Removal of heavy metal ions from wastewater by chemically modified plant wastes as adsorbents: a review

The application of low-cost adsorbents obtained from plant wastes as a replacement for costly conventional methods of removing heavy metal ions from wastewater has been reviewed. It is well known that cellulosic waste materials can be obtained and employed as cheap adsorbents and their performance to remove heavy metal ions can be affected upon chemical treatment. In general, chemically modified plant wastes exhibit higher adsorption capacities than unmodified forms. Numerous chemicals have been used for modifications which include mineral and organic acids, bases, oxidizing agent, organic compounds, etc. In this review, an extensive list of plant wastes as adsorbents including rice husks, spent grain, sawdust, sugarcane bagasse, fruit wastes, weeds and others has been compiled. Some of the treated adsorbents show good adsorption capacities for Cd, Cu, Pb, Zn and Ni.     

A review on economically adsorbents on heavy metals removal in water and wastewater

Heavy metals contamination in water has been an issue to the environment and human health. The persisting contamination level has been observed and concerned by the public due to continuous deterioration of water quality. On the other hand, conventional treatment system could not completely remove the toxic metals in the water, thus alternative purification methods using inexpensive materials were endeavor to improve the current treatment process. Wide ranges of low cost adsorbents were used to remove heavy metal in aqueous solution and wastewater. The low cost adsorbents were usually collected from agricultural waste, seafood waste, food waste, industrial by-product and soil. These adsorbents are readily available in a copious amount. Besides, the pretreatment are not complicated to be conducted on the raw products, which is economically sound for an alternative treatment. The previous studies have provided much evidence of low cost adsorbents’ efficiency in removing metal ions from aqueous solution or wastewater. In this review, several low cost adsorbents in the recent literature have been studied. The maximum adsorption capacity, affecting factors such as pH, contact times, temperature, initial concentration and modified materials were revised and summarized in this review for further reference. Comparisons of the adsorbent between the modified and natural products were also demonstrated to provide a clear understanding on the kinetic uptake of the selected adsorbents. Some of the natural adsorbents appeared as good heavy metal removal, while some were not and require further modifications and improvements to enhance the adsorption capacity. SWOT analysis (strength, weakness, opportunities, threat) was also performed on the low cost adsorbents to identify the advantages of using low cost adsorbents and solve the weaknesses encountered by the utilization of low cost materials. This tool helps to determine the potential quality of low cost materials in the application for water and wastewater treatment.     

Process chromatography: current constraints and future options for the adsorptive recovery of bioproducts

A contemporary review of adsorption chromatography must embrace aspects of fixed-bed, batch suspension and fluidised-bed contacting of complex feedstocks with adsorbents chemically derivatised with ligands with binding specificities for target bioproducts. Advances in the design of adsorbents, ligands and contactors have facilitated opportunities for integrated processing of unclarified feedstocks to benefit purity and yield of macromolecular products. In the face of competition from apparently simpler, yet productive, technologies (e.g. precipitation, crystallisation and aqueous solvent extraction), further advances in chromatographic purification of macromolecules and nanoparticulates demand close collaboration between inventors and/or manufacturers of new products and the suppliers of chromatographic hardware and consumables.     

Synergistic Removal of Pb(II), Cd(II) and Humic Acid by Fe3O4@Mesoporous Silica-Graphene Oxide Composites

The synergistic adsorption of heavy metal ions and humic acid can be very challenging. This is largely because of their competitive adsorption onto most adsorbent materials. Hierarchically structured composites containing polyethylenimine-modified magnetic mesoporous silica and graphene oxide (MMSP-GO) were here prepared to address this. Magnetic mesoporous silica microspheres were synthesized and functionalized with PEI molecules, providing many amine groups for chemical conjugation with the carboxyl groups on GO sheets and enhanced the affinity between the pollutants and the mesoporous silica. The features of the composites were characterized using TEM, SEM, TGA, DLS, and VSM measurements. Series adsorption results proved that this system was suitable for simultaneous and efficient removal of heavy metal ions and humic acid using MMSP-GO composites as adsorbents. The maximum adsorption capacities of MMSP-GO for Pb(II) and Cd (II) were 333 and 167 mg g⁻¹ caculated by Langmuir model, respectively. HA enhances adsorption of heavy metals by MMSP-GO composites due to their interactions in aqueous solutions. The underlying mechanism of synergistic adsorption of heavy metal ions and humic acid were discussed. MMSP-GO composites have shown promise for use as adsorbents in the simultaneous removal of heavy metals and humic acid in wastewater treatment processes.     

