Biodiesel side stream waste glycerol was identified as a cheap carbon source for rhamnolipids (RLs) production which at the same time could improve the management of waste. The present study aimed to produce RLs by using Pseudomonas aeruginosa RS6 utilizing waste glycerol as a substrate and to evaluate their physico-chemicals properties. Fermentation conditions such as temperature, initial medium pH, waste glycerol concentration, nitrogen sources and concentrations resulted in different compositions of the mono- and di-RLs produced. The maximum RLs production of 2.73 g/L was obtained when P. aeruginosa RS6 was grown in a basal salt medium supplemented with 1% waste glycerol and 0.2 M sodium nitrate at 35 °C and pH 6.5. At optimal fermentation conditions, the emulsification index (E₂₄) values of cooking oil, diesel oil, benzene, olive oil, petroleum, and kerosene were all above E₂₄₌50%. The surface tension reduction obtained from 72.13 mN/m to 29.4–30.4 mN/m was better than the surface activity of some chemical-based surfactants. The RLs produced possessed antimicrobial activities against Gram-negative and Gram-positive bacteria with values ranging from 37% to 77% of growth inhibition when 1 mg/mL of RLs was used. Concentrations of RLs below 1500 μg/mL did not induce phytotoxicity effects on the tested seeds (Vigna radiata) compared to the chemical-based- surfactant, SDS. Furthermore, RLs tested on zebrafish (Danio rerio) embryos only exhibited low acute toxicity with an LC₅₀ value of 72.97 μg/mL at 48 h of exposure suggesting a green and eco-biochemical worthy of future applications to replace chemical-based surfactants.

Nitrous oxide (N₂O) is a major greenhouse gas, with elevated emission being reported from subtropical forests that receive high nitrogen (N) deposition. After 10 years of monthly addition of ammonium nitrate (NH₄NO₃) or sodium nitrate (NaNO₃) to a Mason pine forest at Tieshanping, near Chongqing city in Southwest China, the simulated N deposition was stopped in October 2014. The results of soil N₂O emissions monitoring in different seasons during the nitrogen application period showed that nitrogen addition significantly increased soil N₂O emission. In general, the N₂O emission fluxes were positively correlated to nitrate (NO₃⁻) concentrations in soil solution, supporting the important role of denitrification in N₂O production, which was also modified by environmental factors such as soil temperature and moisture. After stopping the application of nitrogen, the soil N₂O emissions from the treatment plots were no longer significantly higher than those from the reference plots, implying that a decrease in nitrogen deposition in the future would cause a decrease in N₂O emission. Although the major forms of N deposition, NH₄⁺ and NO₃⁻, had not shown significantly different effects on soil N₂O emission, the reduction in NH₄⁺ deposition may decrease the NO₃⁻ concentrations in soil solution faster than the reduction in NO₃⁻ deposition, and thus be more effective in reducing N₂O emission from N-saturated forest soil in the future.

Microplastics are an emerging contaminants of concern in aquatic environments. The aggregation behaviors of microplastics governing their fate and ecological risks in aquatic environments is in need of evaluation. In this study, the aggregation behavior of polystyrene microspheres (micro-PS) in aquatic environments was systematically investigated over a range of monovalent and divalent electrolytes with and without natural organic matter (i.e., Suwannee River humic acid (HA)), at pH 6.0, respectively. The zeta potentials and hydrodynamic diameters of micro-PS were measured and the subsequent aggregation kinetics and attachment efficiencies (α) were calculated. The aggregation kinetics of micro-PS exhibited reaction- and diffusion-limited regimes in the presence of monovalent or divalent electrolytes with distinct critical coagulation concentration (CCC) values, followed the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The CCC values of micro-PS were14.9, 13.7, 14.8, 2.95 and 3.20 mM for NaCl, NaNO3, KNO3, CaCl2 and BaCl2, respectively. As expected, divalent electrolytes (i.e., CaCl2 and BaCl2) had stronger influence on the aggregation behaviors of micro-PS as compared to monovalent electrolytes (i.e., NaCl, NaNO3 and KNO3). HA enhanced micro-PS stability and shifted the CCC values to higher electrolyte concentrations for all types of electrolytes. The CCC values of micro-PS were lower than reported carbonaceous nanoparticles CCC values. The CCC[Ca2+]/CCC [Na+] ratios in the absence and presence of HA at pH 6.0 were proportional to Z−2.34 and Z−2.30, respectively. These ratios were in accordance with the theoretical Schulze–Hardy rule, which considers that the CCC is proportional to z−6–z−2. These results indicate that the stability of micro-PS in the natural aquatic environment and the possibility of significant aqueous transport of micro-PS.

