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Green strategies for decontamination of analytical wastes
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Trends in Analytical Chemistry, Vol. 29, No. 7, 2010
Green strategies for decontamination of analytical wastes Salvador Garrigues, Sergio Armenta, Miguel de la Guardia Within the paradigm of green analytical chemistry, we discuss the different options for cleaning analytical wastes in the literature, paying special attention to on-line recycling of solvents, degradation of toxic compounds and trace-element passivation. The objective of this review is to present and to evaluate critically suitable methodologies that can be incorporated into analytical methods in order to reduce or to avoid the generation of toxic wastes, which could cumulate in the laboratory and have to be managed outside, so increasing the risks and the cost of analysis. ª 2010 Elsevier Ltd. All rights reserved. Keywords: Analytical waste; Decontamination; Degradation; Green analytical chemistry; Passivation; Recycling; Solvent; Toxic compound; Toxic waste; Trace element
1. Introduction Salvador Garrigues, Sergio Armenta*, Miguel de la Guardia, Department of Analytical Chemistry, Research Building, University of Valencia, 50th Dr. Moliner St., E-46100 Burjassot, Valencia, Spain
*
Corresponding author. Tel.: +34 963 544 838; Fax: +34 963 544 845; E-mail: [email protected]
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Analytical methods can be considered as processes, in which preliminary information and knowledge, solvents, reagents, samples, energy and instrument measurements are used as inputs to solve a specific problem. The outputs of those processes are data and models, which can answer and provide solutions to these problems. However, analytical methodologies can also have side effects (e.g., wastes that could create risks for operators and damage the environment), so side effects of methods, and waste generation and management are also the responsibility of method developers and users (see Fig. 1). Many solvents and reagents used in the analytical methodologies are toxic and/or carcinogenic [e.g., the majority of analytical methods certified by the US Environmental Protection Agency (EPA) and Food and Drug Administration (FDA) use corrosive and toxic chemicals, with no other options currently available]. The wastes produced are also highly toxic, so strict control of their storage and management is necessary, and they must be considered as byproducts of the analytical methods.
The main goal of the green analytical chemistry (GAC), proposed by J. Namiesnik in 1999 [1–3], is to incorporate analytical wastes, taking into consideration the amount and the toxicity of reagents consumed, and, consequently, the volume and the toxicity of wastes generated during method development and selection, in this way reducing the environmental impact of the activities of analytical chemistry. The basic strategies for greener analytical methods involve [4,5]: i) in-field direct analysis of untreated samples; ii) mandatory search for alternative reagents and solvents; iii) use of alternative sample treatments consuming less energy and less reagents; iv) miniaturization and automation of methodologies; and, v) on-line decontamination of wastes that could be of great value in reducing emissions from the methods used and in eliminating the toxic residues of reagents. In-field direct analysis of untreated samples could be considered the best alternative, as it has no reagents and no wastes, thereby avoiding risks to both operators and the environment. In addition, it is clear that automation and miniaturization offer excellent options to solve problems related to the management of reagents and permit dramatic reduction in the consumption of reagents and waste generation. However, the replacement of widely-used traditional solvents and chemicals with new, innocuous ones, or, at least, less toxic provides greener options.
0165-9936/$ - see front matter ª 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.trac.2010.03.009
Trends in Analytical Chemistry, Vol. 29, No. 7, 2010
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Problem Preliminary information Measurements Samples Reagents and solvents Energy consume
Answers & solutions Data Models Wastes
ANALYTICAL METHOD
Clean wastes
GREEN ANALYTICAL METHOD Figure 1. Inputs and outputs of analytical methods.
Unfortunately, it is not always possible to avoid using hazardous chemicals, so additional efforts must be made to decontaminate analytical wastes or at least to reduce the amounts and the toxicity of residues. On-line recycling or recovery of solvents and reagents, mineralization of organic compounds, and precipitation and passivation of metals could be the best option for greening methods, so it is important to incorporate chemical solutions for solving the problems relating to waste generation, with on-line waste decontamination being preferred to the external treatment, for environmental, risk and economic reasons.
2. Decontamination of analytical waste Different methodologies have been developed to reduce the toxicity of waste streams in both analytical laboratories and the chemical industry. Those methodologies can be grouped into three main types: i) recycling; ii) degradation; and, iii) passivation.
Through use of those methodologies, preferably online [6], the amounts of toxic wastes can be substantially reduced, avoiding safety problems relating to the stock of large amounts of residues and reducing the cost of their external management. 2.1. Recycling of wastes Solvent recycling provides environmental and economic benefits due to the consequent reduction of waste and lowering of the costs. The recovery of organic solvent wastes is traditionally based on distillation, which can separate volatile organic solvents from non-volatile impurities, but additional methodologies to separate organic solvents are based on permeation using selective membrane separation techniques [7]. Nowadays, traditional sample-treatment methods based on liquid–liquid separations are falling into disuse due to their high consumption of organic solvents, and they are being replaced by other methods [e.g., solidphase extraction (SPE), solid-phase microextraction (SPME), liquid–liquid microextraction (LLME) or capillary microextraction (CME)]. However, the recovery of organic solvents is especially significant in some areas of
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analytical chemistry [e.g., liquid chromatography (LC)], where the large amounts of solvents consumed during LC method development and use increase purchase and disposal costs of LC solvents, or IR spectroscopy, where chlorinated solvents are commonly used due to their high transparency in the mid-IR (MIR) spectral region]. In a really interesting discussion article published online, John W. Dolan [8] stated that solvent recycling has been for more than 10 years the main subject of LC troubleshooting [9], and he indicated different ways to reduce the volume of solvent waste from LC analyses. These include reusing all the mobile phase, automated recycling of mobile phase in isocratic elutions, distillation and modifying the size of columns and particles used in the process. The most direct way to reduce solvent consumption in LC analysis is to reuse all of it. This method applies to isocratic methods only. In such cases, recycling the mobile phase implies incorporating a small amount of the sample or standard into the mobile phase reservoir after each run. However, if the volume of the mobile phase is relatively large, the change can be considered negligible. In this way, Abreu et al. evaluated the effect of recycling the mobile phase in isocratic LC on successive analyte quantifications (citric and tartaric acids) using
Threshold value
Recycle
an ultraviolet (UV) detector [10]. Their results demonstrated that, when analyte concentration in the mobile phase exceeds that in the sample, a negative peak is observed, and, when its concentration in the mobile phase is equal to that in the sample, no peak is observed for that analyte. The slopes of the linear regression lines for standards in mobile phase with different concentrations of analyte did not change, although the Y intercept values decreased with increasing concentration of analyte. In this study, it was suggested that, when analyte concentration in the mobile phase approaches the lowest concentration of analyte in samples, it is time to discard the recycled mobile phases. Another option is the so-called closed-loop eluentrecycling system. In this system, the mobile phase is recirculated to the solvent reservoir after removal of dissolved sample constituents by their adsorption onto activated carbon [11], thus restoring the purity of the mobile phase. A further way to reduce mobile-phase consumption significantly is automatically to reuse part of the mobile phase. Once again, this procedure is applicable to isocratic-based separations only. In this case, solvent recycling is done by a microprocessor that uses a sensitive level-sensing circuit to direct the mobile phase to waste whenever the output from the system detector
Delay time
Waste
Recycle
Waste
Recycle
From HPLC system
To solvent reservoir
To waste
Figure 2. Operation of commercially-available automatic solvent-recycling system.
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exceeds a level set by the user (i.e. when an analyte or matrix component is eluting from the column). When the output from the system detector drops below the programmed level, the mobile phase is redirected to the solvent reservoir to be used again, reducing both solvent-disposal and purchasing costs (see Fig. 2). Nowadays, there are commercially-available different devices that can be employed for solvent recycling (see Table 1), and we can conclude that an automatic recycling system can reduce mobile-phase consumption by up to 90%. Distillation of the organic solvent from the mobile phase after analyte separation is another way to reduce waste generation in LC [12,13]. The main advantage of distillation is that it is applicable to both isocratic and gradient-based separations. In this way, P. Stepnowski et al. developed a methodology in 2002 for LC wastes of methanol/water [14] and acetonitrile/water [15] based on a batch-distillation system combined with microorganism biodegradation. The biodegradation was used for the first cuts and heavy ends of the solvent waste, which were unsuitable for further recovery. Moreover, B/R Instrument Corporation (Maryland, USA) produced a fractional distillation system specifically designed for automated or manual recovery of LC solvents. However, solvent recycling is not a panacea, since the distillate is of slightly lower purity than the original feedstock. Also, we need to consider that common solvents (e.g., ethanol and acetonitrile) distill as azeotropes, ethanol-water distills as a 5% water azeotrope, isopropanol-water azeotrope contains 12.6% water and acetonitrile azeotrope contains 14–16% water. As mentioned above, IR spectroscopy is another area of analytical chemistry needing to revise use of organic toxic solvents, as chlorinated hydrocarbons are still preferred solvents due to their high transparency in the MIR region. This topic has been extensively discussed since J.D.R. Thomas raised the matter [16,17]. He stated: ‘‘Clearly, the pressure is really on for laboratory procedures and analytical methods to be adapted in order to avoid the banned solvents, but also those of general environmental and health concerns’’. The problem of chlorinated solvents was therefore well known more than 15 years ago, but the question now is: ‘‘How has Table 1. Devices commercially available for solvent recycling Automatic solvent-recycling systems SRS Pro Solvent Recycling System – Thermo Scientific S-3 HPLC Solvent Recycler – Spectrum Chromatography SolventTrak – Phenomenex SolventTrak – Antech Solutions SolventTrak II – SMI-LabHut Solvent Recycler 3000 – Alltech Associates LA2890 Solvent Recycler – Laserchrom 7206 Solvent Recycler – Micro Solv Solvent Recycler 2000 – Alltech Associates Distillation systems for HPLC solvents 9600 Solvent Recycling – B/R Instrument Corporation
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the community of analytical scientists tried to solve this problem since?’’. The EPA has addressed the replacement of CFC-113 for determining oil and grease in wastewater by different solvents {e.g., the dimer/trimer of chlorotrifluoroethylene (S-316) [18] or carbon disulfide [19]}. Another strategy developed to minimize the impact on the environment of the chlorinated solvents used in IR determinations was based on recycling solvent. In this way, a closed flow-injection analysis (FIA) manifold was incorporated to do the on-line distillation of chlorinated solvents after the IR measurements in order to provide a dramatic reduction of the volume of chlorinated wastes (see Fig. 3a). This system was successfully applied to the determination in pharmaceuticals of ketoprofen [20], and propyphenazone and caffeine [21]. 2.2. Degradation of wastes Development of new methods and technologies for minimizing waste and preserving water quality is a major concern of scientists around the world [22–24]. It is of utmost importance to dispose off chemical residues properly and to keep the concentration of chemicals in effluent streams to a minimum. We should note that research in this field mainly focuses on development of new, more efficient wastewatertreatment technologies, but those achievements can also be applied in treating analytical laboratory residues, thereby minimizing the environmental impact of analytical procedures and the costs of waste treatment. In the following sub-sections, we discuss different methodologies, which are available for degradation of toxic wastes in water streams and which can be used for analytical laboratory residues, outlining their advantages and drawbacks. 2.2.1. Thermal degradation. Until the mid-1980s, waste combustion was widely considered the basic method to eliminate toxic chemical wastes. Thermal processes used for waste treatment can be classified as: i) combustion with excess of oxygen; ii) gasification or partial combustion at oxygen deficit; and, iii) pyrolysis, the main difference being the presence or absence of oxygen in the reactor. Thermal degradation is mainly used to decompose solid organic matter in the food, petrochemical and polymer industries, and it is applied off-line, which implies the storage of large amounts of solid residues [25]. As can be supposed, combustion is not the best option to clean the wastes of the analytical laboratories. The main disadvantages of such methodologies are the difficulty of on-line coupling with the analytical procedure, and the formation of large amounts of toxic emissions (e.g., ashes containing heavy metals, carbon monoxide, http://www.elsevier.com/locate/trac
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a
Solvent recovery unit Refrigerant
Injection valve
Bidirectional valve
Solvent Detector
Solvent cooling unit
Solvent reservoir Heater
Flow cell Peristaltic pump
b
Carrier OVEN Reagent Waste Measurement cell
Accepting solution
Clean waste
Peristaltic pump
c
PAP R1 IO4
-
Waste
R2
45 cm
R3
D 60 cm
NaOH
λ =540 nm
TiO2 H2O
6m Clean UV Lamp waste λ =254 nm
Peristaltic pump
d
Reagent Clean waste
Carrier Waste
Carrier
Injection valve
Filter
Measurement cell Bidirectional valve
Closed-flow of a nutrient solution Nutrient Peristaltic pump Figure 3. Manifolds proposed for on-line generation of clean analytical wastes: a) recycling of carrier solvents by distillation; b) thermal degradation of wastes; c) photoassisted catalytic oxidation of organic compounds; and, d) biodegradation.
