Lin-Feng Zhai

An integrated approach to optimize the conditioning chemicals for enhanced sludge conditioning in a pilot-scale sludge dewatering process

An integrated approach incorporating response surface methodology (RSM), grey relational analysis, and fuzzy logic analysis was developed to quantitatively evaluate the conditioning chemicals in sludge dewatering process. The polyacrylamide (PAM), ferric chloride (FeCl(3)) and calcium-based mineral powders were combined to be used as the sludge conditioners in a pilot-scale sludge dewatering process. The performance of conditioners at varied dosages was comprehensively evaluated by taking into consideration the sludge dewatering efficiency and chemical cost of conditioner. In the evaluation procedure, RSM was employed to design the experiment and to optimize the dosage of each conditioner. The grey-fuzzy logic was established to quantify the conditioning performance on the basis of grey relational coefficient generation, membership function construction, and fuzzy rule description. Based on the evaluation results, the optimal chemical composition for conditioning was determined as PAM at 4.62 g/kg DS, FeCl(3) at 55.4 g/kg DS, and mineral powders at 30.0 g/kg DS.

Preparation, characterization of electrospun meso-hydroxylapatite nanofibers and their sorptions on Co(II)

In this work, mesoporous hydroxylapatite (meso-HA) nanofibers were prepared via calcination process with polyvinyl alcohol/HA (PVA/HA) hybrid nanofibers fabricated by electrospinning technique as precursors, and the removal efficiency of meso-HA nanofibers toward Co(II) was evaluated via sorption kinetics and sorption isotherms. Furthermore, the sorption behaviors of Co(II) on meso-HA nanofibers were explored as a function of pH, ionic strength, and thermodynamic parameters. There existed hydrogen bonds between HA and PVA matrix in precursor nanofibers which could change into meso-HA nanofibers with main pore diameter at 27nm and specific surface area at 114.26m(2)/g by calcination process. The sorption of Co(II) on meso-HA was strongly dependent on pH and ionic strength. Outer-sphere surface complexation or ion exchange was the main mechanisms of Co(II) adsorption on meso-HA at low pH, whereas inner-sphere surface complexation was the main adsorption mechanism at high pH. The sorption kinetic data were well fitted by the pseudo-second-order rate equation. The sorption isotherms could be well described by the Langmuir model. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) calculated from the temperature-dependent sorption isotherms suggested that the sorption process of Co(II) on meso-HA nanofibers was spontaneous and endothermic.

A fuel-cell-assisted iron redox process for simultaneous sulfur recovery and electricity production from synthetic sulfide wastewater

Sulfide present in wastewaters and waste gases should be removed due to its toxicity, corrosivity, and malodorous property. Development of effective, stable, and feasible methods for sulfur recovery from sulfide attains a double objective of waste minimization and resource recovery. Here we report a novel fuel-cell-assisted iron redox (FC-IR) process for simultaneously recovering sulfur and electricity from synthetic sulfide wastewater. The FC-IR system consists of an oxidizing reactor where sulfide is oxidized to elemental sulfur by Fe(III), and a fuel cell where Fe(III) is regenerated from Fe(II) concomitantly with electricity producing. The oxidation of sulfide by Fe(III) is significantly dependent on solution pH. Increasing the pH from 0.88 to 1.96 accelerates the oxidation of sulfide, however, lowers the purity of the produced elemental sulfur. The performance of fuel cell is also a strong function of solution pH. Fe(II) is completely oxidized to Fe(III) when the fuel cell is operated at a pH above 6.0, whereas only partially oxidized below pH 6.0. At pH 6.0, the highest columbic efficiency of 75.7% is achieved and electricity production maintains for the longest time of 106 h. Coupling operation of the FC-IR system obtains sulfide removal efficiency of 99.90%, sulfur recovery efficiency of 78.6 ± 8.3%, and columbic efficiency of 58.6 ± 1.6%, respectively. These results suggest that the FC-IR process is a promising tool to recover sulfur and energy from sulfide.

