Specific Treatment Technologies for Removing Arsenic from Water

Arsenic (As) is a highly toxic metalloid found in ground and surface water. Arsenic contamination in drinking water leads to harmful effects on human health. To eliminate arsenic from drinking water, several technologies such as coagulation, adsorption, ion exchange, filtration, membrane processes, etc., have been used. In this study, three technologies were evaluated for arsenic removal. Results from batch kinetic experiments showed that iron coated sand (IOCS‐2) can remove more than 90 % of As from synthetic water. Experiments were conducted with three different pH values (6, 7, and 8) and an initial As concentration of 260 μg/L. A new material, developed in this study, namely iron coated sponge (IOCSp), was found to have a high capacity in removing both As (V) and As (III). Each gram of IOCSp adsorbed about 160 μg of As within a 9‐hour contact period of IOCSp with As solution. Low pressure nanofiltration removed more than 94 % of As from an influent containing 440 μg/L As. The applied pressure was varied from 85 to 500 kPa.     

Arsenic resistance and removal by marine and non-marine bacteria

Arsenic resistance and removal was evaluated in nine bacterial strains of marine and non-marine origins. Of the strains tested, Marinomonas communis exhibited the second-highest arsenic resistance with median effective concentration (EC(50)) value of 510 mg As l(-1), and was capable of removing arsenic from culture medium amended with arsenate. Arsenic accumulation in cells amounted to 2290 microg As g(-1) (dry weight) when incubated on medium containing 5 mg As l(-1) of arsenate. More than half of the arsenic removed was related to metabolic activity: 45% of the arsenic was incorporated into the cytosol fraction and 10% was found in the lipid-bound fraction of the membrane, with the remaining arsenic considered to be adsorbed onto the cell surface. Potential arsenic resistance and removal were also examined in six marine and non-marine environmental water samples. Of the total bacterial colony counts, 28-100% of bacteria showed arsenic resistance. Some of the bacterial consortia, especially those from seawater enriched with arsenate, exhibited higher accumulated levels of arsenic than M. communis under the same condition. These results showed that arsenic resistant and/or accumulating bacteria are widespread in the aquatic environment, and that arsenic-accumulating bacteria such as M. communis are potential candidates for bioremediation of arsenic contaminated water.     

Arsenic hazards: strategies for tolerance and remediation by plants

Arsenic toxicity has become a global concern owing to the ever-increasing contamination of water, soil and crops in many regions of the world. To limit the detrimental impact of arsenic compounds, efficient strategies such as phytoremediation are required. Suitable plants include arsenic hyperaccumulating ferns and aquatic plants that are capable of completing their life cycle in the presence of high levels of arsenic through the concerted action of arsenate reduction to arsenite, arsenite complexation, and vacuolar compartmentalization of complexed or inorganic arsenic. Tolerance can also be conferred by lowering arsenic uptake by suppression of phosphate transport activity, a major pathway for arsenate entry. In many unicellular organisms, arsenic tolerance is based on the active removal of cytosolic arsenite while limiting the uptake of arsenate. Recent molecular studies have revealed many of the gene products involved in these processes, providing the tools to improve crop species and to optimize phytoremediation; however, so far only single genes have been manipulated, which has limited progress. We will discuss recent advances and their potential applications, particularly in the context of multigenic engineering approaches.     

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.     

Removal of inorganic anions from drinking water supplies by membrane bio/processes

