0, 7, 20, and 40 kg N ha–1year–1) during the plant growing season. The net ecosystem CO2 exchange (NEE), gross ecosystem productivity (GEP), and ecosystem respiration (ER) were measured by a static chamber method. Our results showed that the growing-season NEE, ER and GEP increased gradually over time with increasing N-addition rates. On average, the NEE increased significantly by 55.6 and 65.2% in N20 and N40, respectively (p < 0.05). Nitrogen addition also increased forage grass biomass (GB, including sedge and Gramineae) by 74.3 and 122.9% and forb biomass (FB) by 73.4 and 51.4% in N20 and N40, respectively (p < 0.05). There were positive correlations between CO2 fluxes (NEE and GEP) and GB (p < 0.01), and the ER was positively correlated with functional group biomass (GB and FB) and soil available N content (NO3––N and NH4+–N) (p < 0.01). The N-induced shift in the plant community assembly was primarily responsible for the increase in NEE. The increase in GB mainly contributed to the N stimulation of NEE, and FB and the soil available N content had positive effects on ER in response to N addition. Our results highlight that the plant community assembly is critical in regulating the ecosystem carbon exchange response to the N deposition in alpine ecosystems.

Investigations of the Thermal Parameters of Hybrid Sol–Gel Coatings Using Nondestructive Photothermal Techniques

This article presents the results of comparative investigations of thermal parameters of hybrid sol–gel coatings (named TMZ) prepared from tetraethyl orthosilicate and organically modified 3-methacryloxypropyltrimethoxysilane. The coatings were prepared with the addition of zirconium(IV) tetrapropoxide chelated with methacrylic acid. Two series of samples were investigated: the first series, TMZ-I, TMZ-II and TMZ-III, with different amounts of zirconium, and the second series, TMZ-I/Ce, TMZ-II/Ce and TMZ-III/Ce, with the addition of cerium nitrate. The influence of the amount of zirconium and cerium on the thermal parameters of the sol–gel coatings was next analyzed. Two non-destructive and photothermal techniques were used for this purpose: photothermal radiometry (PTR) and beam deflection spectroscopy (BDS). The thermal diffusivity and conductivity of the coatings were extracted from the frequency experiments and are presented and discussed. The two-layer model was applied to interpret the photothermal spectra. The results obtained using these two techniques are compared and discussed.

Value-added utilization of silicon and iron in copper smelting slag

ABSTRACT The methodology enhanced by synergic catalyzation with sodium nitrate and ultrasonic irradiation under alkaline leaching condition at atmospheric pressure was proposed, for separating silicon and iron in acid leaching residue of copper smelting slag. And the preparation of white carbon black from the alkaline leachate obtained was conducted for utilizing the silicon in the copper smelting slag, as well as the alkaline leaching residue can be used as raw materials with high quality for iron making. The effects of leaching temperature, sodium hydroxide concentration, ultrasonic power, stirring speed, liquid-solid ratio, leaching time and additional amount of sodium nitrate on silica leaching rate were studied. The leaching kinetics of SiO2 from the acid leaching residue of copper smelting slag was also studied. The results showed that under the optimal leaching conditions of temperature 130°C, sodium hydroxide concentration 20 wt.%, ultrasonic power 315 W, stirring rate 500 rpm, liquid-solid ratio 6 mL/g, leaching time 60 min and sodium nitrate addition 2.5 g, the leaching rate of SiO2 reached 94.5 wt.%. Among 90 ~ 130°C, the leaching process was controlled by diffusion and consistent with Johnson Mehl Avrami. The quality of white carbon black prepared was of meeting grade A in Chinese national standard.

