Chao Huang

Precipitation, adsorption and rhizosphere effect: The mechanisms for Phosphate-induced Pb immobilization in soils—A review

Lead (Pb) is one of the most toxic heavy metals that pose a direct threat to organisms and it can not been degraded through microbial activities or chemical reaction. Bioavaibility and eco-toxicity of Pb which mostly depend on Pb chemical speciation play an important role in the remediation of Pb-contaminated soils. Phosphate (P) amendments which could transfer Pb from unstable fraction to stable fraction are commonly used to immobilize Pb in soils and have been extensively studied by researchers during decades. Based on the previous study, it can be concluded that three principal mechanisms may be responsible for P-induced Pb immobilization: 1) the precipitation of Pb-phosphates, including direct precipitation, ion-exchange (or substitution) effect and liming effect; 2) the adsorption of Pb, including the direct adsorption and the adsorption of Pb to iron (hydr)oxides; 3) the rhizosphere effect, including acidification effect and mycorrhizae effect. In this review, these mechanisms have been completely discussed and the internal relationships among them were summarized to give a better understanding of P-induced Pb immobilization in soils and promote the development of P-based remediation technology.

Immobilization of Cd in river sediments by sodium alginate modified nanoscale zero-valent iron: Impact on enzyme activities and microbial community diversity

This paper investigated how sodium alginate (SA)-modified nanoscale zero-valent iron (NZVI), play a constructive role in the remediation of cadmium (Cd) contaminated river sediments. The changes of the fraction of Cd, enzyme activities (urease, catalase, dehydrogenase) and bacterial community structures with the treatment by SNZVI were observed. The sequential extraction experiments demonstrated that most mobile fractions of Cd were transformed into residues (the maximum residual percentage of Cd increases from 15.49% to 57.28% after 30 days of incubation at 0.1xa0wt% SA), with the decrease of bioavailability of Cd. Exclusive of dehydrogenase, the activities of the other two enzymes tested were enhanced with the increase of incubation time, which indicated that dehydrogenase might be inhibited by ferric ions formed from SNZVI whereas no obvious inhibition was found for other enzymes. Polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analyses were used for the detection of microbial community changes, and the results showed that SNZVI and NZVI could increase bacterial taxa and improve bacterial abundance. All the experimental findings of this study provide new insights into the potential consequences of SNZVI treatments on the metal Cd immobilization in contaminated river sediments.

Application of molecularly imprinted polymers in wastewater treatment: a review

Molecularly imprinted polymers are synthetic polymers possessing specific cavities designed for target molecules. They are prepared by copolymerization of a cross-linking agent with the complex formed from a template and monomers that have functional groups specifically interacting with the template through covalent or noncovalent bonds. Subsequent removal of the imprint template leaves specific cavities whose shape, size, and functional groups are complementary to the template molecule. Because of their predetermined selectivity, molecularly imprinted polymers (MIPs) can be used as ideal materials in wastewater treatment. Especially, MIP-based composites offer a wide range of potentialities in wastewater treatment. This paper reviews the latest applications of MIPs in wastewater treatment, highlights the development of MIP-based composites in wastewater, and offers suggestions for future success in the field of MIPs.

Synthesis and evaluation of a new class of stabilized nano-chlorapatite for Pb immobilization in sediment

During the past years, efforts have been made to deal with the Pb contaminated sediment in Xiawangang River in Hunan province, China, but it remains a serious problem since the smelting pollutants were accumulated. According to previous studies, phosphate showed an effective ability to transfer labile Pb to pyromorphite (Pb5(PO4)3X, X=F, Cl, Br, OH) but its application was limited by its solubility and deliverability. Hence a new class of nano-chlorapatite was synthesized by using sodium dodecyl sulfate (SDS) as a stabilizer and characterized by TEM, FESEM, DLS, FTIR, and EDAX. Results demonstrated that the SDS stabilized nano-chlorapatite (SDS-nClAP) was in spherical or spheroidal shape with a hydrodynamic diameter of 40.4nm. Experimental data suggested that SDS-nClAP was effective in transforming labile Pb to stable fraction with a maximum increase of 38.3%, also the reduction of TCLP-leachable Pb from 0.30 to 0mg/L after 45-d treatment. The increase of available phosphorus in both SDS-nClAP and ClAP treated sediment samples verified dissolution-precipitation mechanism involved in Pb immobilization. Additionally, the increment of organic matter in 10:1 treated samples was approximately 5-fold than that in 2:1 treated samples, which revealed that the micro-organisms may play an important role in it.

