Removal Of Nitrogen Species Research Articles

Impacts of nano-titanium dioxide toward Vallisneria natans and epiphytic microbes

In this study, Vallisneria natans plants were exposed to 5 and 20 nm of titanium dioxide nanoparticles (TiO₂ NPs) anatase and 600–1000 nm of bulk at 5 and 20 mg/L for 30 days. SEM images and EDX spectra revealed that epiphytic biofilms were more prone to TiO₂ NPs adhesion than bare plant leaves. TiO₂ NPs injured plant leaf cells, ruptured epiphytic diatoms membranes and increased the ratio of free-living microbes. The TN, NH4⁺-N and NO3ˉ-N concentrations significantly decreased, respectively, by 44.9%, 33.6%, and 23.6% compared to bulk treatments after 30 days due to macrophyte damage and a decline in diversity of epiphytic bacterial community and abundance of nitrogen cycle bacteria. TiO₂ NPs size-dependent decrease in bacterial relative abundance was detected, including phylum Cyanobacteria, Planctomycetes, and Verrucomicrobia. Although TiO₂ NPs increased eukaryotic diversity and abundance, abundances of Bacillariophyceae and Vampyrellidae classes and Gastrotricha and Phragmoplastophyta phylum decreased significantly under TiO₂ NPs exposure compared to bulk and control. TiO₂ NPs reduced intensities of interaction relationships among epiphytic microbial genera. This study shed new light on the potential effects of TiO₂ NPs toxicity toward aquatic plants and epiphytic microbial communities and its impacts on nitrogen species removal in wetlands.

Evaluating the effect of seasonal temperature changes on the efficiency of a rhizofiltration system in nitrogen removal from urban runoff

The study presents an evaluation of nitrogen removal efficiency of a pilot-scale rhizofiltration system in Pretoria, South Africa. The rhizofiltration system was divided into two sections, one side planted with common reeds (Phragmites australis) and the other side was without plants kept as a control. The objective of the study was to evaluate the influence of seasonal temperature on the removal of nitrogen species from the simulated urban runoff using the rhizofiltration system. The final effluent from the filter was collected bimonthly at different sampling points for 10 months after an application time of 5 min and 25 min. Duplicate samples were taken to determine the concentrations of TKN (Total Kjeldahl nitrogen), ammonium, nitrate and chemical oxygen demand (COD) for the raw influent and final effluent from the rhizofiltration system. Temperature and pH were determined on-site.During the monitoring period, there was no significant difference in the inflow concentration of ammonium in colder and warmer months for both planted and control sides. Furthermore, the composition of the feed medium to the rhizofilter was kept the same in both cold and warm season and for both planted and control sides. The removal of ammonium in colder and warmer months was not significant in both systems. At an average temperature increase of 5.2 °C in the warmer months, the ammonium removal efficiency in the planted side increased by 7.5%, while for the control side the removal efficiency increased by 2.4%. The difference in removal was not significant between the averages of effluent ammonium after an application time of 25 min in colder versus warmer months for the planted and control sides of the system. Furthermore, an increased nitrification rate was more evident in the planted than in the control side, which was subsequently denitrified. It was observed that 60.4% of nitrate concentration was potentially removed in the planted side whereas 45.4% was potentially denitrified in the control side. These results suggest positive correlation between nitrate concentration and the potential for denitrification. The nitrate removal efficiency dropped to 32.2% for the planted site and to 26.1% for the control system in colder months. Temperature had an effect on nitrogen removal, since nitrogen removal efficiency decreased in colder months. Complete nitrogen removal could not be achieved under the operating conditions.

Assessment of a three step process using tungsten catalyzed hydrogen peroxide-based oxidative desulfurization for commercial diesel fuels

A three-step oxidative desulfurization (ODS) process comprising of oxidation, liquid–liquid extraction, and adsorption was applied to two compositionally very different commercial diesel samples, namely a straight run middle distillate and a blend of primary and secondary refining streams, to assess the ODS process feasibility. The oxidation of sulfur compounds was achieved using hydrogen peroxide as an oxidant in the presence of tungstic acid catalyst. The diesel feedstocks, intermediate and final products were characterized in detail using standard analytical methods along with state-of-the-art speciation techniques. Under mild conditions (ambient pressure and 80 °C), ODS was found to target sulfur species that are refractory to low-severity hydrodesulfurization (HDS), specifically dibenzothiophenes. The ODS process removed 85.3% and 33.5% of the sulfur compounds in the blend and straight run diesel samples, respectively. A comprehensive material balance for the overall process and each process step was also established, revealing that approximately 80% of the initial diesel could be recovered after desulfurization, when accounting for the removed sulfur compounds. However, any extraction based desulfurization approach has an inherent limit for the achievable overall diesel recovery because of the potentially high mass fraction of organosulfur compounds that is removed in the process. Consequently, ODS should be preceded by an HDS process to target the main bulk of sulfur compounds while the ODS process then removes the remaining HDS refractory compounds. Removal of nitrogen species, which are also undesirable in the final product, was a positive side effect of the studied ODS process.