sulfur and nitrogen oxides, chlorinated compounds and dioxins), it being necessary to apply additional purification strategies to meet environmental standards, thereby increasing operation costs. However, analytical wastes 596
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can be heated on-line inside a GC oven after the analysis of related compounds, providing the organics are thermally decomposed to gaseous products for receipt in an appropriate solution (see Fig. 3b) [26].
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2.2.2. Oxidative degradation. Advanced oxidation processes can remove organic and inorganic materials in wastewater using hydroxyl radicals. Contaminants are oxidized by different reagents (e.g., ozone, hydrogen peroxide, Fenton reagent and combinations of these). These procedures may also be combined with UV irradiation and ultrasound. Organic compounds (e.g., aromatic amines [27], ethers [28], dyes [29], chlorinated phenols [30], pesticides and polycyclic aromatics [31]) can be oxidized effectively by hydroxy radicals produced from Fenton reagent, a mixture of hydrogen peroxide and ferrous iron that produces OHÆ radicals through: H2 O2 þ Fe2þ ! Fe3þ þ OH þ OH We need to highlight that ultrasound irradiation is particularly effective for polymer degradation [32]. A detailed discussion about advanced oxidation processes and the reactions involved can be found in the review of P.R. Gogate and A.B. Pandit [33]. However, the majority of these oxidation technologies do not totally mineralize organic contaminants, combination with biological treatments being necessary for total degradation of organics from toxic wastewater [34,35]. Another problem of this type of process is that the reaction takes place in homogeneous solution in which the oxidants are consumed continuously during the reaction. 2.2.3. Heterogeneous photocatalytic oxidations. Photocatalytic or photochemical degradations are gaining importance in wastewater treatment, since they result in complete mineralization and operate at mild conditions of temperature and pressure. It can be considered a hot topic, taking into consideration the number of books and review papers published on this field in recent times [36,37]. Photocatalysis is based on the ability of the photocatalyst to adsorb simultaneously and efficiently both reactants and photons. A detailed description of the reactions and the fundamentals of heterogeneous catalysis can be found in the review paper of J.M. Herrmann [38]. A wide range of semiconductors may be used for photocatalysis (e.g., oxides TiO2, ZnO, MgO, WO3, ZrO2, CeO2 and Fe2O3, or sulfides CdS and ZnS). For heterogeneous photocatalysis with semiconductors, the photocatalyst can be dispersed in suspension or coated on the inside walls of a reaction chamber. The advantage of the heterogeneous photodegradation of organic pollutants is the possibility of recovering the catalyst by filtration, using a closed system. However, it is also possible to use the catalyst as a stationary phase by coating the inner walls of a glass reactor [39]. Other possibilities to use semiconductors (e.g., TiO2) as stationary phases include their immobilization on different substrates (e.g., silica gel) and later introduction into a
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borosilicate glass tube [40], polymeric membranes [41], porous alumina-silica ceramic prepared in the shape of a coaxial glass cylinder [42], zeolite [43], activated carbon [44], and others. It should be noted that recovery of the catalyst is an important issue, due to its potential toxicity in aquatic systems. In this sense, the toxicity of TiO2, the most widely used heterogeneous catalyst in wastewater treatment, has been deeply investigated by several bioassay procedures using D. magna and V. fischeri [45,46]. It was found that the aggregated TiO2 was not toxic, while the LC50 and the 100% mortality of the filtered TiO2 were 5.5 mg/L and 10 mg/L, respectively, LC50 being defined as the lethal concentration that kills 50% of D. magna in a given time (48 h). A list of the organic pollutants that can be photodegraded by using TiO2 as catalyst can be found in the review of D.M. Blake [47]. Among those organic compounds, we need to highlight the photodegradation of dyes, pesticides, surfactants, phenolic compounds, aromatic and aliphatic compounds, haloaromatics, nitrohaloaromatics and amides. The principle of photocatalytic degradation was successfully applied for on-line degradation of analytical wastes in FIA manifolds for the first time in 1995. Different manifolds were proposed for the degradation of the reagents employed for their colourimetric determinations (see Fig. 3c), being applied for the photo-assisted catalytic detoxification of propoxur [48], formetanate [49] and resorcinol [50] after determination with p-aminophenol. Organic compounds can be degraded into harmless forms from wastewater and various anions can be oxidized to less toxic compounds using TiO2. Nitrite has been successfully oxidized to nitrate [51], sulfide and sulfite converted to sulfate [52], and cyanide to isocyanide [53], nitrogen [54] or nitrate [55]. In addition, heavy metals can be deposited on the surface of the catalysts, forming agglomerates [56]. 2.2.4. Biodegradation. Biological processes make use of the natural metabolism of living cells to degrade or to transform chemical species using a sequence of reactions catalyzed by enzymes. Municipal wastewaters have traditionally been treated with biological processes, typically aerobic organisms in suspended systems or surface-anchored biofilms. However, biodegradation of analytical-laboratory wastes is more challenging due to the presence of less biodegradable, and often toxic, pollutants [57]. Moreover, the stability and the activity of microbial cells can be severely affected by changes in pH, temperature, and the presence of toxins, and their preservation is difficult when they are in contact with analytical wastes. Thus, an ideal waste-treatment system based on biodegradation for the analytical laboratory (see Fig. 3d) should be able to respond to extreme variations in the nature and the concentration of pollutants, http://www.elsevier.com/locate/trac
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with other variables (e.g., presence of toxins, pH and salinity (having values that are largely unpredictable. This is probably the reason of the limited applicability of toxic-waste biodegradation in analytical laboratories [26]. 2.3. Passivation of persistent pollutants Sometimes, degradation of pollutants is impossible, or is expensive or slow. In those cases, passivation of wastes is an option to reduce the potential risks of analytical wastes. The main objective of passivation is effective removal of persistent pollutants from aqueous streams, discharging wastewater as required by strict environmental legislation while reducing the amounts of residues from several liters to a few grams. This type of methodology is widely used in industry, but its application in analytical laboratories is still limited. 2.3.1. Co-precipitation of metal ions. Co-precipitation is one of the usual methods employed to remove heavy metals from wastewater. The main objective of this technique is to remove heavy-metal ions from an aqueous solution to yield a less contaminated aqueous effluent. The method involves co-precipitating the heavy-metal ions with a carrier precipitate that is formed in situ within the aqueous solution. It was patented in 1991 in the USA by W.T. Douglas [58]. The characteristics and the properties of the precipitates directly affect the efficiency of metal removal because large particles of the precipitation product could easily be filtered, while non-uniform and fine particles usually provide low filtration efficiencies [59]. Removal of heavy metals by co-precipitation with ferrite has been well known for more than 40 years [60]. Co-precipitation of metals in laboratory wastes was applied for the first time in 1990 using aluminium hydroxide [61]. This procedure was also successfully applied to the decontamination of residues from cold-vapour atomic fluorescence spectroscopy (CV-AFS) [62]. The liquid effluent obtained from the CV-AFS system, with a high acidic pH (0.5) and probably containing dissolved heavy metals (Cr, Cd, Ba, . . .) was merged with a solution of Fe(III) and later with a solution of NaOH, providing on-line coprecipitation of heavy metals with Fe(OH)3. In 1992, the EPA developed a research project to remove heavy metals from municipal wastewater [63]. A sand bed was used with lime feed to cause coprecipitation of metals and calcium carbonate on the surface of sand grains. Through continuous plating by the precipitates, the sand grains increased in size and could easily be filtered and separated from the solution. Recently, an electrochemical method, named electrocoagulation, has attracted significant attention for removal of inorganic ions [64]. An example of the electrocoagulation process can be found in the removal of Cr in wastewater, where the iron anode dissolved and 598
