Govindarajan Suresh Kumar

Bio: Govindarajan Suresh Kumar is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Fracture (geology) & Mass transfer. The author has an hindex of 4, co-authored 10 publications receiving 34 citations.

Sequential synergetic sorption analysis of Gracilaria Rhodophyta biochar toward aluminum and fluoride: A statistical optimization approach.

Abstract: The present work proposes the synthesis of robust biochar from Gracilaria Rhodophyta red weeds for sequential removal of Al(III) and fluoride from wastewater. The sorption experiments have been modeled by preliminary optimization of operational parameters using 24 factorial statistical modeling. The model has estimated an optimum sequential synergetic removal of 44.5 mg/g of Al(III) and 2.1 mg/g of fluoride onto the biochar. FESEM, BET, XRD, EDX, and FTIR established the potentiality of biochar toward synergetic sorption of Al(III) and fluoride. The thermodynamic analysis projected that the adsorption is physisorption in nature. The adsorption of Al(III) and fluoride follows the Langmuir and Freundlich isotherm models, respectively, and the kinetic analysis established the pseudo-second-order deposition of Al(III) and fluoride ions. The synthesized adsorbent is regenerative enough and could achieve synergetic removal of Al(III) and fluoride ions from industrial- and groundwater-contaminated water bodies. PRACTITIONER POINTS: Biochar from seaweeds is explored in the sequential removal of Al(III) and F- ions. Statistical model is developed for % adsorption and tested for reliability by ANOVA. GRBC sorbed 44.5 and 2.1 mg/g of Al(III) and F- ions, respectively, at optimum levels. FESEM, EDX, XRD, and FTIR characterization confirm the potentiality of the GRBC. GRBC sorbed ⁓90% of Al(III) and F- ions from wastewater and is regenerative.

Biodegradation kinetics of dichlorvos and chlorpyrifos by enriched bacterial cultures from an agricultural soil

Abstract: The study focuses on the biodegradation kinetics of organophosphate pesticides (OPs), chlorpyrifos and dichlorvos by enriched cultures and its application in pesticide transport models. Pseudomonas...

Numerical modeling of two species radionuclide transport in a single fracturematrix system with variable fracture aperture

Abstract: A variable aperture model, instead of a conventional parallel plate model, is utilized to study the transport of radionuclides in a single coupled fracture-matrix system. A fully implicit finite difference model has been developed, which incorporates fracture aperture width variation in the numerical study of two species radionuclide transport. Two distinct geometric profiles namely, sinusoidal and logarithmic have been used to capture the variation of aperture width. The dependence of advection, hydrodynamic dispersion, linear sorption, and matrix diffusion on aperture width is considered in the analysis of radionuclides transport. Two species (parent and daughter) radioactive decay chain is also incorporated. There is a greater retardation of radionuclides in fracture for the variable aperture model than the parallel plate model. Sensitivity analysis on fracture surface sorption coefficient, longitudinal dispersivity, matrix porosity, and matrix diffusion coefficient shows that the conventional parallel plate model overestimate the radionuclide concentration in the fracture when compared to the variable aperture model.

A Comprehensive Analysis on Thermal and Kinetic Aspects of In Situ Combustion: Numerical Approach

Abstract: In-Situ Combustion (ISC) thermal Enhanced Oil Recovery (EOR) methods are aimed at increasing the oil recoveries of heavy oil reserves that are expected to play an instrumental role in near future in meeting the world’s energy demand. The complex multiphase heat and reactive mass transport necessitate a clear understanding of thermal and kinetic models used in modeling of ISC process. A finite difference based numerical analysis is carried out on heat loss and selective productions of light oil components during ISC, which showed a significant effect on peak temperature, thermal front propagation and the corresponding production rates dictating the performance of ISC process.

