Initial Nitrogen Concentration Research Articles

Water purification efficiency and resource utilization of three tuberous emergent aquatic plants

Objective This study aims to investigate the purification capacity for nutrients in polluted water and the yield of tuber starch of three common tuberous aquatic plants, and estimate the feasibility and potential risk of starch resource utilization. Method Purification efficiency of Iris pseudacorus, Canna indica and Calla palustris for polluted water body was compared using hydroponic experiment, and three replicates were set for each group. No plant treatment was used as control group. Removal efficiency of ammonium nitrogen, total nitrogen and total phosphorus in water was investigated. The contents of nitrogen and phosphorus in plant roots, stems, leaves and tubers were analyzed. The content of starch and heavy metals including Cu, Zn, Cr and Pb in plant tubers were measured. Result When initial concentrations of ammonium nitrogen and total phosphorus were 7.37−7.53 and 0.41−0.45 mg·L−1, concentrations of ammonium nitrogen, total nitrogen and total phosphorus in plant treatment groups decreased to 0.01−0.07, 0.61−0.91, and 0.025−0.031 mg·L−1 respectively after 20 days of treatment, which met the Class Ⅲ standard for surface water environmental quality (GB 3838−2002). The starch extracted from tubers of I. pseudacorus, C. indica and C. palustris was 61.3, 14.1 and 64.0 g·kg−1, respectively. Starch yields of these plant species were 14.3, 1.2 and 2.6 kg·m−2 respectively in the 100 m2 trial plot. The tuber could accumulate heavy metals. As initial concentrations of Cu2+, Zn2+, Cr3+ and Pb2+ in water were 2.01−2.08, 2.56−2.87, 0.22−0.26, and 0.24−0.26 mg·L−1, the contents of Cu, Zn, Cr and Pb in tuber starch of I. pseudacorus were 10.30, 46.7, 12.03, and 1.74 mg·kg−1, respectively and those of C. indica were 12.68, 44.67, 8.15 and 1.32 mg·kg−1, respectively, while those of C. palustris were 19.28, 66.91, 9.63 and 3.97 mg·kg−1, respectively. Conclusion The three tuberous aquatic plants can effectively purify nutrients such as nitrogen and phosphorus, and recover a considerable amount of starch. However if heavy metals coexist in the polluted water, plant tubers are not recommended for resource utilization. [Ch, 4 fig. 17 ref.]

Newly developed membrane contactor-based N and P recovery process: Pilot-scale field experiments and cost analysis

In this study, a newly developed nitrogen (N) and phosphorus (P) recovery process using a membrane contactor termed NPHarvest was tested with different liquid waste streams in large-scale trials. Ammonia was captured in ammonium sulfate form using a hydrophobic membrane, while phosphorus was precipitated as sludge using alkali precipitation and coagulation processes. The tested streams were selected to cover the potential liquid waste streams for nitrogen recovery and included two different mesophilic digester reject waters, landfill leachate, and separately collected urine. The NPHarvest pilot was tested with hydraulic loads in the range of 12–133 L/h. Nitrogen recovery efficiency reached a maximum of 92.5% with the reject water of mesophilic digester and a maximum ammonia flux of 481.1 mg/L.h was obtained with a urine stream. A mass transfer coefficient was calculated for the four tested wastewater streams using two different approaches, resulting in two value ranges in the order of 10−3 and 10−7 m/s. It was found that the mass transfer coefficient decreased with increase in the initial nitrogen concentration. The recovery of phosphorus varied between 79% and 97%. The quality of ammonium sulfate was evaluated by employing comprehensive tests that included vegetative cells and coliphages, harmful metals, and organic micropollutant measurements. These measurements confirmed that ammonium sulfate meets the Finnish legislation requirements for agricultural use. The use of a diluted acid wash was proven to be sufficient for maintaining membrane surface properties and was confirmed by the observed insignificant loss of hydrophobicity and the mild development of fouling. Finally, the competitiveness of NPHarvest compared to existing processes was confirmed through a detailed cost analysis.

