Yongsheng Zhao

Characteristics and kinetics of hexavalent chromium reduction by gallic acid in aqueous solutions

Gallic acid (GA) is a naturally occurring plant polyphenol compound. Experiments were conducted to study the kinetics and effects of pH, temperature, irradiation, and initial hexavalent chromium (Cr(VI)) concentration on Cr(VI) reduction by GA. Results indicated that Cr(VI) could be reduced to chromium oxide (Cr(III)) with GA in a wide range of pH values from 2.0 to 8.5. The reaction followed a pseudo-first-order kinetic model with respect to Cr(VI) and GA in acid conditions (pH 2.0-5.0). However, the reaction did not follow the pseudo-first-order kinetic model at pH 6.5 and 8.5. Removal efficiencies and reaction rate constants of Cr(VI) significantly increased with decreasing pH value and increasing temperature. The effect of irradiation on Cr(VI) reduction increased with increasing pH, and irradiation improved the removal efficiency of Cr(VI) by 11.29% at pH 6.5. At pH 2.0, nearly all molar ratios of GA required for the reduction of Cr(VI) were 1:2 (±0.1) under different initial Cr(VI) concentrations; however, the molar ratios of GA required for the reduction of Cr(VI) were 1:1.29, 1:1.43, and 1:1.69, respectively, when the initial Cr(VI) concentrations were 10, 25, and 50 mg/L at pH 5.5.

BTEX biodegradation and its nitrogen removal potential by a newly isolated Pseudomonas thivervalensis MAH1

Benzene, toluene, ethylbenzene, and xylene (BTEX) are of great environmental concern because of their widespread occurrence in groundwater and soil, posing an increasing threat to human health. The aerobic denitrifying BTEX-degrading bacterium Pseudomonas thivervalensis MAH1 was isolated from BTEX-contaminated sediment under nitrate-reducing conditions. The degradation rates of benzene, toluene, ethylbenzene, and xylene by strain MAH1 were 4.71, 6.59, 5.64, and 2.59 mg·L⁻¹day⁻¹, respectively. The effects of sodium citrate, nitrate, and NaH2PO4 on improving BTEX biodegradation were investigated, and their optimum concentrations were 0.5 g·L⁻¹, 100 mg·L⁻¹, and 0.8 mmol·L⁻¹, respectively. Moreover, MAH1, which has nirS and nosZ genes, removed ammonium, nitrate, and nitrite at 2.49 mg NH(4)(+)-N·L⁻¹·h⁻¹, 1.50 mg NO(3)(-)-N·L⁻¹·h⁻¹, and 0.83 mg NO(2)(-)-N·L⁻¹·h⁻¹, respectively. MAH1 could help in mitigating the pollution caused by nitrogen amendments for biostimulation. This study highlighted the feasibility of using MAH1 for the bioremediation of BTEX-contaminated sites.

Migration and transformation behavior of volatile phenol in the vadose zone.

Research on the migration and transformation of phenol with space and temporal variability in the vadose zone is hindered by monitoring technology in field experiments. Four column experiments were conducted to investigate the effect of porous media size, volatilization, biological effects, and oxidation on the transport of phenol in the vadose zone. The initial inflow phenol concentration of each column was 500 mg/L, and the final outflow concentrations were 0, 348, 240, and 365 mg/L, More than 90% of reduction of phenol concentration occurred at the top of the simulation column. Results show that volatilization and oxidation are the main factors that could lead to the decrease of phenol concentration in an open system. However, these two processes cannot be accurately separated. The migration rate of phenol was larger in coarse sands (6.06 cm/d) than in fine sands (4.55 cm/d). Phenol biodegradation did not occur under experimental conditions. However, mercury (as biological inhibitor) could react with phenol to generate a mercury-phenol complex, which could lead to the reduction of phenol concentration to 21.6% in the simulation experiment.

Transport of sucrose-modified nanoscale zero-valent iron in saturated porous media: role of media size, injection rate and input concentration

The growing use of nanoscale zero-valent iron (NZVI) in the remediation of contaminated groundwater raises concerns regarding its transport in aquifers. Laboratory-scale sand-packed column experiments were conducted with bare and sucrose-modified NZVI (SM-NZVI) to improve our understanding of the transport of the nanoparticles in saturated porous media, as well as the role of media size, suspension injection rate and concentration on the nanoparticle behavior. As the main indicative parameters, the normalized effluent concentration was measured and the deposition rate coefficient (k) was calculated for different simulated conditions. Overall, compared to the high retention of bare NZVI in the saturated silica column, SM-NZVI suspension could travel through the coarse sand column easily. However, the transport of SM-NZVI particles was not very satisfactory in a smaller size granular matrix especially in fine silica sand. Furthermore, the value of k regularly decreased with the increasing injection rate of suspension but increased with suspension concentration, which could reflect the role of these factors in the SM-NZVI travel process. The calculation of k-value at the tests condition adequately described the experimental results from the point of deposition dynamics, which meant the assumption of first-order deposition kinetics for the transport of NZVI particles was reasonable and feasible.