Effect of random fracture aperture on the transport of colloids in a coupled fracture-matrix system

Abstract: A variable aperture model, including the random variation of fracture aperture as against the conventional parallel plate model, has been developed to adequately examine the transport of colloids/suspended particles in a single coupled fracturematrix system. Rather than relying on a complex geostatistical method for an accurate representation of fracture aperture, which requires an enormous field data and resource for its validation, a simple statistical method (linear congruential generator) is implemented in the present article. The random variation of fracture aperture is an honest representation of the unpredictable geometry/ morphology of fracture aperture in comparison with widely applied the conventional parallel plate model or the simple mathematical functions based on fractal theory (self-affine structures). A considerable number of parameters are involved in investigating the extent of penetration of colloids into the rock matrix, which creates complexity and ambiguity in the analysis. To overcome this problem, a single parameter “Maximum Penetration Factor” has been introduced for simple and reliable assessment of diffusion of colloids within the rock matrix. Additionally, a non-dimensional parameter ‘Matrix Mitigation Factor’ has been introduced in the present study, which can provide a means of evaluating the diffusion of suspended particles within the rock matrix when it comes to real time applications like microbial enhanced recovery (MEOR) and chemical enhanced recovery (CEOR) in the petroleum industry (nanoparticles and nanofluids). A semi-implicit finite difference model has been adopted for solving the coupled partial differential equations in the present numerical study. Finally, Neumann and Robinson boundary conditions as a function of time have been applied at the fracture inlet to better represent the field scenario as against the conventional constant source condition (Dirichlet). The model results indicate that there is a difference in concentration between the parallel plate model and random fracture model when it comes to colloidal concentration in the fracture and rock matrix. The variance in concentration is due to the inclusion of variation of the aperture in the variable aperture model, which is absent in the parallel plate model. Additionally, the results suggest that the variable source boundary condition has a significant influence on the transport of colloids in fracture-matrix system. Finally, from the evaluation of the extent of diffusion of colloids into rock matrix, it was concluded that that variable aperture model is associated with more mitigation of colloids compared to the parallel plate model, especially in the case of random fracture.

VALIDITY OF CUBIC LAW FOR FLUID FLOW IN A DEFORMABLE ROCK FRACTURE - eScholarship

Abstract: The validity of the cubic law for laminar flow of fluids through open fractures consisting of parallel planar plates has been established by others over a wide range of conditions with apertures ranging down to a minimum of 0.2 µm. The law may be given in simplified form by Q/Δh = C(2b)3, where Q is the flow rate, Δh is the difference in hydraulic head, C is a constant that depends on the flow geometry and fluid properties, and 2b is the fracture aperture. The validity of this law for flow in a closed fracture where the surfaces are in contact and the aperture is being decreased under stress has been investigated at room temperature by using homogeneous samples of granite, basalt, and marble. Tension fractures were artificially induced, and the laboratory setup used radial as well as straight flow geometries. Apertures ranged from 250 down to 4µm, which was the minimum size that could be attained under a normal stress of 20 MPa. The cubic law was found to be valid whether the fracture surfaces were held open or were being closed under stress, and the results are not dependent on rock type. Permeability was uniquely defined by fracture aperture and was independent of the stress history used in these investigations. The effects of deviations from the ideal parallel plate concept only cause an apparent reduction in flow and may be incorporated into the cubic law by replacing C by C/ƒ. The factor ƒ varied from 1.04 to 1.65 in these investigations. The model of a fracture that is being closed under normal stress is visualized as being controlled by the strength of the asperities that are in contact. These contact areas are able to withstand significant stresses while maintaining space for fluids to continue to flow as the fracture aperture decreases. The controlling factor is the magnitude of the aperture, and since flow depends on (2b)3, a slight change in aperture evidently can easily dominate any other change in the geometry of the flow field. Thus one does not see any noticeable shift in the correlations of our experimental results in passing from a condition where the fracture surfaces were held open to one where the surfaces were being closed under stress.

