Showing papers by "Sirshendu De published in 2018"

Antibacterial polymeric membranes: a short review

Abstract: Pathogenic contamination of water is a major issue throughout the world. The growing demand for pure drinking water calls for new promising technologies for efficient removal of bacteria. Over the last few years, the membrane disinfection process has received immense interest as a cost-effective, scalable and environmentally-friendly technology to produce clean and safe drinking water. With the rising population of multi-drug resistant bacteria, different antibacterial agents have been effectively impregnated into polymeric matrixes to impart excellent disinfection properties as well as higher separation efficiency. However, there are many arguments in the current literature about the exact antibacterial mechanism, life span and biocompatibility of these membranes. This review aims to summarize the recent advances in fabrication and antimicrobial efficacy of polymeric membranes, offering knowledge on how different bactericidal agents influence their stability, disinfection potential and environmental safety. Critical discussions are also undertaken about various influencing parameters, like selection of antibacterial additives, membrane properties, disinfection mechanism and operational feasibility.

Defluoridation using novel chemically treated carbonized bone meal: batch and dynamic performance with scale-up studies.

Abstract: Novel defluoridating adsorbent was synthesized by chemical treatment of carbonized bone meal using aluminum sulfate and calcium oxide. Precursor for chemical treatment was prepared by partial carbonization of raw bone meal at 550 °C for 4 h. Maximum fluoride removal capacity was 150 mg/g when carbonized bone meal (100 g/L) was treated with aluminum sulfate (500 g/L) and calcium oxide (15 g/L). Morphological analysis revealed formation of a coating layer consisting of aluminum compounds on the precursor surface. This was verified by stretching frequency of aluminum hydroxide (602 cm−1) in the infrared spectra. Presence of hydroxylapatite (2θ = 30° and 2θ = 24°) and aluminum mineral phases (2θ = 44°) in the adsorbent were identified from the X-ray diffractograms. Adsorption capacity decreased from 150 mg/g (30 °C) to 120 mg/g (50 °C) indicating exothermic adsorption. Adsorption experiments under batch kinetic mode were simulated using shrinking core model. Effective fluoride diffusivity in the adsorbent and the mass transfer coefficient were estimated as 5.8 × 10−12 m2/s and 9 × 10−4 m/s, respectively. Desorption was maximum at basic pH and desorption efficiency was decreased by 31% after third cycle. Dynamic filtration with artificially fluoride-spiked solution showed that the empty bed contact time for a packed column with equal weight of carbonized and chemically treated adsorbent was 4.7 min and number of bed volumes treated (till WHO limit of 1.5 mg/L) was 340 for a column of 3-cm diameter and 18-cm length. The system was successfully tested using contaminated groundwater from an affected area. Fixed-bed column experiments were simulated from the first principles using convective pore diffusion-adsorption model for both synthetic solution and contaminated groundwater. Axial dispersion coefficient was found to be one order of magnitude less than the pore diffusivity indicating dominance of fluoride diffusion within porous network of adsorbent. The developed adsorbent exhibited antibacterial property as well.

Adsorption of Dyes

Abstract: Adsorption is one of the most commonly used, traditional separation technologies utilized for separation. Since it is an equilibrium-governed process, the process efficiency is excellent, but the throughput is relatively low. Nevertheless, because of its simplicity, this is one of the normally used technologies for dye removal from aqueous stream. Therefore, it is imperative to understand the modeling aspects of such adsorbent-based systems which is necessary for design and implementation of the technology. Additionally, the chapter describes the characteristics of the different commonly used adsorbents and its applicability.

Modeling of permeate flux decline and permeation of sucrose during microfiltration of sugarcane juice using a hollow-fiber membrane module

Abstract: Microfiltration (MF) of centrifuged sugarcane juice was used as a pre-clarification step prior to further clarification. MF was performed with the objectives of achieving maximum flux, minimum retention of sucrose and maximum rejection of total solids as well as maximum removal of microorganisms from the permeate keeping the nutritional and physico-chemical profile intact. In this regard, experiments were done using a polyacrylonitrile-based MF membrane of filtration area 0.027 m2 and pore size of 0.1 μm. A detailed investigation of the effects of different operating conditions, namely transmembrane pressure TMP (35, 69, 104 and 138 kPa) and cross flow velocity CFV (0.123, 0.246 and 0.369 m/s) on membrane productivity and juice quality was undertaken. The steady-state permeate flux ranged from 5.41 to 6.23 l/m2∙h for the domain of the operating conditions studied herein. Profiles of permeate flux and sucrose concentration in permeate were modeled using a gel layer controlling model under the framework of boundary layer analysis. The optimized operating conditions were found to be TMP of 104 kPa and CFV at 0.369 m/s, yielding a flux of 6.04 l/m2∙h and having sucrose and polyphenols concentration of 104.8 g/l and 9.38 mg GAE/100 ml, respectively. Total solids (26%) and turbidity (98%) were removed to a great extent during MF along with remarkable improvement of clarity (3 times). Microbiological evaluation confirmed that, MF successfully reduced the total viable plate count by 5 log CFU/mL scale and yeast and mold count by 4 log CFU/mL scale.

