review of literatureshodhganga.inflibnet.ac.in/bitstream/10603/6559/8/08_chapter 2.pdf · water...

REVIEW OF LITERATURE

7

CHAPTER-2

Water pollution fact reveals that only 20% of the pollutants in oceans, rivers,

bays, streams, lakes, and other bodies of water come from water based activities, the

remaining 80% is derived from land based activities most of which are anthropogenic in

nature (Dhankhar & Hooda , 2011). Industrial and mining sources have been proved to

impose a greater threat to human.Though industrial use of water is comparatively very

low, the disposal of industrial effluents on land and/or on surface water bodies makes

water (ground and surface) resources unsuitable for other uses. Data says that

approximately 6X106 chemical compounds have been synthesized, with 1,000 new

chemical being synthesized annually. Almost 60,000 to 95,000 chemicals are in

commercial use (Duruibe, et al., 2007).

Contaminants released from Industrial sector can be broadly classified into

organic, inorganic, radioactive and acid/base. Among all, heavy metal and Radionuclide

pollution by various industrial activities is of significant environmental concern

(Dhankhar & Hooda, 2011). The following four appear are the main priority

anthropogenic point sources of metals, particularly in the industrialized world (Volesky,

2007):

[1] Acid mine drainage (AMD)—associated with mining operations;

[2] Electroplating industry waste solutions (growth industry);

[3] Coal-based power generation (throughput of enormous quantities of coal);

[4]Nuclear power generation (uranium mining/processing and special waste generation).

The contamination from these discharge sources might either mean that these

sources are not complying with the standards or even after their compliance their high

quantum of discharge contributes to elevated levels of contaminants (Rajaram & Das,

2008). Under certain environmental conditions, metals and radionuclides may

accumulate to toxic levels and cause ecological damage (Duruibe, et al., 2007).

Radionuclides such as uranium exhibit a serious threat, even at small

concentrations due to high chemical toxicity and radioactivity altogether. Increasing

demands have caused higher anthropogenic environmental contamination of such toxic

metals along with the natural release. Radionuclides are produced artificially by


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different industrial activities which includes mining, laboratory investigations, nuclear

reactors, particle accelerators, radionuclide generators, power weapon tests, nuclear

energy activities, nuclear power plant accidents, etc. (Cazzola, et al.,2004; IAEA., 2005;

Todorov, et al., 2006; Baca & Florkowski, 2000). These contaminants get deposited on

the ground on the basis of their weight and later heavy rains can bring the radioactive

particle to the ground (EPA, 2006).

Radionuclides persisting in the soil can dissolved into solution or can form a

complex with soil organics precipitate as pure or mixed solids. The immobility of these

radioactive elements in the uppermost layer of the soil creates a problem in the

environment. Radionuclides are accumulated either in the upper layer of soil or

interstitial system of sediments in aquatic system. Metals/radionuclides that seep into

ground water contaminate drinking water. If contamination in drinking water gets

exceeded from the permissible limits, it can harm the consumers of that water

specifically human beings causing disastrous health effects (Cazzola, et al., 2004;

Napier & Reed, 2006). The maximum permissible limits and health effects of

radionuclides like uranium and thorium, along with other heavy metals, are given in

table 2.

Complete understanding about noxious effect caused by release of toxic

metals/radionuclides into the environment and emergence of more severe environment

protection laws, have encouraged studies about removal/recovery of heavy

metal/radionuclides from aqueous solution using certain eco-friendly and economic

treatment method.

Various techniques have been employed for the treatment of heavy metal

bearing industrial effluents, which usually come under two broad divisions: Abiotic and

Biotic methods. Abiotic methods include physico-chemical methods such as chemical

precipitation, ion exchange, evaporation recovery, membrane technologies,

electrochemical technologies, solvent extraction and adsorption on activated carbon

etc., while biotic methods include living organisms and products derived from them

(Dhankhar & Hooda , 2010).

Precipitation, filtration, and Ion-Exchange are widely used treatment

technologies for radionuclides in ground water (FRTR, 2003).Chemical precipitation


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and electrochemical treatment are ineffective, especially when metal ion concentration

in aqueous solution as low as 1 to 100 mg/L (Lodeiro, et al., 2006), they also produce

large amount of sludge to be treated with great difficulties. Ion-exchange, membrane

technologies and activated carbon adsorption process are extremely expensive,

especially when treating a large amount of water and waste water containing heavy

metal in low concentration, so they cannot be used at large scale (Crini, 2006).

The combination of precipitation/flocculation and sedimentation is established

technology for radionuclide removal from ground water. This technology pumps ground

water through extraction wells and then treats it to precipitate radionuclides. Typical

removal of radionuclides employs precipitation with hydroxides, carbonates, or sulfides.

Filtration isolates solid particles by running a fluid stream through a porous medium

(Das, 2012).

Therefore, conventional methods have significant disadvantages including

incomplete metal removal, high capital costs, high reagents and/or energy requirements,

and generation of toxic sludge or other waste products that require disposal (Göksungur,

et al., 2005; Cho & Kim, 2003). These disadvantages have resulted in the development

of alternative separation technologies for recovery of metals from waste water.

Out of all conventional methods, adsorption has been observed to be an effective

process of heavy metal/radionuclide removal from waste water. Many studies have been

undertaken to find low cost adsorbents which include peat, betonite, steel-plant slag, fly

ash, china clay, maize cob, wood shaving, silica, active alumina, zeolite, metal oxides

and so on (Ramkrishna & Viraraghavan, 1997; Gupta, et al., 1992; El-Geundi, 1991;

Abo-Elela & El-Dib, 1987; Ahmed & Ram, 1992, Motoyuki 1990; Nascimento, et al.,

2009; Erdem, et al, 2004; Alinnor, 2007; Abbas, et al., 2010).

Adsorptive removal of heavy metals from aqueous effluents which have

received much attention in recent years is usually achieved by using activated carbon or

activated alumina (Faust & Aly, 1987; Shim, et al., 2001; Ouki, et al., 1997; Ralph, et

al., 1999; Ali, et al., 1998; Monser & Adhoun, 2002; Igwe et al., 2005a). Activated

carbon is a porous material with an extremely large surface area and intrinsic adsorption

to many chemicals. Activated carbon is only able to remove around 30-40 mg/g of Cd,

Zn, and Cr in water and is non-regenerable, which is quite costly to wastewater


Page 20

treatment (Gang & Wiexing, 1998). The ability of the activated carbon to remove

Ni(II), Co(II), Cd(II), Cu(II), Pb(II), Cr(III) and Cr(VI) ions from aqueous solutions by

adsorption was investigated by Kobya, et al., 2005.

Polymer resins that can form complexes with the heavy metal ions are the best

adsorbents (Lu, et al., 1994; Reddy & Reddy, 2003). However, these low cost

adsorbents have generally low adsorption capacities which mean that large amount of

adsorbents are needed. Hence we still need to find new, economical, easily available

and highly effective adsorbtion method.

So, biological methods have emerged as an effective alternative option for metal

sequestration. Of the different biological methods, bioaccumulation and biosorption

have been demonstrated to possess good potential to replace conventional methods for

the removal of metals (Malik, 2004). Biosorption may be defined as passive uptake of

toxicants by dead or inactive biological materials or by material derived from biological

sources (Volesky, 2007).

