Dipak Roy

Adsorption of heavy metals by green algae and ground rice hulls

Abstract This research demonstrates the applicability of low cost, readily available alternate adsorbents to remove and recover toxic heavy metals from water. Heavy metal ion adsorption has been investigated using two different adsorbing biomasses, algae and rice hulls. Algal biomass adsorption studies were conducted with: As, Cd, Co, Cr, Pb, Ni and Zn, and rice hull biomass adsorption studies were conducted with: As, Cd, Cr, Pb and Sr. Both biomasses were dried and pulverized to maximize surface area. The green alga, Chlorella minutissima, adsorbed greater than 90% of the initial Pb, and greater than 98% of the initial Co concentrations. Rice hulls (Mars and Rico Varieties) exhibited similar adsorption percentages: 94% for Sr, and greater than 99% for Pb. The rate of adsorption was fast; the solution metal concentration reached equilibrium within minutes. The cell wall metal complex was found to be stable; the bound metal did not desorb over time under static conditions. Most cationic metal ions could be...

Separation of Organic Dyes from Wastewater by Using Colloidal Gas Aphrons

Abstract Auxiliary chemicals used in the preparation of water-based dyes have been reported to pose problems in conventional wastewater treatment processes. The dye manufacturing industries have to find alternate wastewater treatment processes to remove dyes from their waste effluents. This paper investigates a novel method of separation of dyes by flotation using colloidal gas aphrons (CGAs). The results indicate that this is an effective method for the separation of synthetic dyes from wastewater. The mechanism of removal has been shown to be ion coupling of the oppositely charged species of the surfactant forming the CGA and the dye and flotation of the ion-dye complex on the surface of CGA microbubbles.

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.

Application of surfactant solutions and colloidal gas aphron suspensions in flushing naphthalene from a contaminated soil matrix

Abstract The applicability of conventional surfactant solutions and colloidal gas aphron (CGA) suspensions to remove naphthalene from a contaminated soil matrix was investigated. Laboratory studies were conducted to evaluate the relative suitability of nonionic, cationic and anionic surfactants in removing naphthalene from the soil. Nonionic surfactant was found to be more efficient than the ionic surfactants in removing napthalene from contaminated soil matrix in batch experiments and was selected for further flushing studies. The presence of surfactant reduced the volatilization of naphthalene. Micellar solubilization appears to be the primary mechanism of removal using both surfactant solutions and CGA suspensions. Increasing the concentration of the surfactant solution enhanced the percent removal of naphthalene. Using a CGA suspension as a flushing medium may result in channeling and pore clogging in the soil matrix, thereby affecting the overall efficiency of the process.

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.

A Study of the Size Distribution and Stability of Colloidal Gas Aphrons Using a Particle Size Analyzer

Abstract Application of colloidal gas aphrons (CGA) in decontaminating soils and aqueous solutions is one of the emerging innovative technologies. This paper addresses the size distribution and stability of CGAs as studied by using a particle size analyzer. Cationic, anionic, and nonionic surfactants were used to generate the CGAs. Size distribution spectrum and volume fraction of microbubbles in sample solutions were studied as functions of time. The effects of surfactant concentrations used to produce CGAs and the presence of an electrolyte, such as sodium chloride, on the characteristics of the suspension were also studied.

Removal of hazardous oily waste from a soil matrix using surfactants and colloidal gas aphron suspensions under different flow conditions

Abstract In-situ surfactant flushing is an attractive alternative used for decontamination of subsurface soil. The primary objective of this research is to investigate and examine an innovative technique of in-situ flushing using colloidal gas aphron suspensions (CGA) generated from surfactant solutions. The efficiency of CGA suspensions in the removal of oily waste is compared with conventional surfactant solutions and waterfloods under different flow regimes. Results show that CGA suspensions produced using sodium dodecylsulfate had a higher recovery of waste material (56%) than conventional surfactant solutions (47%) or waterflood (43%) in the downflow (gravity-stable) mode. The efficiency of CGA suspensions was greater in the downflow mode than in upflow (gravity-unstable) or horizontal (gravity-neutral) modes, and increasing the surfactant concen- tration from 8 to 30 mM did not enhance the removal efficiency for either CGA suspensions or conventional surfactant solutions. CGA suspensions appeared to have better removal for the major chlorinated hydrocarbons present in the oily waste.

Fate and enhancement of atrazine biotransformation in anaerobic wetland sediment

Abstract We examined fate and anaerobic microbial transformation/degradation characteristics of atrazine in wetland sediment receiving wastewater from a local sugar mill. Well-known metabolites/intermediates of atrazine were not detected except hydroxyatrazine. Atrazine adsorbed on the sediment linearly with a distribution coefficient of 9.979 ml/g. Although we did not obtain a direct proof of atrazine mineralization, the values of observed yield of total NH3-N were comparable to the theoretical values suggesting the biodegradation of atrazine to its end products of NH3 and CO2. Only about 20% of atrazine was biotransformed to non-triazine species, possibly to the mineral end products, after 38 weeks of incubation in the sample reactors without organic amendments, with methanol and sodium acetate. Acetic acid appeared to enhance the biotransformation of atrazine (both in aqueous and sediment phases) if one only measured the parent atrazine compound alone. However, a comprehensive analysis of atrazine and its metabolites/intermediates showed that most of the disappeared atrazine existed as hydroxyatrazine. Glucose improved the wetland sediments removal rate of the triazine species.

A simplified solution technique for carbon adsorption model

Abstract A new method of solving the homogeneous surface diffusion model for activated carbon absorption makes use of Laplace transforms on the equations developed by applying orthogonal collocation. The simultaneous equations which are developed are non-linear so an interative method is introduced to make them solvable when one wishes to calculate the surface diffusion coefficient, Df, and the film transfer coefficient, Kf, from batch adsorption data. The proposed model has the advantage of being continuous in time in contrast to earlier models which relied on finite difference numerical methods to solve the system of equations comprising the homogeneous surface diffusion model. The model is applied to one data set from the literature. The proposed method gave values of Kf and D1 nearly identical to values found by other investigators. The model was applied to three new data sets obtained in our laboratories: an agricultural waste, a dye waste and an aqueous waste stream containing a herbicide. The industrial wastes were composed of a mixture of species, whereas the herbicide waste contained a single organic compound. The model produced a good match between experiment and prediction for all waste streams. The final form of the equations is presented in a form readily useable by the person interested in applications to carbon adsorption bed practice.