Literature Review

PART III: BIOSORBENTS AND BIOSORPTION FOR WASTEWATER TREATMENT

BIOSORPTION

Definition of biosorption

Up to now, so many definitions of bio-sorption have been given by different researchers. Sahmoune et al. (2010) & Dhankhar & Hooda (2011) suggest that the biosorption process involves a solid phase (biosorbent; biological materials) and a liquid phase (solvent, normally water) containing a dissolved species to be sorbed (sorbates, e.g. metal ions). Meanwhile, most researchers defined biosorption as the ability of materials of biological origin (Bohumil Volesky (2007), Gadd (2009), Chojnacka (2010), Majdik et al. (2010), Dhankhar & Hooda (2011)) to bind and concentrate adsorbate(s) from aqueous solutions (Park et al. (2010), Chojnacka (2010), Mudhoo & Garg (2011), resulting in a reduction of sorbate concentration in the solution (Gadd (2009). Due to higher affinity of the sorbent for the sorbate species, the latter is attracted and removed by different mechanism, including physical and chemical adsorption, ion exchange, complexation, chelation, and micro-precipiation (Lin & Juang (2009), Sahmoune et al. (2010)). Kratochvil & Volesky (…), Dhankhar & Hooda (2011) & Mudhoo & Garg (2011) even point out that biological materials comprise certain types of inexpensive, inactive, dead & microbial biomass. While Chojnacka (2009) argues sorbates are bound to the surface of cellular wall or membrane, Gadd (2009) suggests sorbates are accumulated at the sorbate – biosorbent interface.

Merits and demerits of biosorption

The advantages of the biosorption over conventional methods include low operation costs if low-cost sorbents are used, low quantity of sewage sludge disposed, COD of wastewater does not increase. The process is simple in operation and very similar to conventional adsorption or ion-exchange, except that sorbent of biological origin is employed. Biosorbents are selective and regenerable and a process is in particular highly effective in the treatment of dilute effluents (Kratochvil & Volesky (…), Das et al. (2008b), Gadd (2009), Sahmoune et al. (2010), Park et al. (2010), Chojnacka (2010), Fu & Wang (2011)). The limitations include first of all a shorter life time of biosorbents when compared with conventional sorbents; early saturation i.e. when metal interactive sites are occupied; metal desorption is necessary prior to further use; the potential for biological process improvement (e.g. through genetic engineering of cells) is limited because cells are not metabolizing and there is no potential for biologically altering the meta valency state (Gadd, 2009). In addition, biodegradable and decomposable properties of biomass are drawbacks that hinder their long-term applications in adsorption processes (Park et al. 2010).

Factor affecting biosorption

Since the mechanism was found to be ion exchange, protons compete with metal cations for the binding sites and for this reason pH is the operation condition which influences the process the mostly strong. pH determines protonation or deprotonation of metal ions binding sites and thus influences the availability of the site to the sorbate. By lowering pH it is also possible to release metal ions from the binding site. This property is used for the recovery of metal cations and regeneration of the biosorbent (Chojnacka 2010).

BIOSORBENTS

Classification of biosorbents

There are many ways of classifying bisorbents.

Biosorbents can be classified into low- and high-cost sorbents. The first group includes the materials which can be collected directly from the environment (eg. seaweeds) and waste or by products from industry, eg. yeasts from fermentation processes winery or brewery (Wang & Chen 2006). The latter group includes the materials which are specially propagated for biosorption purposes. They should have very good biosorptive properties and should be easily regenerable (Chojnacka 2010).

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Figure ... Low-cost and high-cost biosorbents (Chojnacka 2009)

Studies using biosorbents have shown that biomass used for biosorption may be living or dead (Das et al. (2008), Gadd (2009), Park et al. (2010)). The use of living biomass has several demerits. Metabolic extracellular products may form complexes with metals to retain them in solution. The maintenance of a healthy microbial population is difficult due to toxicity of the pollutants and other unsuitable environmental factors. Keeping biomass alive requires the addition of nutrients and hence increase the BOD and COD in the effluent. Recovery of valuable metals is also limited in living cells since these may be bound intracellularly , Park et al. (2010)). The advantages of using dead cells are summarized by Dhankhar & Hooda (2011) as follows: (1) absence of toxicity limitations (2) absence of requirements for growth media and nutrients in the feed solution (3) easy absorbance and recovery of biosorbed metals (4) easy regeneration and reuse of biomass (5) possibility of easy immobilization of dead cells (6) avoidance of sudden death of the biomass population (7) easy mathematical modelling of metal uptake reactors. For these reasons, attention has been focused on the use of non-living biomass as biosorbents. Whereas the use of inactivated biomass has been preferred, some disadvantages also deserve mention. Dead cells can not be used where biological alteration in valency of a metal is sought. Moreover, degradation of organometallic species is not possible with dead biomass. Another important drawback associated with dead biomass is that there is no scope for biosorption improvement through mutant isolation (Park et al. 2010).Adsorption capacity of biosorbents

