Abhijit Maiti

Modeling of arsenic adsorption kinetics of synthetic and contaminated groundwater on natural laterite.

A simple shrinking core model is applied to predict the adsorption kinetics of arsenite and arsenate species onto natural laterite (NL) in a stirred tank adsorber. The proposed model is a two-resistance model, in which two unknown parameters, external mass transfer coefficient (K(f)) and pore diffusion coefficient (D(e)) are estimated by comparing the simulation concentration profile with the experimental data using a nonlinear optimization technique. The model is applied under various operating conditions, e.g., initial arsenic concentration, NL dose, NL particle size, temperature, stirring speed, etc. Estimated values of D(e) and K(f) are found to be in the range of 2.2-2.6 x 10(-11)m(2)/s and 1.0-1.4 x 10(-6)m/s at 305K for different operating conditions, respectively. D(e) and K(f) values are found to be increasing with temperature and stirrer speed, respectively. Calculated values of Biot numbers indicate that both external mass transfer and pore diffusion are important during the adsorption. The model is also applied satisfactorily to predict the arsenic adsorption kinetics of arsenic contaminated groundwater-NL system and can be used to scale up.

Comparison of treated laterite as arsenic adsorbent from different locations and performance of best filter under field conditions

Arsenic pollution in groundwater is a worldwide concern due to its chronic effects on human health. Numerous studies have been carried out to obtain cost-effective arsenic removal method. Adsorption using natural materials or its treated forms is found to be cost-effective technology. Raw laterite (RL) or its treated form (TL) is studied recently as arsenic adsorbent for aqueous system. Laterite composition varies with geographical location and extent of lateritization. The study on effects of arsenic adsorption with varying composition of laterite is not explored yet. Four laterite samples with different compositions are examined to remove arsenic from water. These laterite samples are activated using an optimized acid followed by base treatment method in order to determine the effects of RL composition on arsenic adsorption behavior of TL. Higher iron and aluminum containing RL samples show higher arsenic adsorption behavior. Similarly, TL obtained from higher iron and aluminum containing RL sample shows the higher specific surface area (130-180 m(2) g(-1)) and pore volume (0.28-0.35 mL g(-1)). Two household filters using TL are deployed in arsenic affected area of Barasat, 24 Parganas (N), West Bengal, India and their performance is monitored for about a year.

The efficiency of Eichhornia crassipes in the removal of organic and inorganic pollutants from wastewater: a review

Water is a basic necessity of life, but due to overextraction and heavy input of nutrients from domestic and industrial sources, the contamination level of water bodies increase. In the last few decades, a potential interest has been aroused to treat wastewater by biological methodologies before discharge into the natural water bodies. Phytoremediation using water hyacinth is found to be an effective biological wastewater treatment method. Water hyacinth (Eichhornia crassipes), a notorious weed, being the most promising plant for removal of contaminants from wastewater is studied extensively in this regard. It has been successfully used to accumulate heavy metals, dyes, radionuclides, and other organic and inorganic contaminants from water at laboratory, pilot, and large scale. The plant materials are also being used as sorbent to separate the contaminant from water. Other than phytoremediation, the plant has been explored for various other purposes like ethanol production and generation of biogases and green manures. Such applications of this have been good support for the technocrats in controlling the growth of the plant. The present paper reviews the phytoremedial application of water hyacinth and its capability to remove contaminants in produced water and wastewater from domestic and isndustrial sources either used as a whole live plant grown in water or use of plant body parts as sorbent has been discussed.

Removal of As(V) using iron oxide impregnated carbon prepared from Tamarind hull

Iron oxide impregnated tamarind hull carbon (IOITHC) was developed for use as an adsorbent for the removal of As(V) from water. Tamarind hull was used as the source of carbonaceous material, which was first treated with ferric chloride and ammonium hydroxide solutions with successive calcination at 873–974 K in a muffle furnace for 1 h to prepare an arsenic adsorbent. The B.E.T surface area of IOITHC was found to be 304.6 m2 g−1 and the average iron content in the adsorbent was found to be 7 wt%. The point of zero charge (pHzpc) of IOITHC was found to be 6.9. As(V) and arsenic (as total) adsorption on IOITHC were investigated in batch mode using As(V) spiked distilled water and real contaminated groundwater (CGW). The effects of speed of agitation, adsorbent particle size, temperature, pH of the solution, and concentration of the adsorbate on the adsorption process were investigated. The maximum adsorption capacity of about 1.2 mg g−1 As(V) was achieved. The removal of As(V) on IOITHC was compared with the untreated tamarind hull carbon as well as with the activated commercial carbon and IOITHC was found to be better adsorbent. Arsenic adsorption from arsenic contaminated groundwater (CGW) on IOITHC in batch mode indicates that 98% removal was achieved for adsorbent loading of 3.0 g L−1 with initial arsenic concentration of 264 μg L−1. Desorption study of arsenic from As(V)-loaded IOITHC was performed using aqueous solution in the pH range of 3 to 12.