Removal of fluoride from aqueous solution by TiO2 and TiO2–SiO2 nanocomposite

Adsorption plays an important role in the removal of pollutants such as fluoride from aqueous solutions. With the rapid development of environmental technology, TiO₂ particle has become promising material to adsorb fluoride ion because of its low cost, non-toxic, good chemical stability, and good sorption ability. This work used sol-gel and hydrothermal synthesis methods to prepare TiO₂ particles and load them onto SiO₂ particles. The physicochemical properties such as heat stability, particle size, and surface area of the resulting TiO₂ adsorbents were characterized with various analytical methods. In addition, their adsorption abilities to fluoride were determined under various conditions including different initial fluoride concentration, pH and coexisting ions. The maximum adsorption capacity of the TiO₂ adsorbents can reach up to 94.3 mg/g. The adsorption isotherms of fluoride onto the TiO₂ adsorbents can be closely described by the Langmuir model, suggesting the monolayer adsorption process.     

Agricultural waste material as potential adsorbent for sequestering heavy metal ions from aqueous solutions - a review

Heavy metal remediation of aqueous streams is of special concern due to recalcitrant and persistency of heavy metals in environment. Conventional treatment technologies for the removal of these toxic heavy metals are not economical and further generate huge quantity of toxic chemical sludge. Biosorption is emerging as a potential alternative to the existing conventional technologies for the removal and/or recovery of metal ions from aqueous solutions. The major advantages of biosorption over conventional treatment methods include: low cost, high efficiency, minimization of chemical or biological sludge, regeneration of biosorbents and possibility of metal recovery. Cellulosic agricultural waste materials are an abundant source for significant metal biosorption. The functional groups present in agricultural waste biomass viz. acetamido, alcoholic, carbonyl, phenolic, amido, amino, sulphydryl groups etc. have affinity for heavy metal ions to form metal complexes or chelates. The mechanism of biosorption process includes chemisorption, complexation, adsorption on surface, diffusion through pores and ion exchange etc. The purpose of this review article is to provide the scattered available information on various aspects of utilization of the agricultural waste materials for heavy metal removal. Agricultural waste material being highly efficient, low cost and renewable source of biomass can be exploited for heavy metal remediation. Further these biosorbents can be modified for better efficiency and multiple reuses to enhance their applicability at industrial scale.     

Carbon from Cassava peel, an agricultural waste, as an adsorbent in the removal of dyes and metal ions from aqueous solution

Cassava (Manihot esculenta) is a short lived erect perennial shrub, planted vegetatively from hard wood stem cuttings. It is an important crop across a wide range of tropical environments and is a significant component of cropping systems. Cassava peel is an agricultural waste from the food processing industry. Activated carbons prepared from waste cassava peel employing physical and chemical methods were tested for their efficiency in the removal of dyes and metal ions from aqueous solution. While both of these were efficient as adsorbents for dyes and metal ions, the material impregnated with H₃PO₄ showed higher efficiency than the heat treated materials.     

Novel biphasic separations utilising highly selective molecularly imprinted polymers as biorecognition solvent extraction agents

Molecularly imprinted polymers (MIPs) represent a class of artificial receptors that promise an environmentally robust alternative to naturally occurring biorecognition elements of biosensing devices and systems. However, in general, the performance of conventional MIPs in aqueous environments is poor. In the study reported here, this limitation has been addressed by the novel application of MIPs as a solvent extraction solid phase in a biphasic solvent system. This paper describes a previously unreported use of MIPs as solvent extraction reagents, their successful application to aqueous sample media and the opportunities for utilisation of this unique system in novel biosensing and separation procedures. This study demonstrates the development of a novel biphasic solvent system utilising MIP in the extracting phase to enhance both efficiency and selectivity of a simple two phase liquid extraction. Monodisperse propranolol imprinted polymer microspheres [p(divinylbenzene-co-methacrylic acid)] were prepared by precipitation polymerisation. Initially, the affinity of the polymers for (R,S)-propranolol was assessed by established techniques whereby the MIP demonstrated greater affinity for the template than did the non-imprinted control polymer (NIP). Importantly, MIP performance was also assessed using the novel dual solvent system. The depletion of (R,S)-propranolol from the aqueous phase into the polymer containing organic phase was determined. When compared to control extractions containing no polymer the presence of MIP in the extracting solvent phase resulted in an increased extraction of (R,S)-propranolol from the aqueous phase. Importantly, this extraction was significantly greater in the presence of MIP when compared to NIP. This unique principle generates opportunities for MIP based extractions and chemical enrichments in industrial applications, offering commercial, ecological and practical advantages to traditional solvent extraction techniques. The technique is readily transferable to analytical microsystems utilising MIP recognition elements generating promising opportunities for MIP based sensing of aqueous sample media.     