Whereas Kiran, Akar & Tunali (2005) find that the metal adsorption capacity of dead cells may be greater, equivalent to, or less than that of living cells, depending on various factors such as biosorbents, pre-treatment method and type of metal ions, the results obtained from a study conducted by Chen et al. (2005) show that the adsorption capacity of Cu(II) and Zn(II) from aqueous solution by Pseudomonas putida CZ1 for living cells was apparently higher than that of nonliving cells. They attributed this to the intracellular accumulation of metal ions occurring in living cells, resulting in the enhancement in metal uptake capacity. The other possibility is that the autoclave-sterilization step may destroy or lose some of metal binding sites, resulting in the decrease in metal uptake capacity of the nonliving cells Majdik et al. (2010)Functional groups of biosorbents

Within a given group of organisms, biosorption properties are similar, because the chemical composition of cellwall is alike. Seaweeds are presented as very good sorbents, because the cell wall of green and brown algae contains alginate with its carboxyl and hydroxyl groups (Davis et al., 2003; Vieira and Volesky, 2000).Worse sorptive properties possess red algae which contain carrageen, exposing hydroxyl and sulfonate groups (Vieira and Volesky, 2000). The biomass of yeasts and other fungi contains chitin and chitosan and thus amino, amido and hydroxyl groups are found on the cellular surfaces. For this reason fungi have a unique properties of binding both cations and anions to their cell wall. Among the group of bacteria we can distinguish gram positive and

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Low or intermediate sorption capacity (q=10-50 mg/g)

High sorbent concentrations are used

Biosorbents High sorption capacity (q=100-350 mg/g)

Low sorbent concentrations are used

Low-cost sorbents

Wastes,by-products, useless

materials

High-cost sorbents

Plant originAnimal origin

Aquatic plants

Macroalgae Microalgae

Animal bones

Eggshells

Straw Grass Lemnaminor

Riccia fluitans

Naturallycollected

Specially propagated

Leaves

Cladophora sp.

Spirulina sp. Chlorella sp.

gram negative. Cell wall of gram negative bacteria contains peptidoglycan and of gram positive also teichoic acids containing phosphoryl and hydroxyl groups and thus the latter are better biosorbents.

Characterization of biosorption

Table … Some facts on bio-sorption (Chojnacka 2010)

The role of functional groups Participation of functional groups in biosorption depends on (Vieira and Volesky, 2000):

– The concentration and the type of the group in the biomass– The accessibility of the group– The chemical state of the site (eg. availability)– The affinity between site and metal (binding strength)

The role of pH pH (Aksu, 2005; Volesky and Schiewer, 2000)– Affects protonation (=availability) of metal ions binding sites and

ionic state of the sorbate in the solution– At low pH (high level of H+), anionic sites become protonated– Metal cations can be eluted by acidic wash – regeneration,

multiple reuse, better economySorbates Inorganic sorbates:

– Almost all metals (not K+, Mg 2+)– Most thoroughly investigated – key environmental pollutants of

major toxicity: Pb, Cu, Hg, Cd, Cr, As, radionuclides (Co, Sr, U, Th)– In solution sorbates are in cationic, exist as complexes (Cl-), range

of oxidation states, hydroxylated depending on pH.– Studies assume divalent cations – not always true!

Organic sorbates:– Yeasts bind mainly cations, but sometimes anions, eg. Rhizopus

arrhizus (fungus) coordinates U to amine of chitin with further precipitation of hydroxylated derivatives (Vieira and Volesky, 2000).

Table… Comparison of the features of biosorption and bioaccumulation (Dhankhar and Hooda 2011)

Features Bio-sorption Bio-accumulationCost-effectiveness High, as biosorbents used are

mainly waste biomass released from industrial, agricultural and other sources. Cost involves mainly transportation and other simple processing charges

Low, as the living-cell maintenance is cost prone

pH Metal uptake is strongly influenced by pH; however, process can be operated under wide range of pH conditions

In addition to uptake, the living cells themselves are affected under extreme pH conditions

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Temperature No influence Severely affectedMaintenance Easy, as biomass is inactive External metabolic energy is needed in

maintenance of cultureSelectivity Poor, but can be improved by

modification/processing of biomassBetter than biosorption

Versatility Good, as the binding sites can accommodate a variety of ions

Not very flexible, as the process is prone to high metal/salt conditions

Uptake capacity Very high, as biomasses are reported to accommodate an amount of toxicant nearly as high as their dry weight

Low, as living cells are sensitive to high toxicant concentration

Uptake rate Usually rapid Usually slower than biosorption, as intracellular accumulation is time consuming

Regenerabilityand reusability

High with possible reuse over a number of cycles

Low, as toxicants are intracellularly accumulated

Toxicant recovery Possible Not possible Biosorption Mechanisms

Figure … Biosorption mechanisms as classified by Veglio and Beolchini (Park, Yun & Park 2010)

(A) Classified according to the dependence on the cellular metabolism. (B) Classified according to the location where biosorption occurs.

