Xiaoyun Yi

Equilibrium and kinetic studies of adsorption of Cd(II) from aqueous solution using modified corn stalk.

This paper describes the adsorption of cadmium ions from aqueous solution using acrylonitrile (AN)-modified corn stalk (AMCS). AMCS was characterized by elemental analysis, scanning electron microscopy, surface area and porosity analyzer, Fourier transform infrared and solid-state CP/MAS (13)C NMR spectra, and then used to evaluate the adsorption capacity in different pH values, adsorption isotherm, kinetics and thermodynamics in batch experiments. The results showed that AMCS is found to be an effective adsorbent because of its pore size and functional groups (-CN). The pH of 7.0 was an optimal pH for removal of Cd(II) ion and the Langmuir model provides a better fit to the equilibrium data than the Freundlich model, showing a maximum uptake of 12.73 mg g(-1), compared to raw corn stalk (RCS) (3.39 mg g(-1)). Analysis indicated that pseudo-second-order kinetics controlled the adsorption rate. The activation energy (E(a)) was 9.43 kJ mol(-1). Thermodynamic parameters such as DeltaG, DeltaH and DeltaS were also evaluated to predict the nature of adsorption process.

Remediation of soil co-contaminated with pyrene and cadmium by growing maize (Zea mays L.)

Sites co-contaminated with organic and metal pollutants are common and considered to be a more complex problem as the two components often causes a synergistic effect on cytotoxicity. Phytoremediation has been proposed as a cost-effective technology for treating heavy metal or organic contamination and may be suitable for remediation of co-contaminated soil. This study investigated the concurrent removal of pyrene and cadmium in co-contaminated soil by growing maize in a pot experiment. At the end of 60 day culture, pyrene in spiked soil diminished significantly, accounting for 21–31 % of the initial extractable concentration in unplanted soil and 12–27 % in planted soil. With the increment of cadmium level, the residual pyrene both in unplanted and planted soil tended to increase. Although the presence of cadmium increased the accumulation of pyrene in maize, plant accumulation only account for less than 0.30 % of the total amount of the dissipated pyrene in vegetated soils. It implied that plant-promoted microbial biodegradation was the predominant contribution to the plant-enhanced dissipation of pyrene in co-contaminated soil. Unlike pyrene, heavy metal cadmium cannot be degraded. It was observed that maize can concurrently removed about on the average 0.70 % of the total cadmium amount in soil by plant uptake, but cadmium phytoextraction would be inhibited under contamination of pyrene. Maize CT38 can normally grow in the co-contaminated soil with high level cadmium and pyrene and can effectively remedy the sites co-contaminated with these two types of contamination, which suggest the possibility of simultaneous phytoremediation of two different contaminant types.

Removal of cadmium(II) from aqueous solution by corn stalk graft copolymers

Corn stalk was modified using graft copolymerization to produce absorbent (AGCS), which was characterized by elemental analysis, fourier transform infrared, X-ray diffraction, solid-state CP/MAS (13)C NMR spectra, thermogravimetric analysis and differential scanning calorimeter. AGCS, having cyano group (-CN) after grafted successfully, exhibits more high adsorption potential for Cd(II) than unmodified forms. The efficiency of AGCS for removal of cadmium ions was evaluated. Factors affecting Cd(II) adsorption such as pH value and adsorbent dosage were investigated. More than 90% removal was achieved at pH 3.0-7.0 and the adsorption increased from 16.0% to 99.2% with increase of adsorbent dose. In addition, two isotherm models, namely, Langmuir and Freunlich were also analyzed to determine the best fit equation for adsorption of Cd(II) on AGCS.

