Application of low-cost adsorbents for dye removal – A review.pdf

8/11/2019 Application of low-cost adsorbents for dye removal A review.pdf

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Review

Application of low-cost adsorbents for dye removal A review

V.K. Gupta a,*, Suhas b

a Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247 667, Indiab Centro de Qumica de Evora and Departmento de Quimica, Universidade de Evora, Colegio Lus Antonio Verney, 7000-671 Evora, Portugal

a r t i c l e i n f o

Article history:

Received 23 June 2008

Received in revised form

8 November 2008

Accepted 24 November 2008

Available online 4 March 2009

Keywords:

Adsorbents

Adsorption

Dye removal

Dyes

Low-cost adsorbents

Non-conventional adsorbents

Wastewater treatment

a b s t r a c t

Dyes are an important class of pollutants, and can even be identified by the human eye. Disposal of dyes

in precious water resources must be avoided, however, and for that various treatment technologies are inuse. Among various methods adsorption occupies a prominent place in dye removal. The growingdemand for efficient and low-cost treatment methods and the importance of adsorption has given rise to

low-cost alternative adsorbents (LCAs). This review highlights and provides an overview of these LCAs

comprising natural, industrial as well as synthetic materials/wastes and their application for dyesremoval. In addition, various other methods used for dye removal from water and wastewater are alsocomplied in brief. From a comprehensive literature review, it was found that some LCAs, in addition to

having wide availability, have fast kinetics and appreciable adsorption capacities too. Advantages anddisadvantages of adsorbents, favourable conditions for particular adsorbateadsorbent systems, and

adsorption capacities of various low-cost adsorbents and commercial activated carbons as available inthe literature are presented. Conclusions have been drawn from the literature reviewed, and suggestions

for future research are proposed.2008 Elsevier Ltd. All rights reserved.

1. Introduction

Saving water to save the planet and to make the future of

mankind safe is what we need now. With the growth of mankind,society, science, technology our world is reaching to new highhorizons but the cost whichwe are paying or will pay in near futureis surely going to be too high. Among the consequences of this rapid

growth is environmental disorder with a big pollution problem.Besides other needs the demand for water (Water for PeopleWater for Life United Nations World Water Development ReportUNESCO) has increased tremendously with agricultural, industrial

and domestic sectors consuming 70, 22 and 8% of the availablefresh water, respectively and this has resulted in the generation of

large amounts of wastewater (Helmer and Hespanhol, 1997; Lehret al., 1980; Nemerrow, 1978) containing a number of pollutants.

One of the important class of the pollutants is dyes, and once theyenter the water it is no longer good and sometimes difficult to treatas the dyes have a synthetic origin and a complex molecularstructure which makes them more stable and difficult to be bio-

degraded (Forgacs et al., 2004; Rai et al., 2005).Mankind has used dyes for thousands of years (Christie, 2007)

and the earliest known use of a colourant is believed to be by

Neanderthal man about 1,80,000 years ago. However, the firstknown use of an organic colourant was much later, being nearly4000 years ago, when the blue dye indigo was found in the

wrappings of mummies in Egyptian tombs (Gordon and Gregory,1983). Till the late nineteenth century, all the dyes/colourants weremore or less natural with main sources like plants, insects andmollusks, and were generally prepared on small scale. It was only

after 1856 that with Perkins historic discovery (Hunger, 2003;Venkataraman, 1965) of the first synthetic dye, mauveine, that dyeswere manufactured synthetically and on a large scale.

Dye molecules comprise of two key components: the chromo-

phores, responsible for producing the colour, and the auxochromes,which can not only supplement the chromophore but also render

the molecule soluble in waterand give enhanced affinity (to attach)toward the fibers. Dyes exhibit considerable structural diversity

and are classified in several ways. These can be classified (Hunger,2003) both by their chemical structure and their application to thefiber type. Dyes may also be classified on the basis of their solu-bility: soluble dyes which include acid, mordant, metal complex,

direct, basic and reactive dyes; and insoluble dyes including azoic,sulfur, vat and disperse dyes. Besides this, eithera major azo linkageor an anthraquinone unit also characterizes dyes chemically. It isworthwhile noting that the azo dyes are the one most widely used

and accounts 6570% of the total dyes produced. Though, theclassification of dyes on basis of structure is an appropriate system

* Corresponding author. Tel.: 91 1332 285801; fax: 91 1332 273560.

E-mail address: [email protected](V.K. Gupta).

Contents lists available atScienceDirect

Journal of Environmental Management

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j e n v m a n

0301-4797/$ see front matter 2008 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jenvman.2008.11.017

Journal of Environmental Management 90 (2009) 23132342
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and has many advantages, like it readily identifies dyes asbelonging to a group and having characteristic properties, e.g., azo

dyes (strong, good all-round properties, cost-effective) andanthraquinone dyes (weak, expensive), there are a manageablenumberof chemical groups (about a dozen). Besides these, both the

synthetic dye chemist and the dye technologist use this classifica-tion most widely. However, the classification based on applicationis advantageous before considering chemical structures in detailbecause of the complexities of the dye nomenclature from this type

of system. It is also worth to point that classification by applicationis the principal system adopted by the Colour Index (C.I.). In thepresent review we will try to use the dye names based on their

application or their C.I. name/number. This system includes thename of the dye class,its hue, and a number. A five digit C.I. numberis assigned to a dye when its chemical structure has been disclosedby the manufacturer. It is also worth to note here that though a dye

has a C.I. number, the purity and precise chemical constitution mayvary depending upon the name. An example of dye acid blue 92 isgiven inFig. 1(Sabnis, 2008).

Some properties of dyes classified on their usage (Christie, 2007;

Hunger, 2003) are discussed in brief here.

Acid Dyes: used for nylon, wool, silk, modified acrylics, and also

to some extent for paper, leather, ink-jet printing, food, andcosmetics. They are generally water soluble. The principal chemicalclasses of these dyes are azo (including premetallized), anthraqui-none, triphenylmethane, azine, xanthene, nitro and nitroso.

Cationic (Basic) Dyes: used for paper, polyacrylonitrile, modified

nylons, modified polyesters, cation dyeable polyethylene tere-phthalate and to some extent in medicine too. Originally they were

used for silk, wool, and tannin-mordanted cotton. These water-soluble dyes yield coloured cations in solution and thats why arecalled as cationic dyes. The principal chemical classes are dia-zahemicyanine, triarylmethane, cyanine, hemicyanine, thiazine,

oxazine and acridine.

Disperse Dyes: used mainly on polyester and to some extent onnylon, cellulose, cellulose acetate, and acrylic fibers. These aresubstantially water-insoluble nonionic dyes used for hydrophobic

fibers from aqueous dispersion. They generally contain azo,anthraquinone, styryl, nitro, and benzodifuranone groups.

Direct Dyes: used in the dyeing of cotton and rayon, paper,leather, and, to some extent to nylon. They are water-soluble

anionic dyes, and, when dyed from aqueous solution in the pres-ence of electrolytes have high affinity for cellulosic fibers. Generallythe dyes in this class are polyazo compounds, along with somestilbenes, phthalocyanines and oxazines.

Reactive Dyes: generally used for cotton and other cellulosics,but are also used to a small extent on wool and nylon. These dyesform a covalent bond with the fiber and contain chromophoricgroups such as azo, anthraquinone, triarylmethane, phthalocya-

nine, formazan, oxazine, etc. Their chemical structures are simpler,absorption spectra show narrower absorption bands, and the

dyeings are brighter making them advantageous over direct dyes.Solvent Dyes: used for plastics, gasoline, lubricants, oils, and

waxes. These dyesare solvent soluble (waterinsoluble) and generallynonpolar or little polar, i.e., lacking polar solubilizing groups such assulfonic acid, carboxylic acid, or quaternary ammonium. The prin-

cipal chemical classes are predominantly azo and anthraquinone, butphthalocyanine and triarylmethane are also used.

Sulfur Dyes: used for cotton and rayon and have limited usewithpolyamide fibers, silk, leather, paper, and wood. They have inter-

mediate structures and though they form a relatively small group ofdyes the low cost and good wash fastness properties make this classimportant from an economic point of view.

Vat Dyes: used for cotton mainly to cellulosic fibers as soluble

leuco salts and for rayon and wool too. These water-insoluble dyes

are with principal chemical class containing anthraquinone(including polycyclic quinones) and indigoids.

Besides these, there are some other classes too like azoic having

azo groups used for cotton and other cellulosic materials; fluorescentbrighteners havingstilbene,pyrazoles, coumarinand naphthalimidesused for soaps and detergents, fibers, oils, paints, and plastics andmordant having azo and anthraquinone used for wool, leather,

natural fibers after pretreating with metals and anodized aluminium.Overall at present there are more than 100,000 commercial dyes

with a rough estimated production of 7 1051106 tons per year(Christie, 2007; Hunger, 2003; Husain, 2006; Meyer, 1981; Zollinger,1987). Of such a huge production the exact data on the quantity ofdyes discharged in environment is not available. However, it is

reported that 1015% of the used dyes enter the environment

through wastes (Haiet al., 2007; Husain, 2006). The bigconsumers ofdyes are textile, dyeing, paper and pulp, tanneryand paint industries,and hence the effluents of these industries as well as those from

plants manufacturing dyes tend to contain dyes in sufficient quan-tities. Dyes are considered an objectionable type of pollutant becausethey are toxic (Bae and Freeman, 2007; Christie, 2007; Combes and

Havelandsmith, 1982; Nemerow and Doby, 1958) generally due tooral ingestion and inhalation, skin and eye irritation, and skinsensitization leading to problems like skin irritation and skin sensi-tization and also due to carcinogenicity (Christie, 2007; Hatch and

Maibach,1999;Rai et al., 2005). They impart colourto water which isvisible to human eye and therefore, highly objectionable on aestheticgrounds. Not only this, they also interfere with the transmission oflight and upset the biological metabolism processes which cause the

destruction of aquatic communities presentin ecosystem(Kuo,1992;

Fig.1. Acid blue 92 (Sabnis, 2008).C.I. Name: C.I. Acid Blue 92.C.I. Number:C.I.13390.