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produced Fe2+, which reduced Cr6+ to Cr3+, leading to the co-precipitation of Cr(OH)3 and Fe(OH)3. The main advantage of the procedure is that no chemicals need to be added. However, a major disadvantage of this process is the hydrogen gas produced at the cathode, which prevents the flocs from settling properly [65]. Moreover, the particle size of the precipitate makes the filtration process difficult. To overcome these problems, the electrocoagulationelectroflotation combination [66] was applied to float the precipitate and to separate it from the treated water. Iron, nickel, copper, zinc, lead and cadmium were removed at 95% level using the electrocoagulation-electroflotation combination [67]. A similar combined electrocoagulation and electroflotation process was proposed to remove fluoride from drinking water [68] using aluminum electrodes. The main advantages of this methodology over conventional treatments include versatility, energy efficiency, safety, selectivity, possibility to automation and cost effectiveness [69]. Electrocoagulation is an efficient process also for the treatment of organic pollutants from water [70]. 2.3.2. Surfactant-based decontamination. Aqueous surfactant two-phase (ASTP) extraction is a promising method to remove organic contaminants from wastewater [71]. A typical example of such ASTP separation techniques using a non-ionic surfactant is cloud-point extraction (CPE), where the phase separation is caused by elevating the temperature above the cloud point [72]. One phase is the surfactant-rich phase, while the other phase is a bulk aqueous phase known as the surfactantdilute phase containing only a small concentration of surfactant aggregates, the organic contaminants being concentrated in the surfactant-rich phase [73]. In a similar way, aqueous two-phase systems (ATPSs) can be formed with combinations of hydrophilic solutes (e.g., polymers or polymers and certain salts), mixed in aqueous solution above critical concentrations [74]. These processes have been successfully and extensively applied for the recovery of biological products (e.g., enzymes and proteins from different sources) [75]. It has been reported that mixtures of surfactants often offer properties superior to those of single surfactants, enhancing the effectiveness of extraction [76]. Mixtures of anionic and cationic surfactants can also exhibit aqueous–aqueous phase separation and can be used in ASTP extraction [77]. Another type of surfactant-based separation is micellar-enhanced ultrafiltration (MEUF), where a surfactant is added to the wastewater at a concentration higher than its critical micelle concentration (CMC). The amphiphilic aggregates attract metal ions to the micelle surface and the organic molecules are solubilized in the micelle core. Thus, wastewater can be filtered through an ultrafiltration membrane having pore sizes small
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enough to reject the micelles. MEUF has been applied for the removal of arsenic ions from highly polluted waters [78], chlorinated aromatic hydrocarbons, nitrate and chromate [79] and metal ions [80]. Several ultrafiltration-based techniques, in which the surfactant is replaced by water-soluble compounds, have been developed for effective removal of metal ions and small organic contaminants from wastes, {e.g., ion-expulsion enhanced ultrafiltration [81], polymerenhanced ultrafiltration [82], dendrimer-enhanced ultrafiltration [83] and polyelectrolyte-enhanced ultrafiltration [84]}. Admicelles and hemimicelles are relatively newly investigated phenomena [85]. The term ‘‘admicelle’’ was coined for adsorbed micelles formed on surfaces. Hemimicelles are monolayer formations of surfactants on surfaces. Admicelles and hemimicelles are aggregates of surfactants able to solubilize a wide variety of substances. The systems mentioned have been proposed as extraction sorbents for organic analytes in analytical chemistry. This approach, termed admicellar or hemimicellar SPE, involves utilizing surfactants adsorbed onto a solid phase and was tested for the extraction of chlorophenols [86], polyaromatic hydrocarbons [87], and phthalates [88] using SDS-alumina or dialkylsulfosuccinate-alumina sorbents. 2.3.3. Adsorption on different materials. Adsorption has become one of the preferred methods for removal of toxic contaminants from water streams, as it is a very efficient, economical, versatile and simple methodology [89]. Different conventional and non-conventional types of adsorbent have been used to remove metal ions and organic compounds. The adsorbents can be of mineral, organic or biological origin (e.g., activated carbons [90], zeolites [91], clays [92], silica beads [93]), low-cost adsorbents (e.g., industrial by-products [94], agricultural wastes [95] and biomass [96]), and polymeric materials (e.g., organic polymeric resins [97] and macroporous hypercrosslinked polymers [98]). In recent years, natural polymer adsorbents have been used (e.g., chitin [99], starch [100], and their derivatives chitosan [101] and cyclodextrin [102]). G. Crini published a review article in 2005 on recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment [103].
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laboratory wastes, and the majority concern treatment of industrial wastewater or municipal residues. The question we need to address is ‘‘Why is industry developing and applying methods to reduce the volume and the toxicity of their wastes, while analytical laboratories are not involved to the same extent?’’. Other than the obvious answer regarding the smaller volume of toxic wastes generated in the analytical laboratory, compared with industrial processes, most new sample-treatment procedures (e.g., SPE, SPME and LLME) developed by analytical chemists try to reduce the use of organic solvents and to replace toxic reagents by harmless ones. However, it is common practice in analytical laboratories to accumulate analytical wastes for later treatment. The main reason for this practice is that the economic cost of waste management is not usually paid by the analytical laboratory itself but by universities or academic authorities, so it is absolutely necessary to change the mentality of analytical chemists in this sense. The new ecological mentality in analytical laboratories involves introducing and incorporating recycling and decontamination procedures in the development of new methods of analysis. To encourage this change of mentality in 1991, the University of California at Berkeley, USA, implemented a charge-back program in which 25% of the cost of disposal was assumed by the laboratory and the authorities performed inspections and analyzed effluents to identify hazardous wastes properly. After the first period, the charge-back cost of disposal increased to 100%. The University of Wyoming, USA, also established a charge-back program in 1994, where 25% of the cost of waste management of its laboratories was financed by the university, but 75% was assumed by the different departments and research laboratories [104]. In summary, decontamination of analytical wastes and recycling of solvents and reagents should be considered as the last step of the analytical process [26]. Accumulation of wastes must be replaced by their online treatment, avoiding safety problems relating to the storage of large amounts of residues and reducing the cost of their management. Recycling solvents and reagents and decontaminating wastes should be considered as additional, but absolutely necessary, in the effort to eliminate the side effects of analytical laboratories.
References 3. Future trends and conclusions The first conclusion that can be extracted from this review is that there are a lot of procedures available for the removal of toxics, so as to reduce the side effects of chemical activities. However, only a few papers of those we presented here were directly related to analytical
[1] J. Namiesnik, Environ. Sci. Pollut. Res. 6 (1999) 243. [2] P.T. Anastas, J.C. Warner, Green Chemistry: Theory and Practice, Oxford University Press, New York, USA, 1998. [3] P.T. Anastas, Critical Rev. Anal. Chem. 29 (1999) 167. [4] S. Armenta, S. Garrigues, M. de la Guardia, Trends Anal. Chem. 27 (2008) 497. [5] M. Koel, M. Kaljurand, Pure Appl. Chem. 78 (2006) 1993.