Preparation of cellulose derived from corn stalk and its application for cadmium ion adsorption from aqueous solution

Cellulose was isolated from corn stalk and modified by graft copolymerization to produce an absorbent material (AGCS-cell), which was characterized by scanning electron microscope and energy disperse spectroscopy (SEM-EDS), X-ray diffraction (XRD) and solid-state CP/MAS (13)C NMR. The results showed that AGCS-cell had better adsorption potential for cadmium ion than unmodified cellulose because of the addition of functional groups (CN and OH groups) and the lower crystallinity. The Langmuir isotherms gave the best fit to the data and gave an adsorption capacity was 21.37 mg g(-1), which was close to unpurified cellulose (AGCS) and reflected the feasibility of using AGCS-cell as an adsorbent to remove cadmium ions.

Bioaccumulation characterization of cadmium by growing Bacillus cereus RC-1 and its mechanism.

In an effort to explore the protective mechanism of growing Bacillus cereus RC-1 against the toxicity of different Cd(II) concentrations, bacterial growth, cadmium consumption, surface interactions and intra- and extra-cellular Cd(II) contents were examined. Cellular morphology and growth were evidently affected by the initial metal concentrations above 20 mg L(-1), according to the analysis of SEM, AFM, TEM and UV spectrophotometer. Surface complexation and electrostatic attraction played an important role in the different Cd(II) concentrations, as determined by the FTIR and Zeta potential analysis. Intracellular accumulation was the predominant mechanism in culture with lower metal concentrations (below 20 mg L(-1)), but was overshadowed by extracellular adsorption at higher concentrations. This suggested that the growing cells might employ one dominant mechanism at lower concentrations and then shift to another at higher concentrations. These results suggest options could be exploited for bioremediation of aqueous solution in which the Cd(II) concentration is less than 20 mg L(-1).

Enhanced anaerobic dechlorination of polychlorinated biphenyl in sediments by bioanode stimulation.

The application of a low-voltage electric field as an electron donor or acceptor to promote the bioremediation of chlorinated organic compounds represents a promising technology meeting the demand of developing an efficient and cost-effective strategy for in situ treatment of PCB-contaminated sediments. Here, we reported that bioanode stimulation with an anodic potential markedly enhanced dechlorination of 2,3,4,5-tetrachlorobiphenyl (PCB 61) contained in the sediment at an electronic waste recycling site of Qingyuan, Guangdong, China. The 110-day incubation of the bioanode with a potential poised at 0.2 V relative to saturated calomel electrode enabled 58% transformation of the total PCB 61 at the initial concentration of 100 μmol kg(-1), while only 23% was reduced in the open-circuit reference experiment. The introduction of acetate to the bioelectrochemical reactor (BER) further improved PCB 61 transformation to 82%. Analysis of the bacterial composition showed significant community shifts in response to variations in treatment. At phylum level, the bioanode stimulation resulted in substantially increased abundance of Actinobacteria, Bacteroidetes, and Chloroflexi either capable of PCB dechlorination, or detected in the PCB-contaminated environment. At genus level, the BER contained two types of microorganisms: electrochemically active bacteria (EAB) represented by Geobacter, Ignavibacterium, and Dysgonomonas, and dechlorinating bacteria including Hydrogenophaga, Alcanivorax, Sedimentibacter, Dehalogenimonas, Comamonas and Vibrio. These results suggest that the presence of EAB can promote the population of dechlorinating bacteria which are responsible for PCB 61 transformation.

Fate of Fe and Cd upon microbial reduction of Cd-loaded polyferric flocs by Shewanella oneidensis MR-1

Polyferric sulphate has been widely used for emergent control on incidental release of heavy metals such as Cd to surface water, causing precipitation of Cd-loaded polyferric flocs to the sediment. To date, little is known about whether the dissolution of the flocs in the presence of dissimilatory iron reducing bacteria (DIRB) can occur and how the dissolution influences the fate of Fe and Cd in the sediment. Here, we demonstrated that Shewanella oneidensis MR-1, as representative DIRB, has the ability to reduce the flocs, resulting in the release of Fe(2+) and Cd(2+) to the solution. Batch experiment results showed that the concentrations of Fe(2+) and Cd(2+)reached the maximum values at 48 h and then decreased over the remaining incubation time. The characterizations on the solid phase by the scanning electron microscopy coupled with energy dispersive spectrometer, X-ray diffraction, and X-ray photoelectron spectroscopy technologies revealed the formation of iron minerals such as goethite and magnetite as a consequence of microbial Fe(III) reduction. The newly formed iron minerals played a significant role in re-immobilizing Cd by sorption. These results imply that microbial reduction of polyferric flocs is an important contributor to the transport and transformation of metals in the sediment-water interface.