Nitrate and Phosphate Removal Efficiency of Synechococcus elongatus Under Mixotrophic and Heterotrophic Conditions for Wastewater Treatment

Growing nutrient content of surface waters causes environmental concerns about eutrophication due to the immethodical release of nutrient containing effluent. The potential of microorganisms to decrease nitrogen and phosphorus concentration has drawn increasing attention. The present study is performed to evaluate the nutrient removal potential of cyanobacterium Synechococcus elongatus in different trophic cultivations. For this purpose, 15 experiments were designed by the Box-Behnken method using modified BG-11, including the initial concentrations of phosphorus, nitrogen, and glucose up to 10 mg L−1, 600 mg L−1, and 10 g L−1, respectively. Different trophic conditions were applied by changing carbon sources and light–dark cycles. The maximal removal of phosphorus and nitrogen were obtained in mixotrophic condition with 85.1% and 87.4%, respectively, and the specific growth rate of microalga was 0.99 day−1. Besides, its nutrient removal efficiency in dairy effluent was about 92% in mixotrophic culture, while the heterotrophic condition was not efficient. Based on the obtained results, mixotrophic cultivation of the cyanobacteria S. elongatus would be useful for application in N-riched and P-riched effluents.

Evaluation of nitrification kinetics for treating ammonium nitrogen enriched wastewater in moving bed hybrid bioreactor

Nitrification kinetics of wastewater characterized by high nitrogen and very low organic carbon was evaluated using a moving bed hybrid bioreactor (MBHBR) in batch mode by varying initial ammonium nitrogen (NH4+-N) concentration in the range of (500–1000) mg L−1 at a pH of 7.8 ± 0.15 and temperature around 28 ± 2°C. A maximum removal efficiency of 89 % in terms of ammonium nitrogen was achieved with initial NH4+-N concentration of 900 mg L−1 having a total biomass concentration around 2000 mg L−1 and at a batch period of 5 days. The experimental results were analyzed in the light of Monod’s kinetic theory and coefficients for nitrification were obtained as maximum substrate removal rate coefficient (μmax) = 0.52 day−1, yield coefficient (Y) = 0.63 mg VSS/mg NH4+-N, half saturation constant (Ks) =603.11 mg NH4+-NL−1 and endogenous decay constant (kd) = 0.008 day−1. The study confirms better nitrification efficiency in presence of attached biomass as compared to suspended growth condition. An interesting observation from the nitrate nitrogen profile establishes the possibility of denitrification, occurring simultaneously even in absence of organic carbon in the wastewater in aerobic MBHBR. This can be supported by the fact that the suspended flocs and/or attached biofilms in hybrid reactor was deep enough for creating necessary conditions for denitrification and the required organic carbon was partially obtained from endogenous degradation of the microorganisms.

Towards high-quality biodiesel production from microalgae using original and anaerobically-digested livestock wastewater

In this study, we conducted proof-of-concept research towards the simultaneous treatment of livestock wastewater and the generation of high-quality biodiesel, through microalgae technology. Both original (OPE) and anaerobically-digested (DPE) piggery effluents were investigated for the culture of the microalgae, Desmodesmus sp. EJ8-10. After 14 days’ cultivation, the dry biomass from microalgae cultivated in OPE increased from an initial value of 0.01 g/L to 0.33–0.39 g/L, while those growing in DPE only achieved a final dried mass of 0.15–0.35 g/L, under similar initial ammonium nitrogen (NH4+-N) concentrations. The significantly higher microalgal biomass production achieved in the OPE medium may have been supported by the abundance of both macronutrient, such as phosphorus (P), and of micronutrients, such as trace elements, present in the OPE, which may not been present in similar quantities in the DPE. However, a higher lipid content was observed (19.4–28%) in microalgal cells from DPE cultures than those (18.7–22.3%) from OPE cultures. Moreover, the fatty acid compositions in the microalgae cultured in DPE contained high levels of monounsaturated fatty acids (MUFAs) and total C16–C18 acids, which would afford a superior potential for high-quality biodiesel production. The N/P ratio (15.4:1) in OPE was much closer to that indicated by previous studies to be the most suitable (16:1) for microalgae growth, when compared with that determined from the DPE culture medium. This may facilitate protein synthesis in the algal cells and induce a lower accumulation of lipids. Based on these findings, we proposed a new flowsheet for sustainable livestock waste management.