Rhamnolipid stabilized nano-chlorapatite: Synthesis and enhancement effect on Pb-and Cd-immobilization in polluted sediment

Phosphate (P) compounds are usually used as chemical amendment for in situ remediation of heavy metal polluted sediment. However, the low deliverability, weak utilization and potential risk of eutrophication inhibit the application of most P materials. Therefore, rhamnolipid (Rha), a kind of anionic biosurfactant which has algicidal activity, was employed in this study to synthesize a new kind of nano-chlorapatite (nClAP) for Pb and Cd immobilization. Characterization results showed that the Rha stablized nClAP (Rha-nClAP) was uniformly distributed in suspensions within about 5nm. Experimental data demonstrated that the combination of Rha and nClAP could greatly enhance the Pb- and Cd-immobilization efficiencies, promoting their transformation from labile fractions to stable fractions through precipitation or adsorption processes, especially when the Rha approached to its critical micelle concentration. And Rha-nClAP could also decrease both the TCLP-leachable Pb and Cd with maximum reduction efficiencies of 98.12% and 96.24%, respectively, which also presented concentration dependence of Rha. Changes of available phosphorus implied the dissolution of nClAP during the treatment and the detection of organic matter demonstrated that the microorganisms may involve in the remediation.

Effect of Phanerochaete chrysosporium inoculation on bacterial community and metal stabilization in lead-contaminated agricultural waste composting

The effects of Phanerochaete chrysosporium inoculation on bacterial community and lead (Pb) stabilization in composting of Pb-contaminated agricultural waste were studied. It was found that the bioavailable Pb was transformed to stable Pb after composting with inoculum of P. chrysosporium. Pearson correlation analysis revealed that total organic carbon (TOC) and carbon/nitrogen (C/N) ratio significantly (P<0.05) influenced the distribution of Pb fractions. The richness and diversity of bacterial community were reduced under Pb stress and increased after inoculation with P. chrysosporium. Redundancy analysis indicated that C/N ratio, total organic matter, temperature and soluble-exchangeable Pb were the significant parameters to affect the bacterial community structure, solely explained 14.7%, 11.1%, 10.4% and 8.3% of the variation in bacterial community composition, respectively. In addition, the main bacterial species, being related to organic matter degradation and Pb stabilization, were found. These findings will provide useful information for composting of heavy metal-contaminated organic wastes.

The effects of rice straw biochar on indigenous microbial community and enzymes activity in heavy metal-contaminated sediment

Owning to the potential in carbon sequestration and other environmental benefits, biochar has been widely used for in-situ environmental remediation. Understanding the biological effects of biochar is essential. The goal of this study was to explore the response of indigenous microbes under the stress of different concentrations of biochar. The results showed that biochar could significantly change physicochemical properties, enzymes activity and microbial community composition depending on biochar concentration and incubation time. When the concentration of biochar was 50xa0mgxa0kg-1, the activities of invertase and alkaline phosphatase were obviously inhibited. Meanwhile, bacterial 16S rRNA and fungal 18S rRNA coding gene copies were decreased by 74% and 25%, respectively after 90 days of incubation. Additionally, the bacterial community succession occurred and the relative intensity of dominant species decreased when treated with high concentration of biochar. However, the activity of urease and alkaline phosphatase, as well as bacterial and fungal abundance, were increased when sediment was treated with 10xa0mgxa0kg-1 biochar. Relationships among physicochemical properties, heavy metals and microbes were analyzed by correlation analysis and redundancy analysis (RDA). Correlations between invertase activity and pH value in the experiment were significantly negative. Redundancy analysis showed physicochemical properties and heavy metals explained 92% of the variation in the bacterial DGGE profiles and organic matter content explained the majority (45%) of the variation. This study indicated that indigenous microbes could be affected by biochar either directly or indirectly via changing the physicochemical properties and heavy metals of sediment.