Improved light-transmission method for the study of LNAPL migration and distribution rule

In this study, diesel was selected as a pollutant to study the migration and distribution rule of light non-aqueous phase liquid (LNAPL) in the simulated vadose zone. Saturation was regarded as a critical parameter to reflect the LNAPL migration and distribution rule. To get LNAPL saturation distribution figures, an image processing method of saturation was established to improve light-transmission technology, which can deal with digital camera images. Results showed that the vadose zone contains three areas from top to bottom, named dry media, transition zone and capillary zone. The system has two interfaces at which moisture content increased significantly. The significant increase in moisture content induced two apparent horizontal LNAPL diffusions in the two interfaces. Furthermore, the highly saturated LNAPL was mostly distributed near the wet interface, which lay between the dry media and the transition zone. Moreover, the downstream expansion of LNAPL in the capillary zone was promoted by groundwater flow, yet cutting off LNAPL supply could stop the downstream expansion after a period of time. The accuracy of this image processing method of saturation was verified by mass balance theory and reported a relative error of 4.38%.

Enhancing bacterial transport with saponins in saturated porous media for the bioaugmentation of groundwater: visual investigation and surface interactions

The success of bioaugmentation processes for the remediation of groundwater contamination relies on effective transport of the injected microorganisms in a subsurface environment. Biosurfactants potentially affect bacterial attachment and transport behavior in porous media. Although saponins as biosurfactants are abundant in nature, their influence on bacterial transport in groundwater systems remains unknown. In this research, tank visual-transport experiments, breakthrough curve monitoring, and surface property measurement were performed to evaluate the effects of saponins on the transport of Pseudomonas migulae AN-1 cells, which were used as a model bacterium in saturated sand. Results show that the 0.1% saponins could effectively facilitated the AN-1 secondary transport and the addition of saponins decreased the hydrophobicity of AN-1 and sand. The role of the promotion of saponins was more dominant than that of the inhibition of ions on AN-1 transport in a saturated porous medium when ions and saponins coexisted. The interactions between AN-1 and sand grains with saponins and ions were explained in accordance with the Derjaguin–Landau–Verwey–Overbeek theory.

Preparation of Ag-MnFe2O4-bentonite Magnetic Composite for Pb(II)/Cd(II) Adsorption Removal and Bacterial Inactivation in Wastewater

An Ag-MnFe2O4-bentonite composite was synthesized by a chemical co-precipitation method and used for adsorption removal of Pb(II), Cd(II) and disinfection. The result of X-ray diffraction indicate that the diffraction peaks of MnFe2O4 and Ag can be perfectly indexed to the cubic spinel MnFe2O4(JCPDS No.88-1965) and metallic Ag(JCPDS No.41-1402), respectively. The results of scanning electron microscopy and energy dispersive X-ray spectroscopy manifest the deposition of MnFe2O4 and Ag on the bentonite surface and the presence of Mn, Fe and Ag. The result of X-ray photoelectron spectroscopy displayed that the composition of Ag-MnFe2O4-bentonite was Mn(II), Fe(III) and metallic Ag. The analysis of Brunauer-Emmett-Teller showed that the specific surface area of Ag-MnFe2O4-bentonite was the largest compared with that of bentonite, MnFe2O4 and MnFe2O4-bentonite. Thermo-dynamic studies revealed that the adsorption of Pb(II) and Cd(II) ions was spontaneous and endothermic. Langmuir model showed an adsorption capacity of 129.87 mg/g for Pb(II) and 48.31 mg/g for Cd(II) ions. The adsorption ki-netics of Pb(II) and Cd(II) ions onto Ag-MnFe2O4-bentonite can be best described by a pseudo-second-order model. The adsorption rate constant of the pseudo-second-order model was 0.0019 g·mg‒1·min‒1 for Pb(II) and 0.0065 g·mg‒1·min‒1 for Cd(II) ions. In addition to the adsorption experiment, the antibacterial properties of Ag-MnFe2O4-bentonite were studied through plate count method. Gram-negative(G‒) bacteria Escherichia coli and Gram-positive(G+) bacteria Lactobacillus plantarum were used to test the antibacterial properties. The results showed that the composite demonstrated excellent antibacterial activity. Thus, Ag-MnFe2O4-bentonite can be em-ployed as an adsorbent as well as an antimicrobial agent.

Effect of Common Dissolved Ions on the Reduction of Nitrobenzene by Sucrose-Modified Zero-Valent Iron

NB reduction with NZVI will be effected by factors. In this study, batch experiments were carried out to evaluate the single and combined actions of common dissolved ions including HCO3-, Cl-, SO42-, NO3-, Mg2+ and Ca2+. The results showed that the removal efficiency of NB was enhanced with the increase of the concentration of added HCO3-, Cl-, SO42-, NO3- as a descending order, and SO42- would be an inhibitor when its concentration was lower than 250 mg/L. Mg2+ and Ca2+ themselves had no obvious influences on NB reduction with SM-NZVI, but they could weaken the positive effects of other coexisting ions like Cl- and SO42-. Coexistence of these dissolved ions would promote metal carbonate precipitations and thus made against NB degraded and aniline produced.