Role of thermodynamic and kinetic interaction of poly(vinylidene fluoride) with various solvents for tuning phase inversion membranes

Abstract: An extensive study of thermodynamics and kinetics of non-solvent induced phase separation was carried out for poly(vinylidene fluoride)/solvent/water system for four different solvents. Literature available on semicrystalline polymers was mostly based on experimental cloud points, obtained to a narrow range of polymer concentration (<10 wt%), much less than the working range for membrane preparation (20–25 wt%). Aim of this work was to model the thermodynamic phase diagram using extended Flory–Huggins theory which was used as a tool, along with the kinetic data to obtain tailor-made membranes with desired morphology and properties. Interaction parameters involving solvent, nonsolvent, and polymer played an important role to tune the porosity of the membrane. Thermodynamic calculation showed solvent N,N-dimethyl acetamide resulted in the most porous membrane (permeability 5.4 × 10−11 m Pa−1 s−1) followed by N,N-dimethyl formamide (permeability 4.2 × 10−11 m Pa−1 s−1), N-methyl pyrrolidone (permeability 3.8 × 10−11 m Pa−1 s−1), and acetone (impermeable to water even at 1380 kPa), which was the densest one. Prepared membranes were characterized in terms of surface morphology, molecular weight cut-off, tensile strength, pore volume distribution, crystallinity, and surface roughness, which were correlated to inferences based on thermodynamic and kinetic calculations. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

Novel carbonized bone meal for defluoridation of groundwater: Batch and column study

Abstract: Low cost naturally available bone meal was carbonized and its fluoride adsorption capacity was explored. Carbonized bone meal (CBM) produced at 550°C, 4 h carbonization time and a heating rate of 60°C/min, showed fluoride adsorption capacity of 14 mg g-1. Adsorbent was characterized using scanning electron microscopy, X-ray diffraction, X-ray fluoroscence, thermogravimetric analysis and Fourier transform infrared spectroscopy to highlight its physical and chemical properties. Best fluoride uptake capacity was observed for 0.2 mm particle size, 7 g L-1 adsorbent concentration and at pH 6.5. Fluoride uptake was endothermic and chemisorption in nature. Effective diffusivity and mass transfer coefficient were obtained as 6 × 10-11 m2 s-1 and 9 × 10-5 m s-1 from shrinking core model. Sulphate and carbonate showed the highest interference effect on adsorption of fluoride by CBM. Maximum desorption was observed at basic pH (pH 12). Fixed bed study was performed and effect of different parameters (bed height, inlet flow rate and initial concentration) was investigated. Efficiency of the adsorbent using real life fluoride contaminated groundwater solution was also observed.

Fundamental Understanding of Fouling Mechanisms During Microfiltration of Bitter Gourd (Momordica charantia) Extract and Their Dependence on Operating Conditions

Abstract: Microfiltration of bitter gourd (Momordica charantia) extract using hollow fiber membrane module was carried out in the present study. To identify the dominant fouling mechanism, flux decline behavior was examined using Field model. At lower transmembrane pressure, pore blocking mechanism was found to be more important, while cake filtration was dominant at higher pressure. Higher cross flow rate reduced filtration constant indicating slower rate of membrane fouling. Additionally, surface and particle size analyses were undertaken to validate the findings of modeling. Scanning electron microscope analysis clearly showed prevalence of pore blocking mechanism at lower transmembrane pressure drop, whereas cake filtration was dominant fouling mechanism at higher pressure. Fourier transform infrared spectroscopy analysis supported the role of cake layer as a secondary membrane retaining some amount of polyphenols. Analysis of flux decline ratio also confirmed that for transmembrane pressure of 104 kPa and beyond, cake layer became compact, and hence, increase in cross flow rate was unable to influence the improvement of permeate flux. The current study provides an insight into the fouling mechanism involved in scaling up of clarification of bitter gourd extract for successful processing of this medicinal herb.