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[6] F.R.P. Rocha, J.A. Nobrega, O.F. Filho, Green Chem. 3 (2001) 216. [7] C. Streicher, P. Kremer, V. Thomas, A. Hubner, G. Ellinghorst, Development of new pervaporation membrane system and processes to separate alcohols/ether/hydrocarbons mixtures, in: Proc. 7th Int. Conf. Pervaporation in the Chemical Industry, Nevada, 1995, p. 297. [8] J.W. Dolan, LCGC 10 (2007). [9] J.W. Dolan, LCGC Intl. 5 (1991) 14. [10] O. Abreu, G.D. Lawrence, Anal. Chem. 72 (2000) 1749. [11] R.O. Sheth, Closed Loop Recycling of Solvents Used in High Pressure Liquid Chromatograph (HPLC) Analysis, Technical Note, Mason & Hanger-Silas Mason Co., Inc., Pantex Plant, Texas, USA. [12] R.M. Katusz, L. Bellew, J.A. Mangravite, R.F. Foery, J. Chromotagr. 213 (1981) 331. [13] J.A. Mangravite, R.R. Roark, P. Van Triest, Solvent recycling by spinning band distillation: theory, equipment, and limitations, in: P.A. Reinhardt, K.L. Leonard, P.C. Ashbrook (Editors), Pollution Prevention and Waste Minimization in Laboratories, Lewis Publishers, New York, USA, 1996, pp. 239–274. [14] P. Stepnowski, K.H. Blotevogel, B. Jastorff, Environ. Sci. Pollut. Res. 9 (2002) 34. [15] P. Stepnowski, K.H. Blotevogel, P. Ganczarek, U. Fischer, B. Jastorff, Res. Conserv. Recycl. 35 (2002) 163. [16] J.D.R. Thomas, Trends Anal. Chem. 14 (1995) 186. [17] D. Nobel, Anal. Chem. 65 (1993) 693A. [18] ASTM International, Method D7066-04, Standard Test Method for dimer/trimer of chlorotrifluoroethylene (S-316) Recoverable Oil and Grease and Nonpolar Material by Infrared Determination, ASTM International, West Conshohocken, PA, USA, 2004. [19] V.J. Barwick, S.L. Ellison, M.J.Q. Rafferty, T.J. Farrant, Int. J. Environ. Anal. Chem. 72 (1998) 235. [20] M.J. Sanchez-Dasi, S. Garrigues, M.L. Cervera, M. De la Guardia, Anal. Chim. Acta 361 (1998) 253. [21] Z. Bouhsain, S. Garrigues, M. de la Guardia, Analyst (Cambridge UK) 122 (1997) 441. [22] D.T. Sawyer, A.F. Martell, Industrial Environmental Chemistry: Waste Minimization in Industrial Processes and Remediation of Hazardous Wastes, Plenum Press, New York, USA, 1992. [23] D.W. Green, L.L. Smith, J.S. Crain, A.S. Poparai, J.T. Kiely, J.S. Yaeger, J.B. Schilling, Secondary Waste Minimization in Analytical Methods, DOE Report, 2004 (http://www.p2pays.org/ref/ 04/03277.pdf). [24] A. Reinhardt, K.L. Leonard, P.C. Ashbrook (Editors), Pollution Prevention and Waste Minimization in Laboratories, vol. 3, CRC Press, Inc., Boca Raton, FL, USA, 1996. [25] European Commission (EC), Integrated pollution prevention and control. Draft reference document on the best available techniques for waste incineration, EC, Brussels, Belgium, 2004. [26] M. de la Guardia, J. Braz. Chem. Soc. 10 (1999) 429. [27] I. Casero, D. Sicilia, S. Rubio, D. Pe´rez-Bendito, Water Res. 31 (1997) 1985. [28] A.A. Burbano, D.D. Dionysiou, M.T. Suidan, T.L. Richardson, Water Res. 39 (2005) 107. [29] W.G. Kuo, Water Res. 26 (1992) 881. [30] W.Z. Tang, C.P. Huang, Chemosphere 33 (1996) 1621. [31] J.J. Pignatelle, Environ. Sci. Technol. 26 (1992) 944. [32] J. Chakraborty, J. Sarkar, R. Kumar, G. Madras, Polym. Degrad. Stabil. 85 (2004) 555. [33] P.R. Gogate, A.B. Pandit, Adv. Environ. Res. 8 (2004) 501. [34] A. Marco, S. Esplugas, G. Saum, Water Sci. Technol. 35 (1997) 321. [35] E. Chamarro, A. Marco, S. Esplugas, Water Res. 35 (2001) 1047. [36] D.W. Bahnemann, J. Cunningham, M.A. Fox, E. Pelizzetti, P. Pichat, N. Serpone, in: R.G. Zepp, G.R. Helz, D.G. Crosby
600
http://www.elsevier.com/locate/trac
[37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47]
[48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58]
[59] [60] [61] [62]
[63]
[64] [65] [66] [67] [68] [69] [70]
(Editors), Aquatic Surface Photochemistry, Lewis Publishers, Boca Raton, FL, USA, 1994, p. 261. J.M. Herrmann, Helv. Chim. Acta 84 (2001) 2731. J.M. Herrmann, Catal. Today 53 (1999) 115. K. Vinodgopal, U. Stafford, K.A. Gray, P.V. Kamat, J. Phys. Chem. 98 (1994) 6797. Z. Ding, X.J. Hu, G.Q. Lu, P.L. Yue, P.F. Greenfield, Langmuir 16 (2000) 6216. N. Phonthammachai, E. Gulari, A.M. Jamieson, S. Wongkasemjit, Appl. Organometal. Chem. 20 (2006) 499. Y. Peng, J.T. Richardson, Appl. Catal., A 266 (2004) 235. P. Atienzar, A. Corma, H. Garcia, J.C. Scaiano, Chem. Mater. 16 (2004) 982. F.L.Y. Lam, X.J. Hu, Chem. Eng. Sci. 58 (2003) 687. A. Bozzi, M. Dhananjeyan, I. Guasaquillo, S. Parra, C. Pulgarin, C. Weins, J. Kiwi, J. Photochem. Photobiol. Chem. 162 (2004) 179. S.B. Lovern, R. Klaper, Environ. Toxicol. Chem. 25 (2006) 1132. D.M. Blake, Bibliography of Work on Photocatalytic Removal of Hazardous Compounds from Water and Air, NREL/TP-43022197, National Renewable Energy Laboratory, Golden, CO, USA, 1997. M. de la Guardia, K.D. Khalaf, V. Carbonell, A. Morales-Rubio, Anal. Chim. Acta 308 (1995) 462. M.J. Escuriola, A. Morales-Rubio, M. de la Guardia, Anal. Chim. Acta 390 (1999) 147. M. de la Guardia, K.D. Khalaf, B.A. Hasan, A. Morales-Rubio, V. Carbonell, Analyst (Cambridge UK) 120 (1995) 231. A. Zafra, J. Garcia, A. Milis, X. Domenech, J. Mol. Catal. 70 (1991) 343. S.N. Frank, A.J. Bard, J. Phys. Chem. 81 (1977) 1484. S.N. Frank, A.J. Bard, J. Am. Chem. Soc. 99 (1977) 303. H. Hidaka, T. Nakamura, A. Ishizaha, M. Tsuchiya, J. Zhao, J. Photochem. Photobiol., A 66 (1992) 367. C.H. Pollema, J. Hendrix, E.B. Milosavljevic, L. Solujic, J.H. Nelson, J. Photochem. Photobiol., A 66 (1992) 235. J.M. Herrmann, J.J. Disdier, P. Pichat, J. Catal. 113 (1988) 72. M.A. Tarr, Chemical Degradation Methods for Wastes and Pollutants, Marcel Dekker Inc., NY, USA, 2003. W.T. Douglas, US Patent 5013453 - Method for removing heavy metals from aqueous solutions by coprecipitation, No. 042565 filed on 04/16/1987. O. Sohnel, J. Garside, Precipitation, Butterworth Heinemann, Oxford, UK, 1992. W. Dyck, Can. J. Chem. 46 (1968) 1441. T. Chohji, E. Hirai, Y. Hayashi, A. Touda, Environ. Technol. 11 (1990) 421. P. Cava-Montesinos, E. Ro´denas-Torralba, A. Morales-Rubio, M.L. Cervera, M. De la Guardia, Anal. Chim. Acta 506 (2004) 145. J.C. Huang, An innovative coprecipitation technique for removing heavy metals from wastewater, EPA-600/S2–82-053, US Environmental and Protection Agency, Washington, DC, USA, 1982. N. Kongsricharoern, C. Polprasert, Water Sci. Technol. 31 (1995) 109. M.F. Pouet, F. Persin, M. Rumeau, Water Res. 25 (1992) 247. G.H. Chen, X.M. Chen, P.L. Yue, J. Environ. Eng. 126 (2000) 858. B. Merzouk, B. Gourich, A. Sekki, K. Madani, M. Chibane, J. Hazard. Mater. 164 (2009) 215. Q. Zuo, X. Chen, W. Li, G. Chen, J. Hazard. Mater. 159 (2008) 452. M.Y.A. Mollah, R. Schennach, J.R. Parga, D.L. Cocke, J. Hazard. Mater. 84 (2001) 29. M. Bayramoglu, M. Eyvaz, M. Kobya, Chem. Eng. J. 128 (2007) 155.
Trends in Analytical Chemistry, Vol. 29, No. 7, 2010 [71] J.F. Scamehorn, J.H. Harwell, Surfactant-based Separation Processes, Marcel Dekker, New York, USA, 1989. [72] W.L. Hinze, E. Pramauro, Crit. Rev. Anal. Chem. 24 (1993) 133. [73] P. Trakultamupatam, J.F. Scamehorn, S. Osuwan, Separ. Sci. Technol. 37 (2002) 1291. [74] M. Rito-Palomares, J. Chromatogr., B 807 (2004) 3. [75] H. Walter, G. Johansson, D.E. Brooks, Anal. Biochem. 197 (1991) 1. [76] C.C. Ruiz, J. Aguiar, Colloids Surf., A 224 (2003) 221. [77] P. Weschayanwiwat, O. Kunanupap, J.F. Scamehorn, Chemosphere 72 (2008) 1043. [78] F. Beolchini, F. Pagnanelli, I. De Michelis, F. Veglio`, Environ. Sci. Technol. 40 (2006) 2746. [79] K. Baek, J.W. Yang, Chemosphere 57 (2004) 1091. [80] R.S. Juang, Y.Y. Xu, C.L. Chen, J. Membrane Sci. 218 (2003) 257. [81] D.K. Krehbiel, J.F. Scamehorn, R. Ritter, S.D. Christian, E.E. Tucker, Sep. Sci. Technol. 27 (1992) 1775. [82] P. Can˜izares, A. Pe´rez, R. Camarillo, J.J. Linares, J. Membrane Sci. 240 (2004) 197. [83] M.S. Diallo, S. Christie, P. Swaminathan, J.H. Johnson, W.A. Goddard, Environ. Sci. Technol. 139 (2005) 1366. [84] D.J. Ennigrou, L. Gzara, M. Ramzi Ben Romdhane, M. Dhahbi, Desalination 246 (2009) 363. [85] S. Gangula, S.Y. Suen, E.D. Conte, Microchem. J. 95 (2010) 2. [86] T. Saitoh, T. Kondo, M. Hiraide, J. Chromatogr., A 1164 (2007) 40. [87] T. Saitoh, S. Matsushima, M. Hiraide, J.Chromatogr., A 1069 (2005) 271.
Trends [88] T. Saitoh, S. Matsushima, M. Hiraide, J. Chromatogr., A 1040 (2004) 185. [89] A.A. Lewinski, Hazardous Materials and Wastewater: Treatment, Removal and Analysis, Nova Science Publishers, Inc., NY, USA, 2007. [90] J.M. Chern, Y.W. Chien, Water Res. 37 (2003) 2347. [91] S.T. Bosso, J. Enzweiler, Water Res. 36 (2002) 4795. [92] O. Abollino, M. Aceto, M. Malandrino, C. Sarzanini, E. Mentasti, Water Res. 37 (2003) 1619. [93] M. Ghoul, M. Bacquet, M. Morcellet, Water Res. 37 (2003) 729. [94] F.A. Lopez, M.I. Martin, C. Perez, A. Lopez-Delgado, F.J. Alguacil, Water Res. 37 (2003) 3883. [95] T. Robinson, B. Chandran, P. Nigam, Water Res. 36 (2002) 2824. [96] M.X. Loukidou, K.A. Matis, A.I. Zouboulis, M. LiakopoulouKyriakidou, Water Res. 37 (2003) 4544. [97] A. Atia, A.M. Donia, S.A. Abou-El-Enein, A.M. Yousif, Sep. Purif. Technol. 33 (2003) 295. [98] W. Azanova, J. Hradil, React. Funct. Polym. 41 (1999) 163. [99] J. Synowiecki, N.A. Al-Khateeb, Crit. Rev. Food Sci. Nutr. 43 (2003) 145. [100] V.P. Yuryev, A. Cesaro, W.J. Bergthaller, Starch and Starch Containing Origins -Structure, Properties and New Technologies, Nova Science Publishers, Inc., New York, USA, 2002. [101] S. Babel, T.A. Kurniawan, J. Hazard. Mater. 897 (2003) 219. [102] G. Crini, M. Morcellet, J. Sep. Sci. 25 (2002) 789. [103] G. Crini, Prog. Polym. Sci. 30 (2005) 38. [104] D. Mooney, Chemical Health and Safety 11 (2004) 24.
