Publications by authors named "Kannan Pakshirajan"

60 Publications

Novel biologically synthesized metal nanopowder from wastewater for dye removal application.

Environ Sci Pollut Res Int 2022 May 26;29(25):38478-38492. Epub 2022 Jan 26.

Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India.

A novel adsorbent based on metal sulfide nanoparticles (MeSNPs) was biologically synthesized from metallic wastewater and examined for azo dyes removal from aqueous solution in batch and continuous systems. The size of the MeSNPs was in the range of 8-10 nm, with an average specific surface area of 120.4 m/g. Batch adsorption study was then carried out using Direct Red 80 (DR 80) and Mordant Blue 9 (MB 9) as the model azo dyes by varying MeSNPs dosage, contact time, pH, and initial dye concentration. More than 99% removal efficiency of both the dyes was achieved by using MeSNPs at the following optimum conditions: 200 mg dosage, pH 2, 6 min contact time, and 100 mg L initial dye concentration. The batch sorption isotherm results were described using the Sips model, with the maximum predicted capacity values of 143.7 and 198.3 mg of dye per gram of adsorbent for DR 80 and MB 9, respectively. Besides, the sorption kinetic data for both the dyes followed the pseudo-second-order rate. Furthermore, maximum desorption efficiency values of 93% for DR 80 and 97% for MB 9 were achieved using an aqueous solution of pH 12, thus indicating that the adsorbent can be regenerated and reused further. Dynamic adsorption of the dyes was studied using a fixed-bed column with the MeSNPs as a function of liquid flow rates. The results showed an increase in breakthrough time with a decline in the flow rates for both DR 80 and MB 9 and the breakthrough behavior was explained using Thomas, Clark, and Yoon-Nelson models.
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http://dx.doi.org/10.1007/s11356-022-18723-zDOI Listing
May 2022

Chitosan production by using paper mill wastewater and rice straw hydrolysate as low-cost substrates in a continuous stirred tank reactor.

Environ Technol 2022 Feb 3:1-16. Epub 2022 Feb 3.

Department of Chemical Engineering, Indian Institute Technology Guwahati, Guwahati, India.

In this study, paper mill wastewater and hemicellulose hydrolysate were evaluated as low-cost substrates for fungal chitosan production using . Submerged fermentation was first studied using a bioreactor operated under batch, fed-batch and continuous modes with paper mill wastewater as the substrate. Very high removal (91%) of organics as chemical oxygen demand (COD) in the wastewater with 160 mg L chitosan production by was obtained using the bioreactor operated under fed-batch mode for 72 h. Moreover, 86% reduction of phenolics in the wastewater with 89% decolourization efficiency was achieved in the fed-batch experiments with the bioreactor. Under the continuous mode of operation with the bioreactor, maximum chitosan production of 170 mg L was observed. The effect of acetic acid addition to the wastewater for enhancing chitosan production by the fungus was further studied in a batch system. Chitosan productivity of 2.33 mg L h was obtained with 50 mg/L acetic acid. Various models, . Monod, Haldane, Andrews, Webb and Yano, were fitted to the experimental data for understanding the kinetics involved in the process. Haldane model accurately fitted the experimental data on biomass specific growth rate, acetic acid consumption rate and chitosan production rate by with acetic acid addition to the wastewater. Fungal fermentation of another low-cost substrate, rice straw hydrolysate, was further studied using the batch-operated bioreactor; and a maximum chitosan titre of 911 mg L was achieved using the detoxified rice straw hydrolysate.
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http://dx.doi.org/10.1080/09593330.2022.2026486DOI Listing
February 2022

Process intensification through waste fly ash conversion and application as ceramic membranes: A review.

Sci Total Environ 2022 Feb 1;808:151968. Epub 2021 Dec 1.

Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India. Electronic address:

Improper disposal of huge quantities of fly ash generated by thermal power plants and few other industries contributes to both air and water pollution, and therefore, recent advancements in research are focused toward utilizing this waste material in fabricating useful membranes. This article presents an overview of various methods used to fabricate fly ash-based membranes and critical parameters affecting the same. Fly ash-based membranes also act as the support for fabricating composite membranes and therefore, different means of coating the support membranes are discussed in this paper. Among various methods of membrane fabrication, extrusion method can be considered for bulk production of membranes, which is a pre-requisite for industrial implementation. The article also throws light on a wide range of wastewater that have been successfully treated using these fly ash-based ceramic membranes. However, the use of these membranes should be avoided in acidic solutions as it may cause leaching of heavy metals present in fly ash, causing health hazards. Most of these membranes function on the basis of size exclusion principle, whereas membranes with charge-based separation are also well known. Both of these types of membranes are discussed in this work. Utilization of fly ash-based membranes in separation processes not only reduce the cost associated with the process, but will also intensify the process through various other means such as reduced energy consumption, environmental safety and so on. Thus, the main focus of this review is to present the readers with development and important future directions in this research topic.
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http://dx.doi.org/10.1016/j.scitotenv.2021.151968DOI Listing
February 2022

Bacterial strains found in the soils of a municipal solid waste dumping site facilitated phosphate solubilization along with cadmium remediation.

Chemosphere 2022 Jan 21;287(Pt 3):132320. Epub 2021 Sep 21.