Cloud Point Extraction

Abstract: Phase separation of a surfactant-loaded solution happens beyond a certain critical thermodynamic state (known as the cloud point), separating the hydrophobic-rich phase in a nonpolar microenvironment from the aqueous supernatant. The dye molecules are bounded to the surfactant and subsequently separated by changing the environmental factor (temperature is commonly altered in cloud point extraction) beyond the cloud point. This is a popular extraction method in bioseparations but is also applicable for purification of dye solution. The chapter discusses the effect of the various operating conditions and different surfactants on extracting clear water from the dye solution with this technology.

Hydrophilic surface modification of polyacrylonitrile based membrane: effect of low temperature radio frequency carbon dioxide plasma

Abstract: In general, polymeric membranes are hydrophobic in nature and hence are prone to fouling. Plasma treatment can impart functional groups on membrane surface making it more hydrophilic and hence fouling resistant. In plasma environment, carbon dioxide exhibits reactive properties with several exciting species and is likely to modify the membrane surface by imparting hydrophilicity. Low temperature plasma treatment using radio frequency discharge of carbon dioxide gas was employed to make polyacrylonitrile co-polymer membrane more hydrophilic. Permeability of treated membrane was increased by 2.2 times and it was retained up to 100 days. The surface morphology, structure and chemistry of the untreated and plasma-treated membranes were characterized extensively. Wettability of the surface was evaluated by contact angle measurement to show the improvement in hydrophilicity of plasma modified membrane. Effects of plasma conditions, namely, treatment time and power on membrane permeability and hydrophilicity were investigated. Hydrophilicity of modified membrane was enhanced by 22% and it was maintained up to 100 days. The effect of process variables on surface morphology of membrane was examined by scanning electron microscopy and atomic force microscopy. Surface etching due to plasma treatment was ensured by the loss of weight of the modified membranes. About 78% increase in average pore size of the treated membrane was obtained due to surface etching. The surface functionalization of unmodified and plasma modified polyacrylonitrile co-polymer membranes were investigated by X-ray photoelectron spectroscopy. Hydrophilic groups adhered to membrane surface after treatment was also identified.

Emulsion Liquid Membrane

Abstract: Emulsion liquid membranes are widely used for recovery of metal ions and organics due to the fast extraction and are a single-stage operation of stripping-extraction. Essentially emulsion liquid membranes are double emulsions which are made stable with surfactants. Separation of dyes using such an emulsion technique is quite novel and new, being researched only for the last one or two decades. The chapter introduces the details of the technique and the efficacy of the method in removing dye-contaminated wastewater.

Performance evaluation of biosurfactant stabilized microbubbles in enhanced oil recovery

Abstract: Microbubble technology is increasingly finding applications in biomedical engineering, soil remediation and wastewater treatment. Recently, the use of surfactant microbubbles has been studied as an alternate to aqueous solution in pollutant remediation since they have the advantage of improving the contact with the contaminant due to their surface properties. In this research endeavor, the application potential of microbubble suspension generated using a lipopeptide biosurfactant produced by a marine strain of Bacillus megaterium in tertiary oil recovery was investigated. The microbubbles were generated using a high speed homogenizer and their properties such as stability and size distribution were studied. The microbubble suspension was used as flooding agent to recover gear oil from an artificially saturated sand packed column. The performance of microbubbles in tertiary oil recovery was compared with that of aqueous biosurfactant solution. It was found that microbubble suspension generated using biosurfactant had higher oil recovery efficiency (46%) than aqueous solution (36%). Moreover, the pressure buildup across the sand packed column was fairly low while using microbubble suspension. The increased oil recovery using microbubbles can be attributed to their effective permeation through the pores of sand packed column and closer contact between biosurfactant molecules and oil. Thus, the results obtained in this study convincingly indicate that biosurfactant stabilized microbubble suspension, due to its higher performance and lower injection pressure requirement, can serve as a potentially efficient flooding agent for tertiary oil recovery.

Nanofiltration of Dyes

Abstract: Membrane separation process is perhaps one of the promising alternatives in water treatment over adsorption, being a greener mode of separation. Nanofiltration of dye-contaminated wastewater is a potential and viable membrane separation technology to effectively remove dyes from the water stream. Various nanofiltration systems (different flow configurations and types of membrane) are discussed, and the filtration efficiencies are compared. Besides, a simple transport phenomenon-based model is presented to explain the experimental observations and the underlying mechanisms.