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Fig... Mechanism of biosorption (Farooq et al. 2010)

Table … The representative functional groups and classes of organic compounds in biomass (Wang & Chen 2009)

Methods Utilized in Biosorption Research

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The physical and chemical characteristics of biosorbents are important for understanding the metal binding mechanism on the biomass surface. The characterization of the structure and surface chemistry of the biosorbent is of considerable interest for the development of adsorption and separation processes. Depending on the nature of the biosorbents, a variety of techniques are useful for this purpose, e. g., Fourier Transform Infra-Red (FTIR) spectroscopy, X-ray Photo Electron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Energy Dispersive X-ray (EDX) fluorescence spectrophotometry, nitrogen sorption, etc. These methods are commonly utilized in together to obtain a complete description of the structure, morphology and composition of the biosorbents (Arief et al. 2008)

Factors Affecting Biosorption

Influence of Biosorption Conditions

Influence of pH

Influence of Temperature

Effect of Initial Concentration

Effect of Ionic Strength

Effect of Adsorbent Dosage

Table ... Effects of batch processing factors on biosorptive removal of adsorptive pollutants (Park, Yun & Park 2010)

Process factors Effects on biosorption of pollutantsSolution pH ↑ It enhances biosorptive removal of cationic metals or basic dyes, but reduces

that of anionic metals or acidic dyesTemperature ↑ It usually enhances biosorptive removal of adsorptive pollutant by increasing

surface activity and kinetic energy of the adsorbate, but may damage physical structure of biosorbent

Ionic strength↑ It reduces biosorptive removal of adsorptive pollutant by competing with the adsorbate for binding sites of biosorbent

Initial pollutant concentration↑

It increases the quantity of biosorbed pollutant per unit weight of biosorbent, but decreases its removal efficiency

Biosorbent dosage↑ It decreases the quantity of biosorbed pollutant per unit weight of biosorbent, but increases its removal efficiency

Biosorbent size↓ It is favourable for batch process due to higher surface area of the biosorbent, but not for collum process due to its low mechanical strength and clogging of the column

Agitation speed↑ It enhances biosorptive removal rate of adsorptive pollutant by minimizing its mass transfer resistance, but may damage physical structure of biosorbent

Other pollutant concentration↑

If coexisting pollutant competes with a target pollutant for binding sites or forms any complex with it, higher concentration of other pollutants will reduce biosorptive removal of the target pollutant

Effect of Pre-treatment on Biosorption

Table… Sumary of work done by various researchers on effect of modification on heavy metal removal using agro-based biomasses

Biosorbent Modifying agent

Operating conditions Adsorption capacity

qmax(mg/g)

Improvement in adsorption capacity (%)

ReferencepHopt Co (mg/L) T (0C)

BIOSORBENTS

Definition

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Types of biomass or biomaterials

All kinds of microbial, plant and animal biomass, and derived products, have received investigation in a variety forms (Gadd 2008).

Living and non-living (dead) biosorbents

Biomass used for bio-sorption may be living or dead (Gadd 2008).

Feasibility studies for large-scale applications have demonstrated that bio-sorptive processes using non-living biomass are in fact more applicable than the bio-accumulative processes that use living micro-organism. Dead biomass has advantages over living micro-organisms, such as... (Park, Yun & Park 2010)

Untreated and pre-treated biosorbents

Fig ... Schematic diagram for processing different types of native biomass into bio-sorbents (Park, Yun & Park 2010)

Low-cost and high-cost biosorbents

When choosing biomass, for large-scale industrial uses, the main factor to be taken into account is its availability and cheapness (Park, Yun & Park 2010)

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Low or intermediate sorption capacity (q=10-50 mg/g)

High sorbent concentrations are used

Biosorbents High sorption capacity (q=100-350 mg/g)

Low sorbent concentrations are used

Low-cost sorbents

Wastes,by-products, useless

materials

High-cost sorbents

Plant originAnimal origin

Aquatic plants

Macroalgae Microalgae

Animal bones

Eggshells

Straw Grass Lemnaminor

Riccia fluitans

Naturallycollected

Specially propagated

Leaves

Cladophora sp.

Spirulina sp. Chlorella sp.

Figure ... Low-cost and high-cost biosorbents (Chojnacka 2009) Bacteria, Fungi, Algae, Industrial wastes, Agricultural wastes, Natural residues, Others

A broad range of biomass types have been tested for their bio-sorptive capacities under various conditions. Bio-sorbents primarily fall into the following categories: bacteria, fungi, algae, industrial wastes, agricultural wastes, natural residues, and other biomaterials (Park, Yun & Park 2010)

Table ... Types of native biomass that have been used for preparing biosorbents (Park, Yun & Park 2010)

Category Examples

Bacteria Gram-positive bacteria (Bacillus sp., Corynebacterium sp., ect.), Gram-negative bacteria (Escherichia sp., Pseudomonas sp., etc.), Cyanobacteria (Anabaena sp., Synechocytis sp., etc.)

Fungi Molds (Aspergillus sp., Rhizopus sp., etc.), Mushrooms (Agaricus sp., Trichaptum sp., etc), Yeast (Saccharomyces sp., Candida sp., etc.)

Algae Micro-algae (Clorella sp., Chlamydomonas sp., etc.), Macro-algae Green seaweed (Enteromorpha sp., Codium sp., etc.), Brown seaweed (Sargassum sp., Ecklonia sp., etc. ) and Red seaweed (Geildium sp., Porphyra sp., etc.)

