Studies on chromium(VI) adsorption-desorption using immobilized fungal biomass

Surface Modification of Naturally Available Biomass for Enhancement of Heavy Metal Removal Efficiency, Upscaling Prospects, and Management Aspects of Spent Biosorbents: A Review

Heavy metal pollution in water emerges as a severe socio-environmental problem originating primarily from the discharge of industrial wastewater. In view of the toxic, non-biodegradable, and persistent nature of most of the heavy metal ions, remediation of such components becomes an absolute necessity. Biosorption is an emerging tool for bioremediation that has gained momentum for employing low-cost biological materials with effective metal binding capacities. Even though biological materials possess excellent metal adsorption abilities, they show poor mechanical strength and low rigidity. Other disadvantages include solid-liquid separation problems, possible biomass swelling, lower efficiency for regeneration or reuse, and frequent development of high pressure drop in the column mode that limits its applications under real conditions. To improve the biosorption efficiency, biomasses need to be modified with a simple technique for selective/multi-metal adsorption. This review is intended to cover discussion on biomass modification for enhanced biosorption efficiency, mechanism studies using various instrumental/analytical techniques, and future direction for research and development including the fate of spent biosorbent. In most of the previously published researches, difficulty of the process in scaling up has not been addressed. The current article outlines the application potential of biosorbents in the development of hybrid technology integrated with membrane processes for water and wastewater treatment in industrial scale.

M. K. E. H. W, S. S. I, N. P, M. C. M. I. Fuchsine biosorption using Asplenium nidus biosorbent-a mechanism using kinetic and isotherm data

Adsorption is due to covalent and H bonding interactions between fuchsine molecules and functional groups of the adsorbent. Further π–π electron interactions between phenyl rings of the dye molecule and H bonds form multilayers of dye molecules.

Selective recovery of Pd(II) from extremely acidic solution using ion-imprinted chitosan fiber: Adsorption performance and mechanisms

A novel, selective and acid-resisting chitosan fiber adsorbent was prepared by the ion-imprinting technique using Pd(II) and epichlorohydrin as the template and two-step crosslinking agent, respectively. The resulting ion-imprinted chitosan fibers (IIF) were used to selectively adsorb Pd(II) under extremely acidic synthetic metal solutions. The adsorption and selectivity performances of IIF including kinetics, isotherms, pH effects, and regeneration were investigated. Pd(II) rapidly adsorbed on the IIF within 100 min, achieving the adsorption equilibrium. The isotherm results showed that the maximum Pd(II) uptake on the IIF was maintained as 324.6-326.4 mg g(-1) in solutions containing single and multiple metals, whereas the Pd(II) uptake on non-imprinted fibers (NIF) decreased from 313.7 to 235.3 mg g(-1) in solution containing multiple metals. Higher selectivity coefficients values were obtained from the adsorption on the IIF, indicating a better Pd(II) selectivity. The amine group, supposedly the predominant adsorption site for Pd(II), was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The pH value played a significant role on the mechanism of the selective adsorption in the extremely acidic conditions. Furthermore, the stabilized performance for three cycles of sorption/desorption shows a potential for further large-scale applications.

Is biosorption suitable for decontamination of metal-bearing wastewaters? A critical review on the state-of-the-art of biosorption processes and future directions

For the past few decades, biosorption has been widely investigated for the removal of different contaminants in aqueous media. A number of biomasses of different genre have been identified to possess good biosorption capacity. Insights into biosorption mechanisms have been provided by various researchers in order to develop a fundamental scientific understanding of the biosorption process. However, biosorption has not been employed widely for its large-scale commercial applications. The key factors that affect the growth and evolution of biosorption as a practical technology for decontamination of wastewaters include, (1) lack of investigations on multi-component solutions and wastewaters with complex matrix effects, (2) incomplete understanding of physico-chemical characteristics of biomasses of different types, (3) lack of studies to improve the performance of biosorbents through surface functionalization, and (4) non-integration of biosorption in wastewater/water treatment plants. This critical review aims to identify and discuss the practical limitations of biosorption and provide future research directions to make biosorption a technologically viable process with emphasis on selection and modification of biomasses to suit desired treatment applications, identify appropriate operation modes for large-scale applications of biosorption, and perform techno-economic evaluation of overall biosorption processes.

