Browsing by Author "Niaz Mohammed"

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A groundwater velocity and dissolved oxygen on bioremediation of gasoline-contaminated sandy aquifers
(Saudi Digital Library) Niaz Mohammed
Benzene, Toluene and Xylene (BTX) compounds are the main contituents fo gasoline and their presence in groundwater is common because of hydrocarbon spill and leakage of storage tanks. These compounds are relatively highly soluble and mobile in the subsurface and are toxic even at very low concentrations. Bioremediation is the most widely used technique among all the currently employed methods for treating BTX contaminated soil and groundwater. Various factors affecting bioremediation, such as dissolved oxygen, nutrient, temperature, pH, etc. have been well studied in the laboratory soil columns and microcosms. The effect of soil permeability (as groundwater velocity) has been investigated in this study using a pilot scale sand tank model. The effect of dissolved oxygen (DO) and contaminant concentration are also included in the study using a pilot scale sand tank model. The effect of dissolved oxygen (DO) and contaminant concentration are also included in the study. Numerical models have been developed using finite difference and orthogonal collocation to simulate one dimensional transport with time-dependent pore water velocity. The modeling process includes sorption given by linear isotherm and biodegradation given by a variety of kinetics such as first-order, zero-order, Monod, MichalisMenten, Haldane and many other inhibitory and non-inhibitory kinetics. A variety of initial and boundary conditions such as Dirichlet's, Neuman's, mixed, decaying, etc. have been modeled. Three models (firstorder and/or zero-order, non growth associated Monod, and Monod) have been inverted using a GaussMarquardt-Levenberg algorithm to assess the transport parameter, such as retardation constant ( R ), firstorder rate constant (µ) and zero-order rate constant (γ). A 3 (2²) factorial experiment has been conducted to study three factors, groundwater velocity, BTX concentration and dissolved oxygen (DO). Observed concentration data colllected from the sand tank model have been used for estimating the transport parameters. The data has been found to fit well to first-order/zero-order as well as to Monod model. Groundwater velocity has been found to be the most significant factor governing the rate of biodegradation (determined from the first-order rate constant) of BTX compounds. Dissolved oxygen and BTX concentration have also been found to be significant factors.
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Effect of denitrification on dispersion of nitrate in saturated porous media
(Saudi Digital Library) Niaz Mohammed
Nitrate with a concentration of 50 mg/1 as NO-N or greater would cause serious groundwater contamination problem. The natural biological denitrification existing in groundwater systems tends to effect the nitrate build-up in the groundwater zone. Denitrification is a biochemical process that, in presence of denitrifying bacteria and organic matter, converts nitrate in gaseous nitrogen species. The effect of denitrification on dispersion of nitrate on saturated sandy soil has been studied and compared with the temporal and spatial concentration of nitrate in nonreactive (without denitrification) and reactive (with denitrification) cases. A laboratory model has been fabricated to simulate steady one-dimensional flow and to transport nitrate with or without denitrification. Denitrification has been simulated at various rates with varied C:N ratio and detention time. Retardation constant dispersivity and degradation constants has been computed using existing analytical models. A numerical model has also been used to predict spatial and temporal nitrate transport and compared with experimental results.
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