Preparation of Hollow SiO₂@BiOI Nanocomposites and Their Photocatalytic Performance in Ammonia Nitrogen Degradation.

Hollow SiO₂ microsphere-supported bismuth oxyiodide (BiOI) nanocomposites were prepared using Bi(NO₃)₃ · 5H₂O and KI as the precursors of BiOI at 80 °C in an aqueous solution by the liquid chemical deposition method. The BiOI nanosheets with the thicknesses of 25-40 nm and the widths of 1-2 μm were deposited on the hollow SiO₂ microsphere surfaces. There were interactions between the BiOI nanosheets and hollow SiO₂ microspheres, which enlarged the ban gap of the BiOI nanosheet as compared with the pure BiOI. The band gap energy increased with the increase in SiO₂/BiOI weight ratios. The hollow SiO₂@BiOI nanocomposites showed high photocatalytic activity in ammonia nitrogen degradation when the photocatalytic degradation reaction was performed in aqueous solution under visible light irradiation. The degradation extent of ammonia nitrogen was upto 81% when the ammonia nitrogen degradation reaction was photocatalyzed by the hollow SiO₂@BiOI(100:10) nanocomposite at an initial concentration of ammonia nitrogen of 10 mg L-1 and 25 °C for 4 h. The reaction kinetics of ammonia nitrogen degradation was well simulated by the first-order reaction model.

Application of encapsulated algae into MBR for high-ammonia nitrogen wastewater treatment and biofouling control

Low microbial activity and serious membrane biofouling are still critical problems that hinder the extensive application of membrane bioreactor (MBR) for industrial wastewater treatment. To address these bottlenecks, we report a new specialized microorganism encapsulation strategy for constructing a highly efficient MBR system. In our study, the algae-entrapping fiber macrospheres with polymeric coating were first coupled with membrane separation for treating refractory high-ammonia nitrogen wastewater. In comparison with traditional alginate beads, the developed macrocapsule (~0.5 cm) exhibited higher biomass harvesting and lower microbial leakage because of the confined micro-aerobic environment created by dual encapsulation of rigid inorganic macrosphere and porous polymeric layers. Application of algae-encapsulating macrocapsule to MBR presented excellent chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) removal efficiency of 62.23 and 97.38 %, respectively, which were higher than the corresponding values for algae/SA beads and free algae. The biodegradation performance of NH3-N by encapsulated microalgae was similar or superior to that by free cells when the initial content of ammonia nitrogen ranged from 50 to 100 mg/L. The results well demonstrated that the GFS@polymer macrocapsule as a physical barrier reduced the inhibitory effect of higher concentration ammonia nitrogen on the bioactivity of living cells. Importantly, the encapsulated core-shell macrocapsules showed superior anti-biofouling capacity, which had a membrane resistance of 3-5 times lower than that of cell/alginate beads and free cells. This work will open a new avenue to develop a novel encapsulated MBR for various non-degradable wastewater treatments as an energy-saving and sustainable way.

Anaerobic Co-Digestion of Kitchen Waste and Blackwater for Different Practical Application Scenarios in Decentralized Scale: From Wastes to Energy Recovery

This study was performed to investigate the anaerobic digestion feasibility of kitchen waste and blackwater under different scenarios in laboratory tests. According to biochemical methane potential tests, when the kitchen waste to blackwater solid ratio was 1:1, the cumulative methane production reached the highest amount at 313.2 mL/g volatile solids (VSs), which was 26.4% and 29.4% higher than the anaerobic monodigestion of kitchen waste and blackwater, respectively, indicating that the anaerobic codigestion of kitchen waste and blackwater had a synergetic effect. Furthermore, the effect of different initial total ammonia nitrogen concentrations in blackwater on anaerobic digestion was determined based on the above experimental results, thereby proving that reducing the total ammonia nitrogen concentration in blackwater can appropriately improve the efficiency of methane production. Therefore, anaerobic digestion is a suitable method for the biogas production of kitchen waste and blackwater. It is of great significance for the organic waste stream treatment of households in a decentralized scale, especially in rural areas.