Dead biomass seems to be a preferred adsorbent alternative for majority of metal

removal studies reported (Malik, 2004).The wider acceptability of dead cells is due to:

absence of toxicity limitations,

absence of requirements of growth media and nutrients in the feed solution,

easy absorbance and recovery of biosorbed metals,

easy regeneration and reuse of biomass ,

possibility of easy immobilization of dead cells,

avoidance of sudden death of the biomass population,

easy mathematical modeling of metal uptake reactors.

higher flexibility to environmental conditions

Various investigations have been done for the removal by dead and live biomass

(Junlian, et al., 2010; Bunghez, et al., 2010; Igwe & Abia, 2006). Yan & Viraraghavan,

(2003) investigated the difference in biosorption potential of live and dead Mucor rouxii

for biosorption of Pb2+

, Ni2+

, Cd2+

and Zn2+

. The data concluded that metal

sequestration was much convenient and effective in dead biomass.

Generally all type of biomaterial has good biosorption potential towards

different type of metal ions. Various biomaterials have been examined for their


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biosorptive properties and different types of biomass have shown potential of metal

uptake high enough to warrant further research (Volesky & Holan, 1995). Depending on

the source of biomaterial origin, potent metal biosorbents can be categorized as plant

products and microbes.

Plant products:

Biosorbents of plant origin are mainly agricultural by-products or wastes such

as, maize cob and (Igwe & Abia, 2003, Igwe, et al., 2005b,c,d), sunflower stalk (Gang

& Weixing, 1998), medicago sativa (Alfalfa) (Gardea-Torresdey, et al., 1998), cassava

waste (Abia, et al., 2003), wild cocoyam (Horsfall & Spiff, 2004, 2005), sphagnum peat

moss (Ho, et al., 1995), chitosan (Saifuddin & Kururan, 2005). coconut fiber (Igwe, et

al., 2005d), sugar-beet pulp (Reddad, et al., 2003), wheat bran (Dupond & Guillon,

2003), sugarcane bagasse (Krishnani, et al., 2004), wool, rice, exhausted coffee

(Dakiky, et al., 2002), waste tea (Ahluwalia & Goyal, 2005), walnut skin, cork biomass

(Chubar, et al., 2003), seeds of Ocimum basilicum (Melo & D’Souza, 2004), defatted

rice bran, rice hulls, soybean hulls and cotton seed hull (Teixeria, et al., 2004),

hardwood (Dalbergia sissoo), pea pod, cotton and mustard seed cakes (Saeed, et al.,

2002), husk of Bengal gram (Ahalya, et al., 2007), orange peel (Feng, et al., 2011) and

so on.

Rice husk is an agricultural waste produced in excess of 100 million tons as a

by-product of the rice milling industry of which 96% is generated in developing

countries. The utilization of rice husk would solve some disposal problem as well as

access to cheaper materials for adsorption in water pollutants control system (Williams

& Nugranad, 2000). Feasibility of rice husk and its ash as an adsorbentfor the removal

of cadmium ions from aqueous solution was investigated by Mahvi, et al. (2008).

Saw dust of Indian rose wood prepared by treatment with formaldehyde and

sulphuric acid showed efficient removal of chromium (VI) (Garg, et al., 2004). Bark of

the plants such as Peciaglehnii and Abiessac halinensis and dried plant biomass of

parthenium was tried for the removal of cadmium ions (Ajmal, et al., 2006).

Experiments on removal of nickel were conducted on Cassia fistula biomass in its

natural form and results show 99–100% removal efficiency (Hanif, et al., 2007).Waste


Page 22

tea leaves were also tried for sequestering of nickel from aqueous solutions (Ahluwalia

& Goyal, 2005).

Variant adsorbents have also been investigated in modified forms. Tian, et al.,

2011 have used cellulose fibers, prepared through grinding the native cellulose

cardboard as a novel efficient adsorbent for both fluoride and arsenic removal. This

adsorbent had high efficiency in removal of F−, AsO2

− and AsO4

3− from aqueous

solutions, even at low initial concentrations. Similarly adsorption of hexavalent

chromium from aqueous medium by rice husk activated carbon has been described by

Ahmad, et al., 2012. Under optimal condition of 150 minutes contact time, 20 mg/l

initial metal concentration, pH 2and adsorbent dose of 5g/l, the optimum desorption of

hexavalent chromium was found to be 95.2%.Rose petals pretreated with NaOH,

calcium treated sargassum and sugarcane modified with succinic anhydride has also

been utilized for significant removal of lead. (Karnitz, et al., 2007; Nasir, et al., 2007).

Dahiya, et al., 2008 reported that pretreated arca shell biomass could be used for

the removal of cesium and other metals from aqueous solution. Under optimized

condition of different parameters viz. pH, initial concentration, biosorbent dose and

contact time, the maximum uptake of cesium by arca shell biomass was found to be

3.93mg/g. Adsorption of radium (Ra) ions onto coir pith under the influence of humic

acid in aqueous solution was investigated in batch mode (Laili, et al., 2010).

Uranium ion uptake by dried roots of Eichhornia crassipes was analyzed by

Bhainsa and D’Souza, 2001.High capacity of U (VI) metal ion binding by dried

biomass was indicated with maximum biomass loading of 371mg/L dry biomass.

Eroglu, et al., 2009 heralded the effective biosorption of Ga-67 radionuclides from

aqueous solution onto waste pomace of an olive oil factory (WPOOF).Sorption affinity

of pretreated cork biomass toward uranium was reported by Psareva, et al., 2005. Two

fold increases in the sorption capacity toward uranium was noted along with the

increase of the concentration of strong acidic and weak acidic groups on cork biomass

surface.

Microbes:

In concern to metal biosorption, microbial biomass (bacteria, fungi, algae, etc.)

has outperformed the macroscopic materials (plant products). The reason for this


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discrepancy is due to the nature of the cell wall constituents and functional groups

involved in metal binding. A large number of microorganisms belonging to various

groups, viz. bacteria, fungi, yeasts, cyanobacteria and algae have been reported to bind a

variety of heavy metals to different extents. The role of various groups of micro-

organisms in the removal and recovery of heavy metal by biosorption has been well

studied (Davis, et al, 2003; Gavrilesca, 2004; Malik, 2004;Tsezos, 2001; Volesky,

2001). The various subclasses of these microbial biosorbent can be summed up as:

Bacteria:

Bacteria posses metal binding property due to anionic functional groups present

in their cell wall which is because of peptidoglycan, teichoic acids and teichuronic acids

in Gram-positive bacteria and peptidoglycan, phospholipids, and lipopolysaccharides in

Gram-negative bacteria. Several functional groups are present on the bacterial cell wall,

including carboxyl, phosphonate, amine and hydroxyl groups (Vijayraghavan & Yun,

2008a) which cause metal binding. Potent metal biosorbents under the class of bacteria

include genre of Bacillus (Tunali, et al., 2006), Pseudomonas and Streptomyces (Uslu &

Tanyol, 2006) etc.

Sivakumarprakash, et al. 2009 studied dead Bacillus subtilis biomass for its

efficiency to remove Chromium (VI) from aqueous solutions. The biomass has the

maximum biosorption capacity of 14.54 mg/g of biomass at 100 ppm initial chromium

concentration, pH 2.0 and 2 g/l biomass loading. Orhan, et al., 2006 prepared biosolids

by immobilizing Pseudomonas aeruginosa onto granular activated carbon that resulted

in 84, 80, 79, 59 and 42% removal of Cr (VI), Ni (II), Cu (II), Zn (II) and Cd (II) ions

respectively.

Bacterium Citrobacter freudii, was used as a biosorbent to adsorb uranium ions

by Xie, et al., 2008.The bacterium Arthrobacter nicotianae was found to possess a high

uranium adsorption ability of approximately 698 mg (2.58 mmol) uranyl ions g/L dry

weight (Tsuruta, 2002). Streptomyces levoris could adsorb about 0.38 mmol of uranium

g/L dry weight from the solution in one hour (Tsuruta, 2004).

