Ashok K. Gupta

Fluoride in Drinking Water: A Review on the Status and Stress Effects

‘Water is life,’ so central to human life, yet over one billion people across the world have no access to safe drinking water. Of late, there has been increasing global attention focused on resolving water quality problems especially in developing countries, as the lack of access to clean water denies the most essential of all rights, the right to life. The latest estimates suggest that around 200 million people, from among 25 nations the world over, are under the dreadful fate of fluorosis. India and China, the two most populous countries of the world, are the worst affected. India is plagued with numerous water quality problems due to prolific contaminants mainly of geogenic origin and fluoride stands first among them. The weathering of primary rocks and leaching of fluoride-containing minerals in soils yield fluoride rich groundwater in India which is generally associated with low calcium content and high bicarbonate ions. The unfettered ground water tapping exacerbates the failure of drinking water sources and accelerates the entry of fluoride into groundwater. Most of the scientific literature substantiates the benefits of low fluoride concentrations in preventing dental decay. However, as a surprising paradox, incidence of dental, skeletal and crippling skeletal fluorosis was reported in India with average fluoride concentrations as low as 0.5, 0.7 and 2.8 ppm respectively. Fluorosis, turns out to be the most widespread geochemical disease in India, affecting more than 66 million people including 6 million children under 14 years age. Though fluoride has spread its tentacles in 36,988 habitations and the number of people falling prey to fluoride poisoning have been steadily increasing, an exact exposure-health relationship is yet to be properly elucidated. There is an essential relation between poverty and fluorosis as malnutrition is found to play an aggressive role in its severity.

A Conceptual Overview on Sustainable Technologies for the Defluoridation of Drinking Water

Water is precious to us, as it supports every spheres of human life. The increasing reports on pollution of this “sacred resource” from different sources show our scant regard to this pivotal issue. People in more than 35 nations across the globe face issues of excess fluoride in drinking water, the intensity and severity of which varies with the environmental settings in terms of their geographical and economical status. It has been observed that very few proven sustainable options are available for fluoride removal, especially in developing countries, where the impact of the issue is highly intense. Though the considerable amount of research undertaken worldwide has thrown up many technologies, each having its own advantages and limitations, a lasting solution is still at large. The coagulation and adsorption/ion-exchange processes are the most widely opted defluoridation techniques practiced in fluoride-endemic areas. The Nalgonda technique and adsorption by bone char, or a combination of both, have been used in many developing countries like India and Tanzania, at both domestic and community levels. The membrane processes assure good quality water, but are “higher technology and higher cost” options for most of the fluoride-endemic nations. Electrochemical techniques are “energy-intensive” options but offer excellent fluoride removal. However, the lack of concise conceptual reviews is visibly felt in defluoridation research, which prompted us to carry out this study. This article highlights the underlying basic principles and processes involved in existing fluoride removal technologies so as to catalyze further research in this area.

Optimization of photocatalytic degradation of methyl blue using silver ion doped titanium dioxide by combination of experimental design and response surface approach.

Photocatalytic degradation of methyl blue (MYB) was studied using Ag(+) doped TiO(2) under UV irradiation in a batch reactor. Catalytic dose, initial concentration of dye and pH of the reaction mixture were found to influence the degradation process most. The degradation was found to be effective in the range catalytic dose (0.5-1.5g/L), initial dye concentration (25-100ppm) and pH of reaction mixture (5-9). Using the three factors three levels Box-Behnken design of experiment technique 15 sets of experiments were designed considering the effective ranges of the influential parameters. The results of the experiments were fitted to two quadratic polynomial models developed using response surface methodology (RSM), representing functional relationship between the decolorization and mineralization of MYB and the experimental parameters. Design Expert software version 8.0.6.1 was used to optimize the effects of the experimental parameters on the responses. The optimum values of the parameters were dose of Ag(+) doped TiO(2) 0.99g/L, initial concentration of MYB 57.68ppm and pH of reaction mixture 7.76. Under the optimal condition the predicted decolorization and mineralization rate of MYB were 95.97% and 80.33%, respectively. Regression analysis with R(2) values >0.99 showed goodness of fit of the experimental results with predicted values.

A comparison of water quality indices for coastal water.

Abstract The present article discusses and compares five different water quality indices, viz arithmetic water quality index, multiplicative water quality index, unweighted arithmetic water quality index, unweighted multiplicative water quality index, and Harkins water quality index, which were considered for characterizing the coastal water quality at the Jawaharlal Nehru Port Trust, Bombay, India. Dissolved oxygen, pH, biochemical oxygen demand (BOD), temperature, suspended solid, and turbidity were used as the parameters of water quality indices. The value function graphs used for above-mentioned variables were developed using harbour water quality standards and aquatic life. The product moment correlation coefficients for various water quality indices were determined using the SPSS software package to evaluate correlation among various indices. It was found that the unweighted arithmetic water quality index was higher than weighted arithmetic water quality index while the multiplicative water quality index was lower than unweighted multiplicative water quality index. All the indices were well correlated with each other except Harkins water quality index. The Harkins water quality index was different from other water quality indices. The comparison of different form of indices showed that the multiplicative water quality index was the most suitable water quality index for coastal waters.

