Ball-milled sulfide iron-copper bimetals based composite permeable materials for Cr (VI) removal: Effects of preparation parameters and kinetics study.

Zero-valent iron (ZVI) and modified ZVI have been investigated extensively for groundwater remediation. However, ZVI based powder was difficult to be applied directly as permeable reactive barrier (PRB) materials due to their low water permeability and usage rate. In this study, sulfide iron-copper bimetal was prepared by ball milling, which is environment-friendly without second contamination. The optimal preparation parameters of sulfide iron-copper bimetal for Cr(VI) removal were determined (Cu/Fe ratio (w/w), 0.018; FeS/Fe ratio (w/w), 0.1213; ball milling speed, 450 rpm; ball milling time, 5 h). A composite permeable material was prepared by sintering a mixture of sulfide iron-copper bimetal, sludge, and kaolin. The parameters for composite permeable material preparation including sludge content and particle size, and sintering time were optimized, which were 60%, 60-75 mesh, and 4 h, respectively. The optimal composite permeable material was characterized by SEM-EDS, XRD, and FTIR. The results demonstrated preparation parameters can affect the hydraulic conductivity and hardness of composite permeable material. High sludge content, small particles size, and moderate sintering time resulted in high permeability of composite permeable material and were beneficial for Cr(VI) removal. The dominant Cr(VI) removal mechanism was reduction, and the reaction followed pseudo-first order kinetics. Conversely, low sludge content and large particle size, and long sintering time lead to low permeability of composite permeable material. Chromate removal was mainly by chemisorption following pseudo-second order kinetics. The hydraulic conductivity and hardness of the optimal composite permeable material achieved 1.732 cm/s and 50, respectively. The results of column experiments indicated that its Cr(VI) removal capacity was 0.54 mg/g, 0.39 mg/g and 0.29 mg/g at pH 5, 7 and 9, respectively. The ratio of Cr(VI) to Cr(III) on composite permeable material surface was similar under acidic and alkaline conditions. This study will provide an effective reactive material of PRB for field application.

Synergistic solidification of lead-contaminated soil by magnesium oxide and microorganisms.

Although microbially induced carbonate precipitation (MICP) technology effectively promotes the remediation of heavy metal contaminated soils in low concentrations, the high concentration of heavy metals has a toxic effect on microorganisms, which leads to the decline of carbonate yield and makes the soil strength and environmental safety after remediation no up to the standard. This study describes the synergistic curing effect of MgO and microorganisms on soil contaminated with high concentrations of heavy metals. The experimental results with MgO showed 2-6 times increase in unconfined compressive strength (UCS) compared to bio-cemented samples without MgO. Toxicity characteristic leaching procedure experiments indicated that Pb-contaminated soil at 10,000 mg/kg with quantitative MgO for synergistic solidification could meet the international solid waste disposal standards, which leachable Pb2+ are less than 5 mg/L. In addition, the microscopic results showed that the introduction of MgO promoted the formation of magnesium calcite and dolomite, improved the solidification efficiency of heavy metal contaminants, and demonstrated the presence of Pb2+ in carbonate minerals. This study suggests that MgO and microorganisms have broad application prospects for synergistic solidification of Pb2+ soil.

Biocementation of Pyrite Tailings Using Microbially Induced Calcite Carbonate Precipitation.

Tailing sand contains a large number of heavy metals and sulfides that are prone to forming acid mine drainage (AMD), which pollutes the surrounding surface environment and groundwater resources and damages the ecological environment. Microbially induced calcium carbonate precipitation (MICP) technology can biocement heavy metals and sulfides in tailing sand and prevent pollution via source control. In this study, through an unconfined compressive strength test, permeability test, and toxic leaching test (TCLP), the curing effect of MICP was investigated in the laboratory and the effect of grouting rounds on curing was also analyzed. In addition, the curing mechanism of MICP was studied by means of Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction spectroscopy (XRD), and scanning electron microscopy (SEM). The experimental results showed that MICP could induce calcium carbonate precipitation through relatively complex biochemical and physicochemical reactions to achieve the immobilization of heavy metals and sulfides and significantly reduce the impact of tailing sand on the surrounding environment.

