Zhulei Chen

Fe-MoS4: An Effective and Stable LDH-Based Adsorbent for Selective Removal of Heavy Metals

It has always been a serious challenge to design efficient, selective, and stable absorbents for heavy-metal removal. Herein, we design layered double hydroxide (LDH)-based Fe-MoS4, a highly efficient adsorbent, for selective removal of heavy metals. We initially synthesized FeMgAl-LDH and then enriched its protective layers with MoS42- anions as efficient binding sites for heavy metals. Various characterization tools, such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray, X-ray photoelectron spectroscopy (XPS), CHN analysis, and inductively coupled plasma analysis, were applied to confirm structural and compositional changes during the synthesis of Fe-MoS4 as final product. The prepared Fe-MoS4 offered excellent attraction for heavy metals, such as Hg2+, Ag+, Pb2+, and Cu2+, and displayed selectivity in the order Hg2+ ∼ Ag+ > Pb2+ > Cu2+ > Cr6+ > As3+ > Ni2+ ∼ Zn2+ ∼ Co2+. The immense capacities of Hg2+, Ag+, and Pb2+ (583, 565, and 346 mg/g, respectively), high distribution coefficient (Kd ∼ 107-108), and fast kinetics place Fe-MoS4 on the top of materials list known for removal of such metals. The sorption kinetics and isothermal studies conducted on Hg2+, Ag+, Pb2+, and Cu2+ suit well pseudo-second-order kinetics and Langmuir model, suggesting monolayer chemisorption mechanism through M-S linkages. XRD and FTIR studies suggested that adsorbed metals could result as coordinated complexes in LDH interlayer region. More interestingly, LDH structure offers protective space for MoS42- anions to avoid oxidation under ambient environments, as confirmed by XPS studies. These features provide Fe-MoS4 with enormous capacity, good reusability, and excellent selectivity even in the presence of huge concentration of common cations.

Comparison study of landfill gas emissions from subtropical landfill with various phases: A case study in Wuhan, China

The compositions and annual variations of landfill gas (LFG) were studied at two large-scale sites of Chen-Jia-Chong Landfill. Seventy-six wells were built and used for the collection and measurement of LFG. The investigation revealed the similarities and differences of LFG components and variations at two sites with different phases. It was found that ambient temperature and rainfall exhibited strong correlations with LFG components at both sites. Methane (CH4) contents showed excellent correlations with CO2 at both sites. Notable correlations between hydrogen sulfide (H2S) and major components (CH4 and carbon dioxide [CO2]) were only observed in unstable methane phase. Especially, the CH4/CO2 volumetric ratio could act as an excellent indicator for anaerobic reaction stage by judging its phasic variations. The study is beneficial for the efficient operation of LFG collection system and could shed light on gas purification and utilization. Implications: The results in this paper could provide some beneficial information for landfill operators. Especially, the CH4/CO2 volumetric ratio could act as an excellent indicator for anaerobic reaction stage by judging its phasic variations. Moreover, the study could shed light on landfill gas purification and utilization.

Removal of refractory contaminants in municipal landfill leachate by hydrogen, oxygen and palladium: A novel approach of hydroxyl radical production

Municipal solid waste (MSW) leachate contains various refractory pollutants that pose potential threats to both surface water and groundwater. This paper established a novel catalytic oxidation process for leachate treatment, in which OH is generated in situ by pumping both H2 and O2 in the presence of Pd catalyst and Fe(2+). Volatile fatty acids in the leachate were removed almost completely by aeration and/or mechanical mixing. In this approach, a maximum COD removal of 56.7% can be achieved after 4h when 200mg/L Fe(2+) and 1250mg/L Pd/Al2O3 (pH 3.0) are used as catalysts. After oxidation, the BOD/COD ratio in the proposed process increased from 0.03 to 0.25, indicating that the biodegradability of the leachate was improved. By comparing the efficiency on COD removal and economical aspect of the proposed Pd-based in-situ process with traditional Fenton, electro-Fenton and UV-Fenton for leachate treatments, the proposed Pd-based in-situ process has potential economic advantages over other advanced oxidation processes while the COD removal efficiency was maintained.

Removal of volatile fatty acid in landfill leachate by the microwave-hydrothermal method

AbstractIn this study, we report on the rising concern with landfill facility is the safe disposal of leachate and high volatile fatty acid (VFA) concentration in leachate provokes the inhibition of biochemical treatment of landfill leachate to the elimination of these serious problems, a microwave-hydrothermal (MH) method has been employed. This new process, named MH method, was developed for the removal of VFA from leachate. The effects of pH, microwave (MW) power, radiation time, and aeration on the removal were investigated. pH and MW radiation time presented significant influence on the removal of VFA. The optimal removal obtained with 625 W power at initial pH ≈ 7.2 in 8 min. Aeration presented slight enhancement on the removal. With the optimal operating parameters, the removal of VFA in landfill leachate could reach ≈ 30.7% with aeration. The mechanism of VFA removal was proposed as the evaporation of molecular VFA by MW radiation. Compared with heating with an electric oven, MW radiation obtained...