Sorption Kinetics of As(V) with Iron-Oxide-Coated Cement–A New Adsorbent and its Application in the Removal of Arsenic from Real-Life Groundwater Samples

In the search of alternative adsorbents for the removal of arsenic, a new adsorbent (iron-oxide coated cement) was examined under various conditions to evaluate its suitability in removing As(V). A removal of more than 99% was obtained within 2 h for an initial As(V) concentration of 1 mg/L. Kinetic studies showed a removal which became somewhat constant after 2 h. Thorough investigations to understand the mechanism of solute adsorption onto the new sorbent with the help of four kinetic models, viz. ∼ first-order reversible kinetics model, pseudo-first-order kinetic model, second-order kinetic model, and pseudo-second-order kinetic model showed that the sorption kinetics is consistent with the pseudo-second-order model from which it can be inferred that the mechanism of adsorption is chemical interaction or chemisorption. The equilibrium data followed the Langmuir isotherm at low concentrations of As(V) (≤4 mg/L), but followed the Freundlich isotherm over a wide range of concentrations (0.5–10 mg/L) which can be due to solid solution precipitation. Studies on the effect of pH on As(V) removal revealed somewhat constant (∼95%) As(V) removal over a wide pH range of 4–10. The efficiency of this adsorbent was also checked for the removal of arsenic from three real ground water samples containing both As(III) and As(V) with total arsenic in the range of 0.33–1.2 mg/L. The total arsenic removal was 71%, 87% and 75% for the samples containing 0.33, 0.88 and 1.2 mg/L total arsenic, respectively at the same adsorbent dose of 3 g/L. However, increasing the adsorbent dose will enhance removal capacity. Investigations of these real samples with the four kinetic models revealed most reliable fit with the pseudo-second order model. However, good fit was also obtained with the other three models. Values of the diffusion coefficients calculated from the first order kinetics data, indicated that, film diffusion is the rate limiting step for each of the three real life groundwater samples.

Photocatalytic degradation of methylene blue dye from aqueous solution using silver ion-doped TiO2 and its application to the degradation of real textile wastewater

Methylene blue dye (MB) was degraded photocatalytically in aqueous solution using Ag+ doped TiO2 under UV irradiation. The degradations of the dye using untreated TiO2 and Ag+ doped TiO2 were compared. Ag+ doped TiO2 was found to be more efficient. Using Ag+ doped TiO2 the filtration process was eliminated, as the particles became more settleable. The effect of various parameters such as catalyst loading, initial dye concentration, depth of solution, degree of adsorption, pH and O2 on dye degradation was studied. The extent of mineralization was studied by observing the COD removal at different time intervals. The effects of various interfering ions such as Cl−, NO3 −, CO3 2−, SO4 2−, Ca2+ and Fe3+ and electron acceptors such as H2O2, KBrO3 and (NH4)2S2O8 on the dye degradation was also studied. The degradation kinetics fitted well to Langmuir-Hinshelwood pseudo first order rate law. An aqueous solution of MB (20ppm) degraded by more than 99% after UV irradiation for 180 min with Ag+ doped TiO2 (2 g/L) and by more than 95% with untreated TiO2 (2 g/L). The COD removal was more than 91% with Ag+doped TiO2 and more than 86% with untreated TiO2 after 240 min. The degradation and COD removal of 5 times diluted textile wastewater was more than 98% and 79% respectively with 1 g/L Ag+ doped TiO2 after UV irradiation for 420 min.

Diversity, metabolic properties and arsenic mobilization potential of indigenous bacteria in arsenic contaminated groundwater of West Bengal, India.

