Literature Review PART III: BIOSORBENTS AND BIOSORPTION FOR WASTEWATER TREATMENT TREATMENT BIOSORPTION Definition of biosorption Up to now, so many definitions of of bio-sorption have been been given by different researchers. researchers. & sugges suggestt that that the biosor biosorpti ption on proces process s involv involves es a solid solid phase phase (bioso (biosorbe rbent; nt; biolog biologica icall 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), , , , ) to bind and concentrate adsorbate(s) from aqueous solutions (Park et al. (2010), , , resulting in a reduction of sorbate concentration in the solution (Gadd (2009). Due to higher affinity of the sorben sorbentt for the sorbat sorbate e specie species, s, the latter latter is attrac attracted ted and remove removed d by differ different ent mechanism mechanism,, including including physical physical and chemical chemical adsorption adsorption,, ion exchange, exchange, complexat complexation, ion, chelation, chelation, and and micro-pre micro-precipia cipiation tion (, ). ). Kratochvil Kratochvil & Volesk Volesky y (…), & even point point out that that biological biological materials materials comprise comprise certain types of inexpensiv inexpensive, e, inactive, inactive, dead & microbial 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 adso adsorp rpti tion on or ionion-ex exch chan ange ge,, exce except pt that that sorb sorben entt of biol biolog ogic ical al orig origin in is empl employ oyed ed.. Biosorbents are selective and regenerable and a process is in particular highly effective in the treatm treatment ent of dilute dilute efflue effluents nts (Krato (Kratochv chvil il & Volesk Volesky y (…), (…), Das et al. (2008 (2008b), b), Gadd 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 conventio conventional nal sorbents; sorbents; early saturatio saturation n i.e. when metal interactive interactive sites are occupied; 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 metaboliz metabolizing ing and there is no potential potential for biologically biologically altering the meta valency valency state state (Gadd, (Gadd, 2009). 2009). In addition, addition, biodegrada biodegradable ble and decompos decomposable able properties properties of biomass biomass are drawbacks that hinder their long-term applications in adsorption processes (. 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 process the mostly strong. strong. pH determines determines protonation protonation or deprotonat deprotonation ion of metal 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 (Wan (Wang g & Chen Chen 20 2006 06). ). The The latt latter er grou group p incl includ udes es the the mate materi rial als s whic which h are are spec specia iall lly y propagated for biosorption purposes. They should have very good biosorptive properties and should be easily regenerable (Chojnacka 2010).
1
Low or intermediate sorption capacity (q=10-50 mg/g) High sorbent concentrations are used
Biosorbents
Low-cost sorbents Wastes, by-products, useless materials
Animal origin
Anima l bones
Egg shells
Naturally collected
Aquatic plants
Plant origin
Straw
High sorption capacity (q=100-350 mg/g) Low sorbent concentrations are used
Gras s
Lemn a minor
High-cost sorbents
Specially propagated
Macroalga e
Riccia fluitans
Microalga e
Cladophor a sp.
Spirulina sp.
Chlorella sp.
Leave s
Figure ... Low-cost and high-cost biosorbents Studies using biosorbents have shown that biomass used for biosorption may be living or dead (Das et al. (2008), , ). 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 , ). 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 nonliving 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 . Adsorption capacity of biosorbents Whereas 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, pretreatment method and type of metal ions, the results obtained from a study conducted by 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 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.
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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 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
The role of pH
Sorbates
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) 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 economy 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 Cost-effectiveness
Bio-sorption High, as biosorbents used are mainly waste biomass released from industrial,
Bio-accumulation Low, as the living-cell maintenance is cost prone
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pH
Temperature Maintenance Selectivity
Versatility
Uptake capacity
Uptake rate
agricultural and other sources. Cost involves mainly transportation and other simple processing charges Metal uptake is strongly influenced by pH; however, process can be operated under wide range of pH conditions No influence Easy, as biomass is inactive Poor, but can be improved by modification/processing of biomass Good, as the binding sites can accommodate a variety of ions Very high, as biomasses are reported to accommodate an amount of toxicant nearly as high as their dry weight Usually rapid
Regenerability High with possible reuse and reusability over a number of cycles Toxicant recovery Possible Biosorption Mechanisms
In addition to uptake, the living cells themselves are affected under extreme pH conditions
Severely affected External metabolic energy is needed in maintenance of culture Better than biosorption
Not very flexible, as the process is prone to high metal/salt conditions Low, as living cells are sensitive to high toxicant concentration
Usually slower than biosorption, as intracellular accumulation is time consuming Low, as toxicants are intracellularly accumulated Not possible
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.