Arsenite (III) removal via manganese-decoration on cellulose nanocrystal -grafted polyethyleneimine nanocomposite.

The manganese is successfully induced as a "bridge joint" to fabricate a new adsorbent (CNC-Mn-PEI) connecting cellulose nanocrystal (CNC) and polyethyleneimine (PEI) respectively. It was used to remove As (III) from waste water. It has been proved that the incompact CNC and PEI were successfully connected by Mn ions, which induced the formation of O-Mn-O bonds and the removal efficiency is maintained in the broad pH range of 4-8, even with the influence of NO3- and CO32-. The CNC-Mn-PEI was characterized by Brunauer-Emmett-Telley (BET) method and the results showed that the nanoparticle of the specific surface area was 106.5753 m2/g, it has a significant improvement, compared with CNC-Mn-DW (0.1918 m2/g). The isotherm and kinetic parameters of arsenic removal on CNC-Mn-PEI were well-fitted by the Langmuir and pseudo-second-order models. The maximum adsorption capacities toward As (III) was 78.02 mg/g. After seven regeneration cycles, the removal of As (III) by the adsorbent decreased from 80.78% to 68.2%. Additionally, the hypothetical adsorption mechanism of "bridge joint" effect was established by FTIR and XPS, which provided the three activated sites from CNC-Mn-PEI can improve the arsenic removal efficiency, and providing a new stratagem for the arsenic pollution treatment.

Recyclable nitrogen-doped biochar via low-temperature pyrolysis for enhanced lead(II) removal.

Facile and low-cost preparation are essential in the conversation of agricultural waste into biochar. In this work, nitrogen-doped biochar (NBC-350-0.1) was prepared by thermal decomposition of urea (urea/biochar = 0.1:1 mass ratio) at a low temperature of 350 °C. NBC-350-0.1 showed good performance for Pb(II) removal with the maximum adsorption capacity of 130.87 mg g-1 at 25 °C, which was five times that of pristine biochar (BC). Adsorption kinetics, isotherms and thermodynamics studies indicated that the adsorption of Pb(II) by NBC-350-0.1 or BC was the homogeneous monolayer adsorption with chemical action as the rate-limiting step, and was accompanied by spontaneous endothermic. Further analysis showed that the removal of Pb(II) on NBC-350-0.1 and BC depended on the complexation with unsaturated carbon bonds and ion exchange with Ca(II). Moreover, graphitic- and pyridinic-N in NBC-350-0.1 exerted a key part in the adsorption of Pb(II). NBC-350-0.1 regenerated by NaOH exhibited excellent recycling performance keeping the original removal efficiency at 84% after five cycles. In addition, this N doping method is suitable for improving the performance of coffee grounds, sawdust, and bagasse biochar. These results would provide an idea for obtaining recyclable N-doped biochar to treat the Pb(II) polluted wastewater.

Study on preparation and application of a multifunctional microspheric soil conditioner based on Arabic gum, gelatin, chitosan and ß-cyclodextrin.

All kinds of soil conditioners have been used to improve soil quality. The application of many traditional soil conditioners was limited by single performance. In this study, a novel multifunctional microspheric soil conditioner was prepared based on Arabic gum, gelatin, chitosan and ß-cyclodextrin. Arabic gum and gelatin (AG-GL) microspheric carriers, which could load ferrous sulfate (FS), were synthesized via complex coagulation method. The AG-GL(FS) microspheres were covered by chitosan quaternary ammonium salt (CQAS) through single coagulation method. And ß-cyclodextrin (ß-CD) was used as the outermost shell to improve chemical stability of the soil conditioner by saturated solution method. Finally, the novel multifunctional microspheric soil conditioner AG-GL/CQAS/ß-CD-FS was obtained and characterized by Fourier transform infrared spectroscopy, thermogravimetric analyzer, polarizing microscope, scanning electron microscope and particle size analyzer. The novel soil conditioner shows good nutrient slowly-releasing, water retention, heavy metal ions adsorption and antibacterial performances with the particle size of 14-17 µm and high thermal decomposition temperature, which has the potential application in improving soil quality.

