Raghava R. Kommalapati

Aqueous solubility enhancement and desorption of hexachlorobenzene from soil using a plant-based surfactant

A plant-based surfactant extracted from fruit pericarps of Sapindus mukorossi (Ritha) is proposed for remediation of contaminated soil from a local hazardous waste site. Natural surfactants can be prepared using a very simple water extraction of fruit pericarp powder. Natural surfactant solutions are employed to enhance the aqueous solubility of a hydrophobic organic compound, hexachlorobenzene (HCB), and to desorb HCB from soils in batch and one-dimensional flow-through soil column experiments. The solubility of HCB in natural surfactant solutions increased linearly with surfactant concentration beyond the critical micelle concentration. The mass of dry Ritha powder required to solubilize 1 mg of HCB in 1 liter of water was comparable to sodium dodecylsulfate solution and other commercial surfactants. HCB concentration in the aqueous solutions approached 90% of the HCB solubility in the respective natural surfactant solutions when soils contaminated to high levels were used for desorption. HCB recovery was up to 90% of the total HCB for soils contaminated with lower levels. Desorption behavior observed for natural surfactant solutions was similar to SDS solutions. Natural surfactant solutions performed more efficiently than a simple water flood in recovering HCB from one-dimensional soil columns. The HCB concentration in the effluent was found to be as high as 80% of the surfactant-enhanced HCB solubility in respective solutions. The results of this study provide a strong case for pursuing natural surfactant solutions in further research.

Soil flushing of residual transmission fluid: Application of Colloidal Gas Aphron suspensions and conventional surfactant solutions

Abstract An innovative technology using Colloidal Gas Aphrons (CGAs) is applied in this study to flush residual levels of a light non-aqueous phase liquid (LNAPL) such as automatic transmission fluid (ATF) from a Superfund site soil. Performance of CGA suspensions is compared with that of conventional aqueous anionic surfactant solutions under both gravity stable (downflow) and gravity unstable (upflow) conditions. CGA suspensions were found to be more effective in washing ATF under both downflow and upflow modes. The displacement of ATF from the soil pores seems to be the mechanism of removal in the case of water floods. Increasing the surfactant concentration did not increase the removal rate correspondingly. The pressure required to pump the CGA suspension was much lower than that required for conventional surfactant solutions or water flood. Results show enough promise that more research should be directed at this potential technology for in situ remediation of contaminated aquifers.

Soil flushing using colloidal gas aphron suspensions generated from a plant-based surfactant

Abstract Natural surfactant solutions obtained from the fruit pericarps of Sapindus mukorossi , commonly known as Ritha or soapnut, are tested for their ability to remove hydrophobic organic compounds (HOCs) from soil. Colloidal gas aphron (CGA) suspensions generated using the surfactant are used in this study to flush an HOC from a representative soil. Soil is spiked with a chlorinated hydrocarbon, hexachlorobenzene (HCB), serving as a model HOC representative of contamination at a Superfund site north of Baton Rouge, LA. The recovery of HCB from soil columns using CGA suspensions was considerably larger than that for a waterflood. HCB recoveries in the effluent reached a maximum by the fifth pore volume and remained fairly constant for soils contaminated with high levels of HCB. This maximum HCB concentration in the column effluent was proportional to HCB solubility in the corresponding surfactant solutions. Natural surfactant performed marginally better in the form of conventional solutions than CGA suspensions at similar concentration in recovering HCB. HCB removal increased with increasing surfactant concentration due to increased aqueous solubility. The pressure buildup across the soil column remained fairly low when natural surfactant was used at concentrations up to 1%. Alternating the flushing media between CGA and water neither enhanced the recovery of HCB nor changed the pressure buildup across the soil column.

