Zhimin Yuan

Uranium biosorption from aqueous solution onto Eichhornia crassipes.

Batch experiments were conducted to investigate the biosorption of U(VI) from aqueous solutions onto the nonliving biomass of an aquatic macrophyte Eichhornia crassipes. The results showed that the adsorption of U(VI) onto E. crassipes was highly pH-dependent and the best pH for U(VI) removal was 5.5. U(VI) adsorption proceeded rapidly with an equilibrium time of 30 min and conformed to pseudo-second-order kinetics. The Langmuir isotherm model was determined to best describe U(VI) biosorption with a maximum monolayer adsorption capacity of 142.85 mg/g. Thermodynamic calculation results indicated that the U(VI) biosorption process was spontaneous and endothermic. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis implied that the functional groups (amino, hydroxyl, and carboxyl) may be responsible for the U(VI) adsorption process, in which the coordination and ion exchange mechanisms could be involved. We conclude that E. crassipes biomass is a promising biosorbent for the removal of uranium pollutants.

Potentially toxic trace element contamination, sources, and pollution assessment in farmlands, Bijie City, southwestern China

Artisanal zinc smelting activities, which had been widely applied in Bijie City, Guizhou Province, southwestern of China, can pollute surrounding farmlands. In the present study, 177 farmland topsoil samples of Bijie City were collected and 11 potentially toxic trace elements (PTEs), namely Pb, Zn, Cu, Ni, Co, Mn, Cr, V, Hg, As, and Cd were tested to characterize the concentrations, sources, and ecological risks. Mean concentrations of these PTEs in soils were (mg/kg) as follows: Pb (127), Zn (379), Cu (93.1), Ni (54.6), Co (26.2), Mn (1095), Cr (133), V (206), Hg (0.15), As (16.2), and Cd (3.08). Pb, Zn, and Cd had coefficients of variation greater than 100% and showed a high uneven distribution and spatial variability in the study area. Correlation coefficient analysis and principal component analysis (PCA) were used to quantify potential pollution sources. Results showed that Cu, Ni, Co, Mn, and V came from natural sources, whereas Pb, Zn, Hg, As, and Cd came from anthropogenic pollution sources. Geoaccumulation index and potential ecological risk indices were employed to study the pollution degree of PTEs, which revealed that Pb and Cd shared the greatest contamination and would pose serious ecological risks to the surrounding environment. The results of this study could help the local government managers to establish pollution control strategies and to secure food safety.

Monitoring Soil Microbial Activities in Different Cropping Systems Using Combined Methods

Abstract Cropping activities may affect soil microbial activities and biomass, which would affect C and N cycling in soil and thus the crop yields and quality. In the present study, a combination of microcalorimetric, enzyme activity (sucrase, urease, catalase, and fluorescein diacetate hydrolysis), and real–time polymerase chain reaction (RT–PCR) analyses was used to investigate microbial status of farmland soils, collected from 5 different sites in Huazhong Agriculture University, China. Our results showed that among the 5 sites, both positive and negative impacts of cropping activities on soil microbial activity were observed. Enzyme activity analysis showed that cropping activities reduced soil sucrase and urease activities, which would influence the C and N cycles in soil. Much more attentions should be given to microbial status affected by cropping activities in future. According to the correlation analysis, fluorescein diacetate hydrolysis showed a significantly ( P 0.05) negative correlation with the time to reach the maximum power output ( R = −0.898), but a significantly ( P R = 0.817). Soil catalase activity also showed a significantly ( P R = 0.965). Using combined methods would provide virtual information of soil microbial status.

Removal of Pb(II) by adsorption onto Chinese walnut shell activated carbon

The excessive discharge of Pb(II) into the environment has increasingly aroused great concern. Adsorption is considered as the most effective method for heavy metal removal. Chinese walnut shell activated carbon (CWSAC) was used as an adsorbent for the removal of Pb(II) from aqueous solution. Batch experiments were conducted by varying contact time, temperature, pH, adsorbent dose and initial Pb(II) concentration. Adsorption equilibrium was established within 150 min. Although temperature effect was insignificant, the Pb(II) adsorption was strongly pH dependent and the maximum removal was observed at pH 5.5. The Pb(II) removal efficiency increased with increasing CWSAC dosage up to 2.0 g/L and reached a maximum of 94.12%. Langmuir and Freundlich adsorption isotherms were employed to fit the adsorption data. The results suggested that the equilibrium data could be well described by the Langmuir isotherm model, with a maximum adsorption capacity of 81.96 mg/g. Adsorption kinetics data were fitted by pseudo-first- and pseudo-second-order models. The result indicated that the pseudo-first-order model best describes the adsorption kinetic data. In summary, CWSAC could be a promising material for the removal of Pb(II) from wastewater.

Combined effects of antimony and sodium diethyldithiocarbamate on soil microbial activity and speciation change of heavy metals. Implications for contaminated lands hazardous material pollution in nonferrous metal mining areas

The combined effects of antimony (Sb) and sodium diethyldithiocarbamate (DDTC), a common organic flotation reagent, on soil microbial activity and speciation changes of heavy metals were investigated for the first time. The results showed that the exchangeable fraction of Sb was transformed to a stable residual fraction during the incubation period, and the addition of DDTC promoted the transformation compared with single Sb pollution, probably because DDTC can react with heavy metals to form a complex. In addition, the presence of DDTC and Sb inhibited the soil microbial activity to varying degrees. The growth rate constant k of different interaction systems was in the following order on the 28th day: control group ≥ single DDTC pollution > combined pollution > single Sb pollution. A correlation analysis showed that the concentration of exchangeable Sb was the primary factor that affected the toxic reaction under combined pollution conditions, and it significantly affected the characteristics of the soil microorganisms. All the observations provide useful information for a better understanding of the toxic effects and potential risks of combined Sb and DDTC pollution in antimony mining areas.

Degradation of hydrocarbons by indigenous microbial communities from two adjacent oil production wells in one block

ABSTRACT Aerobic acclimatization cultures of oil production water from two adjacent oil production wells (Xi15-14 and Xi51-5) in one block of Dagang oilfield were generated depending on crude oil as the sole carbon source and energy. Both cultures revealed a high degrading efficiency for a wide range of hydrocarbons, but degradation trend were striking different, and surface tension of two phases of oil and water decreased from 60 to 30 mN/m approximately by virtue of indigenous microbial metabolic activities. Meanwhile, cultured indigenous bacteria of wellXi15-14 mainly included Hydrocarboniphaga, Pseudomonas, and Ectothiorhodospiraceae bacterium, while wellXi51-5 contained Sphingomonas and Pseudomonas. Furthermore, abundance of alkane hydroxylase genes alk B and alk M from the two samples also showed an apparent difference. These findings are important that microbial diversity tightly tallies with the fact of a highly compartmentalized stratigraphy of this oilfield, suggesting that it is better to recover oil from extreme reservoirs with the targeted stimulating indigenous microorganisms.