Other names: Acid Blue 92; Acid Blue A; Acid Fast Blue R; Acid Leather Blue R; Acid

Wool Blue RL; Acilan Fast Navy Blue R; Airedale Blue RL; Amacid Fast Blue R; Anazo-

lene sodium; Benzyl Blue R; Benzyl Fast Blue R; Best Acid Blue 3R; Bucacid Fast Wool

Blue R; Coomassie Blue RL. CA Index Name: 2,7-Naphthalenedisulfonic acid, 4-

hydroxy-5-[[4-(phenylamino) 5-sulfo-1- naphthalenyl]azo]-, trisodium salt. CAS

Registry Number: 3861-73-2. Chemical/Dye Class: Azo. Molecular Formula:

C26H16N3O10S3Na3. Molecular Weight: 695.59. Physical Form: Dark bluish-black

powder. Solubility:Soluble in water, acetone; slightly soluble in ethanol, glycerol. UV-

Visible (l

max):571 nm, 585 nm, 580590 nm.

V.K. Gupta, Suhas / Journal of Environmental Management 90 (2009) 231323422314


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Walsh et al., 1980). Further, the dyes have a tendency to sequestermetal and may cause microtoxicity to fish and other organisms

(Walshet al., 1980). As such it is important to treat coloured effluentsfor the removal of dyes.

For this various methodologies have been presented and even

reviewed too (Aksu, 2005; Banat et al., 1996; Crini, 2006; Crini andBadot, 2008; Delee et al.,1998; dosSantos et al., 2007;Forgacs et al.,2004; Fu and Viraraghavan, 2001a; Hai et al., 2007; Kandelbauerand Guebitz, 2005; McMullan et al., 2001; Ozyurt and Atacag, 2003;

Pearce et al., 2003; Rai et al., 2005; Robinson et al., 2001; Sanghiand Bhattacharya, 2002; Slokar and Majcen Le Marechal, 1998;Stolz, 2001; van der Zee and Villaverde, 2005; Vandevivere et al.,

1998; Wesenberg et al., 2003; Wojnarovits and Takacs, 2008). Someof these are discussed in the subsequent paragraphs.

2. Methods of dye removal

Few decades earlier, the dyes selection, application and use werenot given a major consideration with respect to their environmentalimpact. Even thechemical composition of half of the dyes used in the

industry wasestimated to be unknown. Withthe growingconcernonhealth mainly on aestheticgrounds, it was morefrom 80sthat people

started paying much attention to the dye wastes too. In the last fewyears, however, more information on the environmental conse-quences of dyestuff usage has become available and the dye manu-facturers, users and government themselves are taking substantialmeasures to treat the dye containing wastewaters. Since initially

there was no discharge limit the treatment of dyewastewater startedjust with some physical treatments such as sedimentation andequalisation to maintain thepH, total dissolved solids(TDS) andtotalsuspended solids (TSS) of the discharged water. Later secondary

treatmentssuch as theuse of filter beds forbiodegradation and, morerecently, the introduction of the activated sludge process (aerobicbiodegradation) were used to treat the dye wastewater. Normallyindustrial-wastewater treatment processes (Perry et al.,1997) consist

of following steps like: Pretreatment industrial-wastewater

streams prior to discharge to municipal sewerage systems or even toa central industrial sewerage system are pretreated doing equal-isation, neutralization; then they undergo primary treatment and

wastewater is directed toward removal of pollutants with the leasteffort. Suspended solids are removed by either physical or chemicalseparation techniques and handled as concentrated solids; then theyare given a secondary treatment usually involving microorganisms

(biological treatment) primarily bacteria which stabilize the wastecomponents. The third step is physicalchemical treatment ortertiary treatment and the processes included in this are adsorption,ion exchange, stripping, chemical oxidation, and membrane separa-

tions. All of these are more expensive than biological treatment butare used for the removal of pollutants that are not easily removed bybiological methods.Though these aregenerally utilized in series with

biological treatment, sometimes they are used as stand-aloneprocesses too.The finalstep being the sludge processing and disposal.Dye wastewater are also treated in more or less a similar way,nevertheless, there is no single standard methodology/treatment

procedure used for all types of wastes.We are classifying the methodologies generally adopted to treat

dye wastewater in four categories: (i) physical (ii) chemical (iii)biological and (iv) acoustical, radiation, and electrical processes.

Some of the methodologies lying in above mentioned categoriesare discussed in brief in subsequent paragraphs.

Sedimentationis the basic form of primary treatment used atmost municipal and industrial-wastewater treatment facilities

(Cheremisinoff, 2002). There are a number of process optionsavailable to enhance gravity settling of suspended particles,

including chemical flocculants, sedimentation basins, and clarifiers.

Filtration technology is an integral component of drinkingwater and wastewater treatment applications which includesmicrofiltration, ultrafiltration, nanofiltration, and reverse osmosis.This has been investigated for colour removal (Avlonitis et al., 2008;

Cheremisinoff, 2002). Each membrane process is best suited fora particular water treatment function (Cheremisinoff, 2002).Among them, microfiltration is of not much use for wastewater

treatment because of its large pore size, and though ultrafiltrationand nanofiltration (Cheremisinoff, 2002; Marmagne and Coste,1996) techniques are effective for the removal of all classes ofdyestuffs, dye molecules cause frequent clogging of the membrane

pores making the separation systems of limited use for textileeffluent treatment. The main drawbacks are high working pres-sures, significant energy consumption, high cost of membrane and

a relatively short membrane life which makes their use limited fortreating dye wastewater. Reverse osmosis forces water, underpressure, through a membrane that is impermeable to mostcontaminants. The membrane is somewhat better at rejecting salts

than it is at rejecting non-ionized weak acids and bases and smallerorganic molecules generally molecular weight below 200. Reverseosmosis (Al-Bastaki, 2004; Marcucci et al., 2001; Sostar-Turk et al.,2005) is effective decolouring and desalting process against the

most diverse range of dye wastes, and has been successfullyemployed for recycling. The water produced by reverse osmosis,will be close to pure H2O.

Chemical treatment of dye wastewater with a coagulating/flocculating agent (Shi et al., 2007; Wang et al., 2006a; Zhou et al.,2008) is one of the robust ways to remove colour. The processinvolves adding agents, such as aluminum (Al3), calcium (Ca2) or

ferric (Fe3) ions, to the dye effluent and induces flocculation.Besides these other agents (Mishra and Bajpai, 2006; Mishra et al.,2006; Yue et al., 2008) have also been used for the process.Sometimes combination (Wang et al., 2007) of two may also be

added to enhance the process. Generally, the process is economi-cally feasible (but sometimes becomes expensive due to the cost ofchemicals) with satisfactory removal of disperse, sulfur, and vat

dyes. However, the main drawback of the process is that the finalproduct is a concentrated sludge produced in large quantities also,besides this, the removal is pH dependent (Kace and Linford, 1975;Lee et al., 2006). This process is not good forhighly soluble dyes andthe result with azo, reactive, acid and especially the basic dyes (Hai

et al., 2007; Raghavacharya, 1997) are generally not good.

Oxidationis a method by which wastewater is treated by usingoxidizing agents. Generally, two forms viz. chemical oxidation andUV assisted oxidation using chlorine, hydrogen peroxide, fentons

reagent, ozone, or potassium permanganate are used for treatingthe effluents, especially those obtained from primary treatment(sedimentation). They are among the most commonly usedmethods for decolourisation processes since they require low

quantities and short reaction times. They are used to partially or

completely degrade the dyes (generally to lower molecular weightspecies such as aldehydes, carboxylates, sulfates and nitrogen).However, a complete oxidation of dye can theoretically reduce the

complex molecules to carbon dioxide and water. It is worth to notethat pH and catalysts play an important role in oxidation process.

Chlorine is a strong oxidizing agent used and may also be applied

as calcium hypochlorite and sodium hypochlorite. In addition tobeing the most widely used disinfectant for water treatment, it isextensively used for reduction of colour like pulp and textilebleaching. Reactive, acid, direct and metal complex dyes, which are

water soluble are decolourised readily by hypochlorite, but water-insoluble disperse and vatdyes areresistant to decolourisation in thisprocess (Namboodri et al., 1994a,b). It has been reported that decol-ourisation of reactive dyes generally require long reaction times,

while metal complex dye solution remains partially coloured even

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after an extended period of treatment. Dyes (Omura, 1994) havingamino or substituted amino groups on a naphthalene ring, are most

susceptible to chlorine and decolourise more easily than other dyes.Oxidation can be enhanced through control of pH and also by usingcatalysts, e.g., in the decomposition of metal complex dyes metals,

likeiron, copper, nickel and chromium, areliberated and these metalshave a catalytic effect that increases decolourisation. Though the useof chlorine gas is a low-cost methodology for decolourising dyewastewater, its use causes unavoidable side reactions, producing

organochlorine compounds including toxic trihalomethane, therebyincreasing the absorbable organic halogens content of the treatedwater, also the liberation of metals in metal complex dyes may cause

corrosion in metallic vessels.Hydrogen peroxide (H2O2) is a very pale blue liquid which

appears colourless in a dilute solution, slightly more viscous thanwater. It has strong oxidizing properties and is therefore a powerfulbleaching agent that is used for bleaching paper besides other uses.About 50% of the worlds production of hydrogen peroxide in 1994

was used for paper and pulp bleaching (Hage and Lienke, 2006).Hydrogen peroxide is also used for making peroxidase enzymes,which are used for decolourisation of dyes (Morita et al., 1996).

However, the process is pH dependent and produces sludge.