4
Fig... Mechanism of biosorption Table … The representative functional groups and classes of organic compounds in biomass
Methods Utilized in Biosorption Research
5
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 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 Process factors Solution pH ↑ Temperature ↑
Ionic strength↑ Initial pollutant concentration↑ Biosorbent dosage↑ Biosorbent size↓
Agitation speed↑
Other pollutant concentration↑
Effects on biosorption of pollutants It enhances biosorptive removal of cationic metals or basic dyes, but reduces that of anionic metals or acidic dyes 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 It reduces biosorptive removal of adsorptive pollutant by competing with the adsorbate for binding sites of biosorbent It increases the quantity of biosorbed pollutant per unit weight of biosorbent, but decreases its removal efficiency It decreases the quantity of biosorbed pollutant per unit weight of biosorbent, but increases its removal efficiency 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 It enhances biosorptive removal rate of adsorptive pollutant by minimizing its mass transfer resistance, but may damage physical structure of biosorbent 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 Operating conditions Biosorbe nt
Modifyin g agent
pHopt
Co (mg/L)
0
T ( C)
Adsorptio n capacity qmax(mg/g )
Improveme nt in adsorption capacity (%)
Referen ce
BIOSORBENTS
6
Definition 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 microorganisms, 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) Low or intermediate sorption capacity (q=10-50 mg/g) High sorbent concentrations are used
Biosorbents
Low-cost sorbents Wastes, by-products, useless materials
Animal origin
Anima l bones
Egg shells
Naturally collected
Aquatic plants
Plant origin
Straw
High sorption capacity (q=100-350 mg/g) Low sorbent concentrations are used
Gras s
Leave s
Lemn a minor
High-cost sorbents
Specially propagated
Macroalga e
Riccia fluitans
Microalga e
Cladophor a sp.
Spirulina sp.
Chlorella sp.
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Figure ... Low-cost and high-cost biosorbents 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 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.) • Molds ( Aspergillus sp., Rhizopus sp., etc.), • • Mushrooms ( Agaricus sp., Trichaptum sp., etc), • Yeast (Saccharomyces sp., Candida sp., etc.) • 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.) Fermentation wastes, food/beverage wastes, activated sludges, anaerobic sludges, etc. Fruit, vegetable wastes, rice straws, wheat bran, soybean hulls, etc. •
Fungi
Algae
•
Industrial wastes Agricultural wastes Natural residues Others
Plant residues, sawdust, tree barks, weeds, etc 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)
Cu(II) and Zn(II)
1.46 and 1.97
Cr(VI)
10.61 and 112.36
References
MACRO ALGAE Green algae
Codium vermilara Chaetomorpha linum Spirogyra insignis Ulva lactuca and its activated carbon Ulva reticulata Enteromorpha compressa Cladophora sp. Cladophora fascicularis Spirulina sp.
Brown algae
Ni
62.3
Cd(II)
9.50
Cu(II), Ni(II), Cr(III), Cr(VI)
819, 504, 347, 168
Pb(II)
198.5
Cu(II), Ni(II), Cr(III), Cr(VI)
576, 1108, 306, 202
Fucus spiralis Padina sp.
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Sargassum baccularia Sargassum filipendula Sargassum fluitants Sargassum sinicola
Cd
62.4
Sargassum lapazeanum
Cd
71.2
Cd(II) and Pb(II)
1.65 and 1.71
Cd(II) and Pb(II)
1.71 and 1.79
Pb
145.0
Pb
93.5
Zn
209.6
Zn
836.5
Sargassum vulgare Sargassum sp. Lobophora variegata ( raw biomass) Lobophora variegata (chemically modified biomass) Red algae
Asparagopsis armata Chondrus crispus Gracilaria edulis Gracilaria sp.