This paper is designed to provide an overview of the main membrane-assisted processes that can be used for the removal of toxic inorganic anions from drinking water supplies. The emphasis has been placed on integrated process solutions, including the emerging issue of membrane bioreactors. An attempt is made to compare critically recently reported results, reveal the best existing membrane technologies and identify the most promising integrated membrane bio/processes currently being under investigation. Selected examples are discussed in each case with respect to their advantages and limitations compared to conventional methods for removal of anionic pollutants. The use of membranes is particularly attractive for separating ions between two liquid phases (purified and concentrated water streams) because many of the difficulties associated with precipitation, coagulation or adsorption and phase separation can be avoided. Therefore, membrane technologies are already successfully used on large-scale for removal of inorganic anions such as nitrate, fluoride, arsenic species, etc. The concentrated brine discharge and/or treatment, however, can be problematic in many cases. Membrane bioreactors allow for complete depollution but water quality, insufficiently stable process operation, and economical reasons still limit their wider application in drinking water treatment. The development of more efficient membranes, the design of cost-effective operating conditions, especially long-term operations without or with minimal membrane inorganic and/or biological fouling, and reduction of the specific energy consumption requirements are the major challenges.     

Resistance to Arsenic- and Antimony-Based Drugs

Organic arsenicals were the first antimicrobial agents specifically synthesized for the treatment of infectious diseases such as syphilis and sleeping sickness. For the treatment of diseases caused by trypanosomatid parasites, organic derivatives of arsenic and the related metalloid antimony are still the drugs of choice. Arsenic trioxide, As203, has been used for a long time in traditional Chinese medicines for treatment of various diseases, and it has recently been shown to be clinically active in acute promyelocytic leukemias. Resistance to metalloid salts is found in bacteria, fungi, parasites and animals. In some organisms, resistance involves overproduction of intracellular thiols. In many cases, resistance to arsenic salts is the result of removal of the metalloid from the cytosol usually by extrusion from the cell. In eukaryotes resistance to arsenic and antimony is conferred by membrane transport proteins of the MRP family. The human MRP1, a member of this family, is frequently amplified in cancer cells and it is well-documented that MRPl-overexpressing cells poorly accumulate arsenic and antimony because of enhanced cellular effiux which depends on the presence of GSH.     

Co-mutagenic activity of arsenic and benzo[a]pyrene in mouse skin

Exposure to inorganic arsenic in drinking water is linked to skin, lung and bladder cancer in humans. The mechanism of arsenic-induced cancer is not clear, but exposure to arsenic and polycyclic arylhydrocarbons (PAH) is more carcinogenic than exposure to either type of carcinogen alone. Arsenic can also generate reactive oxygen species, suggesting that oxidation of DNA may play a role in carcinogenesis. Oxidization of guanosines in polyG tracts is known to cause frameshift mutations, and such events can be detected in situ using the G11 placental alkaline phosphatase (PLAP) transgenic mouse model, which reports frameshift mutations in a run of 11 G:C basepairs by generating cells containing heat-resistant alkaline phosphatase activity. PAH can also induce frameshift mutations. In the study described here, FVB/N mice carrying the G11 PLAP transgene were crossed to C57Bl/6 mice. Half of the hybrid mice were given drinking water with sodium arsenite (10 mg/L) for 10 weeks. Half of the arsenic treated mice were also exposed to benzo[a]pyrene (BaP) by skin painting (500 nmol/week) for 8 weeks. Another group of mice was exposed to BaP but not arsenic. The effect on frameshift mutation was assessed by staining sections of skin tissue to detect cells with PLAP activity. Arsenic alone had no significant effect. On average, mice given BaP alone had approximately three times more PLAP-positive (PLAP+) cells. By contrast, mice exposed to both arsenic and BaP exhibited 10-fold more PLAP+ cells in the skin, and these cells were often arranged in large clusters, suggesting derivation from stem cells. Whereas combined treatment produced more PLAP+ cells, stable BaP adduct levels and arsenic burdens were not higher in mice exposed to both agents compared to mice exposed to either one agent or the other.     

Arsenic and weight loss: At a crossroad between lipogenesis and lipolysis

Arsenic is found in soil, food, water and earth crust. Arsenic exposure is associated with chronic diseases such as cancer, cardiovascular disease as well as diabetes. One of complex effects of arsenic is on weight gain or loss. Involvement of arsenic in both weight loss and gain signaling pathways has previously been reported; however, too little attention has been paid to its weight reducing effect. Animal studies exhibited a role of arsenic in weight loss. In this regard, arsenic interference with endocrine system, leptin and adiponectin hormones as well as thermogenesis is more evidence. Apparently, arsenic-induced weight lossis generally meditated by its interaction with thermogenesis. In this review we have discussed the irregularities in metabolic pathways induced by arsenic that can lead to weight loss.     