Controlling the synergistic effect of oxygen vacancies and N dopants to enhance photocatalytic activity of N-doped TiO2 by H2 reduction

This paper focuses on improving photocatalytic activity of N-doped TiO2 photocatalyst for efficiently utilizing solar energy. A simple H2 reduction is found to remarkably enhance the photocatalytic activity of N-doped TiO2 for ethylene oxidation under visible light or simulated solar light irradiation. Ultraviolet/visible diffuse reflectance spectra (UV/vis DRS), X-ray photoelectron spectra (XPS) and electron paramagnetic resonance (EPR) spectra were employed to characterize the surface properties and chemical states of nitrogen dopants in H2-reduced N-doped TiO2. The results reveal that H2 reduction facilitates the creation of oxygen vacancies and Ti3+ species in N-doped TiO2 but without removal of nitrogen species from catalyst surface. The formed oxygen vacancies and Ti3+ species seriously influence electron excitation from doped nitrogen species and subsequently tune the generation of active oxygen species O2− radicals on N-doped TiO2. The synergistic effect of oxygen vacancies and doped nitrogen species contributes to the enhancement of photocatalytic activity of N-doped TiO2 samples, but the formed Ti3+ ions largely suppress the photocatalytic activity.

Characterization of Microbial Communities Transforming and Removing Nitrogen in Wetlands

The community structure of bacteria responsible for transformation and removal of nitrogen species from farmyard runoff within two different full-scale integrated constructed wetland (ICW) systems was studied. Microbial communities in litter and sediment components were investigated using denaturing gradient gel electrophoresis (DGGE) and band sequencing of the 16S ribosomal ribonucleic acid gene fragments of putative ammonia-oxidizing bacteria and the nitrite reductase genes (nirK/S) of putative denitrifying bacteria. Findings show that retrieved sequences of ammonia-oxidizing bacteria communities in litter samples were related to Nitrosomonas and Nitrosospira, while those from sediment samples were related to only Nitrosospira. A more diverse denitrifying community was present in the litter compared to the sediment samples. Non-metric multi-dimensional scaling analysis showed that microbial communities were readily distinguishable with respect to site and source (sediment and litter) for the two representative example ICW systems. A comparison of the species composition of the ammonia-oxidizing bacteria and denitrifiers in the systems revealed that the communities were no more similar or dissimilar than if they had been assembled by chance.

HYDROTREATMENT KATALITIK MINYAK RINGAN DENGAN KATALIS NiMo DAN PENGARUH SPESIES NITROGEN

Gas Oil fraction of petroleum was hydrotreated (hydrodesulfurization, HDS) overNiMo/Al2O3 catalyst in a 100 ml autoclave reactor. The reaction was conducted at340 oC under 5MPa H2 pressure for 60 min. to investigate the correlation ofnitrogen species in the HDS. The inhibition effects of these species are alsoinvestigated by using original and its N-free gas oil. Hydrogen renewal betweenstages was attempted to reveal an additional effect of the by-products such asH2S. All species in the gas oils were analyzed by GC-AED before and afterhydrotreatment. HDS over NiMo/Al2O3 was largely improved by removal ofnitrogen species. Refractory sulfur species were effectively removed by theremoval of nitrogen species and renewal of hydrogen in staged HDS, showingsynergy effects due to simultaneous removal of two inhibitors.Kata kunci: gas oil, hydrodesulfurization, nitrogen inhibition, GC-AED

Performance of spent sulfide catalysts in hydrodesulfurization of straight run and nitrogen-removed gas oils

After the test run of several months two kinds of commercial catalysts (NiMo/Al 2O 3 and CoMo/Al 2O 3) were examined in hydrodesulfurization (HDS) of straight run (SRGO) and nitrogen-removed gas oils, at 340 °C under 50 kg/cm 2 H 2. Hydrogen renewal between stages was attempted to show additional inhibition effects of the by-products such as H 2S and NH 3. Spent NiMo/Al 2O 3 and CoMo/Al 2O 3 catalysts showed contrasting activities in HDS and susceptibility to nitrogen species, according to their catalytic natures, compared to those of their virgin ones. HDS over spent NiMo/Al 2O 3 was significantly improved by removal of nitrogen species, while that over spent CoMo/Al 2O 3 was much improved by H 2 refreshment. The activity for refractory sulfur species such as 4,6-dimethyldibenzothiophene was reduced more severely than that for the reactive sulfur species such as benzothiophenes over spent catalysts. The effects of both two-stage hydrodesulfurization and nitrogen-removal were markedly reduced over the spent NiMo when compared with those over virgin NiMo one. The acidity of the catalysts was correlated with the inhibition susceptibility by nitrogen species as well as H 2S and NH 3. Spent catalysts apparently lost their activity due to the carbon deposition, which covered the active sites more preferentially. The spent NiMo catalyst carried more deposited carbon with larger C/H ratio and nitrogen content. Higher acidity was found to be present on the NiMo catalyst, but this was greatly decreased by the carbon deposition. Additionally, the reactivity of nitrogen species in HDS was briefly discussed in relation to the acidity of the catalyst and its deactivation by carbon deposition.