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Green strategies for decontamination of analytical wastes Salvador Garrigues, Sergio Armenta, Miguel de la Guardia Within the paradigm of green analytical chemistry, we discuss the different options for cleaning analytical wastes in the literature, paying special attention to on-line recycling of solvents, degradation of toxic compounds and trace-element passivation. The objective of this review is to present and to evaluate critically suitable methodologies that can be incorporated into analytical methods in order to reduce or to avoid the generation of toxic wastes, which could cumulate in the laboratory and have to be managed outside, so increasing the risks and the cost of analysis. ª 2010 Elsevier Ltd. All rights reserved. Keywords: Analytical waste; Decontamination; Degradation; Green analytical chemistry; Passivation; Recycling; Solvent; Toxic compound; Toxic waste; Trace element
1. Introduction Salvador Garrigues, Sergio Armenta*, Miguel de la Guardia, Department of Analytical Chemistry, Research Building, University of Valencia, 50th Dr. Moliner St., E-46100 Burjassot, Valencia, Spain
*
Corresponding author. Tel.: +34 963 544 838; Fax: +34 963 544 845; E-mail: [email protected]
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Analytical methods can be considered as processes, in which preliminary information and knowledge, solvents, reagents, samples, energy and instrument measurements are used as inputs to solve a specific problem. The outputs of those processes are data and models, which can answer and provide solutions to these problems. However, analytical methodologies can also have side effects (e.g., wastes that could create risks for operators and damage the environment), so side effects of methods, and waste generation and management are also the responsibility of method developers and users (see Fig. 1). Many solvents and reagents used in the analytical methodologies are toxic and/or carcinogenic [e.g., the majority of analytical methods certified by the US Environmental Protection Agency (EPA) and Food and Drug Administration (FDA) use corrosive and toxic chemicals, with no other options currently available]. The wastes produced are also highly toxic, so strict control of their storage and management is necessary, and they must be considered as byproducts of the analytical methods.
The main goal of the green analytical chemistry (GAC), proposed by J. Namiesnik in 1999 [1–3], is to incorporate analytical wastes, taking into consideration the amount and the toxicity of reagents consumed, and, consequently, the volume and the toxicity of wastes generated during method development and selection, in this way reducing the environmental impact of the activities of analytical chemistry. The basic strategies for greener analytical methods involve [4,5]: i) in-field direct analysis of untreated samples; ii) mandatory search for alternative reagents and solvents; iii) use of alternative sample treatments consuming less energy and less reagents; iv) miniaturization and automation of methodologies; and, v) on-line decontamination of wastes that could be of great value in reducing emissions from the methods used and in eliminating the toxic residues of reagents. In-field direct analysis of untreated samples could be considered the best alternative, as it has no reagents and no wastes, thereby avoiding risks to both operators and the environment. In addition, it is clear that automation and miniaturization offer excellent options to solve problems related to the management of reagents and permit dramatic reduction in the consumption of reagents and waste generation. However, the replacement of widely-used traditional solvents and chemicals with new, innocuous ones, or, at least, less toxic provides greener options.
0165-9936/$ - see front matter ª 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.trac.2010.03.009
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Problem Preliminary information Measurements Samples Reagents and solvents Energy consume
Answers & solutions Data Models Wastes
ANALYTICAL METHOD
Clean wastes
GREEN ANALYTICAL METHOD Figure 1. Inputs and outputs of analytical methods.
Unfortunately, it is not always possible to avoid using hazardous chemicals, so additional efforts must be made to decontaminate analytical wastes or at least to reduce the amounts and the toxicity of residues. On-line recycling or recovery of solvents and reagents, mineralization of organic compounds, and precipitation and passivation of metals could be the best option for greening methods, so it is important to incorporate chemical solutions for solving the problems relating to waste generation, with on-line waste decontamination being preferred to the external treatment, for environmental, risk and economic reasons.
2. Decontamination of analytical waste Different methodologies have been developed to reduce the toxicity of waste streams in both analytical laboratories and the chemical industry. Those methodologies can be grouped into three main types: i) recycling; ii) degradation; and, iii) passivation.
Through use of those methodologies, preferably online [6], the amounts of toxic wastes can be substantially reduced, avoiding safety problems relating to the stock of large amounts of residues and reducing the cost of their external management. 2.1. Recycling of wastes Solvent recycling provides environmental and economic benefits due to the consequent reduction of waste and lowering of the costs. The recovery of organic solvent wastes is traditionally based on distillation, which can separate volatile organic solvents from non-volatile impurities, but additional methodologies to separate organic solvents are based on permeation using selective membrane separation techniques [7]. Nowadays, traditional sample-treatment methods based on liquid–liquid separations are falling into disuse due to their high consumption of organic solvents, and they are being replaced by other methods [e.g., solidphase extraction (SPE), solid-phase microextraction (SPME), liquid–liquid microextraction (LLME) or capillary microextraction (CME)]. However, the recovery of organic solvents is especially significant in some areas of
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analytical chemistry [e.g., liquid chromatography (LC)], where the large amounts of solvents consumed during LC method development and use increase purchase and disposal costs of LC solvents, or IR spectroscopy, where chlorinated solvents are commonly used due to their high transparency in the mid-IR (MIR) spectral region]. In a really interesting discussion article published online, John W. Dolan [8] stated that solvent recycling has been for more than 10 years the main subject of LC troubleshooting [9], and he indicated different ways to reduce the volume of solvent waste from LC analyses. These include reusing all the mobile phase, automated recycling of mobile phase in isocratic elutions, distillation and modifying the size of columns and particles used in the process. The most direct way to reduce solvent consumption in LC analysis is to reuse all of it. This method applies to isocratic methods only. In such cases, recycling the mobile phase implies incorporating a small amount of the sample or standard into the mobile phase reservoir after each run. However, if the volume of the mobile phase is relatively large, the change can be considered negligible. In this way, Abreu et al. evaluated the effect of recycling the mobile phase in isocratic LC on successive analyte quantifications (citric and tartaric acids) using
Threshold value
Recycle
an ultraviolet (UV) detector [10]. Their results demonstrated that, when analyte concentration in the mobile phase exceeds that in the sample, a negative peak is observed, and, when its concentration in the mobile phase is equal to that in the sample, no peak is observed for that analyte. The slopes of the linear regression lines for standards in mobile phase with different concentrations of analyte did not change, although the Y intercept values decreased with increasing concentration of analyte. In this study, it was suggested that, when analyte concentration in the mobile phase approaches the lowest concentration of analyte in samples, it is time to discard the recycled mobile phases. Another option is the so-called closed-loop eluentrecycling system. In this system, the mobile phase is recirculated to the solvent reservoir after removal of dissolved sample constituents by their adsorption onto activated carbon [11], thus restoring the purity of the mobile phase. A further way to reduce mobile-phase consumption significantly is automatically to reuse part of the mobile phase. Once again, this procedure is applicable to isocratic-based separations only. In this case, solvent recycling is done by a microprocessor that uses a sensitive level-sensing circuit to direct the mobile phase to waste whenever the output from the system detector
Delay time
Waste
Recycle
Waste
Recycle
From HPLC system
To solvent reservoir
To waste
Figure 2. Operation of commercially-available automatic solvent-recycling system.
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exceeds a level set by the user (i.e. when an analyte or matrix component is eluting from the column). When the output from the system detector drops below the programmed level, the mobile phase is redirected to the solvent reservoir to be used again, reducing both solvent-disposal and purchasing costs (see Fig. 2). Nowadays, there are commercially-available different devices that can be employed for solvent recycling (see Table 1), and we can conclude that an automatic recycling system can reduce mobile-phase consumption by up to 90%. Distillation of the organic solvent from the mobile phase after analyte separation is another way to reduce waste generation in LC [12,13]. The main advantage of distillation is that it is applicable to both isocratic and gradient-based separations. In this way, P. Stepnowski et al. developed a methodology in 2002 for LC wastes of methanol/water [14] and acetonitrile/water [15] based on a batch-distillation system combined with microorganism biodegradation. The biodegradation was used for the first cuts and heavy ends of the solvent waste, which were unsuitable for further recovery. Moreover, B/R Instrument Corporation (Maryland, USA) produced a fractional distillation system specifically designed for automated or manual recovery of LC solvents. However, solvent recycling is not a panacea, since the distillate is of slightly lower purity than the original feedstock. Also, we need to consider that common solvents (e.g., ethanol and acetonitrile) distill as azeotropes, ethanol-water distills as a 5% water azeotrope, isopropanol-water azeotrope contains 12.6% water and acetonitrile azeotrope contains 14–16% water. As mentioned above, IR spectroscopy is another area of analytical chemistry needing to revise use of organic toxic solvents, as chlorinated hydrocarbons are still preferred solvents due to their high transparency in the MIR region. This topic has been extensively discussed since J.D.R. Thomas raised the matter [16,17]. He stated: ‘‘Clearly, the pressure is really on for laboratory procedures and analytical methods to be adapted in order to avoid the banned solvents, but also those of general environmental and health concerns’’. The problem of chlorinated solvents was therefore well known more than 15 years ago, but the question now is: ‘‘How has Table 1. Devices commercially available for solvent recycling Automatic solvent-recycling systems SRS Pro Solvent Recycling System – Thermo Scientific S-3 HPLC Solvent Recycler – Spectrum Chromatography SolventTrak – Phenomenex SolventTrak – Antech Solutions SolventTrak II – SMI-LabHut Solvent Recycler 3000 – Alltech Associates LA2890 Solvent Recycler – Laserchrom 7206 Solvent Recycler – Micro Solv Solvent Recycler 2000 – Alltech Associates Distillation systems for HPLC solvents 9600 Solvent Recycling – B/R Instrument Corporation
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the community of analytical scientists tried to solve this problem since?’’. The EPA has addressed the replacement of CFC-113 for determining oil and grease in wastewater by different solvents {e.g., the dimer/trimer of chlorotrifluoroethylene (S-316) [18] or carbon disulfide [19]}. Another strategy developed to minimize the impact on the environment of the chlorinated solvents used in IR determinations was based on recycling solvent. In this way, a closed flow-injection analysis (FIA) manifold was incorporated to do the on-line distillation of chlorinated solvents after the IR measurements in order to provide a dramatic reduction of the volume of chlorinated wastes (see Fig. 3a). This system was successfully applied to the determination in pharmaceuticals of ketoprofen [20], and propyphenazone and caffeine [21]. 2.2. Degradation of wastes Development of new methods and technologies for minimizing waste and preserving water quality is a major concern of scientists around the world [22–24]. It is of utmost importance to dispose off chemical residues properly and to keep the concentration of chemicals in effluent streams to a minimum. We should note that research in this field mainly focuses on development of new, more efficient wastewatertreatment technologies, but those achievements can also be applied in treating analytical laboratory residues, thereby minimizing the environmental impact of analytical procedures and the costs of waste treatment. In the following sub-sections, we discuss different methodologies, which are available for degradation of toxic wastes in water streams and which can be used for analytical laboratory residues, outlining their advantages and drawbacks. 2.2.1. Thermal degradation. Until the mid-1980s, waste combustion was widely considered the basic method to eliminate toxic chemical wastes. Thermal processes used for waste treatment can be classified as: i) combustion with excess of oxygen; ii) gasification or partial combustion at oxygen deficit; and, iii) pyrolysis, the main difference being the presence or absence of oxygen in the reactor. Thermal degradation is mainly used to decompose solid organic matter in the food, petrochemical and polymer industries, and it is applied off-line, which implies the storage of large amounts of solid residues [25]. As can be supposed, combustion is not the best option to clean the wastes of the analytical laboratories. The main disadvantages of such methodologies are the difficulty of on-line coupling with the analytical procedure, and the formation of large amounts of toxic emissions (e.g., ashes containing heavy metals, carbon monoxide, http://www.elsevier.com/locate/trac
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a
Solvent recovery unit Refrigerant
Injection valve
Bidirectional valve
Solvent Detector
Solvent cooling unit
Solvent reservoir Heater
Flow cell Peristaltic pump
b
Carrier OVEN Reagent Waste Measurement cell
Accepting solution
Clean waste
Peristaltic pump
c
PAP R1 IO4
-
Waste
R2
45 cm
R3
D 60 cm
NaOH
λ =540 nm
TiO2 H2O
6m Clean UV Lamp waste λ =254 nm
Peristaltic pump
d
Reagent Clean waste
Carrier Waste
Carrier
Injection valve
Filter
Measurement cell Bidirectional valve
Closed-flow of a nutrient solution Nutrient Peristaltic pump Figure 3. Manifolds proposed for on-line generation of clean analytical wastes: a) recycling of carrier solvents by distillation; b) thermal degradation of wastes; c) photoassisted catalytic oxidation of organic compounds; and, d) biodegradation.