Phytoremediation of an arsenic-contaminated site using Pteris vittata L.: a two-year study

A field study was conducted to determine the efficiency of Chinese brake fern (Pteris vittata L.), an arsenic hyperaccumulator, on removal of arsenic from soil at an arsenic-contaminated site. Chinese brake ferns were planted on a site previously used to treat wood with chromated copper arsenate (CCA). Arsenic concentrations in surface and profile soil samples were determined for 2000, 2001, and 2002. In both 2001 and 2002, senesced and senescing fronds only, as well as all fronds, were harvested. Frond arsenic concentrations were not significantly different between the three harvests. Compared to senesced fronds, live fronds resulted in the greatest amount of arsenic removal. There were no significant differences in soil arsenic concentrations between 2000, 2001, and 2002, primarily due to the extreme variability in soil arsenic concentrations. However, the mean surface soil arsenic was reduced from 190 to 140 mg kg(-1). Approximately 19.3 g of arsenic were removed from the soil by Chinese brake fern. Therefore, this fern is capable of accumulating arsenic from the CCA -contaminated site and may be competitive, in terms of cost, to conventional remediation systems. However, better agronomic practices are needed to enhance plant growth and arsenic uptake to obtain maximum soil arsenic removal and to minimize remediation time.     

Integration of aerobic granular sludge and membrane bioreactors for wastewater treatment

Environmental deterioration together with the need for water reuse and the increasingly restrictive legislation of water quality standards have led to a demand for compact, efficient and less energy consuming technologies for wastewater treatment. Aerobic granular sludge and membrane bioreactors (MBRs) are two technologies with several advantages, such as small footprint, high-microbial density and activity, ability to operate at high organic- and nitrogen-loading rates, and tolerance to toxicity. However, they also have some disadvantages. The aerobic granular sludge process generally requires post-treatment in order to fulfill effluent standards and MBRs suffer from fouling of the membranes. Integrating the two technologies could be a way of combining the advantages and addressing the main problems associated with both processes. The use of membranes to separate the aerobic granules from the treated water would ensure high-quality effluents suitable for reuse. Moreover, the use of granular sludge in MBRs has been shown to reduce fouling. Several recent studies have shown that the aerobic granular membrane bioreactor (AGMBR) is a promising hybrid process with many attractive features. However, major challenges that have to be addressed include how to achieve granulation and maintain granular stability during continuous operation of reactors. This paper aims to review the current state of research on AGMBR technology while drawing attention to relevant findings and highlight current limitations.     

LIVE AND DEAD SPIRULINA SP. TO REMOVE ARSENIC (V) FROM WATER

Arsenic (As)-contaminated water is a grave health hazard and its removal from water poses a great challenge. Conventional methods are associated with many shortcomings. Biosorption of arsenic using blue-green algae is an interesting alternative to conventional methods. In this article, the results of the biosorption of As(V) as AsO₄ ^{? 3} by live and dead Spirulina sp. are reported. The sorption of arsenic could be explained satisfactorily both by the Freundlich and the Langmuir isotherms. The maximum sorption capacities of live and dead Spirulina were estimated to be 525 and 402mg/g, respectively. These values are high in comparison with those reported for other arsenic sorbents. The sorption kinetics of arsenic by both live and dead Spirulina sp. could be well modeled by Lagergrens pseudosecond order-rate equation. Infrared spectra have been employed to understand how Spirulina sp. binds with arsenate. Scanning electron micrography and fluorescent microscopic images are used to discuss the extent of uptake. Preferential uptake of Cu(II), Ni(II), Cd(II), and AsO₄ ^?3 by live Spirulina sp. was investigated and explained with the help of rate constants for sorption.     