Fungal transformation of metallic lead to pyromorphite in liquid medium

Many approaches have been proposed to reduce the toxicity of hazardous substances such as lead in the environment. Several techniques using microorganisms rely on metal removal from solution by non-specific biosorption. However, immobilization of metals through formation of biominerals mediated by metabolic processes offers another solution but which has been given limited attention. In this work, we have investigated lead biomineralization by Paecilomyces javanicus, a fungus isolated from a lead-contaminated soil, in a liquid medium. P. javanicus was able to grow in the presence of metallic lead, supplied as lead shot, and secondary lead minerals were deposited on the lead surfaces as revealed by scanning electron microscopy. Energy dispersive X-ray analysis and X-ray powder diffraction revealed that pyromorphite was formed in the presence of the fungus, but not in abiotic controls. Our results clearly demonstrate that fungal activities can play an important role in lead biocorrosion and biomineralization in an aqueous environment. These findings are relevant to bioremediation approaches for liquid wastes contaminated with lead, or other metals, and also to the immobilization and biorecovery of rare or valuable elements. They also provide further understanding of microbial roles in environmental lead cycling.

Potential use of low-cost lignocellulosic waste for the removal of direct violet 51 from aqueous solution: equilibrium and breakthrough studies

An efficient biosorbent, sugarcane bagasse was used in native, HCl-treated, and Na-alginate immobilized form for the removal of Direct Violet 51 dye from aqueous solutions. Batch study was performed to optimize important process parameters, such as pH, contact time, biosorbent dose, initial dye concentration, and temperature. Removal of Direct Violet 51 was found to be favorable at pH 2 with the biosorbent dose of 0.05 g. Biosorption process was found to be exothermic in nature. Maximum dye biosorption (39.6 mg/g) was achieved by using HCl-treated biomass. The pseudo-second-order kinetic and Langmuir adsorption isotherm models showed best fitness to the experimental data. Thermodynamic study was also performed to determine the feasibility of biosorption process. Continuous mode study was performed to optimize the important process parameters, such as bed height, flow rate, and initial dye concentration for maximum removal of Direct Violet 51 dye. The higher bed height, low flow rate, and high initial dye concentration were found to be the better conditions for maximum dye biosorption (17.28 mg/g). The linearized form of the Thomas model equation fitted well to the experimental data. The bed depth service time model was used to express the effect of bed height on breakthrough curves. Characterization of biosorbent was performed by scanning electron microscopy and Fourier transform infrared (FT-IR) analysis. The FT-IR spectral analyses showed the involvement of hydroxyl, carbonyl, and carboxyl groups in biosorption process. These results indicated that sugarcane bagasse biomass could be used as a novel biosorbent for the removal of Direct Violet 51 dye from real textile and related industries.

Waste Material Adsorbents for Zinc Removal from Wastewater: A Comprehensive Review

This review examines a variety of adsorbents and discusses mechanisms, modification methods, recovery and regeneration, and commercial applications. A summary of available researches has been composed by a wide range of potentially low-cost modified adsorbents including activated carbon, natural source adsorbents (clay, bentonite, zeolite, etc.), biosorbents (black gram husk, sugar-beet pectin gels, citrus peels, banana and orange peels, carrot residues, cassava waste, algae, algal, marine green macroalgae, etc.), and byproduct adsorbents (sawdust, lignin, rice husk, rice husk ash, coal fly ash, etc.). From the literature survey, different adsorbents were compared in terms of Zn2+adsorption capacity; also Zn2+adsorption capacity was compared with other metals adsorption. Thus, some of the highest adsorption capacities reported for Zn2+are 168 mg/g powdered waste sludge, 128.8 mg/g dried marine green macroalgae, 73.2 mg/g lignin, 55.82 mg/g cassava waste, and 52.91 mg/g bentonite. Furthermore, modification of adsorbents can improve adsorption capacity. Regeneration cost is important, but if consumption of virgin adsorbent is reduced, then multiple economic, industrial, and environmental benefits can be gained. Finally, the main drawback of the already published Zn2+adsorption researches is that their use is still in the laboratory stage mostly without scale-up, pilot studies, or commercialization.

Biological removing of Cadmium from contaminated media by fungal biomass of Trichoderma species

BACKGROUND

Environment pollution by heavy metals is a global disaster and there are several cleaning methods including bioremediation. Trichoderma species inhibit the growth of pathogenic fungi and play a useful role in agriculture and ecosystem management.

METHODS

In this study, the removing of cadmium ions by three species of Trichoderma (T. asperellum, T. harzianum and T. tomentosum) were studied under different pH (5, 7, 9) and different concentrations of Cd (1, 100, 200 ppm) in liquid media containing potato extract and dextrose. Above mentioned fungal strains were cultured in the Cd-polluted media and the remaining amount of metal ions in the media was measured after two months growth, using atomic absorption.

