Kuo-Lun Tung

Typical lignocellulosic wastes and by-products for biosorption process in water and wastewater treatment: A critical review

Biosorption on lignocellulosic wastes and by-products has been identified as a proper alternative to the existing technologies applied for toxic metal ion and dye removal from wastewater streams. This paper deals with utilization of typical low cost wastes and by-products produced in different food agricultural and agro-industries as biosorbent and reviews the current state of studies on a wide variety of cheap biosorbents in natural and modified forms. The efficiency of each biosorbent has been also discussed with respect to the operating conditions (e.g. temperature, hydraulic residence time, initial metal concentration, biosorbent particle size and its dosage), chemical modification on sorption capacity and preparation methods, as well as thermodynamics and kinetics.

Optimal conditions for preparation of banana peels, sugarcane bagasse and watermelon rind in removing copper from water.

In this study, three agro-waste materials were used as biosorbents for removal of copper (Cu) from water. This work aims to optimise conditions for preparation of these materials to obtain maximum Cu adsorption capacity. The optimal conditions were determined in terms of Cu removal efficiency and/or energy consumption. The results indicate that banana peels dried at 120°C for 2h and ground into powder form led to a better performance in terms of both copper removal efficiency and energy consumption. For sugarcane bagasse and watermelon rind, 120°C was the suitable drying temperature. However, the best drying time was 1h for sugarcane bagasse and 3h for watermelon rind. The powder form with size of <150 μm was optimal for all biosorbents in terms of removal efficiency and equilibration time. The findings are beneficial to the application of these agro-waste materials for Cu removal from water and wastewater treatment.

Surface self-assembled PEGylation of fluoro-based PVDF membranes via hydrophobic-driven copolymer anchoring for ultra-stable biofouling resistance.

Stable biofouling resistance is significant for general filtration requirements, especially for the improvement of membrane lifetime. A systematic group of hyper-brush PEGylated diblock copolymers containing poly(ethylene glycol) methacrylate (PEGMA) and polystyrene (PS) was synthesized using an atom transfer radical polymerization (ATRP) method and varying PEGMA lengths. This study demonstrates the antibiofouling membrane surfaces by self-assembled anchoring PEGylated diblock copolymers of PS-b-PEGMA on the microporous poly(vinylidene fluoride) (PVDF) membrane. Two types of copolymers are used to modify the PVDF surface, one with different PS/PEGMA molar ratios in a range from 0.3 to 2.7 but the same PS molecular weights (MWs, ∼5.7 kDa), the other with different copolymer MWs (∼11.4, 19.9, and 34.1 kDa) but the similar PS/PEGMA ratio (∼1.7 ± 0.2). It was found that the adsorption capacities of diblock copolymers on PVDF membranes decreased as molar mass ratios of PS/PEGMA ratio reduced or molecular weights of PS-b-PEGMA increased because of steric hindrance. The increase in styrene content in copolymer enhanced the stability of polymer anchoring on the membrane, and the increase in PEGMA content enhanced the protein resistance of membranes. The optimum PS/PEGMA ratio was found to be in the range between 1.5 and 2.0 with copolymer MWs above 20.0 kDa for the ultrastable resistance of protein adsorption on the PEGylated PVDF membranes. The PVDF membrane coated with such a diblock copolymer owned excellent biofouling resistance to proteins of BSA and lysozyme as well as bacterium of Escherichia coli and Staphylococcus epidermidis and high stable microfiltration operated with domestic wastewater solution in a membrane bioreactor.

CONSTANT PRESSURE FILTRATION OF MONO-DISPERSED DEFORMABLE PARTICLE SLURRY

Constant pressure filtration experiments of Ca-alginate gel particle, Saccharomyces cerevisiae, and polymethyl methacrylate (PMMA) were conducted to study the local properties of cake layer formation by deformable particles. Effects of particle deformation due to frictional drag and cake mass on cake compression and contact area among particles were examined. The factors that lead to the increase in filtration resistance were discussed. The dynamic analysis proposed by Lu and Hwang in 1993 was modified to analyze formation and compression of cake during cake filtration of deformable particle slurry. A thin skin layer of low porosity and high resistance was formed next to the filter medium due to severe deformation, caused by frictional drag, of the first layer. The results of this study clearly indicate that neglecting the area-contact effect among particles will lead to an overestimate of cake porosity, and neglecting the transient effect of cake compression during gel layer formation will result in an underestimate of cake porosity. The characteristic values of filter cake obtained from dynamic analysis can be used to predict the performance of the filtration of slurries containing deformable particles.

A Drying-Free, Water-Based Process for Fabricating Mixed-Matrix Membranes with Outstanding Pervaporation Performance.

Despite much progress in the development of mixed matrix membranes (MMMs) for many advanced applications, the synthesis of MMMs without particle agglomeration or phase separation at high nanofiller loadings is still challenging. In this work, we synthesized nanoporous zeolitic imidazole framework (ZIF-8) nanoparticles with a particle size of 60 nm and a pore size of 0.34 nm in water and directly added them into an aqueous solution of the organic polymer poly(vinyl alcohol) (PVA) without an intermediate drying process. This approach led to a high-quality PVA/ZIF-8 MMM with enhanced performance in ethanol dehydration by pervaporation. The permeability of this MMM is three times higher than that of pristine PVA, and the separation factor is nearly nine times larger than that of pristine PVA. The significantly improved separation performance was attributed to the increase in the fractional free volume in the membranes.