Long-term and seasonal nitrate trends illustrate potential prevention of large cyanobacterial biomass by sediment oxidation in Hamilton Harbour, Lake Ontario

Several studies have shown that large, experimental additions of nitrate (NO3) to eutrophic systems can mitigate large populations of nuisance cyanobacteria and that high NO3 concentrations can oxidize anoxic sediments. These studies are consistent with observations from numerous aquatic systems across a broad trophic range showing development of reduced surficial sediments precedes the formation of large cyanobacteria populations. We use 50+ years of data to explore whether high NO3 concentrations may have been instrumental both in the absence of large populations of cyanobacteria in eutrophic Hamilton Harbour, Lake Ontario in the 1970s when total phosphorus (TP) and total nitrogen (TN) concentrations were high, and in delaying large populations until August and September in recent decades despite much lower TP and TN. Our results indicate that large cyanobacteria population events do not occur at the central station in July-September when epilimnetic NO3 > 2.2 mg N L−1. The results further suggest that remedial improvements to wastewater treatment plant oxidation capacity may have been inadvertently responsible for high NO3 concentrations > 2.2 mg N L−1 and thus for mitigating large cyanobacteria populations. This also implies that large cyanobacteria populations may form earlier in the summer if NO3 concentrations are lowered.

Enhanced CO2 capture over Li-containing β-NaFeO2 materials: Effect of lithium nitrate addition

Herein, we present a feasible methodology for the improvement of the CO2 capture properties of sodium-ferrite-based materials through the addition of lithium nitrate. Initially, the pristine material (β-NaFeO2) was synthetized through the nitrate pyrolysis method and then it was mechanically mixed with different amounts of LiNO3 (2.5, 5, 10, 15 and 25 mol% of lithium). Materials were structural and microstructurally characterized and the CO2 capture properties were evaluated through TGA analyses, using two different approaches; dynamic and isothermal tests. Result show that the best CO2 capture performance is achieved in the sample containing 5 mol% of lithium nitrate, identified as 5Li-NaFeO2. The CO2 capture enhancement resulted from the formation of a LiNO3-Na2CO3 eutectic phase, acting as a liquid carrier and promoting the surface and bulk carbonation of the sodium ferrite particles. In fact, the 5Li-NaFeO2 dioxide capture enhancement was reflected by increasing the amount of CO2 captured as well as by reducing the temperature range of capture, compared to the pristine β-NaFeO2 material.

Methanotrophy Alleviates Nitrogen Constraint of Carbon Turnover by Rice Root-Associated Microbiomes.

The bioavailability of nitrogen constrains primary productivity, and ecosystem stoichiometry implies stimulation of N2 fixation in association with carbon sequestration in hotspots such as paddy soils. In this study, we show that N2 fixation was triggered by methane oxidation and the methanotrophs serve as microbial engines driving the turnover of carbon and nitrogen in rice roots. 15N2-stable isotope probing showed that N2-fixing activity was stimulated 160-fold by CH4 oxidation from 0.27 to 43.3 μmol N g–1 dry weight root biomass, and approximately 42.5% of the fixed N existed in the form of 15N-NH4+ through microbial mineralization. Nitrate amendment almost completely abolished N2 fixation. Ecophysiology flux measurement indicated that methane oxidation-induced N2 fixation contributed only 1.9% of total nitrogen, whereas methanotrophy-primed mineralization accounted for 21.7% of total nitrogen to facilitate root carbon turnover. DNA-based stable isotope probing further indicated that gammaproteobacterial Methylomonas-like methanotrophs dominated N2 fixation in CH4-consuming roots, whereas nitrate addition resulted in the shift of the active population to alphaproteobacterial Methylocystis-like methanotrophs. Co-occurring pattern analysis of active microbial community further suggested that a number of keystone taxa could have played a major role in nitrogen acquisition through root decomposition and N2 fixation to facilitate nutrient cycling while maintaining soil productivity. This study thus highlights the importance of root-associated methanotrophs as both biofilters of greenhouse gas methane and microbial engines of bioavailable nitrogen for rice growth.

