PhD Theses (Environment)

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Advanced process control for continuous bioprocessing of biotherapeutic protein production
(2022) Nivedhitha, S
The global biotherapeutics market has been tremendously growing with a compound annual growth rate (CAGR) of 13.8%, and is expected to reach a total sales value close to half a trillion USD within the next five years. The rising demand for the production of high-quality therapeutic products in affordable price range, especially in developing countries, has made the manufacturers to focus on the implementation of a continuous manufacturing process for the production of the same. Efficient measurement and control of the critical process parameters (CPPs) governing the critical quality attributes (CQAs) of the therapeutic products can be achieved by implementing the mechanisms of Process analytical technology (PAT) as imparted by the FDA. The work presented herein attempts to implement the different components of PAT to venture the possibility of acquiring reliable real-time process measurements and utilizing them in a process model to develop an efficient control strategy. The expression of the therapeutic product Ranibizumab (also called Lucentis) in recombinant Escherichia coli has been chosen as the system for exploring the various concepts of PAT. The physiological changes associated with cellular population would impact product quality, and therefore, real-time monitoring and estimation of the biomass concentration using an emerging PAT tool, namely, dielectric spectroscopy (DS), was explored in the first phase of this study. The real-time scanning capacitance data from DS were pre-processed and then modelled through a nonlinear theoretical Cole-Cole model. The obtained model parameters were further applied to estimate the physiological properties like cell diameter and viable cell concentration (VCC), which were validated using traditional offline analytical methods like particle size analyzer and flow cytometry, respectively. The Cole-Cole model predicted the cell diameter and viable cell concentration with an error of 1.03% and 7.72%, respectively. The proposed approach can enable the operator to take real-time process decisions to achieve desired productivity and product quality. The second phase of the study focused on developing a mechanistic model based on mass balances of the various state variables of fermentation and the application of the model to optimize the total biomass with the aid of online capacitance measurements. The developed mechanistic model was validated using experimental data sets obtained from the production of a therapeutic product, Ranibizumab, from E. coli. The model predicted the experimental results of the calibration set and validation set within an average error value of 12.64% and 14.97%, respectively. The final phase of the study focuses on the development of different optimization case studies for achieving enhanced productivity. The objective of the case study (1) focused on maximizing the total biomass in the reactor at a minimum broth volume. A validated mechanistic model was employed to formulate a multiobjective optimization (MOO) problem. The substrate flow rate during the fed-batch phase (F) was taken as the decision variable for the MOO. The Pareto front resulting from MOO revealed that for a minimum broth volume (V) of 1.96 L, a maximum of 58.8 g of total biomass (XV) could be generated. The total biomass obtained from the optimal substrate feeding profile was 20.6% higher than the experimentally achieved total biomass. Enhanced productivity was achieved by the proposed MOO formulation, which facilitates the choice of any operating point from the Pareto front based on downstream expenses of the therapeutic product. The case study (2) focuses on the development of optimization strategies for predicting an optimal fed-batch harvest time. The harvest of a batch is typically linked to the time of induction. Rather than using time as the control criterion, basing harvest on biomass concentration is likely to result in more consistent process performance. The previously developed MOO was used along with a third objective of optimizing final harvest time tf (tend). Simulation studies were carried out with different tend values to predict the optimal fed-batch harvest time. The Pareto for different tend values were obtained, and the objective functions were compared at different λ values. The optimal feeding profiles and fed-batch harvest time can be chosen based on the desired volume of operation. In a nutshell, the approach presented in this work integrated the real-time process measurements in a validated process model and explored the application of different optimization strategies for a therapeutic protein production process. The combination of enhanced measurement, modelling and control strategies will significantly improve the product quantity and quality, thereby paving way for better process performance.
Advanced treatment methods of melanoidin for the effective remediation of distillery spentwash
(2023) Verma, Rahul
The melanoidin-containing wastewater, particularly distillery spentwash possesses very high loads of chemical oxygen demand (COD) and other organic and inorganic pollutants. The discharge of this dark brown colour wastewater to water bodies results in eutrophication, reduction of dissolved oxygen level, obstruction of sunlight penetration, inhibition of photosynthesis of aquatic plants and groundwater contamination. The treatment efficacies of the conventional methods are quite low due to the poor biodegradability of melanoidin. In this regard, the present study explores adsorption, advanced oxidation process, and photocatalysis to remove melanoidin from wastewater. In addition, the bioprocessing of molasses to produce alternative metabolite biosurfactants has been investigated to decrease the pollution load of wastewater. Chapter 1 and chapter 2 demonstrate the introduction and literature review on melanoidin removal in distillery spentwash.
Anaerobic digestion of water hyacinth : Effect of pretreatment and co-digestion on biogas production
(2018) Barua, Visva Bharati
Water hyacinth is considered to be the world’s worst aquatic due to its phenomenal reproduction potential. It can grow within a week and cover an entire freshwater body by forming thick dense mats. These thick dense mats hamper the aquatic ecosystem alongwith the health, livelihood and recreation of human beings. Water hyacinth is difficult to manage as it can re-grow miraculously even if it is completely eradicated. Presence of cellulose and its availability in abundance makes water hyacinth an attractive feedstock for biogas production through anaerobic digestion. Biogas production from water hyacinth can effectively manage the aquatic weed as well as mitigate environmental pollution which is caused by burning of fossil fuel. But the presence of lignin in water hyacinth makes hydrolysis the bottleneck of anaerobic digestion thereby delaying the hydrolysis phase and producing decreased amount of biogas. Therefore pretreatment of water hyacinth is essential for accelerated hydrolysis period and enhanced biogas production. In this study, thermal, electrohydrolysis and biological (microbial) pretreatment were investigated to enhance solubilisation of water hyacinth. Hot air oven pretreatment of water hyacinth at 90ºC for 1h demonstrated the highest solubilisation and biogas production when compared to the other pretreatment techniques. Even mono-digestion of water hyacinth produces lesser amount of biogas therefore co-digestion of water hyacinth is essential to balance the nutrients and dilute the toxic inhibitors. During the BMP assay F/M ratio 2 was observed to be ideal for untreated water hyacinth whereas for the pretreated water hyacinth F/M ratio 1.5 was observed to be ideal. Co-digestion of water hyacinth was tried not only with cow dung as inoculum but also with other organic wastes (i.e., food waste, Hydrilla verticillata, banana peels) with and without pretreatment. Pretreatment and anaerobic co-digestion of water hyacinth not only enhanced the quantity of biogas production but also the quality of the produced biogas by increasing the percentage of methane content. At last, a novel anaerobic digester was designed, fabricated and operated in continuous mode. The novel anaerobic digester proved its immense prospective in treating water hyacinth in untreated, pretreated or co-digested form. The design of the novel anaerobic digester is proficient in minimising the cost, difficulty in operation and manages space constraint when compared to the traditional two stage anaerobic digesters with mixing operation.