Fentons reagent, a solution of hydrogen peroxide and an ironcatalyst is also used to oxidize dye wastewaters (Meric et al., 2003;Wang, 2008) and is stronger than hydrogen peroxide. Generally, it is

effective (Kim et al., 2004) in decolourization of both soluble andinsoluble dyes (acid, reactive, direct, metal complex dyes) thoughsome dyes like vat and disperse were found to be resistant to it, e.g.,dyes (Gregor, 1992) like palanil blue 3RT was resistant to Fentons

reagent, dyes like remazol brilliant blue B, sirrus supra blue BBR,indanthrene blue GCD, irgalan blueFGL and helizarinblue BGT, havebeen reported to be significantly decolourised. It is to be noted that,

not only is colour removed, but chemical oxygen demand (exceptwith reactive dyes), total organic carbon and toxicity are alsoreduced. The process is also applicable even with high-suspendedsolid concentration and is preferred for wastewater treatmentwhen

a municipality allows the release of Fentons sludge into sewage.From a biologicalpoint of view, it is belived that not only the qualityof the sludge is improved, but the phosphates can also be elimi-nated. The main drawbacks are that it is usually effective within

narrow pH range (Cheng et al., 2004) of


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functionalities can be found in review ofKonstantinou and Albanis(2004). The authors suggested that the degradation of dyes depend

on several parameters such as pH, catalyst concentration, substrateconcentration and the presence of electron acceptors such ashydrogen peroxide and ammonium persulfate besides molecular

oxygen. A study of photocatalytic degradation of methyl orange(MO) and rhodamine 6 G (R6 G), employing heterogeneous pho-tocatalytic process, and photocatalytic activity of various semi-conductors such as titanium dioxide (TiO2), zinc oxide (ZnO),stannic oxide (SnO2), zinc sulfide (ZnS) and cadmium sulfide (CdS)

has been carried out byKansal et al. (2007). The effect of processparameters viz., amount of catalyst, concentration of dye and pH onphotocatalytic degradation of MO and R6G was studied. Authorsobserved that irradiating the aqueous solutions of dyes containing

photocatalysts with UV and solar light resulted in maximumdecolourization (more than 90%) with ZnO catalyst at basic pH. Themaximum adsorption of MO was noticed at pH 4, and of R6G at pH10. The percentage reduction of MO and R6G was estimated under

UV/solar system and it was found that COD reduction takes place ata faster rate under solar light as compared to UV light. In case ofR6G, highest decolourizing efficiency was achieved with lower dose

of catalyst (0.5 g L1) than MO (1 g L1) under similar conditions.

Authors observed that the performance of photocatalytic systememploying ZnO/solar light was better than ZnO/UV system. Nor-mally, the advantages of the process are potential of solar light

utilization, no sludge production, considerable reduction of COD.However, the main drawbacks of process are that there is limitationof light penetration, fouling of catalysts, and problem of fine cata-lyst separation from the treated liquid (slurry reactors).

Sonolysis, i.e., use of ultrasonic waves has been used for thedecolourization and degradation of dyes. The mechanism proposedfor the sonochemical processes is usually based on the formation ofshort-lived radical species generated in violent cavitation events.

The sonochemical degradation of dyes alizarin and procion bluewas studied byHong et al. (1999), the authors found the process tobe dependent on ultrasound power and, total solution volume, and

a decrease in reaction rate was observed upon changing the gasphase in the reactor from air to argon.

The degradation of acid orange 52 in aqueous solutions wasinvestigated byMaezawa et al. (2007)using three processes viz.photocatalysis, sonolysis, and photocatalysis with sonication. The

authors found that in the case of photocatalysis, although theconcentration of acid orange 52 decreased to 35% in 480 min,the colour of the solution did not disappear, while in the case of

sonolysis it decomposed completely in 300 min and the totalorganic carbon concentration decreased by only about 13% in480 min. However, in the case of photocatalysis with sonication,the concentration of acid orange 52 reached 0 in 240 min and the

total organic carbon concentration decreased by about 87% in480 min. These results indicate that the ultrasonic irradiation

enhanced the photocatalytic degradation. The authors (Maezawaet al., 2007) suggested that the photocatalysis with sonication ismost effective for the decomposition of dye in the three processesstudied.

Nevertheless, in general AOPs have the drawback of producing

some undesirable by-products, complete mineralization is notpossible and the process is pH dependent. Also, depending on theprocess the limitation may vary, e.g., in the process involving colourremoval by the UV/H2O2 treatment the important factors thatinfluence colour removal are peroxide concentration, time of

treatment, intensity of UV radiation, pH, chemical structure of thedye and dyebath additives. Though the advanced oxidationprocesses have proven potential and found technically sound forcolour removal they are quite expensive especially for small-scale

sector of developing countries.

Biological treatment is the most common and widespread

technique used in dye wastewater treatment (Barragan et al., 2007;Bromley-Challenor et al., 2000; dos Santos et al., 2007; Frijters et al.,2006; van der Zee and Villaverde, 2005; Zhang et al., 1998). A largenumber of species have been used for decolouration and mineral-

ization of various dyes. The methodology offers considerableadvantages like being relatively inexpensive, having low runningcosts and the end products of complete mineralization not being

toxic. The process can be aerobic (in presence of oxygen), anaerobic(without oxygen) or combined aerobicanaerobic.

Aerobic treatment: Bacteria and fungi arethe two microorganismgroups that have been most widely studied for their ability to treat

dye wastewaters. In aerobic conditions, enzymes secreted bybacteria present in the wastewater break down the organiccompounds. The work to identify and isolate aerobic bacteriacapable of degrading various dyes has been going on since more

than two decades (Rai et al., 2005). A number of triphenylmethanedyes, such as magenta, crystal violet, pararosaniline, brilliant green,malachite green and ethyl violet, have been found to be efficientlydecolourized (92100%) by the strainKurthia sp. (Sani and Bane-

rjee, 1999b). It was reported by the workers (Sani and Banerjee,1999b) that after biotransformation, the extent of COD reduction of

the cell free extracts of triphenylmethane dyes was more than 88%in all dyes except in the case of ethyl violet (70%). Nevertheless, it isworthwhile pointing that synthetic dyes are not uniformlysusceptible to decomposition by activated sludge in a conventionalaerobic process (Husain, 2006). Attempts to develop aerobic

bacterial strains for dye decolourization often resulted in a specificstrain, which showed a strict ability on a specific dye structure(Kulla, 1981).

Fungal strains capable of decolourizing azo and triphenyl-

methane dyes have been studied in detail by various workers(Bumpus and Brock, 1988; Sani and Banerjee, 1999a; Vasdev et al.,1995). Among various fungi, Phanerochaete chrysosporium, has beeninvestigated extensively since last two decades for its ability to

decolourize a wide range of dyes by various workers (Fu and Vir-

araghavan, 2001a; Pazarlioglu et al., 2005; Sani and Banerjee,1999a). Besides this, microorganisms including Rhyzopus oryzae,

Cyathus bulleri, Coriolus versicolour, Funalia trogii, Laetiporous sul-

phureus, Streptomyces sp., Trametes versicolourand other microor-ganisms have also been tested for the deolorization of dyes (Nigamet al., 2000; Salony et al., 2006; Zhang et al., 1999). Various factorslike concentration of pollutants, dyestuff concentration, initial pH

and temperature of the effluent, affect the decolourisation process.It has been suggested that after the fungal treatment, animprovement in the treatability of the effluent by other microor-ganisms can be observed (Christie, 2007). Although the treatments

are suitable for some dyes, most of them are recalcitrant to bio-logical breakdown or are nontransformable under aerobic condi-tions (Pagga and Brown, 1986; Rai et al., 2005).

Anaerobic Treatment: the potential of anaerobic treatmentapplications for the degradation of a wide variety of synthetic dyeshas been well demonstrated and established by (Delee et al., 1998;Forgacs et al., 2004; Rai et al., 2005). Though some efforts in therecent past to decolourize dyes under aerobic conditions have met

with success the general perception of nonbiodegradability of most

azo dyes in conventional aerobic systems still persists (Rai et al.,2005). Since its investigations from early 1970s on anaerobicdecolourization (Rai et al., 2005) of azo dyes various successfulstudies have been reported. In a study Razo-Flores et al. (1997)

found that the two azo dyes mordant orange 1 and azodisalicylatecould be reduced and decolourized under anaerobic conditionsusing methanogenic granular sludge. Another study (Zee van deret al., 2001) proved the feasibility of the application of anaerobic

granular sludge for the total decolourization of 20 azo dyes. An



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anaerobic pretreatment (Delee et al., 1998) step could be a cheapalternative compared with aerobic systems as expensive aeration is

omitted and problems with bulking sludge are avoided. In a reviewon anaerobic treatment of textile effluents, Delee et al. (1998)suggested the advantages of anaerobic treatment to be that dyes

can be reductively decolourised with the efficient and cheapremoval of BOD levels, heavy metals can be retained throughsulfate reduction, no foaming problems with surfactants, higheffluent temperatures can be favourable, high pH effluent can be

acidified and degradation of refractory organics can be initiated(e.g., surfactants, chlorinated aromatics). Nevertheless, the draw-backs were suggested (Delee et al., 1998) to be that BOD removal

can be insufficient, dyes and other refractory organics are notmineralized, nutrients (N, P) are not removed and sulfates give riseto sulfide.

Combined aerobicanaerobic treatment: in order to get better

remediation of coloured compounds from the textile effluents,a combination of aerobic and anaerobic treatment is suggested togive encouraging results. An advantage of such system is thecomplete mineralization which is often achieved due to the syner-

gistic action of differentorganisms (Stolz, 2001). Also, the reductionof the azo bond can be achieved under the reducing conditions in

anaerobic bioreactors (Brown and Laboureur, 1983b) and theresulting colourless aromatic amines may be mineralized underaerobic conditions (Brown and Laboureur, 1983a), thereby makingthe combined anaerobicaerobic azo dye treatment system attrac-tive. Thus an anaerobic decolourization followed by aerobic post-

treatment is generally recommended for treating dye wastewaters(Brown and Hamburger, 1987).

Generally the factors like concentration of dyes, initial pH andtemperature of the effluent, affect the decolourisation process.

Though this methodology is cost-competitive, and biologicaltreatments are suitable for variety of dyes, the main drawbacks ofthe biological treatment is low biodegradability of the dyes, lessflexibility in design and operation, larger land area requirement

and longer times required for decolourisationfermentation

processes thereby making it incapable of removing dyes fromeffluent on a continuous basis in liquid state fermentations (Bhat-tacharyya and Sarma, 2003; Crini, 2006; Robinson et al., 2001).

3. Adsorption and ion exchange

In addition to already mentioned methods, the adsorption

process has been widely used for colour removal. Adsorption is oneof the processes, which besides being widely used for dye removalalso has wide applicability in wastewater treatment (Bansal andGoyal, 2005; Danis et al., 1998; Freeman, 1989; Imamura et al.,

2002; Liapis, 1987; Mantell, 1951; Mattson and Mark, 1971; Pirba-zari et al., 1991; Quignonet al.,1998; Weber Jr. et al., 1970). The termadsorption refers to a process wherein a material is concentrated at

a solid surface from its liquid or gaseous surroundings. The historyof carbon adsorption in the purification of water dates back toancient times (Cheremisinoff, 2002). Adsorption on porous carbonswas described as early as 1550 B.C. in an ancient Egyptian papyrus

and later by Hippocrates and Pliny the Elder, mainly for medicinalpurposes. However, on scientific records the phenomenon ofadsorption (Mantell, 1951; Tien, 1994) was observed by C.W.Scheele in 1773 for gases exposed to carbon. This was followed by

observations made by Lowitz in 1785 of the reversible removal ofcolour and odour producing compounds from water by woodcharcoal. Larvitz in 1792 and Kehl in 1793 observed similarphenomenon with vegetable and animal charcoals, respectively.