Agro-ecotechnology Laboratory, School of Agro and Rural Technology, Indian Institute of Technology Guwahati, Assam, 781039, India. Electronic address:

Phosphate solubilizing bacteria (PSB) that can withstand high cadmium (Cd) stress is a desired combination for bioremediation. This study evaluated the Cd bioremediation potential of four PSB strains isolated from the contaminated soils of a municipal solid waste (MSW) discarding site (Guwahati, India). PSB strains were cultured in Pikovskaya (PVK) media, which led to higher acid phosphatase (ACP) activity and the release of organic acid. Optical density (OD) measurements were performed to determine the growth pattern of PSB; furthermore, Cd uptake by PSB was evaluated using infrared spectroscopy (IR) and X-Ray Diffraction (XRD) analyses. The 16S rRNA taxonomic analysis revealed that all the four promising PSB strains belonged to either Bacillus sp. or Enterobacter sp. One strain (SM_SS8) demonstrated higher tolerance towards Cd (up to 100 mg L). Flow cytometry analysis revealed 70.92%, 46.93% and 20.4% viability of SM_SS8 in 10, 50 and 100 mg L, respectively in PVK media containing Cd. This study has therefore substantiated the bioremediation of Cd from polluted soil by the PSB isolates. Thus, experimental results revealed a potential combo benefit, phosphate solubilization along with Cd remediation.
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http://dx.doi.org/10.1016/j.chemosphere.2021.132320DOI Listing
January 2022

Mass balance and kinetics of biodegradation of endocrine disrupting phthalates by Cellulosimicrobium funkei in a continuous stirred tank reactor system.

Bioresour Technol 2022 Jan 12;344(Pt B):126172. Epub 2021 Nov 12.

Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India. Electronic address:

This study investigated the potential ofCellulosimicrobium funkeifor degrading dimethyl phthalate (DMP) and diethyl phthalate (DEP). Effect of different initial concentrations of phthalates on their biodegradation and growth ofC. funkeiwas examined using shake flasks and a continuous stirred tank reactor (CSTR). Complete degradation of both DMP and DEP was achieved in CSTR, even up to 3000 and 2000 mg/L initial concentrations, respectively. Simultaneous degradation of the phthalates in mixture, i.e. more than 80% and 55% biodegradation efficiency were achieved at 1000 and 2000 mg/L initial concentrations of DMP and DEP, respectively, using the CSTR. Mass balance analysis of the degradation results suggested proficient degradation of DMP and DEP with biomass yield values of 0.64 and 0.712, respectively. The high values of inhibition constant Kiestimated using the Tessier and Edward substrate inhibition models indicated very good tolerance ofC. funkeitoward biodegradation of DMP and DEP.
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http://dx.doi.org/10.1016/j.biortech.2021.126172DOI Listing
January 2022

Bioelectricity production and shortcut nitrogen removal by microalgal-bacterial consortia using membrane photosynthetic microbial fuel cell.

J Environ Manage 2022 Jan 4;301:113871. Epub 2021 Oct 4.

Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India.

Membrane photosynthetic microbial fuel cell (MPMFC) utilizes O, NO and NO as cathodic electron acceptors, enabling simultaneous treatment of nitrogen, CO and organic carbon in the cathode compartment. In this work, development of a novel cathodic process with in situ nitritation via microalgal photosynthesis during the light period is reported for achieving shortcut nitrogen removal (SNR) from ammonium-rich wastewater. Moreover, a tubular low-cost ceramic membrane was used to separate and recycle the microalgal-bacterial biomass to the cathode compartment during the continuous operation. The influence of NH concentration and ratio of chemical oxygen demand to total nitrogen on the MPMFC performance was examined. Denitritation under dark and anoxic conditions occurred due to denitrifying bacteria (DNB) subsequent to nitritation under light and aerobic conditions by ammonia-oxidizing bacteria (AOB) in the consortia. Final concentrations of NH and NO in the effluent of 0.10 mg NH-L and 0.02 mg NO-L, respectively, were obtained using MPMFC which resulted in a nitrogen removal efficiency of 99 ± 0.5%. The maximum electricity production achieved using the MPMFC was 56 ± 0.1 mA. This study demonstrated that combining microalgal photosynthesis, nitritation and denitritation in the cathode compartment of MPMFC is advantageous for avoiding the cost due to external aeration and organic carbon source necessary for ammonium removal as well as utilization of NO or NO as an electron acceptor.
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http://dx.doi.org/10.1016/j.jenvman.2021.113871DOI Listing
January 2022

A novel rotating wide gap annular bioreactor (Taylor-Couette type flow) for polyhydroxybutyrate production by Ralstonia eutropha using carob pod extract.

J Environ Manage 2021 Dec 26;299:113591. Epub 2021 Aug 26.

Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India. Electronic address:

An annular bioreactor (ABR) with wide gap was used for PHB production from Ralstonia eutropha. Hydrodynamic studies demonstrated the uniform distribution of fluid in the ABR due to the Taylor-Couette flow. Thereafter, the ABR was operated at different agitation and sparging rates to study its effect on R. eutropha growth and PHB production. The ABR operated at 500 rpm with air sparge rate of 0.8 vvm yielded a maximum PHB concentration of 14.89 g/L, which was nearly 1.4 times that obtained using a conventional stirred-tank bioreactor (STBR). Furthermore, performances of the bioreactors were compared by operating the reactors under fed-batch mode. At the end of 90 h of operation, the ABR resulted in a very high PHB production of 70.8 g/L. But STBR resulted in a low PHB concentration of 44.2 g/L. The superior performance was due to enhanced oxygen and nutrient mass transfer in the ABR.
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http://dx.doi.org/10.1016/j.jenvman.2021.113591DOI Listing
December 2021

Selenite bioreduction and biosynthesis of selenium nanoparticles by Bacillus paramycoides SP3 isolated from coal mine overburden leachate.

Environ Pollut 2021 Sep 4;285:117519. Epub 2021 Jun 4.

Department of Chemistry and Biochemistry, University of Texas at El Paso, 500 W. University Ave., El Paso, TX, 79968, USA.