Benzylic Organosulfides and Analogues: Greener Synthesis, Anti-cancer Activities and the Feasibilities of H2S Donation
(2023) Bhattacherjee, Debojit
The thesis comprises four chapters. Chapter 1 highlights the general introduction of H2S and its role in biological systems. This chapter briefly discusses the production, metabolism, and biochemical pathways of H2S regulation and its detection techniques. Additionally, a brief and concise review has been made on the reported synthetic and natural donors of H2S and their biological implications in different diseases, notably cancer. In chapter 2, we presented a series of 4-substituted benzylic derivatives of DADS as well as their diselenide analogues for detailed structure-activity relationship (SAR) studies regarding their anti-cancer properties against ER+ breast cancer cell lines (MCF-7) and other organ-specific cancer cells. The SAR study revealed that the anti-cancer activity of the benzylic disulfides/diselenides could be enhanced significantly upon the incorporation of 4-cyano group on the benzene ring. Further investigations revealed the notable increase in intracellular ROS level upon the administration of diselenides towards MCF-7 cells correlating with their anti-proliferative activity. Treatment of 4-cyanobenzyl diselenide in MCF-7 cells induced prominent nuclear fragmentation and induced the apoptosis pathway, confirmed by evaluating the expression level of several oncogenic marker proteins (Bcl2, Survivin, and Procaspase 3). In chapter 3, we described a very simple and convenient method for the selective synthesis of garlic-derived allyl sulfides and related derivatives utilizing a wide variety of alkyl, alkenyl, and benzyl halides as precursors under a greener and catalyst-free condition. We show for the first time that, the selectivity among symmetrical trisulfides, disulfides, and monosulfides could be achieved by variation of several reaction parameters. Our study further revealed that the reaction temperature and solvent were two crucial parameters for an effective selectivity toward trisulfides over disulfides. The detailed mechanistic studies by experimental and computational methods indicated that the co-formation of disulfides along with trisulfides is due to the formation of sodium sulfite (Na2SO3) as a by-product that interfere in the reaction. Furthermore, results from the preliminary anti-proliferative activities by trisulfides towards MCF-7 revealed potent anti-cancer activities of most of the trisulfides in general. Importantly, the 4-methyl substituted trisulfide exhibited the highest anti-proliferative activity in MCF-7 cells and it was capable of donating H2S in a sustained manner in the presence of biothiols. The mechanistic investigations on the potent anti-proliferative activity of the benzylic organotrisulfide (3,5-dimethoxybenzyl) against the highly aggressive triple-negative breast cancer cells (MDA-MB-231) was carried out in chapter 4. From the pool of different substituted benzylic organotrisulfides, 3,5-dimethoxybenzyl trisulfide (4.0) exhibited highest selectivity towards the MDA-MB-231 over the normal cells (HEK-293). The selected trisulfide compound further studied the detailed mechanistic aspects for evaluating its anti-proliferative activity. Trisulfide 4.0 exhibited the anti-cancer activity mainly by targeting and suppressing the Wnt/β-catenin signaling pathway. The detailed mechanistic studies revealed that compound 4.0 facilitated the GSK-3β-induced phosphorylation of β-catenin and subsequent proteasomal degradation, which was supported by the G2/M phase arrest of the cell cycle and the significant down-regulation of downstream signaling genes such as Cyclin D1 and c-Myc. Unlike the disulfide and monosulfide moieties, the presence of a trisulfide functionality facilitated the release of H2S, which was found to be important for the desired inactivation of β-catenin expression. Surprisingly, combination with DATS and our synthesized sustained donor 4.0 exhibited cytoprotective effect due to the optimum level of H2S donation. Moreover compound 4.0 or the released H2S induced down-regulation of the p53 protein, possibly through S-sulfhydration process observed by western blot experiment.