Characteristics and metabolic pathway of the bacteria for heterotrophic nitrification and aerobic denitrification in aquatic ecosystems

The present study investigated the nitrogen removal characteristics and metabolic pathway of bacteria in aquatic ecosystem, with a focus on heterotrophic nitrification and aerobic denitrification. The bacteria demonstrated significant heterotrophic nitrification and aerobic denitrification capacity. The highest ammonium-N, nitrate-N, and nitrite-N removal efficiencies were 95.31 ± 0.11%, 98.91 ± 0.05%, and 98.79 ± 0.09%, respectively. The Monod model was used to estimate the maximum rate of substrate utilization (Rmo) and the half-saturation concentration (Ks) for the two substrates, i.e., ammonium and nitrate. The kinetic coefficients were 3.34 mg/L/d (Rmo) and 30.59 mg/L (Ks) for ammonium-N, respectively, and 14.23 mg/L/d (Rmo) and 215.24 mg/L (Ks) for nitrate-N, respectively. The effects of initial nitrogen (ammonium-N or nitrate-N) concentration, temperature, and dissolved oxygen (DO) on nitrogen removal rate were investigated using response surface methodology (RSM), and the optimal conditions for nitrogen removal were determined. The principal nitrogen removal pathway of the bacteria was proposed as complete heterotrophic nitrification and aerobic denitrification, which was performed by six key genera: Arthrobacter, Pseudomonas, Rhodococcus, Bacillus, Massilia, and Rhizobium. Chryseobacterium and other denitrifying species may also reduce nitrification products (NOX−) via aerobic denitrification.

Non-thermal plasma combined with zeolites to remove ammonia nitrogen from wastewater

In this work, non-thermal plasma combined with zeolites was used to remove inorganic pollutant ammonia nitrogen from wastewater. Ammonia nitrogen elimination performances at various operating parameters were investigated. Roles of active species in the removal of ammonia nitrogen were also discussed. The experimental results showed that 69.97% ammonia nitrogen can be removed from the plasma/zeolites synergistic system after 30 min treatment. The removal efficiency was 16.23% and 61.55% higher than that in sole zeolites adsorption system and that in sole discharge plasma system, respectively. Higher applied voltage, lower initial ammonia nitrogen concentration and weak acidic conditions were favorable for ammonia nitrogen removal. After the addition of zeolites, part of O3 and H2O2 generated in the plasma/zeolites system were decomposed into other oxygen species (•OH and 1O2), which improved the oxidation degree of ammonia nitrogen. In addition, the reaction mechanism of ammonia nitrogen in water by plasma/zeolites process was discussed. After repeated use three times, the effect of the zeolites in the plasma/zeolites system remained stable. Characterization of the zeolites after reaction was analyzed through BET, SEM, XRD and FT-IR. The experiments have confirmed the applicability of the plasma/zeolites system for the further treatment of low-concentration ammonia nitrogen wastewater.

Mathematical model of liquefied natural gas evaporation and analysis of original composition effect on evaporation speed

Subject of Research. The paper proposes a model for predicting evaporation of liquefied natural gas (LNG) stored in tanks of regasification terminals. The model is a combination of the strict thermodynamic LNG vapor-liquid equilibrium and heat transfer realistic models. Analysis of the initial composition effect and the stock of LNG, the initial content of nitrogen and the value of the outside air temperature on the LNG evaporation rate is carried out. Method. A numerical experiment using a mathematical model of the LNG evaporation process was based on the LNG composition data and its storage time in aboveground tanks. The proposed method provided a number of advantages compared to previously developed models: the heat input to the low-temperature part of the LNG storage tank was calculated taking into account the outdoor temperature and the LNG composition; the evaporation coefficient was not an input parameter, but was calculated as part of the simulation; the LNG density was calculated by experimental correlation. Main Results. An important parameter in assessing the LNG loss from its evaporation is the nitrogen content in the liquid, which evaporates at a higher rate than methane, the main LNG component. Analysis of the initial composition effect on the LNG evaporation rate has shown that the growth of the nitrogen content in the initial mixture causes noticeable decrease in the evaporation rate due to the nitrogen priority evaporation and, as a consequence, the growth of latent mixture heat vaporization. Analysis of the initial LNG supply value at the evaporation rate has shown that a large degree of the tank filling causes an outstripping reduction in losses from evaporation. The result is an earlier reduction in the amount of boil-off gas (BOG, stripping gas) for more filled tank. Analysis of the outdoor temperature effect on the rate of LNG evaporation has shown that the ambient temperature change of 1 °C leads to the decrease in the BOG amount by 0.2 %. Practical Relevance. The proposed mathematical model of the LNG evaporation process reduces BOG formation during long-term storage, maintain the original LNG quality, optimizes the operational parameters of regasification terminals, and provides the consumers with reliable supply of high-quality natural gas.