Uptake of hexavalent uranium by a bacterial strain Pseudomonas aeruginosa

CSU was reported by Hu, et al., 2000. Pantoea sp., Pseudomonas sp. and Enterobacter

sp. isolated from mine soils, reduced Uranium from hexa- to tetravalent state,


Page 24

U(OH)4(aq), at pH 5–6. Up to 88% removal after 24 h was reported in batches with the

initial U (VI) metal ion concentration of 400 mg/l (Chabalala & Chirwa, 2010).

Selenska-Pobell and Merroun, 2001 reported the interactions of three eco-types of

Acidithiobacillus ferrooxidans withU (VI) metal ion.

The cultures of Enterobacter cloacae generally showed high resistance against

U (VI) metal ion toxicity, and good performance under stress conditions. High capacity

of uranium and thorium sorption by bacterial biosorbent was noted with maximum

biomass loading of 541mg/g for Uranium or 430mg/g for thorium (Sar, et al., 2004).

Chemolithoautrophic bacteria, such as Acidithiobacillus ferrooxidans were isolated

from different uranium mining waste piles and the mechanisms and genetic basis for

sequestration of uranium by eco-types of bacterium were investigated by Pobell, 2002.

Aerobic granular biomass consisting of mixed species of bacteria enclosed in an

extracellular polymeric matrix has also been developed as a novel biomaterial for

efficient uranium removal (Nancharaiah, et al., 2006)

The suggested mechanisms, by which bacteria may immobilize the uranyl ion,

are therefore: (a) biosorption on spent biomass, (b) bioaccumulation by viable biomass,

(c) precipitation by reaction with inorganic ligands such as phosphate, and (d) microbial

reduction of soluble metal species to insoluble species (Chojnacka, 2010; N’Guessan, et

al., 2008).

Algae:

Eukaryotic algal cell wall is mainly cellulosic and the potential metal binding

groups in this class of microbe are carboxylate, amine, imidazole, phosphate, sulfhydril,

sulfate and hydroxyl (Crist, et al., 1981). The wide range of marine algal biosorbent

including microalgae and macroalgae has been investigated by Moreno-Garrido, et al.,

2005. Marine algae popularly known as seaweeds include red, green and brown

seaweeds out of which brown sea weeds are found to be excellent biosorbent (Davis, et

al., 2003). Sea weed has proved to be the most popular biosorbent due to its bulk

availability in many parts of the world. Davis, et al., (2000); Volesky, et al., (2003),

Sorption capacity of six different algae (green, red and brown) was evaluated in

the recovery of cadmium, nickel, zinc, copper and leadfrom aqueous solutions.

Experimental data fitted a Langmuir model very well according to the following


Page 25

sequence of the sorption values: Pb> Cd >Cu > Zn > Ni. The best results were obtained

with Fucus spiralis (Romera etal., 2007). Thirty strains of algae were examined for

their biosorption abilities for the uptake of cadmium, lead, nickel and zinc from aqueous

solutions. Most of the examined algae strains exhibited remarkably preferential

adsorption of the metal lead. The chlorophyceae Chlorella salina and the cyanophycae

Scytonema hofmanii as well as L. tayloriis howed highest metal uptake (Wilke, et al.,

2006).

Sargassum uitans effectively sequestered uranyl ions from aqueous solution,

with the maximum uranium sorption capacity exceeding 560 mg/g, 330 mg/g and 150

mg/g at pH 4.0, 3.2 and 2.6, respectively (Yang & volesky, 1999). Binding of uranium

ions was also studied onto Cystoseria indica (Khani, et al., 2008) and Catenella repens

(a red alga) (Bhat, et al., 2008). Khani, et al., 2006 found that the maximum uranium

adsorption capacity on the Ca-pretreated, protonated and non-pretreated Cystoseira

indica algae predicted by Langmuir isotherm at pH 4 and 30ºC was 454, 322 and 224

mg/g respectively.

Accumulation of uranium metal ion by filamentous green algae under natural

environmental conditions was also reported by Aleissa, 2004. A macromarine algae

(Ulva sp.) clay composite adsorbent was tested for recovering U (VI) metal ion from

aqueous solution (Donat & Aytas, 2005). Algae and clay (Na bentonite) when used as

composite adsorbent, which proved to be suitable as sorbent material for recovery and

biosorption of uranium ions from aqueous solutions. Biosorption of uranium ions onto

alga Cystoseria indica were studied in a batch system (Khani, et al., 2008)

It is necessary to search for and select the most promising types of biomass

from an extremely large pool of readily available and inexpensive biomaterials. As

sorption is a surface reaction, biosorption potential of a biosorbent depends on its

surface area and its polarity or it can be said that performance of the biosorbent depends

on the ionic state of the biomass. Depending on this fact the benefits of fungal

biosorbents can be summarized as follows:

Firstly, fungus shows excellent metal binding capacity because of variety of

functional groups present due to high percentage of cell wall material.


Page 26

Secondly, fungus is easy to cultivate at large scale as it has short multiplication

rate. Moreover, it can be easily grown using unsophisticated fermentation techniques

and inexpensive growth media (Kapoor & Viraraghavan, 1995). Apart from these, the

yield of biomass is also quite high.

Thirdly, easy availability of fungal biomass as industrial waste product e.g.

Aspergillus niger (Citric acid production waste) and Saccharomyces cerevisiae

(brewery industry waste). A variety of fungal biomass types arise from many industrial

fermentations and the food, brewing and distilling industries and these also receive

continued study (Wang & Chen, 2006). This provides an economic advantage to the

fungal biosorbents as compared to other types of microbial biomass.

Fourthly, major portion of fungal biosorbent are non-pathogenic, thus it is

generally regarded as safe and thus, can be easily accepted by public when applied

practically.

Fifthly, one of the fungi, S. cerevisiae is an ideal model organism to identify the

mechanism of biosorption in metal ion removal, especially to investigate the interaction

of metal-microbe at molecular level. Peregol & Howell (1997) reported that the use of

yeasts as model systems is particularly attractive because of ease of genetic

manipulation and availability of complete genomic sequence of S. cerevisiae.

Knowledge accumulated on the molecular biology of yeast is very helpful to identify

the molecular mechanism of biosorption in metal ion removal (Eide, 1998). At the same

time, S. cerevisiae can be easily manipulated genetically and morphologically, which is

helpful to genetically modify the yeast more appropriate for various purposes of metal

removal (Wang & Chen, 2006).

Akhtar, et al. (2007a) compared the removal and recovery of uranium from

dilute aqueous solutions by indigenously isolated viable and non-viable fungus

(Trichoderma harzianum) and algae (RD256, RD257), by performing biosorption—

desorption tests. Fungal strain was found comparatively better candidate for uranium

biosorption than algae. The process was highly pH dependent. At optimized

experimental parameters, the maximum uranium biosorption capacity of T. harzianum

was 612mg/g whereas maximum values of uranium biosorption capacity exhibited by

algal strains (RD256 and RD257) were 354 and 408mg/g and much higher in


Page 27

comparison with commercially available resins (Dowex-SBR-P and IRA-400). Mass

balance studies revealed that uranium recovery was 99.9%, for T. harzianum, and 97.1

and95.3% for RD256 and RD257, respectively. Some of the important and recent

results of metal biosorption using various fungal biosorbents are summarized in Table3.

A successful biosorption process requires preparation of good biosorbent. The

process starts with selection of most promising type of biomass; exploring the

mechanism involved; physico-chemical conditions affecting the process; pretreatment

and immobilization to increase the efficiency of the metal uptake; biosorption

experimental studies that are carried out by batch and column process and finally;

removal of adsorbed metal by desorption process and the reuse of biosorbent for further

treatments (Vijayaraghavan & Yun, 2008). Researchers have revealed each and every

aspects of biosorption including requirements that are needed to transfer the process

from lab to field.