Nitrate accumulation in aquatic reservoirs from agricultural pollution has often been overlooked as a water quality hazard, yet a growing body of literature suggests negative effects on human and wildlife health following nitrate exposure. This research seeks to understand differences in oxygen consumption rates between different routes of laboratory nitrate exposure, whether via immersion or injection, in zebrafish (Danio rerio) embryos. Embryos were exposed within 1 h post fertilization (hpf) to 0, 10, and 100 mg/L NO₃-N with sodium nitrate, or to counter ion control (CIC) treatments using sodium chloride. Embryos in the immersion treatments received an injection of 4 nL of appropriate treatment solution into the perivitelline space. At 24 hpf, Oxygen Consumption Rates (OCR) were measured and recorded in vivo using the Agilent Technologies XFᵉ96 Extracellular Flux Analyzer and Spheroid Microplate. Immersion exposures did not induce significant changes in OCR, yet nitrate induced significant changes when injected through the embryo chorion. Injection of 10 and 100 mg/L NO₃-N down-regulated OCR compared to the control treatment group. Injection of the 100 mg/L CIC also significantly down-regulated OCR compared to the control treatment group. Interestingly, the 100 mg/L NO₃-N treatment further down-regulated OCR compared to the 100 mg/L CIC treatment, suggesting the potential for additive effects between the counter ion and the ion of interest. These data support that elevated nitrate exposure can alter normal metabolic activity by changing OCR in 24 hpf embryos. These results highlight the need for regularly examining the counter ion of laboratory nitrate compounds while conducting research with developing zebrafish, and justify examining different routes of laboratory nitrate exposure, as the chorion may act as an effective barrier to nitrate penetration in zebrafish, which may lead to conservative estimates of significant effects in other species for which nitrate more readily penetrates the chorion.

The Diffusive Gradients in Thin Films (DGT) technique using PIWBA resin (The Dow Chemical Company) was developed and validated for the measurement of uranium (U) concentration in natural and uranium mining influenced waters. The U uptake on the PIWBA resin gel was 97.3 ± 0.4% (batch method; Vsol = 5 mL; [U] = 20 μg L−1; 0.01 M NaNO3; pH = 7.0 ± 0.2). The optimal eluent was found to be HNO3conc/70 °C with an elution efficiency of 88.9 ± 1.4%. The laboratory DGT investigation demonstrated that the PIWBA resin gel exhibits a very good performance across a wide range of pH (3–9) and ionic strength (0.001–0.7 M NaNO3) at different time intervals. Neither effect of PO43− (up to 1.72 × 10−4 M), nor of HCO3− (up to 8.20 × 10−3 M) on the quantitative measurement of uranium by DGT-PIWBA method were observed. Only at very high Ca2+ (2.66 × 10−4 M), and SO42− (5.55 × 10−4 M) concentration, the U uptake on DGT-PIWBA was appreciably lessened. In-situ DGT field evaluation was carried out in the vicinity of three former uranium mining sites in France (Loire-Atlantique and Herault departments), which employ different water treatment technologies and have different natural geochemical characteristics. There was a similar or inferior U uptake on DGT-Chelex®-100 in comparison with the U accumulation on a DGT-PIWBA sampler. Most likely, the performance of Chelex®-100 was negatively affected by a highly complex matrix of mining waters. The high concentration and identity of co-accumulating analytes, typical for the mining environment, did not have a substantial impact on the quantitative uptake of labile U species on DGT- PIWBA.The use of the polyphenol impregnated anion exchange resin leads to a significant advancement in the application and development of the DGT technique for determination of U in the vicinity of the former uranium mining sites.

