Ligy Philip

Pilot scale studies were carried out to evaluate the suitability of bioremediation of Cr(VI) contaminated aquifers using bio-barrier and reactive zone technologies, employing chromium reducing bacteria. Experimental results showed that a 10. cm thick bio-barrier with an initial biomass concentration of 0.44. mg/g of soil was able to completely contain a Cr(VI) plume of 50. mg/L concentration, when the Darcy velocity was 0.0196. cm/h. In the case of reactive zone technology, a system with four injection wells was effective even when Cr(VI) concentration in the plume was as high as 250. mg/L, when 150. g (wet weight) of bacteria were injected into each injection well. A mathematical model was proposed for simulating the bioremediation process. Though the model could predict the over all trends observed in the experiments, it is limited by the assumption of homogeneous conditions. © 2010 Elsevier B.V.

Ex situ treatment of hexavalent chromium (Cr(VI)) contaminated soil using a bioreactor-biosorption system was evaluated as a novel remediation alternative. Leaching of Cr(VI) from the contaminated soil using various eluents showed that desorption was strongly affected by the solution pH. The leaching process was accelerated at alkaline conditions (pH 9). Though, desorption potential of ethylene diamine tetra acetic acid (EDTA) was the maximum among various eluents tried, molasses (5 g/L) could also elute 72% of Cr(VI). Cr(VI) reduction studies were carried out under aerobic and facultative anaerobic conditions using the bacterial isolates from contaminated soil. Cr(VI) reduction was moderately higher in aerobic conditions than in facultative anaerobic conditions. The effect of various electron donors on Cr(VI) reduction was also investigated. Among five electron donors screened, peptone (10 g/L) showed maximum Cr(VI) reduction followed by molasses (10 g/L). The time required for complete Cr(VI) reduction was increased with increase in the initial Cr(VI) concentration. However, specific Cr(VI) reduction was increased with increase in initial Cr(VI) concentration. Sulfates and nitrates did not compete with Cr(VI) for accepting the electrons. A bioreactor was developed for the detoxification of Cr(VI). Above 80% of Cr(VI) reduction was achieved in the bioreactor with an initial Cr(VI) concentration of 50 mg/L at an HRT of 8 h. An adsorption column was developed using Ganoderm lucidum (a wood rooting fungus) as the adsorbent for the removal of trivalent chromium (Cr(III)) and excess electron donor from the effluent of the bioreactor. The specific Cr(III) adsorption capacity of G. lucidum in the column was 576 mg/g. The new biosystem seems to be a promising alternative for the ex situ bioremediation of Cr(VI) contaminated soils. © 2005 Elsevier B.V. All rights reserved.

In this paper, we have presented the results of Cr(VI) and Cr(III) removal from aqueous phase by different aquatic weeds as biosorbents. Batch kinetic and equilibrium experiments were conducted to determine the adsorption kinetic rate constants and maximum adsorption capacities of selected biosorbents. In most of the cases, adsorption followed a second-order kinetics. For Cr(III), maximum adsorption capacity was exhibited by reed mat (7.18 mg/g). In case of Cr(VI), mangrove leaves showed maximum removal/reduction capacity (8.87 mg/g) followed by water lily (8.44 mg/g). There was a significant difference in the concentrations of Cr(VI) and total chromium removed by the biosorbents. In case of Cr(VI) removal, first it was reduced to Cr(III) with the help of tannin, phenolic compounds and other functional groups on the biosorbent and subsequently adsorbed. Acid treatment significantly increased Cr(VI) removal capacity of the biosorbents whereas, alkali treatment reduced the Cr(VI) removal capacities of the biosorbents. FTIR spectrum showed the changes in functional groups during acid treatment and biosorption of Cr(VI) and Cr(III). Aquatic weeds seem to be a promising biosorbent for the removal of chromium ions from water environment. © 2007 Elsevier B.V. All rights reserved.