Biodegradation of Phenolic and Petroleum Wastewater by Isolated Bacillus cereus
(2011) Banerjee, Aditi
The thesis mainly focuses on the isolation of phenol-degrading bacteria from oilcontaminated sites and their application in the biodegradation of phenolic and petroleum wastewaters. Firstly, two potential phenol-degrading bacterial strains were isolated from two different site specific petroleum wastewaters and identified as Bacillus cereus MTCC 9817 strain AKG1 and Bacillus cereus MTCC 9818 strain AKG2, based on the 16S rDNA gene sequencing. In addition to the various morphological and biochemical characterizations, the optimum growth conditions and growth kinetics for both AKG1 and AKG2 were investigated. Next, biodegradation of phenol at various initial concentrations by isolated B. cereus strains were studied at their optimum physiological condition. The degradation kinetics revealed that the Haldane model fitted the experimental data fairly well. The phenol degradation mechanism in the isolated strains was also elucidated. Treatment of real petroleum wastewater samples, studied in batch mode by free cultures, demonstrated that coculture of the free cells (AKG1 and AKG2) was most efficient in removing COD, TOC and ammonium nitrogen. Probable identification of bio-degradation products was performed by liquid chromatography and mass spectroscopy. Also, an attempt has been made to probe the structural changes of bacterial cell membrane as a result of the bacterial adaptation to the toxic environment of the petroleum wastewater. The investigation with Ca-alginate immobilized AKG1 and AKG2 demonstrated enhanced tolerance of the immobilized cells to higher phenol concentrations (~ 2000 mg L-1). The storage stability of the immobilized strains and their potential application in repeated batch biodegradation has also been evaluated. Degradation kinetics indicated that phenol degradation by immobilized strains could well be fitted by Haldane model. Moreover, biodegradation of petroleum wastewater samples by alginate immobilized strains have been investigated and the reduction in COD, TOC and ammonium nitrogen level evaluated. The immobilized cells were found to be less effective than the free cell systems in treating petroleum wastewater. Finally, the fabrication and initial optimization of lab scale bioreactors for degrading phenolic and petroleum wastewater Ca-alginate immobilized Bacillus cereus (AKG1 and AKG2) were investigated. The performance of immobilized strains in phenol degradation in a packed bed reactor was studied and the combined effect of external mass transfer with biochemical reaction on the mass transfer correlation was determined in terms of Colburn factor (JD) and Reynolds number (NRe). Continuous biodegradation of the petroleum wastewater was carried out in re-circulated packed bed reactors by the isolated strains immobilized in either Ca-alginate beads or polyurethane foam (PUF) cubes. The biodegradation performances of both the immobilized systems demonstrated the excellent efficacy of the immobilized AKG1 and AKG2 strains in treating petroleum wastewater in continuous mode of operation. Continuous biodegradation of petroleum refinery wastewater in re-circulated fluidized bed reactors also demonstrated that the microbial treatment reduced the initial COD level and concentration of phenolic compounds efficiently...
Biodegradation of Polycyclic Aromatic Hydrocarbons: Mechanistic Insights & Intensification
(2021) Kashyap, Niharika
Different pollutants arising from natural and anthropogenic sources have contaminated our nature and have grave impact on human health. Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutant which cause great damage to terrestrial and aquatic ecosystems. Efficient and safe removal of these pollutants from environment has been an intensely active research area. Bioremediation is a well– established technique employed for the clean–up of PAHs. In this thesis, we have studied the process of PAHs removal through yeast, Candida tropicalis. This type of non–ligninolytic fungi have an edge over other fungi owing to their higher tolerance towards pollutants. To begin with, we have addressed the primary facet of a typical bioprocess, i.e. optimization of physical parameters and kinetic analysis of microbial growth. The model system was phenanthrene and pyrene as pollutants and native yeast strain of Candida tropicalis MTCC 184. The physical parameters related to phenanthrene and pyrene biodegradation were optimized using statistical design of experiments. The tolerance test revealed marked decrease in yeast cell growth after 100 and 75 mg L-1 of phenanthrene and pyrene, respectively. The values of the optimised parameters were similar for both the PAHs. Under optimum conditions, ~ 66% of phenanthrene and ~ 53% of pyrene was degraded in 14 days. Kinetics of the process was studied using different substrate inhibition models. The profiles were best described with Haldane substrate inhibition model. Next intensification of biodegradation of PAHs with ultrasound was studied from a mechanistic viewpoint. After optimization of sonication duty cycle, ultrasound was applied in the log phase of yeast growth cycle. A marked rise of ~ 25% in phenanthrene removal and ~ 30% in pyrene removal was seen with sonication. Kinetic analysis revealed that the biomass yield coefficient increased while the decay coefficient of the cells reduced in presence of sonication. No significant alteration in the cellular morphology and topography was seen with ultrasound treatment. Further, we have studied the biomechanism of degradation of phenanthrene and pyrene by Candida tropicalis. It was found that same route of degradation (meta– pathway) was followed in both test and control experiments, thereby signifying that ultrasound did not alter the route of degradation. SDS–PAGE analysis revealed higher protein expression in the test samples as compared to control samples. GC–MS analysis of intermediate metabolites revealed two parallel pathways of degradation, first triggered by intracellular cytochrome P450 monooxygenase enzyme, and second initiated by dioxygenase enzymes. Finally, the co-bioremediation of both the PAHs have been studied. Experimental results have been analyzed using a kinetic model for cell growth that takes into account self- and cross-inhibition of both substrates. In dual substrate system, specific degradation rate of phenanthrene was significantly higher than pyrene, which indicated relatively lower tolerance of C. tropicalis cells towards pyrene. The values of interaction parameters of inhibition revealed strong competitive cross-inhibition between two substrates, due to which biomass yield with dual substrates was reduced significantly. Inhibition induced by pyrene on cell growth was higher than phenanthrene. On a whole the thesis presents a complete lab scale process design and intensification of bioremediation of PAHs through non–ligninolytic fungi. Moreover, the methodology presented in the thesis forms a general framework that can be extended to other bioremediation systems.