An anaerobic incubation was launched with varying nitrate (1, 5, 10 and 20 mM exogenous NaNO₃) and molybdate (20 mM Na₂MoO₄, a sulfate-reducing inhibitor) additions to investigate the characteristics of PCP dechlorination, as well as the reduction of natural co-occurring electron acceptors, including NO₃⁻, Fe(III) and SO₄²⁻, and the responses of microbial community structures under a unique reductive mangrove soil. Regardless of exogenous addition, nitrate was rapidly eliminated in the first 12 days. The reduction process of Fe(III) was inhibited, while that of SO₄²⁻ reduction depended on addition concentration as compared to the control. PCP was mainly degraded from orth-position, forming the only intermediate 2,3,4,5-TeCP by anaerobic microbes, with the highest PCP removal rate of average 21.9% achieved in 1 and 5 mM NaNO₃ as well as 20 mM Na₂MoO₄ treatments and the lowest of 7.5% in 20 mM NaNO₃ treatment. The effects of nitrate on PCP dechlorination depended on addition concentration, while molybdate promoted PCP attenuation significantly. Analyses of the Illumina sequencing data and the relative abundance of dominant microorganisms indicated that the core functional groups regulated PCP removal at genera level likely included Bacillus, Pesudomonas, Dethiobacter, Desulfoporosinus and Desulfovbrio in the nitrate treatments; while that was likely Sedimentibacter and Geosporobacter_Thermotalea in the molybdate treatment. Nitrate supplement but not over supplement, or addition of molybdate are suggested as alternative strategies for better remediation in the nitrate-deficient and sulfur-accumulated soil ecosystem contaminated by PCP, through regulating the growth of core functional groups and thereby coordinating the interaction between dechlorination and its coupled soil redox processes due to shifts of more available electrons to dechlorination. Our results broadened the knowledge regarding microbial PCP degradation and their interactions with natural soil redox processes under anaerobic soil ecosystems.

Simultaneous measurements of gaseous SO2, NO2, HNO3, NH3 and particulate SO42–, NO3– and NH4+ were carried out in a suburban area in Cairo during summer 2009 and winter 2009–2010. PTFE membrane filters were used to collect particulate SO42–, NH4+ and NO3–, followed by the impregnated filter to collect HNO3. Colorimetric methods were used for determination of NO2, SO2, NH3, SO42–, NH4+ NO3–, and HNO3 levels. The mean concentrations of NO2, SO2 and NH3 were 75.0, 40.1 and 29.1 µg/m3 in winter and 54.1, 25.1 and 44.9 µg/m3 in summer, respectively. The daytime/nighttime concentration ratios were 1.3 and 1.2 for NO2, 1.3 and 1.2 for SO2 and 0.6, and 0.8 for NH3 during the winter and summer, respectively. The mean values of NH4+, SO42–, NO3–, HNO3 and total NO3– were 4.4, 19.0, 3.4, 1.1 and 4.5 µg/m3 in winter and 7.5, 28.0, 4.2, 3.1 and 7.3 µg/m3 in summer, respectively. The levels of NH4+, SO42–, NO3– and HNO3 were relatively higher in daytime than in nighttime. Sulfur conversion (Fs) and nitrogen conversion ratios (Fn) in summer were about 1.78 and 2.15 times higher than in winter, respectively. Fs and Fn were higher in daytime than in nighttime. Significant positive correlation was found between Fs and relative humidity. The positive correlation between Fn and relative humidity was insignificant. The correlation between the concentration of NH4+ and NO3– indicates that NO3– may be found in fine mode (NH4NO3) in winter and it may be present predominantly as a coarse mode, such as Ca(NO3)2, Mg(NO3)2 and NaNO3 in summer. The concentration of SO42– was significantly correlated with NH4+ concentration, suggesting neutralization by NH3 and indicating that the forms of (NH4)2SO4 and/or NH4HSO4 exist in the aerosol. The NH4+/SO42– molar ratio indicates that SO42– in aerosol may be present as (NH4)2SO4, (NH4)2SO4.CaSO4.2H2O and CaSO4.