Influences of nitrogen species on the hydrodesulfurization reactivity of a gas oil over sulfide catalysts of variable activity

The inhibition effects of nitrogen species in gas oil on staged hydrodesulfurization (HDS) over commercial NiMoS/Al 2O 3 and CoMoS/Al 2O 3 catalysts of variable activity were investigated at 340 °C under initial 50 kg/cm 2 H 2 using as-distilled and nitrogen-free gas oils. Hydrogen renewal between stages was attempted to reveal an additional inhibition effects of the by-products such as H 2S and NH 3. All species in the gas oils were analyzed by GC-AED before and after hydrotreatment. NiMoS/Al 2O 3 and CoMoS/Al 2O 3 catalysts showed contrasting activities in HDS and susceptibility to nitrogen species according to their catalytic natures. HDS over NiMoS-2/Al 2O 3 of higher activity was largely improved by removal of nitrogen species, while that over NiMoS-1 catalyst of limited activity looked insensitive. Basically, HDS of reactive sulfur species suffered less inhibitions by nitrogen species than that of refractory species. In contrast, two CoMoS catalysts showed significant influences of nitrogen species. One of the most refractory species, 4,6-DMDBT, was effectively hydrodesulfurized by the removal of nitrogen species and renewal of hydrogen in the staged HDS, showing synergy effects due to simultaneous removal of two inhibitors. It must be noted that 107 ppm level of nitrogen species, basically carbazoles, which remained after the first stage HDS, influenced still the HDS of refractory sulfur species which is most expected in the second stage for the deep desulfurization. The acidity of the catalysts is compared to their inhibitions by nitrogen species as well as H 2S and NH 3 in the products. Additionally, the reactivity of nitrogen species in HDS is briefly discussed.

Real‐Time Monitoring and Control of Sequencing Batch Reactors for Secondary Treatment of a Poultry Processing Wastewater

Two sequencing batch reactors were operated to evaluate their efficiency for the pretreatment of a poultry processing wastewater. Although the primary goal was to evaluate the removal efficiency for oxidizable carbon as required by the National Pollutant Discharge Elimination System, this study also examined the relationship between the removal of nitrogen species and the reactor oxidation–reduction potential (ORP). On‐site, pilot‐scale units treated a postprimary treatment side stream, with 4‐hour processing cycles, four cycles per day, with no treatment on weekends. State‐of‐the‐art instrumentation for real‐time pH, ORP, and dissolved oxygen (DO) monitoring and process control based on ORP set points were used. Consistent effluent quality was achieved while treating a variable composition wastewater. By using ORP set points to control the duration of aeration, thus minimizing air blower operation time, removal efficiencies of greater than 93 and 35% were achieved for oxygen demand and ammonia, respectively. Characteristic features of the ORP profiles depicted the transition to low DO levels (≪ 1.0 mg/L). In addition, pH monitoring enhanced the usefulness of ORP readings as the means of identifying the onset of anoxic conditions and the dynamics of the nitrogen transformation processes.

Removal of basic nitrogen species in coal-tar pitch by metal sulphates supported on silica gel

Removal of nitrogen species in the toluene soluble fraction of a coal-tar pitch using metal sulphates (NiSO 4, CuSO 4 and Al 2(SO 4) 3) supported on silica gel (MB-3A and MB-4B) was studied with the objective of preparing a feedstock of low nitrogen content for needle coke production. The adsorbent of supported NiSO 4 (10 wt% on MB-4B) reduced the content of nitrogen in the fraction from 0.91 to 0.45 wt% (methanol insoluble-toluene soluble (MI-TS)) and from 1.1 to 0.69 wt% (TS) at recovered pitch yields of 82 and 74 wt%, respectively at a pitch/adsorbent ratio of 0.5. The major portion of the adsorbed pitch was recovered by extraction with a mixed solvent of toluene, methanol and water. The nitrogen content of recovered pitches was enriched to 3.1 wt% (TS). Aluminium sulphate (10 wt% supported on MB-4B) exhibited the largest adsorption capacity of the sulphates examined. MB-4B with larger pores was the better support. The acidity of the sulphate, controlled by the extent of hydration, is the key for such adsorption and desorption of nitrogen species from coal-tar pitch. The support medium with larger pores dispersed the sulphate on the accessible surface to increase the number of accessible active sites for the large nitrogen-carrying species. The adsorption capacity of the sulphate and the nitrogen content of the purified pitch are balanced because the acidity of the former and basicity of the latter range from strong to weak.