Industrial wastes Fermentation wastes, food/beverage wastes, activated sludges, anaerobic sludges, etc.Agricultural wastes Fruit, vegetable wastes, rice straws, wheat bran, soybean hulls, etc.Natural residues Plant residues, sawdust, tree barks, weeds, etcOthers Chitosan-driven materials, cellulose-driven materials, etc.

Algae as Biosorbent

Advantages over other bio-sorbents

Typical representatives

Different forms (wild-type, pristine, pre-treated)

Table ... Maximum capacity of biosorption (qmax) reported for several algae

Species Metals qmax (mg g-1) References

MACRO ALGAE

Green algae Codium vermilara

Chaetomorpha linum Cu(II) and Zn(II) 1.46 and 1.97 Ajjabi & Chouba 2009

Spirogyra insignis

Ulva lactuca and its activated carbon

Cr(VI) 10.61 and 112.36 El-Sikaily et al. 2007

Ulva reticulata Ni 62.3 Vijayaraghavan 2008

Enteromorpha compressa Cd(II) 9.50 Sahmurova et al. 2010

Cladophora sp. Cu(II), Ni(II), Cr(III), Cr(VI) 819, 504, 347, 168 Doshi et al. 2008

Cladophora fascicularis Pb(II) 198.5 Deng et al. 2007

Spirulina sp. Cu(II), Ni(II), Cr(III), Cr(VI) 576, 1108, 306, 202 Doshi et al. 2008

Brown algae Fucus spiralis

Padina sp.

Sargassum baccularia

Sargassum filipendula

Sargassum fluitants

Sargassum sinicola Cd 62.4 Patrón-Prado et al. 2011

Sargassum lapazeanum Cd 71.2 Patrón-Prado et al. 2011

Sargassum vulgare

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Sargassum sp.

Lobophora variegata

(raw biomass)

Cd(II) and Pb(II) 1.65 and 1.71 Jha et al. 2009

Lobophora variegata

(chemically modified biomass)

Cd(II) and Pb(II) 1.71 and 1.79 Jha et al. 2009

Red algae Asparagopsis armata

Chondrus crispus

Gracilaria edulis

Gracilaria sp.

Freshwater Oedogonium sp

(green algae)

Pb 145.0 Gupta & Rastogi 2008

Nostoc sp.

(blue green algae)

Pb 93.5 Gupta & Rastogi 2008

MICRO ALGAE

Scenedusmus obliquus

(heat-inactivated cells)

Zn 209.6 Monteiro et al. 2011)

Scenedusmus obliquus

(living cells)

Zn 836.5 Monteiro et al. 2011)

Fungi as Biosorbent

Species Metal ions Biosorption capacity (mg/g)

References

RhizopusRhizopus cohnii Cd 40.5 Luo et al. 2010Rhizopus oligosporus Hg (II) 33.33 Ozsoy 2010Rhizopus arrhizus (dried) Cr (VI) 78.0 Aksu & Balibek 2007Rhizopus arrhizus (living biomass) Ni 618.5 Tahir & Zahid 2008Rhizopus oryzae (viable and pre-treated biomass)

Cu 19.4 and 43.7 Bhainsa & D’Souza 2008

PenicilliumPenicillium simplicissimum Cd(II), Zn(II) and

Pb(II)52.50, 65.60 and 76.90 Fan et al. 2008

AspergillusAspergillus niger Mn 12.15 Parvathi et al. 2007Aspergillus niger Cd(II), Ni(II) and

Pb(II)2.2, 1.6 and 4.7 Amini & Younesi 2009

Aspergillus niger (NaOH pre-treated biomass) Ni(II) 4.82 Amini et al. 2000Aspergillus niger (PVA-immobilized fungal biomass)

Cu(II) and Cd(II) 34.13 and 60.24 Tsekova et al. 2010

Aspergillus niger (free biomass) Cu(II) and Cd(II) 17.60 and 69.44 Tsekova et al. 2010Aspergillus versicolor Pb 45.0 Bairagi et al. 2011Aspergillus nidulans (dry, heat-treated and NaOH-treated biomass)

As(III) 127, 178 and 166 Maheswari & Murugesan 2011

Aspergillus terreus (immobilized on loofa sponge discs)

Pb (II), Hg (II) and Cd(II)

247.2, 37.7 and 23.8 Sun et al. 2010

YeastSaccharomyces cerevisiae Mn 10.53 Parvathi et al. 2007Saccharomyces cerevisiae (immobilized) Cd(II) 5.96 Tonk et al. 2011Saccharomyces cerevisiae (immobilized) Cd (II) and Cu (II) 38.08 and 39.02 Zan et al. 2011Saccharomyces cerevisiae subsp. Uvarum (magnetically modified)

Cu(II) 76.8 Uzun et al. 2011

Saccharomyces cerevisiae (non-living biomass) Cu(II) 2.59 Cojocaru et al. 2009Pichia stipites yeast Cu(II) and Cr(III) 15.85 and 9.10 Yilmazer & Saracoglu 2009