Effect of remediation reagents on bacterial composition and ecological function in black-odorous water sediments

Black-odorous urban water bodies and sediments pose a serious environmental problem. In this study, we conducted microcosm batch experiments to investigate the effect of remediation reagents (magnesium hydroxide and calcium nitrate) on native bacterial communities and their ecological functions in the black-odorous sediment of urban water. The dominant phyla (Proteobacteria, Actinobacteria, Chloroflexi, and Planctomycetes) and classes (Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria, Actinobacteria, Anaerolineae, and Planctomycetia) were determined under calcium nitrate and magnesium hydroxide treatments. Functional groups related to aerobic metabolism, including aerobic chemoheterotrophy, dark sulfide oxidation, and correlated dominant genera (Thiobacillus, Lysobacter, Gp16, and Gaiella) became more abundant under calcium nitrate treatment, whereas functional genes potentially involved in dissimilatory sulfate reduction became less abundant. The relative abundance of chloroplasts, fermentation, and correlated genera (Desulfomonile and unclassified Cyanobacteria) decreased under magnesium hydroxide treatment. Overall, these results indicated that calcium nitrate addition improved hypoxia-related reducing conditions in the sediment and promoted aerobic chemoheterotrophy.

Iron release and characteristics of corrosion scales and bacterial communities in drinking water supply pipes of different materials with varied nitrate concentrations

Changes of drinking water quality can lead to iron release in drinking water distribution systems (DWDSs), which is one of the most important reasons for the deterioration of tap water quality. The objective of this study was to investigate the effects of nitrate on the iron release and characteristics of corrosion scales and bacterial communities in DWDSs using simplified pipe section reactors. With nitrate addition, the percentages of goethite (α-FeOOH), hematite (Fe2O3), and lepidocrocite (γ-FeOOH) in scales were decreased, whereas those of magnetite (Fe3O4) were increased. The growth of nitrate-reducing bacteria (NRB) was promoted significantly, with the fractions of 25.70% and 23.79% in the steel and cast iron pipes, respectively. Approximately 3.40% of iron-reducing bacteria (IRB) were reduced in both pipes. Moreover, under higher nitrate levels, iron release was inhibited obviously. The maximum decreased percentages of total iron in the steel and cast iron pipes were 44.90% (with 10.00 mg/L NO3−-N) and 88.29% (with 30.00 mg/L NO3−-N), respectively. This study may be helpful for improving drinking water supply safety.

Comparison of Syngas-Fermenting Clostridia in Stirred-Tank Bioreactors and the Effects of Varying Syngas Impurities.

In recent years, syngas fermentation has emerged as a promising means for the production of fuels and platform chemicals, with a variety of acetogens efficiently converting CO-rich gases to ethanol. However, the feasibility of syngas fermentation processes is related to the occurrence of syngas impurities such as NH3, H2S, and NOX. Therefore, the effects of defined additions of NH4+, H2S, and NO3− were studied in autotrophic batch processes with C. autoethanogenum, C. ljungdahlii, and C. ragsdalei while applying continuously gassed stirred-tank bioreactors. Any initial addition of ammonium and nitrate curbed the cell growth of the Clostridia being studied and reduced the final alcohol concentrations. C. ljungdahlii showed the highest tolerance to ammonium and nitrate, whereas C. ragsdalei was even positively influenced by the presence of 0.1 g L−1 H2S. Quantitative goals for the purification of syngas were identified for each of the acetogens studied in the used experimental setup. Syngas purification should in particular focus on the NOX impurities that caused the highest inhibiting effect and maintain the concentrations of NH3 and H2S within an acceptable range (e.g., NH3 < 4560 ppm and H2S < 108 ppm) in order to avoid inhibition through the accumulation of these impurities in the bioreactor.