Synthesis of hierarchical micro/mesoporous structures via solid-aqueous interface growth: zeolitic imidazolate framework-8 on siliceous mesocellular foams for enhanced pervaporation of water/ethanol mixtures.

A new hierarchical micro/mesoporous composite is synthesized via direct growth of microporous zeolitic imidazolate framework-8 (ZIF-8) on siliceous mesocellular foams (MCF). Depending on different synthetic conditions, ZIF-8 with two different particle sizes, i.e., ZIF-8 microparticles and ZIF-8 nanoparticles, were successfully formed on the external surface of amine-functionalized MCF (denoted as microZIF-8@MCF and nanoZIF-8@MCF, respectively). The synthesized hierarchical micro/mesoporous ZIF-8@MCF structures were characterized with several spectroscopic techniques including X-ray diffraction (XRD), solid-state NMR, and FT-IR and electron microscopic techniques (scanning electron microscope, SEM, and transmission electron microscopy, TEM). In addition, the pervaporation measurements of the liquid water/ethanol mixture show that nanoZIF-8@MCF/PVA (poly(vinyl alcohol) mixed-matrix membrane exhibits enhanced performance both on the permeability and separation factor. Compared to conventional routes for chemical etching, this study demonstrates a promising and simple strategy for synthesizing novel hierarchical porous composites exhibiting both advantages of mesoporous materials and microporous materials, which is expected to be useful for gas adsorption, separation, and catalysis.

Comparison between sequential and simultaneous application of activated carbon with membrane bioreactor for trace organic contaminant removal

The removal efficiency of 22 selected trace organic contaminants by sequential application of granular activated carbon (GAC) and simultaneous application of powdered activated carbon (PAC) with membrane bioreactor (MBR) was compared in this study. Both sequential application of GAC following MBR treatment (MBR-GAC) and simultaneous application of PAC within MBR (PAC-MBR) achieved improved removal (over 95%) of seven hydrophilic and biologically persistent compounds, which were less efficiently removed by MBR-only treatment (negligible to 70%). However, gradual breakthrough of these compounds occurred over an extended operation period. Charged compounds, particularly, fenoprop and diclofenac, demonstrated the fastest breakthrough (complete and 50-70%, in MBR-GAC and PAC-MBR, respectively). Based on a simple comparison from the long-term performance stability and activated carbon usage points of view, PAC-MBR appears to be a better option than MBR-GAC treatment.

Residual Solvent Effects on Free Volume and Performance of Fluorinated Polyimide Membranes: A Molecular Simulation Study

In this study, molecular simulation techniques were used to investigate the residual solvent effects on the free volume and performance of 6FDA-mPDA polyimide (PI) membranes. A molecular dynamics (MD) simulation was used to analyze how the residual solvent in the 6FDA-mPDA PI membrane affects the fluctuation and flexibility of the polymer segment and the free volume. The gas sorption in the membrane was analyzed by a Monte Carlo (MC) technique. The energy analysis of the MD simulation indicates that the presence of solvent molecules tends to favor the fluctuation, and flexibility of polymer segments tended to be encouraged due to the presence of solvent molecules through the energy analysis by MD simulation. The free volume analysis revealed that the free space in the membrane would be enlarged by extracting the solvent from the membrane. The gas sorption behavior, analyzed by the MC technique, showed that gas solubility increased in the lower residual solvent membranes. This was caused by the free volume released by extracting the solvent, thus providing more suitable sites for gas sorption. The sorption ability was also affected by the intermolecular attractive energy, while the free volumes inside the membranes were similar. In addition, the residual solvent effect on gas sorption would be eliminated at higher pressure. From the thermal motion analysis of gas molecules, it was found that the effective thermal motion of gaseous molecules improved as residual solvent molecules remained in the membrane matrix, but this did not have an effective influence on gas permeation.

Mesoporous Fluorocarbon-Modified Silica Aerogel Membranes Enabling Long-Term Continuous CO2 Capture with Large Absorption Flux Enhancements

The use of a membrane contactor combined with a hydrophobic porous membrane and an amine absorbent has attracted considerable attention for the capture of CO2 because of its extensive use, low operational costs, and low energy consumption. The hydrophobic porous membrane interface prevents the passage of the amine absorbent but allows the penetration of CO2 molecules that are captured by the amine absorbent. Herein, highly porous SiO2 aerogels modified with hydrophobic fluorocarbon functional groups (CF3 ) were successfully coated onto a macroporous Al2 O3 membrane; their performance in a membrane contactor for CO2 absorption is discussed. The SiO2 aerogel membrane modified with CF3 functional groups exhibits the highest CO2 absorption flux and can be continuously operated for CO2 absorption for extended periods of time. This study suggests that a SiO2 aerogel membrane modified with CF3 functional groups could potentially be used in a membrane contactor for CO2 absorption. Also, the resulting hydrophobic SiO2 aerogel membrane contactor is a promising technology for large-scale CO2 absorption during the post-combustion process in power plants.

Reusable methyltrimethoxysilane-based mesoporous water-repellent silica aerogel membranes for CO2 capture

For the first time, highly mesoporous and water-repellent SiO2 aerogels were successfully coated onto a macroporous Al2O3 membrane using methyltrimethoxysilane (MTMS) precursors. The MTMS-derived hydrophobic SiO2 aerogel membranes exhibited at least 500% higher CO2 absorption flux than the uncoated MTMS-based aerogel membranes and could be reused and continuously operated for CO2 absorption for extended periods of time. As a result, MTMS-derived water-repellent silica aerogel membrane contactors are a potential candidate for large-scale CO2 absorption in industrial power plants.