Bacteria as Biosorbent

Species Metal ions Biosorption capacity References

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(mg/g)StreptomycesStreptomyces ciscaucasicus CCNWHX 72-14 (live and dead cells)

Zn(II) 42.75 and 54 Li et al. 2010

S. maltophilia ZA-6 (dried biomasses) Cr(III) 10.2 Alam & Ahmad 2011PseudomonasP. aeruginosa ASU 6a Zn(II) 83.33 Joo et al. 2010P. cepacia 120S (dead biomass) Ni(II) 169.8 Abdel-Monem et al. 2010BacillusB. cereus AUMC B52 Zn(II) 66.6 Joo et al. 2010B. subtilis 117S (living and dead biomass) Ni(II) 155.5 and 175.6 Abdel-Monem et al. 2010OthersExiguobacterium sp. ZM-2 (living and dead biomass)

Cr(VI) 29.8 and 20.1 Alam & Ahmad 2011

Exiguobacterium sp. ZM-2 (dried biomasses) Cr(III) 9.0 Alam & Ahmad 2011Pantoea sp. KS-2 (living and dried biomass) Cr(III) 11.25 and 11.7 Alam & Ahmad 2011Aeromonas sp. KS-14 (living and dried biomass) Cr(III) 8.45 and 10.45 Alam & Ahmad 2011

Yeast as Biosorbent

Plant origin biosorbents

Table 1. Maximum capacity of biosorption (qmax) and removal efficiency (%) reported for several plant origin biosorbents

Plant origin biosorbents Metal ionsBiosorption capacity

(mg/g)Removal efficiency

(%)References

Moringa oleifera bark Ni(II) 30. 38 Reddy et al. 2011Potato peels Cu(II) 99.8% Aman et al. 2008Fluted pumpkin (Telfairia occidentalis) seed shell

Pb(II) 14.286 Okoye et al. 2010

Onion skins (formaldehyde-treated)

Pb(II) 200 Saka et al. 2011

Pre-boiled treated onion skins and formaldehyde-treated onion skins

Pb(II) 84.8% and 93.5% Saka et al. 2011

Orange peel (mercapto-acetic acid modified)

Cu(II) and Cd(II)

70.67 and 136.05 Liang et al. 2009

Mangifera sp. (non-living biomass)

Pb(II), Cu(II),

Zn(II) and Ni(II)

24.4 (Pb); 22.506 (Cu); 18.932(Zn) and 17.618

(Ni)Ashraf et al. 2011

Oyster mushroom (Pleurotus platypus)

Cd(II) 34.96

Button mushroom (Agaricus bisporus)

Pb(II) 33.78 Vimala & Das 2009

Maize tasselCr(VI) and

Cd(II)Cr(79.1%) and Cd(88%) Zvinowanda et al. 2009

Coffee husks (untreated biomass)

Cu(II), Cd(II),

and Zn(II)

Cu (89–98%); Cd (65–85%) and Zn (48–79%)

Oliveira et al. 2008

Mangifera sp. (mango)

Pb(II), Cu(II),

Zn(II) and Ni(II)

Pb (92%); Cu (86.84%); Zn (83.96%) and Ni

(82.29%) Ashraf et al. 2011

Papaya wood Cu(II), Cu(97.8%), Cd(94.9%) Saeed et al. 2005

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Cd(II) and Zn(II)

and Zn(66.8%)

Comparison of Sorption Performance

Which sorbent is ‘better’ ? There is no direct answer to that until this question is qualified: at which residual concentration?

The comparison of single-sorbate sorption performance is best based on a complete single-sorbate sorption isotherm curves derived under the same environmental conditions (e.g. pH, temperature, ionic strength, etc.). Sorption isotherms are plots between the sorption uptake (q ) and the final equilibrium concentration of the residual sorbate remaining in the solution (Cf ). Classical models of Langmuir (Langmuir, 1918) and Freundlich (Freundlich, 1907) are often used to describe the relationship.

Langmuir: q = qmax (bCf)/ (1+ bCf) (1)

Freundlich: q = K C1/nf (2)

A steep initial slope of a sorption isotherm indicates a sorbent which has a high capacity for the sorbate in the low residual (final, Cf ) concentration range (high affinity). This affinity is indicated by the coefficient b in the Langmuir equation which is often conveniently fitted to experimental sorption results although it does not correspond to the biosorption (ion exchange) phenomena. The lower the value of langmuirian b the higher the affinity. In conclusion, for ‘good’ sorbents in general, one is looking for a high qmax and a steep initial sorption isotherm slope as indicated by e.g. low values of Langmuir parameter b.