RESULTS

Results showed that all three fungal species were able to reduce the amount of Cd in the all three pH of the medias; but their removal ability varies depending on the species and cultural conditions. T. asperellum was showed maximum removal efficiency of cadmium (76.17%), (10.75 mg/g, at fungal dry weight). Based on our results, the most removal efficiency of Cd ions for the fungal species was evaluated in the alkaline pH.

CONCLUSIONS

Trichoderma species are important fungi in decreasing of Cadmium ions. They have bioremediation potency under various pH and concentration conditions.

Synthesis and application of a unified sorbent for simultaneous preconcentration and determination of trace metal pollutants in natural waters

A flat sheet sorbent with poly(hydroxamic acid) groups anchored on the microporous structure of poly(propylene) membrane was developed and applied for the preconcentration and determination of heavy elements from natural waters. The designing of the sorbent involved UV-irradiation induced graft polymerization of acrylamide using N,N'-methylene-bis-acrylamide (MBA) as the crosslinker on the poly(propylene) base followed by chemical modification of the grafted membrane to generate crosslinked poly(hydroxamic acid) (PHA) groups in its pores. The synthesized PHA-membrane was found to preconcentrate U, V, Cu, Cr, Fe and Pb quantitatively (95%) from aqueous samples over a wide pH range of 4-9. The sorbed trace elements were quantified by direct analysis of the membrane using Energy Dispersive X-ray Fluorescence (EDXRF). To test the applicability of the developed sorbent to real samples, interference effect of common matrix elements like Na, K, Ca and Mg on the uptake of the analytes at sub μg mL(-1) level was studied. The PHA sorbent was found to be immune to interferences from Na, K and Mg up to 1000 μg mL(-1) and Ca up to 100 μg mL(-1) for an analyte concentration of 1 μg mL(-1). The method detection limit for EDXRF measurement was 6-30 ng using a 2 cm × 2 cm sorbent.

Plate column biosorption of Cu(II) on membrane-type biosorbent (MBS) of Penicillium biomass: optimization using statistical design methods

Based on the coupling of biosorption and membrane separation, a low cost membrane-type biosorbent (MBS) of Penicillium biomass was prepared. The surface morphology, pore properties and functional groups were studied via the characterization of MBS. Batch biosorption experiments indicated the maximum biosorption capacity of Cu(II) on MBS was 126.58 mg/g and about 90% of that on chitosan membrane. A plate column reactor filled with multi-layer of MBS was built for treatment of wastewater contaminated by Cu(II). The biosorption process factors were screened using Plackett-Burman design and three significant variables were selected for further optimization via response surface methodology (RSM) based on Box-Behnken model. A statistically second-order polynomial model was constructed with the error below 1.22%, on the basis of which the three-dimensional response surfaces were plotted. The prepared membrane-type biosorbent could be used successfully for 10 biosorption-desorption-regeneration cycles without decreasing its biosorption ability obviously.

Adsorptive removal of hazardous materials using metal-organic frameworks (MOFs): a review

Efficient removal of hazardous materials from the environment has become an important issue from a biological and environmental standpoint. Adsorptive removal of toxic components from fuel, waste-water or air is one of the most attractive approaches for cleaning technologies. Recently, porous metal-organic framework (MOF) materials have been very promising in the adsorption/separation of various liquids and gases due to their unique characteristics. This review summarizes the recent literatures on the adsorptive removal of various hazardous compounds mainly from fuel, water, and air by virgin or modified MOF materials. Possible interactions between the adsorbates and active adsorption sites of the MOFs will be also discussed to understand the adsorption mechanism. Most of the observed results can be explained with the following mechanisms: (1) adsorption onto a coordinatively unsaturated site, (2) adsorption via acid-base interaction, (3) adsorption via π-complex formation, (4) adsorption via hydrogen bonding, (5) adsorption via electrostatic interaction, and (6) adsorption based on the breathing properties of some MOFs and so on.

Removal of chromium (VI) from electroplating wastewater using an anion exchanger derived from rice straw

An anion exchanger from rice straw was used to remove Cr (VI) from synthetic wastewater and electroplating effluent. The exchanger was characterized using Fourier transform infrared (FTIR) spectrum and scanning electron microscopy (SEM), and it was found that the quaternary amino group and hydroxyl group are the main functional groups on the fibrous surface of the exchanger. The effect of contact time, initial concentration and pH on the removal of Cr (VI), and adsorption isotherms at different temperature, was investigated. The results showed that the removal of Cr (VI) was very rapid and was significantly affected by the initial pH of the solution. Although acidic conditions (pH = 2-6) facilitated Cr (VI) adsorption, the exchanger was effective in neutral solution and even under weak base conditions. The equilibrium data fitted well with Langmuir adsorption model, and the maximum Cr (VI) adsorption capacities at pH 6.4 were 0.35, 0.36 and 0.38 mmol/g for 15, 25 and 35 degrees C, respectively. The exchanger was finally tested with real electroplating wastewater, and at sorbent dosage of 10 g/L, the removal efficiencies for Cr (VI) and total Cr were 99.4% and 97.8%, respectively. In addition, the positive relationship between adsorbed Cr (VI) and desorbed Cl- suggested that Cr (VI) was mainly removed by ion exchange with chlorine.

