Research:
 
My research activity is focused on the following areas:
Biological Wastewater Treatment: Pollution of water due to the discharge of various organic and inorganic compounds into the water bodies is a major cause of concern. Our work is more focused on two most abundantly found pollutants, one is phenol and the other is chromium in its hexavalent from. Biological treatment methods have many advantages over traditional treatment processes such as: complete mineralization of the pollutants (for organic compounds) and reduction in toxicity level (for inorganic compounds), low cost of operation and steady performance. Among the various biological methods of treatment biosorption and biodegradation have gained a lot of attention since last two decades. Biosorption involves uptake of pollutants by both live and dead biomass whereas biodegradation is a metabolically oriented process by live microorganisms which can be aerobic or anaerobic. The most important aspect of biological wastewater treatment is the selection of a suitable biomass. We have developed and characterized various biosorbents from fish scale, Hydrilla weed, nutshell of gulmohur tree etc. which were successfully utilized for biosorption of Cr(VI) from wastewater. Both shake flask as well as packed bed studies were carried out and encouraging results were found. Similarly for the treatment of phenol, a mixed microbial culture was isolated from wastewater of a local refinery and tested. Complete degradation of phenol was achieved up to a concentration of 1000 mg L-1. More work on isolation of microorganisms at various temperatures is going on. Treatment of Cr(VI) rich wastewater using P. chrysosporium, a white rot fungi and Halomonas sp., a bacteria was carried out in our laboratory successfully. It was evident from this study that the free cells of Halomonas sp. and its CFE (Cell free extracts) can be used for the reduction of lower concentration Cr(VI) in an ecofriendly manner. One bacterial strain isolated from soil samples contaminated with tannery wastewater and identified as Bacillus cereus was used for the bioreduction of Cr(VI). We are working on the mechanism of heavy metal detoxification by fungus which is very ill understood. Work on enzymatic detoxification of heavy metals is also planned.
 
Biofuels: Developing country like India needs advanced production and processing technology to secure its energy needs. Hydrogen and ethanol derived from lignocellulosic biomass are promising biofuels and of great potential to become alternatives to fossil fuels. Pretreated lignocellulosic biomass results in two main streams: one rich in cellulose (hexose: glucose) and the other rich in hemicellulose (pentose: xylose and arabinose). By choosing appropriate biocatalyst, cellulosic part can be effectively converted to ethanol and the hemicellulosic part can be utilized to produce hydrogen in the same reactor. However, the metabolic pathway for hydrogen and ethanol production often conflicts with each other from the perspective of metabolic electron transfer thereby limiting the production to a single biofuel (either hydrogen or ethanol). We are working on the methods to optimize the metabolic pathway to produce both hydrogen and ethanol simultaneously. Pretreatment of lignocellulosic biomass to produce carbohydrate is an indispensible part towards biofuels production. North-East India is blessed with a huge biomass reserve and we have collected various waste and unutilized biomasses such as Areca nut (Areca catheu) husk, Moz (Albizia lucida), Bon bogori (Ziziphus rugosus), arjun nut (nut of Tamarindus indica), rice husk etc. Work on complete characterization of these biomasses by several pretreatment techniques such as dilute acid pretreatment, ultrasound assisted lime pretreatment and hot water treatment at subcritical pressure is currently going on. Apart from bio-H2 and bioethanol, work on microalgal based carbon dioxide sequestration as well as biodiesel production is also going on. The microalgal biomass has certain potentiality over the other bio-feedstocks for alternative biofuel production owing to their high oil yielding efficiency, faster growth rate, higher CO2 fixation and wide range of tolerance to varying environmental conditions. Currently work on isolation and screening of various potential microalgae species especially from NE India is in progress. One microalga strain S. obliquus SA1 was isolated from a biodiversity rich fresh water body of Assam, India that showed tolerance to 13.8 - 1.5% CO2 as well as to high temperature of 40 oC. SA1 has an attractive biochemical profile and thereby could find commercial application.
 