A native strain of Bacillus paramycoides isolated from the leachate of coal mine overburden rocks was investigated for its potential to produce selenium nanoparticles (SeNPs) by biogenic reduction of selenite, one of the most toxic forms of selenium. 16S rDNA sequencing was used to identify the bacterial strain (SP3). The SeNPs were characterized using spectroscopic (UV-Vis absorbance, dynamic light scattering, X-ray diffraction, and Raman), surface charge measurement (zeta potential), and ultramicroscopic (FESEM, EDX, FETEM) analyses. SP3 exhibited extremely high selenite tolerance (1000 mM) and reduced 10 mM selenite under 72 h to produce spherical monodisperse SeNPs with an average size of 149.1 ± 29 nm. FTIR analyses indicated exopolysaccharides coating the surface of SeNPs, which imparted a charge of -29.9 mV (zeta potential). The XRD and Raman spectra revealed the SeNPs to be amorphous. Furthermore, biochemical assays and microscopic studies suggest that selenite was reduced by membrane reductases. This study reports, for the first time, the reduction of selenite and biosynthesis of SeNPs by B. paramycoides, a recently discovered bacterium. The results suggest that B. paramycoides SP3 could be exploited for eco-friendly removal of selenite from contaminated sites with the concomitant biosynthesis of SeNPs.
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http://dx.doi.org/10.1016/j.envpol.2021.117519DOI Listing
September 2021

Techno-economic assessment of a sustainable and cost-effective bioprocess for large scale production of polyhydroxybutyrate.

Chemosphere 2021 Dec 30;284:131371. Epub 2021 Jun 30.

Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India. Electronic address:

The rapid depletion of crude-oil resource which sustains a conventional petroleum refinery together with its environmental impact has led to the search for more sustainable alternatives. In this context, biorefinery serves to fulfil the aim by utilizing waste resources. Hence, this study focused on techno-economic assessment of PHB production at large scale from waste carob pods in a closed-loop biorefinery setup. Firstly, the use of pure sugars in SC1 was shifted to use of carob pods as feedstock in SC2, upgradation of stirred tank bioreactor with novel annular gap bioreactor in SC3 and replacing the conventional centrifugation process with the upcoming ceramic membrane separation process in SC4. An Aspen plus™ flowsheet was developed by including the aforementioned novel strategies for PHB production. The effectiveness of PHB production under various scenarios was evaluated based on its pay-out period and turnover accumulated at the end of 7th year of a PHB plant operation. Instead of pure sugars as the feedstock (SC1), carob pod extract (SC2) reduced the pay-out period from 12.6 to 6.8 years. Likewise, switching onto ABR from the conventional STBR further decreased the pay-out period to 4.8 years. Finally, the use of ceramic membranes (SC4) instead of centrifugation resulted in a similar pay-out period of 4.8 years with increased turnover of about 1.4 billion USD. Thus, the use of carob pods along with an improved PHB titre in ABR and incorporation of affordable ceramic membrane technology for PHB rich biomass separation resulted in a highly cost-effective PHB production strategy.
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http://dx.doi.org/10.1016/j.chemosphere.2021.131371DOI Listing
December 2021

Recent advances in heavy metal recovery from wastewater by biogenic sulfide precipitation.

J Environ Manage 2021 Jan 3;278(Pt 2):111555. Epub 2020 Nov 3.

Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India.

Biological sulfide precipitation by sulfate reducing bacteria (SRB) is an emerging technique for the recovery of heavy metals from metal contaminated wastewater. Advantages of this technique include low capital cost, ability to form highly insoluble salts, and capability to remove and recover heavy metals even at very low concentrations. Therefore, sulfate reduction under anaerobic conditions has become a suitable alternative for the treatment of wastewaters that contain metals. However, bioreactor configurations for recovery of metals from sulfate rich metallic wastewater have not been explored widely. Moreover, the recovered metal sulfide nanoparticles could be applied in various fields such as solar cells, dye degradation, electroplating, etc. Hence, metal recovery in the form of nanoparticles from wastewater could serve as an incentive for industries. The simultaneous metal removal and recovery can be achieved in either a single-stage or multistage systems. This paper aims to present an overview of the different bioreactor configurations for the treatment of wastewater containing sulfate and metal along with their advantages and drawbacks for metal recovery. Currently followed biological strategies to mitigate sulfate and metal rich wastewater are evaluated in detail in this review.
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http://dx.doi.org/10.1016/j.jenvman.2020.111555DOI Listing
January 2021

A closed-loop biorefinery approach for polyhydroxybutyrate (PHB) production using sugars from carob pods as the sole raw material and downstream processing using the co-product lignin.

Bioresour Technol 2020 Jul 24;307:123247. Epub 2020 Mar 24.

Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India. Electronic address:

A novel closed-loop biorefinery model using carob pods as the feed material was developed for PHB production. The carob pods were delignified, and as the second step, sugars present in the delignified carob pods were extracted using water. Ralstonia eutropha and Bacillus megaterium were cultivated on the carob pod extract and its performance was evaluated using Taguchi experimental design. R. eutropha outperformed the B. megaterium in terms of its capability to grow at a maximum initial sugar concentration of 40 g L with a maximum PHB production of 12.2 g L. Finally, the concentrated lignin from the first step was diluted with different proportion of chloroform to extract PHB from the bacterial biomass. The PHB yield and purity obtained were more than 90% respectively using either R. eutropha or B. megaterium. Properties of the PHB produced in this study were examined to establish its application potential.
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http://dx.doi.org/10.1016/j.biortech.2020.123247DOI Listing
July 2020

Preparation and characterization of environmentally safe and highly biodegradable microbial polyhydroxybutyrate (PHB) based graphene nanocomposites for potential food packaging applications.