Flotation of cadmium-loaded biomass

Biosorption of heavy metal ions such as Cd(2+) by dead biomass has been recognized as a potential alternative to existing removal technologies applied to wastewater treatment. Two bacterial strains were studied in the laboratory, streptomyces griseus and S. clavuligerus, an industrial by-product. Both washed and unwashed samples were examined. Foam flotation proposed in this work as the separation state following biosorption. Effective biomass separation was conducted in the presence of a frother, ethanol. The pH of the solution was a crucial parameter for flotation and also for metal binding. Other basic parameters of flotation examined were the initial cadmium concentration in the dilute aqueous solution and the quantity of biomass used. A study of zeta-potential measurements of the actinomycetes was carried out under the conditions used in the separation; surface tension was also measured. These provided useful information on the process. (c) 1994 John Wiley & Sons, Inc.     

Microbial and plant derived biomass for removal of heavy metals from wastewater

Discharge of heavy metals from metal processing industries is known to have adverse effects on the environment. Conventional treatment technologies for removal of heavy metals from aqueous solution are not economical and generate huge quantity of toxic chemical sludge. Biosorption of heavy metals by metabolically inactive non-living biomass of microbial or plant origin is an innovative and alternative technology for removal of these pollutants from aqueous solution. Due to unique chemical composition biomass sequesters metal ions by forming metal complexes from solution and obviates the necessity to maintain special growth-supporting conditions. Biomass of Aspergillus niger, Penicillium chrysogenum, Rhizopus nigricans, Ascophyllum nodosum, Sargassum natans, Chlorella fusca, Oscillatoria anguistissima, Bacillus firmus and Streptomyces sp. have highest metal adsorption capacities ranging from 5 to 641 mg g(-1) mainly for Pb, Zn, Cd, Cr, Cu and Ni. Biomass generated as a by-product of fermentative processes offers great potential for adopting an economical metal-recovery system. The purpose of this paper is to review the available information on various attributes of utilization of microbial and plant derived biomass and explores the possibility of exploiting them for heavy metal remediation.     

Reverse micellar extraction and precipitation of lysozyme using sodium di(2-ethylhexyl) sulfosuccinate

Sodium di(2-ethylhexyl) sulfosuccinate, referred to as Aerosol-OT or AOT, was used to remove lysozyme from an aqueous phase via reverse micellar extraction and precipitation method. For both methods, when the surfactant was in excess, a complete removal of lysozyme from the aqueous phase was obtained at the values of pH below the pI of lysozyme. However, for the reverse micellar method, a solubilization limit of lysozyme in the organic phase was observed, and a white precipitate was formed at the aqueous-organic interface. This observation suggested using AOT directly as a precipitating ligand. The lysozyme precipitated with AOT was fully recovered, with its original enzymatic activity, using acetone as a recovery solvent. A mechanism is suggested to explain the solubilization of lysozyme in an AOT reverse micellar system. It is shown that a direct precipitation method can be used with advantage instead of using the reverse micellar extraction method to recover lysozyme from an aqueous phase.     