Freshwater
Oedogonium sp (green algae) Nostoc sp. (blue green algae)
MICRO ALGAE Scenedusmus obliquus (heat-inactivated cells) Scenedusmus obliquus (living cells)
Fungi as Biosorbent Species Rhizopus Rhizopus cohnii Rhizopus oligosporus Rhizopus arrhizus (dried) Rhizopus arrhizus (living biomass) Rhizopus oryzae (viable and pretreated biomass) Penicillium Penicillium simplicissimum Aspergillus Aspergillus niger Aspergillus niger Aspergillus niger (NaOH pre-treated biomass) Aspergillus niger (PVA-immobilized fungal biomass) Aspergillus niger (free biomass) Aspergillus versicolor Aspergillus nidulans (dry, heattreated and NaOH-treated biomass) Aspergillus terreus (immobilized on loofa sponge discs) Yeast Saccharomyces cerevisiae Saccharomyces cerevisiae (immobilized) Saccharomyces cerevisiae (immobilized) Saccharomyces cerevisiae subsp. Uvarum (magnetically modified) Saccharomyces cerevisiae (non-living biomass) Pichia stipites yeast
Metal ions
Biosorption capacity (mg/g)
References
Cd Hg (II) Cr (VI) Ni Cu
40.5 33.33 78.0 618.5 19.4 and 43.7
Cd(II), Zn(II) and Pb(II)
52.50, 65.60 and 76.90
Mn Cd(II), Ni(II) and Pb(II) Ni(II)
12.15 2.2, 1.6 and 4.7 4.82
Cu(II) and Cd(II)
34.13 and 60.24
Cu(II) and Cd(II) Pb As(III)
17.60 and 69.44 45.0 127, 178 and 166
Pb (II), Hg (II) and Cd(II)
247.2, 37.7 and 23.8
Mn Cd(II)
10.53 5.96
Cd (II) and Cu (II) Cu(II)
38.08 and 39.02 76.8
Cu(II)
2.59
Cojocaru et al. 2009
Cu(II) and Cr(III)
15.85 and 9.10
Yilmazer
Aksu & Balibek 2007 Tahir & Zahid 2008 Bhainsa & D’Souza 2008
Parvathi et al. 2007
Bairagi et al. 2011
Parvathi et al. 2007
&
Saracoglu
9
2009
Bacteria as Biosorbent Species Streptomyces Streptomyces ciscaucasicus CCNWHX 72-14 (live and dead cells) S. maltophilia ZA-6 (dried biomasses) Pseudomonas P. aeruginosa ASU 6a P. cepacia 120S (dead biomass) Bacillus B. cereus AUMC B52 B. subtilis 117S (living and dead biomass) Others Exiguobacterium sp. ZM-2 (living and dead biomass) Exiguobacterium sp. ZM-2 (dried biomasses) Pantoea sp. KS-2 (living and dried biomass) Aeromonas sp. KS-14 (living and dried biomass)
Metal ions
Biosorption capacity (mg/g)
References
Zn(II)
42.75 and 54
Li et al. 2010
Cr(III)
10.2
Zn(II) Ni(II)
83.33 169.8
Zn(II) Ni(II)
66.6 155.5 and 175.6
Cr(VI)
29.8 and 20.1
Cr(III)
9.0
Cr(III)
11.25 and 11.7
Cr(III)
8.45 and 10.45
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 Moringa oleifera bark Potato peels Fluted pumpkin (Telfairia occidentalis) seed shell Onion skins (formaldehydetreated) Pre-boiled treated onion skins and formaldehyde-treated onion skins
Metal ions Ni(II) Cu(II)
Biosorption capacity (mg/g) 30. 38
Pb(II)
14.286
Pb(II)
200
Orange peel (mercapto-acetic acid modified)
Cu(II) and Cd(II) Pb(II), Cu(II), Zn(II) and Ni(II)
Mangifera sp. ( nonliving biomass) Oyster mushroom (Pleurotus platypus) Button mushroom ( Agaricus bisporus) Maize tassel Coffee husks
99.8%
Pb(II)
References Reddy et al. 2011 Aman et al. 2008
84.8% and 93.5%
70.67 and 136.05
24.4 (Pb); 22.506 (Cu); 18.932(Zn) and 17.618 (Ni)
Cd(II)
34.96
Pb(II)
33.78
Cr(VI) and Cd(II) Cu(II),
Removal efficiency (%)
Ashraf et al. 2011
Vimala & Das 2009 Cr(79.1%) and Cd(88%)
Zvinowanda et al. 2009
Cu (89–98%); Cd
Oliveira et al. 2008
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(untreated biomass)
Mangifera sp. (mango)
Papaya wood
Cd(II), and Zn(II) Pb(II), Cu(II), Zn(II) and Ni(II) Cu(II), Cd(II) and Zn(II)
(65–85%) and Zn (48–79%) Pb (92%); Cu (86.84%); Zn (83.96%) and Ni (82.29%) Cu(97.8%), Cd(94.9%) 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 singlesorbate 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, C f ) 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 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 Operating Conditions Biosorbents
Metal Ions
pH
0
T, ( C)
C0 (mg L-1)
