Md. Saifur Rahaman

Electrochemical Multiwalled Carbon Nanotube Filter for Viral and Bacterial Removal and Inactivation

Nanotechnology has potential to offer solutions to problems facing the developing world. Here, we demonstrate the efficacy of an anodic multiwalled carbon nanotube (MWNT) microfilter toward the removal and inactivation of viruses (MS2) and bacteria (E. coli). In the absence of electrolysis, the MWNT filter is effective for complete removal of bacteria by sieving and multilog removal of viruses by depth-filtration. Concomitant electrolysis during filtration results in significantly increased inactivation of influent bacteria and viruses. At applied potentials of 2 and 3 V, the electrochemical MWNT filter reduced the number of bacteria and viruses in the effluent to below the limit of detection. Application of 2 and 3 V for 30 s postfiltration inactivated >75% of the sieved bacteria and >99.6% of the adsorbed viruses. Electrolyte concentration and composition had no correlation to electrochemical inactivation consistent with a direct oxidation mechanism at the MWNT filter surface. Potential dependent dye oxidation and E. coli morphological changes also support a direct oxidation mechanism. Advantages of the electrochemical MWNT filter for pathogen removal and inactivation and potential for point-of-use drinking water treatment are discussed.

Electrochemical carbon-nanotube filter performance toward virus removal and inactivation in the presence of natural organic matter.

The performance of an electrochemical multiwalled carbon nanotube (EC-MWNT) filter toward virus removal and inactivation in the presence of natural organic matter was systematically evaluated over a wide range of solution chemistries. Viral removal and inactivation were markedly enhanced by applying DC voltage in the presence of alginate and Suwannee River natural organic matter (SRNOM). Application of 2 or 3 V resulted in complete (5.8 to 7.4 log) removal and significant inactivation of MS2 viral particles in the presence of 5 mg L(-1) of SRNOM or 1 mg L(-1) of alginate. The EC-MWNT filter consistently maintained high performance over a wide range of solution pH and ionic strengths. The underlying mechanisms of enhanced viral removal and inactivation were further elucidated through EC-MWNT filtration experiments using carboxyl latex nanoparticles. We conclude that enhanced virus removal is attributed to the increased viral particle transport due to the applied external electric field and the attractive electrostatic interactions between the viral particles and the anodic MWNTs. The adsorbed viral particles on the MWNT surface are then inactivated through direct surface oxidation. Minimal fouling of the EC-MWNT filter was observed, even after 4-h filter runs with solutions containing 10 mg L(-1) of natural organic matter and 1 mM CaCl(2). Our results suggest that the EC-MWNT filter has a potential for use as a high performance point-of-use device for the removal of viruses from natural and contaminated waters with minimal power requirements.

Control of biofouling on reverse osmosis polyamide membranes modified with biocidal nanoparticles and antifouling polymer brushes

Thin-film composite (TFC) polyamide reverse osmosis (RO) membranes are prone to biofouling due to their inherent physicochemical surface properties. In order to address the biofouling problem, we have developed novel surface coatings functionalized with biocidal silver nanoparticles (AgNPs) and antifouling polymer brushes via polyelectrolyte layer-by-layer (LBL) self-assembly. The novel surface coating was prepared with polyelectrolyte LBL films containing poly(acrylic acid) (PAA) and poly(ethylene imine) (PEI), with the latter being either pure PEI or silver nanoparticles coated with PEI (Ag-PEI). The coatings were further functionalized by grafting of polymer brushes, using either hydrophilic poly(sulfobetaine) or low surface energy poly(dimethylsiloxane) (PDMS). The presence of both LBL films and sulfobetaine polymer brushes at the interface significantly increased the hydrophilicity of the membrane surface, while PDMS brushes lowered the membrane surface energy. Overall, all surface modifications resulted in significant reduction of irreversible bacterial cell adhesion. In microbial adhesion tests with E. coli bacteria, a normalized cell adhesion in the range of only 4 to 16% on the modified membrane surfaces was observed. Modified surfaces containing silver nanoparticles also exhibited strong antimicrobial activity. Membranes coated with LBL films of PAA/Ag-PEI achieved over 95% inactivation of bacteria attached to the surface within 1 hour of contact time. Both the antifouling and antimicrobial results suggest the potential of using these novel surface coatings in controlling the fouling of RO membranes.

