Xue Li

Integrating hierarchical bioavailability and population distribution into potential eco-risk assessment of heavy metals in road dust: A case study in Xiandao District, Changsha city, China

Modified eco-risk assessment method (MEAM) integrated with the hierarchical bioavailability determined by the fraction detection of Cd, Pb, Zn, Cu, Cr in road dust samples and the local population distribution derived from the local land use map, was proposed to make the hierarchical eco-risk management strategy in Xiandao District (XDD), China. The geo-accumulation index (Igeo), the original potential eco-risk index (Er(i)) and the modified eco-risk assessment index (MEAI) were used to identify the priority pollutant. Compared with the Hunan soil background values, evaluated metal concentrations were found to different extent. The results of mean Igeo, Er(i) and bioavailability of studied metals revealed the following orders: Cd>Pb ≈ Zn>Cu ≈ Cr, Cd>Pb>Cu>Cr>Zn and Cd>Zn>Cu ≈ Pb>Cr, respectively. Therefore, Cd was regarded as the priority pollutant. To identify the priority areas taking into account cost consideration, the hierarchical risk map based on the results of the modified eco-risk assessment index with overlay of the population density map was needed and made. The west and partly south areas of XDD were under higher eco-risk generally. Moreover, the whole XDD area was divided into 4 area categories with different management priorities based on the possibility of occurrence of eco-risk, and the hierarchical risk management strategy associated with protecting local population was suggested to facilitate allocation of funds for risk management.

Micellar-enhanced ultrafiltration of cadmium and methylene blue in synthetic wastewater using SDS

Single and simultaneous removal of Cd(2+) and methylene blue (MB) with sodium dodecyl sulfate (SDS) by micellar-enhanced ultrafiltration under different experimental conditions was investigated. In single removal process, with initial SDS concentration increasing, the removal efficiency of Cd(2+) and MB kept increasing and then decreased. When the initial concentrations of SDS and Cd(2+) were 1.0 cmc and 50 mg L(-1), respectively, the maximum removal efficiency of Cd(2+) was obtained as 99.2%. Removal efficiency of MB could achieve more than 99.9% with initial SDS concentration below 2.0 cmc. As compared with single Cd(2+) removal, the removal efficiency of Cd(2+) in the presence of MB was slightly higher with initial SDS concentration below 1.0 cmc, while decreased with the SDS concentration above 1.0 cmc. The maximum removal efficiency of Cd(2+) was 98.8% when initial concentrations of SDS and MB were 1.0 cmc and 4 mg L(-1), respectively. The removal efficiency of MB in the presence of Cd(2+) could achieve higher than 96.5%, which was only 3.4% less than the optimum result of the single removal. Meanwhile, effect of pH on removal efficiency of Cd(2+) was more significant than that of MB.

Effect of groups difference in surfactant on solubilization of aqueous phenol using MEUF

Micellar-enhanced ultrafiltration (MEUF) was used to remove phenol from simulant aqueous solutions. The effect of groups difference of cationic surfactant on the solubilization of phenol was investigated through orthogonal experiment, namely, surfactants with the same length of hydrocarbon chain but different hydrophilic head group and vice versa. The effects on the solubilization of phenol of various operating parameters in the practical application of MEUF with OTAB were studied, including surfactant concentration, electrolyte concentration, feed phenol concentration, operating pressure, temperature, respectively. The results showed that the rejection of phenol increased in the order as follows: cetyltrimethylammonium bromide (CTAB)<octadecyl trimethyl ammonium bromide (OTAB)<cetylpyridinium chloride (CPC). With the introduction of feed surfactant concentration, the retention recovery of phenol increased. Electrolyte concentration, feed phenol concentration, operating pressure and temperature all had a slight influence on the retention of phenol.

Adsorption of surfactant micelles and Cd2+/Zn2+ in micellar-enhanced ultrafiltration

Micellar-enhanced ultrafiltration (MEUF) is a powerful treatment developed to remove heavy metals from wastewater. Efficient removal of Cd(2+)/Zn(2+) from wastewater was performed by MEUF using a polysulfone hollow ultrafiltration membrane, with sodium dodecyl sulfate (SDS) as the surfactant. The adsorption of surfactant micelles and Cd(2+)/Zn(2+) in MEUF was studied by changing the surfactant dosage and the Cd(2+)/Zn(2+) concentration in the feed. In addition, kinetics, adsorption isotherms, and thermodynamic rules were analyzed, and X-ray photoelectron spectroscopy (XPS) was conducted. It was found that when the Cd(2+)/Zn(2+) feed concentration was 50 mg/L, and the SDS dosage reached 2.15 g/L, the concentration of heavy metal ions in the permeate stabilized at around 1-4 mg/L, and the adsorption of Cd(2+)/Zn(2+) on SDS micelles followed second-order kinetics and the Langmuir isotherm laws. Adsorption is a spontaneous endothermic process in which the adsorption force is principally the attraction of opposite electrical charges.