Micellar-Enhanced Ultrafiltration (MEUF)

Abstract: Typically, the micelles are charged globular particles formed due to agglomeration of surfactant molecules when present above a critical concentration in water. Due to the charge interactions, micelles act as excellent binding agent to the dye molecules, thus solubilizing it. Even in case of uncharged dyes, nonionic surfactant micelles can solubilize it inside the micelle core. Once the low molecular weight dyes are solubilized by the micelles, the micelle-dye complex can be effectively separated by an open membrane (large pore size, large molecular weight cutoff), thus producing high throughput of clean water per unit pressure drop. This chapter deals with various types of dyes and surfactant combination in different membrane separation systems, analyzing its performance and relative separation efficiencies.

Surfactant-Enhanced Carbon Regeneration

Abstract: To make a process sustainable, it is often important to regenerate the adsorbent for reuse. One of the commonly used technique in this case is surfactant-enhanced regeneration which is inexpensive and low-energy intensive. This chapter presents a comprehensive study of this case, the surfactant regeneration process using different types of surfactants, including a simple theoretical model for the adsorbent regeneration.

Hybrid Treatment Method of Industrial Effluent

Abstract: It can be envisaged that a series system using two technologies can be advantageous in improving the overall efficiency and performance. Two proposed configurations were studied in this chapter: (1) adsorption followed by nanofiltration and (2) advance oxidation followed by nanofiltration. Quantitative comparison of the performance of both of these hybrid methods is elaborated in detail in this chapter.

Fabrication and Applications of Functionalized Membranes in Drinking Water Treatment

Abstract: This chapter presents an overview of the synthesis of a new class of inorganic additive doped functionalized polymeric membranes or mixed matrix membranes (MMM) and their application in water treatment. Different inorganic additives, with particle sizes ranging from a nanometer to a few micrometers, improve membrane properties such as water flux, hydrophilicity, surface zeta potential and fouling. Morphological characteristics in the micrographic structures of these membranes clearly portray the difference in the performance of pure polymeric and functionalized membranes. The incorporation of functional groups also testifies the uniqueness in behaviour. The alteration in molecular weight cut-off of these membranes due to the impregnation of these particles clearly suggests a change in the pore size of the membrane. It can also be observed that the inorganic additives in the membrane have a selective affinity for ionic contaminants. An increase in surface roughness results in the adherence of the contaminants to the doping material. This behaviour can also be exploited to remove harmful contaminants including fluoride, arsenic, potentially toxic heavy metals such as lead, chromium, copper, etc., selectively. Water treatment by this class of membranes can be cost-effective in comparison to most of the conventional remedial techniques, since removal is maximum at comparatively lower pressure and flow rate, dissipating less energy.

Adsorption of Dyes from Actual Effluent

Abstract: Adsorption of color components from the effluent in practice is a challenge as often the actual efficiency of the adsorption process is masked by the competitive adsorption of multiple species present in an effluent. The chapter illustrates the adsorption phenomena using one of the commonly used adsorbents detailed in Chap. 2 for removal of toxic dyes from an effluent. Further analyses were done for the kinetics and isotherm for multicomponent adsorption.

Criteria for a unique steady state for enzymatic depectinization of bael (Aegle marmelos) juice in a continuous stirred tank reactor

Abstract: The depectinization kinetics of bael (Aegle marmelos) juice using the enzyme pectinase was evaluated and it was observed to follow the Michaelis–Menten model. The suitable reaction time and enzyme concentration were estimated to be 60 min and 0.25% w/w, respectively. The conditions to obtain a unique steady state for such a reaction in a continuous stirred tank reactor were determined using the fixed point theorem and contraction mapping. The phase space plot was generated using parameters and , involving the operating conditions and kinetic constants (V is the reactor volume, vmax and KM are the kinetic parameters of the Michaelis–Menten model, v0 is the volumetric flow rate and CA0 is the feed concentration of the substrate), and the envelope of a unique steady state was developed. From the iso-conversion curves, the values of α and β were identified so that the reactor can operate at a unique steady state. It was found that β > 4 results in a feasible steady state. The range of α was reduced at a higher β in order to get a unique steady state. The critical residence time of the reactor decreased with the enzyme concentration and became invariant beyond 0.20% w/w. Deviation of the CSTR from ideal behavior led to an increase in the critical residence time. The present analysis is extendable to other reaction kinetic models as well, for appropriate design and scale up of commercial reactors so as to prevent the occurrence of multiple steady states leading to inaccurate product specifications.