Gamma radiation shielding performance and physico-chemical properties of poly (vinyl alcohol)/Cd(NO3)2 composite films

Abstract To improve a radiation shielding performance of the polymer composite, poly (vinyl alcohol) (PVA) was composited with cadmium nitrate. Its radiation shielding capabilities of PVA/Cd(NO3)2 composite films were investigated at three different Cd(NO3)2 concentration levels: 5, 10, and 15% wt. The structural, thermal, and optical properties of the synthesized composite films were examined. The addition of cadmium nitrate to the polymer worsened its thermal stability and improved its optical energy band gap by lowering its direct bandgap energy from 4.56 to 3.25 eV for PVA and PVA/15 wt% Cd(NO3)2 films, respectively. The gamma-ray shielding capacity of the composite was examined using radioactive sources including 241Am (59.5 keV),57Co (122 keV), 192Ir (346 keV) and 137Cs (662 keV). The Micro-Shielding program was used to compare the experimental results of gamma transmittance with theoretical calculations, and the results were found to be in good agreement. Radiation shielding performance of PVA/Cd(NO3)2 composite films was examined by the determination of the linear attenuation coefficient (µ), mass attenuation coefficient (µ m), half value layer (HVL) and exposure buildup factor (EBF). The reinforcement of PVA matrix with 15 wt% Cd(NO3)2 supported to increase the radiation shielding capacity by 13.7% for gamma photons of 57Co radioisotope.

Investigation and mitigation of reagent ageing during the continuous flow synthesis of patchy particles

Patchy particles, which comprise a core particle of one material partially covered by a thin layer of another, offer great promise for tailored particle-based materials and devices in the future. This study concerns the investigation and improvement of a potentially gram-scalable continuous flow process based on a cascade of two T-mixers for the synthesis of thin, conformal silver patches on colloidal silica particles. The starting point of the work is the observation that on seemingly random occasions the process results in patches having undesired spiky protrusions. Through a systematic study of reagent ageing supported by scanning electron microscopy, optical spectroscopy and chemical equilibrium calculations it can be ascertained that the desired product morphology is only obtained through carbon dioxide absorption by the dilute ammonia solution used in the reaction. It is shown that the ageing process can be emulated for fresh reagents by addition of ammonium nitrate or nitric acid.

Combined Electron Microscopy Approaches for Arterial Glycocalyx Visualization.

Mainly constituted of glycosaminoglycans and proteoglycans, the glycocalyx is anchored in the plasma membrane, covering, in particular, the extracellular face of the arterial endothelium. Due to its complex three-dimensional (3D) architecture, the glycocalyx interacts with a wide variety of proteins, contributing to vascular permeability, the flow of mechanotransduction, and the modulation of local inflammatory processes. Alterations of glycocalyx structure mediate the endothelial dysfunction and contribute to the aggravation of peripheral vascular diseases. Therefore, the exploration of its ultrastructure becomes a priority to evaluate the degree of injury under physiopathological conditions and to assess the impact of therapeutic approaches. The objective of this study was to develop innovative approaches in electron microscopy to visualize the glycocalyx at the subcellular scale. Intravenous perfusion on rats with a fixing solution containing aldehyde fixatives enriched with lanthanum ions was performed to prepare arterial samples. The addition of lanthanum nitrate in the fixing solution allowed the enhancement of the staining of the glycocalyx for transmission electron microscopy (TEM) and to detect elastic and inelastic scattered electrons, providing complementary qualitative information. The strength of scanning electron microscopy (SEM) was used on resin-embedded serial sections, allowing rapid and efficient large field imaging and previous correlative TEM observations for ultrastructural fine details. To demonstrate the dynamic feature of the glycocalyx, 3D tomography was provided by dual-beam focus-ion-beam-SEM (FIB-SEM). These approaches allowed us to visualize and characterize the ultrastructure of the pulmonary artery glycocalyx under physiological conditions and in a rat pulmonary ischemia-reperfusion model, known to induce endothelial dysfunction. This study demonstrates the feasibility of combined SEM, TEM, and FIB-SEM tomography approaches on the same sample as the multiscale visualization and the identification of structural indicators of arterial endothelial glycocalyx integrity.