Int J Biol Macromol 2020 Jul 19;154:866-877. Epub 2020 Mar 19.

Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India. Electronic address:

Polyhydroxybutyrate (PHB) is a natural polyester of microbial origin and is an excellent substitute for petroleum-based food packaging materials. However, moderate mechanical, thermal and barrier properties limit utilization of PHB for commercial food packaging applications. In order to overcome these drawbacks, the present study evaluated the solution casting method for the preparation of PHB nanocomposite by incorporating various concentration (0-1.3 wt%) of graphene nanoplatelets (Gr-NPs). The prepared nanocomposites were tested for their morphology, mechanical, thermal, barrier, cytotoxicity and biodegradable properties. A Gr-NPs concentration of 0.7 wt% was found to be optimum without any agglomeration. In comparison with pristine PHB, the PHB/Gr-NPs nanocomposite showed a higher melting point (by 10 °C), thermal stability (by 10 °C), tensile strength (by 2 times) along with 3 and 2 times reduction in oxygen and water vapour permeability, respectively. The penetration of UV and visible light was greatly reduced with the addition of Gr-NPs. Furthermore, cytotoxic effect of the prepared nanocomposite was found to be statistically insignificant in comparison with the pristine PHB. A four-fold increase in the shelf life was demonstrated by a simulation study conducted using moisture and oxygen-sensitive food items (potato chips and milk product).
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http://dx.doi.org/10.1016/j.ijbiomac.2020.03.084DOI Listing
July 2020

Acute toxicity of cyanide in aerobic respiration: Theoretical and experimental support for murburn explanation.

Biomol Concepts 2020 Mar 17;11(1):32-56. Epub 2020 Mar 17.

Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, Assam, India-781039.

The inefficiency of cyanide/HCN (CN) binding with heme proteins (under physiological regimes) is demonstrated with an assessment of thermodynamics, kinetics, and inhibition constants. The acute onset of toxicity and CN's mg/Kg LD50 (μM lethal concentration) suggests that the classical hemeFe binding-based inhibition rationale is untenable to account for the toxicity of CN. In vitro mechanistic probing of CN-mediated inhibition of hemeFe reductionist systems was explored as a murburn model for mitochondrial oxidative phosphorylation (mOxPhos). The effect of CN in haloperoxidase catalyzed chlorine moiety transfer to small organics was considered as an analogous probe for phosphate group transfer in mOxPhos. Similarly, inclusion of CN in peroxidase-catalase mediated one-electron oxidation of small organics was used to explore electron transfer outcomes in mOxPhos, leading to water formation. The free energy correlations from a Hammett study and IC50/Hill slopes analyses and comparison with ligands ( CO/ H 2 S/ N 3 - ) $\left( {\text{CO}}/{{{{\text{H}}_{2}}\text{S}}/{\text{N}_{3}^{\text{-}}}\;}\; \right)$ provide insights into the involvement of diffusible radicals and proton-equilibriums, explaining analogous outcomes in mOxPhos chemistry. Further, we demonstrate that superoxide (diffusible reactive oxygen species, DROS) enables in vitro ATP synthesis from ADP+phosphate, and show that this reaction is inhibited by CN. Therefore, practically instantaneous CN ion-radical interactions with DROS in matrix catalytically disrupt mOxPhos, explaining the acute lethal effect of CN.
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http://dx.doi.org/10.1515/bmc-2020-0004DOI Listing
March 2020

Acute toxicity of cyanide in aerobic respiration: Theoretical and experimental support for murburn explanation.

Biomol Concepts 2020 03 17;11(1):32-56. Epub 2020 Mar 17.

Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, Assam, India-781039.

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http://dx.doi.org/10.1515/bmc-2020-0004DOI Listing
March 2020

Gas-phase trichloroethylene removal by Rhodococcus opacus using an airlift bioreactor and its modeling by artificial neural network.

Chemosphere 2020 May 6;247:125806. Epub 2020 Jan 6.

Biochemical Engineering Laboratory, Department of Chemical Engineering, Annamalai University, Cuddalore, 608001, India. Electronic address:

This study evaluated the biological removal of trichloroethylene (TCE) by Rhodococcus opacus using airlift bioreactor under continuous operation mode. The effect of inlet TCE concentration in the range 0.12-2.34 g m on TCE removal has studied for 55 days. During the continuous bioreactor operation, a maximum of 96% TCE removal was obtained for low inlet TCE concentration, whereas the highest elimination capacity was 151.2 g m h for the TCE loading rate of 175.0 g m h. The carbon dioxide (CO) concentration profile from the airlift bioreactor revealed that the degraded TCE has primarily converted to CO with a fraction of organic carbon utilized for bacterial growth. The artificial neural network (ANN) based model was able to successfully predict the performance of the bioreactor system using the Levenberg-Marquardt (LM) back propagation algorithm, and optimized biological topology is 3:12:1. The prediction accuracy of the model was high as the experimental data were in good agreement (R = 0.9923) with the ANN predicted data. Overall, from the bioreactor experiments and its ANN modeling, the potential strength of R. opacus in TCE biodegradation is proved.
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http://dx.doi.org/10.1016/j.chemosphere.2019.125806DOI Listing
May 2020

Selenite removal from wastewater using fungal pelleted airlift bioreactor.

Environ Sci Pollut Res Int 2020 Jan 9;27(1):992-1003. Epub 2019 Dec 9.

Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, Assam, 781039, India.