sulfur and nitrogen oxides, chlorinated compounds and dioxins), it being necessary to apply additional purification strategies to meet environmental standards, thereby increasing operation costs. However, analytical wastes 596
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can be heated on-line inside a GC oven after the analysis of related compounds, providing the organics are thermally decomposed to gaseous products for receipt in an appropriate solution (see Fig. 3b) [26].
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2.2.2. Oxidative degradation. Advanced oxidation processes can remove organic and inorganic materials in wastewater using hydroxyl radicals. Contaminants are oxidized by different reagents (e.g., ozone, hydrogen peroxide, Fenton reagent and combinations of these). These procedures may also be combined with UV irradiation and ultrasound. Organic compounds (e.g., aromatic amines [27], ethers [28], dyes [29], chlorinated phenols [30], pesticides and polycyclic aromatics [31]) can be oxidized effectively by hydroxy radicals produced from Fenton reagent, a mixture of hydrogen peroxide and ferrous iron that produces OHÆ radicals through: H2 O2 þ Fe2þ ! Fe3þ þ OH þ OH We need to highlight that ultrasound irradiation is particularly effective for polymer degradation [32]. A detailed discussion about advanced oxidation processes and the reactions involved can be found in the review of P.R. Gogate and A.B. Pandit [33]. However, the majority of these oxidation technologies do not totally mineralize organic contaminants, combination with biological treatments being necessary for total degradation of organics from toxic wastewater [34,35]. Another problem of this type of process is that the reaction takes place in homogeneous solution in which the oxidants are consumed continuously during the reaction. 2.2.3. Heterogeneous photocatalytic oxidations. Photocatalytic or photochemical degradations are gaining importance in wastewater treatment, since they result in complete mineralization and operate at mild conditions of temperature and pressure. It can be considered a hot topic, taking into consideration the number of books and review papers published on this field in recent times [36,37]. Photocatalysis is based on the ability of the photocatalyst to adsorb simultaneously and efficiently both reactants and photons. A detailed description of the reactions and the fundamentals of heterogeneous catalysis can be found in the review paper of J.M. Herrmann [38]. A wide range of semiconductors may be used for photocatalysis (e.g., oxides TiO2, ZnO, MgO, WO3, ZrO2, CeO2 and Fe2O3, or sulfides CdS and ZnS). For heterogeneous photocatalysis with semiconductors, the photocatalyst can be dispersed in suspension or coated on the inside walls of a reaction chamber. The advantage of the heterogeneous photodegradation of organic pollutants is the possibility of recovering the catalyst by filtration, using a closed system. However, it is also possible to use the catalyst as a stationary phase by coating the inner walls of a glass reactor [39]. Other possibilities to use semiconductors (e.g., TiO2) as stationary phases include their immobilization on different substrates (e.g., silica gel) and later introduction into a
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borosilicate glass tube [40], polymeric membranes [41], porous alumina-silica ceramic prepared in the shape of a coaxial glass cylinder [42], zeolite [43], activated carbon [44], and others. It should be noted that recovery of the catalyst is an important issue, due to its potential toxicity in aquatic systems. In this sense, the toxicity of TiO2, the most widely used heterogeneous catalyst in wastewater treatment, has been deeply investigated by several bioassay procedures using D. magna and V. fischeri [45,46]. It was found that the aggregated TiO2 was not toxic, while the LC50 and the 100% mortality of the filtered TiO2 were 5.5 mg/L and 10 mg/L, respectively, LC50 being defined as the lethal concentration that kills 50% of D. magna in a given time (48 h). A list of the organic pollutants that can be photodegraded by using TiO2 as catalyst can be found in the review of D.M. Blake [47]. Among those organic compounds, we need to highlight the photodegradation of dyes, pesticides, surfactants, phenolic compounds, aromatic and aliphatic compounds, haloaromatics, nitrohaloaromatics and amides. The principle of photocatalytic degradation was successfully applied for on-line degradation of analytical wastes in FIA manifolds for the first time in 1995. Different manifolds were proposed for the degradation of the reagents employed for their colourimetric determinations (see Fig. 3c), being applied for the photo-assisted catalytic detoxification of propoxur [48], formetanate [49] and resorcinol [50] after determination with p-aminophenol. Organic compounds can be degraded into harmless forms from wastewater and various anions can be oxidized to less toxic compounds using TiO2. Nitrite has been successfully oxidized to nitrate [51], sulfide and sulfite converted to sulfate [52], and cyanide to isocyanide [53], nitrogen [54] or nitrate [55]. In addition, heavy metals can be deposited on the surface of the catalysts, forming agglomerates [56]. 2.2.4. Biodegradation. Biological processes make use of the natural metabolism of living cells to degrade or to transform chemical species using a sequence of reactions catalyzed by enzymes. Municipal wastewaters have traditionally been treated with biological processes, typically aerobic organisms in suspended systems or surface-anchored biofilms. However, biodegradation of analytical-laboratory wastes is more challenging due to the presence of less biodegradable, and often toxic, pollutants [57]. Moreover, the stability and the activity of microbial cells can be severely affected by changes in pH, temperature, and the presence of toxins, and their preservation is difficult when they are in contact with analytical wastes. Thus, an ideal waste-treatment system based on biodegradation for the analytical laboratory (see Fig. 3d) should be able to respond to extreme variations in the nature and the concentration of pollutants, http://www.elsevier.com/locate/trac
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with other variables (e.g., presence of toxins, pH and salinity (having values that are largely unpredictable. This is probably the reason of the limited applicability of toxic-waste biodegradation in analytical laboratories [26]. 2.3. Passivation of persistent pollutants Sometimes, degradation of pollutants is impossible, or is expensive or slow. In those cases, passivation of wastes is an option to reduce the potential risks of analytical wastes. The main objective of passivation is effective removal of persistent pollutants from aqueous streams, discharging wastewater as required by strict environmental legislation while reducing the amounts of residues from several liters to a few grams. This type of methodology is widely used in industry, but its application in analytical laboratories is still limited. 2.3.1. Co-precipitation of metal ions. Co-precipitation is one of the usual methods employed to remove heavy metals from wastewater. The main objective of this technique is to remove heavy-metal ions from an aqueous solution to yield a less contaminated aqueous effluent. The method involves co-precipitating the heavy-metal ions with a carrier precipitate that is formed in situ within the aqueous solution. It was patented in 1991 in the USA by W.T. Douglas [58]. The characteristics and the properties of the precipitates directly affect the efficiency of metal removal because large particles of the precipitation product could easily be filtered, while non-uniform and fine particles usually provide low filtration efficiencies [59]. Removal of heavy metals by co-precipitation with ferrite has been well known for more than 40 years [60]. Co-precipitation of metals in laboratory wastes was applied for the first time in 1990 using aluminium hydroxide [61]. This procedure was also successfully applied to the decontamination of residues from cold-vapour atomic fluorescence spectroscopy (CV-AFS) [62]. The liquid effluent obtained from the CV-AFS system, with a high acidic pH (0.5) and probably containing dissolved heavy metals (Cr, Cd, Ba, . . .) was merged with a solution of Fe(III) and later with a solution of NaOH, providing on-line coprecipitation of heavy metals with Fe(OH)3. In 1992, the EPA developed a research project to remove heavy metals from municipal wastewater [63]. A sand bed was used with lime feed to cause coprecipitation of metals and calcium carbonate on the surface of sand grains. Through continuous plating by the precipitates, the sand grains increased in size and could easily be filtered and separated from the solution. Recently, an electrochemical method, named electrocoagulation, has attracted significant attention for removal of inorganic ions [64]. An example of the electrocoagulation process can be found in the removal of Cr in wastewater, where the iron anode dissolved and 598