A green strategy for desorption of trihalomethanes adsorbed by humin and reuse of the fixed bed column

The objective of the present work was to develop a thermal desorption method for the removal of trihalomethanes (THM) adsorbed by humin, followed by multiple recycling of the fixed bed column in order to avoid excessive consumption of materials and reduce operating costs. The results obtained for adsorption on a fixed bed column confirmed the effectiveness of humin as an adsorbent, extracting between 45.9% and 90.1% of the total THM (TTHM). In none of the tests was the column fully saturated after 10h. Experiments involving thermal desorption were used to evaluate the potential of the technique for column regeneration. The adsorptive capacity of the humin bed increased significantly (p<0.05) between the first and fifth desorption cycle, by 18.9%, 18.1%, 24.2%, 20.2% and 24.2% for CHBr(3), CHBr(2)Cl, CHBrCl(2), CHCl(3) and TTHM, respectively.

Reutilization of immobilized fungus Rhizopus sp. LG04 to reduce toxic chromate

AIMS

Most of the researches investigating immobilized fungi in chromate [Cr(VI)] bioremediation have used dead cells to adsorb Cr(VI). Therefore, the aim was to identify a Cr(VI)-reducing fungus with the ability of reducing the toxic Cr(VI) into the much less toxic Cr(III) and to apply the immobilized living fungus in continual reduction of Cr(VI).

METHODS AND RESULTS

Cr(VI) reduction occurred using both free fungi and immobilized living Rhizopus sp. LG04. The Cr(VI) bioreduction by the free fungi was achieved mainly by bioreduction coupled with a small amount of biosorption on the cell surfaces. LG04 spores immobilized with 3% polyvinyl alcohol and 3% sodium alginate produced the most stable and efficient biobeads. When the LG04 biobeads were washed and transferred into fresh medium containing 42 mg l(-1) of Cr(VI), the biobeads could be reused to reduce Cr(VI) for more than 30 cycles during an 82-day operation period. Interestingly, as the cycles increased, the time required for complete reduction stabilized at approximately 2·5 days, which was faster than that obtained using the free fungi (4·5 days). The pH value of the solution decreased from 6·60 ± 0·10 to 3·85 ± 0·15 after each reduction cycle, which may be because the metabolic products of the fungus changed the environmental pH or because there was an accumulation of the organo-Cr(III) complex.

CONCLUSIONS

The results indicate that using the immobilized living fungus for the removal of Cr(VI) has the advantages in being stable, long-term treatment, easy to re-use and less biomass leakage.

SIGNIFICANCE AND IMPACT OF THE STUDY

To our knowledge, this study reports the first successful use of immobilized living Rhizopus for the repeated reduction of Cr(VI).

High-capacity adsorption of hexavalent chromium from aqueous solution using magnetic microspheres by surface dendrimer graft modification

The magnetic poly-(methyl acrylate-divinyl benzene) (MA-DVB) microspheres with micron size were synthesized by modified suspension polymerization method. Through stepwise reaction with methyl acrylate (MA) and ethylenediamine (EDA), the magnetic poly-(MA-DVB) microspheres with surface dendrimer containing amino groups were obtained. The above mentioned magnetic microspheres were applied for the adsorption of hexavalent chromium from aqueous solution. The effects of solution pH value, adsorption temperature, and adsorption and desorption of Cr(VI) were studied. The results showed that the optimum pH value for Cr(VI) adsorption was found at pH=3, and the adsorption capacity increased with the increase in adsorption temperature. The adsorption equilibrium of Cr(VI) was obtained in about 12 min and more than 98% of adsorbed Cr(VI) were desorbed from the magnetic microspheres in about 30 min using Na(2)SO(4) solution. By fitting the experimental data to Langmuir equation, the maximum capacity for Cr(VI) of magnetic poly-(MA-DVB) microspheres was estimated at 231.8 mg/g.