Bioremediation of Petroleum Hydrocarbons Using Acinetobacter sp. SCYY-5 Isolated from Contaminated Oil Sludge: Strategy and Effectiveness Study.

Biodegradation has been considered as an ideal technique for total petroleum hydrocarbon (TPH) contamination, but its efficiency is limited by its application in the field. Herein, an original TPH-degrading strain, SCYY-5, was isolated from contaminated oil sludge and identified as Acinetobacter sp. by 16S rDNA sequence analysis. The biological function of the isolate was investigated by heavy metal tolerance, carbon, and nitrogen source and degradation tests. To enhance its biodegradation efficiency, the response surface methodology (RSM) based on a function model was adopted to investigate and optimize the strategy of microbial and environmental variables for TPH removal. Furthermore, the performance of the system increased to 79.94% with the further addition of extra nutrients, suggesting that the RSM and added nutrients increased the activity of bacteria to meet the needs of the co-metabolism matrix during growth or degradation. These results verified that it is feasible to adopt the optimal strategy of combining bioremediation with RSM to improve the biodegradation efficiency, for contaminated oil sludge.

Facile fabrication of pH-sensitive nanoparticles based on nanocellulose for fast and efficient As(V) removal.

This study reported a facile method to synthesize novel pH-sensitive nanoparticle based on nanocellulose, involving cross-linking polyethyleneimine and glutaraldehyde. The adsorbent was characterized and found to be sensitive to the solution pH, especially at pH 3. Additionally, the biosorbent exhibited rapid adsorption during the initial 10 min and the As(V) adsorption capacity of the nanoparticles reached approximately 255.19 mg g-1 at pH 3, which was five times greater than that achieved with the As(V) solution at its initial pH (44.33 mg g-1). To reflect its performance in actual acidic wastewater, the effects of coexisting anions were also investigated, showing that these anions had little influence on As(V) adsorption. Meanwhile, the adsorbent displayed excellent performance even after eight regeneration cycles. This novel material demonstrates enormous potential for the removal of arsenic contaminants and for the development of pH-sensitive materials.

Novel Controlled Release Microspheric Soil Conditioner Based on the Temperature and pH Dual-Stimuli Response.

A novel type of temperature and pH dual-stimuli-responsive microspheric soil conditioner was prepared for the controlled release of urea. First, poly(N-isopropylacrylamide-co-methacrylic acid) [P(NIPAM-co-MAA)] was synthesized, and the microspheric soil conditioner was prepared on the basis of chitosan-coated P(NIPAM-co-MAA) via the emulsion cross-linking method. The structure and morphology of the microsphere were characterized by Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance, polarization optical microscopy, and scanning electron microscopy. The microsphere showed controlled release behavior in different temperature and pH conditions, indicating good stimuli responsiveness. The plant experiment revealed that the microsphere can effectively promote plant growth in acidified soil and high-temperature conditions, and the pH value of acidified soil could be improved. In addition, the microsphere possessed good biodegradation property in the soil. Therefore, the multi-responsive microspheric soil conditioner owns a great potential value to amend soil conditions and promote plant growth in agriculture applications.

The fabrication and arsenic removal performance of cellulose nanocrystal-containing absorbents based on the "bridge joint" effect of iron ions.

By using the "bridge joint" effect of iron ions, cellulose nanocrystal-containing high-performance adsorbents were synthesized via coprecipitation method, which enhanced the cross-linking action of cellulose nanocrystal and polyethyleneimine. The morphology, specific surface area, surface chemistry and chemical valence of the adsorbents were characterized by SEM, FTIR, BET and XPS. According to the results, the iron ions successfully connect the two dispersed polymers together, inducing a large number of O-Fe-O bonds and, providing more adsorption active sites for the removal of seriously polluted and high-toxicity As(III)/As(V). Furthermore, the arsenic removal performance of the adsorbents was studied, and the adsorption mechanism was revealed according to the spectral characteristics of the chemical components. Of note, the synthesized iron-containing adsorbents are suitable for a wide pH range, which may offer a new application for nanocellulose in the treatment of arsenic pollution.