Tsezos (2001) clearly pointed out that successful biosorption technology not

only depends on the biosorption potential, but also on its origin, availability, cost

effectiveness and finally continuous supply of biomass for the process. Fungal biomass

suits the criteria because of its availability as industrial waste in mass.

Spent waste yeast biomass S. cerevisiae, collected from the fermentor at a

brewery located near Chennai, India, was successfully utilized at laboratory scale for

remediation of lead from a battery manufacturing industrial effluent (Parvathi, et al.,

2007). Similarly Saccharomyces cerevisiae, waste biomass originated from beer

fermentation industry, was used to removal of copper ion from aqueous solution

(Jialong, 2002) and uranyl ions from low radioactive solutions (Tsuruta, 2004; Popa, et

al., 2003).

The isolates of Aspergillus sp., Penicillium sp. and Cephalosporium sp. were

tested to evaluate their applicability for heavy metal (Cu, Cd and Pb) removal from

industrial wastewaters. The biosorption of dead fungal cells of Aspergillus sp.,

Penicillium sp. and Cephalosporium sp. adsorbed Cu (46%), Cd (95%) and Pb (70%)

respectively (Hemambika, et al., 2011).

Goyal, et al., 2003 confirmed that biosorption of metal ions by living cells is a

two step process. The first step is thought to be physical adsorption or ion exchange at


Page 28

the cell surface, reaching the adsorption equilibrium within 30–40 min and is

metabolism independent. The second step is energy dependent and all the metal ions

gain access to the cell membrane and cell cytoplasm come across the cell wall mainly

through chemical functional groups of the material.

Further insight into the mechanism of biosorption process by fungal biosorbent

can be ascertained by integrative analysis of various parameters involved during the

process like factors effecting, surface chemistry, alterations in surface chemistry by

pretreatment and functional group modification (which are finally explored through

SEM and FTIR analysis).

Surface electron microscopy (SEM) has sufficient resolution to study the spatial

relationship between cells and reduction products, as well as their chemistry

(Srivastava, 2006). Thus, SEM is widely used to investigate the morphological features

and surface characteristics of the biosorbent (Aytas, et al., 2011). Surface properties of

dried and carboxymethylcellulose immobilized Trametes versicolor and Phanerochaete

chrysosporium were revealed through SEM. The SEM micrograph of fungus

immobilized beads is completely different from the empty one and revealed a uniform

fungal growth on the bead surface, indicating that immobilization is not localized. This

uniform distribution is an important criterion for the proper biosorption of metal ions on

the whole surface area of the fungus-immobilized beads (Genc, et al., 2003). Similar

SEM observations were recorded during U (VI) metal ion biosorption onto R. arrhizus

(Wang, et al., 2010). More regular surface of Penicillium citrinum of unloaded form as

compared to native form depicted the U (VI) metal ion biosorption (Pang, et al., 2011).

The surface structure of biomass of A. fumigates before Th uptake showed many small

grooves which become less prominent after uptake (Bhainsa & D’Souza, 2009.

After uranium sorption, SEM image of Ca-alginate beads shows that the average

size of gel particles was in the region of 0.6–1.05mm. These pores are very suitable

places for the uranium biosorption (Gok & Aytas, 2009). Aytas, et al., 2011 studied that

the pore size of the biocomposite was approximately 5 μm as calculated from SEM

analysis and concluded that Uranium complexes can get into these pores easily.

Biosorption, being a surface phenomenon need to be understood by analyzing

surface (cell wall) alterations. In this context extensive literature is available regarding


Page 29

use of Fourier transform infrared spectroscopy (FTIR) can individuate the presence of

changes in native functional groups after chemical treatment (Corte, et al., 2010).

Bishnoi, et al., 2007 observed that the functional groups present on the cell wall of

Trichoderma viride were amide group (-NH), carboxylate anion (-COO), carbonyl

groups (-CO), C-F and C-Br. FTIR analysis of Phanerochaete chrysosporium before

and after Cr(VI) removal disclosed the biosorbent heterogeneity through different

characteristic peaks of amino, carboxylic, hydroxyl and carbonyl groups (Marandi et al,

2011).

Mechanism of Cr (VI) biosorption by heat inactivated fungal biomass of

Termitomyce sclypeatus was studied by analyzing IR spectra. The roles played by

functional groups in chromium biosorption were found to be in the order: carboxyl >

phosphates > lipids > sulfhydryl > amines. The results concluded that Cr(VI)

biosorption involved more than one mechanism such as physical adsorption, ion

exchange, complexation and electrostatic attraction and followed in two subsequent

steps – Cr2O72−

biosorption at the protonated active sites (amino, carboxyl and phosphate

groups) and reduction of Cr(VI) to Cr(III) by reductive groups (hydroxyl and carbonyl

groups) on the biomass surface (Ramrakhiani, et al., 2011).

FTIR spectroscopy analysis of Rhodotorula glutinis revealed that amino and

carboxyl groups were involved in uranium binding (Bai, et al., 2010). Wang, et al.,

(2010) indicated that the –NH group play a critical role in U binding. The decrease of

the absorption intensity at 3400–3200cm−1

, 1745cm−1

, and1040cm−1

after U adsorption

indicated that hydroxyl and carboxyl groups are also involved in U binding.

The mechanism of UO22+

biosorption by untreated, heat and alkali-treated L.

sajor-caju biomass was also elucidated on the basis of biomass treatment; FT-IR and

SEM studies which confirm the biosorbents heterogeneity and evidence the presence of

different characteristics peaks in agreement with the possible presence of amino,

carboxylic, hydroxyl and carbonyl groups (Bayramoglu, et al., 2006).

Chemical modification (masking) of functional groups is a useful technique in

characterizing the functional group responsible for biosorption process (Bai, et al.,

2010). Variant literature is available regarding protein and lipid extraction, along with

masking of functional groups (carboxyl, amino, phosphates, sulfhydril groups) on


Page 30

biosorbent cell wall. Native brewery yeast was chemically treated to study the roles of

specific functional groups like amines, carboxylic acids, phosphates, sulfhydryl group

and lipids in lead biosorption. The results thus obtained revealed that Methylation of

amines, esterification of carboxylic acids, esterification of phosphates and Extraction of

lipids reduced the biosorption capacity of native biosorbent by 53.38%, 96.34%,

17.61% and 35.68% respectively. Modification of sulfhydryl group did not have any

significant effect on lead uptake. The extent of contribution of the functional groups and

lipids to lead biosorption was in the order: carboxylic acids > lipids >amines >

phosphates. (Paravathi, et al., 2007). The data analysis revealed that the results were

proportionate and in similar fashion as of Parvathi, et al, (2007).

Bai and Abraham, 2002 studied the enhancement of Cr(VI) biosorption by

chemically modified biomass of Rhizopus nigricans. Results indicated a gradual decline

in Cr binding by the formaldehyde treated biomass. Acetylation of amino and hydroxyl

groups caused reduction of amino groups and addition of imimo group on cell wall.

Enhancement in the binding of chromate anions was also noticed when biomass was

employed with reagents such as Polyethylenimine (PEI), Cetyltrimethyl ammonium

bromide (CTAB) and 3-(2- Aminoethyl amino) propyl tri methoxysilane. FTIR analysis

showed that amino and carboxyl groups were the important functional groups involved

in uranium binding by chemically modified Rhodotorula glutinis (Bai, et al., 2010).

Extensive literature is available on the variant factors affecting the sorption

process, can provide useful information for understanding the mechanism of metal

uptake by fungal biomass. The important parameters that affect biosorption process are:

Type and nature of biomass

Initial solute concentration

Biomass concentration in solution

Physico-chemical factors like temp., pH, Ionic strength etc.