Nitrogen Content in Craft Malts: Effects on Total Ester Concentration in Beer

Malt is an essential ingredient in beer; not only because it provides yeast with essential nutrients such as amino acids and fermentable sugars, it also adds to the beer’s color, body and flavor. The objective of this project was to look at the initial concentration of total nitrogen (TN) found within base malts of different varietal and cultivar origins and its impact on the esters produced in beers made using these malts. The experimental beer was brewed with a target OG of 10° Plato wort using five different base malts; four of which were produced by independent craft maltsters (Texas, Oregon, Indiana, and Canada) and a macro-industrial produced malt served as the control. TN and free amino nitrogen (FAN) were analyzed and compared with volatile and semi-volatile flavor analysis in order to identify correlations between nitrogen concentration and ester development within the final beer. One-way ANOVA coupled with a Tukey HSD paired comparison test was run to determine statistical differences in TN and FAN, while Kruskal-Wallis one-way analysis of variance test was utilized to determine statistical differences between total esters production. TN wort values ranged from 627 to 909 mg/L, while FAN wort values ranged from 191 to 467 mg FAN/L. There were statistical differences seen between all of the beers in total ester production. The beers produced with malts of higher TN resulted in greater ester production. From this, one can conclude that there is a correlation between a malt’s TN and esters produced in the final beer product.

B, N co-doped carbon nanosheets derived from graphene quantum dots: Improving the pseudocapacitive performance by efficient trapping nitrogen

Doping heteroatoms especially nitrogen is widely applied for improving the capacitive energy storage performance of carbon materials. However, preserving nitrogen in carbon skeleton is still challenging because nitrogen species are unstable at high temperature. Herein, we develop a simple boric acid-assisted method for trapping nitrogen into carbon skeleton. Using the graphene quantum dots with an initial nitrogen content of 5.0 at.% as precursors, the B, N co-doped carbon nanosheets with an increased nitrogen content of 7.2 at.%, a boron content of 4.4 at.%, and a surface area of 817 m2 g−1 are prepared. Benefiting from the high heteroatom content, the nanosheets show a significantly improved capacitance of 257 F g−1 at 1 A g−1 and a good rate performance of 150 F g−1 at 50 A g−1. The pseudocapacitance contribution at 10 mV s−1 is as high as 48%. The assembled symmetric capacitor shows a superior cycle stability with no obvious fading after 10,000 cycles at 10 A g−1. Our work can help to understand the synergistic effect of heteroatoms for co-doping of carbon and broaden the avenue for designing functional carbon materials.

Solar drying in the vineyard: a sustainable technology for the recovery of nutrients from winery organic waste.

The present study describes a pilot-scale experimental validation of a forced-convection greenhouse solar dryer, combined with a biofilter, for controlled atmospheric emissions. This set-up was applied to the dewatering of sewage sludge from a biological plant that treated process wastewater in a commercial Mediterranean winery. Experiments were performed after the harvest, from September onwards, during the peak generation of sludge. The average drying rate during the first 10 days of operation ranged from 1.17 to 2.24 kg m-2 d-1, depending on the measurement method, during which the water content of the sludge was reduced from 90% down to 67%. Biofiltration was quite inefficient against greenhouse gases (methane and dinitrous oxide), and direct emissions during the drying process were on average 57 g CO2-eq m-2 d-1. Ammonia and volatile organic compounds were removed with average efficiencies of 71% and 35%, but ammonia losses through volatilization represented less than 2% of the initial nitrogen content. The sludge was dried further during November, to the lowest possible water content of 14%. Both the intermediate and final sludge dried materials were characterized for their agronomical value as organic fertilizers.

