Kaushik Bandyopadhyay

Cadmium Removal by Lemna minor and Spirodela polyrhiza

The present study investigates the ability of two genus of duckweed (Lemna minor and Spirodela polyrhiza) to phytoremediate cadmium from aqueous solution. Duckweed was exposed to six different cadmium concentrations, such as, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mg/L and the experiment was continued for 22 days. Water samples were collected periodically for estimation of residual cadmium content in aqueous solution. At the end of treatment period plant samples were collected and accumulated cadmium content was measured. Cadmium toxicity was observed through relative growth factor and changes in chlorophyll content. Experimental results showed that Lemna minor and Spirodela polyrhiza were capable of removing 42–78% and 52–75% cadmium from media depending upon initial cadmium concentrations. Cadmium was removed following pseudo second order kinetic model. Maximum cadmium accumulation in Lemna minor was 4734.56 mg/kg at 2 mg/L initial cadmium concentration and 7711.00 mg/kg in Spirodela polyrhiza at 3 mg/L initial cadmium concentration at the end of treatment period. Conversely in both cases maximum bio-concentration factor obtained at lowest initial cadmium concentrations, i.e., 0.5 mg/L, were 3295.61 and 4752.00 for Lemna minor and Spirodela polyrhiza respectively. The present study revealed that both Lemna minor and Spirodela polyrhiza was potential cadmium accumulator.

Arsenic Uptake by Lemna minor in Hydroponic System

Arsenic is hazardous and causes several ill effects on human beings. Phytoremediation is the use of aquatic plants for the removal of toxic pollutants from external media. In the present research work, the removal efficiency as well as the arsenic uptake capacity of duckweed Lemna minor has been studied. Arsenic concentration in water samples and plant biomass were determined by AAS. The relative growth factor of Lemna minor was determined. The duckweed had potential to remove as well as uptake arsenic from the aqueous medium. Maximum removal of more than 70% arsenic was achieved at initial concentration of 0.5 mg/l arsenic on 15th day of experimental period of 22 days. Removal percentage was found to decrease with the increase in initial concentration. From BCF value, Lemna minor was found to be a hyperaccumulator of arsenic at initial concentration of 0.5 mg/L, such that accumulation decreased with increase in initial arsenic concentration.

Forensic Study on the Causes of Failure of Stone Columns Under Water Storage Tanks and Possible Remedial Measures

Water storage tanks of diameter 30 m and height 14.50 m were erected at a site near the coastal region of West Bengal. Detailed soil exploration work revealed that the deposit consisted of typical soft marine clay with standard penetration (SPT) values lying in the range of 2–6 up to 28.0 m depth below the ground level. Varying percentage of decomposed vegetation and laminated silt was observed between 11.50 and 28.00 m depth below EGL. Overall ground improvement was proposed, and accordingly, stone columns were installed up to the depth of 10.00 m below EGL. After one year of installation, total settlements of 800 mm and differential settlement of about 150 mm were observed and these have been continuing unabated. Subsequently, detailed forensic investigation was made, and it was observed that the stone columns had showed telltale signs of failure, and consequently, huge settlement resulted. The present paper discusses on the various causes of failure and suggests some remedial measures for arresting the settlements.

A Laboratory Column Study for Adsorptive Removal of Cadmium by Fly Ash

The use of heavy metals and the concomitant adverse effects has increased to a great extent over the recent times. Cadmium is one of the most harmful toxic metals. This metal is being increasingly consumed in the industries like nickel-cadmium batteries, pigments, and stabilizers for PVC, electroplating and other coatings, metallurgical, electronics, petroleum and coal, pulp and paper, fertilizers, photography, etc. Its pollution potential, has therefore given rise to the necessity of removing the metal from wastewater. On the other hand fly ash, which is produced in huge quantities even in a medium sized coal-fired thermal power plant, is a major cause of concern with regard to its safe disposal. Findings of a few earlier investigations in this regard have lent support to the belief that cadmium-bearing wastewater could possibly be safely disposed of on a land filled-up with fly ash. The fly ash would adsorb cadmium and hence reduce the problem of ground water pollution due to leaching. In the present investigation a column study experiments has been carried out to evaluate performance of fixed bed adsorption columns made of fly ash exposing them to cadmium bearing wastewaters. The gathered characteristic information from the pertinent breakthrough curve can be used as a design rationale for a fly ash bed as a liner overlying a clay mantle for safe disposal of cadmium bearing wastewater. The leaching behaviour of exchangeable cations from the fly ash column has also been studied.