An integrated approach to remove Cr(VI) using immobilized Chlorella minutissima grown in nutrient rich sewage wastewater

The potential of an integrated system for sewage wastewater treatment and biosorption of chromium(VI) was evaluated using immobilized Chlorella minutissima cells. Immobilized algal cells were grown in sewage wastewater in designed photobioreactor for 48 h and then subjected to removal of Cr(VI) from synthetic wastewater. The effect of pH, Cr(VI) concentration, biosorbent dose on Cr(VI) removal was investigated. C. minutissima showed a higher NH(4)(+)-N and PO(4)(3-)-P removal efficiency (above 99% removal) than the NO(3)(2-)-N (58% removal) in 48 h. Biosorption of Cr(VI) was found to be highly dependent on solution pH, biosorbent dose and initial Cr(VI) concentration. Maximum Cr(VI) uptake 57.33 mg Cr(VI)/g dry biosorbent/L of solution was observed at pH2 with 20% (w/v) biosorbent. Further more than 90% of total Cr adsorbed could be recovered using 0.5 M NaOH as desorption medium.

Biosorption Potential ofTrichoderma gamsiiBiomass for Removal of Cr(VI) from Electroplating Industrial Effluent

The potential use of acid-treated biomass ofTrichoderma gamsiito remove hexavalent chromium ions from electroplating industrial effluent was evaluated. Electroplating industrial effluent contaminated with 5000 mg/L of Cr(VI) ions, collected from industrial estate of Gujarat, India, was mixed with acid-treated biomass ofT. gamsiiat biomass dose of 10 mg/mL. Effect of contact time and initial Cr(VI) ions was studied. The biosorption of Cr(VI) ions attained equilibrium at time interval of 240 minutes with maximum removal of 87% at preadjusted initial Cr(VI) concentration of 100 mg/L. The biosorption of Cr(VI) ions by biomass ofT. gamsiiincreased as the initial Cr(VI) ion concentration of the effluent was adjusted in increasing range of 100–500 mg/L. At 500 mg/L, initial Cr(VI) concentration, acid-treated biomass ofT. gamsiishowed maximum biosorption capacity of 44.8 mg/g biomass from electroplating effluent. The Cr(VI) biosorption data were analysed using adsorption isotherms, that is, Freundlich and Langmuir isotherm. The correlation regression coefficients (R2) and isotherm constant values show that the biosorption process follows Freundlich isotherm (R2>0.9,n>1, andKf=8.3). The kinetic study shows that biosorption of Cr(VI) ions by acid-treated biomass ofT. gamsiifollows pseudo-second-order rate of reaction at increasing concentration of Cr(VI). In conclusion, acid-treated biomass ofT. gamsiican be used as biosorbent for Cr(VI) ions removal from Cr(VI)-contaminated wastewater generated by industries.

The Study of Bioremediation on Heavy Metal of Cultured Seawater by Sphingomonas sp. XJ2 Immobilized Sphingomonas Strain

In this study, the bacterium was identified as Sphingomonas sp. XJ2 by means of microscopic examination, physiological, biochemical detection, and modern molecular biology technology. After acclimatization for several times, this bacterium has good performance in removing heavy metals and organic matter from seawater. Alginate immobilized cells has obvious holes on the surface and has big specific surface area, which are conducive to the adsorption of metal ions. Hydration heat of Pb2+ is small, and is most likely to drop out of ligand water then become exposed Pb2+; in addition, the ionic radius of Pb2+ and is very similar to the ball K+ and is adsorbed by the ball easily. FTIR and XPS study indicated that Pb (II) was complexed by C-H and C-O bonds. The concentration of Pb(Ⅱ)of mine wastewater reach the first class of irrigation water quality standards after the first time of adsorption treatment, and reach the first class of fishery water quality standard after the second treatment. 1． Introduction Mine waste water mainly comes from mine production, the main pollutants including heavy metals, acid, organic pollutants, oil pollutants, cyanide, fluoride and soluble salts and so on. Heavy metal pollution and acid pollution are the most common water pollutions, the mainly heavy metals from wastewater are lead, zinc, nickel, copper, mercury, chromium, cadmium, cobalt, manganese, titanium, vanadium and bismuth. Hazards of mine waste water including environmental degradation and toxic to organisms; mine waste water contains heavy metal ions and other metal ions, through infiltration, percolation and runoff channels walk into the environment, then pollute water. After precipitation, absorption, complexation, chelation and redox, migrate and change in the water, and ultimately affect human health and aquatic growth. Heavy metals and metalloids and other pollutants in wastewater once enter the water environment, they can not be biodegradable, but by precipitation - dissolution, oxidation - reduction, coordinate effect, colloid formation effect, adsorption - desorption process and a series of physical and chemical migration transformation, which will eventually as one or more form stay in the environment for a long term, causing permanent potentially damage [1]. How to prevent non-ferrous metal mine waste water polluting water and farmland is one of the current problems which arising large public attention. Traditional treat methods of heavy metal waste water are chemical precipitation, ion exchange, evaporation and electrolysis, etc., these methods have disadvantages of high investment and operating costs, precipitation removal is not satisfactory, and could easily lead to secondary pollution and other defects. Since 1980s, people began to turn to research microbial treatment of heavy metal waste water, and found that microbial treatment of wastewater had advantages of low cost, effective and no secondary pollution. The economical and ecological feasibility of biosorption processes depend on the biosorbent metal uptake capacity to reach metal concentration legal limits for wastewater discharge and the ability of eluants to release sequestered metal in subsequent recovery [2-4]. Recovery allows metal recycling, leading to energy savings and materials conservation[5]. Finally, biosorbent regeneration used in multiple adsorption–desorption cycles [6], contributes to process cost effectiveness. Living cells have so broad assortment of mechanisms for surviving in environment that have elevated metal concentrations, including transport and intracellular and extracellular sequestration .The active process of metal accumulation by cells is usually referred to as bioaccumulation, while the passive metal sequestration by cell components is generally called biosorption. The physicochemical basis for metal sequestration at the cell surface may include complexation, coordination, chelation, ion exchange, adsorption, and inorganic microprecipitation processes. Bacteria make excellent biosorbents because of their high surface-to-volume ratios. Metal-binding behaviour has been evaluated on the basis of bacterial cell Gram reaction for viable cells and cell walls and envelopes. In this study, we conducted separation domesticated culture to Sphingomonas sp. XJ2 and used them to treat waste water preliminarily. Establishing an efficient, cheap, adaptable and easy to operate way of treating non-ferrous metal mine wastewater is a new development.