Ammonium nitrogen adsorption from aqueous solution by poly(sodium acrylate)s: Effect on the amount of crosslinker and initiator

AbstractIn this work, we discuss the ammonium nitrogen adsorption and reusability from aqueous solution by using poly(sodium acrylate) (PANa) hydrogels (Polymers 1–6) under different amount of crosslinker and initiator. The PANa hydrogels were synthesized from the neutralized acrylic acid (AA) monomer via free radical thermal polymerization by using ammonium persulfate (APS) as an initiator and N,N′‐methylene‐bisacrylamide (MBA) as a crosslinker. These polymers exhibited glass transition temperatures (Tg) of 68–88°C and Td values (5% weight loss temperature) in the range of 190–221°C under nitrogen atmosphere. The PANa hydrogels had swollen ratios ranging from 387 to 4,063%, related to the crosslinking density. The final equilibrium adsorption capacity of the polymers was in the range of 20–39 ppm with an initial ammonium nitrogen concentration of 100 ppm. Among them, Polymer 3 without MBA crosslinker displayed the highest swollen characteristic along with the most efficient adsorption capacity. In comparison, the as‐prepared high crosslinking density hydrogels showed relative lower adsorption capability but higher reusability. The polymer composition in this work determines the ability to absorb and desorb ammonium nitrogen compound.

Comprehensive utilization of the filamentous oleaginous microalga Tribonema utriculosum for the production of lipids and chrysolaminarin in a biorefinery concept

Previous studies have focused on the accumulation of lipid and palmitoleic acid in Tribonema spp., while chrysolaminarin produced by these filamentous oleaginous microalgae has rarely been reported. In this study, the effects of different initial nitrogen concentrations on the growth, lipid and chrysolaminarin accumulation of T. utriculosum were investigated, and the extraction route of lipid was also optimized, accompanied by the isolation and characterization of chrysolaminarin. The results showed that the highest biomass concentration (6.21 ± 0.17 g/L) of T. utriculosum was obtained at 3 mM of initial nitrogen concentration with the lowest level of chrysolaminarin (10.74 ± 0.42% of dry weight (DW)), while higher initial nitrogen concentrations were more conducive to lipid and chrysolaminarin accumulation, especially for 18 mM, leading to the highest lipid content (43.80 ± 0.57% of DW). To minimize the biorefinery process cost, an optimized route for lipid extraction was suggested to simultaneously achieve the goal of disintegration of algal structure and extraction of intracellular polysaccharides by dilute acid pretreatment, which improved lipid extraction efficiency from 38.70% to 87.09%. Most importantly, a homogeneous chrysolaminarin was successfully isolated from T. utriculosum and characterized with an average molecular weight of 5.99 kDa. It was found to mainly comprise glucose (60.13%) and was linked by the β-D-(1 → 3) (main chain) and β-D-(1 → 6) (branch chain) glycosidic bonds. This study is the first report on the isolation and characterization of chrysolaminarin from microalgae Tribonema, and provides new insights into fully utilizing T. utriculosum biomass for broadening the potential applications of microalgae-based products.

The Adsorption of Ammonium Nitrogen from Milking Parlor Wastewater Using Pomegranate Peel Powder for Sustainable Water, Resources, and Waste Management

Agricultural wastewater poses serious risks to the environment due to how it is injudiciously used and managed. We investigated the use of pomegranate peel powder (PPP) to adsorb ammonium ions from milking parlor wastewater, which is applied as a nitrogen source for cropland fertilization despite its environmental ramifications. As a valueless by-product of juice and jam industries, PPP shows promising features and characteristics as a potential bio-adsorbent for ammonium nitrogen removal and recovery. The surface characterization of PPP was performed by zeta potential measurement and attenuated total reflectance Fourier transform infrared Spectroscopy (ATR-FTIR) analysis. The adsorption studies were carried out by batch experiments where the initial ammonium nitrogen (NH4–N) concentration of studied wastewater was 80 mg/L. The effects of different operational parameters, such as pH, adsorbent dose, contact time, stirring speed, and temperature, were investigated. From kinetic studies, the equilibrium time was found to be 120 min, achieving an 81.8% removal synonym of ~2.5 mg/g NH4–N uptake. The adsorption isotherm data fitted well with Langmuir model with correlation (R2) > 0.99. Meanwhile, the kinetics followed pseudo-second order model with correlation (R2) > 0.99.