Removal of chromium (VI) from electroplating wastewater using an anion exchanger derived from rice straw

An anion exchanger from rice straw was used to remove Cr (VI) from synthetic wastewater and electroplating effluent. The exchanger was characterized using Fourier transform infrared (FTIR) spectrum and scanning electron microscopy (SEM), and it was found that the quaternary amino group and hydroxyl group are the main functional groups on the fibrous surface of the exchanger. The effect of contact time, initial concentration and pH on the removal of Cr (VI), and adsorption isotherms at different temperature, was investigated. The results showed that the removal of Cr (VI) was very rapid and was significantly affected by the initial pH of the solution. Although acidic conditions (pH=2−− 6) facilitated Cr (VI) adsorption, the exchanger was effective in neutral solution and even under weak base conditions. The equilibrium data fitted well with Langmuir adsorption model, and the maximum Cr (VI) adsorption capacities at pH 6.4 were 0.35, 0.36 and 0.38 mmol/g for 15, 25 and 35°C, respectively. The exchanger was finally tested with real electroplating wastewater, and at sorbent dosage of 10 g/L, the removal efficiencies for Cr (VI) and total Cr were 99.4% and 97.8%, respectively. In addition, the positive relationship between adsorbed Cr (VI) and desorbed Cl− suggested that Cr (VI) was mainly removed by ion exchange with chlorine.

Uptake and Distribution of Cd in Sweet Maize Grown on Contaminated Soils: A Field-Scale Study

Maize is an economic crop that is also a candidate for use in phytoremediation in low-to-moderately Cd-contaminated soils, because the plant can accumulate high concentration of Cd in parts that are nonedible to humans while accumulating only a low concentration of Cd in the fruit. Maize cultivars CT38 and HZ were planted in field soils contaminated with Cd and nitrilotriacetic acid (NTA) was used to enhance the phytoextractive effect of the maize. Different organs of the plant were analyzed to identify the Cd sinks in the maize. A distinction was made between leaf sheath tissue and leaf lamina tissue. Cd concentrations decreased in the tissues in the following order: sheath > root > lamina > stem > fruit. The addition of NTA increased the amount of Cd absorbed but left the relative distribution of the metal among the plant organs essentially unchanged. The Cd in the fruit of maize was below the Chinese governments permitted concentration in coarse cereals. Therefore, this study shows that it is possible to conduct maize phytoremediation of Cd-contaminated soil while, at the same time, harvesting a crop, for subsequent consumption.

The effects of nutrient amendment on biodegradation and cytochrome P450 activity of an n-alkane degrading strain of Burkholderia sp. GS3C.

The promotion of hexadecane biodegradation activity by an n-alkane degrading strain of Burkholderia cepacia (GS3C) with yeast extract amendment was studied using various carbon, nitrogen, vitamin, and amino acid amendments. Cytochrome P450 monooxygenase enzymes play a very important role and are especially required to introduce oxygen in n-alkane degradation. These enzymes from GS3C were located and detected using amino acid amendments. It was shown that biodegradation activity was promoted with amino acids amendments. However, only specific amino acids (L-phenylalanine, L-glutamic acid, L-proline, L-lysine, L-valine and L-leucine) have biodegradation promoting ability for GS3C. Cell protein concentration and cytochrome P450 activity were promoted significantly with the addition of L-phenylalanine and yeast extract. Furthermore, a significant positive linear relationship between cytochrome P450 activity and biodegradation efficiency of GS3C was observed. The results indicate that amino acid is the primary factor of nutrient amendment in promoting hexadecane biodegradation by influencing cytochrome P450 activity in GS3C.