Arsenic removal from water/wastewater using adsorbents—A critical review

The contamination of groundwater by arsenic in Bangladesh is the largest poisoning of a population in history, with millions of people exposed. This paper describes the history of the discovery of arsenic in drinking-water in Bangladesh and recommends intervention strategies. Tube-wells were installed to provide ‘‘pure water’’ to prevent morbidity and mortality from gastrointestinal disease. The water from the millions of tube-wells that were installed was not tested for arsenic contamination. Studies in other countries where the population has had long-term exposure to arsenic in groundwater indicate that 1 in 10 people who drink water containing 500mg of arsenic per litre may ultimately die from cancers caused by arsenic, including lung, bladder and skin cancers. The rapid allocation of funding and prompt expansion of current interventions to address this contamination should be facilitated. The fundamental intervention is the identification and provision of arsenic-free drinking water. Arsenic is rapidly excreted in urine, and for early or mild cases, no specific treatment is required. Community education and participation are essential to ensure that interventions are successful; these should be coupled with follow-up monitoring to confirm that exposure has ended. Taken together with the discovery of arsenic in groundwater in other countries, the experience in Bangladesh shows that groundwater sources throughout the world that are used for drinking-water should be tested for arsenic.

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Contamination of drinking-water by arsenic in Bangladesh: a public health emergency

http://ntur.lib.ntu.edu.tw/bitstream/246246/175878/1/19.pdf

Application of factor analysis in the assessment of groundwater quality in a blackfoot disease area in Taiwan

Arsenic is a metalloid whose name conjures up images of murder. Nonetheless, certain prokaryotes use arsenic oxyanions for energy generation, either by oxidizing arsenite or by respiring arsenate. These microbes are phylogenetically diverse and occur in a wide range of habitats. Arsenic cycling may take place in the absence of oxygen and can contribute to organic matter oxidation. In aquifers, these microbial reactions may mobilize arsenic from the solid to the aqueous phase, resulting in contaminated drinking water. Here we review what is known about arsenic-metabolizing bacteria and their potential impact on speciation and mobilization of arsenic in nature.

https://science.sciencemag.org/content/sci/300/5621/939.full.pdf

The Ecology of Arsenic

The contamination of ground waters, abstracted for drinking and irrigation, by sediment-derived arsenic threatens the health of tens of millions of people worldwide, most notably in Bangladesh and West Bengal1,2,3. Despite the calamitous effects on human health arising from the extensive use of arsenic-enriched ground waters in these regions, the mechanisms of arsenic release from sediments remain poorly characterized and are topics of intense international debate4,5,6,7,8. We use a microscosm-based approach to investigate these mechanisms: techniques of microbiology and molecular ecology are used in combination with aqueous and solid phase speciation analysis of arsenic. Here we show that anaerobic metal-reducing bacteria can play a key role in the mobilization of arsenic in sediments collected from a contaminated aquifer in West Bengal. We also show that, for the sediments in this study, arsenic release took place after Fe(iii) reduction, rather than occurring simultaneously. Identification of the critical factors controlling the biogeochemical cycling of arsenic is one important contribution to fully informing the development of effective strategies to manage these and other similar arsenic-rich ground waters worldwide.

Role of metal-reducing bacteria in arsenic release from Bengal delta sediments

The natural contamination of drinking water by arsenic needs to be urgently addressed. The pollution by naturally occurring arsenic of alluvial Ganges aquifers, which are used for the public water supply in Bangladesh and West Bengal, has been discussed by Nickson
 et al.1. We agree with their main conclusion that arsenic is released by reductive dissolution of iron oxyhydroxides, as was proposed earlier2. Our observations indicate that arsenic- rich pyrite and other arsenic minerals, which were proposed in previous models (cited by Nickson et al.1) to give rise to arsenic pollution, are rare or even absent in the sediments of the Ganges delta. We believe that arsenic is more likely to be co-precipitated with or scavenged by iron (III) and manganese (IV) in the sedimentary environment.

Arsenic poisoning in the Ganges delta

Surfactants above their critical micelle concentration can solubilize hydrophobic contaminants into their micelles This process enhances the apparent solubility of contaminants such as hydrocarbon

Biodegradation Kinetics of Phenanthrene Partitioned into the Micellar Phase of Nonionic Surfactants

The apparent solubility of polycyclic aromatic hydrocarbon compounds such as phenanthrene can be increased in the presence of surfactants above their critical micelle concentration. A fraction of the phenanthrene partitioned into the micellar phase of some nonionic surfactants can be directly bioavailable to phenanthrene-degrading microorganisms. A model describing the biodegradation of the directly bioavailable micellar-phase substrate is presented. The hypothesis on which the model is based considers the following steps:  (a) the contaminant is transported by filled micelles from the bulk solution to the proximity of the cells; (b) the exchange of the filled micelle with the hemimicellar layer around the cell delivers the contaminant to the cell; (c) the contaminant diffuses into the cell and is biodegraded. The biodegradation kinetics were explained in terms of a series of mass-transfer processes, which lead to a similar equation as the Monod kinetics. The theoretically derived expression, describing t...

Bioavailability of Hydrophobic Compounds Partitioned into the Micellar Phase of Nonionic Surfactants

The aim of this mini-review is to synthesize and analyze information on how the process of granulation is affected by environmental and operational conditions in the reactor. The factors reviewed are temperature, pH, alkalinity, organic loading rate, upflow velocity, nature and strength of substrate, nutrients, multivalent cations and heavy metals, microbial ecology of seed sludge, exo-cellular polymer, and addition of natural and synthetic polymers. Careful temperature control and adequate alkalinity is required for generation and maintenance of granules. Nature and strength of substrate in conjunction with intra-granular diffusion to a large extent determines the microstructure of the granules. The divalent cations such as calcium and iron may enhance granulation by ionic bridging and linking exo-cellular polymers. However, their presence in excess may lead to cementation due to precipitation leading to increased ash content and mass transfer limitation. The addition of external additives such as ionic polymers may enhance granulation in the upflow anaerobic sludge blanket reactors.

Influence of extrinsic factors on granulation in UASB reactor.

Enhanced solubilization of naphthalene, phenanthrene, and pyrene in micellar solutions of Triton X-100 was studied for single compounds and their binary and ternary mixtures. Experimental results were obtained for the following conditions:  (i) naphthalene, phenanthrene, and pyrene as single compounds at saturation; (ii) naphthalene, phenanthrene, and pyrene as binary and ternary mixtures at satura tion; (iii) phenanthrene at saturation in a range of naphthalene concentrations; (iv) pyrene at saturation in a range of naphthalene concentrations. The solubility enhancement of naphthalene was slightly reduced in the presence of phenanthrene and/or pyrene. A synergistic effect on the solubilization of phenanthrene was observed in the presence of different amounts of naphthalene. The solubility of phenanthrene was greatly enhanced in both binary mixtures and in the ternary mixture. The solubility of pyrene was slightly reduced in the presence of naphthalene, remained unaffected in the presence of phenanthrene,...

Saumyen Guha

Papers

Arsenic poisoning in the Ganges delta

Biodegradation Kinetics of Phenanthrene Partitioned into the Micellar Phase of Nonionic Surfactants

Bioavailability of Hydrophobic Compounds Partitioned into the Micellar Phase of Nonionic Surfactants

Influence of extrinsic factors on granulation in UASB reactor.

Solubilization of PAH Mixtures by a Nonionic Surfactant