Enhanced removal of trace Cr(VI) ions from aqueous solution by titanium oxide-Ag composite adsorbents

Titanium oxide-Ag composite (TOAC) adsorbents were prepared by a facile solution route with Ag nanoparticles being homogeneously dispersed on layered titanium oxide materials. The as-synthesized TOAC exhibited a remarkable capability for trace Cr(VI) removal from an aqueous solution, where the concentration of Cr(VI) could be decreased to a level below 0.05 mg/L within 1h. We have systematically investigated the factors that influenced the adsorption of Cr(VI), for example, the pH value of the solution, and the contact time of TOAC with Cr(VI). We found that the adsorption of Cr(VI) was strongly pH-dependent. The adsorption behavior of Cr(VI) onto TOAC fitted well the Langmuir isotherm and a maximum adsorption capacity of Cr(VI) as 25.7 mg/g was achieved. The adsorption process followed the pseudo-second-order kinetic model, which implied that the adsorption was composed of two steps: the adsorption of Cr(VI) ions onto TOAC followed by the reduction of Cr(VI) to Cr(III) by Ag nanoparticles. Our results revealed that TOAC with high capacity of Cr(VI) removal had promising potential for wastewater treatment.

Biological removal of arsenic pollution by soil fungi

Fifteen fungal strains were isolated from arsenic contaminated (range 9.45-15.63 mg kg(-1)) agricultural soils from the state of West Bengal, India. Five fungal strains were belonged to the Aspergillus and Trichoderma group each, however, remaining five were identified as the Neocosmospora, Sordaria, Rhizopus, Penicillium and sterile mycelial strain. All these fungal strains were cultivated on medium supplemented with 100, 500, 1000, 5000 and 10,000 mg l(-1) of sodium arsenate. After 30-day cultivation under laboratory conditions, radial growth of these strains was determined and compared with control. Toxicity and tolerance of these strains to arsenate were evaluated on the basis of tolerance index. Out of fifteen, only five fungal strains were found resistant and survived with tolerance index pattern as 0.956 (sterile mycelial strain)>0.311 (Rhizopus sp.)>0.306 (Neocosmospora sp.)>0.212 (Penicillium sp.)>0.189 (Aspergillus sp.) at 10,000 mg l(-1) of arsenate. The arsenic removal efficacy of ten fungal strains, tolerant to 5000 mg l(-1) arsenate, was also assayed under laboratory conditions for 21 days. All these strains were cultivated individually on mycological broth enriched with 10 mg l(-1) of arsenic. The initial and final pH of cultivating medium, fungal biomass and removal of arsenic by each fungal strain were evaluated. Fungal biomass of ten strains removed arsenic biologically from the medium which were ranged from 10.92 to 65.81% depending on fungal species. The flux of biovolatilized arsenic was determined indirectly by estimating the sum of arsenic content in fungal biomass and medium. The mean percent removal as flux of biovolatilized arsenic ranged from 3.71 to 29.86%. The most effective removal of arsenic was observed in the Trichoderma sp., sterile mycelial strain, Neocosmospora sp. and Rhizopus sp. fungal strains. These fungal strains can be effectively used for the bioremediation of arsenic-contaminated agricultural soils.