However, it was Kayser who introduced for the first time in 1881the term adsorption to differentiate surface accumulation from

intermolecular penetration. He postulated that the basic feature of

an adsorption process is surface accumulation of material. It is nowcustomary to differentiate between two types of adsorption. If theattraction between the solid surface and the adsorbed molecules isphysical in nature, the adsorption is referred to as physical

adsorption (physiosorption). Generally, in physical adsorption theattractive forces between adsorbed molecules and the solid surfaceare van der Waals forces and they being weak in nature result in

reversible adsorption. On the other hand if the attraction forces aredue to chemical bonding, the adsorption process is called chemi-sorption. In view of the higher strength of the bonding in chemi-sorption, it is difficult to remove chemisorbed species from the

solid surface.Ion exchange is basically a reversible chemical process wherein

an ion from solution is exchanged for a similarly charged ion

attached to an immobile solid particle. Ion exchange (LeVan et al.,1997) shares various common features along with adsorption, inregard to application in batch and fixed-bed processes and they canbe grouped together as sorption processes for a unified treatment

to have high water quality. Ion exchange has been fruitfully usedtoo for the removal of colours. By far the largest application of ionexchange (Clifford, 1999) to drinking water treatment is in the area

of softening, that is, the removal of calcium, magnesium, and other

polyvalent cations in exchange for sodium. Various studies havebeen carried out using ion exchange for the removal of dyes ( Liuet al., 2007; Raghu and Ahmed Basha, 2007; Wu et al., 2008a ).

Delval et al. (2005) prepared starch-based polymers by a cross-linking reaction of starch-enriched flour using epichlorohydrin asa crosslinking agent in the presence of NH4OH. The yield, mobilityand structural properties of crosslinked starch materials with

various compositions were investigated and authors founda correlation between the structure, mobility and degree of cross-linking of these sorbents. These crosslinked starch-based materials,containing tertiary amine groups were used for the recovery of

various dyes from aqueous solutions. The authors suggested thatthe sorption mechanism was correlated to the structure of thepolymer.

One of the most important characteristics of an adsorbent is thequantity of adsorbate it can accumulate which is usually calculatedfrom the adsorption isotherms. The adsorption isotherms areconstant-temperature equilibrium relationship between thequantity of adsorbate per unit of adsorbent (qe) and its equilibrium

solution concentration (Ce). Several equations or models are avail-able that describe this function like the Freundlich and the Lang-muir equations. Dyes that are difficult to biological breakdown canoften be removed by using the adsorbents. A good adsorbent

(Linsen, 1970; Tien, 1994) should generally possess a porousstructure (resulting in high surface area) and the time taken foradsorption equilibrium to be established should be as small aspossible so that it can be used to remove dye wastes in lesser time.

Some of the adsorbents, which are generally used for dye

wastewater treatment, are:Alumina, a synthetic porous crystalline gel, which is available in

the form of granules of different sizes having surface area (Do,

1998) ranging from 200 to 300 m2 g1. Bauxite a naturally occur-ring porous crystalline alumina contaminated with kaolinite andiron oxides normally having surface area (Mantell, 1951) ranging

from 25 to 250 m2 g1. Alumina has been studied by variousworkers for the removal of dyes (Adak et al., 2005, 2006; Huanget al., 2007).

Silica Gel, prepared by the coagulation of colloidal silicic acid

results in the formation of porous and noncrystalline granules ofdifferent sizes. It shows a higher surface area (Do, 1998) ascompared to alumina, which ranges from 250 to 900 m2 g1.Various workers likeAlexander and McKay (1977)and Allingham

et al. (1958)investigated the adsorption of basic dyes onto silica,



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although the adsorption capacities were highbut the drawback wasthat silica is expensive adsorbent (McKay et al., 1999).

Zeolites, are important microporous adsorbents, which arefound naturally and are prepared synthetically too. They are alsoconsidered as selective adsorbents and show ion exchange prop-

erty (Adebajo et al., 2003; Kesraouiouki et al., 1994; Menon andKomarneni, 1998) as well as molecular adsorption (Caputo andPepe, 2007; Curkovic et al., 1997; Kesraouiouki et al., 1994). Anumber of zeolites have been used for the removal of dyes (Alpat

et al., 2008; Armagan et al., 2003b; Handreck and Smith, 1988;Meshko et al., 2001; Nur et al., 2005; Ozdemir et al., 2004; Wangand Ariyanto, 2007; Wang et al., 2006b,c; Yuan et al., 2007) as well

as forother pollutants too (Ellis and Korth,1993; Okolo et al., 2000).Besides zeolites, it was shown in 1934 by Adams and Holmes thatphenol-formaldehyde resins exhibit cation exchange properties.This led to the development of a different type of resins which are

used as adsorbents through a cation or anion exchange mechanismlike polystyrene sulfonate, sulfonated phenolic resin, phenolicresin, polystyrene phosphonate, polystyrene amidoxime, poly-styrene-based trimethyl benzyl ammonium, epoxy-polyamine and

aminopolystyrene. A number of exchange resins have been usedquite efficiently for the removal of dyes (Fan et al., 2006; Karcher

et al., 2001, 2002; Yu et al., 2001, 2004; Zhang et al., 2006).Activated carbon, is the oldest adsorbent known and is usually

prepared from coal, coconut shells, lignite, wood etc., using one ofthe two basic activation methods: physical and chemical (Bansalet al., 1988; Carrott et al., 2003; Hassler, 1963; Lillo-Rodenas et al.,

2007; Phan et al., 2006). Generally, the physical activation requireshigh temperature and longer activation time as compared tochemical activation, however, in chemical activation the AC needa thorough washing due to the use of chemical agents. A schematic

diagram of the process of producing activated carbons generallyadopted by workers is shown inFig. 2.

The product formed by either of the methods is known asactivated carbon and normally has a very porous structure with

a large surface area ranging from 500 to 2000 m2 g1 (Carrott et al.,

1991). It has been found that adsorption on activated carbon is notusually selective as it occurs through van der Waals forces. Theability of charcoal to remove odour and taste was recorded centu-ries ago. The literature (Freeman, 1989; Tien, 1994) shows thataccording to a Sanskrit manuscript from circa 200 BC, It is good to

keep water in copper vessels, to expose it in sunlight and to filter itthrough charcoal. However, the credit of developing commercialactivated carbon (Smsek and Cerny, 1970) goes to Raphael vonOstrejko whose inventions were patented in 1900 and 1901. The

applicability of activated carbon for water treatment has beendemonstrated by various workers (Stenzel, 1997; Weber Jr. et al.,1970). Besides these, various authors (Bansal and Goyal, 2005;Hassler, 1963) have discussed and summarized in their book the

successful applications of activated carbons. Activated carbon is

available in two main forms: powdered activated carbon (PAC) andgranular activated carbon (GAC). Most of the work on the removalof pollutants from water has been on GAC, due to the fact that the

granular form is more adaptable to continuous contacting andthere is no need to separate the carbon from the bulk fluid. On theother hand, the use of PAC presents some practical problems

because of the requirement to separate the adsorbent from the fluidafter use. However, in spite of these problems PAC is also used forwastewater treatment due to low capital cost and lesser contacttime requirement (Najm et al., 1991). Besides PAC and GAC two

other forms of ACs are also available, Activated Carbon Pellet andActivated Carbon Fiber (ACF). The pelletized activated carbons aregenerally prepared from coal where coal is pulverized and reag-glomerated with suitable binder and then physically activated.

These materials are made especially for use in vapor applications.

Theyare normally available in sizes of 1.5, 3 and 4 mm diameter. ForACF, the carbon fibers are generally prepared from polymericprecursor materials such as polyacrylonitrile(PAN), cellulose, pitchand polyvinylchloride; of these PAN based carbon fibers predomi-

nate and have good strength and modulus properties, whereascarbon fiber can be made with a higher modulus, albeit a lowerstrength, using a pitch-based precursor. These carbon fibers afteractivation using same methodology results in high surface area

carbons.The activated carbons which are used as adsorbents, not only

remove different types of dyes (Al-Degs et al., 2001; DiGiano and

Natter, 1977; Pelekani and Snoeyink, 2000; Walker and Weatherley,1999), but also other organic and inorganic pollutants such as metalions (Carrott et al.,1998,1997; Gabaldon et al., 2000; Kuennen et al.,1992; Macias-Garcia et al., 1993), phenols (Carrott et al., 2005;Caturla et al., 1988; Mourao et al., 2006; Paprowicz, 1990; Zogorski

et al., 1976), pesticides (Hu et al., 1998; Pirbazari et al., 1991; Pir-bazari and Weber Jr., 1984), chlorinated hydrocarbons (Urano et al.,1991), humic substances (Lee et al., 1983), PCBs (Pirbazari et al.,

1992), detergents (Bele et al., 1998; Malhas et al., 2002), organiccompounds which cause taste and odour (Flentje and Hager, 1964;Lalezary et al., 1986) and many other chemicals and organisms(Annesini et al., 1987; Carrott et al., 2000; Donati et al., 1994; Giusti

et al., 1974; McKay et al., 1985a; Najm et al., 1993; Saito, 1984;Smith, 1991). It is well known that adsorptionby activated carbon is

an effective and commercially applicable method for removing

Physical activation

Carbonization

(600-900C, N2/Ar)

Activation

(600-1200C, CO2/O2/H2O)

Washing and drying

Chemical activation

Mixing precursor with

chemical

(H3PO4/KOH/NaOH)

Activation

(450-900C, N2)

Washing and drying

Sieving

Final

Storage

Raw material

(coal, coconut shells, lignite)

Fig. 2. Schematic diagram of the process of producing activated carbons generally

adopted by workers.