Microbial transformation of elements: the case of arsenic and selenium

Microbial activity is responsible for the transformation of at least one third of the elements in the periodic table. These transformations are the result of assimilatory, dissimilatory, or detoxification processes and form the cornerstones of many biogeochemical cycles. Arsenic and selenium are two elements whose roles in microbial ecology have only recently been recognized. Known as "essential toxins", they are required in trace amounts for growth and metabolism but are toxic at elevated concentrations. Arsenic is used as an osmolite in some marine organisms while selenium is required as selenocysteine (i.e. the twenty-first amino acid) or as a ligand to metal in some enzymes (e.g. FeNiSe hydrogenase). Arsenic resistance involves a small-molecular-weight arsenate reductase (ArsC). The use of arsenic and selenium oxyanions for energy is widespread in prokaryotes with representative organisms from the Crenarchaeota, thermophilic bacteria, low and high G+C gram-positive bacteria, and Proteobacteria. Recent studies have shown that both elements are actively cycled and play a significant role in carbon mineralization in certain environments. The occurrence of multiple mechanisms involving different enzymes for arsenic and selenium transformation indicates several different evolutionary pathways (e.g. convergence and lateral gene transfer) and underscores the environmental significance and selective impact in microbial evolution of these two elements. Electronic Publication     

Environmental hazards of arsenic associated with black shales: a review on geochemistry, enrichment and leaching mechanism

Black shales are high organic matter-rich dark coloured mudstones those are often deposited during ??oceanic anoxia events??. Most of the black shale horizons are rich in arsenic far above their average crustal abundance and are susceptible to weathering eventually leaching high As contents to the surrounding environment causing As enrichment in soil and water which adversely affect the living beings. Numerous arsenic contaminations are being reported from black shale hosted areas globally, hence, making extremely crucial to understand the processes of enrichment, leaching and broader prospective of environmental hazards. Few studies have shown arsenic concentrations as high as 6,000?mg/kg within black shales causing groundwater enrichment up to hundreds mg/L. Arsenic is commonly attached to sulphide mineral structure and partly to organic matter and clay contents during deposition and diagenetic processes. Majority of sulphide bound arsenic becomes available to oxidative dissolution processes in presence of atmospheric oxygen and water which is further triggered by certain microbial community such as Acidophilus ferrooxidans hence, enhancing arsenic release. Physical weathering processes carry the arsenic-rich shale constituents to the depositional site where it is dissolved subsequently. Chemical diffusion and mechanical transport are two prime processes transporting arsenic from black shale horizons to the water bodies or soil columns, while air pollutions are caused by combustions of organic matter-rich coaly shales.     

Arsenic exposure and cancer risk reduction with local ordinance requiring whole-house dual-tank water treatment systems

Arsenic, a known human carcinogen, occurs naturally in groundwater in New Jersey and many other states and countries. A number of municipalities in the Piedmont, Highlands, and Valley and Ridge Physiographic Provinces of New Jersey have a high proportion of wells that exceed the New Jersey maximum contaminant level (MCL) of 5 µg/L. Hopewell Township, located in Mercer County and the Piedmont Province, has a progressive local ordinance which requires the installation of dual-tank, point-of-entry treatment systems on affected wells. This provided a unique study opportunity. Of the 55 homes with dual-tank POE treatment systems recruited into this study, 51 homes (93%) had arsenic levels under the MCL at the kitchen sink, regardless of years in service and/or maintenance schedule adherence. Based on the study participants’ water consumption and arsenic concentrations, we estimate that Hopewell's arsenic water treatment ordinance, requiring POE dual-tank arsenic treatment, reduced the incidence of excess lifetime (70-year) bladder and lung cancers from 121 (1.7 cancer cases/year) to 16 (0.2 cancer cases/year) preventing 105 lifetime cancer cases (1.5 cases/year). Because the high risk of cancer from arsenic can be mitigated with effective arsenic water treatment systems, this ordinance should be considered a model for other municipalities.     