Effects of various process parameters on struvite precipitation kinetics and subsequent determination of rate constants

In this paper, struvite (MgNH(4)PO(4).6H(2)O) precipitation kinetics were studied with different operating conditions (varying supersaturation, pH, Mg:P ratio, degree of mixing and seeding conditions) and relevant rate constants were determined by fitting a slightly modified first-order kinetic model to the experimental data obtained. The rate of change of ortho-P concentration in the bulk solutions increases with increasing supersaturation ratio. The estimated rate constants are 2.034, 1.716 and 0.690 hr(-1) for the supersaturation ratio of 9.64, 4.83, and 2.44, respectively. Kinetic parameters were also evaluated for the Mg:P ratio between the ranges of 1.0 and 1.6, indicating higher phosphorus removal efficiency with increasing Mg:P ratio. The rate constants were found to be 0.942, 2.034 and 2.712 hr(-1) for Mg:P ratios of 1.0, 1.3 and 1.6, respectively. The experimental observations for kinetic study of struvite precipitation with different stirrer speeds clearly show that the mixing intensity used had little effect on the intrinsic rate constants. K values found to be 2.034 and 1.902 h(-1) for 100 and 70 rpm, respectively. Seeding, with 250-500 microm of seed crystals during the struvite precipitation kinetics test, was found to have very little effect on the ortho-P removal.

Electrospun novel super-absorbent based on polysaccharide–polyvinyl alcohol–montmorillonite clay nanocomposites

A novel super-absorbent material was fabricated by electrospinning the natural polysaccharide pullulan (PULL) with polyvinyl alcohol (PVA) and montmorillonite (MMT) clay to form nonwoven webs, which were then heat treated. Transmission electron microscopy (TEM) micrographs, X-ray diffraction (XRD) patterns, and Fourier transform infrared (FTIR) analysis of the novel super-absorbent nanofibers suggest the coexistence of PULL, PVA, and MMT through the exfoliation of MMT layers in the super-absorbent nanofiber composite. The heat-treated PULL/PVA/MMT webs loaded with 5 wt% MMT electrospun nanofibers exhibited a water absorbency of 143.42 g g(-1) in distilled water and a water absorbency of 39.75 g g(-1) in a 0.9 wt% NaCl solution. Under extremely dry conditions, the PULL/PVA/MMT webs exhibited the ability to retain 43% distilled water and 38% saline water after being exposed to the atmosphere for one week. The heat treatment improved the crystallinity of the electrospun PULL/PVA/MMT super-absorbent webs and thus made the webs highly stable in aqueous environments. Overall, the addition of MMT resulted in improved thermal stability and mechanical properties and increased the water absorbency of the PULL/PVA/MMT composite.

Modeling phosphorus removal and recovery from anaerobic digester supernatant through struvite crystallization in a fluidized bed reactor.