Bioinspired Engineering of Nanomaterials for Electrocatalytic Sensing of Heavy Metals and Organic Analytes
(2021) Dash, Smruti Ranjan
This work focuses on the bioinspired synthesis of various spherical and tailor-made nanoparticles using reducing and capping agents present in the leaves extract of the Psidium guajava (guava) plant. These bioinspired synthesized nanoparticles were used in the modification of graphite paste electrodes (GPEs) and glassy carbon electrodes (GCEs) by drop-casting method for electrochemical sensing of different organic analytes like ascorbic acid, dipyrone (drug), chlorpyrifos (organophosphate pesticide), and inorganic analytes (heavy metal ions). The mass spectra analysis of the bio-extract revealed the presence of various antioxidants and polyphenols like ascorbic acid, quercetin, chlorogenic acid, caffeic acid, naringenin, and rutin. These components could successfully reduce metal precursors like silver nitrate and chloroplatinic acid to produce stable silver, platinum, and tailor-made bimetallic core-shell Ag@Pt nanoparticles. The biomass residue generated during bio-extract preparation was also used to synthesize carbon dots for electrocatalytic sensing of chlorpyrifos. The fabrication of a miniaturized three-electrode system was also successful for the electrochemical sensing of heavy metal ions. A portable electrochemical sensing device that can be applied for on-field monitoring of heavy metal ions was successfully developed using a fluorine-doped tin oxide based three-electrode system. Silver-coated copper nanorods (Cu@Ag) synthesized in an environmentally friendly method showed improved sensing capabilities than copper nanorods modified FTOs. Cu@AgNR/FTOs could successfully quantify Pb(II), Zn(II), Cd(II), and Hg(II) both in single metal systems and in mixed metal matrices with the detection limits in the nanomolar range. The device showed repeatability of up to 4 cycles, thus providing an alternative to the conventional screen-printed electrodes that are typically single-use devices and generate a lot of plastic wastes
Biological sulfate reduction for batch and continuous removal of heavy metals from wastewater
(2017) Kiran, Mothe Gopi
Heavy metals are extensively used for several applications, and as a consequence of which these metals are discharged into the environment from different sources. Owing to their non biodegradable and non persistent nature, metals can merely be transformed to less toxic and insoluble forms. Besides heavy metals, sulfate is found abundant in wastewater streams which pose many environmental issues. Therefore, elimination of metals and sulfate from wastewater prior their discharge into the environment is mandatory. This study was focused on the application of sulfidogenic bioreactor systems for heavy metal removal from metallic wastewater. Initial studies were carried out to screen suitable anaerobic biomass for the removal of different heavy metals and to investigate the mechanism of metal removal from both single and multi-component systems by SRB. The SRB biomass obtained from the experiments was characterized using FTIR, TEM-EDS and FESEM-EDX and the heavy metal removal mechanism was attributed to the sulfate reducing capability of the biomass, which resulted in precipitation of the metals as their corresponding sulfide salts. FTIR spectroscopy analysis of the biomass confirmed the presence of functional groups in the SRB that were similar to that of an earlier reported SRB, Desulfovibrio. species. For a successful application of this method, the choice of a suitable reactor system is essential. Therefore, continuous metal removal from synthetic wastewater by immobilized SRB was evaluated using two lab-scale sulfidogenic bioreactor systems: anaerobic rotating biological contactor (An-RBC) reactor and a downflow column reactor (DFCR) packed with immobilized SRB beads. Best heavy metal removal results were obtained at 48 h HRT than at 24 h HRT in case of both the reactor systems. However, the removal values were reduced at a high inlet concentration of the heavy metals, which matched well with low COD and sulfate removal efficiencies, but the metal removal results were better using the An-RBC reactor than those results obtained using the DFCR. V3-V4 metagenomics sequencing and analysis revealed that SRB immobilized in the An-RBC reactor is predominant with Desulfovibrio. sp. Combined effect of different heavy metals on the removal of metals, sulfate and COD by SRB using both the reactor systems was evaluated under continuous operating condition by employing the statistically valid fractional factorial design of experiments. Continuous metal removal from a mixture of the heavy metals showed that Cu(II) removal was maximum (> 98%), followed by Zn (II) (96%) and other heavy metals at their respective low inlet concentrations, and metal removal order in the mixture study using both the reactor systems was Cu > Zn > Cd > Pb > Fe > Ni. These results strongly indicate that the passive biofilm based bioreactor (An-RBC reactor) could be preferred over DFCR for large-scale treatment of sulfate and metal rich wastewater
Biosorption of Pb(II) by bacterial strain bacillus badius AK isolated from rotary drum compost of water hyacinth
(2017) Vishan, Isha
Composting of biological waste is mainly governed by the diversity of microorganisms working intermittently or in succession in order to carry out the biochemical reactions for their metabolism. The rotary drum composting is relatively a faster method as compared to the conventional pile (windrow) composting method. The water hyacinth (Eichhornia crassipes) being a free-floating aquatic weed is creating nuisance in waterbodies, composting is found to be one of the most effective method of management and utilization of this weed. From the previous studies it was found that the total content of metal has increased to a significant amount in final compost of water hyacinth. Therefore, current study was performed to detect the microbial succession in the rotary drum composting of water hyacinth along with the stability and maturity analysis in form of different trials. Major microbial communities in the best trial (6:3:1) of water hyacinth compost were observed Bacteria. Therefore, in this thesis work rotary drum compost of water hyacinth was used as a source for isolation of bacteria. Twelve bacterial isolates were isolated and identified, which majorly belonged to the Bacillus and Entrobacter genera. The biosorption study of heavy metals such as lead (Pb(II)) and cadmium (Cd(II)) were performed with isolated bacterial strain Bacillus badius AK. Live (non-pretreated) and dried (pretreated) bacterial cells were utilized for biosorption of Pb(II) and Cd(II). Batch biosorption study of live (non-pretreated) biomass of Bacillus badius AK demonstrated maximum biosorption of Pb(II) at biomass concentration of 1.7×1016 CFU/mL. The specific growth rate and maximum specific growth rate of bacterial cells under the influence of Pb(II) were determined as 0.05/h and 2.54/h. respectively. The rate of biosorption in batch study with dried (pretreated) biomass of Bacillus badius AK was observed to be high in the first 30 min. The maximum adsorption capacity was 138.88 mg (Pb(II)) /g (dried biomass). Biosorption of Cd(II) by dried biomass of Bacillus badius AK was found to have maximum biosorption capacity of 131.58 mg (Cd(II)/g (dried biomass). The continuous column mode operation of dried biomass of Bacillus badius AK in biosorption of Pb(II) was observed with higher breakthrough capacity as compared to the batch process. The dried (pretreated) biomass of Bacillus badius AK has much potential as a biosorbent for removal of heavy metals such as Pb(II) and Cd(II) from aqueous solution at lab scale. Additionally, it is an economical and promising substitute of biosorbent for heavy metal removal as compared with the existing conventional methods of biosorption.