Study on three-dimensional fracture network connectivity path of rock mass and seepage characteristics based on equivalent pipe network

Abstract: Nuclear waste repositories have extremely stringent requirements for geological environment. However, natural fractures in rock mass can be potential channels for nuclide migration, therefore, the influence of fractures on the permeability of rock mass must be assessed. In this paper, a well research was conducted on well-exposed granite outcrops in the Xinchang site (the Chinese high-level radioactive waste repository). The high-precision three-dimensional model of a typical outcrop is built to obtain fracture information combined with field measurement, and then the three-dimensional fracture network model is generated using the relevant parameters by Monte Carlo method. To obtain more comprehensive fracture connectivity while avoiding the traditional method of searching the connectivity path in the complicated 3D fracture model taking up a lot of storage space and costing a lot of time, this paper presents an approach using MATLAB cell array instead of traditional adjacency matrix to search and store fracture network connectivity paths. In DFN model, the fracture disc with certain thickness is equivalent to three-dimensional pipe network model (EPNM) with variable diameter, and the equivalent path permeability coefficient (EPC) is proposed to objectively study the permeability characteristics of the seepage path in fractured rock mass based on that. Especially noteworthy is that some fractures in a certain strike range belong to open type, while those in another range belong to cemented closed fractures, when fresh fractures were exposed by cutting off the surface rock to a certain depth. The calculation of EPC under different conditions shows that the order of magnitude of EPC mean value is 1e−7m/s and 1e−3m/s, respectively, when fractures are cemented and not partly. On this basis, the size of the representative elementary volume (REV) of the fractured rock mass in the study area is determined to be about 25 m. By rotating the matrix in model, the spatial permeability tensor of the region (including permeability principal value and main direction) is obtained, which is within the range of borehole data. The predicted results may provide some reference for the related projects in the future.

Chlorpyrifos in environment and food: a critical review of detection methods and degradation pathways

Abstract: Chlorpyrifos (CP) is a class of organophosphorus (OP) pesticides, which find extensive applications as acaricide, insecticide and termiticide. The use of CP has been indicated in environmental contamination and disturbance in the biogeochemical cycles. CP has been reported to be neurotoxic and has a detrimental effect on immunological and psychological health. Therefore, it is necessary to design and develop effective degradation methods for the removal of CP from the environment. In the past few years, physicochemical (advanced oxidation process) and biological treatment approaches have been widely employed for the pesticide removal. However, the byproducts of this process are more toxic than the parent compound and along with an incomplete degradation of CP. This review focuses on the toxicity of CP, the sources of contamination, degradation pathways, physicochemical, biological, and nano-technology based methods employed for the degradation of CP. In addition, consolidated information on various detection methods and materials used for the detection have been provided in this review.

Effect of Salinity on Silica Nanoparticle Adsorption Kinetics and Mechanisms for Fluid/Rock Interaction with Calcite.

Abstract: This study addresses the kinetics of silica nanoparticle adsorption on calcite from a solution at three salinities: deionized water (DIW), synthetic seawater (SSW), and low salinity water (LSW). The nanoparticle adsorption mechanisms and the effects on calcite dissolution are addressed. It was shown that nanoparticle adsorption was best described with the second-order-kinetic model and that silica nanoparticle adsorption reduced calcite dissolution. This was confirmed by measuring the Ca2+ ion concentration, the pH, and by estimating the amount of calcite dissolved. This is an important conclusion of this work, especially as LSW as an enhanced oil recovery technique is a candidate for use in chalk fields. Less formation damage/dissolution of chalk when silica nanoparticles are combined with LSW can lower the risk of reservoir subsidence. Intraparticle diffusion and the pseudo-second-order models, indicated a reduction in the adsorption rate with increasing nanoparticle concentration in LSW. This is explained by possible repulsive forces among the nanoparticles as they diffuse from the bulk fluid onto the calcite surface. Ion charges reduce the repulsion among the nanoparticles through shielding. However, an increasing nanoparticle concentration reduces the shielding efficiency by the ions. Estimates of the surface forces confirmed that nanoparticle–mineral interaction is less attractive in LSW as compared to SSW and DIW.