The comparison of sorbents based on “% Removal” is often encountered in the literature. However, it is so approximate that it could lead to outright misleading conclusions on the relative sorption performance. It can only serve the purpose of crude orientation, perhaps adequate only for quick and very approximate screening of (bio)sorbent materials (Kratochvil & Volesky )

When choosing biomass, for large-scale industrial uses, the main factor to be taken into account is its availability and cheapness (Park, Yun & Park 2010)

Table… Summary of work done by various researchers using variety of bio-sorbents for the removal of heavy metals

Biosorbents Metal Ions

Operating Conditions

qmax, (mg g-1)

Removal

efficiency (%)

ReferencespH T, (0C) C0 (mg L-

1)

Natural bio-sorbents

Algae

Fungi

Bacteria

Agricultural waste materials

It should be noted that the bio-sorptive capacity of a certain type of biosorbent depends on its pre-treatment methods, as well as, on experimental conditions like pH and temperature (Park, Yun & Park 2010)

Development of Novel Biosorbents

Biosorbents are prepared from naturally abundant and/ or waste biomass of algae, moss, fungi, or bacteria which is inactivated and usually pretreated by washing with acids and/ or bases before final drying and granulation (Kratochvil & Volesky )

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Figure … Schematic diagram for processing different types of native biomass into biosorbents (Park, Yun & Park 2010)

While simple cutting and/or grinding of the dry biomass may yield stable biosorbent particles (Kratochvil & Volesky ), chemical modification methods could increase/activate the binding sites on the biomass surface, they include pre-treatment, binding site enhancement, binding site modification and polymerization (Wang & Chen 2009)

Table ... Modification methods for converting raw biomass into better biosorbents (Park, Yun & Park 2010; Park, Yun & Park 2010)

Category Detailed methodsPhysical modification Autoclaving, steam, thermal drying, lyophilization,

cutting, grinding, etc.Chemical modification Pre-treatment

(washing) Acids (HCl, H2SO4, HNO3, H3PO4, citric acid, etc.) Alkalis (NaOH, KOH, NH4OH, Ca(OH)2, etc.) Organic solvents (methanol, ethanol, acetone, toluene,

formaldehyde, epichlorohydrin, salicylic acid, NTA, EDTA, SDS, L-cysteine, Triton X-100, etc.),

Other chemicals (NaCl, CaCl2, ZnCl2, Na2CO3, NaHCO3, K2CO3, (NH4)2SO4, H2O2, NH4CH3COO, etc.)

Cell modification (during growth)

Enhancement of binding groups

Animation of hydroxyl group, carboxylation of hydroxyl group, phosphorylation of hydroxyl group, carboxylation of amine group, amination of carboxyl group, saponification of ester group, sulphonation, xanthanation, thiolation, halogenation, oxidation, etc.

Elimination of inhibiting groups

Decarboxylation/ elimination of carboxyl group Deamination/ elimination of amine group, etc.

Graft polymerization

High energy radiation grafting (using γ-irradiation, microwave radiation, electro-magnetic radiation, etc.)

Photochemical grafting (with/without sensitizers like benzoin ethyl ether, acrylated azo dye and aromatic ketones under UV light)

Chemical initiation grafting (using ceric ion, permanganate ion, ferrous ammonium nitrate/ H2O2, KMnO4/ citric acid, etc)

Cell modification(during growth)

Culture optimization

Optimization of culture conditions for enhancing biosorptive capacity of cells

Genetic engineering

Over-expression of cysteine-rich peptides (glutathione, phytochelatins, metallothioneins, etc.) and Expression of hybrid proteins on the surface of cells

BIOSORBATES

Heavy metals

Types of heavy metals

Much work has been reported on cationic metal species. Among these metals, Cd, Ni, Zn, Cu and Pb are the most widely studied in the literature. Cr, Hg, As, Mn, Co, Fe, Pt, Pd, Th, U, etc. are investigated too. Not many studies have been carried out regarding anionic metal species like MoO4

2-, TcO4-, PtCl4

3-, CrO42-, SeO4

2-, Au(CN)2. The information available in connection with multi-metallic systems is very poor (Kratochvil & Volesky )

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Organic matters (phenols, dyes and pesticides)

Nutrients (phosphate, nitrate and amonia)

Why need to remove these pollutants

Table … Sources and toxic effects of heavy metals on human beings (Farooq et al. 2010)

Metal Source Toxic effect ReferencesLead Electroplating, manufacturing

of batteries, pigments, ammunition

Anaemia, brain damage, anorexia, malaise, loss of appetite, diminishing IQ

Gaballah and Kilbertus (1998), Low et al. (2000), Volesky (1993)

Cadmium Electroplating, smelting, alloy manufacturing, pigments, plastic, mining, refining

Carcinogenic, renal disturbances, lung insufficiency,bone lesions, cancer, hypertension, Itai–Itai disease,weight loss

Chen and Hao (1998), Godt et al. (2006), Low et al. (2000), Sharma (1995), Singh et al. (2006)

Mercury Weathering of mercuriferous areas, volcanic eruptions, naturally-caused forest fires, biogenic emissions, battery production, fossil fuel burning, mining and metallurgical processes, paint and chloralkali industries

Neurological and renal disturbances, impairment ofpulmonary function, corrosive to skin, eyes, muscles,dermatitis, kidney damage

Boening (2000), Manohar et al. (2002), Morel et al. (1998)

Chromium (VI)

Electroplating, leather tanning, textile, dyeing, electroplating, metal processing, wood preservatives, paints and pigments, steelfabrication and canning industry

Carcinogenic, mutagenic, teratogenic, epigastric pain nausea, vomiting, severe diarrhoea, producing lung tumors