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produced Fe2+, which reduced Cr6+ to Cr3+, leading to the co-precipitation of Cr(OH)3 and Fe(OH)3. The main advantage of the procedure is that no chemicals need to be added. However, a major disadvantage of this process is the hydrogen gas produced at the cathode, which prevents the flocs from settling properly [65]. Moreover, the particle size of the precipitate makes the filtration process difficult. To overcome these problems, the electrocoagulationelectroflotation combination [66] was applied to float the precipitate and to separate it from the treated water. Iron, nickel, copper, zinc, lead and cadmium were removed at 95% level using the electrocoagulation-electroflotation combination [67]. A similar combined electrocoagulation and electroflotation process was proposed to remove fluoride from drinking water [68] using aluminum electrodes. The main advantages of this methodology over conventional treatments include versatility, energy efficiency, safety, selectivity, possibility to automation and cost effectiveness [69]. Electrocoagulation is an efficient process also for the treatment of organic pollutants from water [70]. 2.3.2. Surfactant-based decontamination. Aqueous surfactant two-phase (ASTP) extraction is a promising method to remove organic contaminants from wastewater [71]. A typical example of such ASTP separation techniques using a non-ionic surfactant is cloud-point extraction (CPE), where the phase separation is caused by elevating the temperature above the cloud point [72]. One phase is the surfactant-rich phase, while the other phase is a bulk aqueous phase known as the surfactantdilute phase containing only a small concentration of surfactant aggregates, the organic contaminants being concentrated in the surfactant-rich phase [73]. In a similar way, aqueous two-phase systems (ATPSs) can be formed with combinations of hydrophilic solutes (e.g., polymers or polymers and certain salts), mixed in aqueous solution above critical concentrations [74]. These processes have been successfully and extensively applied for the recovery of biological products (e.g., enzymes and proteins from different sources) [75]. It has been reported that mixtures of surfactants often offer properties superior to those of single surfactants, enhancing the effectiveness of extraction [76]. Mixtures of anionic and cationic surfactants can also exhibit aqueous–aqueous phase separation and can be used in ASTP extraction [77]. Another type of surfactant-based separation is micellar-enhanced ultrafiltration (MEUF), where a surfactant is added to the wastewater at a concentration higher than its critical micelle concentration (CMC). The amphiphilic aggregates attract metal ions to the micelle surface and the organic molecules are solubilized in the micelle core. Thus, wastewater can be filtered through an ultrafiltration membrane having pore sizes small
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enough to reject the micelles. MEUF has been applied for the removal of arsenic ions from highly polluted waters [78], chlorinated aromatic hydrocarbons, nitrate and chromate [79] and metal ions [80]. Several ultrafiltration-based techniques, in which the surfactant is replaced by water-soluble compounds, have been developed for effective removal of metal ions and small organic contaminants from wastes, {e.g., ion-expulsion enhanced ultrafiltration [81], polymerenhanced ultrafiltration [82], dendrimer-enhanced ultrafiltration [83] and polyelectrolyte-enhanced ultrafiltration [84]}. Admicelles and hemimicelles are relatively newly investigated phenomena [85]. The term ‘‘admicelle’’ was coined for adsorbed micelles formed on surfaces. Hemimicelles are monolayer formations of surfactants on surfaces. Admicelles and hemimicelles are aggregates of surfactants able to solubilize a wide variety of substances. The systems mentioned have been proposed as extraction sorbents for organic analytes in analytical chemistry. This approach, termed admicellar or hemimicellar SPE, involves utilizing surfactants adsorbed onto a solid phase and was tested for the extraction of chlorophenols [86], polyaromatic hydrocarbons [87], and phthalates [88] using SDS-alumina or dialkylsulfosuccinate-alumina sorbents. 2.3.3. Adsorption on different materials. Adsorption has become one of the preferred methods for removal of toxic contaminants from water streams, as it is a very efficient, economical, versatile and simple methodology [89]. Different conventional and non-conventional types of adsorbent have been used to remove metal ions and organic compounds. The adsorbents can be of mineral, organic or biological origin (e.g., activated carbons [90], zeolites [91], clays [92], silica beads [93]), low-cost adsorbents (e.g., industrial by-products [94], agricultural wastes [95] and biomass [96]), and polymeric materials (e.g., organic polymeric resins [97] and macroporous hypercrosslinked polymers [98]). In recent years, natural polymer adsorbents have been used (e.g., chitin [99], starch [100], and their derivatives chitosan [101] and cyclodextrin [102]). G. Crini published a review article in 2005 on recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment [103].
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laboratory wastes, and the majority concern treatment of industrial wastewater or municipal residues. The question we need to address is ‘‘Why is industry developing and applying methods to reduce the volume and the toxicity of their wastes, while analytical laboratories are not involved to the same extent?’’. Other than the obvious answer regarding the smaller volume of toxic wastes generated in the analytical laboratory, compared with industrial processes, most new sample-treatment procedures (e.g., SPE, SPME and LLME) developed by analytical chemists try to reduce the use of organic solvents and to replace toxic reagents by harmless ones. However, it is common practice in analytical laboratories to accumulate analytical wastes for later treatment. The main reason for this practice is that the economic cost of waste management is not usually paid by the analytical laboratory itself but by universities or academic authorities, so it is absolutely necessary to change the mentality of analytical chemists in this sense. The new ecological mentality in analytical laboratories involves introducing and incorporating recycling and decontamination procedures in the development of new methods of analysis. To encourage this change of mentality in 1991, the University of California at Berkeley, USA, implemented a charge-back program in which 25% of the cost of disposal was assumed by the laboratory and the authorities performed inspections and analyzed effluents to identify hazardous wastes properly. After the first period, the charge-back cost of disposal increased to 100%. The University of Wyoming, USA, also established a charge-back program in 1994, where 25% of the cost of waste management of its laboratories was financed by the university, but 75% was assumed by the different departments and research laboratories [104]. In summary, decontamination of analytical wastes and recycling of solvents and reagents should be considered as the last step of the analytical process [26]. Accumulation of wastes must be replaced by their online treatment, avoiding safety problems relating to the storage of large amounts of residues and reducing the cost of their management. Recycling solvents and reagents and decontaminating wastes should be considered as additional, but absolutely necessary, in the effort to eliminate the side effects of analytical laboratories.
References 3. Future trends and conclusions The first conclusion that can be extracted from this review is that there are a lot of procedures available for the removal of toxics, so as to reduce the side effects of chemical activities. However, only a few papers of those we presented here were directly related to analytical
[1] J. Namiesnik, Environ. Sci. Pollut. Res. 6 (1999) 243. [2] P.T. Anastas, J.C. Warner, Green Chemistry: Theory and Practice, Oxford University Press, New York, USA, 1998. [3] P.T. Anastas, Critical Rev. Anal. Chem. 29 (1999) 167. [4] S. Armenta, S. Garrigues, M. de la Guardia, Trends Anal. Chem. 27 (2008) 497. [5] M. Koel, M. Kaljurand, Pure Appl. Chem. 78 (2006) 1993.
http://www.elsevier.com/locate/trac
599
Trends
Trends in Analytical Chemistry, Vol. 29, No. 7, 2010