Towards a better understanding on mercury adsorption by magnetic bio-adsorbents with γ-Fe 2 O 3 from pinewood sawdust derived hydrochar: Influence of atmosphere in heat treatment

Pyrolysis under protective atmosphere was regarded as an indispensable process for the preparation of biomass-based adsorbents to achieve higher surface areas. In this paper, magnetic carbon composites (MCC) that fabricated under air atmosphere showed an adsorption capacity of 167.22 mg/g in 200 ppm Hg(II), which was significantly higher than magnetic biochar (MBC, 31.80 mg/g) that fabricated under traditional nitrogen protection, and this remarkable performance of MCC was consistent in a wide range of pHs. Based on BET, XRD, FTIR, SEM and Boehm titration, MCC was demonstrated with limited surface area (43.29 m2/g) but large amount of surface functional groups comparing with MBC. Additionally, γ-Fe2O3 with a high degree of crystallization was generated in MCC, which led to a better magnetic property and recyclability. Moreover, characterizations, Langmuir isotherm and pseudo-second-order kinetics demonstrated the chemisorption was dominant for MCC in mercury capture, and surface complexation co-precipitate of Hg4Fe8O16C56H40 were also formed.

One-step preparation and application of magnetic sludge-derived biochar on acid orange 7 removal via both adsorption and persulfate based oxidation

Magnetic sludge-derived biochar (MSDBC) was synthetized via a one-step co-precipitation method and conducted as a novel heterogeneous catalyst of persulfate (PS) activation for the oxidative removal of acid orange 7 (AO7). The porous structure and large surface area benefits the enrichment of the pollutant, while abundant Fe3O4 species and oxygen-containing functional groups promoted the generation of oxidative radicals, thus leading to the remarkable performance of AO7 removal. MSDBC also exhibited good stability with low iron leaching and consistent efficiency in reusability experiments. Radical scavenger experiments and electron paramagnetic resonance studies identified SO4˙− and OH˙ as the dominant oxidative radicals. The magnetic properties and feasible preparation method of MSDBC guaranteed the stability, which was evidenced in detail by the satisfactory reusability performance and low iron leaching during the degradation process. Distinguished from other PS based advanced oxidation processes, acidic conditions favored AO7 removal, while two halide irons Cl− and Br− could promote AO7 removal by MSDBC/PS system. The current outcomes demonstrated our approach of converting solid waste into stable, cheap and multifunctional biochar as a feasible resource utilization method, and was highly suggestive to the treatment of both wastewater and sewage sludge.

Immobilization of Cd in landfill-leachate-contaminated soil with cow manure compost as soil conditioners: A laboratory study

ABSTRACT Introducing cow manure compost as an amendment in landfill-leachate-contaminated soils is proved to be an effective technique for the immobilization of Cd in this study. Landfill-leachate-contaminated soil was collected from an unlined landfill in China and amended with a different blending quantity of cow manure compost (0, 12, 24, 36, and 48 g per 200 g soil), which was made by mixing cow manure and chaff at a ratio of 1/1 and maturing for 6 months. pH values of five different blending quantity mixtures increased by 0.2–0.4, and the organic matter levels increased by 2.5–7%, during a remediation period of 5 weeks. Four fractions of Cd named exchangeable Cd, reducible Cd, oxidizable Cd, and residual Cd in soil were respectively analyzed by a sequential extraction procedure. Introducing the cow manure compost application resulted in more than 40% lower exchangeable Cd but a higher concentration of oxidizable Cd in soils, and mass balance results showed nearly no Cd absorption by applied material, indicating that transformation of exchangeable Cd into oxidization forms was the main mechanism of Cd immobilization when cow manure compost was used as an amendment. The Pearson correlation showed that increasing of pH values significantly improved the efficiency of Cd immobilization, with a correlation coefficiency of 0.940 (p < 0.05). This is the first attempt at heavy metal immobilization in landfill-leachate-contaminated soil by cow manure compost, and findings of this work can be integrated to guide the application. Implications: Addition of cow manure compost (CMC) was effective in reducing exchangeable Cd in landfill-leachate-contaminated soils (LLCS). The immobilization effect of Cd was mainly assigned to the redistribution of labile soil Cd. Organic matter (OM) and pH value increased with CMC application. The pH values were more sensitive to Cd immobilization efficiency. It was proved that CMC can be safely and effectively used for the restoration of LLCS.

Urban Night Soil Transportation and Treatment in China

With the growth of population, night soil had become an important influencing factor for ecological environment of China. The situation of urban night soil transportation and treatment in China was investigated and described. Depending on the China Urban Construction Statistical Yearbooks and other references, relative data of urban night soil are statistically treated. By correlation analysis and variance analysis, the chronological changes and their relations with other factors of the night soil transportation and treatment were studied. Over the last twenty two years, urban night soil transportation quantity was affected by the urban non-agricultural population and latrines. Urban night soil non-hazardous treatment quantity had significant positive correlation with the urban night soil transportation quantity. Urban night soil transportation quantity of Eastern region was higher than that of Central region and Western region, and urban night soil non-hazardous treatment quantity of Eastern region was highest. The urban night soil treatment model of China is diverse, co-treating night soil with sewage or establishing separate night soil treatment plant, but the level of technology is below that of some developing countries. Due to lack of enough urban environmental sanitation funds, large amount of urban night soil were untreated, and most untreated night soil had been discharged directly, which caused environmental pollution. The problems of urban night soil system of China were also discussed.