The cost associated with the disposal of phosphate-rich sludge, the stringent regulations to limit phosphate discharge into aquatic environments, and resource shortages resulting from limited phosphorus rock reserves, have diverted attention to phosphorus recovery in the form of struvite (MAP: MgNH4PO4·6H2O) crystals, which can essentially be used as a slow release fertilizer. Fluidized-bed crystallization is one of the most efficient unit processes used in struvite crystallization from wastewater. In this study, a comprehensive mathematical model, incorporating solution thermodynamics, struvite precipitation kinetics and reactor hydrodynamics, was developed to illustrate phosphorus depletion through struvite crystal growth in a continuous, fluidized-bed crystallizer. A thermodynamic equilibrium model for struvite precipitation was linked to the fluidized-bed reactor model. While the equilibrium model provided information on supersaturation generation, the reactor model captured the dynamic behavior of the crystal growth processes, as well as the effect of the reactor hydrodynamics on the overall process performance. The model was then used for performance evaluation of the reactor, in terms of removal efficiencies of struvite constituent species (Mg, NH4 and PO4), and the average product crystal sizes. The model also determined the variation of species concentration of struvite within the crystal bed height. The species concentrations at two extreme ends (inlet and outlet) were used to evaluate the reactor performance. The model predictions provided a reasonably good fit with the experimental results for PO4-P, NH4-N and Mg removals. Predicated average crystal sizes also matched fairly well with the experimental observations. Therefore, this model can be used as a tool for performance evaluation and process optimization of struvite crystallization in a fluidized-bed reactor.

Surface modification of thin film composite forward osmosis membrane by silver-decorated graphene-oxide nanosheets

Forward osmosis (FO), as an emerging technology for seawater desalination and wastewater reuse, has been attracting significant interest because of its energy efficiency. However, membrane fouling represents one of the major limitations for this technology, notably for thin film composite (TFC) polyamide (PA) membranes, which are prone to chlorine attack. In this study, silver nanoparticle (AgNPs)-decorated graphene oxide (GO) nanosheets (as an effective biocidal material) were covalently bonded to the PA surface to impart improved hydrophilicity and antibacterial properties to the membrane. AgNPs were synthesized in situ by the wet chemical reduction of silver nitrate onto the surface of GO nanosheets. The formation of the composite was verified by UV-vis spectroscopy, X-ray diffraction, and transmission electron microscopy techniques. The synthesized GO/Ag nanocomposites were then covalently bonded onto the TFC PA membrane surface using cysteamine through an amide forming condensation reaction. ATR-FTIR and XPS results confirmed the covalent bonding of the nanocomposite onto the TFC PA surface. Overall, the GO/Ag nanocomposite functionalized membranes exhibited super-hydrophilic properties (contact angles below 25°) and significant bacterial (E. coli) inactivation (over 95% in static bacterial inactivation tests) without adversely affecting the membrane transport properties.

Exploring the Determination of Struvite Solubility Product from Analytical Results

The solubility of magnesium ammonium phosphate hexahydrate (struvite) was determined in different water and wastewater solutions, by using the analytical results of the solubility tests conducted in the Environmental Engineering Lab at the University of British Columbia. The various factors affecting the struvite solubility such as pH, ionic strength and the temperature of the solutions were also studied in this project. The struvite solubility product values were found to vary significantly from one solution to another and over the range of the experimental conditions as well. For instance, the solubility product (Ksp ) determined at 20°C for anaerobic digester supernatant from the Penticton, B.C. Advanced Wastewater Treatment Plant, was found to vary from 8.46 × 10−15 (pKsp =14.07) to 1.3x10−13 (pKsp =12.89), over a pH range of 6.45 to 8.97; while in the case of distilled water, with the same struvite crystals and at the identical temperature, it was found to vary from 5.21 × 10−15 (pKsp =14.28) to 2.12 × 10−13 (pKsp =12.67) over a pH range of 7.01 to 9.62. These results explore the possible reasons for widely varying struvite solubility reported in the literature. A possible correlation was also developed to correlate struvite solubility product with varying temperature. Furthermore, an attempt was made to establish a correlation between conductivity and calculated ionic strength of the solutions. A significant gap, between the values predicted by the correlation developed in this study and those predicted by the existing correlation, was also observed.