Removal of chromium on Polyalthia longifolia leaves biomass

Adsorption is an environmental friendly process for removal and/or recovery of heavy metals from wastewater. In recent years, it has been substantiated as a popular technique to treat industrial waste effluents, with significant advantages. In this work, batchwise removal of chromium (III) ions from water by Polyalthia longifolia leaves was studied as a function of adsorbent dose, pH, contact time, and agitation speed. Surface characteristics of the leaves were evaluated by recording IR spectra. The Langmuir, Freundlich, and Temkin adsorption isotherms were employed to explain the sorption process. It was found that one gram of leaves can remove 1.87 mg of trivalent chromium when working at pH 3.0. It has been concluded that Polyalthia longifolia leaves can be used as cost-effective and benign adsorbents for removal of Cr(III) ions from wastewater.

Fungal biosorption--an alternative to meet the challenges of heavy metal pollution in aqueous solutions

The removal of heavy metal from the environment, especially wastewater, is now shifting from the use of conventional methods to the use of biosorption, which may be defined as the binding and concentration of selected heavy metal ions or other molecules on to certain biological material. Although most biosorption research concerns metal and related pollutants, including radionuclides, the term is now applied for particulates and all manner of organic pollutants as well. Such pollutants can be in gaseous, soluble and insoluble forms. Biosorption is a physical process carried out through mechanisms such as ion exchange, surface complexation and precipitation. It is a property of both living and dead organisms (and their components) and has been heralded as a promising biotechnology for pollutant removal from solution. Various biomasses such as plant products (tree bark, peanut skin, sawdust, plant weeds etc.) have been tested for metal biosorption with very encouraging results. In this comprehensive review, biosorptive ability of fungal biomass toward heavy metals is emphasized. A detailed description of adsorption properties and mode of action of fungal biosorbents is offered in order to explain the heavy metal selectivity displayed by these biosorbents. The cell structure and cell wall of the fungal cell is evaluated in terms of metal sequestration. The parameters influencing the passive uptake of pollutants are analysed. The binding mechanism is discussed, including the key functional groups involved in the process. Quantification of metal-biomass interactions is fundamental to evaluation of potential implementation strategies; hence sorption isotherms and sorption kinetics, as well as models used to characterize fungal biosorbent sorption, are reviewed. Despite the continuing dramatic increase in published research on biosorption, there has been little or no exploitation in an industrial context. Thus, the current status and future directions regarding biosorption at an industrial level are discussed. A systematic comparative review of the literature, based on the metal-binding capacity of fungal biomass under different conditions, is also provided. The problems associated with fungal biosorption are analysed and suitable remedies are discussed. Thus, this article reviews the achievements and current status of fungal biosorption technology and hopes to provide insights into future research.

Surface-modified Phanerochaete chrysosporium as a biosorbent for Cr(VI)-contaminated wastewater

To improve the removal efficiency of heavy metals from wastewater, the surface of a fungal biomass was modified to obtain a high-capacity biosorbent for Cr(VI) in wastewater. The effects of pH, initial concentration, and sorption time on Cr(VI) removal by polyethylenimine (PEI)-modified Phanerochaete chrysosporium were investigated. The biomass adsorption capacity was significantly dependent on the pH of the solution, and the optimum pH was approximately 3.0. The maximum removal for Cr(VI) was 344.8 mg/g as determined with the Langmuir adsorption isotherm. Pseudo-first-order Lagergren model is better than pseudo-second-order Lagergren model when simulating the kinetic experiment results. Furthermore, an amount of Cr(VI) was reduced to Cr(III), indicating that some reactions occurred on the surface of the biomass leading to the reduction of Cr(VI). The point of zero potential for the modified biomass increased from an initial pH of 3.0 to a much higher value of 10.8, indicating that the PEI-modified biomass is better than the pristine biomass for adsorption of anionic adsorbates. Results showed that the PEI-modified biosorbent presented high efficiency in treating Cr(VI)-contaminated wastewater.