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colour and other pollutants from textile and dye wastes. Porter(1972)suggested that carbon adsorption is a complete treatment

for textile water. In order to demonstrate the versatility of activatedcarbon, different workers (Al-Degs et al., 2000, 2001; DiGiano andNatter,1977; Pelekani and Snoeyink, 2000; Walker and Weatherley,

1999) have used this adsorbent for different types of dyes. McKay(1982)used activated carbon of Filtrasorb type for the removal ofacidic, basic, disperse and direct dyes and found it to be excellentfor the removal of all except direct dyes. Walker and Weatherley

(1999)studied the kinetics of acid dye, tectilon red 2B, on GAC. Theadsorption of three reactive dyes used in textile industry on Fil-trasorb 400 activated carbon was studied byAl-Degs et al. (2000)

and same workers (Al-Degs et al., 2001) further studied variousactivated carbons for the removal of cationic dye (methylene blue)and anionic dye (reactive black), and reported that there existsa good relationship between performance of activated carbons and

methylene blue capacity/surface area.Studies have shown that activated carbons are good materials

for the removal of different types of dyes in general but there use issometimes restricted in view of higher cost. Also, the activated

carbons after their use (treatment of wastewater) becomeexhausted and are no longer capable of further adsorbing the dyes.

Once AC has been exhausted, it has to be regenerated for furtheruse in purifying water and a number of methods like thermal,chemical, oxidation, electrochemical (Freeman, 1989; Hemphillet al., 1977; Kilduff and King, 1997; Martin and Ng, 1987; Narbaitzand Cen, 1994; Newcombe and Drikas, 1993; Notthakum et al.,

1993; Rollar et al., 1982; Taiwo and Adesina, 2005; Zhou and Lei,2005) are used for this purpose, the most common being thermal. Itis worthwhile noting that regeneration of activated carbon addscost, furthermore, any regeneration process results in a loss of

carbon and the regenerated product may have a slightly loweradsorption capacity in comparisonwith the virgin activated carbon.This has resulted in attempts by various workers to prepare low-cost alternative adsorbents (Ali and Gupta, 2007) which may

replace activated carbons in pollution control through adsorption

process.

4. Low-cost alternative adsorbents

Natural materials or the wastes/by-products of industries orsynthetically prepared materials, which cost less and can be used assuch or after some minor treatment as adsorbents are generally

called low-cost adsorbents (LCAs). A protocol based on thenumerous studies for the development, utilization and applicationof low-cost adsorbents generally adopted by researchers has beensuggested byGupta et al. (in press). The LCAs as reported in liter-

ature are usually called substitutes for activated carbons because oftheir similar wide use; however, in a broad and clearer way theyarebasically substitutes for all expensive adsorbents. These low-cost

alternative adsorbents (Gupta et al., in press) may be classified intwo ways either (i) on basis of their availability, i.e., (a) Naturalmaterials such as wood, peat, coal, lignite etc. (b) Industrial/Agri-cultural/Domestic wastes or by-products such as slag, sludge, fly

ash, bagasse flyash, red mud etc and (c) Synthesized products; or(ii) depending on their nature, i.e., (a) Inorganic and (b) Organic.Some review articles discussing low-cost alternative adsorbents(Ahluwalia and Goyal, 2007; Aksu, 2005; Babel and Kurniawan,

2003; Bailey et al., 1999; Crini, 2005, 2006; Gerente et al., 2007;Gupta and Ali, 2002; Mohan and Pittman, 2006; Pollard et al.,1992;Shukla et al., 2002) have already been available. For example, a nicereview on the removal of metals by low-cost adsorbents has been

presented byBailey et al. (1999), an overview of low-cost adsor-bents for heavy metal removal has been presented by Babel and

Kurniawan (2003), and heavy metals removal by metabolically

inactive non-living biomass of microbial or plant origin has beenreviewed by Ahluwalia and Goyal (2007). An application of bio-sorption using fungi, yeasts and bacteria for the removal of organicpollutants has been reviewed byAksu (2005). A nice review has

been presented byCrini (2006)regarding the feasibility of variousnon-conventional low-cost adsorbents for removal of dyes, thepossible use of sawdust for removal of various contaminants such

as dyes and metals, has been discussed byShukla et al. (2002), useof polysaccharide based materials as adsorbents have beenreviewed by Crini (2005), and application of chitosan for metal

removal has been discussed byGerente et al. (2007). Also, reviewon waste materials both conventional (from agriculture and woodindustry) and non-conventional (from municipal and industrialactivities) for the preparation of AC, that can be applied in various

aqueous treatment processes to remove organic pollutants, dyes,volatile organic compounds, and heavy metals has been presentedbyDias et al. (2007).

One of the aim of this review is to give a rough idea to thereaders of the step-by-step approach of the why, what and how ofthe low-cost adsorbents and dye wastewater treatment, besides thecritical discussions. Among various ways of treating dye waste-

water one can be utilizing as much as possible our resources

including inexpensive waste/little use materials, combining withinexpensive techniques. We aimed to let researchers know more

and more about maximum of the materials which can be used asadsorbents. Without going into too much detail, a summary ofsome relevant published data with some of the latest importantresults and giving a source of up-to-date literature on the adsorp-

tion properties of some alternative adsorbents used for acid, basic,direct and other dyes removal is presented in Tables 13, and someof the results are discussed here.

Natural materials: Natural materials generally used as LCAs arethe one existing in nature and used as such or with minor treat-ment. Some of the materials used are:

Wood as an adsorbent was investigated byPoots et al. (1976b,

1978)who studied the removal of acidic (telon blue, i.e., acid blue

25) as well as basic (astrazone blue, i.e., basic blue 69) dyes therebymaking an attempt to overcome the economic disadvantages ofactivated carbon. The adsorbent was studied without any

pretreatment and was sieved into different size ranges prior to use.The kinetics of the process was found to be dependent on theparticle size, being minimum (>3 h) for small particle size (150250 mm) and maximum (>6 h) for large particle sizes (7101000 mm) in case of acidic dye, however compared to the acid dyethe removal of basic dye (astrazone blue) was found to be in less

contact time (2 h). The monolayer coverage of telon dye on woodvaried from 6.95 to 11.56 mg g1 for particle sizes ranging from 710to 1000 and 150 to 250mm, respectively. However, a higheradsorption capacity of 100.1 mg g1 for particles of size 150

250 mm was observed for basic dye astrazone blue. Authors sug-

gested that because of its low cost the wood adsorbent does notneed to be regenerated after use and may be disposed off byburning and the heat so evolved can be used for generating steam.

The drawbacks according to the author of the study were longercontact time (8 h) and also low adsorption capacity of the wood foracidic dye telon blue. Morais et al. (1999) used eucalyptus bark

without any pretreatment for removing reactive dyes. Theadsorption on bark was suggested because of its high tannincontent (Bailey et al., 1999; Morais et al., 1999), the polyhydroxypolyphenol groups of tannin are thought to be the active species in

the adsorption process. The process was found to be exothermicand dye adsorption varying from 4 to 90 mg g1, depending onexperimental conditions. The higher value of 90 mg g1 wasobserved at pH 2.5 and with 50 g L 1 sodium chloride

concentration.



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Table 1

Adsorption capacities and other parameters for the removal of acid dyes by commercial activated carbons and other alternative adsorbents.

Material Adsorbate Surface area of adsorbent

Adsorptioncapacity

Concentrationrange

Contacttime

pH Percentageadsorption

Source

GAC Filtrasorb 400

(Chemviron Carbon UK)

Acid blue 40

(CI 62125)

1100 m2 g1 57.47 mg g1 25200 mg L1 90 min 1 Ozacar and Sengil

(2002)

Filtrasorb F 400 Acid blue 80 (1.05

1.2)106 m2 kg1112.3 mg g1 21 days Choy et al. (2000)

Filtrasorb F 400 Acid red 114 (1.051.2)106 m2 kg1 103.5 mg g1

21 days Choy et al. (2000)

Filtrasorb 400, Calgon

Corporation

Acid red 88

(C.I. No. 15620)

109 mg g1 400 min 7.020.1 Venkata Mohan et al.

(1999)Filtrasorb F 40 0 Acid yellow 117 (1.05

1.2)106 m2 kg1155.8 mg g1 21 days Choy et al. (2000)

GAC Filtrasorb 400

(Chemviron Carbon UK)

Acid yellow 17

(C.I. 10310)

1100 m2 g1 133.3 mg g1 25200 mg L1 90 min 1 Ozacar and Sengil

(2002)

PAC Chemviron GW Acid brown 283 1026 m2 g1 22 mg g1 30250 mg L1 2 h Martin et al. (2003)

AC-Charcoal Acid blue

(Polar blue)

100.9 mg g1 1025 mg dm3 21 days Choy et al. (1999)

AC-Charcoal Acid yellow 128.8 mg g1 1025 mg dm3 21 days Choy et al. (1999)

AC-Charcoal Acid red 114 101 mg g1 1025 mg dm3 21 days Choy et al. (1999)

Fly ash-Czech Republic Acid black 26 5.47 m2 g1 0.0033 mmol g1 0.050.20 mmol L1

72 h Janos et al. (2003)

AC Rice husk Acid blue

(CI 73015)

352 m2 g1 50 mg g1 150 ppm 10 h Mohamed (2004)

Carbonaceous adsorbent Acid blue 113 380 m2 g1 219 mg g1 180 min 7.00.5 Jain et al. (2003c)

Blast furnace sludge Acid blue 113 28 m2 g1 2.1 mg g1 180 min 7.00.5 Jain et al. (2003c)

DTMA-bentonite Acid blue 193 767 m2 g1 740.5 mg g1 60 min Ozcan et al. (2004a)

Wood sawdust (raw) Acid blue 25 5.92 mg g1 8 h Ho and McKay

(1998a)

Modified silica Acid blue 25 187 m2 g1 45.8 mg g1 Phan et al. (2000)

Peat Acid blue 25 12.7 mg g1 Ho and McKay

(1998b)

Treated cotton Acid blue 25 589 mg g1 Bouzaida and

Rammah (2002)Chitosan/cyclodextrin

material

Acid blue 25 77.4 mg g1 Martel et al. (2001)

Hazelnut shell Acid blue 25 60.2 mg g1 50500 mg L1 60

180 min

Ferrero (2007)

Saw dust-walnut Acid blue 25 36.98 mg g1 50500 mg L1 60

180 min

Ferrero (2007)

Saw dust-cherry Acid blue 25 31.98 mg g1 50500 mg L1 60

180 min

Ferrero (2007)

Saw dust-oak Acid blue 25 27.85 mg g1 50500 mg L1 60180 min

Ferrero (2007)

Saw dust-pitch pine Acid blue 25 26.19 mg g1 50500 mg L1 60

180 min

Ferrero (2007)