This study investigated the removal of selenite from wastewater using the fungus Asergillus niger KP isolated from a laboratory scale inverse fluidized bed bioreactor. The effect of different carbon sources and initial selenite concentration on fungal growth, pellet formation and selenite removal was first examined in a batch system. The fungal strain showed a maximum selenite removal efficiency of 86% in the batch system. Analysis of the fungal pellets by field-emission scanning electron microscopy, field-emission transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed the formation of spherical-shaped elemental selenium nanoparticles of size 65-100 nm. An increase in the initial selenite concentration in the media resulted in compact pellets with smooth hyphae structure, whereas the fungal pellets contained hair like hyphae structure when grown in the absence of selenite. Besides, a high initial selenite concentration reduced biomass growth and selenite removal from solution. Using an airlift reactor with fungal pellets, operated under continuous mode, a maximum selenite removal of 94.3% was achieved at 10 mg L of influent selenite concentration and 72 h HRT (hydraulic retention time). Overall, this study demonstrated very good potential of the fungal-pelleted airlift bioreactor system for removal of selenite from wastewater. Graphical abstract.
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http://dx.doi.org/10.1007/s11356-019-06946-6DOI Listing
January 2020

Chemiosmotic and murburn explanations for aerobic respiration: Predictive capabilities, structure-function correlations and chemico-physical logic.

Arch Biochem Biophys 2019 11 14;676:108128. Epub 2019 Oct 14.

Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, St. Institutskaya 3, 630090, Novosibirsk, Russia. Electronic address:

Since mid-1970s, the proton-centric proposal of 'chemiosmosis' became the acclaimed explanation for aerobic respiration. Recently, significant theoretical and experimental evidence were presented for an oxygen-centric 'murburn' mechanism of mitochondrial ATP-synthesis. Herein, we compare the predictive capabilities of the two models with respect to the available information on mitochondrial reaction chemistry and the membrane proteins' structure-function correlations. Next, fundamental queries are addressed on thermodynamics of mitochondrial oxidative phosphorylation (mOxPhos): (1) Can the energy of oxygen reduction be utilized for proton transport? (2) Is the trans-membrane proton differential harness-able as a potential energy capable of doing useful work? and (3) Whether the movement of miniscule amounts of mitochondrial protons could give rise to a potential of ~200 mV and if such an electrical energy could sponsor ATP-synthesis. Further, we explore critically if rotary ATPsynthase activity of Complex V can account for physiological ATP-turnovers. We also answer the question- "What is the role of protons in the oxygen-centric murburn scheme of aerobic respiration?" Finally, it is demonstrated that the murburn reaction model explains the fast kinetics, non-integral stoichiometry and high yield of mOxPhos. Strategies are charted to further demarcate the two explanations' relevance in the cellular physiology of aerobic respiration.
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http://dx.doi.org/10.1016/j.abb.2019.108128DOI Listing
November 2019

Experimental studies and neural network modeling of the removal of trichloroethylene vapor in a biofilter.

J Environ Manage 2019 Nov 12;250:109385. Epub 2019 Sep 12.

Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India.

In this study, bamboo carrier based lab scale compost biofilter was evaluated to treat synthetic waste air containing trichloroethylene (TCE) under continuous operation mode. The effect of inlet TCE concentration and gas flow rate and its removal was investigated. Maximum TCE removal efficiency was found to be 89% under optimum conditions of inlet 0.986 g/m TCE concentration corresponding to a loading rate of 43 g/m h and 0.042 m/h gas flow rate at empty bed residence time (EBRT) of 2 min. For the first time, Artificial Neural Network (ANN) was applied to predict the performance of the compost biofilter in terms of TCE removal. The ANN model used a three layer feed forward based Levenberg-Marquardt algorithm, and its topology consisted of 3-25-1 as the optimum number for the three layers (input, hidden and output). An excellent match between the experimental and ANN predicted the value of TCE removal was obtained with a coefficient of determination (R) value greater than 0.99 during the model training, validation, testing and overall. Furthermore, statistical analysis of the ANN model performance mediated its prediction accuracy of the bioreactor to treat TCE contaminated systems.
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http://dx.doi.org/10.1016/j.jenvman.2019.109385DOI Listing
November 2019

Novel shortcut biological nitrogen removal method using an algae-bacterial consortium in a photo-sequencing batch reactor: Process optimization and kinetic modelling.

J Environ Manage 2019 Nov 28;250:109401. Epub 2019 Aug 28.

Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India.

This study evaluated a novel shortcut nitrogen removal method using a mixed consortium of microalgae, enriched ammonia oxidizing bacteria (AOB) and methanol utilizing denitrifier (MUD) in a photo-sequencing batch reactor (PSBR) for treating ammonium rich wastewater (ARWW). Alternating light and dark periods were followed to obtain complete biological nitrogen removal (BNR) without any external aeration and with the addition of methanol as the sole carbon source, respectively. The results showed that influent NH was oxidized to NO by AOB during the light periods at a rate of 8.09 mg NH-N Lh. Subsequently, NO was completely reduced during the dark period due to the action of MUD in presence of methanol. The high activities of ammonia monooxygenase (AMO) and nitrite reductase (NIR) enzymes revealed the strong role of AOB and MUD for achieving shortcut nitrogen removal from the wastewater. The reduced activities of nitrate reductase (NR) and nitrite oxidoreductase (NOR) at a high concentration of DO, NH and NOin the system further confirmed the nitrogen removal pathway involved in the process. The biomass produced from these experiments showed good settling properties with a maximum sedimentation rate of 0.7-1.8 m h, a maximum sludge volume index (SVI) of 193 ml g- 256 ml gand floc size of 0.2-1.2 mm. In order to describe the growth and interaction among the algae, AOB and MUD for nitrogen removal in the system, the experimental results were fitted to four metabolic models, which revealed best fit of the experimental data due to the models based on algae-AOB and algae-AOB-MUD activities than with the other two models.
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http://dx.doi.org/10.1016/j.jenvman.2019.109401DOI Listing
November 2019

A novel carbon monoxide fed moving bed biofilm reactor for sulfate rich wastewater treatment.