Reusable adsorbents for dilute solution separation. 1. Adsorption of phenanthrene on surfactant-modified alumina Kalliat

Activated γ-alumina surface was modified by adsorption of an anionic surfactant, sodium dodecylsulfate (SDS) from the aqueous phase. Typical S-shaped isotherms of surfactants on mineral oxides were observed for the adsorption of SDS on alumina. The formation of surfactant aggregates (hemi-micelles) on the surface made the alumina hydrophobic and increased the capacity of the oxide surface for an organic compound, namely, phenanthrene (PHE). The sorption of phenanthrene was directly related to the concentration of surfactant adsorbed. The partitioning of phenanthrene normalized to the adsorbed surfactant concentration was independent of pH. The linear sorption constant for a number of organic compounds was correlated to the octanol-water partition constant and activity coefficient in water, which are indicators of compound hydrophobicity. It is suggested that the ability to easily regenerate a modified alumina surface could be exploited in using it for wastewater treatment of contaminants at dilute concentrations.

Partition Constants and Adsorption/Desorption Hysteresis for Volatile Organic Compounds on Soil from a Louisiana Superfund Site

The adsorption of four volatile organic compounds (1,4-dichloro-benzene, 1,2-dichloroethane, 1,2,2-trichloroethane and 1,1,2,2,-tetrachloroethane) on three soil types from a Superfund site (Petroprocessors Inc) in Baton Rouge, LA was studied with the purpose of obtaining an overall correlation for inclusion in a groundwater transport model being developed for site remediation. The soil-water partition constant, Kd was determined using a standard ASTM procedure (E–1195–87). Using the data for different soil types (fraction organic carbon between 0.11% and 1.13%) and different mineral surface areas (7 to 45 m2/g), the organic carbon contribution (Koc) and the mineral matter contribution (Kmin) to the partition constant were determined. The soils obtained were either from the Pleistocene period or recent shallow deposits at the site. Both log Koc and log Kmin were linearly correlated to log Kow, the octanol-water partition constant. This data provided the basis for obtaining a general correlation for Kd on different soil types at the site. The predicted values were in agreement with that for a composite soil from the same site. The desorption of compounds from the high clay soil after the 24 hour adsorption period was observed to show a biphasic behavior, namely, an easily desorbed fraction and a desorption resistant fraction. The easily desorbed fraction was found to be satisfactorily predicted using the conventional Kd as obtained from the adsorption experiment. The slowly desorbing fraction had a time constant of several weeks. The concentration in the desorption resistant compartment was found to be dependant on the initial amount of contaminant available for adsorption. The aqueous phase concentration in equilibrium with the desorption resistant fraction was found to be ∼ 8 μg/L for dichlorobenzene and ∼ 12 μg/L for dichloroethane.

Characterization of colloidal gas aphron suspensions generated from plant-based natural surfactant solutions

Colloidal gas aphron (CGA) suspensions generated using commercial surfactants are found to have great potential in the remediation of contaminated soils and waste streams. A plant-based natural surfactant solution prepared from the fruit pericarps of Sapindus mukorossi was used in this study to generate CGA suspensions. The CGA suspensions generated from this surfactant solution have size distributions similar to those of commercial surfactants. The stability of the CGA suspensions generated with natural surfactant solutions was observed to be higher than those generated using synthetic surfactants. However, the quality or the gas fraction of the suspensions is lower for a natural surfactant solution than that for commercial surfactants. The crude solution of natural surfactant prepared using simple water extraction contains saponins, the essential surface-active agent, and many other extraneous natural organic compounds. Yet, the CGA suspensions prepared from the crude solution seem to be comparable to those generated using synthetic surfactants in size distribution and stability.

Rate-limited desorption of volatile organic compounds from soils and implications for the remediation of a Louisiana Superfund site.