Impact of nitrate addition on the resistome and mobilome from a full-scale sewer

Oxidative chemicals, such as nitrate, are periodically added to sewer systems to mitigate sulfide production and its accumulation but data are lacking on how these treatments affect sewage microbiota and alter their gene expression and mobilization. The present study investigated such effects on the biofilm of a full-scale sewer collected at two different locations, namely a pumping station and at the inlet of an urban wastewater treatment plant (WWTP), before and 15 days after nitrate dosage using a combination of culture-dependent and -independent approaches. Nitrate dosing resulted ineffective on the concentration of antibiotic-resistant Escherichia coli (AR-EC) in biofilms but greatly affected the composition of biofilm bacterial communities and the associated resistome and mobilome, especially at the pumping station where nitrate was dosed. Such responses consisted of a clear reduction on strict anaerobes; an almost twofold increase on the expression of recA gene (stress-response marker); and a significant increase on the relative abundance of most antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs). In turn, the effects of nitrate dosing at the WWTP inlet were barely visible, suggesting that they vanished into the distance from the pumping site (2.4 km). Remarkably, however, the relative abundance of both resistance and mobilization gene biomarkers at the inlet of the studied WWTP clearly oversized that at the pumping station confirming that these facilities are sinks where these resistance determinants accumulate and propagate. Considering the abundance of resistant bacteria and genes in urban sewage, the effects of dosing chemicals should be carefully assessed to lessen the load of such biological pollutants into WWTPs.

Hypolimnetic oxygenation 6. Improvement in fisheries, hydropower, and drought management with costs of installation and operation in Camanche Reservoir, California, United States

Horne AJ, Faisst WK. 2022. Hypolimnetic oxygenation 6. Improvement in fisheries, hydropower, and drought management with costs of installation and operation in Camanche Reservoir, California, United States. Lake Reserv Manage. XX:XXX–XXX. A hypolimnetic oxygenation system (HOS) was installed in Camanche Reservoir, California, in 1993 to eliminate hatchery fish kills caused by hydrogen sulfide in dam tailwaters. It operates from about June through October each year. Algae, nutrients, heavy metals, and turbidity also declined. Fall run Chinook salmon (Oncorhynchus tshawytscha) increased by 3550/yr or 265%. Threatened steelhead trout (O. mykiss), which spend more time in the river than Chinook, benefited more (625%). A 3 yr delay in elevated adult returns indicated that the HOS’s main effect was improved in-river water quality for juvenile fish, rather than better adult attraction flows. Using the California State economist’s value of $1172 for an adult Chinook to freshwater anglers, the increase due to HOS added $6.5 million/yr to California’s recreation. The in-reservoir coldwater fishery improved because dissolved oxygen in the hypolimnion increased from <1 mg/L to ∼5 mg/L. Oxygenation allowed summer operation of a 10.7 MW hydropower plant, making HOS carbon neutral. During droughts, improved water quality at lower reservoir levels reduced dependence on alternative supplies and supported full hatchery operation and in-river spawning. Oxygen addition ($0.64/kg) was much cheaper than nitrate addition ($104/kg). Averaged over 20 yr, HOS reduced phosphorus ($19.3/kg vs. alum addition at $16/kg) and ammonia/nitrate ($2/kg). Iron ($0.0005/kg) and manganese were reduced at lower cost than for conventional methods ($9/kg). Copper ($4441/kg) and zinc ($2169/kg) fell below chronic toxicity levels. Capital cost for HOS was $1.87 million in 1993 or $30,390/km2 ($1248/acre). Operation and management averaged $191,288/yr (1993–2000).

Accelerating gametophytic growth in the model hornwort Anthoceros agrestis.

PremiseHornworts belong to a unique lineage of bryophytes with critical traits for elucidating the evolution of land plants; however, the development of functional genetic tools for hornworts has been hampered by their relatively slow gametophytic growth.MethodsTo identify the external factors that influence the development of hornwort gametophytes and potentially augment their growth, we evaluated the contributions of several culture medium components on the axenic gametophytic growth of Anthoceros agrestis, a model hornwort. A streamlined growth assay utilizing semiautomated image analysis was developed to rapidly quantify and compare tissue development spanning four weeks of culture on solidified medium.ResultsThe addition of sucrose, ammonium nitrate, activated charcoal, pH buffering, and growth regulators (2,4‐dichlorophenoxyacetic acid, 6‐benzylaminopurine, and thidiazuron) affected gametophyte tissue survival, growth patterns, and the rate of thalli growth. Subsequently, an optimized medium composition and growth regimen for accelerating A. agrestis gametophytic growth were formulated, which at four weeks of culture increased the tissue wet weight by 2.1‐ to 8.5‐fold compared with other previously utilized hornwort growth media.DiscussionOur protocol for generating vigorous starting material and accelerated tissue regeneration is pertinent for advancing gene function characterization and genome editing in hornworts.