Type and nature of biomass is quite important including nature of its application as

biomass can be used in many forms, for example living/dead, free/immobilized,

raw/pretreated, wild/mutant cells, engineered/non-engineered, lab culture/waste

industrial biomass and biomass from different industries (Park, et al., 2003).

Comparing the results of metal biosorption using different forms of biomass can also


Page 31

give useful information for understanding the mechanism of metal uptake by fungal

biomass.

Uptake of americium using biomasses of various fungal species, Rhizopus

species viz. R. arrhizus (wild type), R. arrhizus NCIM 877, R. arrhizus NCIM 878, R.

arrhizus NCIM 879, R. arrhizus NCIM 997, R. nevius NCIM 958, R. nevius NCIM 959,

and R. oryzae NCIM 1009 were reported in batch and column mode (Dhami, et al.,

2002). Among the fungal species tested, R. arrhizus NCIM 997 proved to be an

excellent and inexpensive biomaterial for sorption of americium. High amount (95%) of

recovery of americium was noticed using 1M nitric acid as eluent without generating a

large volume of secondary waste. Removal and recovery of uranium ion from aqueous

solutions by Trichoderma harzianum was reported by Akhtar, et al., 2007. Parekh, et

al., 2008 reported that soil and saprophytic fungi couldcontribute to the sorption of

137Cs and 85Sr in organic systems.

The initial solute concentration seems to have impact on biosorption, with a

higher concentration resulting in a high solute uptake (Ho & McKay, 1999; Ho &

McKay, 2000; Binupriya, et al., 2007). This is because at lower initial solute

concentrations, the ratio of the initial moles of solute to the available surface area is

low; subsequently, the fractional sorption becomes independent of the initial

concentration. However, at higher concentrations, the sites available for sorption

become fewer compared to the moles of solute present and; hence, the removal of solute

is strongly dependent upon the initial solute concentration. It is always necessary to

identify the maximum saturation potential of a biosorbent, for which experiments

should be conducted at the highest possible initial solute concentration.

Biosorption of copper by Aspergillus niger biomass was tested at 100, 50, 25

and 10 mg/l of metal solution with 0.002 g/ml of biomass. The maximum uptake in this

condition as calculated from Langmuir isotherm was 0.41 mmol/L (Mukhopadhyay, et

al, 2008).Similar trend was obtained for biosorption of uranium by various fungal

bisorbents. Uranium ion biosorption capacities of the carboxymethylcellulose and

immobilized, dried powdered P. chrysosporium and T. versicolor biomass were

presented as a function of initial metal ion concentration ranging from 100–1000 mg/l.

The amount of UO22 +

ions adsorbed on the plain carboxymethylcellulose beads was


Page 32

29.15 mg/g. Maximum biosorption capacity for immobilized fungal mycelia of P.

chrysosporium and T. versicolor was found as 158.01 mg /g and 309.08 mg/g,

respectively (Genc, et al., 2003).

Omar, et al., 2008 found that when the concentrations of uranium ion in the

range between 0.1 and 0.5 mol/litre, the fungal dry biomass is capable of adsorbing

between 84% and 98% of this metal in solution and Aytas, et al., 2011 found that

biosorption yield of algal and fungal bicomposite adsorbent, varies between 91% and

94% for the investigated range of uranium concentration (25–150 mg/L). The

biosorption isotherms of uranium onto the raw and chemically modified biomass were

also investigated with varying uranium concentrations 40 to 350 mg/L (Li, et al., 2004).

The percentage removal of U (VI) metal ion by R. arrhizus, increased within range of

10–100mg/L, decreased a little within 100–200mg/L and finally decreased sharply in

the range of 200–400mg/L. Maximum biosorption capacity was up to 112.2mg/g at the

initial U (VI) metal ion concentration of 300mg/L (Wang, et al., 2010a).

The dosage of a biosorbent strongly influences the extent of biosorption. In

many instances, lower biosorbent dosages yield higher uptakes and lower percentage

removal efficiencies (Aksu & Çağatay, 2006). An increase in the biomass concentration

generally increases the amount of solute biosorbed, due to the increased surface area of

the biosorbent, which in turn increases the number of binding sites (Esposito, et al.,

2001). Conversely, the quantity of biosorbed solute per unit weight of biosorbent

decrease with increasing biosorbent dosage, which may be due to the complex

interaction of several factors. An important factor at high sorbent dosages is that the

available solute is insufficient to completely cover the available exchangeable sites on

the biosorbent, usually resulting in low solute uptake (Esposito, et al., 2001). Similar

results were obtained by Mukhopadhyay, et al.,2008, who studied the biosorption of

copper by pretreated Aspergillus niger biomass. The highest uptake observed was at

23.62 mg of copper per g of biomass at metal to biomass ratio of 250:1000 in the

biomass dosage ranging from 2 to 5 g/l.

Parvathi, et al., 2007 analyzed different doses of waste beer yeast

Saccharomyces cerevisiae for biosorbing lead from battery manufacturing industrial

effluent. Lead uptake rose from 0.38 mg/g to 2.34 mg/g with increase in biosorbent


Page 33

concentration from 0.5% to 2%. Lead uptake decreased slightly when the biosorbent

concentration reached 4% (2 mg/g). Biosorption of Cr (VI) was studied using different

Phanerochaete chrysosporium biomass dosage in the range, 0.5-5 g/l, in 100 ml Cr (VI)

solution (100 ppm) under optimized conditions of pH, contact time and temperature

25°C. The biosorption of Cr (VI) ion increased with increasing biomass dosage and

approximately constant at a dose higher than 4.0 g/L (Marandi, et al., 2011). The

percentage of uranium removal from aqueous solution was found to increase

concomitantly with increments inbiomass concentration and percentage removal values

of 97.5% for T. harzianum (Akhtar, et al., 2007).

Apart from these, physico-chemical factors such as pH, temperature, ionic

strength, pollutant solubility etc. also have an influence on the running process.

Physico-chemical factors, pH is possibly the most important. The pH value of solution

strongly influences not only the site dissociation of the biomass’ surface, but also the

solution chemistry of heavy metals: hydrolysis, complexation by organic and/or

inorganic ligands, redox reactions, precipitation, the speciation and the biosorption

availability of the heavy metals (Esposito, et al., 2002; Wang, 2002). At higher solution

pH, the solubility of metal complexes decreases sufficiently allowing precipitation,

which may complicate the sorption process.

Yan and Viraraghavan, (2003) studied the biosorption of lead, cadmium, nickel

and zinc by Mucor rouxii biomass over a range of pH 2.0 to 6.0. At initial pH 4.0 or

lower, little biosorption occurred. A sharp increase in biosorption capacity took place in

the pH range of 4.0–5.0. The low biosorption capacity at pH values below 4.0 was

attributed to hydrogen ions that compete with metal ions on the sorption sites. The

increase observed in final pH values of reaction mixtures could be either from the

adsorption of hydrogen ions from aqueous solutions by fungal biomass or neutralization

of H+ with OH

- released from the biomass.

Biosorption of Zn(II) on the different Ca-alginate beads (embedded by

Phanerochaete chrysosporium, orange peel) from aqueous solution were studied by Lai

et al., 2008, at pH ranging from 4 to 8. P. chrysosporium was also investigated for Cr

(VI) biosorption at varying the pH of metal solution from 1.0 to 9.0 with highest

efficiency obtained at pH 2.0 (Marandi et al., 2011). Özer and Özer, 2003 explored the


Page 34

optimum pH range for biosorption of different metals by S. cerevisiae. They found that

optimal pH value for Pb(II) and Ni(II) ion uptake is 5.0, for Cr(VI) is 1.0.The effect of

pH on copper biosorption by baker’s yeast was examined in the pH range 2.0-6.0. The

highest uptake of both Cu+2

(120.7 mg g-1

) and Th (67.7mg/g) was obtained at pH 4.0

(Gokunsungur, et al., 2005, Bhainsa & D’Souza, 2009).