J Environ Manage 2019 Nov 23;249:109402. Epub 2019 Aug 23.

Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India. Electronic address:

In this study, a moving bed biofilm reactor was used for biodesulfuruization using CO as the sole carbon substrate. The effect of hydraulic retention time (HRT), sulfate loading rate and CO loading rate on sulfate and CO removal was examined. At 72, 48 and 24 h HRT, the sulfate removal was 93.5%, 91.9% and 80.1%, respectively. An increase in the sulfate loading reduced the sulfate reduction efficiency, which, however, was improved by increasing the CO flow rate into the MBBR. Best results in terms of sulfate reduction (>80%) were obtained for low inlet sulfate and high CO loading conditions. The CO utilization was very high at 85% throughout the study, except during the last phase of the continuous bioreactor operation it was around 70%. An artificial neural network based model was successfully developed and optimized to accurately predict the bioreactor performance in terms of both sulfate reduction and CO utilization. Overall, this study showed an excellent potential of the moving bed biofilm bioreactor for efficient sulfate reduction even under high loading conditions.
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http://dx.doi.org/10.1016/j.jenvman.2019.109402DOI Listing
November 2019

Rice based distillers dried grains with solubles as a low cost substrate for the production of a novel rhamnolipid biosurfactant having anti-biofilm activity against Candida tropicalis.

Colloids Surf B Biointerfaces 2019 Oct 10;182:110358. Epub 2019 Jul 10.

Environmental Biotechnology Laboratory, Life Sciences Division, Institute of Advanced Study in Science and Technology, Guwahati, 781035, Assam, India.

In this study, rhamnolipid (RL) production by Pseudomonas aeruginosa SS14 utilizing rice based Distillers Dried Grains with Solubles (rDDGS) as the sole carbon source was evaluated and the production parameters were optimized using response surface methodology. Highest RL (RL-rDDGS) yield was 14.87 g/L in a culture medium containing 12% (w/v) rDDGS and 11% (v/v) inoculum concentration after 48 h of fermentation at 35 °C. RL-rDDGS was produced as a mixture of mono and di-RL congeners with four novel homologues Rha-C, Rha-C, Rha-C, and Rha-Rha-C. The RL reduced the surface tension of water to 34.8 mN/m at a critical micelle concentration (CMC) value of 100 mg/L, exhibited high stability at a wide range of pH (6-12), heating time (0-120 min), and salinity (2-12% NaCl). Furthermore, RL-rDDGS demonstrated appreciable biofilm disruptive property against Candida tropicalis. This is the first report on the usage of rDDGS for sustainable and low cost production of RL.
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http://dx.doi.org/10.1016/j.colsurfb.2019.110358DOI Listing
October 2019

Novel waste-derived biochar from biomass gasification effluent: preparation, characterization, cost estimation, and application in polycyclic aromatic hydrocarbon biodegradation and lipid accumulation by Rhodococcus opacus.

Environ Sci Pollut Res Int 2019 Aug 29;26(24):25154-25166. Epub 2019 Jun 29.

Center for the Environment, Indian Institute of Technology Guwahati, Guwahati, Assam, 781039, India.

This study evaluated an enhancement of simultaneous polycyclic aromatic hydrocarbon (PAH) biodegradation and lipid accumulation by Rhodococcus opacus using biochar derived cheaply from biomass gasification effluent. The chemical, physical, morphological, thermal, and magnetic properties of the cheaply derived biochar were initially characterized employing different techniques, which indicated that the material is easy to separate, recover, and reuse for further application. Batch experiments were carried out to study biochar-aided PAH biodegradation by R. opacus clearly demonstrating its positive effect on PAH biodegradation and lipid accumulation by the bacterium utilizing the synthetic media containing 2-, 3- or 4-ring PAH compounds, at an initial concentration in the range 50-200 mg L, along with 10% (w/v) inoculum. An enhancement in PAH biodegradation from 79.6 to 92.3%, 76.1 to 90.5%, 74.1 to 88.2%, and 71.6 to 82.3% for naphthalene, anthracene, phenanthrene, and fluoranthene, respectively, were attained with a corresponding lipid accumulation of 68.1%, 74.2%, 72.4%, and 63% (w/w) of cell dry weight (CDW). From contact angle measurements carried out in the study, enhancement in PAH biodegradation and lipid accumulation due to the biochar was attributed to an improved bioavailability of PAH to the degrading bacterium.
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http://dx.doi.org/10.1007/s11356-019-05677-yDOI Listing
August 2019

Assessment of raw, acid-modified and chelated biomass for sequestration of hexavalent chromium from aqueous solution using Sterculia villosa Roxb. shells.

Environ Sci Pollut Res Int 2019 Aug 15;26(23):23625-23637. Epub 2019 Jun 15.

Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, Assam, 781039, India.