 
Membrane Technology: Membrane based separation process is an emerging technology and is being used in a large number of process and allied industries. The membrane processes have several advantages such as, low energy consumption, easy up-scaling and non requirement of any additives. Moreover they can be applied for continuous separation and easily coupled with other separation processes (hybrid processes). However the commercial membranes are very costly which often restricts its use in small-scale industries. Thus our focus in this area is to develop low-cost membranes and test their suitability for various applications. Key outcomes of the work done so far include the development of low-cost ceramic membrane from local clay of IITG and it's successful use for the removal of chromate ions and crystal violet dye from wastewater. Two hybrid processes namely, micellar enhanced microfiltration (MEMF) and advanced oxidation followed by microfiltration were proposed for the removal of above mentioned pollutants. Further this ceramic membrane was used as a support for preparing composite membranes using chitosan, polyvinyl alcohol and polyvinyl acetate. These composite membranes resulted in pore size of ultrafiltration range and were applied for separation of heavy metals and proteins. The findings of these works were presented in many conferences and published in referred journals.
Separation and purification of proteins (antibodies) is a major challenge in the downstream processing of any biopharmaceutical industries. There is a need to develop less costly as well as faster processes to meet the ever-growing market demand of various proteins. Based on my earlier experience with membrane based bioseparation during my post-doctoral tenure at McMaster University, Canada, we focused on the development of low-cost membranes for the separation of proteins. We have developed low-cost ceramic supported composite membranes and used it successfully for the separation of BSA as well as fractionation of lysozyme and ovalbumin from chicken egg white. An overall rejection of 94% ovalbumin and transmission of 95% lysozyme was achieved using a 9 nm pore sized polyvinyl acetate coated membrane. Similarly an overall BSA rejection of more than 95% was obtained for a mixed matrix membrane of 10 nm pore size. More work on separation of other proteins and antibodies from cell culture supernatant is currently going on.
 
Ionic liquids: Recently we have started to work on ionic liquids, which are a class of green solvents. They are prepared by combination of organic cations and inorganic or organic anions depending upon their need. Their properties can be greatly varied by appropriate combinations of different cations and anions. At ambient conditions they remain as liquids with no detectable vapor pressure and are non flammable. Therefore IL's can be regarded as clean and green solvents for chemical synthesis and catalysis. IL's are nonvolatile, noncorrosive, thermally stable and posses excellent solubility for both organic and inorganic compounds. However, the higher price of most of the IL's restricts its use even for lab-scale experiments. To overcome this, we have carried out theoretical screening of IL's using COSMO-RS (COnductor like Screening Model for Real Solvents) model to select the best IL for a particular component that need to be removed from liquid phase. Key results of this theoretical approach include screening of best ILs for the removal of phenol and cresol from water phase and separation of transesterification products. Work on aromatic extraction using ILs and Co-solvents is also being carried out in our laboratory. Co-solvents basically reduce the viscosity of ionic liquid and break the hydrogen bonds which appear between cation and anion which ultimately leads to higher mixing rates while retaining the inherent property of ionic liquids. More work on screening of suitable for IL for various organic pollutants is currently going on. We plan to use the best screened ILs in bulk as well as supported IL membranes. The best screened ILs, based on their commercial availability were chosen and used as membrane phase to prepare supported ionic liquid membranes (SILM). These SILMs were successfully used to remove various endocrine disrupting compounds such as Endosulfan and Bisphenol A from wastewater. Another work, which is recently started is the dispersion and dissolution of Coals in ILs. Nonpolar hydrocarbon solvents, such as toluene or hexane, have limited ability to swell coals and extract only small amounts of soluble material. We hope that ILs with judicious selection of cations and anions can make a better contribution in this field. Works on ILs are done in collaboration with Dr. T. Banerjee who has expertise in the area of molecular simulation along with statistical thermodynamics.
 