Climate Change in the Brahmaputra Valley and Impact on Rice and Tea Productivity
(2013) Deka, Rajib Lochan
Given the vulnerability of agricultural sector to variations in weather conditions, it will be one of the sectors most affected by climate change. This study assesses the state of climate change and variability in the Brahmaputra valley of India and consequent implications on productivity of two important crops rice and tea grown extensively in the valley. The trends and fluctuations of the major climatic variables were assessed using statistical techniques. A quantitative assessment of the impact of observed as well as projected climate on rice and tea productivity was carried out in the study area through statistical and process-based simulation models. Historical rainfall data from 1901 temperature data from 1951 and sunshine duration data from 1971 were analyzed for assessing long-term trends. A suite of climate change indices derived from daily rainfall (1955 and temperature (1971 data, with a primary focus on extreme events, were computed and analyzed to understand the trends. The impact of climate change and its variability on yield patterns of rice and tea were based on 26 years of district level rice yield data (1985 and 20 years of estate level tea yield data (1991 The CERES-Rice crop simulation model was used to predict rice yield under future climate scenarios. The likely impact of future climate changes on tea yield was based on the statistical models developed for monthly yields and climate data of 1991 to 2010. Annual and monsoon rainfall in the study area exhibited a weak diminishing tendency during 1901 due to significant decrease in rainfall in the eastern part of the valley. Significant declining trend of monsoon rainfall during the recent 30-year period was due to significant decrease of July and September rainfall and this trend was consistent at different spatial scales. The intensity of monsoon rainfall was found to diminish over the entire valley due to decrease in the extreme fractions of rainfall, marked by extremely wet, very wet and moderately wet days during the recent three decades (1981 Decrease of rainfall fraction due to moderately wet days was particularly significant in the eastern and western parts of the valley. Rainfall during pre-monsoon and post monsoon season showed increasing tendency during the most recent 30-year period due rise in extreme rainfall indices over the valley. Increase of rainfall during pre-monsoon was primarily contributed by significant increase of April rainfall in the western part of the valley.
CO2 Sequestration using Microalga Scenedesmus Obliquus SA1 Isolated from Bio-diversity Hotspot Region of Assam
(2016) Basu, Samarpita
Flue gases emitted from coal-fired thermoelectric plants is responsible for up to 7% (v/v) of global CO2 emissions, about 10-15% (v/v) of the flue gases emitted from the power plants being in the form of CO2. Increased CO2 concentration in the atmosphere is responsible for global warming and climate change. The thesis focuses on the isolation and characterization of high CO2 and temperature tolerant microalga capable of sequestering CO2 from flue gas and subsequent cultivation of the microalga in bench scale open system and lab scale photobioreactor for enhanced CO2 sequestration. Microalga strain SA1 was isolated from a freshwater body of Assam and identified as Scenedesmus obliquus (KC733762). At 13.8 ± 1.5% inlet CO2 concentration and 25 °C, maximum biomass of 4.975 ± 0.003 g L−1 and maximum CO2 fixation rate of 252.883 ± 0.361 mg L−1 d−1 were obtained in the lab scale closed system studies. Also, at elevated temperature (40 °C) and 13.8 ± 1.5% CO2 supply maximum biomass value of 0.883 ± 0.001 g L−1 and maximum specific growth rate of 0.54 ± 0.020 d−1 were obtained. . The carbohydrate, protein, lipid, and chlorophyll content of the CO2 treated SA1 obtained in the lab scale closed system studies were 30.87 ± 0.64%, 9.48 ± 1.65%, 33.04 ± 0.46 and 6.03 ± 0.19% respectively. The inlet CO2 concentration of 13.8 ± 1.5% was reduced to 0.5% during logarithmic growth phase of SA1. Since the power plant flue gas contains high concentration of CO2 (around 12-15%) and is released from the power plant at high temperature (around 40-50 ºC after the desulfurization process), tolerance of high CO2 concentration and high temperature of 40 ºC temperature by S. obliquus SA1 makes it a potential strain for CO2 sequestration from flue gases. SA1 strain was subsequently cultivated in bench scale open system at varying CO2 levels ranging from 0.03-35% (v∕v) and subsequently the carbonic anhydrase activity (CA) and the biochemical properties were monitored. Maximum biomass concentration (1.39 ± 0.023 g L−1), CO2 fixation rate (97.65 ± 1.03 mg L−1 d−1) and total Carbonic anhydrase (CA) activity (166.86 ± 3.30 E.U. /mg chla) were obtained at 35% CO2 at a culture depth of 0.17 m. The culture depth was varied at 15% CO2 concentration from 0.0425 m to 0.17 m. Overall biomass productivity (54.33 ± 0.19 mg L−1 d−1), CO2 fixation rate (102.13 ± 0.36 mg L−1 d−1) and maximum biomass productivity (156.8 ± 4.37 mg L−1 d−1) were the highest at a culture depth of 0.085m. As evident from literature reports, CA activity is strongly induced when algae are grown in a low-CO2 environment. This fact was evident from our experimental finding, as CA activity of control culture (grown at ambient CO2 concentration) > CA activity of 15% CO2 treated culture > CA activity of 35% CO2 treated culture for most of the experimental period. CA inhibitors: acetazolamide and ethoxyzolamide inhibited the external and internal enzyme activity respectively in SA1, thereby confirming the presence of periplasmic (external) and intracellular CA in the SA1 strain. High CO2 levels were favorable for the accumulation of lipids and chlorophyll in the SA1 strain the values of which were 41.17 ± 0.77% and 8.47 ± 0.15% respectively. The increased lipid content could make the SA1 strain useful in biodiesel production. Also, chlorophyll is a useful commercial pigment and is regarded as an economically valuable co-product of the CO2 sequestration process. Finally, the operational parameters were varied to maximize the CO2 utilization efficiency by the SA1 strain. In these optimization studies, SA1 strain was cultivated in a lab scale cylindrical glass photobioreactor (open system) under 15% CO2 concentration at varied operational conditions (light intensity, CO2 sparging duration and CO2 flow rates). At light intensity of 4351 lux, CO2 sparging duration of 12 h per day and flow rate of 0.43 liter per hour, maximum biomass concentration of 3.32 ± 0.022 g L−1, maximum specific growth rate of 1.24 ± 0.028 d−1, maximum CO2 fixation rate of 1035.25 ± 52.98 mgL−1d−1 and maximum CO2 utilization efficiency of 10.23% were obtained which were higher than most of the relevant literature reports. These parameters were thus inferred to be the optimum condition for maximum CO2 utilization by the microalga in lab scale photobioreactor. SA1 has high biomass productivity, fast growth rates, an attractive biochemical profile, high CO2 fixation rates and utilization efficiency when cultivated in presence of 15% CO2 (typical flue gas concentration). It can thus prove to be a potential candidate for...
