Indumathi M. Nambi

Bio: Indumathi M. Nambi is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topic(s): Mass transfer & Dissolution. The author has an hindex of 21, co-authored 80 publication(s) receiving 1777 citation(s). Previous affiliations of Indumathi M. Nambi include University of Illinois at Urbana–Champaign & Indian Institutes of Technology.

Enhanced fluoride removal from drinking water by magnesia-amended activated alumina granules

Abstract: This paper describes the fluoride removal potential of a novel sorbent, magnesia-amended activated alumina (MAAA) from drinking water. MAAA, prepared by calcining magnesium hydroxide impregnated alumina at 450 °C has shown high fluoride sorption potential than activated alumina from drinking water. Batch sorption studies were performed as a function of contact time, pH, initial fluoride concentration, and adsorbent dose. Studies were also performed to understand the effect of various other co-existing ions present in real ground water samples. X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray (EDAX) and a gas adsorption porosimetry analyses were used to characterize the physicochemical properties of MAAA. More than 95% removal of fluoride (10 mg l−1) was achieved within 3 h of contact time at neutral pH. Sorption of fluoride onto MAAA was found to be pH dependant and a decrease in sorption was observed at higher pHs. Among the kinetic models tested, pseudo-second-order model fitted the kinetic data well, suggesting the chemisorption mechanism. Among the various isotherm model tested, Sips model predicted the data well. The maximum sorption capacity of fluoride deduced from Sips equation was 10.12 mg g−1. Most of the co-existing ions studied have negligible effect on fluoride sorption by MAAA. However, higher concentrations of bicarbonate and sulfate have reduced the fluoride sorption capacity.

Toward a Comprehensive Strategy to Mitigate Dissemination of Environmental Sources of Antibiotic Resistance.

Abstract: Antibiotic resistance is a pervasive global health threat. To combat the spread of resistance, it is necessary to consider all possible sources and understand the pathways and mechanisms by which resistance disseminates. Best management practices are urgently needed to provide barriers to the spread of resistance and maximize the lifespan of antibiotics as a precious resource. Herein we advise upon the need for coordinated national and international strategies, highlighting three essential components: (1) Monitoring, (2) Risk Assessment, and (3) Mitigation of antibiotic resistance. Central to all three components is What exactly to monitor, assess, and mitigate? We address this question within an environmental framework, drawing from fundamental microbial ecological processes driving the spread of resistance.

Mass transfer correlations for nonaqueous phase liquid dissolution from regions with high initial saturations

Abstract: [1] The application of existing correlations for nonaqueous phase liquid (NAPL) dissolution, which were developed in small, one-dimensional columns, to larger-scale, heterogeneous or multidimensional systems has shown the predicted dissolution behavior depends greatly on the correlation used. Variation among existing correlations is due to the system scale, NAPL-water interfacial area, and the nature of mass transfer or hydrodynamic mechanisms that are lumped in the correlation. In this paper, new mass transfer correlation is developed using NAPL dissolution data from a small 2-D experimental cell that contained a well-characterized heterogeneous distribution of grain sizes. The new correlation can be used for quantifying NAPL dissolution rates over a wide range of NAPL saturations and aqueous phase velocities within the NAPL source zone. When incorporated in a finite difference transport model, the correlation provides reasonably good predictions for systems with initially high NAPL saturations that are then reduced through the dissolution process. It is shown that NAPL dissolution is slower in this case due to the larger amorphous blobs that result from preferential flow and dissolution pathways. These large blobs have significantly less surface area in comparison with small discrete blobs that result from capillary entrapment. In comparison with other published dissolution correlations, the slower mass transfer rate is characterized with a significantly higher exponent on the NAPL saturation term.

