Masterarbeit, 2019
81 Seiten
Chapter no 1: INTRODUCTION
Heavy metals pollution in water sources:
Strontium:
Occurrence:
Importance of Strontium:
Conventional methods for heavy metals removal:
Biosorption:
Chapter no 2: REVIEW OF LITERATURE
Heavy metals sources:
Definition of Biosorption
Biosorbents
Significance of biosorbents for wastewater treatment
Strontium recovery by using different biosorbents
Chapter no 3: MATERIAL AND METHOD
Methodology:
Preparation of stock solution
Collection of Biosorbent
F Preparation of Rice straws biochar
Preparation of alginate beads
Biosorption experiment
Preparation of indicator
EDTA solution for titration
Determination of metal concentration by titrimetric method
Optimization of biosorption parameters
Fourier Transform Infrared Spectrometer (FTIR)
SEM Analysis
Chapter no. 4: RESULTS AND DISCUSSION
Effect of contact time
Effect of dosage of RSBC
Effect of Temperature
Effect of initial concentration
Effect of agitation
Chapter no. 5: SUMMARY
References:
Figure 1 Synthetic solution of strontium nitrate
Figure 2 Collection of Rice straws
Figure 3 washing and drying of rice straws
Figure 4 grinding and sieving of rice straws
Figure 5 grinding and sieving of biochar powder
Figure 6 biochar powder stirring process
Figure 7 Formation of RSBC Beads
Figure 8 Shaking of solution in orbital shaker
Figure 9 Indicator solution for titration
Figure 10 EDTA solution of 0.1 M
Figure 11 Direct titration
Figure 12 Fourier Transform Infrared spectrometer
Figure 13 Scanning Electron microscope
Figure 14 Flow sheet diagram of overall biosorption process
Figure 15 Biosorption samples at different contact times
Figure 16 Effect of contact time on strontium biosorption at pH 7.0, 35°C temperature, 10g/L initial metal concentration by using1 g beads at 120 rpm
Figure 17 Biosorbent dosage effect on strontium ions biosorption at pH 7.0, 35°C temperature, 10g/L initial metal concentration, 2 h of contact time at 120 rpm.
Figure 18 Biosorption samples at different temperature
Figure 19 Temperature effect on biosorption process by using rice straws beads as biomass and keeping other parameters constant as contact time 2 h, pH 7.0, 3 g biosorbent dose and using 10g/L of initial metal concentration at 120 rpm.
Figure 20 Biosorption samples at different pH
Figure 21 pH effect on biosorption process by using rice straws beads as biomass and keeping other parameters constant as contact time 2 h, 3g biosorbent dose, 55°C temperature and using 10g/L of initial metal concentration at 120 rpm.
Figure 22 biosorption samples of metal initial conc.
Figure 23 Effect of initial metal concentration on biosorption process by using rice straws beads as biomass when other factors are kept constant as time of contact of 2 h, 3g biosorbent dose, 55°C temperature and using, pH 7.0 at 120 rpm.
Figure 24 Biosorption samples at different agitation
Figure 25 Effect of agitation on biosorption at 55°C temperature, contact time of 2 hours, 15g/L initial metal concentration using 3 g beads.
Figure 26 SEM image of rice straws bio-char beads before biosorption
Figure 27 SEM analysis of rice straws bio-char beads after biosorption
Figure 28 FTIR Spectrum of rice straws biochar beads before biosorption
Figure 29 FTIR spectra of rice straws biochar beads after biosorption
Figure 30 Overall flow sheet diagram of biosorption process
Table 1 Conventional techniques for metals removal from industrial waste water (William et al., 2008).
Table 2 Permissible limits as well as effects on health of several heavy metals (Sud et al., 2008).
Table 3 Common industrial units releasing heavy metals into water sources.
Table 4 apparatus and glassware’s
Table 5 Material and Chemicals
Table 6 Instruments
Table 7 Effect of different contact times on biosorption
Table 8 Biosorption samples of different biomass dosage
Table 9 Effect of different biosorbent dosage
Table 10 Effect of different temperatures on biosorption
Table 11 pH effect on biosorption process
Table 12 Effect of initial strontium concentration on biosorption
Table 13 Agitation effect on biosorption
In present study, biosorption behavior of rice straws biochar beads was investigated for strontium removal from wastewater bodies. Strontium occurs naturally at average amount of 0.04% and is considered the 15th abundant element of earth’s crust. It is recognized one of the environmentally hazardous constitutes and act as a major pollutant in nuclear water discharges. It is widely used in electronics, pharmaceutical, pyrotechnics and metallurgical industries that release strontium rich wastewaters. Therefore, it is vital to remove it from the wastewater bodies. Biosorption process was carried out by using beads of rice straws biochar used as bio-sorbent. This study revealed that beads of rice straws being proficient biosorbent has good sorption capacity for removal of strontium ions. Different physicochemical variables like time of contact, temperature, initial metal’s concentration, pH, agitation as well as biosorbent doses were also optimized. At optimum condition with 3g biosorbent dose treated to 50mL strontium solution for 2 h at pH 7.0 and temperature 55°C, the maximum 94% strontium is adsorbed by RBSC beads. Quantitative and qualitative analysis of strontium were also done by using FTIR and titrimetric techniques.