 
Biolubricant: The last decade has seen a slow but steady move toward the use of "environmentally friendly" or more readily biodegradable lubricant fluids. Biodegradability has become one of the most important design parameters both in the selection of the base fluid and in the overall formulation of the finished lubricant. By more readily biodegradable it is meant that the fluids, using standard methods and assays, are converted from the lubricating fluids to lower molecular weight components that have essentially no environmental impact. Their chemical structure affects their properties, many of which affect performance in the various tests for biodegradability. Vegetable oils cost approximately twice that of mineral oils, are biodegradable, and renewable. Vegetable oils in general are deficient relative to mineral oils, chemically modified mineral oils, and most synthetic lubricants in terms of their thermal and oxidative stability. There are also, in some cases, serious limitations to the use of vegetable oils when used in applications requiring operation at low temperatures. However, due to certain properties vegetable oils are not used directly as lubricants. Due to the presence of bisallylic protons, their oxidative stability is very low. Their viscosity is too low to be used directly as lubricant apart from poor corrosion protection. Vegetable oils have much higher pour point than petroleum based lubricants. Our group is currently using varieties of non-edible oils, as they are out of food chain to convert them to biolubricant.
Selection of proper catalyst for biolubricant synthesis is an important issue. We are working on preparation of heterogeneous catalyst from large-scale bio-wastes. Whilst the use of such wastes in this context, by definition, does not alleviate disposal problems, which are significant and also costly in some cases, high volume waste can provide an inexpensive route to active systems. A number of different approaches to the utilization of waste materials in this context have been reported: (i) their direct application as active materials, (ii) their direct use as pre-catalysts (i.e. materials which undergo transformation to active phases under reaction conditions), (iii) their modification to yield catalytically active phases and (iv) their use as precursors for the synthesis of active catalysts.
 
 
 
Biomass Pyrolysis: Pyrolysis is a common method to convert organic rich biomass into fuel. It is an irreversible process during which phase change occurs along with a change in composition. During pyrolysis, the internal structure of the biomass is thermally decomposed at elevated temperatures with or without the supply of oxygen. Biomass pyrolysis usually results in three different types of products viz. solid, liquid and gas, all of them having high economic value. The solid product is carbon-rich, usually known as bio-char and can be used as a solid fuel or bio-adsorbent. Higher volatility of the char makes it very flammable as similar to coal. It can be stored in open atmosphere for a long period. The non-condensable volatiles which contains mainly CO, CO2, CH4 and H2 (syngas) formed due to the primary and secondary reaction and can be used as gaseous fuel. The liquid product obtained from the condensable volatiles is rich in organic compounds and known as pyrolytic oil (or bio-oil). This is the most important product of pyrolysis. The pyrolytic oil can be used with or without up-gradation as an alternative fuel for diesel engine which has closer physical and chemical properties to that of diesel. The characteristic and composition of the pyrolytic oil is a function of feed types, composition (hemicelluloses, cellulose, lignin and extractive) and the initial moisture content. Higher percent of cellulose and hemicelluloses are responsible for formation of more liquid, while lignin is responsible for production of more char with less amount of liquid. The presence of extractives in feed is responsible for high organic liquid yield. With an aim to have more yield of bio-oil, we have chosen various non-edible oil seeds such as Mahua, Karanja and Niger seeds as feedstock for pyrolysis. The results of our study confirmed that the total pyrolytic liquid is a mixture of both organic and inorganic liquid. The organic liquid is considered as oil and rich in hydrocarbon, aromatics, esters, acids, phenols, ketones and aldehydes whereas the inorganic liquid is mixture of water and water soluble chemicals. Detail characterization of the fuel properties of the bio-oil is being carried out. Catalytic pyrolysis in the presence of various catalysts are undertaken to improve the fuel properties of the bio-oil. More work is going on to determine the optimized condition for maximizing the yield and quality of bio-oil oil from non-edible oil seeds followed by various up-gradation techniques.