Arsenic (As) mobilization in alluvial aquifers is caused by a complex interplay of hydro-geo-microbiological activities. Nevertheless, diversity and biogeochemical significance of indigenous bacteria in Bengal Delta Plain are not well documented. We have deciphered bacterial community compositions and metabolic properties in As contaminated groundwater of West Bengal to define their role in As mobilization. Groundwater samples showed characteristic high As, low organic carbon and reducing property. Culture-independent and -dependent analyses revealed presence of diverse, yet near consistent community composition mostly represented by genera Pseudomonas, Flavobacterium, Brevundimonas, Polaromonas, Rhodococcus, Methyloversatilis and Methylotenera. Along with As-resistance and -reductase activities, abilities to metabolize a wide range carbon substrates including long chain and polyaromatic hydrocarbons and HCO3, As3+ as electron donor and As5+/Fe3+ as terminal electron acceptor during anaerobic growth were frequently observed within the cultivable bacteria. Genes encoding cytosolic As5+ reductase (arsC) and As3+ efflux/transporter [arsB and acr3(2)] were found to be more abundant than the dissimilatory As5+ reductase gene arrA. The observed metabolic characteristics showed a good agreement with the same derived from phylogenetic lineages of constituent populations. Selected bacterial strains incubated anaerobically over 300 days using natural orange sand of Pleistocene aquifer showed release of soluble As mostly as As3+ along with several other elements (Al, Fe, Mn, K, etc.). Together with the production of oxalic acid within the biotic microcosms, change in sediment composition and mineralogy indicated dissolution of orange sand coupled with As/Fe reduction. Presence of arsC gene, As5+ reductase activity and oxalic acid production by the bacteria were found to be closely related to their ability to mobilize sediment bound As. Overall observations suggest that indigenous bacteria in oligotrophic groundwater possess adequate catabolic ability to mobilize As by a cascade of reactions, mostly linked to bacterial necessity for essential nutrients and detoxification.

A comprehensive risk assessment framework for offsite transportation of inflammable hazardous waste

A framework for risk assessment due to offsite transportation of hazardous wastes is designed based on the type of event that can be triggered from an accident of a hazardous waste carrier. The objective of this study is to design a framework for computing the risk to population associated with offsite transportation of inflammable and volatile wastes. The framework is based on traditional definition of risk and is designed for conditions where accident databases are not available. The probability based variable in risk assessment framework is substituted by a composite accident index proposed in this study. The framework computes the impacts due to a volatile cloud explosion based on TNO Multi-energy model. The methodology also estimates the vulnerable population in terms of disability adjusted life years (DALY) which takes into consideration the demographic profile of the population and the degree of injury on mortality and morbidity sustained. The methodology is illustrated using a case study of a pharmaceutical industry in the Kolkata metropolitan area.

Size Distribution of Atmospheric Aerosols in Kolkata, India and the Assessment of Pulmonary Deposition of Particle Mass

Aerosol size distributions were measured at three stations in Kolkata city, during December 2003 to February 2004 using an 8-stage cascade impactor with a back-up filter. Hi-volume samplers were used at the 3 sites for measuring PM2.5 and PM10 concentration. The results showed that the total average number distributed in the size range of 0 to 10 μ m for particulates of size Dp could be represented as a Junge distribution dN/d log(Dp) = 1282.6 (Dp) − 3.803. Aerosol mass distribution by size showed that of the collected fractions most of the PM10 were in the size range of 0 ≤ Dp ≤ 0.43 μ m (15.73%) followed by 0.65 ≤ Dp ≤ 1.1 μ m (15.72%) and then 0.43 ≤ Dp ≤ 0.65 μ m (14.73%). Particle size distributions were trimodal with fine mode Dp ≤ 1.1 μ m (MMAD = 0.51 μ m, GSD = 2.15), medium mode 1.1 ≤ Dp ≤ 4.7 μ m (MMAD = 2.53 μ m, GSD = 1.54) and coarse mode 4.7 ≤ Dp ≤ 10 μ m (MMAD = 8.16 μ m, GSD = 1.38). Average concentrations of PM2.5 and PM10 were in the range of 96.31–363.63 μ gám − 3and 140.50–637.70 μ gám −3, respectively. Correlation analysis showed that the highest correlation (0.91) was observed between the particle ranges of 9.0–10.0 μ m and 3.3–4.7 μ m followed by 0.89 between 9.0–10.0 and 5.8–9.0 μ m. Regression analysis showed that PM2.5 was about 60% of PM10 concentration. A widely used ICRP model was used to estimate pulmonary deposition. The result showed that 36% of deposited PM10 was accumulated in the alveolar region and nearly 49% of deposited PM10 was accumulated in the tracheobronchial region.

Arsenic biotransformation and release by bacteria indigenous to arsenic contaminated groundwater

Arsenic (As) biotransformation and release by indigenous bacteria from As rich groundwater was investigated. Metabolic landscape of 173 bacterial isolates indicated broad catabolic repertoire including abundance of As(5+) reductase activity and abilities in utilizing wide ranges of organic and inorganic respiratory substrates. Abundance of As homeostasis genes and utilization of hydrocarbon as carbon/electron donor and As(5+) as electron acceptor were noted within the isolates. Sediment microcosm study (for 300 days) showed a pivotal role of metal reducing facultative anaerobic bacteria in toxic As(3+) release in aqueous phase. Inhabitant bacteria catalyze As transformation and facilitate its release through a cascade of reactions including mineral bioweathering and As(5+) and/or Fe(3+) reduction activities. Compared to anaerobic incubation with As(5+) reducing strains, oxic state and/or incubation with As(3+) oxidizing bacteria resulted in reduced As release, thus indicating a strong role of such condition or biocatalytic mechanism in controlling in situ As contamination.