Optimal Nitrate Supplementation in Phaeodactylum tricornutum Culture Medium Increases Biomass and Fucoxanthin Production.

Phaeodactylum tricornutum is a model diatom with numerous potential applications in the industry, including the production of high-value carotenoid pigments such as fucoxanthin. This compound is a potent antioxidant currently extracted mainly from brown macroalgae. Fucoxanthin exhibits several biological properties with well-known beneficial effects in the treatment and prevention of lifestyle-related diseases. P. tricornutum offers a valuable alternative to macroalgae for fucoxanthin production as it has a specific productivity that is 10-fold higher as compared with macroalgae. However, production processes still need to be optimised to become a cost-effective alternative. In this work, we investigated the optimal supplementation of nitrate in a cultivation medium that is currently used for P. tricornutum and how this nitrate concentration affects cell growth and fucoxanthin production. It has previously been shown that the addition of sodium nitrate increases productivity, but optimal conditions were not accurately determined. In this report, we observed that the continuous increase in nitrate concentration did not lead to an increase in biomass and fucoxanthin content, but there was rather a window of optimal values of nitrate that led to maximum growth and pigment production. These results are discussed considering both the scale up for industrial production and the profitability of the process, as well as the implications in the cell’s metabolism and effects in fucoxanthin production.

Concept of Fluorescent Transport Activity Biosensor for the Characterization of the Arabidopsis NPF1.3 Activity of Nitrate.

The NRT1/PTR FAMILY (NPF) in Arabidopsis (Arabidopsis thaliana) plays a major role as a nitrate transporter. The first nitrate transporter activity biosensor NiTrac1 converted the dual-affinity nitrate transceptor NPF6.3 into fluorescence activity sensors. To test whether this approach is transferable to other members of this family, screening for genetically encoded fluorescence transport activity sensor was performed with the member of the NPF family in Arabidopsis. In this study, NPF1.3, an uncharacterized member of NPF in Arabidopsis, was converted into a transporter activity biosensor NiTrac-NPF1.3 that responds specifically to nitrate. The emission ratio change of NiTrac-NPF1.3 triggered by the addition of nitrate reveals the important function of NPF1.3 in nitrate transport in Arabidopsis. A functional analysis of Xenopus laevis oocytes confirmed that NPF1.3 plays a role as a nitrate transporter. This new technology is applicable in plant and medical research.

Contrasting response of soil N2O release to ammonium, nitrate, and urea addition rates is determined by substrate availability and microbial community abundance and composition

Although nonlinear responses of soil nitrous oxide (N2O) release to exogenous nitrogen (N) input have been reported, the contrasting effects of oxidized and reduced N forms and their driving mechanisms have rarely been investigated. Here, a 91-day microcosm incubation experiment with three forms (ammonium, nitrate, and urea) and eleven rates (0, 1, 2, 4, 6, 8, 10, 12, 14, 28, and 56 g N m−2 yr−1) of N addition was conducted to determine the response dose, saturation threshold, and turning point of N2O release from the temperate forest soil. Simultaneously, soil biochemical properties, N-cycling functional gene abundances, and bacterial and fungal community composition were determined to assess the biotic and abiotic contributions to changes in soil N2O release. The responses of soil N2O release rate to ammonium, nitrate, and urea addition rates exhibited saturation, sigmoidal, and exponential curves, respectively. The response dose of soil N2O release was higher in urea addition than in ammonium and nitrate additions (28 g N m−2 yr−1 vs. 8 g N m−2 yr−1). The tipping point and saturation thresholds for ammonium and nitrate additions were estimated to be 14 g N m−2 yr−1 and 56 g N m−2 yr−1, respectively, whereas neither occurred in urea addition. Except high rate of ammonium addition (≥28 g N m−2 yr−1), N inputs significantly increased AOB abundance and promoted soil NO3−-N accumulation. Also, N addition, especially high-rate ammonium, led to a shift in bacterial community from oligotrophic to copiotrophic groups. Oxidized nitrate input increased soil NO3−-N content and changed bacterial and fungal community structure, whereas reduced ammonium and urea additions increased soil NH4+-N content and AOB abundance, as well as altered bacterial community. These findings highlight that N forms contrastingly affect soil N2O release. Substrate availability, functional gene abundance, and microbial community composition equally contribute to soil N2O release, which should be considered in terrestrial ecosystem process models.