Dupont and Guillon (2003), Granados-Correa and Serrano-Gomez (2009), Kobya (2004), Singh et al. (2009)

Arsenic Smelting, mining, energy production from fossil fuels,

Gastrointestinal symptoms, disturbances of cardiovascular

Chilvers and Peterson (1987), Dudka and

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rock sediments and nervous system functions, bone marrow depression, haemolysis, hepatomegaly, melanosis, polyneuropathy and encephalopathy, liver tumors

Markert (1992), Robertson (1989)

Copper Printed circuit board manufacturing, electronics plating, plating, wire drawing,copper polishing, paint manufacturing, wood preservatives and printing operations

Reproductive and developmental toxicity, neurotoxicity, and acute toxicity, dizziness, diarrhoea

Chuah et al. (2005), Papandreou et al. (2007),Yu et al. (2000)

Zinc Mining and manufacturing processes

Causes short term ‘‘metal-fume fever”,gastrointestinal distress, nausea and diarrhoea

WHO (2001)

Nickel Non-ferrous metal, mineral processing, paint formulation, electroplating, porcelain enameling, copper sulphate manufacture and steam-electric power plants

Chronic bronchitis, reduced lung function, lung cancer

Akhtar et al. (2004), Ozturk (2007)

Table … The effects of heavy metals on human health (Arief et al. 2008)Heavy metal ToxicitiesCr (VI) Headache, nausea, severe diarrhea, vomiting, epigastric pain, hemorrhage, carcinogenic

and has an adverse potential to modify the DNA transcription processCr(III) Allergic skin reactions and cancerZn(II) Depression, lethargy, neurologic signs such as seizures and ataxia, and increased thirstCu(II) Liver damage, Wilson's disease, insomniaCd(II) Kidney damage, renal disorder, Itai-Itai (excruciating pain in the bone), hepatic damage,

cancer, and hypertensionPb(II) Encephalophathy, seizures and mental retardation, reduces haemoglobin productionNi (II) Dermatitis, nausea, chronic asthma, coughing, bronchial hemorrhage, gastrointestinal

distress, weakness and dizziness

Types of forms of these contaminants (cations, anions…)

Total phosphorus PtParticular phosphorus Pp (organic and inorganic)

Dissolved phosphorus Pd

Dissolved poly phosphatePDp (inorganic)

Hydrolysed dissolved phosphorous PDh

Orthophosphate PO4-P(inorganic)

Dissolved phosphorus POx

(organic)

Figure ... Different forms of phosphorous in wastewater (Wiesmann 2007)

Table... Typical dyes used in textile dyeing operations (Demirbas 2009)

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Dye class DescriptionAcid Water soluble anionic compoundsBasic Water soluble, applied in weakly acidic dyebaths; very bright dyesDirect Water-soluble, anionic compounds; can be applied directly to cellulosics without

mordants (or metals like chromium and copper)Disperse Not water-solubleReactive Water-soluble, anionic compounds; largest dye classSulphur Organic compounds containing sulphur or sodium sulphideVat Water-insoluble; oldest dyes; more chemically complex

Advantages and limitations of bio-sorption over conventional/ traditional treatment methods for removal of bio-sorptive pollutants from wastewater

Table … Some methods to remove metal ions from wastewaters (Farooq et al. 2010)

Method Advantages DisadvantagesChemical Precipitation Simple

Inexpensive Most of metals can be removed

Large amounts of sludge produced Disposal problems

Chemical coagulation Sludge settling Dewatering

High cost Large consumption of chemicals

Ion-exchange High regeneration of materials Metal selective

High cost Less number of metal ions removed

Electrochemical methods Metal selective No consumption of chemicals Pure metals can be achieved

High capital cost High running cost Initial solution pH and Current density

AdsorptionUsing activated carbon

Most of metals can be removed High efficiency (>99%)

Cost of activated carbon No regeneration Performance depends upon adsorbent

Using natural zeolite Most of metals can be removedRelatively less costly materials

Low efficiency

Membrane process and ultrafilteration

Less solid waste producedLess chemical consumptionHigh efficiency (>95% for single metal)

High initial and running costLow flow ratesRemoval (%) decreases with the presence of other metals

Research in biosorption suggests the following advantages over other techniques (Farooq et al. 2010): The materials can be found easily as wastes or by-products and at almost no cost. There is no need of costly growth media. The process is independent of physiological constraints of living cells. Process is very rapid, as non-living material behaves as an ionexchange resin, metal loading is very high. The conditions of the process are not limited by the living biomass, no aseptic conditions required. Process is reversible and metal can be desorbed easily thus recycling of the materials is quite possible. Chemical or biological sludge is minimized.

However, there are certain disadvantages as well (Farooq et al. 2010): Irrespective of the value of the metal, it needs to be desorbed from the material to be further re-

employed. The characteristics of the biosorbents can not be biologically controlled.