Arsenic and fluoride removal by potato peel and rice husk (PPRH) ash in aqueous environments

Finding appropriate adsorbent may improve the quality of drinking water in those regions where arsenic (As) and fluoride (F^?) are present in geological formations. In this study, we evaluated the efficiency of potato peel and rice husk ash (PPRH-ash)-derived adsorbent for the removal of As and F from contaminated water. Evaluation was done in batch adsorption experiments, and the effect of pH, initial adsorbate concentration, contact time, and adsorbent dose were studied. Characteristics of adsorbents were analyzed using scanning electron micropcope (SEM) and Fourier transform infrared (FTIR) spectroscopy. Both the Langmuir and Freundlich isotherm models fitted well for F^? and As sorption process. The maximum adsorption capacity of adsorbent for As and F^? was 2.17 μg g^?1 and 2.91 mg g^?1, respectively. The As and Fi removal was observed between pH 7 and 9. The sorption process was well explained with pseudo-second order kinetic model. Arsenic adsorption was not decreased in the presence of carbonate and sulfate. Results from this study demonstrated potential utility of this agricultural biowaste, which could be developed into a viable filtration technology for As and F^? removal in As- and F-contaminated water streams.     

Arsenic release and attenuation in low organic carbon aquifer sediments from West Bengal

High arsenic concentrations in groundwater are causing a humanitarian disaster in Southeast Asia. It is generally accepted that microbial activities play a critical role in the mobilization of arsenic from the sediments, with metal‐reducing bacteria stimulated by organic carbon implicated. However, the detailed mechanisms underpinning these processes remain poorly understood. Of particular importance is the nature of the organic carbon driving the reduction of sorbed As(V) to the more mobile As(III), and the interplay between iron and sulphide minerals that can potentially immobilize both oxidation states of arsenic. Using a multidisciplinary approach, we identified the critical factors leading to arsenic release from West Bengal sediments. The results show that a cascade of redox processes was supported in the absence of high loadings of labile organic matter. Arsenic release was associated with As(V) and Fe(III) reduction, while the removal of arsenic was concomitant with sulphate reduction. The microbial populations potentially catalysing arsenic and sulphate reduction were identified by targeting the genes arrA and dsrB, and the total bacterial and archaeal communities by 16S rRNA gene analysis. Results suggest that very low concentrations of organic matter are able to support microbial arsenic mobilization via metal reduction, and subsequent arsenic mitigation through sulphate reduction. It may therefore be possible to enhance sulphate reduction through subtle manipulations to the carbon loading in such aquifers, to minimize the concentrations of arsenic in groundwaters.     

Bacterial metabolism of environmental arsenic—mechanisms and biotechnological applications

Arsenic causes threats for environmental and human health in numerous places around the world mainly due to its carcinogenic potential at low doses. Removing arsenic from contaminated sites is hampered by the occurrence of several oxidation states with different physicochemical properties. The actual state of arsenic strongly depends on its environment whereby microorganisms play important roles in its geochemical cycle. Due to its toxicity, nearly all organisms possess metabolic mechanisms to resist its hazardous effects, mainly by active extrusion, but also by extracellular precipitation, chelation, and intracellular sequestration. Some microbes are even able to actively use various arsenic compounds in their metabolism, either as an electron donor or as a terminal electron acceptor for anaerobic respiration. Some microorganisms can also methylate inorganic arsenic, probably as a resistance mechanism, or demethylate organic arsenicals. Bioavailability of arsenic in water and sediments is strongly influenced by such microbial activities. Therefore, understanding microbial reactions to arsenic is of importance for the development of technologies for improved bioremediation of arsenic-contaminated waters and environments. This review gives an overview of the current knowledge on bacterial interactions with arsenic and on biotechnologies for its detoxification and removal.     

