nan Manasi

Effective adsorption of hexavalent chromium through a three center (3c) co-operative interaction with an ionic liquid and biopolymer

Biopolymers as well as ionic liquids are known for their potential applications. In this work, we report the utility of chitosan as an excellent platform for impregnating the ionic liquid, tetraoctylammonium bromide by ultrasonication and its subsequent adsorption for chromium(VI). The effective mass transfer due to sonication coupled with the hydrogen bonding interaction between chitosan-ionic liquid and the electrostatic interaction involving the amino groups in chitosan and hexavalent chromium governs this three center (3c) co-operative mechanism. The adsorption followed a pseudo second order kinetics with a Langmuir adsorption capacity of 63.69 mg g(-1). Various isotherm models were used to correlate the experimental data and the adsorption process is exothermic with a decreased randomness at the solid-solution interface. The thermodynamics of the spontaneous adsorption process could be explained through a positive co-operative effect between the host (chitosan) and the guest (ionic liquid). The adsorbed chromium(VI) could be converted to ammonium chromate using ammonium hydroxide, thereby regenerating the adsorbent. The method could be translated into action in the form of practical application to a real sample containing chromium.

Prospective application of Aspergillus species immobilized in sodium montmorillonite to remove toxic hexavalent chromium from wastewater

An interdisciplinary approach involving chemistry and biotechnology offers greener solutions to mitigate heavy metal pollution originating from wastewaters. Aspergillus species (fungi) were isolated from bread and immobilized in sodium montmorillonite (an inorganic clay material). This biosorbent has good ability to remove toxic Cr(VI) from an acidic medium with a Langmuir adsorption capacity of 45.72 mg g−1. FTIR, SEM-EDAX, optical imaging and TGA techniques were used to explore the characteristics of the biosorbent before and after Cr(VI) adsorption. Optimum pH and temperature for Cr(VI) biosorption were 2.0 and 30 °C, respectively and the kinetics followed the pseudo second order model. The biosorbent regeneration was accomplished using sodium hydroxide. As a proof of concept, the method was validated in an industrial effluent wastewater sample of BCR-715, a certified reference material. The biosorbent can also be very useful to treat tannery and electroplating wastewaters discharging chromium.

An indigenous Halomonas BVR1 strain immobilized in crosslinked chitosan for adsorption of lead and cadmium.

Biomacromolecules play an important role in the adsorption of metals. In this context, we have studied the potential of an indigenous Halomonas BVR1 strain (isolated from an electronic industry effluent) immobilized in a glutaraldehyde crosslinked chitosan matrix for the adsorption of lead and cadmium. Adequate physico-chemical characterizations and the study of thermodynamic and kinetic parameters authenticated the experimental observations and the interaction mechanism. The adsorption was facile in the pH range 5-7 and pseudo second order kinetic model was favourable for both the metals. The Langmuir adsorption capacities for lead and cadmium were found to be 24.15 mg g(-1) and 23.88 mg g(-1) respectively. The negative ΔG values confirmed the thermodynamic feasibility and this lucid approach highlights the utility of green methodology for heavy metal adsorption.

Identification and Characterization of the microbial communities found in electronic industrial effluent and their potential for bioremediation

Microbial communities are dynamic systems that develop depending on the ecological niche in which they survive. Electronic industry effluent, rich in heavy metals and salts is one such ecosystem where diverse heavy metal resistant microbes exist. Taxonomic identification of this microbial community would be interesting as no information on the microbial diversity from electronic industry effluent is available till date. Our paper attempts to characterize the microbial inhabitants of this niche. Culture dependent microbiological methods were used to establish and identify various microbial species from the effluent. Culture independent methods of identification involving biochemical tests and molecular biology based methods like 16 S- r DNA sequencing and lipid analyses (FAME analysis) were also carried out to confirm the identity of isolated species. Our study, first of its kind revealed the presence of a diverse group of resistant aerobic microbes and disclosed a total of ten bacterial and two fungal isolates. All these isolates were found to survive in presence of heavy metals like cadmium, lead and zinc and were resistant to antibiotics like ampicillin, tetracycline, streptomycin, penicillin and chloramphenicol as indicated by their Minimum Inhibitory Concentrations (MIC). Such resistant isolates harbor possibilities of metal adaptive/selective pathways which render them as economically beneficial bio-sorbent alternatives in bioremediation of heavy metals.

Impact of heavy metal lead stress on polyamine levels in Halomonas BVR 1 isolated from an industry effluent

In living systems, environmental stress due to biotic and abiotic factors triggers the production of myriad metabolites as a potential mechanism for combating stress. Among these metabolites are the small polycationic aliphatic amine molecules - polyamines, which are ubiquitous in all living organisms. In this work, we demonstrate a correlation between cellular concentration of three major polyamines (putrescine, spermidine and spermine) with lead exposure on bacteria for a period of 6–24 h. We report that indigenously isolated Halomonas sp. strain BVR 1 exhibits lead induced fluctuations in their cellular polyamine concentration. This response to lead occurs within 6 h post metal treatment. During the same time interval there was a surge in the growth of bacteria along with an enhancement in the putrescine levels. We conclude that in Halomonas sp. strain BVR 1, an early response is seen with respect to modulation of polyamines as a result of lead treatment and hypothesize that endogenous polyamines contribute towards scavenging lead in these bacteria.

Evaluation of the genetic basis of heavy metal resistance in an isolate from electronic industry effluent

Halomonas BVR 1 isolated from an electronic industry effluent had high level of resistance to heavy metals like cadmium, lead, zinc and to various antibiotics. Minimum Inhibitory Concentration (MIC) of the strain toward cadmium and lead was found to be 200 mg L−1 and 400 mg L−1 respectively, while it could tolerate zinc up to 250 mg L−1 and chromium up to 150 mg L−1. The present study proved the genetic contribution of heavy metal resistance in this strain to be plasmid mediated. Isolation of the plasmid from Halomonas BVR 1 and its subsequent linearization with Bam H1 confirmed the presence of a plasmid of size >10 kb. Plasmid curing experiments affirmed plasmid mediated heavy metal resistance. Additionally, genetic transformation of a non metal resistant lab strain Escherichia coli and the cured strain of Halomonas BVR 1 with the isolated plasmid increased their metal tolerance level by 50% confirming the genetic determinant to be present in the plasmid.