Comprehensive Investigation of the gut microbial community of Antheraea assamensis Helfer through Meta-omic Approach
(2023) Saikia, Dharitri
Antheraea assamensis Helfer, commonly known as the Muga silkworm, is an endemic, economically important Lepidopteran species explicitly found in the northeastern part of India and its neighbouring areas. This semi-domesticated, multivoltine, polyphagous, edible insect produces an economically important, lustrous golden-coloured silk with high tensile strength and durability. The cultivation of Muga silkworm for silk production has been in practice for ages in Assam, a state of India. Due to its extreme durability, magnificent colour and lustre, Muga silk is considered one of the most expensive natural fibers in the world. The fibroin part of the Muga silk is also a promising material for tissue engineering. Unlike mulberry-feeding silkworms, A. assamensis is semi-domesticated and can be grown only in outdoor conditions. Lack of genetic variation and low adaptability to changing environmental conditions and limited knowledge of its host plants are the key bottlenecks towards its domestication. The role of gut microbiota in host metabolism, growth, development, nutrition and immune regulation is becoming increasingly evident in humans and other organisms. To date, the gut microbiota of A. assamensis has remained largely unexplored. The present work aims to comprehensively identify and characterize the gut microbial community of A. assamensis through a culture-independent approach. The gene expression analysis of the gut microbial community was studied through metatranscriptome analysis. The influence of the host leaf–associated microbiota on larval gut microbial composition and its variation to changes in host plants was also investigated. The results have indicated that the 5th instar larva of A. assamensis contains a highly diverse gut microbial community dominated by Proteobacteria, Patescibacteria, Planctomycetota, Chloroflexi, Acidobacteriota and Actinobacteriota. Functional analysis of A. assamensis gut microbiome through shotgun metagenomics and metatranscriptomics revealed key associations between the insect and its gut microbial community including host leaf digestion, metabolite detoxification, chitinase production and fat body metabolism. The host leaf-associated microbiota was found to occupy a major portion of the total larval gut microbiota. However, the diversity of the larval gut microbiota was greater than the host leaf-associated microbiota. The findings of this study will illustrate the structure of the gut microbial community of A. assamensis, their key interactions with the host organism and the role of host leaf-associated microbiota on the holobiont. The thesis also describes the global metabolome of the host plant leaf, larval gut and silk gland of 5th instar larvae of A. assamensis and how the change in the host plant affects the gut and silk gland metabolite composition. For this, larvae reared on Som and Mejankari plants were considered. The results of this experiment identified hundreds of metabolites from the larval gut, silk gland and host plant leaf of A. assamensis larvae reared on the two host plants. The identified metabolites can be clustered into different categories like amino acids, sugars, fatty acids, alkaloids, secondary metabolites, pigments vitamins and others. Change in the host plant was found to change the metabolite composition of the larval gut and the silk gland. The findings of this study will help to extend our knowledge of the global metabolomes of the studied samples.
Developing Ecofriendly Nano-Particulate Adsorbents using lron-Plant Polyphenols, Understanding the Molecular Properties and their Environmental Applications
(2022) Aktar, Jinat
Removing pollutants using adsorbents made from natural ingredients is an exciting proposition from the standpoint of their cost-effectiveness and safety. Polyphenols are a class of chemicals widely distributed in leaves, seeds, and other parts of plants. They are known for their health benefits and antioxidant properties. Two iron(lll) based new materials were synthesized from tannic acid (tttlat-1) and guava leaf extract (Mat-2) in -10 g scale under identical conditions. The physical properties, surface properties, and chemical properties of all three materials were analyzed using FESEM, FETEM, DLS, BET, pHzpc, CHNS analysis, Magnetic susceptibilities, EPR, XPS, Mass analysis, TGA, PXRD, FTIR. The results of FESEM and TEM showed the materials as clusters of nano-sized particles. The adsorbent properties of the materials were tested with anionic fluoride and cationic dyes. The biosafety of Mat-1 and Mat-2 was checked on mung beans (Vrgna radiata) and on a number of bacteria.