Desorption kinetics and leaching study of arsenic from arsenite/arsenate-loaded Natural Laterite

Desorption kinetics of arsenite- and arsenate-loaded Natural Laterite (NL) is performed under varying NaOH concentration (0.05-0.3 mol/L) and pH (4.0-11.0) of the desorption medium. The kinetic desorption data are well fitted to pseudo-second order kinetic model. The leaching of NL under aqueous medium is performed in the pH range of 2-12. Separately arsenite- and arsenate-loaded NL is leached according to Toxicity Characteristic Leaching Procedure (TCLP) protocol. However, recent studies indicate that TCLP significantly underestimate the leaching behaviour of arsenic. So, arsenic leaching from arsenic-loaded NL is conducted under synthetic leachate condition and results are compared with TCLP results.

The efficacy of bacterial species to decolourise reactive azo, anthroquinone and triphenylmethane dyes from wastewater: a review

The industrial dye-contaminated wastewater has been considered as the most complex and hazardous in terms of nature and composition of toxicants that can cause severe biotic risk. Reactive azo, anthroquinone and triphenylmethane dyes are mostly used in dyeing industries; thus, the unfixed hydrolysed molecules of these dyes are commonly found in wastewater. In this regard, bacterial species have been proved to be highly effective to treat wastewater containing reactive dyes and heavy metals. The bio-decolourisation of dye occurs either by adsorption or through degradation in bacterial metabolic pathways under optimised environmental conditions. The bacterial dye decolourisation rates vary with the type of bacteria, reactivity of dye and operational parameters such as temperature, pH, co-substrate, electron donor and dissolved oxygen concentration. The present paper reviews the efficiency of bacterial species (individual and consortia) to decolourise wastewater containing reactive azo, anthroquinone and triphenylmethane dyes either individually or mixed or with metal ions. It has been observed that bacteria Pseudomonas spp. are comparatively more effective to treat reactive dyes and metal-contaminated wastewater. In recent studies, either immobilised cell or isolated enzymes are being used to decolourise dye at a large scale of operations. However, it is required to investigate more potent bacterial species or consortia that could be used to treat wastewater containing mixed reactive dyes and heavy metals like chromium ions.

Fe–Al NANO-OXIDE PREPARED BY SOL–GEL METHOD USING PRECURSOR OF HCl DIGESTED LIQUID FRACTION OF LATERITE: ARSENIC ADSORPTION PERFORMANCE

Nanoparticle oxide of Fe–Al with surface area 68.9 m2/g and pore volume of 0.10–0.11 mL/g is synthesized using Fe–Al precursor obtained from HCl digested liquid fraction of laterite. Acid digestion of laterite is performed using solid acid ratio of 50 g raw laterite to 200 mL 6 N HCl. The liquid fraction is filtered through Whatman filter of grade 1 and 200 mL filtrate consists mainly of ~ 0.5 mol/L Fe and ~ 0.11 mol/L Al ions. Sol–gel method is used to prepare nano-oxide of Fe–Al. SEM, HRTEM and surface area analyzer are used for textural characterization of the nanoparticles. HRTEM micrograph indicates that sizes of prepared nanoparticles of Fe–Al oxide are in the range of 50 nm to 100 nm. In batch mode operation, 1.5 g/L adsorbent concentration is found to be capable to reduce the arsenic concentration of contaminated groundwater (collected from Dhobdhobi, Mallikpur, 24 Paraganas (s), West Bengal, India) from ~ 440 to ~ 11 μg/L. The Langmuir maximum capacities of As(V) and As(III) from synthetic solution and arsenic (as total) from contaminated groundwater on Fe–Al nano-oxide are obtained as 20.74 mg/g, 6.13 mg/g and 6.8 mg/g, respectively.