qmax, (mg g-1)
Remo val efficie ncy (%)
Referenc es
Natural biosorbents Algae •
•
Fungi
•
Bacteria
Agricultural waste materials
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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 )
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 Table ... Modification methods for converting raw biomass into better biosorbents
Category Physical modification Chemical modification
Detailed methods Autoclaving, steam, thermal drying, lyophilization, cutting, grinding, etc. 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, K 2CO3, (NH4)2SO4, H2O2, NH4CH3COO, etc.) 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. Decarboxylation/ elimination of carboxyl group Deamination/ elimination of amine group, etc. High energy radiation grafting (using γ• irradiation, microwave radiation, electromagnetic 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) Optimization of culture conditions for enhancing biosorptive capacity of cells Over-expression of cysteine-rich peptides (glutathione, phytochelatins, •
Pre-treatment (washing)
•
Cell modification (during growth)
Enhancement of binding groups
Elimination of inhibiting groups Graft polymerizatio n
•
•
•
•
Cell modification (during growth)
Culture optimization Genetic engineering
•
•
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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 MoO42-, TcO4-, PtCl43-, CrO42-, SeO42-, Au(CN)2. The information available in connection with multi-metallic systems is very poor
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 Metal Lead
Cadmiu m
Mercury
Source Electroplating, manufacturing of batteries, pigments, ammunition Electroplating, smelting, alloy manufacturing, pigments, plastic, mining, refining
Weathering of mercuriferous areas, volcanic eruptions, naturally-caused forest fires, biogenic emissions, battery
Toxic effect Anaemia, brain damage, anorexia, malaise, loss of appetite, diminishing IQ Carcinogenic, renal disturbances, lung insufficiency, bone lesions, cancer, hypertension, Itai–Itai disease, weight loss Neurological and renal disturbances, impairment of pulmonary function, corrosive to skin, eyes, muscles,
References Gaballah and Kilbertus (1998), Low et al. (2000), Volesky (1993) Chen and Hao (1998), Godt et al. (2006), Low et al. (2000), Sharma (1995), Singh et al. (2006)
Boening (2000), Manohar et al. (2002), Morel et al. (1998)
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Chromiu m (VI)
Arsenic
Copper
Zinc
Nickel
production, fossil fuel burning, mining and metallurgical processes, paint and chloralkali industries Electroplating, leather tanning, textile, dyeing, electroplating, metal processing, wood preservatives, paints and pigments, steel fabrication and canning industry Smelting, mining, energy production from fossil fuels, rock sediments
Printed circuit board manufacturing, electronics plating, plating, wire drawing, copper polishing, paint manufacturing, wood preservatives and printing operations Mining and manufacturing processes Non-ferrous metal, mineral processing, paint formulation, electroplating, porcelain enameling, copper sulphate manufacture and steam-electric power plants
dermatitis, kidney damage
Carcinogenic, mutagenic, teratogenic, epigastric pain nausea, vomiting, severe diarrhoea, producing lung tumors
Dupont and Guillon (2003), GranadosCorrea and SerranoGomez (2009), Kobya (2004), Singh et al. (2009)
Gastrointestinal Chilvers and Peterson symptoms, disturbances (1987), Dudka and of cardiovascular and Markert (1992), nervous system Robertson (1989) functions, bone marrow depression, haemolysis, hepatomegaly, melanosis, polyneuropathy and encephalopathy, liver tumors Reproductive and Chuah et al. (2005), developmental toxicity, Papandreou et al. neurotoxicity, and acute (2007), toxicity, dizziness, Yu et al. (2000) diarrhoea