Batch and continuous removal of arsenic using hyacinth roots

Arsenic is considered a primary pollutant in drinking water because of its high toxicity. The unique property of water hyacinth roots (Eichhornia crassipes) to remove heavy metals is of great signiicance for the development of a cost-effective phytoremediation technology. An experimental test program was conducted at the United States Environmental Protection (USEPA) Test and Evaluation (T&E) Facility in Cincinnati, Ohio, to investigate the potential of water hyacinth roots to remove arsenic from spiked drinking water samples. Water hyacinth roots were washed, dried, and powdered to provide dried hyacinth roots (DHR) for batch and continuous column experiments, Various quantities of DHR were added to water spiked with 300 micrograms per liter (microg/L) arsenic. A concentration of 20 g/L DHR was found adequate for greater than 90% arsenic removal in the batch tests. Based on the batch test results, continuous column experiments were performed using a 2-L column. In a continuous system, 15 L of water containing 300 microg/L arsenic were treated to below 20 microg/L using 50 g DHR, and 44 L of water containing 600 microg/L arsenic were treated to below 20 microg/L using 100 g DHR, giving a specific accumulation rate of approximately 260 microg As/g DHR.     

Recent advances in membrane bio-technologies for sludge reduction and treatment

This paper is designed to critically review the recent developments of membrane bio-technologies for sludge reduction and treatment by covering process fundamentals, performances (sludge reduction efficiency, membrane fouling, pollutant removal, etc.) and key operational parameters. The future perspectives of the hybrid membrane processes for sludge reduction and treatment are also discussed. For sludge reduction using membrane bioreactors (MBRs), literature review shows that biological maintenance metabolism, predation on bacteria, and uncoupling metabolism through using oxic-settling-anaerobic (OSA) process are promising ways that can be employed in full-scale applications. Development of control methods for worm proliferation is in great need of, and a good sludge reduction and MBR performance can be expected if worm growth is properly controlled. For lysis-cryptic sludge reduction method, improvement of oxidant dispersion and increase of the interaction with sludge cells can enhance the lysis efficiency. Green uncoupler development might be another research direction for uncoupling metabolism in MBRs. Aerobic hybrid membrane system can perform well for sludge thickening and digestion in small- and medium-sized wastewater treatment plants (WWTPs), and pilot-scale/full-scale applications have been reported. Anaerobic membrane digestion (AMD) process is a very competitive technology for sludge stabilization and digestion. Use of biogas recirculation for fouling control can be a powerful way to decrease the energy requirements for AMD process. Future research efforts should be dedicated to membrane preparation for high biomass applications, process optimization, and pilot-scale/full-scale tracking research in order to push forward the real and wide applications of the hybrid membrane systems for sludge minimization and treatment.     

Multi-faceted strategy based on enzyme immobilization with reactant adsorption and membrane technology for biocatalytic removal of pollutants: A critical review

In the modern era, the use of sustainable, environmentally friendly alternatives for removal of recalcitrant pollutants in streams resulting from industrial processes is of key importance. In this context, biodegradation of phenolic compounds, pharmaceuticals and dyes in wastewater by using oxidoreductases offers numerous benefits. Tremendous research efforts have been made to develop novel, hybrid strategies for simultaneous immobilization of oxidoreductase and removal of toxic compounds. The use of support materials with the options for combining enzyme immobilization with adsorption technology focused on phenolic pollutants and products of biocatalytic conversion seems to be of particular interest. Application of enzymatic reactors based on immobilized oxidoreductases for coupling enzyme-aided degradation and membrane separation also attract still growing attention. However, prior selection of the most suitable support/sorbent material and/or membrane as well as operational mode and immobilization technique is required in order to achieve high removal efficiency. Thus, in the framework of this review, we present an overview of the impact of support/sorbent material on the catalytic properties of immobilized enzymes and sorption of pollutants as well as parameters of membranes for effective bioconversion and separation. Finally, future perspectives of the use of processes combining enzyme immobilization and sorption technology as well as application of enzymatic reactors for removal of environmental pollutants are discussed.