In order to establish the effect of pH on the biosorption of UO22 +

ions onto the

plain carboxymethylcellulose beads and immobilized and dried powdered preparations,

thebatch equilibrium studies at different pH values were repeated in the range of 2.0–

5.0.The maximum adsorption in both cases were observed at pH 4.5 (Genc, et al.,

2003). Sorption of UO22+

, Pu4+

, Am3+

, and Ce3+

by yeast was found to be >95% in the

pH range from 1 to 2 of the aqueous solutions (Kedari, et al., 2001). Uranium

biosorption by the Lentinus sajor-caju preparations increased with increasing pH from

2.0 to 4.5 then reached a plateau value at pH between 4.5 and 5.5. Within this pH range,

the fungal biomass was successfully regenerated using 10mM sodium carbonate, with

up to 93% recovery (Bayramoglu, et al., 2006).

Removal of U (VI) metal ion onto R. arrihizus increased with the increase of pH

in the range of 2.0–4.0, but decreased in the range of 4.0–6.0, then increased a little in

the range of 6.0–8.0 (Wang, et al., 2010). The maxima of Uranium biosorption by T.

harzianum was achieved at 4.5 (Akhtar, et al., 2007).

Over modest physiological type ranges, temperature usually has little effect

which seems not to influence the biosorption performances in the range of 20-35ºC.

Higher temperatures usually enhance sorption due to the increased surface activity and

kinetic energy of the solute (Vijayaraghavan & Yun, 2007); however, physical damage

to the biosorbent can be expected at higher temperatures. Low temperature; however

affect living cell systems and any auxiliary metabolism-dependent processes that aid

biosorption. It is always desirable to conduct/evaluate biosorption at room temperature,

as this condition is easy to replicate.

Biosorption of U (VI) metal ion when was tested over the temperature range

(25–50ºC), higher temperature was found to enhance the surface activity of the cells and

kinetic energy of the solution, the removal of U (VI) metal ion increased a little, but was

not obvious. This phenomenon indicated that this process is temperature independent


Page 35

(Wang, et al., 2010). Similar results have been found by Sag, et al., 2000. While

Uranium biosorption was enhanced with increments in temperature from10 to 30°C

(39–50%). Further rise in temperature from 30 to 70 °C, decreased the biosorption

capacity (33–48%) during Uranium biosorption on T. harzianum (Akhtar, et al., 2007).

Another important parameter in biosorption is the ionic strength, which

influences the adsorption of solute to the biomass surface (Borrok & Fein, 2005). The

effect of ionic strength may be ascribed to the competition between ions, changes in the

metal activity, or in the properties of the electrical double layer. When two phases,

biomass surface and solute in aqueous solution are in contact, they are bound to be

surrounded by an electrical double layer owing to electrostatic interaction. Thus,

adsorption decreases with increase in ionic strength (Dönmez & Aksu, 2002). Yan and

Viraraghavan, 2003 explored biosorption of lead, cadmium, nickel and zinc by Mucor

rouxii biomass. It was concluded that for bi- or multi-metal ion adsorption, biosorption

capacity of individual metal ion was reduced in the presence of other metal ions, but the

total biosorption capacity increased, indicating the capability of M. rouxii biomass in

adsorbing multi-metal ions.

Three species of Basidiomycetous fungi namely Schizophyllum commune fries,

Ganoderma lucidum (Curt. Fr.) and Pleurotuso streatus (Jacq.) Quélet was investigated

for removing heavy metal ions viz., Cu(II), Cr(VI), Ni(II) and Zn(II) from electroplating

industrial effluents. In general, the test species displayed maximum biosorption capacity

for Ni(II) (22-52 mg/g) and minimum for Zn(II) (4-7 mg/g). The remaining metallic

ions that is Cu(II) and Cr(VI) were also adsorbed in considerable amounts, but the

removal of former (13-15 mg/g) was comparatively greater than the later (11.67-15.72

mg/g). In general, biosorption capacity of the test fungi for metal ions was observed to

follow the sequence in following mode: Ni(II) >Cu(II) >Cr(VI) > Zn(II) (Javaid &

Bajwa, 2011).

Roy, et al., 2008 reported the bioaccumulation of 152,154Eu radioisotopes in

yeast cells. Saccharomyces cerevisiae were found to accumulate 152,154Eu

radioisotopes selectively from a synthetic mixture of 152,154Eu, 137Cs, and 60Co

radiotracers at neutral pH and the uptake of Eu increased with time.


Page 36

Biosorbent are prepared initially by pretreating the raw biomass with different

chemicals that causes cell wall modification of biomaterial by creating derivatives with

altered metal binding abilities and affinities (Aksu, 2006; Yu, et al., 2007; Bai, et al.,

2000) which in turn affects the biosorption potential. The pretreatment have suggested

modifying the surface characteristics/groups either by removing or masking the groups

or by exposing more metal binding sites. Common chemical pretreatments include acid,

alkaline, ethanol and acetone treatments of the biomass (Yu, et al., 2007; Bai, et al.,

2002).

The success of a chemical pretreatment strongly depends on the cellular

components of the biomass itself. Alkali treatment of fungal biomass has increased the

metal uptake capacity significantly, whereas acid treatment of biomass almost has no

influence on metal biosorption (Wang, 2002; Wang, et al., 2000). Aspergillus niger

mycelium was modified by introducing additional carboxy, ethaldiamino groups which

increased metal biosorption (Kramer & Meish, 1999).

Waste baker’s yeast (Saccharomyces cerevisiae) was used as a biosorbent for

Cu+2

biosorption. The yeast cells were treated with caustic soda, ethanol and heat to

increase their biosorption capacity. Among the treatment methods used, the highest

copper uptake (21 mg/g) was obtained with the caustic treatment of bakers yeast

(Gokunsungur, et al., 2005). The biosorption of cadmium and lead ions from synthetic

aqueous solutions using pretreated yeast biomass was also investigated by Gokunsagar,

et al., (2005).

Yan and Viraraghavan, (2001) studied the effect of chemicals pretreatment of

Mucor rouxii biomass on bioadsorption of Pb2+

, Cd2+

, Ni2+

and Zn2+

. Pretreatment with

detergent and alkali chemicals such as NaOH, Na2CO3 and NaHCO3 were found to

improve or maintain the bioadsorption capacity in comparison with live M. rouxii

biomass. Treatment of the R. nigricans as biosorbent with mild alkalies (0.01N NaOH

and ammonia solution) and formaldehyde (10%, w/v) deteriorated the biosorption

efficiency for Cr (VI) removal by 25%, However, extraction of the biomass powder in

acids (0.1N HCl and H2SO4), alcohols (50% v/v, CH3OH and C2H5OH) and acetone

(50%, v/v) improved the Cr uptake capacity by 8-22% (Bai and Abraham, 2002).


Page 37

Similar results were noticed when removal of Ni (II) and Cu (II) ions were tested from

aqueous solution using alkali/base treated A. niger (Javaid, et al., 2011).

Biosorption of uranium onto chemically modified yeast cells, Rhodotorula

glutinis, was reported by Bai, et al., 2010.Increase in uranium sorption capacity was

found to be 31% for the methanol treated biomass and 11% for the formaldehyde

treated biomass. The untreated and alkali-treated Lentinus sajor-caju mycelia were used

for the recovery of uranium from aqueous solutions. The alkali treated form had a high

biosorption capacity (378 mg/g) than those of the untreated (268 mg/g) which is about

41% higher as compared to the untreated fungal biomass. (Bayramoglu, et al., 2006).