The rates of desorption of trichloroethylene (TCE) and 1,3-dichlorobenzene (DCB) from a silty soil at a Superfund site and a silty-clayey soil from an uncontaminated bottomland hardwoodswamp in Baton Rouge, Louisiana were studied in laboratory batchsystems. The effect of the age of soil contamination was studiedusing a laboratory-spiked soil incubated for 3 days, 3 months and5 months. An empirical non-linear model was used to describe thebi-phasic nature of desorption with one fraction (labile) beingreleased in relatively short periods of time (typically 24–100 hr) and a second fraction (non-labile or irreversible) beingresistant to desorption. The non-linear model parameters, viz.,the fraction of the chemical released rapidly (F), and the firstorder desorption rate coefficients, k1 and k2respectively for the labile and slowly released fractions weredetermined by fitting the experimental data to the model. Thedata fit the model well as indicated by the high r2 values.The estimate of k1 was good. However, the values of k2are known with less precision due to the limited duration of theexperiment and number of samples taken at long times. In addition, desorption kinetics of 3 and 5-month old contaminatedsoils showed that progressively less amount of contaminant was available for facile desorption (lower F) compared to freshly contaminated soil. The labile fraction had desorption rate constants of the order of 10-1 h-1, whereas the slowlyreleased fraction had rate constants of the order of 10-4 h-1 in accord with literature reported values for a varietyof other compounds and soils. Possible mechanisms describing these rates and implications for the site clean up are discussed.

Bioenhancement of soil microorganisms in natural surfactant solutions.II. Anaerobic

Abstract Natural surfactant solutions obtained from fruit pericarps of Sapindus mukorossi are shown to solubilize significant quantities of hydrophobic organic compounds and mobilize them from soil matrix. It is very crucial to determine the fate of surfactants employed for soil flushing in the subsurface and also in the effluent recovered. This paper appraises the bioenhancement of soil microorganisms in natural surfactant solutions under anaerobic conditions. Sealed 125 ml serum bottles are used for developing the anaerobic cultures. The cultures are maintained in anoxic conditions by degassing and filling the bottles with nitrogen. Three concentrations of natural surfactant 0.1, 1 and 2% and two different nutrient media, basal salt media (BSM) and heterotrophic media are used in the studies. Natural surfactant solutions can serve as both carbon and energy source for anaerobic microorganisms and also degrade to considerable extent. The growth curves for anaerobic cultures followed similar trends as thos...

Soil-Water Partitioning and Desorption Hysteresis of Volatile Organic Compounds from a Louisiana Superfund Site Soil

The adsorption and desorption of three volatile organic compounds (1,2- dichloroethane, 1,1,2- trichloroethane and 1,1,2,2-tetrachloroethane) from a previously uncontaminated clayey soil sample from a Superfund site in North Baton Rouge,Louisiana was studied. In the linear range of the adsorption isotherm, the partition constants were not affected by the presence of the co-solutes. The adsorption isotherms over a wide concentration range on the soil followed the nonlinearFreundlich isotherm. The desorption of the compounds showedsignificant hysteresis at all concentrations studied. Approximately 20 to 70% of the adsorbed mass of organic compounds resisted the desorption even after five months ofsuccessive desorption steps. The desorption of four compounds(1,2-dichloroethane, 1,1,2-trichloroethane, 1,4-dichlorobenzeneand hexachlorobutadiene) from a contaminated soil sample fromthe same site was also studied. The aqueous concentration declined as the successive desorption steps progressed. For hexachlorobutediene the desorption can be visualized as occurring in two stages. The first stage involved a ‘loosely bound’ or ‘reversible’ fraction and the second stage involveda ‘tightly bound’ or ‘resistant’ fraction.

Optimization of Wind Turbine Airfoil Using Nondominated Sorting Genetic Algorithm and Pareto Optimal Front

A Computational Fluid Dynamics (CFD) and response surface-based multiobjective design optimization were performed for six different 2D airfoil profiles, and the Pareto optimal front of each airfoil is presented. FLUENT, which is a commercial CFD simulation code, was used to determine the relevant aerodynamic loads. The Lift Coefficient () and Drag Coefficient () data at a range of 0° to 12° angles of attack () and at three different Reynolds numbers (, 479, 210, and 958, 422) for all the six airfoils were obtained. Realizable turbulence model with a second-order upwind solution method was used in the simulations. The standard least square method was used to generate response surface by the statistical code JMP. Elitist Non-dominated Sorting Genetic Algorithm (NSGA-II) was used to determine the Pareto optimal set based on the response surfaces. Each Pareto optimal solution represents a different compromise between design objectives. This gives the designer a choice to select a design compromise that best suits the requirements from a set of optimal solutions. The Pareto solution set is presented in the form of a Pareto optimal front.