A COMPREHENSIVE APPROACH FOR MODELING SORPTION OF LEAD AND COBALT IONS THROUGH FISH SCALES AS AN ADSORBENT

ABSTRACT Removal of lead and cobalt cations from both industrial and municipal water is of extreme importance for waste water disposal standards. Using fish scales as an adsorbent, 95% of the lead cations and 70% of the cobalt ions can be removed. The processes related to the removal of the cations include adsorption and precipitation. The effect of precipitation of the cations in a neutral medium (pH 7) is studied and is found to be insignificant. Although the effect of precipitation is negligible in the studied experimental runs, it may assume significance in a highly nonporous medium. As sorption dictates the interactions between the bulk and adsorbed phases, it is the most important factor influencing the transport of the chemical species through the medium. Mobility of the cations has extreme importance to overall sorption characteristics because of high adsorption coefficients of the fish scales. It can be further concluded that even at cation concentration levels of 1000 ppm, sorption behavior is insensitive to change. To investigate the nature of the sorption mechanism, a series of experimental runs was conducted using fish scales of the Gadus Morhua (Atlantic cod) and Lethrinus nebulosus (spangled emperor or shouairi) species as substrates. A simulation model based on the theory of surface excess with mechanical entrapment is developed in this study. Numerical simulation results demonstrate reasonable agreements with the experimental results. This study illustrates that variations of flow rates of the cations did have a considerable effect on breakthrough time intervals. An increase in flow rate led to earlier contaminant breakthrough. However, variance of the cation concentrations did not have a dominant effect on the corresponding breakthrough values. The effect of porosity of the adsorbents is observed, and it is determined it has a profound impact on adsorption phenomena. The dispersion parameter is found to be a function of porosity, and its effect was studied in relation to the flow rate of the bulk phase. A decrease in porosity of the adsorbent results in an increase of the retardation factor of the contaminant in bulk phase and an equivalent delay in the breakthrough interval. In order to study the adsorption characteristics by surface excess model, the pH parameter was maintained at a constant pH value of 7 for all the experimental runs. The adsorption coefficient (K) was coupled into the numerical model as a parameter independent of the pH values. The numerical simulations did fit reasonably well with the experimental data. The surface excess theory has been tested in the past only for anionic solutions. The significance of this research is that this model has been applied for the first time with respect to a bio-adsorbent in relation to heavy metal cations. It is found to be suitable for describing adsorption behavior of metallic contaminants at neutral pH. For studying adsorption with respect to the pH variable, a different adsorption model based on, the Langmuir isotherm is proposed.

Electrochemical efficacy of a carboxylated multiwalled carbon nanotube filter for the removal of ibuprofen from aqueous solutions under acidic conditions.

This study provides insight into the efficiency of a functionalized multiwalled carbon nanotube filter for the removal of an anti-inflammatory drug, ibuprofen, through conventional filtration and electrochemical filtration processes. A comparison was made between carboxylated multiwalled carbon nanotubes (MWNTs-COOH) and pristine multiwalled carbon nanotubes (MWNTs) in order to emphasize the enhanced performance of MWNTs-COOH for the removal of ibuprofen using an electrochemical filtration process under acidic conditions. Ibuprofen-removal trials were evaluated based on absorbance values obtained using a UV/Vis spectrophotometer, and possible degradation products were identified using liquid chromatography mass spectrometry (LC-MS). The results exhibited near complete removal of ibuprofen by MWNTs-COOH at lower applied potentials (2 V), at lower flow rates, and under acidic conditions, which can be attributed to the generation of superoxides and their active participation in simultaneous degradation of ibuprofen, and its by-products, under these conditions. At higher applied potential (3 V), the possible participation of both bulk indirect oxidation reactions, and direct electron transfer were hypothesized for the removal behavior over time (breakthrough). At 3 V under acidic conditions, near 100% removal of the target molecule was achieved and was attributed to the enhanced generation of electroactive species toward bulk chemical reactions and a possible contribution from direct electron transfer under these conditions. The degradation by-products of ibuprofen were effectively removed by allowing longer residence time during the filtration process. Moreover, the effect of temperature was studied, yet showed a non-significant effect on the overall removal process.