AC-Corncob Acid blue 25(C.I. No. 62055)

943 m2 g1 1060 mg g1 4.1 Juang et al. (2002)

AC-Bagasse Acid blue 25

(C.I. No. 62055)

607 m2 g1 674 mg g1 4.1 Juang et al. (2002)

AC-Plum kernel Acid blue 25

(C.I. No. 62055)

1162 m2 g1 904 mg g1 4.1 Juang et al. (2002)

Cane (bag asse) pith Acid blue 25

(C.I. No. 62055)

606.8 m2 g1 673.6 mg g1 5 days 5.9 Juang et al. (2001)

Bagasse pith(raw) Acid blue 25

(C.I. No. 62055)

17.5 mg g1 101000 mg dm3 5 days Chen et al. (2001)

Wood Acid blue 25(Telon blue)

3.86.4 m2 g1 7.011.6 mg g1 Poots et al. (1976b)

Maize cob Acid blue 25,

Acid Red 114

41.4, 47.7 mg g1 0.05 dm3 5 days El-Geundi and Aly

(1992)Pine sawdust (raw) Acid blue 256 280.3 mg g1 120 min 3.5 Ozacar and Sengil

(2005)

AC-Pinewood Acid blue 264 902 m2 g1 1176 mg g1 5 days 6.4 Tseng et al. (2003)

Dead fungusAspergillus

niger

Acid blue 29 1.4413.82 mg g1 50 mg L1 30 h Fu and Viraraghavan

(2001b)

Living biomassAspergillus

niger

Acid blue 29 6.63 mg g1 50 mg L1 30 h Fu and Viraraghavan

(2001b)

Modified fungal biomass(Aspergillus niger)

Acid blue 29 17.58 mg g1 45.96 mg L1 4.0 Fu and Viraraghavan

(2002b)

Calcined alunite Acid blue 40 42.8 m2 g1 212.8 mg g1 25200 mg L1 90 min 2 Ozacar and Sengil

(2002)Activated sewage sludge Acid blue 74

(Indigo carmine)

390 m2 g1 60.04 mg g1 1001000 mg L1 165 min Otero et al. (2003b)

Pyrolysed sewage sludge Acid blue 74

(Indigo carmine)

80 m2 g1 30.82 mg g1 1001000 mg L1 180 min Otero et al. (2003b)

(continued on next page)



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Table 1(continued )

Material Adsorbate Surface area of

adsorbent

Adsorption

capacity

Concentration

range

Contact

time

pH Percentage

adsorption

Source

AC-Bagasse Acid blue 80 1433 m2 g1 391 mg g1 201050 mg dm3 7.4 Valix et al. (2004)

Activated clay/carbons

mixture

Acid blue 9 64.7 mg g1 2.5 h 3.0 Ho and Chiang

(2001)Activated clay Acid blue 9

(C.I. 42090)

57.8 mg g1 2 h 3.0 Ho et al. (2001)

Soy meal hull Acid blue 92 0.7623 m2

g1

114.94 mg g1

50150 mg L1

24 h 2 Arami et al. (2006)Banana pith Acid brilliant blue 4.42 mg g1 Namasivayam et al.

(1998)

Coir pith (raw) Acid brilliant blue

(C.I. 42645)

16.67 mg g1 220 min Namasivayam et al.

(2001a)

AC sludge based Acid brown 283 253 m2 g1 20.5 mg g1 30250 mg L1 2 h Martin et al. (2003)

Leather industry waste

(buffing dust)

Acid brown dye 2.846.24 mg g1 50125 mg L1 60 min Sekaran et al. (1995)

Chitosan Acid green 25 645.1 mg g1 24 h 4.0 0.1 Wong et al. (2004)

Chitosan Acid orange 10 922.9 mg g1 24 h 4.0 0.1 Wong et al. (2004)

AC-Sugarcane bagasse Acid orange 10(C.I.16230)

790 m2 g1 5.78 mg g1 525 mg dm3 20 h Tsai et al. (2001)

Chitosan Acid orange 12 973.3 mg g1 24 h 4.0 0.1 Wong et al. (2004)

Banana peel Acid orange 52

(methyl orange)

20.623.5 m2 g1 21 mg g1 10120 mg L1 24 h Annadurai et al.

(2002)

Orange peel Acid orange 52

(methyl orange)

20.623.5 m2 g1 20.5 mg g1 10120 mg L1 24 h Annadurai et al.

(2002)

Fly ash- Czech Republic Acid orange 7 5.47 m2 g1 0.2364 mmol g1 0.05

0.20 mmol L172 h Janos et al. (2003)

Chitosan bead (chemically

crosslinked)

Acid orange12, acid

red14, acidorange7

1954, 1940,

1940 mg g1 5 days 34 Chiou et al. (2004)

Fly ash-Czech Republic Acid red 1 5.47 m2 g1 0.1405 mmol g1 0.05


Sewage sludge Acid red 1 3573 mg g1 101000 mg L1 72 h Seredych andBandosz (2007)

Bagasse pith (raw) Acid red 114 20 mg g1 101000 mg dm3 5 days Chen et al. (2001)

AC from gingelly seed shell Acid red 114 229.65 m2 g1 102.04 mg g1 8 h Thinakaran et al.

(2008)

AC from cotton seed shell Acid red 114 124.35 m2 g1 153.85 mg g1 8 h Thinakaran et al.

(2008)

AC from pongam seed shell Acid red 114 324.79 m2 g1 204.08 mg g1 8 h Thinakaran et al.

(2008)

Bagasse pith Acid red 114,

Acid blue 25

22.9, 21.7 mg g1 200 mgdm3 5 days McKay et al. (1997)

Soy meal hull Acid red 14 0.7623 m2 g1 109.89 mg g1 50150 mg L1 24 h 2 Arami et al. (2006)

Chitosan Acid red 18 693.2 mg g1 24 h 4.0 0.1 Wong et al. (2004)Hen feathers Acid red 51 2.314105

mol g11 105

6 105 M

24 h 3 Gupta et al. (2006c)

Chitosan Acid red 73 728.2 mg g1 Wong et al. (2004)

Charfines (raw) Acid red 88

(C.I.15620)

33.3 mg g1 60 min 7.02 0.1 Venkata Mohan et al.

(1999)

Lignite coal (raw) Acid red 88

(C.I.15620)

30.9 mg g1 60 min 7.02 0.1 Venkata Mohan et al.

(1999)

Bituminous coal (raw) Acid red 88

(C.I.15620)

26.1 mg g1 60 min 7.02 0.1 Venkata Mohan et al.(1999)

Coir pith (raw) Acid violet

(C.I. 42650)

1.65 mg g1 120 min Namasivayam et al.

(2001a)Coir pith carbonized Acid viole t

(C.I. 42650)

259 m2 g1 8.06 mg g1 40 min Namasivayam et al.

(2001b)

Orange peel (raw) Acid violet 17 19.88 mg g1 80 min 6.3 Sivaraj et al. (2001)

Fly ash-Czech Republic Acid yellow 11 5.47 m2 g1 0.0052 mmol g1 0.05


Pine sawdust (raw) Acid yellow 132 398.8 mg g

1

120 min 3.5 Ozacar and Sengil(2005)

Calcined alunite Acid yellow 17 42.8 m2 g1 151.5 mg g1 25200 mg L1 90 min 2 Ozacar and Sengil

(2002)

Sawdust carbon Acid yellow 36

(C.I.13065)

516.3 m2 g1 183.8 mg g1 60 min 3 Malik (2003)

Rice husk carbon Acid yellow 36

(C.I.13065)

272.5 m2 g1 86.9 mg g1 180 min 3 Malik (2003)

Carbonaceous adsorbent Acid yellow 36

(Metanil yellow)

380 m2 g1 211 mg g1 180 min 7.0 0.5 Jain et al. (2003c)

Blast furnace sludge Acid yello w 36

(Metanil yellow)

28 m2 g1 1.4 mg g1 180 min 7.0 0.5 Jain et al. (2003c)

Treated cotton Acid yellow 99 448 mg g1 Bouzaida and

Rammah (2002)

Carbonace ous adsorbent Et hy l orange 380 m2 g1 198 mg g1 180 min 7.0 0.5 Jain et al. (2003c)

Blast furnace sludge Ethyl orange 28 m2 g1 1.3 mg g1 180 min 7.0 0.5 Jain et al. (2003c)



11/30

Natural coal was studied byMittal and Venkobachar (1993)fortheremoval of twobasic dyes, rhodamine B andmethylene blue and

acidic dye sandola rhodine. The coal was sulfonated and heated ina water bath prior to the study. Authors found that the nature ofadsorption of acid dye(sandola rhodine) was physisorption while ofbasic dyes (methylene blue and rhodamine B) was not. Coal based

sorbents, namely charfines, lignite coal and bituminous coal, havebeen used by Venkata Mohan et al. (2002) who presentedresults onthe adsorption of colour removal of the trisazo direct dye C.I. direct

brown 1:1 by these adsorbents and compared the results withactivated carbon (Filtrasorb 400). The coal based adsorbents werefound to achieve equilibrium in a short time (60 min) compared toactivated carbon (400 min) which was suggested to be due to the

presence of acidic groups (carboxyl and hydroxyl) present on thecoal based adsorbents and which in turn also resulted in a chemi-sorption mechanism. Thesorptioninteraction of thedirectdye on tothe coal based sorbents obeyed a first-order irreversible rate

equation suggesting a chemisorption mechanism while on activatedcarbon the data fitted a first-order reversible rate equation indi-cating physisorption. Coal not being a pure material is suggested to

have a variety of surface properties and in turn sorption properties.It has also been proposed (Karaca et al., 2004) that the nature oforiginal vegetation and the physical and chemical changes afterpretreatment usually determines its sorption properties.

Peat is one of the natural materials widely available and studiedas an alternative adsorbent for different pollutants as well as dyes(Allen et al.,1988a,b, 2004; Ho and McKay, 1998b, 2003; Poots et al.,1976a; Ramakrishna and Viraraghavan, 1997; Sun and Yang, 2003)

bya numberof researchers. It covers3% of the worldslandarea, andthe production of peat for energy use was 70 million m3 in 2005(Olsson, 2006), thereby, making it important material. The majorconstituents of peat are lignin, cellulose, fulvic and humic acid andthe carbon content is generally just over 50% (http://www.

torvproducenterna.se/english/basic-facts.shtml (accessed 20.6.08)).