Causes short term ‘‘metal-fume fever”, gastrointestinal distress, nausea and diarrhoea Chronic bronchitis, reduced lung function, lung cancer
WHO (2001)
Akhtar et al. (2004), Ozturk (2007)
Table … The effects of heavy metals on human health (Arief et al. 2008) Heavy Toxicities metal Cr (VI) Headache, nausea, severe diarrhea, vomiting, epigastric pain, hemorrhage, carcinogenic and has an adverse potential to modify the DNA transcription process Cr(III) Allergic skin reactions and cancer Zn(II) Depression, lethargy, neurologic signs such as seizures and ataxia, and increased thirst
14
Cu(II) Cd(II)
Liver damage, Wilson's disease, insomnia Kidney damage, renal disorder, Itai-Itai (excruciating pain in the bone), hepatic damage, cancer, and hypertension Encephalophathy, seizures and mental retardation, reduces haemoglobin production Dermatitis, nausea, chronic asthma, coughing, bronchial hemorrhage, gastrointestinal distress, weakness and dizziness
Pb(II) Ni (II)
•
Types of forms of these contaminants (cations, anions…) Total phosphorus Pt
Particular phosphorus Pp (organic and inorganic)
Dissolved phosphorus Pd Dissolved poly phosphate PDp (inorganic)
Hydrolysed dissolved phosphorous PDh Orthophosphate PO4-P (inorganic)
Dissolved phosphorus P Ox (organic)
Figure ... Different forms of phosphorous in wastewater (Wiesmann 2007) Table... Typical dyes used in textile dyeing operations Dye class Acid Basic Direct Disperse Reactive Sulphur Vat
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Description Water soluble anionic compounds Water soluble, applied in weakly acidic dyebaths; very bright dyes Water-soluble, anionic compounds; can be applied directly to cellulosics without mordants (or metals like chromium and copper) Not water-soluble Water-soluble, anionic compounds; largest dye class Organic compounds containing sulphur or sodium sulphide 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 Method Chemical Precipitation
Chemical coagulation
Ion-exchange
Electrochemical methods
Adsorption Using activated carbon
Advantages Simple Inexpensive Most of metals can be removed Sludge settling Dewatering High regeneration of materials Metal selective Metal selective No consumption of chemicals Pure metals can be achieved Most of metals can be removed High efficiency (>99%)
Disadvantages Large amounts of sludge produced Disposal problems High cost Large consumption of chemicals High cost Less number of metal ions removed High capital cost High running cost Initial solution pH and Current density Cost of activated carbon No regeneration Performance depends upon
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Using natural zeolite
Membrane process and ultrafilteration
Most of metals can be removed Relatively less costly materials Less solid waste produced Less chemical consumption High efficiency (>95% for single metal)
adsorbent Low efficiency
High initial and running cost Low flow rates Removal (%) decreases with the presence of other metals
Research in biosorption suggests the following advantages over other techniques : 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 : 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 DESOPRTION COMMENTS AND SUGGESTIONS
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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), . REFFERENCES
Algae as Bio-sorbent
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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.
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.
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… explored the use of agro-waste biosorbents for aqueous Cr(III) removal in batch experiments.
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