Nitrogen and sulfur co-doped biochar derived from peanut shell with enhanced adsorption capacity for diethyl phthalate.

Doping of nitrogen and sulfur on biochar (NS-B) was investigated by a novel and improved method for diethyl phthalate (DEP) removal. The preparation parameters including pyrolysis temperature and size of peanut shell biochar as well as thiourea/biochar mass ratio were selected as independent variables at three levels by applying the Box-Behnken design. The ANOVA results indicated that thiourea/biochar mass ratio exhibited the most significant effect. The comprehensive effects of the three factors on DEP removal efficiency were further elaborated, combining with the characterization results of the obtained NS-B materials. The formation of the pyridinic N and oxidized S groups examined by XPS was responsible for enhancing the DEP removal efficiency. The adsorption kinetic model fitting illustrated that large micropores and numerous adsorption sites improved the adsorption capacity of NS-B. According to the adsorption isotherm model fitting, NS-B (temperature 375 °C, size 300 mesh and thiourea/biochar mass ratio 0.1) possessed much higher maximum adsorption capacity for DEP (14.34 mg g-1) than biochar (6.57 mg g-1). NS-B exhibited excellent reusability towards DEP removal after five times recycling. Moreover, NS-B also had the potential in peroxydisulfate activation. These findings provide new insights into the environmental implications of NS-B.

Preparation and properties of soil conditioner microspheres based on self-assembled potassium alginate and chitosan.

Fulvic acid (FA), as one type of soil conditioner, can enhance drought tolerance, improve nutrient ingestion, stabilize pH values of soil, and reduce fertilizer extracting behaviors. Moreover, it shows a good effect on increasing the permissiveness of plants to various environments, and the stress of salinity and drought is included. Therefore, it can be used as an ideal soil conditioner. In order to extend its effect, it may be loaded into the core-shell polymer microspheres. In this study, FA was added to calcium carbonate (CaCO3) microspheres, potassium alginate (PAL) and chitosan (CS) were assembled outside. Thus, PAL/CS/FA-CaCO3 microspheres were prepared using layer-by-layer self-assembly methods. The surface morphology, encapsulation efficiency and in vitro drug release characteristics were investigated. It was revealed that PAL/CS/FA-CaCO3 microspheres were formed with a particle size distribution between 2 and 6 µm due to self-assembly between PAL and CS. Drug release behavior analysis exhibited the sustained release processes were delayed to varying degrees due to different degradation degrees of CaCO3 microspheres at different pH values. Results also illustrated that these microspheres had a high loading capacity for FA, and possessed good biodegradability. Thus, PAL/CS/FA-CaCO3 microspheres exhibited promise for future applications compared with that of traditional soil conditioners.

Aqueous Antibacterial Enhancement Using Kapok Fibers Chemically Modified in 3-D Crosslinked Structure.

The surface of a kapok fiber was coated with Dopamine (DOPA) through a three-dimensional (3-D) polymerization. Such surface-modified kapok fiber was useful in deactivating microbial activity of microorganisms such as bacteria. The morphology of the surface-modified kapok fiber was analyzed with a field emission scanning electron microscope (FE-SEM). After a silver coating process along with DOPA functionalization, a strong antibacterial property was observed against Escherichia coli (E. coli), using a direct contact method. Almost 100% of bacterial cells were deactivated in 4 h, also showing a complete hindrance to a bacterial growth for 48 h. With the help of the images of FE-SEM and its analysis, the mechanism of an antibacterial assay was enlightened and reasonably estimated that silver ions from the poly-DOPA-coated kapok fiber with silver (KF-DOPA/Ag) led to alterations of cell morphology. This 3-D composite successfully interacted in vitro with functional groups in terms of bacterial deactivation.