This study reveals the efficient bio-sorption of Cr(VI) species from simulated wastewater using raw (RSV), acid-activated (PSV) and chelated-activated (PSV-C) Sterculia villosa Roxb. shells. Batch optimization experiments were carried out for determining the optimal pH, dosage of bio-sorbent, initial Cr(VI) concentration and incubation temperature. Physico-chemical alterations in the bio-sorbents prior and following bio-sorption of Cr(VI) species were characterized. Equilibrated experimental data at different temperatures was evaluated as a function of time for understanding the isotherm, kinetics and thermodynamics of the bio-sorption process. Sorption rates for all the bio-sorbents (RSV, PSV and PSV-C) alternately fitted to the Langmuir isotherm model and Langmuir maximum adsorption capacity for RSV, PSV and PSV-C were found to be 57.78, 163.51 and 188.68 mg/g, respectively. Cr(VI) sorption by these bio-sorbents followed pseudo-second-order kinetics. Thermodynamic studies suggest endothermic interaction and increased degree of randomness between the bio-sorbents and Cr(VI) species. Regeneration of the bio-sorbents following sorption-desorption revealed that it can be reused and recycled for several times for Cr(VI) removal from wastewater. Graphical abstract.
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http://dx.doi.org/10.1007/s11356-019-05582-4DOI Listing
August 2019

Activated red mud as a permeable reactive barrier material for fluoride removal from groundwater: parameter optimisation and physico-chemical characterisation.

Environ Technol 2020 Nov 5;41(25):3375-3386. Epub 2019 May 5.

Department of Chemical Engineering, GMR Institute of Technology, Rajam, India.

The main aim of this work is to test the performance of red mud as a permeable reactive barrier (PRB) material for fluoride removal from water. Batch experiments were carried out to optimise the fluoride removal efficiency (RE) of activated red mud (ARM) based on four selected parameters, namely, the initial fluoride concentration (3-40 mg/L), adsorbent dose (0.5-5 g/L), pH (3.0-11.0) and ionic strength (0.001-0.5 M). Statistical analysis of the results revealed the optimum conditions as initial fluoride concentration -21.46 mg/L, adsorbent dose -2.77 g/L, pH 7.01 and ionic strength -0.24 M, respectively. Under the optimum conditions, fluoride RE of 87.3% was achieved. The individual effects due to initial fluoride concentration, adsorbent dose and ionic strength on fluoride removal were highly significant (= 59.69; < 0.005); whereas adsorbent dose, pH and ionic strength showed the greatest squared effects ( = 26.05; < 0.001). The interaction effect due to initial fluoride concentration and adsorbent dose was also found to be significant ( = 12.52;  = 0.002) for fluoride removal. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) analyses were performed to identify the change in functional group and surface topography following red mud activation.
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http://dx.doi.org/10.1080/09593330.2019.1609591DOI Listing
November 2020

Sustainable and green approach of chitosan production from Penicillium citrinum biomass using industrial wastewater as a cheap substrate.

J Environ Manage 2019 Jun 5;240:431-440. Epub 2019 Apr 5.

Department of Biosciences and Bioengineering, Indian Institute Technology Guwahati, Guwahati, 781039, Assam, India. Electronic address:

Marine sources especially crustaceans have been extensively used worldwide for the production of chitosan. However, limited availability as well as variations in the properties of the derived chitosan is a serious drawback of utilizing marine sources for chitosan production. This study investigated sustainable and green approach of fungal chitosan production using paper mill wastewater as a cheap and easily available substrate. The fungus Penicillium citrinum IITG_KP1 used in this study was initially isolated from an infected bamboo shoot. Addition of acetic acid at low levels led to a 150% increase in the yield of chitosan from 95 g/kg to 138 g/kg of dry fungal biomass. This result correlated well with an increase in xylose uptake rate due to acetic acid addition that was confirmed by enhanced activity of xylose reductase (XR) and xylitol dehydrogenase (XDH) enzymes in the presence of acetic acid. Very high COD removal efficiency (75%) along with 70% phenolic reduction and 84% decolourization efficiency of the raw paper mill wastewater without any prior pre-treatment was further achieved by carrying out the fungal fermentation using a bioreactor under batch mode of operation. The fungal chitosan showed properties comparable with those of a commercially available standard.
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http://dx.doi.org/10.1016/j.jenvman.2019.03.085DOI Listing
June 2019

Novel advanced porous concrete in constructed wetlands: preparation, characterization and application in urban storm runoff treatment.

Water Sci Technol 2018 Dec;78(11):2374-2382

Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India.

Common porous concrete templates (CPCT) and advanced porous concrete templates (APCT) were employed in this study to construct wetlands for their applications in pollutant removal from storm runoff. The planting ability of the concrete was investigated by growing Festuca elata plants in them. Strength of the porous concrete (7.21 ± 0.19 Mpa) decreased by 1.8 and 4.9% over a period of six and 12 months, respectively, due to its immersion in lake water. The height and weight of Festuca elata grass growth on the porous concrete were observed to be 12.6-16.9 mm and 63.4-95.4 mg, respectively, after a duration of one month. Advanced porous concrete template based constructed wetland (APCT-CW) showed better removal of chemical oxygen demand (COD) (49.6%), total suspended solids (TSS) (58.9), NH-N (52.4%), total nitrogen (TN) (47.7%) and total phosphorus (TP) (45.5%) in storm water, when compared with the common porous concrete template based constructed wetland (CPCT-CW) with 20.6, 29.8, 30.1, 35.4 and 26.9%, respectively. The removal of Pb, Ni, Zn by the CPCT-CW unit were 28.9, 33.3 and 42.3%, respectively, whereas these were 51.1, 62.5 and 53.8%, respectively, with the APCT-CW unit. These results demonstrate that the advanced porous concrete template in constructed wetland could be employed successfully for the removal of pollutants from urban storm water runoff.
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http://dx.doi.org/10.2166/wst.2018.528DOI Listing
December 2018

A novel integrated biodegradation-microfiltration system for sustainable wastewater treatment and energy recovery.