Selective removal of BPA from aqueous solution using molecularly imprinted polymers based on magnetic graphene oxide

Bisphenol A (BPA) is a chemical with the potential to cause estrogenic and genotoxic effects on humans and wildlife. In this study, a novel and quick method was employed for selective removal of BPA from aqueous solutions, which used magnetic graphene oxide-based molecularly imprinted polymers as the adsorbent. Adsorption experiments were carried out to examine the effect of pH, initial concentration of BPA, isotherms and sorption kinetics on the adsorption of BPA by magnetic molecularly imprinted polymers (MMIPs). Results revealed the maximum adsorption capacity of BPA by MMIPs was 106.38 mg g−1 at 298 K and the equilibrium data of MMIPs were described well by a Langmuir isotherm model. Furthermore, the sorption kinetics followed the pseudo-second-order equation, which indicated that the chemical process might be the rate limiting step in the adsorption process for BPA. In addition, selective binding experiments were performed using 2,4-dichlorophenol and phenol as competitive compounds, and the resulting selectivity coefficients for the experiment were 2.505 and 2.440, respectively. All these results revealed that the prepared MMIPs had good selectivity and effective adsorption for BPA.

Simultaneous removal of Cr(VI) and phenol in consortium culture of Bacillus sp. and Pseudomonas putida Migula (CCTCC AB92019)

Abstract The simultaneous removal of Cr(VI) and phenol in a consortium culture containing Cr(VI) reducer, Bacillus sp . and phenol degrader, Pseudomonas putida Migula (CCTCC AB92019) was studied. Phenol was used as the sole carbon source. Bacillus sp . utilized metabolites formed from phenol degradation as electron donors and energy source for Cr(VI) reduction. Optimum Cr(VI) reduction was observed at a phenol concentration of 150 mg/L and an initial Cr(VI) concentration of 15 mg/L. Both the Cr(VI) reduction and phenol degradation were influenced by the cell composition of the culture, but the phenol degradation was not significantly affected by the content of Bacillus sp . The experiments also showed that the amount of phenol degraded was more than that stoichiometrically required for Cr(VI) reduction.

Preparation of water-compatible molecularly imprinted thiol-functionalized activated titanium dioxide: Selective adsorption and efficient photodegradation of 2, 4-dinitrophenol in aqueous solution

A novel water-compatible surface molecularly imprinted thiol-functionalized titanium dioxide (TiO2) material (CMIP-coated TiO2) was prepared in water, using 2, 4-dinitrophenol (2, 4-DNP) as template molecule and o-phenylenediamine (OPDA) as both functional monomer and cross-linker. The as-synthesized materials were characterized by FESEM, FTIR, XRD, BET and UV-vis DRS. Moreover, we have investigated the adsorption capacity, adsorption selectivity and photodegradation activity of the CMIP-coated TiO2 and non-molecular imprinted materials (CNIP-coated TiO2). Additionally, the effects of pH and concentration of 2, 4-DNP on the degradation rate of 2, 4-DNP were also investigated. Results showed that CMIP-coated TiO2 exhibited higher adsorption capacity, greater selectivity and faster photodegradation activity for 2, 4-DNP compared with the CNIP-coated TiO2. Meanwhile, the specific selectivity to 2, 4-DNP over its structural analogue 4-nitrophenol (4-NP) and the enhanced photodegradation capacity were mainly attributed to the imprinted cavities on the surface of CMIP-coated TiO2. Taking advantage of efficient removal capacity, high reusability and no-additional chemicals in imprinted process, the prepared materials can be potentially applied to green removal of 2, 4-DNP in wastewater.