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Lu H.,Guangdong Provincial Academy of Environmental Science | Lu H.,Sun Yat Sen University | Zhang W.,Sun Yat Sen University | Zhang W.,Guangdong Key Laboratory of Environmental Pollution Control and Remediation Technology | And 6 more authors.
Journal of Analytical and Applied Pyrolysis | Year: 2013

The surface characteristics of sludge-derived biochar (SDBC) made from three feedstocks of wastewater sludge under different pyrolysis temperatures were investigated. Results showed that the sludge from Waste Water Treatment Plant (WWTP) with pure domestic wastewater influent and less mixed industrial wastewater produced the highest biochar yield, and these SDBC samples have the highest isoelectric point (IEP) and the most uniform charge distribution, compared with other sources. For different pyrolysis temperatures, 400 C tend to achieve more uniform surface charge distribution of SDBC, due to the oxidation process more occurred on the external surface than internal matrix at this temperature. In addition, a pyrolysis temperature of 300 C resulted in the most reduction in DTPA-extractable metals of SDBCs, owing to the organo-metallic complex formed with the abundant presence of functional groups and available phosphorus content, which were easily decomposed or degraded at higher temperatures. © 2013 Elsevier B.V. All rights reserved. Source

Lu H.,Sun Yat Sen University | Lu H.,Guangdong Provincial Academy of Environmental Science | Zhang W.,Sun Yat Sen University | Zhang W.,Guangdong Key Laboratory of Environmental Pollution Control and Remediation Technology | And 5 more authors.
Water Research | Year: 2012

Lead sorption capacity and mechanisms by sludge-derived biochar (SDBC) were investigated to determine if treatment of acid mine drainage (AMD) containing metals with SDBC is feasible. It was found that the biochar derived from pyrolysis treatment of sewage sludge could effectively remove Pb 2+ from acidic solution with the capacities of 16.11, 20.11, 24.80, and 30.88mgg -1 at initial pH 2, 3, 4 and 5, respectively. Lead sorption processes were pseudo-second order kinetic and faster at a higher pH. Furthermore, the relative contribution of both inorganic mineral composition and organic functional groups of SDBC for Pb 2+ removal mechanisms, was quantitatively studied at pH 2-5. The results showed that Pb sorption primarily involved the coordination with organic hydroxyl and carboxyl functional groups, which was 38.2-42.3% of the total sorbed Pb varying with pH, as well as the coprecipitation or complex on mineral surfaces, which accounted for 57.7-61.8% and led to a bulk of Ca 2+ and Mg 2+ release during sorption process. A new precipitate was solely observed on Pb-loaded SDBC as 5PbO·P 2O 5·SiO 2(lead phosphate silicate) at initial pH 5, confirmed by XRD and SEM-EDX. The coordination of Pb 2+ with carboxyl and hydroxyl functional groups was demonstrated by FT-IR, and the contribution of free carboxyl was significant, ranging from 26.1% to 35.5%. Results from this study may suggest that the application of SDBC is a feasible strategy for removing metal contaminants from acid solutions. © 2011 Elsevier Ltd. Source

Bai J.,Sun Yat Sen University | Yang X.,Sun Yat Sen University | Yang X.,Guangdong Key Laboratory of Environmental Pollution Control and Remediation Technology | Du R.,Sun Yat Sen University | And 5 more authors.
Journal of Environmental Sciences (China) | Year: 2014

Mechanisms of soil Pb immobilization by Bacillus subtilis DBM, a bacterial strain isolated from a heavy-metal-contaminated soil, were investigated. Adsorption and desorption experiments with living bacterial cells as well as dead cells revealed that both extracellular adsorption and intracellular accumulation were involved in the Pb2+ removal from the liquid phase. Of the sequestered Pb(II), 8.5% was held by physical entrapment within the cell wall, 43.3% was held by ion-exchange, 9.7% was complexed with cell surface functional groups or precipitated on the cell surface, and 38.5% was intracellularly accumulated. Complexation of Pb2+ with carboxyl, hydroxyl, carbonyl, amido, and phosphate groups was demonstrated by Fourier transform infrared spectroscopic analysis. Precipitates of Pb5(PO4)3OH, Pb5(PO4)3Cl and Pb10(PO4)6(OH)2 that formed on the cell surface during the biosorption process were identified by X-ray diffraction analysis. Transmission electron microscopy-energy dispersive spectroscopic analysis confirmed the presence of the Pb(II) precipitates and that Pb(II) could be sequestered both extracellularly and intracellularly. Incubation with B. subtilis DBM significantly decreased the amount of the weak-acid-soluble Pb fraction in a heavy-metal-contaminated soil, resulting in a reduction in Pb bioavailability, but increased the amount of its organic-matter-bound fraction by 71%. The ability of B. subtilis DBM to reduce the bioavailability of soil Pb makes it potentially useful for bacteria-assisted phytostabilization of multi-heavy-metal-contaminated soil. © 2014. Source

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