Solar light–driven photocatalysis using BaFe2O4/rGO for chlorhexidine digluconate–contaminated water: comparison with artificial UV and visible light–mediated photocatalysis

Synthesis and characterization of dual functioning material is an effective approach for the promotion of organic pollutant degradation through adsorption as well as photocatalysis. Herein, graphene oxide was modified by the addition of barium nitrate and iron to construct a smooth sheet-like structure (BaFe2O4/rGO) for the removal of chlorhexidine digluconate (CHD). Compared with GO (75.69%-UV light; 88.17%-visible light), BaFe2O4/rGO showed significant adsorption-photocatalysis effect under visible light (93.95%) than that under UV light (78.17%). The introduction of barium nitrate and iron into graphene oxide leads to a smooth porous structure with increased surface area (93.66 m2g-1), which resulted in a large number of adsorption active sites and great photocatalytic activity with efficient charge separation. Although catalysts did not mineralize CHD completely, butthe parent compound mineralized to some extent, which was confirmed by the TOC measurement and UV254 absorbance variation. In addition, toxicity of degraded products was analysed by bacterial susceptibility test on Bacillus cereus DPAML065, suggesting that nontoxic by-products of CHD were formed, which leads to their safe disposal. Based on the identified transformed products, the possible degradation pathway was proposed. Batch studies demonstrated that BaFe2O4/rGO is highly photoactive based on reaction rate constant (R2 = 0.984), where the kinetics data were well-fitted using the pseudo-first order. Moreover, efficiency of catalysts was examined under solar light to achieve the sustainability.

Experimental and modeling investigations on the unexpected hydrogen sulfide rebound in a sewer receiving nitrate addition: Mechanism and solution

Biogenic hydrogen sulfide is an odorous, toxic and corrosive gas released from sewage in sewers. To control sulfide generation and emission, nitrate is extensively applied in sewer systems for decades. However, the unexpected sulfide rebound after nitrate addition is being questioned in recent studies. Possible reasons for the sulfide rebounds have been studied, but the mechanism is still unclear, so the countermeasure is not yet proposed. In this study, a lab-scale sewer system was developed for investigating the unexpected sulfide rebounds via the traditional strategy of nitrate addition during 195-days of operation. It was observed that the sulfide pollution was even severe in a sewer receiving nitrate addition. The mechanism for the sulfide rebound can be differentiated into short-term and long-term effects based on the dominant contribution. The accumulation of intermediate elemental sulfur in biofilm resulted in a rapid sulfide rebound via the high-rate sulfur reduction after the depletion of nitrate in a short period. The presence of nitrate in sewer promoted the microorganism proliferation in biofilm, increased the biofilm thickness, re-shaped the microbial community and enhanced biological denitrification and sulfur production, which further weakened the effect of nitrate on sulfide control during the long-term operation. An optimized biofilm-initiated sewer process model demonstrated that neither the intermittent nitrate addition nor the continuous nitrate addition was a sustainable strategy for the sulfide control. To minimize the negative impact from sulfide rebounds, a (bi)monthly routine maintenance (e.g., hydraulic flushing with nitrate spike) to remove the proliferative microorganism in biofilm is necessary.