The free cells generally have low mechanical strength and small particle size,

because of these excessive hydrostatic pressures are required to generate suitable flow

rates which can cause disintegration of free biomass and thus are not suited for column

packing in industrial applications (Dhankhar & Hooda, 2011). Several established

techniques are available to make biosorbents suitable for process applications. Among

these, immobilization techniques such as entrapment and cross linking have been found

to be practical for biosorption (Volesky, 2001).

Immobilization of fungal biomass within polymeric matrix has exhibited greater

potential, especially packed or fluidized bed reactors, with benefits including control of

particle size, regeneration and reuse of the biomass, easy separation of biomass and

effluent, high biomass loading and minimal clogging under continuous-flow conditions

(Hu & Reeves, 1997; Gadd, 2002). Important immobilization matrices used

biosorbentimmobilization include sodium alginate (Bai & Abraham, 2003; Xiangliang,

et al., 2005), polysulfone (Beolchini, et al., 2003; Vijayaraghavan, et al., 2007) and

polyacrylamide (Bai & Abraham, 2003). The choice of immobilization matrix is a key

factor in environmental application of immobilized biomass. The polymeric matrix

determines the mechanical strength and chemical resistance of the final biosorbent

particle to be utilized successive sorption–desorption cycles (Bai & Abraham, 2003).

Khoo and Ting, (2001) examined and compared for the uptake of gold by a

fungal biomass (Fomitopsis carnea) by the characteristics of polyvinyl alcohol (PVA)

and calcium alginate as immobilization matrices. PVA-immobilized biomass showed

superior efficiency. Biosorption efficiency of powdered Trichoderma viride fungal


Page 38

biomass entrapped in polymeric metric of calcium alginate beads were analyzed by

Bishnoi, et al., 2007.

Effluent samples containing Cu, Cd and Pb from an electroplating industry were

treated by locally isolated fungal strains of Aspergillus sp., Penicillium sp. and

Cephalosporium sp. in both non-immobilized and Ca-alginate immobilized forms.

Experimental results reveal that all the immobilized isolates have potential application

for the removal of Cu, Cd and Pb from industrial wastewater than the dead fungal cells

(Hemambika, et al., 2011). Phanerochaete chrysosporium, biomass powder stabilized

in the polymeric matrix of calcium alginate was also investigated with similar results,

for sequestration of Cr (VI) by Marandi, 2011.

The performance of a new biosorbent system, consisting of a fungal biomass

immobilized within an orange peel cellulose absorbent matrix, for the removal of Zn2+

heavy metal ions from an aqueous solution was tested by Lai, et al, 2008. The amount

of Zn(II) ion sorption by the beads was as follows; orange peel cellulose with

Phanerochaete chrysosporium immobilized Ca-alginate beads (OPCFCA) (168.61

mg/g) > orange peel cellulose immobilized Ca-alginate beads (OPCCA) (147.06 mg/g)

>P. chrysosporium(F) (125mg/g) > orange peel cellulose (OPC) (108 mg/g) > plain Ca-

alginate bead (PCA) (98 mg/g).

Immobilized and dried powdered Phanerochaete chrysosporium and Trametes

versicolor basidiospores were also used for the recovery of uranium from aqueous

solutions. Maximum biosorption capacities for immobilized and dried powdered fungal

mycelia of T. versicolor and P. chrysosporium was found as 309.1 mg/g and 158.0

mg/g, respectively as compared to plain beads which was 29.2 mg/g. (Genc, et al.,

2003). Immobilized cells of Saccharomyces cerevisiae (biomatrix) were studied for the

biosorption of radionuclides viz. 233U, 241Am, 144Ce, 137Cs, and 90Sr (Kedari,et al.,

2001). Gok and Aytas, (2009) noticed that Trichoderma harzianum (a chitin-containing

fungus) once immobilized in Ca alginate performed much better than free biomass in

the removal of uranium as Ca alginate itself contributed to the removal efficiency

significantly (42–43% removal was achieved in controls).

From the extensive study of literature available, it can be concluded that the

equilibrium data validation and thus the description of mechanism involved in


Page 39

biosorption process can be done through kinetic, isothermal and thermodynamic studies.

Biosorption of copper (II) from aqueous solution by mycelial pellets of Rhizopus oryzae

was studied by Fu, et al., (2012). Mufedah, at al., 2012 while studyng biosorption of

lead and chromium onto A. versicolor noticed that the value of the correlation

coefficient (R2) for the pseudo-second-order model was ≥ 0.999, and the adsorption

capacity calculated by the model (34.84 mg/g) was also close to that determined by

experiment (34.2 mg/g).

Analysis of biosorption of Cr (VI) by Trichoderma gamsii revealed that the

values of equilibrium uptake capacity increased (from7.26 to 44.8mg/g biomass)

whereas second-order rate constant(k2) was found to decrease (from 0.376 to 0.075)with

increasing concentration of Cr(VI) ions (from 100 to 500 mg/L) (Kavita & Keharia,

2012). The value of adsorption Pseudo-second order rate constant K2 is 0.0049

mg/g/min for Cr(VI), 0.0048 mg/g/min for Zn(II) and 0.0035 mg/g/min for Ni(II) and

also have high value of correlation coefficient (r2is 0.99) for the Cr(VI), Zn(II) and

Ni(II) ions also indicated its better fitness of data obtained during their biosorption onto

A. niger (Kumar, et al., 2012). Danis, et al., 2012 concluded that pseudo second order

model provided the best description of data with a correlation coefficient 0.97-0.99 for

different initial metal concentrations and temperatures for biosorption of Cu (II) on

Pleurotuso streatus.

The kinetic of U (VI) metal ion biosorption onto R. arrihizus was studied at

optimized conditions concluded that pseudo second-order models were suited the

biosorption process. The correlative coefficient (r2) value obtained was 0.999 (Wang,et

al., 2010). Applicability of pseudo-second order kinetic model was favored by wide

range of biosorbents, used for uranium biosorption (Wang, et al., 2010; Khani, et al.,

2008; Akhtar, et al., 2009; Hu, et al., 2000; Xie, et al., 2008;Bayramoglu, 2006; Huang,

et al., 2012).

The biosorption isotherm curve represents the equilibrium distribution of metal

ions between the aqueous and solid phase. The isotherms indicate that the biosorption

rate increases with an increase in equilibrium concentration (Mufedah, et al., 2012). Fu,

et al., (2012) studied biosrption of Cu (II) by Rhizopus oryzae. Comparison of

coefficients indicated that the Langmuir model fitted more precisely (R2=0.9987,


Page 40

0.9978, 0.9981) than the Freundlich model (R2=0.9844, 0.981, 0.9793) at three different

temperature (298, 308 and 318K). The maximum adsorption capacities for Pb2+

and

Cu2+

biosorption by A. versicolor calculated from Langmuira dsorption isotherm were

25.25 and 13.15 mg g-1

, respectively and The Langmuir constant, ‘b’, values obtained

for Pb2+

and Cu2+

were found to be 0.070 and 0.035, respectively (Mufedah, et al.,

2012).

Kavita and Keharia, (2012) found that the correlation regression coefficients

(R2) and isotherm constant values show that the biosorption of Cr (VI) by Trichoderma

gamsii follows Freundlich isotherm (R2>0.9, n >1, and Kf= 8.3). Removal of Cu from

aqueous solution was analyzed in batch experiments by Danis, et al., 2012. The values

of ΔGo

obtained in this study was in the range of (-3.85 to -4.73) kJ/mol, ΔHo(4.87 kj

mol-1

), ΔSo(29.63J/mol K) confirms that the sorption process was endothermic and

highly spontaneous. Gok and Aytas, (2011) found that equilibrium data obtained during

biosorption of uranium(VI) from aqueous solution using calcium alginate beads fitted

well to Langmuir isotherm with constant Q0 (mg/g) to be 400, b (l/g) to be 48.83 and R2

0.9918.