Water as valuable source survives all living things on planet earth. Availability of hygienic water is of great concern for human population in the current world. According to a report designed by UN revealed that approximately one billion of people do not have resources of unpolluted water for drinking purposes in third country of world (Murthy, 2017). Water is a fundamental need and critical source of economic tasks along with robust cultural as well as symbolic standards in all over the world. According to supply and demand law, when availability of water is abundant it is inexpensive and when it is scarce it becomes expensive (Adebayo, 2007). However, the access to water used for drinking is steadily growing but situations are not substantial even today. Consumption of water is increasing by increasing the population of world. According to a prediction, more than half world population will face the crisis of water in 2025 (Swain, 2001; Rijsberman, 2006). Water pollution by various noxious soluble metals is the matter of extreme concern for the health and safety of living beings (Ahmad et al., 2011). Lack of clean water has adverse impacts on biodiversity of aquatic life as well as the life present on earth. One of major causes of water pollution is heavy metals disposal to groundwater or other water resources by various human activities including battery formation, paper and electronic industries, mining and metal fabrication activities, electrolyzing, smelting, drug preparation, paint making, alloy formation, printing, making of paper, dyeing, preparation of ceramics as well as inorganic dyestuffs (Liu et al., 2008). Water contamination, by various toxic heavy metal ions through industrial wastewater discharge is now a universal environmental problem.
Heavy metals elimination from wastewaters has become the matter of central concern for protection of both industrial & environmental agencies in Pakistan as well as in abroad. Wastewaters having various heavy metals are annually discharged by many industries and control of heavy metals level in wastewater before their disposal into nature has become crucial. Because of non-biodegradable natures of heavy metals unlike that of organic pollutants, these accumulate in bodies of living organisms through food chain and some of these metals are very toxic in less concentration. Therefore, heavy metal’s contamination is main concern for health of human beings and for diverse ecosystem (Ahmad et al., 2006). Rapid industrialization generate wastewater contaminated by means of heavy metals including chromium lead, copper, cadmium as well as zinc which mostly comes from manmade sources such as electronics, battery, pulp and paper industries, fabrication of metals, mining activities, electrolyzing, smelting, drug preparation, paint formation , alloy preparation , printing, galvanizing, dyeing, pulp and paper making, manufacturing of ceramics. (Sari et al., 2007; Liu et al., 2008). Uncontrolled and untreated discharge of wastewaters containing heavy metals in natural environments might be toxic for humans, animals and plants (Ahmad et al., 2010). Minor amount of heavy metal ions might be lethal and cause harmful effects when absorbed by the bodies of living organisms (Gavrilescu, 2004) . However, increase uptake of Cu (II) may cause serious health problems like failure of liver as well as kidney and Wilson disease, gastrointestinal disturbance & insomnia in humans, although high intake of cadmium may lead to kidney damage, defects of birth, disorders of renal, hepatic destruction, cancer and hypertension (Kurniawan et al., 2006; Han et al., 2009). Pb(II) has numerous undesirable effects to the human body such as encephalopathy, mental retardation, kidney damage, nervous system disorder and reduces the production of haemoglobin (Igwe and Abia, 2006; Qaiser et al., 2007). Likewise, Zinc can create various severe effects including lethargy, depression and neurologic signs like ataxia and seizures, and increases the thirst (Kurniawan et al., 2006). Presence of high level of these metal ions in surface as well as ecosystems of groundwater prevent the growth of aquatic organisms and also inhibits the valuable uses of water resources. These ions of heavy metals may accumulate in bodies of fishes as well as other organisms of aqueous environment and finally reach the humans body by means of bio-accumulation and bio-concentration processes through food & drink chains (Hong et al., 2006; Hu et al., 2007). Other heavy metal sources including wood processing industry that yields wastes having inorganic pigments of arsenic and chromium compounds, refining of petroleum that produces catalyst polluted by nickel, chromium as well as vanadium, operations of photography generating films having high concentration of ferrocyanide and silver. All of these producers yield wastewaters, sludges and residues at a large scale that may be characterized as harmful wastes and demand widespread treatments of waste (Sörme and Lagerkvist, 2002). Ions of heavy metals may be absorbed on biological solids due to the greater affinities between metal ions and solids. Urban runoff is causing severe problems of metals (Raskin et al., 1997). Metal contents is quite high in the fertilizers and may enter the surface as well as groundwater when these fertilizers are applied. (Chang et al., 1987). Sewage sludge comprises of high concentration of heavy metal ions that yield dangerous and undesirable environmental impacts like microbial toxicity and contamination of ground water and food chain (Boller, 1997; Bhogal et al., 2003)