NAPL dissolution in heterogeneous systems: an experimental investigation in a simple heterogeneous system

Abstract: Dissolution experiments were conducted in a two-dimensional cell with simple heterogeneous packing consisting of well-defined coarse lenses contaminated by NAPL surrounded by a clean fine sand matrix. Experiments were conducted for a range of conditions by varying the grain size of sand, initial NAPL saturations, and size and number of the coarse lenses. Experimental results show that aqueous phase concentrations at the effluent port were always well below equilibrium concentrations, while concentrations at the local sampling port were at equilibrium for S n >0.3. Sufficient experimental conditions were tested to suggest three important mechanisms affect the overall mass transfer behavior in this heterogeneous system. (1) Variability in the effective permeabilities affect the relative volume of water flowing through the NAPL source zone and therefore, the extent of dilution of contaminated water with clean water flowing around the source zone. (2) The perimeter surface area of the NAPL source zone affects the total interfacial area for mass transfer. This is an especially important contribution to the overall mass transfer rate during early phases of the experiment when there is little flow of water through this zone. (3) Within the NAPL source zone, decreased mass transfer rates due to limited interfacial area and/or increased aqueous phase flow rates becomes the overall rate-limiting factor in this system for S n

Non-aqueous phase liquid dissolution in heterogeneous systems: Mechanisms and a local equilibrium modeling approach

Abstract: Experiments quantifying rates of non–aqueous phase liquid (NAPL) dissolution from heterogeneous media are presented and compared with model simulations. This work specifically addresses the overall dissolution of NAPL entrapped in a coarse sand lens at a high saturation. To explore the mechanisms governing dissolution rates, mathematical models describing the hydrodynamics of flow through the heterogeneous system were developed and coupled with a mass balance equation and a local equilibrium assumption (LEA) to quantify interphase mass transfer processes. Variations in the effective permeabilities as a function of NAPL saturation and the intrinsic permeabilities of the sands were employed to characterize the hydrodynamic aspects of flow through the heterogeneous system. Relative to errors generated by the ill-defined aqueous phase relative permeabilities at high NAPL saturations, the model incorporating the system hydrodynamics as the sole rate-limiting process provided a reasonable first estimate of effluent concentrations. With the representative elemental volume defined here, rate-limited dissolution becomes important for low-NAPL saturations (Sn < ∼0.05–0.15) causing tailing in the observed dissolution data and deviations between these data and the LEA model.

Resistance in the Environment

Abstract: Antibiotics, disinfectants and bacteria resistant to them have been detected in environmental compartments such as waste water, surface water, ground water, sediments and soils. Antibiotics are released into the environment after their use in medicine, veterinary medicine and their employment as growth promoters in animal husbandry, fish farming and other fields. There is increasing concern about the growing resistance of pathogenic bacteria in the environment, and their ecotoxic effects. Increasingly, antibiotic resistance is seen as an ecological problem. This includes both the ecology of resistance genes and that of the resistant bacteria themselves. Little is known about the effects of subinhibitory concentrations of antibiotics and disinfectants on environmental bacteria, especially with respect to resistance. According to the present state of our knowledge, the impact on the frequency of resistance transfer by antibacterials present in the environment is questionable. The input of resistant bacteria into the environment seems to be an important source of resistance in the environment. The possible impact of resistant bacteria on the environment is not yet known. Further research into these issues is warranted.

Fluoride removal from water by adsorption—A review

Abstract: Fluoride contamination in drinking water due to natural and anthropogenic activities has been recognized as one of the major problems worldwide imposing a serious threat to human health. Among seve ...

Review of fluoride removal from drinking water.

Abstract: Fluoride in drinking water has a profound effect on teeth and bones. Up to a small level (1-1.5 mg/L) this strengthens the enamel. Concentrations in the range of 1.5-4 mg/L result in dental fluorosis whereas with prolonged exposure at still higher fluoride concentrations (4-10 mg/L) dental fluorosis progresses to skeletal fluorosis. High fluoride concentrations in groundwater, up to more than 30 mg/L, occur widely, in many parts of the world. This review article is aimed at providing precise information on efforts made by various researchers in the field of fluoride removal for drinking water. The fluoride removal has been broadly divided in two sections dealing with membrane and adsorption techniques. Under the membrane techniques reverse osmosis, nanofiltration, dialysis and electro-dialysis have been discussed. Adsorption, which is a conventional technique, deals with adsorbents such as: alumina/ aluminium based materials, clays and soils, calcium based minerals, synthetic compounds and carbon based materials. Studies on fluoride removal from aqueous solutions using various reversed zeolites, modified zeolites and ion exchange resins based on cross-linked polystyrene are reviewed. During the last few years, layered double oxides have been of interest as adsorbents for fluoride removal. Such recent developments have been briefly discussed.

Wastewater Engineering Treatment Disposal And Reuse

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