High titer fatty alcohol production in Lipomyces starkeyi by fed-batch fermentation

Abstract Extracellular production of long chain fatty acid-based products, such as fatty alcohols, are being investigated as intermediates amenable to separations and catalytic upgrading to hydrocarbon fuels. We previously demonstrated that the oleaginous yeast, Lipomyces starkeyi expressing the fatty acyl-CoA reductase (FAR) gene from Marinobacter aquaeolei VT8, produced up to 770 mg/L of fatty alcohols. The FAR genes expressed in L. starkeyi transformants exhibited different fatty alcohol production levels. To better understand fatty alcohol production and potentially further increase fatty alcohol titer and yields, we investigated the expression levels, copy numbers, and enzymatic activities of the expressed FAR genes. Our results showed that fatty alcohol production is dependent on the above factors for higher titers of fatty alcohols. Fatty alcohol titer was further increased in the highest producing transformant by testing different basic process configurations (batch and fed-batch) with different initial nitrogen concentrations and feed rates. In fed-batch, a maximum of 4.2 g/L fatty alcohols were produced in 5-L bioreactor. The oleaginous yeast L. starkeyi can produce high titers of fatty alcohols particularly when periodically fed glucose and nitrogen.

Kinetics study of nitrogen removal from liquid IN718 alloy during vacuum induction melting

The kinetics of nitrogen removal from the molten IN718 alloy has been investigated by the sampling method under reduced pressure. The effects of initial nitrogen concentrations, alloying elements (carbon, titanium, and aluminum), and the intensity of inductive stirring on the nitrogen removal are discussed in the temperature range from 1773 to 1923 K. Experimental results indicate that the nitrogen removal is a 1.5th-order reaction at different initial nitrogen concentrations and temperatures, and the nitrogen removal reaction is controlled by a mixed interfacial and diffusion process. Moreover, the nitrogen removal reaction can be accelerated when the [C]+[O] = CO(g) reaction exists in the melt, and the kinetics changes gradually from a 1.5th-order reaction to a second-order reaction with increasing temperature from 1773 to 1873 K. The nitrogen removal is a second-order reaction in low-speed stirring. Meanwhile, the rate constant of nitrogen removal under the condition of where the mass transfer resistance in the gas phase is negligible, is evaluated. The rate constant of the nitrogen removal increases with increasing temperature. It is also found that titanium decreases the rate constant of nitrogen removal, and aluminum and carbon significantly increase the rate constant of nitrogen removal.

Dynamic characteristics of immobilized microorganisms for remediation of nitrogen-contaminated groundwater and high-throughput sequencing analysis of the microbial community

The aim of this study was to investigate the effect of adsorption by a composite active medium (nitrogen-degrading bacteria immobilized on scoria) on the removal of ammonium nitrogen (NH4+-N), nitrite nitrogen (NO2–N) and nitrate nitrogen (NO3–N). Transport of these three forms of nitrogen was investigated using columns with different flow rates, initial concentrations and depths. Immobilization of the bacteria on the scoria significantly enhanced the ability of the composite active medium to remove nitrogen during the remediation process. As the flow rate increased, the shear force increased and solute diffusion decreased, thereby improving the tolerance of the bacteria for the three forms of nitrogen and reducing the penetration time. Increasing the initial nitrogen concentration resulted in a decrease in the adsorption rate constant (KTh). The nitrogen-degrading bacteria immobilized on scoria rapidly reached saturation with regards to their nitrogen adsorption capacity. The initial nitrogen concentration of each media layer was different, and the composite active medium had a certain blocking effect, which resulted in a slow increase in the concentration of nitrogen in the deeper media layer. The transport experiments showed that the process accords with the thomas model and the Bohart-Adams model. The contents of the three forms of nitrogen were within acceptable standards for drinking water after 2 months of a column containing the composite active medium. The composite active medium can be used for in situ and ex situ remediation of groundwater containing excessive nitrogen. High-throughput sequencing analysis was used to monitor the composition of the bacterial community present within the composite active medium. During the remediation process, there were only slight changes in the structure and composition of the nitrogen-degrading bacterial community, although there were clear differences in abundance. Pseudomonas, Stenotrophomonas and Serratia were the three bacterial genera that were effective removal of all three forms of nitrogen.