Strontium is the soft and silver white yellow colored alkaline-earth metal which is highly reactive chemically. The atomic number as well as atomic weight of this metal is 38 and 87.62 correspondingly, with density of about 2.64 g/cm3. Strontium have melting and boiling points of about 1050 K and 1650 K respectively. Physical and chemical properties of strontium are similar to its two vertically present neighbors, calcium and barium of the periodic table. Like calcium, strontium also has tendency to deposit in teeth, bones and blood making tissues. Strontium illustrates serious dangers for population of humans and for flora and fauna of receipt water sources. It could be immersed and may accumulate into human bodies causing severe problems relate to health such as cancer and damaging of organs and nervous system. It also lessens the growth and development (Babel and Kurniawan, 2003). Among isotopes of strontium metal, 84Sr, 86Sr, 87Sr and 88Sr are stable and 90Sr and 89Sr are radioactive isotopes and main products of nuclear fission, which are present in liquid wastes of nuclear industries (Jin et al., 2018). Radioactive isotopes of strontium are carcinogenic and lower the amount of blood cells (Long et al., 2017). Various industries such as electronics, pharmaceutical, pyrotechnics and metallurgical which yield glass products, ceramics, fluorescent lights and paint pigments etc. release wastewater of strontium rich (Ahmadpour et al., 2010). Stable isotopes of strontium also causes osteoporosis, rachitic rosary, reduce in bone resorption, defective bone mineralization, decreases size of bones, hypocalcemia and inhibit the synthesis of vitamin D on absorption by the body (Oliveira et al., 2012). Thus, development of an efficient and economic treatment of strontium containing wastewaters has received substantial attention. Increased dose of bone marrow as a result of 90Sr is correlated to variations in the composition of blood, growth retardation, bone tumors and leukemia in animals (Boyer, 2017).
According to Mineral Education Coalition (MEC), strontium is the 15th abundant element of earth crust. Among naturally occurring compounds of strontium, only strontium carbonate (SrCO3) and strontium sulfate (SrSO4) minerals have commercial significance. The Average concentration of strontium is about 0.04% in earth crust. Strontium is recognized as 10th abundantly present eiement having concentration of about 8×10–4 in seawater (García-Ruiz et al., 2007).
According to estimation of USGS, more than 85% of total strontium metal was consumed in manufacturing of ceramics and glass, mostly in glass of television faceplate. It is also used in magnets of ceramic ferrite in 2000. Since 1970, manufacturing of faceplate glass for picture tubes of color televisions had been the foremost use of strontium. Strontium may also utilized for removing lead impurities during zinc electrolytic manufacturing. By adding strontium carbonate into sulfuric acid to electrolyte, decreases the lead contents of electrolyte as well as of the zinc which was deposited onto cathode (Bratt and Smith, 1965).
Most reliable and continuing application of strontium was in devices of pyrotechnic. Strontium burns with a flame of bright red color. For this purpose, compound of strontium nitrate was used most commonly in pyrotechnic device. Although, strontium chlorate, strontium oxalate, strontium sulfate may also be utilized. Pyrotechnic devices had usage in the military as well as nonmilitary applications. Tracer ammunition, marine distress signals and military flares are included in military applications of pyrotechnic devices while fireworks and warning devices are included in non-military applications (Conkling, 1981).
Strontium carbonate is considered as a vital industrial compound. It is mainly utilized in the production of X-rays absorbing glass used in cathode ray tubes, to remove Pb from solution of zinc sulfate during the electrolytic process of zinc as well as it is also utilized in order to manufacture the strontium metal, oxide superconductors and electroceramics (Roskill, 1992).
Strontium was required by all the colored televisions as well as other devices comprising of colored cathode-ray tubes (CRTs) which was sold in United States, in faceplate glass of picture tubes for blocking the x-ray emissions. Main constructors of T.V picture tubes glass incorporated nearby 8% of strontium oxide by weight in their material of glass faceplate. Strontium increases the appearance of glass as well as the quality of picture along with blocking of x-rays (Wagner, 1986).