Bioremediation of heavy metals in liquid media through fungi isolated from contaminated sources

Wastewater particularly from electroplating, paint, leather, metal and tanning industries contain enormous amount of heavy metals. Microorganisms including fungi have been reported to exclude heavy metals from wastewater through bioaccumulation and biosorption at low cost and in eco-friendly way. An attempt was, therefore, made to isolate fungi from sites contaminated with heavy metals for higher tolerance and removal of heavy metals from wastewater. Seventy-six fungal isolates tolerant to heavy metals like Pb, Cd, Cr and Ni were isolated from sewage, sludge and industrial effluents containing heavy metals. Four fungi (Phanerochaete chrysosporium, Aspegillus awamori, Aspergillus flavus, Trichoderma viride) also were included in this study. The majority of the fungal isolates were able to tolerate up to 400 ppm concentration of Pb, Cd, Cr and Ni. The most heavy metal tolerant fungi were studied for removal of heavy metals from liquid media at 50 ppm concentration. Results indicated removal of substantial amount of heavy metals by some of the fungi. With respect to Pb, Cd, Cr and Ni, maximum uptake of 59.67, 16.25, 0.55, and 0.55 mg/g was observed by fungi Pb3 (Aspergillus terreus), Trichoderma viride, Cr8 (Trichoderma longibrachiatum), and isolate Ni27 (A. niger) respectively. This indicated the potential of these fungi as biosorbent for removal of heavy metals from wastewater and industrial effluents containing higher concentration of heavy metals.

Reversible removal of SO2 at low temperature by Bacillus licheniformis immobilized on γ-Al2O3

Bacillus licheniformis R08 biomass was immobilized on γ-Al2O3 and the effects of R08 biomass loading, SO2 concentration, water vapor, oxygen and temperature on removal of SO2 were investigated. The experimental results indicated that SO2 saturation capacity increased with increasing R08 biomass loading and SO2 concentration, but decreased with increasing adsorption temperature. Water vapor activated the adsorbent and promoted SO2 removal. An increase in oxygen concentration from 5 to 10% had little effect on SO2 removal. FTIR analysis revealed that the R08 biomass bound to γ-Al2O3 mainly by forming R-CO-O-Al bonds. X-ray photoelectron spectroscopy analysis indicated that γ-Al2O3 reacted with SO2 and formed aluminum sulfate in the presence of oxygen when R08 biomass loading was 13.8%, but that amido groups of the R08 biomass reacted with SO2 and formed sulfite when biomass loading was 32.4%. Ten continuous adsorption-desorption cycles showed that the adsorbent had an excellent regeneration performance.

Arsenic accumulating and transforming bacteria isolated from contaminated soil for potential use in bioremediation

Arsenic (As) is a metalloid and considered harmful due to its toxic and carcinogenic effects. Removal of arsenic is of great importance for human welfare. The main objective of this study was to isolate arsenic-resistant bacteria that are capable of removing arsenic from the environment. Soil samples were collected from an arsenic-affected area of West Bengal, India and 10 different bacterial strains were isolated. The minimum inhibitory concentration (MIC) values of the isolates varied widely in the range 50-125 mM (As) as arsenate and 10-100 mM (As) as arsenite. TEM and EDAX analysis were done to confirm intracellular accumulation of arsenic. The 16s RNA and phylogenetic analysis showed that seven isolates belonged to γ-proteobacterium, two isolates belonged to Firmicutes and one was identified as Kocuria genera. Some of these bacteria could oxidize arsenite to arsenate and all others could reduce arsenate to arsenite. The growth pattern of the bacterial strains in presence and absence of arsenic was also observed. All the 10 isolates exhibited multiple heavy metal (like Ni, Zn, Cu, Pb, Co, etc.) tolerances. Thus, these new bacterial strains could conveniently be used for bioremediation of soil and effluents and the enzymes produced by them may be used for commercial exploitation.

Adsorption of surfactant micelles and Cd2+/Zn2+ in micellar-enhanced ultrafiltration

Micellar-enhanced ultrafiltration (MEUF) is a powerful treatment developed to remove heavy metals from wastewater. Efficient removal of Cd(2+)/Zn(2+) from wastewater was performed by MEUF using a polysulfone hollow ultrafiltration membrane, with sodium dodecyl sulfate (SDS) as the surfactant. The adsorption of surfactant micelles and Cd(2+)/Zn(2+) in MEUF was studied by changing the surfactant dosage and the Cd(2+)/Zn(2+) concentration in the feed. In addition, kinetics, adsorption isotherms, and thermodynamic rules were analyzed, and X-ray photoelectron spectroscopy (XPS) was conducted. It was found that when the Cd(2+)/Zn(2+) feed concentration was 50 mg/L, and the SDS dosage reached 2.15 g/L, the concentration of heavy metal ions in the permeate stabilized at around 1-4 mg/L, and the adsorption of Cd(2+)/Zn(2+) on SDS micelles followed second-order kinetics and the Langmuir isotherm laws. Adsorption is a spontaneous endothermic process in which the adsorption force is principally the attraction of opposite electrical charges.