[6] F.R.P. Rocha, J.A. Nobrega, O.F. Filho, Green Chem. 3 (2001) 216. [7] C. Streicher, P. Kremer, V. Thomas, A. Hubner, G. Ellinghorst, Development of new pervaporation membrane system and processes to separate alcohols/ether/hydrocarbons mixtures, in: Proc. 7th Int. Conf. Pervaporation in the Chemical Industry, Nevada, 1995, p. 297. [8] J.W. Dolan, LCGC 10 (2007). [9] J.W. Dolan, LCGC Intl. 5 (1991) 14. [10] O. Abreu, G.D. Lawrence, Anal. Chem. 72 (2000) 1749. [11] R.O. Sheth, Closed Loop Recycling of Solvents Used in High Pressure Liquid Chromatograph (HPLC) Analysis, Technical Note, Mason & Hanger-Silas Mason Co., Inc., Pantex Plant, Texas, USA. [12] R.M. Katusz, L. Bellew, J.A. Mangravite, R.F. Foery, J. Chromotagr. 213 (1981) 331. [13] J.A. Mangravite, R.R. Roark, P. Van Triest, Solvent recycling by spinning band distillation: theory, equipment, and limitations, in: P.A. Reinhardt, K.L. Leonard, P.C. Ashbrook (Editors), Pollution Prevention and Waste Minimization in Laboratories, Lewis Publishers, New York, USA, 1996, pp. 239–274. [14] P. Stepnowski, K.H. Blotevogel, B. Jastorff, Environ. Sci. Pollut. Res. 9 (2002) 34. [15] P. Stepnowski, K.H. Blotevogel, P. Ganczarek, U. Fischer, B. Jastorff, Res. Conserv. Recycl. 35 (2002) 163. [16] J.D.R. Thomas, Trends Anal. Chem. 14 (1995) 186. [17] D. Nobel, Anal. Chem. 65 (1993) 693A. [18] ASTM International, Method D7066-04, Standard Test Method for dimer/trimer of chlorotrifluoroethylene (S-316) Recoverable Oil and Grease and Nonpolar Material by Infrared Determination, ASTM International, West Conshohocken, PA, USA, 2004. [19] V.J. Barwick, S.L. Ellison, M.J.Q. Rafferty, T.J. Farrant, Int. J. Environ. Anal. Chem. 72 (1998) 235. [20] M.J. Sanchez-Dasi, S. Garrigues, M.L. Cervera, M. De la Guardia, Anal. Chim. Acta 361 (1998) 253. [21] Z. Bouhsain, S. Garrigues, M. de la Guardia, Analyst (Cambridge UK) 122 (1997) 441. [22] D.T. Sawyer, A.F. Martell, Industrial Environmental Chemistry: Waste Minimization in Industrial Processes and Remediation of Hazardous Wastes, Plenum Press, New York, USA, 1992. [23] D.W. Green, L.L. Smith, J.S. Crain, A.S. Poparai, J.T. Kiely, J.S. Yaeger, J.B. Schilling, Secondary Waste Minimization in Analytical Methods, DOE Report, 2004 (http://www.p2pays.org/ref/ 04/03277.pdf). [24] A. Reinhardt, K.L. Leonard, P.C. Ashbrook (Editors), Pollution Prevention and Waste Minimization in Laboratories, vol. 3, CRC Press, Inc., Boca Raton, FL, USA, 1996. [25] European Commission (EC), Integrated pollution prevention and control. Draft reference document on the best available techniques for waste incineration, EC, Brussels, Belgium, 2004. [26] M. de la Guardia, J. Braz. Chem. Soc. 10 (1999) 429. [27] I. Casero, D. Sicilia, S. Rubio, D. Pe´rez-Bendito, Water Res. 31 (1997) 1985. [28] A.A. Burbano, D.D. Dionysiou, M.T. Suidan, T.L. Richardson, Water Res. 39 (2005) 107. [29] W.G. Kuo, Water Res. 26 (1992) 881. [30] W.Z. Tang, C.P. Huang, Chemosphere 33 (1996) 1621. [31] J.J. Pignatelle, Environ. Sci. Technol. 26 (1992) 944. [32] J. Chakraborty, J. Sarkar, R. Kumar, G. Madras, Polym. Degrad. Stabil. 85 (2004) 555. [33] P.R. Gogate, A.B. Pandit, Adv. Environ. Res. 8 (2004) 501. [34] A. Marco, S. Esplugas, G. Saum, Water Sci. Technol. 35 (1997) 321. [35] E. Chamarro, A. Marco, S. Esplugas, Water Res. 35 (2001) 1047. [36] D.W. Bahnemann, J. Cunningham, M.A. Fox, E. Pelizzetti, P. Pichat, N. Serpone, in: R.G. Zepp, G.R. Helz, D.G. Crosby
600
http://www.elsevier.com/locate/trac
[37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47]
[48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58]
[59] [60] [61] [62]
[63]
[64] [65] [66] [67] [68] [69] [70]
(Editors), Aquatic Surface Photochemistry, Lewis Publishers, Boca Raton, FL, USA, 1994, p. 261. J.M. Herrmann, Helv. Chim. Acta 84 (2001) 2731. J.M. Herrmann, Catal. Today 53 (1999) 115. K. Vinodgopal, U. Stafford, K.A. Gray, P.V. Kamat, J. Phys. Chem. 98 (1994) 6797. Z. Ding, X.J. Hu, G.Q. Lu, P.L. Yue, P.F. Greenfield, Langmuir 16 (2000) 6216. N. Phonthammachai, E. Gulari, A.M. Jamieson, S. Wongkasemjit, Appl. Organometal. Chem. 20 (2006) 499. Y. Peng, J.T. Richardson, Appl. Catal., A 266 (2004) 235. P. Atienzar, A. Corma, H. Garcia, J.C. Scaiano, Chem. Mater. 16 (2004) 982. F.L.Y. Lam, X.J. Hu, Chem. Eng. Sci. 58 (2003) 687. A. Bozzi, M. Dhananjeyan, I. Guasaquillo, S. Parra, C. Pulgarin, C. Weins, J. Kiwi, J. Photochem. Photobiol. Chem. 162 (2004) 179. S.B. Lovern, R. Klaper, Environ. Toxicol. Chem. 25 (2006) 1132. D.M. Blake, Bibliography of Work on Photocatalytic Removal of Hazardous Compounds from Water and Air, NREL/TP-43022197, National Renewable Energy Laboratory, Golden, CO, USA, 1997. M. de la Guardia, K.D. Khalaf, V. Carbonell, A. Morales-Rubio, Anal. Chim. Acta 308 (1995) 462. M.J. Escuriola, A. Morales-Rubio, M. de la Guardia, Anal. Chim. Acta 390 (1999) 147. M. de la Guardia, K.D. Khalaf, B.A. Hasan, A. Morales-Rubio, V. Carbonell, Analyst (Cambridge UK) 120 (1995) 231. A. Zafra, J. Garcia, A. Milis, X. Domenech, J. Mol. Catal. 70 (1991) 343. S.N. Frank, A.J. Bard, J. Phys. Chem. 81 (1977) 1484. S.N. Frank, A.J. Bard, J. Am. Chem. Soc. 99 (1977) 303. H. Hidaka, T. Nakamura, A. Ishizaha, M. Tsuchiya, J. Zhao, J. Photochem. Photobiol., A 66 (1992) 367. C.H. Pollema, J. Hendrix, E.B. Milosavljevic, L. Solujic, J.H. Nelson, J. Photochem. Photobiol., A 66 (1992) 235. J.M. Herrmann, J.J. Disdier, P. Pichat, J. Catal. 113 (1988) 72. M.A. Tarr, Chemical Degradation Methods for Wastes and Pollutants, Marcel Dekker Inc., NY, USA, 2003. W.T. Douglas, US Patent 5013453 - Method for removing heavy metals from aqueous solutions by coprecipitation, No. 042565 filed on 04/16/1987. O. Sohnel, J. Garside, Precipitation, Butterworth Heinemann, Oxford, UK, 1992. W. Dyck, Can. J. Chem. 46 (1968) 1441. T. Chohji, E. Hirai, Y. Hayashi, A. Touda, Environ. Technol. 11 (1990) 421. P. Cava-Montesinos, E. Ro´denas-Torralba, A. Morales-Rubio, M.L. Cervera, M. De la Guardia, Anal. Chim. Acta 506 (2004) 145. J.C. Huang, An innovative coprecipitation technique for removing heavy metals from wastewater, EPA-600/S2–82-053, US Environmental and Protection Agency, Washington, DC, USA, 1982. N. Kongsricharoern, C. Polprasert, Water Sci. Technol. 31 (1995) 109. M.F. Pouet, F. Persin, M. Rumeau, Water Res. 25 (1992) 247. G.H. Chen, X.M. Chen, P.L. Yue, J. Environ. Eng. 126 (2000) 858. B. Merzouk, B. Gourich, A. Sekki, K. Madani, M. Chibane, J. Hazard. Mater. 164 (2009) 215. Q. Zuo, X. Chen, W. Li, G. Chen, J. Hazard. Mater. 159 (2008) 452. M.Y.A. Mollah, R. Schennach, J.R. Parga, D.L. Cocke, J. Hazard. Mater. 84 (2001) 29. M. Bayramoglu, M. Eyvaz, M. Kobya, Chem. Eng. J. 128 (2007) 155.
Trends in Analytical Chemistry, Vol. 29, No. 7, 2010 [71] J.F. Scamehorn, J.H. Harwell, Surfactant-based Separation Processes, Marcel Dekker, New York, USA, 1989. [72] W.L. Hinze, E. Pramauro, Crit. Rev. Anal. Chem. 24 (1993) 133. [73] P. Trakultamupatam, J.F. Scamehorn, S. Osuwan, Separ. Sci. Technol. 37 (2002) 1291. [74] M. Rito-Palomares, J. Chromatogr., B 807 (2004) 3. [75] H. Walter, G. Johansson, D.E. Brooks, Anal. Biochem. 197 (1991) 1. [76] C.C. Ruiz, J. Aguiar, Colloids Surf., A 224 (2003) 221. [77] P. Weschayanwiwat, O. Kunanupap, J.F. Scamehorn, Chemosphere 72 (2008) 1043. [78] F. Beolchini, F. Pagnanelli, I. De Michelis, F. Veglio`, Environ. Sci. Technol. 40 (2006) 2746. [79] K. Baek, J.W. Yang, Chemosphere 57 (2004) 1091. [80] R.S. Juang, Y.Y. Xu, C.L. Chen, J. Membrane Sci. 218 (2003) 257. [81] D.K. Krehbiel, J.F. Scamehorn, R. Ritter, S.D. Christian, E.E. Tucker, Sep. Sci. Technol. 27 (1992) 1775. [82] P. Can˜izares, A. Pe´rez, R. Camarillo, J.J. Linares, J. Membrane Sci. 240 (2004) 197. [83] M.S. Diallo, S. Christie, P. Swaminathan, J.H. Johnson, W.A. Goddard, Environ. Sci. Technol. 139 (2005) 1366. [84] D.J. Ennigrou, L. Gzara, M. Ramzi Ben Romdhane, M. Dhahbi, Desalination 246 (2009) 363. [85] S. Gangula, S.Y. Suen, E.D. Conte, Microchem. J. 95 (2010) 2. [86] T. Saitoh, T. Kondo, M. Hiraide, J. Chromatogr., A 1164 (2007) 40. [87] T. Saitoh, S. Matsushima, M. Hiraide, J.Chromatogr., A 1069 (2005) 271.
Trends [88] T. Saitoh, S. Matsushima, M. Hiraide, J. Chromatogr., A 1040 (2004) 185. [89] A.A. Lewinski, Hazardous Materials and Wastewater: Treatment, Removal and Analysis, Nova Science Publishers, Inc., NY, USA, 2007. [90] J.M. Chern, Y.W. Chien, Water Res. 37 (2003) 2347. [91] S.T. Bosso, J. Enzweiler, Water Res. 36 (2002) 4795. [92] O. Abollino, M. Aceto, M. Malandrino, C. Sarzanini, E. Mentasti, Water Res. 37 (2003) 1619. [93] M. Ghoul, M. Bacquet, M. Morcellet, Water Res. 37 (2003) 729. [94] F.A. Lopez, M.I. Martin, C. Perez, A. Lopez-Delgado, F.J. Alguacil, Water Res. 37 (2003) 3883. [95] T. Robinson, B. Chandran, P. Nigam, Water Res. 36 (2002) 2824. [96] M.X. Loukidou, K.A. Matis, A.I. Zouboulis, M. LiakopoulouKyriakidou, Water Res. 37 (2003) 4544. [97] A. Atia, A.M. Donia, S.A. Abou-El-Enein, A.M. Yousif, Sep. Purif. Technol. 33 (2003) 295. [98] W. Azanova, J. Hradil, React. Funct. Polym. 41 (1999) 163. [99] J. Synowiecki, N.A. Al-Khateeb, Crit. Rev. Food Sci. Nutr. 43 (2003) 145. [100] V.P. Yuryev, A. Cesaro, W.J. Bergthaller, Starch and Starch Containing Origins -Structure, Properties and New Technologies, Nova Science Publishers, Inc., New York, USA, 2002. [101] S. Babel, T.A. Kurniawan, J. Hazard. Mater. 897 (2003) 219. [102] G. Crini, M. Morcellet, J. Sep. Sci. 25 (2002) 789. [103] G. Crini, Prog. Polym. Sci. 30 (2005) 38. [104] D. Mooney, Chemical Health and Safety 11 (2004) 24.
http://www.elsevier.com/locate/trac
601