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Figure ... A comparison of some nitrate removal technologies (Bhatnagar & Sillanpää 2011)

DESOPRTION

COMMENTS AND SUGGESTIONS

Many researchers have made valuable comments and/or suggestions on bio-sorption. We have summarized these comments and suggestions, and have added our own ideas:

It is evident from the literature survey of 185 articles that ion-exchange, adsorption and membrane filtration are the most frequently studied for the treatment of heavy metal wastewater (Fu & Wang 2011)

The major challenge faced by bio-sorption researchers was to select the most promising types of biomass from an extremely large pool of readily available and inexpensive biomaterials (Park, Yun & Park 2010). It is necessary to further search for better and more selective bio-sorbents (Chojnacka 2010). Factors other than simply the availability and cheapness of biomass, especially the biosorptive capacity, need to be considered when selection of biomass is made (Park, Yun & Park 2010).

Unlike laboratory solutions, industrial effluents contain various pollutants. Therefore, it is desirable to develop general-purpose biosorbents that can remove a variety of pollutants (Park, Yun & Park 2010).

Further study is required to drop the overall cost for pre-treatments or develop new methods that are both cheap and effective (Park, Yun & Park 2010).

It is necessary to optimize bio-sorption process (Das, Vimala & Karthika 2008)

The difficulties existing for biosorption application urge people to consider applying hybrid technology which comprise of various processes to treat real effluents ((Park, Yun & Park 2010), (Wang & Chen 2009)(Wang & Chen 2009).

REFFERENCES

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Algae as Bio-sorbent

Advantages over other bio-sorbents

Most common representatives

Different forms

Bio-sorption capacity in relation to other bio-sorbents

Several algae species have been used as bio-sorbents for recovery of … from industrial effluents. These include Oedogonium hatei, Sargassum sp., spirogyra sp, Spirogyra condensate, Rhizoclonium hieroglyphicum, Cyanobacterial strains.

… studied batch … removal from aqueous solutions by raw and acide-treated algal biomass …

… explored the use of … for

… reported batch sorption of aqueous … using native and pretreated …biomass.

two algae namely, … and … have been employed to remove … from … effluent.

… …. were investigated as adsorbents for the removal of … from water.

Fungi as Bio-sorbent

Fungi has been recognized as promising low-cost adsorbents for heavy metal removal from aqueous solutions.

… investigated … biosorption on ...

… examined … biosorption by …

… studied biosorption of .. using suspended and immobilized cells of … in both batch and packed bed reactor.17

Bacteria as Bio-sorbent

Various types of bacterial biomass have been used for the removal of heavy metals from wastewater. These include Bacillus lichenniformis, Bacillus subtilis, Staphylococcus xylosus, Pseudomonas sp., Rhodococcus opacus, and Streptomyces rimosus. … studied … biosorption by dead … biomass. The results showed that….

… reported … biosorption onto … in batch experiments. Optimum pH and temperature for biosorption of … were found to be … and … respectively

… tested the … bisorption from … as a function of pH, biomass concentration, and contact time.

… explored the use of … for aqueous … removal in batch experiments.

… studied batch …. Removal from aqueous solutions by …. biomass.

Yeast as Bio-sorbent

Waste Materials of Food and Agricultural Industry as Bio-sorbents

Agricultural and industrial wastes have been applied as adsorbents for … biosorption frowm wastewater. The most commonly used biosorbents include sawdust, sunflower, maize brain, agro-waste biosorbents.

… reported batch sorption of aqueous … using …. Biomass.

… attempted to utilize … produced from the paper industry as a Cr(III) removal adsorbent.

The ability of sawdust to remove Cr(VI) from aqueous solutions was studied as a function of pH, contact time, adsorbent amount and concentration of metal solutions.

… explored the use of agro-waste biosorbents for aqueous Cr(III) removal in batch experiments.

Arief, V.O., Trilestari, K., Sunarso, J., Indraswati, N. & Ismadji, S. 2008, 'Recent progress on biosorption of heavy metals from liquids using low cost biosorbents: Characterization, biosorption parameters and mechanism studies', Clean - Soil, Air, Water, vol. 36, no. 12, pp. 937-62.

Bhatnagar, A. & Sillanpää, M. 2011, 'A review of emerging adsorbents for nitrate removal from water', Chemical Engineering Journal, vol. 168, no. 2, pp. 493-504.

Chojnacka, K. 2009, Biosorption and bioaccumulation in practice, Nova Science Publishers, New York.

Demirbas, A. 2009, 'Agricultural based activated carbons for the removal of dyes from aqueous solutions: A review', Journal of hazardous materials, vol. 167, no. 1-3, pp. 1-9.

Farooq, U., Kozinski, J.A., Khan, M.A. & Athar, M. 2010, 'Biosorption of heavy metal ions using wheat based biosorbents – A review of the recent literature', Bioresource technology, vol. 101, no. 14, pp. 5043-53.

Kratochvil, D. & Volesky, B. 'Advances in biosorption of heavy metals', Department of Chemical Engineering, McGill University, 3610 University Str., Montreal, Canada, .

Park, D., Yun, Y. & Park, J.M. 2010, 'The past, present, and future trends of biosorption', Biotechnology and Bioprocess Engineering : BBE, vol. 15, no. 1, pp. 86,86-102.

Wang, J. & Chen, C. 2009, 'Biosorbents for heavy metals removal and their future', Biotechnology Advances, vol. 27, pp. 195-226.

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