The ability of non-living biomass of Penicillium citrinum has been explored for

the removal and recovery of uranium from aqueous solutions. U (VI) metal

ionbiosorption on adsorption could be well defined by Freundlich isotherm than

Langmuir isotherm (Pang, et al., 2011). Along with that, Wang, et al., (2010); Bhainsa

and D’souza, (2009); Bayramoglu, (2006) have also described the uranium biosorption

by corresponding biosorbent on the assumptions based of freundlich isothermal model.

While Langmuir model describing monolayer adsorption process was favoured by

Bhainsa and D’souza, (2009), Akhtar, et al., (2009); Hu, et al., 2000; Khani, et al.,

2008).

Analysis of thermodynamic parameters helps in clear understanding the

spontaneity of sorption process. During analysis of Uranium biosorption onto

Penicillium citrinum, Pang, et al., (2011) determined that the thermodynamic

parameters: ΔG° (308 K), ΔH°, and ΔS° for Uranium sorption process were−20.48

kJ/mol, 10.76 kJ/mol, and 101.43 J/mo1/K, respectively concludes that U (VI) metal ion

biosorption is a spontaneous and endothermic process showing increased randomness at


Page 41

the solid–solution interface during adsorption. This conclusion is also favored by Xie, et

al., (2008); Tsuruta, (2004) and Aytas, (2011). Biosorption of copper (II) from aqueous

solution by mycelial pellets of Rhizopus oryzae was studied by Fu, et al., 2012. Values

of ΔG° were found to be negative with ΔH° to be 19.505KJ/mol and ΔS° to be

KJ/mol/K.

The biggest achievement of a biosorption process is to concentrate the solute,

i.e., sorption followed by desorption. A successful desorption process requires the

proper selection of elutants, which strongly depends on the type of biosorbent and the

mechanism of biosorption (Dhankhar & Hooda, 2011). Even though some chemical

agents perform well in desorption, they may be detrimental to the biosorbent. Dilute

mineral acids (HCl, H2SO4, HNO3) have been used for the removal of metals from

fungal biomass and also organic acids (Citric, acetic, lactic) and complexing agents

(EDTA, thiosulphate etc) can be used for metal elution without affecting the biosorbent

(Vijayaraghavan & Yun, 2008).

The elution of Ni, Cu, Zn and Cd biosorbed on Penicillium biomass cab be

achieved by dilute NaOH solution and dilute HCl. Elution with 0.1N NaOH and

washing to pH 5.5-6.0 resulted in a 2-6 increase in mycelial uptake in subsequent use.

Pethkar, et al., 2001 determines the mechanism involved in adsorption and desorption

of gold ions by two strains of fungus Cladosporium cladosporioides. Lin, et al., 2005

characterized the biosorption of Au (III) to brewery waste S. cervisiae. Godleweska and

Zylkiewicz, (2005) further explained the binding of Pd and Pt by S. cerevisiae. In most

cases, in fact, a strong metal chelating agent such as acidified thiourea is needed in

order to recover quantities any significance from the sorbent surface (Godleweska &

Zylkiewicz, 2005; Ma, et al., 2006).

Continuous biosorption are considered as best study for evaluating the technical

feasibility of a process for real applications (Dhankhar & Hooda , 2011). Among the

different column configurations, packed bed columns have been established as an

effective, economical and most convenient for biosorption processes (Saeed & Iqbal,

2004; Chu, 2004). They make best use of the concentration difference, which is known

to be the driving force for sorption, and allow more efficient utilization of the sorbent

capacity, resulting in better effluent quality (Aksu & Gönen, 2004).Also, packed bed


Page 42

sorption has a lot of process engineering merits, including a high operational yield and

the relative ease of scaling up procedures (Aksu, 2005). Column studies use

‘breakthrough curves’ to assess sorbent efficiency, Here, the breakthrough/service

concentration can be fixed, which depends on the toxicity of the solute. For most

solutes, 0.01 to 1 mg/L is considered the breakthrough concentration (Hatzikioseyian, et

al., 2001).S shaped breakthrough curve is important to evaluate the characteristics and

dynamic response of a biosorption column (Aksu, 2005).

Numerous models have been tested for fixed bed biosorption columns,

including: Bohart–Adams model, Thomas model, Yoon–Nelson model, Modified dose–

response model and Clark model (Vijayaraghvan & Yun, 2008). The successful design

of a column sorption process requires the concentration-time profile or effluent

breakthrough curve to be predicted; the maximum sorption capacity of a sorbent is also

required in the design. Both the Bohart–Adams and Thomas models have been found to

fulfill this purpose and thus widely applied to many investigations (Vijayaraghvan &

Yun, 2008).

Removal of zinc in a continuous flow system by Aspergillus sp. was studied by

Sharma, et al., 2003.Zinc uptake of 44mg was obtained at 10g/L sugar concentration. At

same conditions, complete removal of the metal has been noticed from an actual

industrial effluent (46mg/L).The dynamic removal of Cr (VI) ion was studied using

continuously fed column packed with immobilized A. niger beads. Column experiments

were carried out to study the effect of various bed heights under different flow rates on

efficiency of biosorption (Chhikara, et al., 2010). Ramesh, et al., 2011 carried out

continuous adsorption study in a fixed-bed column by using Coir pith as an adsorbent

for the removal of Cd (II) from aqueous solution. Marandi, et al., 2011 explored the

biosorption of Cr(VI) using Phanerochaete crysosporium . The rate of absorption

resulted from the fixed bed process is equal to 74.23% with inlet velocity of 2 ml/min,

and this value is approximately two timed greater than the amount of absorption

obtained from the batch process. Yun model plotted the breakthrough at 60 min.

Kogej and Pavko, (2001) performed the laboratory experiments of lead

biosorption by self-immobilized Rhizopus nigricans pellets in the batch stirred tank

reactor and the packed bed column. The metal uptake 80.8 mg/g dry wt., determined


Page 43

with the minimal tested biomass concentration 25 g wet wt/L at the initial Pb2+

concentration 300 mg/L, approaches the maximum biosorption capacity 83.5 mg g–1

dry

wt. and consequently the corresponding efficiency is 0.98. This experimental data of the

biosorption of manganese onto Sargassum filipendula in both batch and fixed-bed

column systems was studied by Henriques, et al., (2011).

At a bed height of 20 cm and flow rate of 5 ml min−1

, the metal-uptake capacity

of xanthated chitosan and plain chitosan flakes for hexavalent chromium was found to

be 202 and 130mg/g respectively. The bed depth service time (BDST) model was

successfully used to analyze the experimental data (Chauhan & Sankararamakrishnan,

2011). The removal of Cd (II) from industrial wastewater by macrofungus Pleurotus

platypus was investigated in afixed bed column. Experiments were conducted to study

the effect of important parameters such as bed depth (5–15 cm) and flow rate (5–15

ml/min). The bed depth service time model (BDST) fitted well with the experimental

data and the adsorption capacity (N0) estimated from this model was 2418.12 mg/L

(Vimala, et al., 2011). Uranium(II) metal ion biosorption from aqueous solution by

Cystoseira indica biomass was studied in a packed bed column by Ghasemi, et al.,

2011. Results showed 0.1 M CaCl2 solution at pH=4, used as pretreatment, increased

the uptake capacity more than 30% (371.39 mg/g).

The review of the available literature on the subject of biosorption of U

(VI) reveals that a little attention has been paid on uranium biosorption using fungal

biosorbents. Keeping this in view, the present study has been designed in such a way,

that an efficient sequestration of uranium metal ion can be carried out from uranium ion

contaminated water.

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