The present study has been designed to optimise certain important process parameters for Scenedesmus vacuolatus to achieve efficient carbon dioxide extenuation as well as suitable fatty acid profile in context to improve biodiesel properties. The effect of varying sodium bicarbonate concentration was evaluated in single and multicomponent system such as nitrate, phosphate, inoculum size to observe interactive effects on algae biomass production, carbon dioxide (CO₂) removal efficiency and fatty acid methyl ester (FAME) profile. Maximum biomass productivity of 117.0 ± 7.7 mg/L/day with 3 g/L of sodium bicarbonate was obtained i.e. approximately 2 folds higher than the control. Under multicomponent exposure, maximum biomass of 1701.5 ± 88.8 mg/L and maximum chlorophyll concentration of 15.3 ± 6.4 mg/L were achieved on 14th day at 3 g/L sodium nitrate, 0.1 g/L dipotassium hydrogen phosphate, 2 g/L of sodium bicarbonate and initial cell density of 0.3 (N₃P₀.₁B₂OD₀.₃). FAME content of 46.1 mg/g of biomass was obtained at this combination which is approximately 3 folds higher than the FAME content obtained under nitrogen and phosphate deprivation (16.6 mg/g at N₀P₀B₂OD₀.₃). Confocal microscopy images confirmed the results with enhanced lipid droplet accumulation at high bicarbonate concentration as compared with the control. This interactive study concluded the variability in FAME profile along with the exposure to varying nutrient concentrations.

Biosurfactants have been considered as promising candidates for oil spill cleanup as they are generally more biodegradable, less toxic, and better in enhancing biodegradation than chemical surfactants. This study targeted the marine microbial biosurfactants to examine their enhanced production methods and application for the removal of crude oil from soil. The biosurfactants generated by Bacillus subtilis, which was isolated from the Atlantic Ocean, were investigated in this study. The economic production medium using different carbon (n-hexadecane, diesel oil, glycerol, glucose, starch, and sucrose) and nitrogen sources (NaNO₃, (NH₄)₂SO₄, and yeast extract) was studied. The best performance of biosurfactant production was achieved when using glycerol as carbon source and sodium nitrate and yeast extract as nitrogen sources in the substrate. The production rate was enhanced five times compared with that of the original screening recipe. The fermentative production of the generated biosurfactants could reduce the surface tension of water to 27 mN/m and with strong surface activity (∼36.4 mN/m) even after dilution for 10 times. The critical micellar concentration (CMC) of the product was 507 mg/L. A thin layer chromatography (TLC) analysis indicated that the purified product was a mixture of lipopeptide and glycolipid. The microbially produced biosurfactants were further examined as a soil-washing agent to enhance crude oil removal in a soil column system. The removal rates of 58 and 65 % were achieved using the biosurfactant solution with concentrations of 4 and 8 g/L, respectively. The results demonstrated the potential of marine microbial biosurfactants in cleaning crude oil-contaminated soil.

The microbial fuel cell (MFC) is one of the sustainable technologies, which alongside treating wastewater, can generate electricity. However, its performance is limited by factors like methanogenesis where methanogens compete with the anode respiring bacteria for substrate, reducing the power output. Thus, sodium nitrate, which has been previously reported to target the hydrogenotrophic methanogens, was used as a methanogenic suppressor in this study. The performance of MFC with and without sodium nitrate was studied during the treatment of rice mill wastewater. A significantly higher power density and coulombic efficiency (CE) were noted in the MFC with sodium nitrate (MFCT) (271.26 mW/m³) as compared to the control MFC (MFCC) (107.95 mW/m³). Polarization studies showed lower internal resistance for the MFCT (330 Ω) as compared to MFCC (390 Ω). Linear sweep voltammetry and cyclic voltammetry indicated a higher electron discharge on the anode surface due to enhancement of electrogenic activity. Considerable reduction (76.8%) in specific methanogenic activity was also observed in anaerobic sewage sludge mixed with sodium nitrate compared to the activity of anaerobic sewage sludge without any treatment. Due to the inhibition of methanogens, a lower chemical oxygen demand (COD) and phenol removal efficiency were observed in MFCT as compared to MFCC. The COD balance study showed an increase in substrate conversion to electricity despite the increase in nitrate concentration. Therefore, selective inhibition of methanogenesis had been achieved with the addition of sodium nitrate, thus enhancing the power generation by MFCs.