Synthesis and bioactivity of gelatin/multiwalled carbon nanotubes/hydroxyapatite nanofibrous scaffolds towards bone tissue engineering

The objective of this study was to develop a novel three-dimensional biomimetic gelatin/multiwalled carbon nanotubes/hydroxyapatite (gelatin/MWNTs/HA) nanofibrous scaffold via electrospinning technique for bone tissue engineering. The mechanical properties, structure, morphology and the bioactivity of nanofibrous scaffolds in vitro were investigated. Attentions were focused on the adhesion, mineralization, viability and proliferation of human fetal osteoblastic cells (hFOBs) on scaffold. Resulting scaffolds provided relative good mechanical support (7.9 ± 0.32 MPa) and high porosity (91.2%) to mimic a favorable environment for hFOBs. The hydrogen bonds between gelatin molecules and MWNTs/HA units were confirmed, and the incorporation of HA or MWNTs/HA nanoparticles caused an increase in porosity and strength of scaffolds, meanwhile the surface of nanofibers tended to be rough. HA nanoparticles showed a chelating effect to promote osteogenesis and mineralization of bone, and MWNTs had a synergetic effect with HA to induce the apatite formation. As compared to gelatin and gelatin/HA scaffolds, gelatin/MWNTs/HA scaffold exhibited the best viability hFOB cells cultured in vitro, most excellent morphology of hFOB cells seeded into scaffold and a significantly increasing in proliferation. The nanofibrous scaffold will have great potential as an excellent scaffold for in bone tissue engineering.

Diffusion and Antibacterial Properties of Nisin-Loaded Chitosan/Poly (L-Lactic Acid) Towards Development of Active Food Packaging Film

Nisin-loaded chitosan/poly (L-lactic acid) (nisin-CS/PLLA) antimicrobial films were prepared by coating method. The structure and mechanical properties of nisin carrier CS/PLLA films were investigated, and the antibacterial behavior of nisin-CS/PLLA against Staphylococcus aureus ATCC6538 was assessed. Furthermore, the diffusion behaviors of nisin from films were evaluated by diffusion kinetics and thermodynamics, and the diffusion efficiency was investigated as a function of CS/PLLA ratio, pH, and ionic strength. When CS/PLLA ratio was at 1:1 (w/w) and above, a notable enhancement was observed in the tensile strength with the increase of PLLA content, while the elongation at break was decreased slightly at the same time. However, a significant decrease in tensile strength and elongation at break were present when the CS/PLLA ratio was below 1:1. There existed intermolecular hydrogen bonds between CS and PLLA molecules. The diffusion of nisin from film was strongly dependent on pH and ionic strength. The thermodynamic parameters (ΔHo, ΔSo, and ΔGo) indicated that the diffusion process of nisin from film was spontaneous and endothermic. From diffusion and antimicrobial activity results, nisin-CS/PLLA films revealed well-controlled release and better antimicrobial activity against S. aureus, which may have potential as a novel active food packaging film.

Synthesis, antimicrobial and release of chloroamphenicol loaded poly(l-lactic acid)/ZrO2 nanofibrous membranes

Electrospinning technique was used to fabricate chloroamphenicol loaded poly (L-lactic acid)/ZrO2 (CP-PLLA/ZrO2) nanofibrous membranes. The average diameter of drug carrier PLLA/ZrO2 nanofibers increased with ZrO2 concentration increasing and ribbon-shape fibers were present when ZrO2 content reached 3% and above. The existence of hydrogen and ZrOC bonds between PLLA and ZrO2 units improved the thermal stability of PLLA. The model drug CP loading showed no significant changes on the size and shape of nanofibers when CP content was below 8%, but the fibers were uneven and interspersed with ball-shape beads when CP content rose up to 10%. From the antimicrobial activity and release experimental result, the CP-PLLA/ZrO2 nanofibrous membranes revealed well controlled release and better antimicrobial activity against Staphylococcus aureus, which may have potential as a new nanofibrous membrane in drug delivery and wound dressing.

Carbonate-mediated Fe(II) oxidation in the air-cathode fuel cell: a kinetic model in terms of Fe(II) speciation.