Micellar-enhanced ultrafiltration for the solubilization of various phenolic compounds with different surfactants

Micellar-enhanced ultrafiltration (MEUF) was applied to the separation of phenolic compounds p-nitrophenol (PNP), p-chlorophenol (PCP), p-cresol (PC) and phenol (P) from effluents using a hydrophilic polyethersulfone ultrafiltration membrane. Cationic cetylpyridinium chloride (CPC), nonionic TX-100 and anionic sodium dodecyl benzene sulfonate (SDBS) were chosen as the surfactants. Several important parameters, i.e. the separation efficiency, the distribution coefficient of phenolic compounds and the removal ratio of surfactants, were investigated. It was shown that the separation efficiency and the distribution coefficient of phenolic compounds ascended with the increasing surfactant concentration and could be arranged as the following order: PNP>PCP>PC>P. Moreover, in the case of phenolic compound separation, CPC achieved the highest treatment efficiency, and the separation efficiency of SDBS was a little lower than that of TX-100. The removal ratios of the same surfactant when treating different phenolic effluents were nearly similar. However, when treating the same phenolic compound, the sequence of the surfactant rejection was in the following order: TX-100>CPC>SDBS. These results indicate that CPC has a distinct superiority in the treatment of phenolic effluents via the MEUF process, and PNP easily solubilizes in the surface of the micelles.

Removal of organic matter and heavy metals of low concentration from wastewater via micellar-enhanced ultrafiltration: an overview

As a new and effective means of wastewater treatment, the micellar-enhanced ultrafiltration (MEUF) has been extensively studied. In this paper, MEUF was introduced from the aspects of theory basis, ultrafiltration membranes, and surfactants. Additionally, the latest research achievements in removing organic matter and heavy ions, its application in actual wastewater, and the characterization parameters of MEUF were introduced and summarized. Then, influences and mechanisms of the primary operation parameters, including surfactant concentration, pH, electrolytes, and transmembrane pressure on the performance of the MEUF process were analyzed. Finally, existing problems in the MEUF process were identified and developmental trends were predicted.

Characterization and mechanism of lead and zinc biosorption by growing Verticillium insectorum J3

Verticillium insectorum J3 was isolated from a local lead-zinc deposit tailing, and its biosorption characteristics and reaction to the toxicities of different Pb(II) and Zn(II) concentrations were investigated. SEM, FTIR, a pH test and a desorption experiment were carried out to identify a possible mechanism. The biosorption of J3 presented an inhibition trend at low concentrations (25-75 mg L-1) and promotion at high concentrations (100-300 mg L-1). J3 absorbed Pb(II) prior to Zn(II) and produced alkaline substances, while mycelial and pellet morphology modifications were important for the removal of Pb(II) and Zn(II) under different stressful conditions (SEM results). Both intracellular accumulation and extracellular absorption may contribute to the removal of Pb(II) at lower concentrations (25-50 mg L-1), although mainly extracellular biosorption occurred at higher concentrations (75-300 mg L-1). However, Zn(II) bioaccumulation occurred at all concentrations assayed. Verticillium insectorum J3 may have evolved active defenses to alleviate the toxicity of heavy metals and proved to be a highly efficient biosorbent, especially for Pb(II) at high concentrations. This study is a useful reference for the development of biotreatment technologies to mitigate heavy metal waste.

Landfill leachate treatment by coagulation/flocculation combined with microelectrolysis-Fenton processes

ABSTRACT Landfill leachate was pretreated by chemical flocculation with polyaluminum chloride (PAC) as a flocculant, and subsequently purified by the microelectrolysis-Fenton (MEF) process. Response surface methodology was employed to optimize the MEF process, and the optimal conditions were initial pH 3.20, H2O2 concentration 3.57 g/L, and Fe-C dosage 104.52 g/L. The PAC coagulation combined with MEF processes obtained a superior decontamination performance, and the predicted chemical oxygen demand (COD) and humic acids (HA) removal were respectively 90.27% and 93.79%. The strong fluorescence peak at 425 nm and the trapping experiment showed that was generated during MEF, which had a strong oxidation ability to degrade organic recalcitrant pollutants. The ultraviolet–visible spectra and three-dimensional excitation–emission matrices spectra (3D-EEMs) indicated that PAC coagulation could preferentially remove protein-like substances, while the MEF process was effective in destructing organic recalcitrant pollutants, especially humic-like and fulvic-like substances.