Peat was used byPoots et al. (1976a)as an adsorbent without anypretreatment for studying the adsorption of telon blue on it. Theauthors found that the performance of peat was significantly better

than that of wood, referred to above, and achieved an equilibriumadsorption capacity of 16.3 mg g1 for particles of size 150250 mmand with a contact time of 2 h. Like wood, the exhausted peat

adsorbent may be disposed off by burning and the heat used forsteam generation. The same adsorbentadsorbate system was alsostudied byMcKay and Allen (1980)for assessing parameters influ-encing the surface mass transfer coefficients during the adsorption

process.Ramakrishna and Viraraghavan (1997)studied the perfor-mance of peat, slag, bentoniteclayand flyash forthe removal of acid,basic and disperse dyes.

Similar to other adsorbents peat canalso be modified with some

chemical pretreatment to improve its sorption properties and

selectivity. In a study, Sun and Yang (2003) prepared modified

peatresin by mixing oxidizing peat with polyvinylalcohol andformaldehyde. The material so prepared was found to have a mac-roreticular porous structure with enhanced physical characteristics.Authors found that modified peat can be used for the removal of

a variety of basic dyes, with maximum adsorption capacities for

basic violet 14 and basic green 4 as 400 and 350 mg g1, respec-tively. Nevertheless, the mechanism of adsorption of dyes by peathas been a matter of considerable debate due to the studies with

different conclusions which are probably due to different peattypes as well as due to difference in sample preparation, and alsodue to various pollutant-binding mechanisms involved in the bio-sorption process.

Chitin and chitosan are mechanically tough polysaccharideswith chemical structures similar to cellulose, studied as adsorbents.Chitin is a fairly abundant natural biopolymer and is generallyfound in the exoskeletons of crabs and other arthropods and also in

the cell wall of some fungi whereas chitosan or glucosamine isa deacetylated derivative of chitin and can be chemically preparedfrom it. Both chitin and chitosan are being used as an attractive

source of adsorbents, especially for metal removal. Nevertheless,they are versatile materials and have been used successfully for theremoval of dyes (Annadurai, 2000; Annadurai et al., 2008; Cestariet al., 2008; Chatterjee et al., 2007; Cheung et al., 2007; Chiou et al.,2004; Chiou and Li, 2003; Hasan et al., 2008; Hu et al., 2006b;

Morais et al., 2007; Niramol et al., 2005; Prado et al., 2004; Ratta-naphani et al., 2007; Rosa et al., 2008; Sakkayawong et al., 2005;Wong et al., 2004; Wu et al., 2001a; Yoshida and Takemori, 1997;Zubieta et al., 2008) and reviewed too (Crini and Badot, 2008).

These materials can be used in different forms, from flake-types togels, bead-types or fibers. The efficiency of chitosan as an adsorbentto remove acid dyes has been presented by Wong et al. (2004), who

found the maximum adsorption capacities of chitosan for acidorange 12, acid orange 10, acid red 73 and acid red 18 as 973.3,

922.9, 728.2, and 693.2 mg g1

, respectively.In search for alternatives to activated carbon, Figueiredo et al.

(2000, 2005)studied squid, sepia pens and anodonta shells con-

taining chitin as adsorbents for colour removal from textilewastewaters. The materials were studied with and without chem-ical treatment, either by demineralization followed by deprotei-

nation, or only by one of the two steps. It was reported by theseauthors that chemical treatment of the materials under investiga-tion enhanced their adsorption capacity which was most probablydue to the increase in the relative chitin content. However, they

suggested that the dye removal was better in continuous operationin a packed column mainly because of biodegradation. Theadsorption of reactive dyes in neutral solutions using chitosan (Wuet al., 2000) also showed large adsorption capacities (1000

1100 mg g

1

). In a study Al-Degs et al. (2000) observed the

Table 1(continued )


adsorbent

Adsorption

capacity

Concentration

range

Contact

time

pH Percentage

adsorption

Source

Fly ash Metomega chrome

orange

0.7428 mg g1 10 mg L1 110 min 92.25 Gupta and Shukla

(1996)

Wollastonite Metomega chromeorange

0.6957 mg g1 10 mg L1 150 min 73.04 Gupta and Shukla(1996)

Kaolnite Metomega chrome

orange


(1996)Coal Metomega Chrome

orange


(1996)

Activated bentonite Sella fast brown H 360.5 mg kg1 3 h Espantaleon et al.

(2003)

AC activatedcarbon;GAC granularactivatedcarbon;PAC powdered activated carbon;CAC commercial activated carbon;DTMA dodecyltrimethylammonium bromide-

modified.

http://www.torvproducenterna.se/english/basic-facts.shtmlhttp://www.torvproducenterna.se/english/basic-facts.shtmlhttp://www.torvproducenterna.se/english/basic-facts.shtmlhttp://www.torvproducenterna.se/english/basic-facts.shtml


12/30

Table 2

Adsorption capacities and other parameters for the removal of basic dyes by commercial activated carbons and other alternative adsorbents.

Material Adsorbate Surface area of adsorbent

Adsorptioncapacity

Concentration range Contacttime

pH Percentageadsorption

Source

Commercial AC

(E. Merck India)

Basic blue 9

(Methylene

blue)

980.3 mg g1 100400 mg L1 90 min 7.4 Kannan and Sundaram

(2001)

CAC granular Wako

(Wako pure chemicals)

Basic blue 9 1150 m2 g1 260 mg g1 2 h Okada et al. (2003)

CAC fiber FE400

(Toho Rayon Co.)


CAC felt KF1500(Toyobo Co.)


Activated carbon Basic blue 3 648.6 mg g1 50600 mg dm3 7 days Nassar and Magdy (1997)

GAC (Miloje Zakic) Basic dye

Maxilon

Goldgelb GL EC

159.0 mg g1 20200 mg dm3 410

days

Meshko et al. (2001)

GAC (Miloje Zakic) Basic dye

Maxilon.

Schwarz FBL-01

309.2 mg g1 50500 mg dm3 410

days


CAC Merck Basic green 4

(Malachitegreen)

765 m2 g1 222.22 mg g1 15 min Malik et al. (2007)

Chemviron F-400 Basic red 22 720 mg g1 501000 mg dm3 21 days Allen et al. (2003)

Activated carbon Basic red 22 790 mg g1 50600 mg dm3 7 days Nassar and Magdy (1997)PAC Chemviron GW Basic red 46 1026 m2 g1 106 mg g1 30250 mg L1 2 h Martin et al. (2003)

Chemviron F-400 Basic yellow 21 860 mg g1 501000 mg dm3 21 days Allen et al. (2003)

Activated carbon Basic yellow 21 600 mg g1 50600 mg dm3 7 days Nassar and Magdy (1997)

Activated sludge biomass Basic blue 3 36.5 mg g1 6 h Chu and Chen (2002a)

Palm-fruit bunch (raw) Basic blue 3 92 mg g1 50600 mg dm3 7 days Nassar and Magdy (1997)



Carbonaceous adsorbent Basic blue 6

(Meldolas blue)

380 m2 g1 170 mg g1 120 min 6.5

7.5

Jain et al. (2003b)

Blast furnace (BF) sludge,BF dust, BF slag

Basic blue 6(Meldolas blue)

28, 13, 4 m2 g1 67, 34, 3.7 mg g1 120 min 6.57.5

Jain et al. (2003b)

AC-Pinewood Basic blue 69 902 m2 g1 1119 mg g1 5 days 5.4 Tseng et al. (2003)

Bagasse pith raw Basic blue 69 152 mg g1 101000 mg dm3 5 days Chen et al. (2001)

Wood sawdust (raw) Basic blue 69 71.9 mg g1 8 h Ho and McKay (1998a)

Peat Basic blue 69 195 mg g1 Ho and McKay (1998b)

Wood Basic blue 69

(Astrazone blue)

100.1 mg g1 2 h Poots et al. (1978)

Peat Basic blue 69

(Astrazone blue)

0.430.91 g g1 200 mgdm3 5 days 4.0

4.3

McKay et al. (1981)

Hardwood sawdust Basic blue 69(Astrazone blue)

82.2105.7 mg g1 200 mgdm3 3 h Asfour et al. (1985)

Activated clay Basic blue 69,

basic red 22

585, 488.4 mg g1 90.23, 61.78 El-Guendi et al. (El-Guendi

et al., 1995)Bagasse pith Basic blue 69,

basic red 22

157.4, 76.6 mg g1 200 mgdm3 5 days McKay et al. (1997)

AC-Pinewood Basic blue 9 902 m2 g1 556 mg g1 5 days 6.6 Tseng et al. (2003)

AC-Waste newspaper Basic blue 9 1740 m2 g1 390 mg g1 2 h Okada et al. (2003)

Bentonite Basic blue 9

(Methylene

blue)

28 m2 g1 1667 mg g1 1001000 mg L1 180 min 7.9 Ozacar and Sengil (2006)

Coal Basic blue 9 250 mg g1 101000 ppm 6 h McKay et al. (1999)

Bark Basic blue 9 914 mg g1 101000 ppm 6 h McKay et al. (1999)

Rice husk Basic blue 9 312 mg g1 101000 ppm 6 h McKay et al. (1999)

Cotton waste Basic blue 9 277 mg g1 101000 ppm 6 h McKay et al. (1999)

Hair Basic blue 9 158 mg g1 101000 ppm 6 h McKay et al. (1999)

Sewage sludge Basic blue 9 114.94 mg g

1

Otero et al. (2003a)Bamboo dust carbon Basic blue 9 143.2 mg g1 100400 mg L1 40 min 7.2 Kannan and Sundaram

(2001)

Coconut shell carbon Basic blue 9 277.9 mg g1 100400 mg L1 90 min 7.2 Kannan and Sundaram

(2001)

Groundnut shell carbon Basic blue 9 164.9 mg g1 100400 mg L1 45 min 7.2 Kannan and Sundaram

(2001)

Rice husk carbon Basic blue 9 343.5 mg g1 100400 mg L1 40 min 7.2 Kannan and Sundaram

(2001)Straw carbon Basic blue 9 472.1 mg g1 100400 mg L1 35 min 7.2 Kannan and Sundaram

(2001)Raw Date pits Basic blue 9 80.3 mg g1 20400 mg L1 24 h Banat et al. (2003)

AC-Apricot shell Basic blue 9 783 m2 g1 4.11 mg g1 24 h Aygun et al. (2003)