Development of novel sulfonium containing drug carriers with inherent antimicrobial activities to combat drug resistance
(2023) Patel, Anjali
This Thesis title “Development of novel sulfonium containing drug carriers with inherent antimicrobial activities to combat drug resistance” deals with the study of sulfonium containing liposome and polymers which contains membrane directed bactericidal activity and hence it can counteract different drug resistance mechanism of the drug resistance due to efflux transporter, reduced number of porins, metabolic drug inactivation and hence it can rejuvenate the activity of the clinically proven antibiotics against drug resistant bacterial strains
Direct Electrochemical Reduction of Gaseous Carbon Dioxide to Value Added Products: Investigations on Electrocatalysts
(2015) Singh, Surya
This thesis is aimed to find a solution for one of the environmental problems viz. increasing CO2 concentration in the atmosphere. The thesis focuses over this subject for the mitigation of CO2 through its utilization. Direct electrochemical reduction of gaseous CO2 (dERC) has been found to be a suitable technology which not only helps in the utilization of the CO2, but at the same time produce such reaction products which have the high calorific value. Thus, these reaction products can be used as fuels, which will also help to combat the problem of decreasing fossil fuel reserves. With this aim, the CO2 is electrocatalytically reduced and converted into a variety of products. For screening the suitable electrocatalysts form the group of many, a catalytic activity protocol has also been developed to make the dERC process quick and easy. For the conversion of CO2, different types of electrocatalysts; such as metals, metal oxides, metal complexes, and bimetal, have been developed and successfully used for the electrochemical CO2 reduction and formation of value added products. Keywords: Bimetal, Catalytic activity protocol; Electrocatalysts; Direct electrochemical reduction of CO2; Metal oxides; Salen metal complexes.
Ecological study of Brahmaputra River Floodplain in Selected Areas of Majuli and kamrup and Potential Bioresource Utilization Perspectives
(2014) Gogoi, Nayanmoni
A primary objective of ecological monitoring programs is to detect changes in ecosystem functions and processes. Healthy ecosystem functions are the key components to balanced ecosystem services.
Electrocatalysing CO2 Conversion to Value-added Products using Metal Oxides and Metal-Salen Complexes
(2021) Bose, Paulomi
The electrochemical reduction of carbon dioxide (ERC) is a promising technique for storing energy and producing carbon-based chemicals from CO2. The concentration of CO2 is increased from 280 to 416.3 ppm (43.3%) over the past 60 years, which is about 66 ppm higher than the safety limit. This rise in CO2 concentration causes an increase in global temperature by 1-2°C. This doctoral work researches in synthesizing catalysts for ERC into valuable products. The study begins with the synthesis of selected transition and main group metal oxides (Cu, Ni, and Pb). The Cu2O, PbO and NiO nanoparticles were synthesized using a chemical route. The electrochemical studies were conducted using the synthesized catalysts. A custom-made Htype reactor was tested for the electrochemical analyses throughout the study using 0.5 M aqueous KHCO3 solution saturated with CO2 (each catholyte and anolyte of 120 mL). The effects of fundamental electroparameters were investigated through linear sweep voltammetry, cyclic voltammetry, and constant-potential analyses. The working electrodes (WEs) were prepared by brush coating the synthesized catalysts on the graphite plate. Platinum wire and Ag/AgCl (saturated 3 M KCl) were employed as the counter electrode (CE) and reference electrode (RE). The Cu2O electrocatalyst was active for the formation of mainly HCOOH (22%) with a trace amount of CH3OH at a higher potential (−2.00 V vs. Ag/AgCl). In the constant-potential analysis, it was also found that the NiO as an electrocatalyst could produce only H2 and was inactive in reducing CO2. PbO could form HCOOH at different potentials (−1.40 to −2.20 V) and a maximum Faradaic efficiency (FE) of 23% was achieved at −2.00 V vs. Ag/AgCl. Using these metal oxide catalysts, the hydrogen evolution reaction (HER) was quite high which could adversely affect ERC. Thus, to increase the yield of value-added products and to supress the HER, the salen metal complexes (Cu, Ni, and Pb) were designed, synthesized and introduced in ERC. At first, salen ligand 1 (H2LNO2) was synthesized from the reaction of 4-Nitro-o-phenylenediamine and salicylaldehyde at 1:6 molar ratios. Ligand 1 was reacted with Na2S•H2O to produce salen ligand 2 (H2LNH2). The metal complexes (1, 2, and 4) and 3 were synthesized by the metalation reaction from the ligand 2 and 1, respectively, in the presence of triethylamine. The complexes were also brush-coated on the graphite plates and used as the Wes for ERC. Using Cu-salen complex (1) as an electrocatalyst, the ERC products were obtained in the order as HCOOH>CH3COOH>CH3OH>C2H5OH with a total FE of 36%. The highest selectivity (SE) was achieved for the formation of non-alcoholic ERC products such as HCOOH (SE 35%) and CH3COOH (SE 21%). Using Ni-salen complex (2), the abundance of the product formation was found in the order as C2H5OH>HCOOH>CH3OH with a higher FE (total 49%). The maximum FE and SE of ethanol production achieved was 29% and 50%, respectively, at −1.80 V vs. Ag/AgCl. Finally, two Pb(II)-salen complexes (3 = [PbII(LNO2)], 4 = [PbII(LNH2)]) could produce majorly C2 products. While C2H5OH was formed as the single C2 product with FE of 57% and SE of 66% in the presence of complex 3. A mixture of C1 and C2 products, CH3COOH (FE 36%, SE 54%), CH3CHO (FE 12%, SE 14%) and CH3OH (FE 12%, SE 14%) with a total FE of 68% was realized using complex 4. Whereas, the NH2 and NO2 free [PbII(L)] complex, primarily favored ERC to HCOOH and CH3OH (FE 27%, SE 59%). The incorporation of electron-withdrawing -NO2 or electron-donating basic -NH2 functional groups in the backbone of the parent ligand preferentially generated multiple electrons-multiple protons reduced C2 products by stabilizing *CO, *CHO/*CH3 intermediates and increased the availability of CO2/CO near the electrode surface which could enhance the chance of CO2 to be reduced. Thus, the metal complexes could not only supress the HER but also could produce a variety of C1 as well as C2 products with high FE than the metal oxides.