Strontium ferrite was used to make the permanent ceramics magnets which were extensively used in small motors of direct current for loudspeakers, automobiles, windshield wipers and in some types of electronic equipment such as toys and decorative items of magnets. These magnets of strontium ferrite are highly forcible and contain high thermal & electrical resistivity and are inert chemically. They retain well magnetism and are not badly affected by both electrical currents as well as high temperatures. They also have low density and do not react with most of the chemical solvents (Ely et al., 1959).
Strontium also enhances the quality of some ceramic glazes by eliminating the toxicity that might be present in the glazes comprising of lead or barium. Strontium titanate has some applications in semiconductors as substrate as well as in certain optical and piezoelectric devices. Strontium chloride had been used in toothpastes for temperature sensitive teeth. Strontium phosphate was utilized in the manufacturing of fluorescent lights and most of the strontium chemicals were used in laboratories of analytical chemistry.
Strontium chromate was utilized as an additive in corrosion resistant paints for efficiently coating of aluminum especially on ships and aircraft fuselages. These paints were also used in aluminum packaging at some extent to prevent from corrosion (Roskill, 1992). Small quantity of strontium is added in molten aluminum to increase the cast ability of metal and to make it more appropriate for casting items. Machinability of casting is improved by adding the strontium in melt aluminum. Instead of steel, Cast aluminum parts were commonly used in automotive industry due to the reduced weight as well as improved gas mileage. (Lidman, 1984).
Methods to treat the industrial wastewater having heavy metals frequently involve certain technologies to reduce their toxicity by a standard technology base treatment. Common conventional chemical methods for remove of heavy metals from sources of wastewaters comprising of ion exchange, chemical precipitation, electrochemical deposition as well as flotation.
Chemical precipitation due to modest operation, is usually used to eliminate the heavy metals from effluents of industry. Chemical precipitation yields unsolvable precipitates containing metals like sulfide, carbonate, phosphate and hydroxide. During the process, percentage removal of metals ions into solution can be improved upto optimized value by varying main factors including pH, initial concentration, temperature etc. In precipitation process, fined particles are produced. Chemical coagulants and flocculation methods are utilized to increase the size of particles for removing these in the form of sludge (Ku and Jung, 2001; Fu and Wang, 2011).
The coagulation flocculation process depending on measurement of zeta potential (ζ) for explaining electrostatic collaboration among agents of coagulant and flocculation and pollutants (López-Maldonado et al., 2014). The coagulation process reduces the charge on colloidal particles surface in order to stabilize through electrostatic repulsion. The flocculation process constantly enhances the particle size for separating the particles by means of supplementary collisions and interaction by inorganic polymers. (Tripathy and De, 2006). Sludge production, chemicals usage and shifting of poisonous compounds towards solid phase are main shortcomings of that procedure.
Electrochemical wastewater treatment included electro deposition, electro flotation and electrocoagulation (Shim et al., 2014). It is frequently used process of precipitation making coagulants through destabilizing pollutants and electrostatic oxidation (Mollah et al., 2001). This procedure is categorized by minimum production of slurry, no use of chemicals and easiness of process. Although, precipitation method needs a more quantity of chemicals for decreasing metals to an adequate level for release. It alters the problems of aqueous pollution to problems of solid wastes removal without metal recovery. Other drawbacks included sludge production, poor settling, long lasting environmental influences of sludge disposal and the slow precipitation of metals (Aziz et al., 2008).
Ion exchange could draw soluble ions made liquid phase toward solid phase and is mostly utilized process for water treatments of industries. This method may be utilized only for low concentration solution of metals is greatly sensitive to pH of aqueous phase. Ionic exchange resins are solid substances of water insoluble which can adsorb negative as well as positive charged ions by solution of electrolyte. Ion exchange resins is considered an economical method due to having suitable operations. It is also proved very effectual method for eliminating toxic metal ions from aquatic solution (Dizge et al., 2009; Hamdaoui, 2009)
Membrane filtration was commonly used in order to treat the inorganic effluents. It has ability of eliminating organic compounds, suspended solid and pollutants of inorganic based including heavy metals. Dependent on size of particles several kinds of membrane filtration like ultrafiltration and reverse osmosis and ultrafilteration may be utilized for heavy metals elimination from wastewaters. The ultrafiltration uses porous membrane for separation of macromolecules, suspended solids and heavy metals from inorganic solutions (Vigneswaran et al., 2004). Polymer supported ultrafiltration method introduces polymeric ligands which are water soluble for binding the metal ions as well as to make macromolecular complexes by generating free targeted effluent of metal (Rether and Schuster, 2003). It is a hybrid method to recover ions of heavy metals from solutions. In UF complexation method heavy metals of cationic nature are compiled by using macro ligands for increasing the molecular weight with larger pores size than that of the certain membrane (Petrov and Nenov, 2004; Trivunac and Stevanovic, 2006).