AC-Hazelnut shell Basic blue 9 793 m2 g1 8.82 mg g1 24 h Aygun et al. (2003)

AC-Walnut shell Basic blue 9 774 m2 g1 3.53 mg g1 24 h Aygun et al. (2003)

Fly ash-Slovakia Basic blue 9 3.26 m2 g1 0.0046 mmol g1 0.050.20 mmol L1 72 h Janos et al. (2003)

Fly ash- Czech Republic Basic blue 9 5.47 m2 g1 0.0189 mmol g1 0.050.20 mmol L1 72 h Janos et al. (2003)



13/30

Table 2(continued )


adsorbent

Adsorption

capacity

Concentration range Contact

time

pH Percentage

adsorption

Source

Fe(III)/Cr(III) hydroxide Basic blue 9 22.8 mg g1 Namasivayam and

Sumithra (2005)

Banana peel (raw) Basic blue 9 20.623.5 m2 g1 20.8 mg g1 10120 mg L1 24 h Annadurai et al. (2002)Orange peel (raw) Basic blue 9 20.623.5 m2 g1 18.6 mg g1 24 h Annadurai et al. (2002)

Clay Basic blue 9 71 m2 g1 300 mg g1 Bagane and Guiza (2000)

Diatomite Basic blue 9 27.8 m2

g1

198 mg g1

100400 mg dm3

48 h Al-Ghouti et al. (2003)Diatomite Basic blue 9 33 m2 g1 0.42 mmol g1 0.131.87 mmol L1 3 days Shawabkeh and Tutunji

(2003)

Clay Basic blue 9 30 m2 g1 6.3 mg g1 1 h Gurses et al. (2004)

Activated sludge Basic blue 9 256.41 mg g1 300 min 7 Gulnaz et al. (2004)

Spirodela polyrrhiza

biomass

Basic blue 9 144.93 mg g1 24 h 9 Waranusantigul et al.

(2003)

Dead fungus

Aspergillus niger

Basic blue 9 10.49

18.54 mg g150 mg L1 2 days Fu and Viraraghavan (2000)

Living biomass

Aspergillus niger

Basic blue 9 1.17 mg g1 50 mg L1 2 days Fu and Viraraghavan (2000)

Neem sawdust Basic blue 9 3.622 mg g1 12 mg L1 30 min 7.2 75.47 Khattri and Singh (2000)

Yellow passion fruit Basic blue 9 30 m2 g1 44.7 mg g1 48 h 8 Pavan et al. (2008)

Guava leaf powder Basic blue 9 295 mg g1 100800 mg dm3 Ponnusami et al. (2008)

Beer brewery waste Basic blue 9 4.5 m2 g1 4.92 mg g1 24 h 7 Tsai et al. (2008)

Jack fruit peel Basic blue 9

(Methylene

blue)

285.713 mg g1 35400 mg L1 180 min Hameed (2009a)

Spent tea leaves Basic blue 9

(Methylene

blue)

300.052 mg g1 30390 mg L1 180 min Hameed (2009b)

Sugarcane dust Basic blue 9 3.745 mg g1 12.0 mg L1 30 min 78.02 Khattri and Singh (1999)

Carbonaceous adsorbent Basic blue 9

(Methyleneblue)

380 m2 g1 92 mg g1 120 min 6.5

7.5

Jain et al. (2003a)

Blast furnace (BF) sludge,

BF dust, BF slag

Basic blue 9

(Methylene

blue)

28, 13, 4 m2 g1 6.4, 3.3, 2.1 mg g1 120 min 6.5

7.5

Jain et al. (2003a)

Diatomite Basic blue 9

(Methylene

blue)

27.80 m2 g1 198 mg g1 100400 mg dm3 48 h 11 Al-Ghouti et al. (2003)

Cedar sawdust, crushed brick Basic blue 9

(Methylene

blue)

142.36,

96.41 mg g1 5 h Hamdaoui (2006)

Fly ash (treated with H2SO4) Basic blue 9

(Methyleneblue)

6.236 m2 g1 0.0021 mmol g1 2.675105

2.675104 M

72 h Lin et al. (2008)

Fly ash, zeolite,

unburned carbon

Basic blue 9

(Methylene

blue)

15.6, 16.0,

224 m2 g10.02, 0.045

0.25 mmol g11 1061105 M

100,

400 h

Wang et al. (2005b)

PET carbon Basic blue 9

(Methylene

blue)

33.4 mg g1 2 h Zhang and Itoh (2003)

Hazelnut shell Basic blue 9 76.9 mg g1 501000, 50500 mg L1

60180 min

Ferrero (2007)

Saw dust-walnut Basic blue 9 59.17 mg g1 501000, 50

500 mg L160

180 min

Ferrero (2007)

Saw dust-cherry Basic blue 9 39.84 mg g1 501000, 50

500 mg L160

180 min

Ferrero (2007)

Saw dust-oak Basic blue 9 29.94 mg g1 501000, 50

500 mg L160

180 min

Ferrero (2007)

Saw dust-pitch pine Basic blue 9 27.78 mg g1 501000, 50

500 mg L

160

180 min

Ferrero (2007)

Sunflower stalk Basic blue 9

(Methylene

blue),

Basic red 9

1.2054 m2 g1 205, 317 mg g1 1002000, 100

2000 mg L15 days 80 Sun and Xu (1997)

Beech sawdust untreated Basic blue 9(Methylene

blue),

Red basic 22

9.78, 20.2 mg g1 14 days Batzias and Sidiras (2004)

Zeolite Basic dye

Maxilon

Goldgelb GL EC

14.91 mg g1 20200 mg dm3 410

days


Zeolite Basic dye

Maxilon.

Schwarz FBL-01

55.86 mg g1 50500 mg dm3 410

days


Sawdust carbon Basic green 4 74.5 mg g1 50250 mg L1 Garg et al. (2003)

(continued on next page)



14/30

Table 2(continued )


adsorbent

Adsorption

capacity

Concentration range Contact

time

pH Percentage

adsorption

Source

Neem sawdust Basic green 4 3.42 mg g1 12 mg L1 30 min 7.2 71.25 Khattri and Singh (2000)

AC from pine sawdust Basic gree n 4 1390 m2 g1 370.37 mg g1 502000 mg L1 3 h Akmil-Basar et al. (2005)

Oil palm trunk fiber Basic green 4(Malachite

green)

149.35 mg g1 25300 mg L1 120 min Hameed and El-Khaiary(2008)

AC-groundnut shell Basic green 4(Malachite

green)

1114 m2

g1

222.22 mg g1

30 min Malik et al. (2007)

Waste material from paper

industry, pine bark

Basic green 4

(Malachite

green)

100 mg L 1 1 h 98.5, 69.3 Mendez et al. (2007)

Carbonaceous material Basic green 4

(Malachite

green)

629 m2 g1 75.08 mg g1 1104

1103 M

68 h w10066 Gupta et al. (1997)

Sugarcane dust Basic green 4

(Malachite

green)

3.999 mg g1 12.0 mg L1 30 min 83.32 Khattri and Singh (1999)

Carbonaceous adsorbent Basic orange 2

(Chrysoidine G)

380 m2 g1 75 mg g1 120 min 6.5

7.5

Jain et al. (2003b)

Blast furnace (BF) sludge,

BF dust, BF slag

Basic orange 2

(Chrysoidine G)

28, 13, 4 m2 g1 10.1, 5.4,

1.9 mg g1 120 min 6.5

7.5

Jain et al. (2003b)

Tree fern Basic red 13 408 mg g1 24 h 5 Ho et al. (2005)

Activated sludge Basic red 18 285.71 mg g1 300 min 7 Gulnaz et al. (2004)

Activated sludge biomass Basic red 18 133.9 mg g1 6 h Chu and Chen (2002a)

Activated clay Basic red 18 (C.I.

11085)

157 mg g1 2 h 3 Ho et al. (2001)

Coal Basic red 2 (C.I.

50240)

120 mg g1 101000 ppm 6 h McKay et al. (1999)

Bark Basic red 2 (C.I.50240)


Rice husk Basic red 2 (C.I.

50240)


Cotton waste Basic red 2 (C.I.

50240)


Human Hair Basic red 2 (C.I.

50240)


Bentonite Basic red 2 (C.I.

50240)

47.73 m2 g1 274 mg g1 50450 mg L1 60 min Hu et al. (2006a)

AC-Plum kernel Basic red 22 1162 m2 g1 710 mg g1 4.1 Juang et al. (2002)Sugar-industry-mud Basic red 22 519 mg g1 502000 mg L1 3 days Magdy and Daifullah (1998)

Kudzu Basic red 22 210 mg g1 501000 mg dm3 21 days Allen et al. (2003)Bagasse pith raw Basic red 22 75 mg g1 101000 mg dm3 5 days Chen et al. (2001)

Palm-fruit bunch RAW Basic red 22 180 mg g1 50600 mg dm3 7 days Nassar and Magdy (1997)

AC-Bagasse Basic red 22 (C.I.

11055)

607 m2 g1 942 mg g1 4.1 Juang et al. (2002)

Cane pith Basic red 22 (C.I.

11055)

606.8 m2 g1 941.7 mg g1 5 days 4.1 Juang et al. (2001)

AC-Corncob Basic red 22 (C.I.

11055)

943 m2 g1 790 mg g1 4.1 Juang et al. (2002)

Activated sludge biomass Basic red 29 113.2 mg g1 6 h Chu and Chen (2002a)

AC sludge based Basic red 46 253 m2 g1 188 mg g1 30250 mg L1 2 h Martin et al. (2003)

Neem sawdust Basic violet 10 2.355 mg g1 12 mg L1 30 min 7.2 49.08 Khattri and Singh (2000)Fly ash-Slovakia Basic violet 10 3.26 m2 g1 0.0040 mmol g1 0.050.20 mmol L1 72 h Janos et al. (2003)

Fly ash-Czech Republic Basic violet 10 5.47 m2 g1 0.0115 mmol g1 0.050.20 mmol L1 72 h Janos et al. (2003)

Banana peel Basic violet 10 20.623.5 m2 g1 20.6 mg g1 10120 mg L1 24 h Annadurai et al. (2002)

Orange peel Basic violet 10 20.623.5 m2 g1 14.3 mg g1 10120 mg L1 24 h Annadurai et al. (2002)

Coir pith carbonized Basic violet 10

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