J Hazard Mater 2019 03 11;365:707-715. Epub 2018 Nov 11.

Center for the Environment, Indian Institute Technology Guwahati, Guwahati, Assam 781039, India; Department of Chemical Engineering, Indian Institute Technology Guwahati, Guwahati, Assam 781039, India.

This work assessed the treatment of wastewater generated from three different industries viz., paper and pulp, biomass gasification and dairy by biodegradation followed by membrane filtration. Batch biodegradation was first carried out using wastewater as the potential substrate for oleaginous Rhodococcus opacus with lipid accumulation intracellular; subsequently, a microfiltration system was applied to recover the bacterial biomass grown as well as for residual chemical oxygen demand (COD) removal from the effluent. The combined process showed excellent results in terms of COD removal from the industrial wastewaters, with the values 56.8%, 46.1% and 68.9% for dairy, paper and pulp and biomass gasification wastewaters, respectively, by biodegradation. These values were further improved to 92.7%, 87.6% and 88.2%, respectively, following the microfiltration step performed by employing a low-cost ceramic membrane. In addition, lipids accumulated by the bacterium were extracted and characterized for biodiesel production potential. Lipid characterization using H NMR confirmed the presence of saturated fatty acids. Gas chromatography analysis of the transesterified lipids revealed the presence of methyl palmitate and methyl stearate. In addition, the estimated properties of the transesterified product affirmed its potential for biofuel application.
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http://dx.doi.org/10.1016/j.jhazmat.2018.11.029DOI Listing
March 2019

Process integration for biological sulfate reduction in a carbon monoxide fed packed bed reactor.

J Environ Manage 2018 Aug 9;219:294-303. Epub 2018 May 9.

Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India. Electronic address:

This study examined immobilized anaerobic biomass for sulfate reduction using carbon monoxide (CO) as the sole carbon source under batch and continuous fed conditions. The immobilized bacteria with beads made of 10% polyvinyl alcohol (PVA) showed best results in terms of sulfate reduction (84 ± 3.52%) and CO utilization (98 ± 1.67%). The effect of hydraulic retention time (HRT), sulfate loading rate and CO loading rate on sulfate and CO removal was investigated employing a 1L packed bed bioreactor containing the immobilized biomass. At 48, 24 and 12 h HRT, the sulfate removal was 94.42 ± 0.15%, 89.75 ± 0.47% and 61.08 ± 0.34%, respectively, along with a CO utilization of more than 90%. The analysis of variance (ANOVA) of the results obtained showed that only the initial CO concentration significantly affected the sulfate reduction process. The reactor effluent sulfate concentrations were 27.41 ± 0.44, 59.16 ± 1.08, 315.83 ± 7.33 mg/L for 250, 500 and 1000 mg/L of influent sulfate concentrations respectively, under the optimum operating conditions. The sulfate reduction rates matched well with low inlet sulfate loading rates, indicating stable performance of the bioreactor system. Overall, this study yielded very high sulfate reduction efficiency by the immobilized anaerobic biomass under high CO loading condition using the packed bed reactor system.
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http://dx.doi.org/10.1016/j.jenvman.2018.04.033DOI Listing
August 2018

Heavy metal removal from aqueous solution using sodium alginate immobilized sulfate reducing bacteria: Mechanism and process optimization.

J Environ Manage 2018 Jul 27;218:486-496. Epub 2018 Apr 27.

Centre for the Environment, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India; Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India.

Heavy metal removal was evaluated using sodium alginate immobilized sulfate reducing bacteria (SRB) under batch and continuous mode. Under batch conditions, more than 95% metal removal was achieved due to formation of insoluble metal sulfides exterior to the bead surface. Best heavy metal removal results were obtained at 48 h hydraulic retention time (HRT). Metal loading rate values upto 2.20 mg/L∙h for Fe(III), Zn(II), Cd(II), Pb(II) and Ni(II) and upto 4.29 mg/L∙h for Cu(II) were proved to be favorable for their removal using the continuous downflow column reactor packed with the immobilized SRB beads. Continuous metal removal from a mixture of the heavy metals showed that Cu(II) removal was maximum (99%), followed by Zn(II) (95.8%) and other metals at their respective low inlet concentrations. However, the removal values were reduced at a high inlet concentration of these metals, which matched well with low COD and sulfate reduction values.
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http://dx.doi.org/10.1016/j.jenvman.2018.03.020DOI Listing
July 2018

Chromium tolerance, bioaccumulation and localization in plants: An overview.

J Environ Manage 2018 Jan 7;206:715-730. Epub 2017 Dec 7.

Department of Biosciences and Bioengineering, Indian Institute of Technology, Guwahati, Assam 781039, India.

In the current industrial scenario, chromium (Cr) as a metal is of great importance, but poses a major threat to the environment. Phytoremediation provides an environmentally sustainable, ecofriendly, cost effective approach for environmental cleanup of Cr. This review presents the current status of phytoremediation research with particular emphasis on cleanup of Cr contaminated soil and water systems. It gives a detailed account of the work done by different authors on the Cr bioavailability, uptake pathway, toxicity and storage in plants following the phytoextraction mechanism. This paper also describes recent findings related to Cr localization in hyperaccumulator plants. It gives an insight into the processes and mechanisms that allow plants to remove Cr from contaminated sites under varying conditions. These detailed knowledge of changes in plant metabolic pool in response to Cr stress would immensely help understand and improve the phytoextraction process. Further, this review provides a detailed understanding of Cr uptake and detoxification mechanism by plants that can be applied in developing a suitable approach for a better applicability of the process.
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http://dx.doi.org/10.1016/j.jenvman.2017.10.033DOI Listing
January 2018
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