Due to the high redox activity of Fe(II) and its abundance in natural waters, the electro-oxidation of Fe(II) can be found in many air-cathode fuel cell systems, such as acid mine drainage fuel cells and sediment microbial fuel cells. To deeply understand these iron-related systems, it is essential to elucidate the kinetics and mechanisms involved in the electro-oxidation of Fe(II). This work aims to develop a kinetic model that adequately describes the electro-oxidation process of Fe(II) in air-cathode fuel cells. The speciation of Fe(II) is incorporated into the model, and contributions of individual Fe(II) species to the overall Fe(II) oxidation rate are quantitatively evaluated. The results show that the kinetic model can accurately predict the electro-oxidation rate of Fe(II) in air-cathode fuel cells. FeCO3, Fe(OH)2, and Fe(CO3)2(2-) are the most important species determining the electro-oxidation kinetics of Fe(II). The Fe(II) oxidation rate is primarily controlled by the oxidation of FeCO3 species at low pH, whereas at high pH Fe(OH)2 and Fe(CO3)2(2-) are the dominant species. Solution pH, carbonate concentration, and solution salinity are able to influence the electro-oxidation kinetics of Fe(II) through changing both distribution and kinetic activity of Fe(II) species.

Effective sulfur and energy recovery from hydrogen sulfide through incorporating an air-cathode fuel cell into chelated-iron process

The chelated-iron process is among the most promising techniques for the hydrogen sulfide (H2S) removal due to its double advantage of waste minimization and resource recovery. However, this technology has encountered the problem of chelate degradation which made it difficult to ensure reliable and economical operation. This work aims to develop a novel fuel-cell-assisted chelated-iron process which employs an air-cathode fuel cell for the catalyst regeneration. By using such a process, sulfur and electricity were effectively recovered from H2S and the problem of chelate degradation was well controlled. Experiment on a synthetic sulfide solution showed the fuel-cell-assisted chelated-iron process could maintain high sulfur recovery efficiencies generally above 90.0%. The EDTA was preferable to NTA as the chelating agent for electricity generation, given the Coulombic efficiencies (CEs) of 17.8 ± 0.5% to 75.1 ± 0.5% for the EDTA-chelated process versus 9.6 ± 0.8% to 51.1 ± 2.7% for the NTA-chelated process in the pH range of 4.0-10.0. The Fe (III)/S(2-) ratio exhibited notable influence on the electricity generation, with the CEs improved by more than 25% as the Fe (III)/S(2-) molar ratio increased from 2.5:1 to 3.5:1. Application of this novel process in treating a H2S-containing biogas stream achieved 99% of H2S removal efficiency, 78% of sulfur recovery efficiency, and 78.6% of energy recovery efficiency, suggesting the fuel-cell-assisted chelated-iron process was effective to remove the H2S from gas streams with favorable sulfur and energy recovery efficiencies.

Functional effectiveness and diffusion behavior of sodium lactate loaded chitosan/poly(L-lactic acid) film with antimicrobial activity

The present work aimed to evaluate the functional effectiveness and diffusion behavior of sodium lactate loaded chitosan/poly(L-lactic acid) (SL-CS/PLLA) film prepared by coating method as a novel active packaging, using Escherichia coli (E. coli, 8099) as test bacterium. The hydrogen bonds formed between CS and PLLA improved the thermal stability and caused a decrease in crystalline of the composite film. The incorporation of PLLA increased the hydrophobicity of film and resulted in a decrease in water gain percentage at equilibrium with decreasing CS/PLLA ratio. The PLLA was valid in blocking visible light and invalid in blocking ultraviolet light through films, and the surface color of CS/PLLA films changed distinctively as compared to neat CS film. The decrease of CS/PLLA ratio caused a decrease in both water vapor permeability (WVP) and oxygen permeability (OP), which reached their minimum values at 1.95 × 10−3 g m−1 d−1 kPa−1 and 2.1 × 10−3 cm2 d−1 kPa−1 for CS/PLLA ratio at 1:1, respectively. The SL-CS/PLLA film displayed well controlled release and the initial diffusion of SL (Mt/M∞ < 2/3) could be well described by Fickian diffusion equation. The thermodynamic parameters suggested that the diffusion of SL was endothermic and spontaneous, and the increase of temperature and PLLA content in film favored the diffusion of SL.