Enhancement of biogas production from rice straw by co-digestion and pretreatment techniques
(2019) Kainthola, Jyoti
Due to rapid economic development over the past few decades, global energy consumption has intensified continuously, causing not only greenhouse gas emissions, but also energy shortage, and in some areas even energy crises. This imminent energy consumption and demand have been the motivation for world scientists to explore alternative energy sources that could replace fossil fuels. Agricultural residues (i.e., wheat straw, rice straw, corn straw, etc.) are the most abundant resource of lignocellulosic wastes, and contribute a major role in producing low-cost and sustainable forms of energy via anaerobic digestion. Anaerobic digestion is a realistic approach to concurrently manage rice straw and harness renewable energy. Inoculum plays a major role in the process of anaerobic digestion; selecting appropriate inoculum is a crucial factor to initiate the anaerobic digestion process.It not only validates the several biochemical and microbial processes, but also enhances the overall methane yield. In order to select the appropriate inoculum for rice straw, biochemical methane potential (BMP) assay of anaerobic digestion of rice straw with digested cow dung and fresh cow dung revealed methane yields of 125.77 and 72mL/g-VSadded, respectively. The 16S metagenomics sequencing revealed that DCD is enriched with majority of anaerobes.
Environmentally benign synthesis of Sn(II)-based metal-organic-framework and its derivative SnO2 nanoparticles for the decontamination of water
(2021) Ghosh, Arnab
In summary, the thesis has some substantial and promising results in the domain of sustainable environmental chemistry and engineering where environmentally toxic organic compounds or cations/ anions are captured by a series of hydrothermally/ solvothermally synthesized water-stable Sn-based metal-organic-framework. Analytical methods, especially FT-IR, IC, DLS, and AAS, heavily corroborated the efficient sorption of the target analytes on the synthesized adsorbent material. In general, the findings will help understand the relatively underexplored space of Sn(II) as inorganic metal ion for stable composite material synthesis and its potential application in environmental remediation. Each of the synthesized Sn(II)-MOF unveiled interesting characteristic properties that were exploited in the remediation of toxic environmental pollutants from the aqueous medium. The rhomboidal shaped benzene-1,4-dicarboxylate based Sn(II)-MOF illustrated excellent anionic dye removal capacity along with multi-cyclic reusability. The findings demonstrated that the low surface area of the adsorbent was not a limiting factor for dye removal from the aqueous medium. The findings clearly suggest that the electrostatic interaction and the presence of the abundant amount of C═O and –OH functional groups played a vital role in preferential adsorption of the anionic dye. On the other hand, the spherical Sn(II)- benzene-1,3,5-tricarboxylate MOF displayed significant fluoride removal efficiency and remarkable anti-interference activity in the presence of other co-existing anions. Besides, the 1,2,4,5-benzenetetracarboxylate based Sn(II)-MOF exhibited selective sensing of the CrO42− ions from the aqueous medium and displayed good high-pressure CO2 adsorption potential at atmospheric pressure. Furthermore, the Sn(II)-MOF synthesized using BDC recovered from waste PET bottles demonstrated remarkable removal efficiency of the environmentally hazardous anions viz. AsO43− and PO43−. Moreover, the SnO2 NPs synthesized following the Sn(II)-MOF calcination route, displayed high colloidal stability. The present finding also elucidates the role of surface charge reversal in excellent Mn(II) ions removal efficiency from the aqueous medium. Importantly, the present work can prove to be an economically viable method of recycling the waste PET bottle into value-added adsorbent material for the decontamination of water.
Evaluation of Aniline formaldehyde condensate polymer in two different forms for heavy metals and anionic dyes adsorption from wastewater
(2018) Terangpi, Praisy
Adsorption technique for wastewater treatment is considered to be the most economically feasible method. Various literatures reported the removal of dyes, heavy metals, etc., by adsorbents such as activated carbon, fly ash, fruit peels, polymeric adsorbents, clay materials, etc. Removal of metal ions and dyes by functionalized polymer like amine groups have been found to be one of the most efficient functional groups for adsorption in which the mechanisms have been attributed to the formation of complexes between the amine groups present on the adsorbents and the adsorbates to be removed. The objective of the thesis was to investigate anionic dyes removal by two amine coated polymer – a) AFC-silica (aniline formaldehyde coated silica gel) and b) PANI-jute (short chain polyaniline coated jute fiber) and to synthesize a new support less amine based polymer (modified-AFC) with detail characterization and study the removal conditions of heavy metals from very dilute solution. Electrostatic attraction with protonated amine group and hydrophobic-hydrophobic interaction and hydrogen bonding were responsible for dye uptake besides which dye molecular weight was also found to play an important role. The support less amine polymer (modified-AFC) was powdered mesoporous material with round shaped clusters. Batch adsorption experiments of chromium and mercury in single system and lead, coper and chromium in multicomponent system was carried out from aqueous solution under operating conditions. Ion exchange as well as redox interaction between chromate ion and protonated amine group of the polymer was found to be the key factor for chromium adsorption. The residual concentration of total chromium (1.74 mg/L) was found within the discharge limit (2 mg/L) of wastewater which supports the adsorbent application in real wastewater treatment. For mercury removal interaction between protonated amine group and anionic species of mercury was the main adsorption mechanism. In multicomponent metal system adsorption due to the coordinate bond between metal ions and nitrogen present in amine group of modified-AFC was the main factor for the removal mixed metals. Finally, the results obtained from this research work gave an insight view of an efficient amine based polymer with and without any supporting material as a high potential adsorbent.

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