In this paper, results of Cr(VI) and Cr(III) sorption from aqueous phase by palm flower (Borassus aethiopum) is presented. Batch kinetic and equilibrium experiments were conducted to determine the adsorption kinetic rate constants and maximum adsorption capacities. Both Cr(III) and Cr(VI) adsorption followed a second-order kinetics. For Cr(III), maximum adsorption capacity was 6.24 mg/g by raw adsorbent and 1.41 mg/g by acid treated adsorbent. In case of Cr(VI), raw adsorbent exhibited a maximum adsorption capacity of 4.9 mg/g, whereas the maximum adsorption capacity for acid treated adsorbent was 7.13 mg/g. There was a significant difference in the concentrations of Cr(VI) and total chromium removed by palm flower. In case of Cr(VI) adsorption, first it was reduced to Cr(III) with the help of tannin and phenolic compounds and subsequently adsorbed by the biosorbent. Acid treatment significantly increased Cr(VI) adsorption capacity of the biosorbent whereas, alkali treatment reduced the adsorption capacities for Cr(VI). However, in case of Cr(III), acid treatment significantly reduced the adsorption capacity whereas the adsorption capacity of alkali treated biosorbent was slightly less than that of raw adsorbent. FT-IR spectrum showed the changes in functional groups during acid treatment and biosorption of Cr(VI) and Cr(III). Column studies were conducted for Cr(III) to obtain the design parameters require for scale-up. © 2007 Elsevier B.V. All rights reserved.

Cr(VI) reduction studies were carried out with chromium reducing bacteria (CRB), sulphate reducing bacteria (SRB) and iron reducing bacteria (IRB), individually and in combination. Biokinetic parameters such as maximum specific growth rate (μmax), half saturation constant (Ks), yield coefficient (YT) and inhibition coefficient (Ki) for individual cultures were evaluated. A mathematical model was proposed for simulating the chromium reduction, COD utilization and biomass growth, by individual cultures as well as by a combination of two or three different cultures, for different initial Cr(VI), SO42- and Fe(III) concentrations. The biokinetic parameters evaluated from one set of experiments for individual cultures were utilized in all the validation studies. The performance of the mathematical model in terms of the dimensionless modified coefficient of efficiency (E) indicated that the proposed model simulates the system behavior very well. © 2009 Elsevier B.V. All rights reserved.

Bioremediation studies were carried out for the treatment of Cr(VI) bearing sludge using indigenous microorganisms isolated from a chromium contaminated site. Effects of moisture content, initial substrate and biomass concentrations on the bioremediation process were studied by conducting batch and continuous experiments. The leachability of total chromium and Cr(VI) from remediated soil was evaluated and compared with that of untreated soil. Experimental data was used to determine biokinetic parameters and validate a mathematical model. Single objective and multi-objective management models were developed by embedding the mathematical model describing the process in a simulation-optimization framework. Single objective management models considered either cost minimization or minimization of time for treatment. Genetic Algorithm, available in MATLAB tool box was used for solving the optimization problems. Applicability of proposed management models was demonstrated for the remediation of Cr(VI) bearing sludge in Ranipet, Tamilnadu, India. Multi-objective management model was used to derive the Pareto-optimal front, which describes the trade off between the cost of treatment and the time taken for treatment. © 2010 Elsevier B.V.

Bench scale transport and biotransformation experiments and mathematical model simulations were carried out to study the effectiveness of bio-barriers for the containment of hexavalent chromium in contaminated confined aquifers. Experimental results showed that a 10 cm thick bio-barrier with an initial biomass concentration of 0.205 mg/g of soil was able to completely contain a Cr(VI) plume of 25 mg/L concentration. It was also observed that pore water velocity and initial biomass concentration are the most significant parameters in the containment of Cr(VI). The mathematical model developed is based on one-dimensional advection-dispersion reaction equations for Cr(VI) and molasses in saturated, homogeneous porous medium. The transport of Cr(VI) and molasses is coupled with adsorption and Monod's inhibition kinetics for immobile bacteria. It was found that, in general, the model was able to simulate the experimental results satisfactorily. However, there was disparity between the numerically simulated and experimental breakthrough curves for Cr(VI) and molasses in cases where there was high clay content and high microbial activity. The mathematical model could contribute towards improved designs of future bio-barriers for the remediation of Cr(VI) contaminated aquifers. © 2006 Elsevier B.V. All rights reserved.

Studies were conducted to understand the transport and biotransformation of Cr(VI) through porous media in presence of chromium reducing bacteria (CRB), sulphate reducing bacteria (SRB) and iron reducing bacteria (IRB). Column experiments were conducted using sand and soil, and different bacterial strains working individually and in combination. Results showed that 20. mg/L of Cr(VI) in the feed was completely contained within 500-648. h by different combinations of bacterial strains. A one-dimensional mathematical model, based on advection-dispersion-adsorption equations for transport of Cr(VI) and molasses in saturated, homogeneous porous medium, coupled with Monod's inhibition kinetics for immobile bacteria was able to simulate the experimental results satisfactorily. The proposed mathematical model will be very helpful in the development of a management model for in situ bioremediation of chromium contaminated aquifers using either reactive zones or bio-barriers. © 2011 Elsevier B.V.