Separation and recovery of radioactive and non-radioactive toxic trace elements from aqueous industrial effluents

An update is presented on liquid membrane-based processes as viable and relevant alternatives to conventional approaches such as precipitation, solvent extraction, ion exchange processes and electrochemical techniques for the removal and recovery of some toxic and/or valuable trace metal ions including some actinides and fission products e.g. U, Am, Y etc and As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Zn etc from radioactive as well as non-radioactive aqueous waste solutions respectively. In particular, results of experiments aimed at developing supported liquid membrane(SLM)-based process using commercially available porous membranes and indigenously prepared track--etch membranes (TEMs) have been critically examined in laboratory studies to generate basic data needed to evaluate their utility for continuous operation without regeneration. These include effect of pore size, porosity, optimum pore size and their reusability. It is clearly demonstrated that indigenously prepared 10 microm thick TEMs with a porosity in the range of 2-5% give comparable transport rates for metal ions-matching with that of commercial membranes of much higher thickness (160 microm) and higher porosity of 60-85%. The smaller thickness of TEMs more than compensates for their lower porosity. It is shown that because of their well defined pore characteristics TEMs could serve as model supports in SLM studies. By comparing the values of permeability coefficient (P) for TEM and polytetraflouroethylene (PTFE) supports for the transport of Pb2+ chosen as a typical divalent metal ion, and using di-2 ethyl hexyl phosphoric acid (D2EHPA) as the carrier, it is unambiguously proved that diffusion of the metal complex across the membrane is the rate controlling step in metal ion transport in SLM-based processes. An overview of the experimental findings along with future outlook and suggestions for further work are presented in this paper.     

Olive oil waste as a biosorbent for heavy metals

The sourcing of novel, inexpensive biowastes such as olive mill waste (OMW) from the two-decanter olive-oil-production system offers potential for the removal of metal ions by biosorption. OMW can be used in repeated regeneration cycles for the adsorption of heavy metals from aqueous solutions. The metal ions sequestered can be released in an acid solution until the concentration of these metal ions reaches a level where conventional methods can be used to provide economic metal recovery and potential revenue generation. The ability of this biomass to adsorb more than one metal ion from solution may increase its potential for application in the wastewater industry since the majority of industrial effluents contain more than one metallic species. Metal ion adsorption was found to increase with the speed of agitation and at an optimum pH value of between 4 and 7.     

Interface interactions between insecticide carbofuran and tea waste biochars produced at different pyrolysis temperatures

Biochars showed a potential as adsorbents for organic contaminants, however, have not been tested for carbofuran, which has been detected frequently in water. This study provides evidences for the use of infused tea residue derived biochar for carbofuran removal. Biochars were produced at 300, 500 and 700 °C by slow pyrolysis and were characterized by proximate and ultimate analysis, FT-IR, SEM, BET and pore size distribution. Pyrolysis temperature showed a pronounced effect on biochar properties. The maximum carbofuran removal was achieved at pH 5. Freundlich and Temkin models best fit the equilibrium data. Biochars produced at 700 °C showed the highest sorption intensity. The adsorption process was likely to be a favorable chemisorption process with electrostatic interactions between carbofuran molecules and biochar surface. Acid-base interactions, electrophilic addition reactions and amide bond formations are the possible mechanisms of carbofuran adsorption. Overall, biochars prepared from tea waste can be utilized as effective adsorbents for removal of aqueous carbofuran.     

Cadmium(II) sorption from water samples by powdered marble wastes

Abstract

A series of batch adsorption experiments were carried out, with the aim of removing cadmium ions from aqueous solutions and water samples using powdered marble wastes (PMW) as an effective inorganic sorbent. PMW is inexpensive, widespread, and may be considered as environmental problem. The main parameters (i.e. solution pH, sorbent and cadmium concentrations, stirring time, and temperature) influencing the sorption process were investigated. The results obtained for sorption of cadmium ions onto PMW are well described by the Freundlich and Langmuir models. The Dubinin-Radushkevick (D–R) isotherm model was applied to describe the nature of the adsorption of the metal ion; it was found that the adsorption process was chemical in nature. The thermodynamic parameters were also calculated from the Gibbs free energy change (ΔG°), enthalpy (AH°) and entropy (ΔS°). These parameters indicated that the adsorption process of cadmium(II) ions on PMW was spontaneous and endothermic in nature. Under the optimum experimental conditions employed the removal of ca ~100% of Cd²⁺ ions was attained. The procedure was successfully applied to removal of the cadmium ions from aqueous and various natural water samples. The adsorption mechanism is discussed.     

Qualitative Characterization of the Aqueous Fraction from Hydrothermal Liquefaction of Algae Using 2D Gas Chromatography with Time-of-flight Mass Spectrometry

Two-dimensional gas chromatography coupled with time-of-flight mass spectrometry is a powerful tool for identifying and quantifying chemical components in complex mixtures. It is often used to analyze gasoline, jet fuel, diesel, bio-diesel and the organic fraction of bio-crude/bio-oil. In most of those analyses, the first dimension of separation is non-polar, followed by a polar separation. The aqueous fractions of bio-crude and other aqueous samples from biofuels production have been examined with similar column combinations. However, sample preparation techniques such as derivatization, solvent extraction, and solid-phase extraction were necessaryprior to analysis. In this study, aqueous fractions obtained from the hydrothermal liquefaction of algae were characterized by two-dimensional gas chromatography coupled with time-of-flight mass spectrometry without prior sample preparation techniques using a polar separation in the first dimension followed by a non-polar separation in the second. Two-dimensional plots from this analysis were compared with those obtained from the more traditional column configuration. Results from qualitative characterization of the aqueous fractions of algal bio-crude are discussed in detail. The advantages of using a polar separation followed by a non-polar separation for characterization of organics in aqueous samples by two-dimensional gas chromatography coupled with time-of-flight mass spectrometry are highlighted.     

Interactions of microorganisms with rare earth ions and their utilization for separation and environmental technology

In recent years, rare earth elements (REEs) have been widely used in various modern technological devices and the global demand for REE has been increasing. The increased demand for REEs has led to environmental exposure or water pollution from rare earth metal mines and various commercial products. Therefore, the development of a safe technology for the separation and adsorption of REEs is very important from the perspective of green chemistry and environmental pollution. In this review, the application and mechanisms of microorganisms for the removal and extraction of REEs from aqueous solutions are described. In addition, the advantages in using microorganisms for REE adsorption and future studies on this topic are discussed.     

Downstream processing of biotechnological produced succinic acid

Succinic acid is a promising chemical which has a wide range of applications and can be biologically produced. The separation of succinic acid from fermentation broth makes more than 50?% of the total costs in their microbial production. This review summarizes the present state of methods studied for the recovery and purification of biologically produced succinate. Previous studies on the separation of succinic acid primarily include direct crystallization, precipitation, membrane separation, extraction, chromatography, and in situ separation. No single method has proved to be simple and efficient, and improvements are especially needed with regard to yield, purity, and energy consumption. It is argued that separation technologies coupled with upstream technology, in situ product removal, and biorefining strategy deserve more attentions in the future.     

改性微生物吸附剂在重金属废水处理中的应用进展

高效、低耗、环境友好的重金属废水处理方法是当前的研究热点之一,微生物吸附法因具有优良的吸附性能、不产生二次污染、环境友好性等优点,在重金属废水处理中有巨大的应用潜力。细菌、真菌、藻类等微生物可通过静电吸附、络合作用等将重金属结合到细胞壁表面。但未经处理的微生物往往吸附效果不佳,通过对微生物进行物理、化学等方法的改性处理,能显著增加微生物与重金属离子结合的活性位点,提高去除效果。本文对国内外微生物的改性方法以及改性微生物吸附剂对废水中重金属的吸附能力和影响因素进行阐述,讨论微生物吸附剂存在的相关问题,并对其未来的研究方向做简要展望。     

Magnetic chitosan composite particles: Evaluation of thorium and uranyl ion adsorption from aqueous solutions

Magnetic chitosan composite particles with 40 μm average size and 24 emu/g saturation magnetization obtained by an in situ procedure were evaluated as a new low-cost adsorbent for radioactive wastewater decontamination. Sorbent characterization by SEM, EDX, FTIR and magnetization measurements proved that the target ions were bound and their surface distribution was uniform. The 18 emu/g magnetization of the metal loaded particles was high enough to ensure their easy magnetic field separation and recovery. The parameters influencing the sorption process were optimized with respect to sorbent mass, target ion concentration and contact time. The material under study had superior adsorption capacity both for uranyl (666.67 mg/g) and thorium (312.50 mg/g) ions when compared to other low-cost adsorbents reported in literature. The adsorption process is spontaneous and endothermic. The material may be regenerated and re-used.