Reverse osmosis is a separation technique that employs pressure in order to power any solution by membranes which keep solute at one side and permits pure solvent toward other side. Here membrane acts as semipermeable which permits the solvent passage but retains the metal. Membranes which are used in reverse osmosis contain thick obstacles in its polymeric medium, where mostly separation take place. Reverse osmosis may remove numerous kinds of molecules ions from solutions such as bateria and is employed in industrial processes. Reverse osmosis includes a diffusive mechanism. Hence, departure efficacy depends upon concentration of solute, rate of water flux as well as pressure (Crittenden et al.).
Electro dialysis involves the usage of electrical potential to pass the ionized species of solution are through the membrane of ion exchange. These membranes may be thin plastic sheets making of plastic materials having properties of anionic or cationic nature. While solution comprising of ionic species is passed through the compartments of cell, then anions travel to anode and the cations toward the cathode by crossing the cationic as well as anionic exchange membranes. A visible disadvantage is corrosion process and membrane displacement (Kurniawan et al., 2006). Membranes having higher ion exchange capability causes the better performance of cell. Factors including rate of flow, voltage and temperature at various concentration using two kinds of commercial membranes, employing a Electro dialysis cells for removing lead were also considered (Mohammadi and Pironneau, 2004).
These process are neither cost efficient nor echo-friendly. Physical as well as some most commonly used chemical procedures created toxic sludge that is incapable of settle down within industries. Factors that can bounds the use and competence of these chemical methods included high clay contents and silt, calcite, heavy metals, humid, excessive buffering as well as anions (Fu and Wang, 2011).
Table 1 Conventional techniques for metals removal from industrial waste water (William et al., 2008).
Abbildung in dieser Leseprobe nicht enthalten
The searching of a low cost and freely present biosorbent leading to investigate the materials of biotic origin as latent metal biosorbents. During recent years, great number of studies were done to remove the heavy metals from aqueous media by non-living, sedentary biomass have been directed worldwide. That method of wastewaters remediation is termed as biosorption, and dead biomass is utilized in that methodology is recognized as biosorbent.
Biosorption is recognized as an economical, effectual and substantial separation technique for elimination of heavy metals by waste water of industries having benefits of definite attraction, less cost and modest strategy (Al-Asheh et al., 2000). biosorption is basically a mass transmission procedure in which substances bound to the solid surface by physical & chemical interactions (Babel and Kurniawan, 2003). Numerous less-cost sorbents which are derived from wastes of agriculture, industries byproducts, modified material, or modified biopolymers, have recently established and applied to eliminate the heavy metals by metal polluted wastewaters. Using of activate biosorption with adsorbents making of agricultural as well as industrial byproducts can be utilized generally for removing heavy metals by aqueous media because of their copious presence, less cost, and auspicious physical or chemical and surface features (Safarik et al., 2007).
Heavy metals removal employing biosorption is comparatively a novel as well as emerging technology in fields of wastewater sanitization (Schiewer and Volesky, 2000). It is considered a physical or chemical as well as metabolically autonomous method which is founded on various mechanisms such as sorption, ionic exchange, precipitation as well as surface complexation. Biosorption has obtained great importance in environmental as well as conventional bio treatment processes. Biosorption is directed for elimination and regaining of organic as well as inorganic materials from solutions through organic materials including living and dead microbes or their constituents, natural residues, plants materials, seaweeds, agricultural or industrial wastes. For many years biosorption has been indicated as a favorable cost-effective and cleaning biotechnology. Despite of considerable advancement of understanding about this multifaceted process and dramatic rise in publications of the research area, commercialization of biosorption processes become inadequate.
Biological treatments are best removal, cost effective and eco-friendly methods. Many adsorbents could be found in the nature. Chemical as well as other physical methods yield toxic slurry that is not able of settling down inside the industries. The major benefits of process of biosorption as compared to other conventional procedures included less cost, maximum efficiency, Minimum biological or chemical sludge, not requirement of additional nutrient, bio-sorbents regeneration as well as probability of recovery of metals (Ahalya et al., 2003).
Objectives:
The objectives of present study will be:
- For efficient elimination of strontium heavy metal from wastewaters several parameters like biosorbent dose, temperature, pH, time of contact, agitation as well as initial strontium concentrations will be optimized.
- Systematic study of each step will be carried out.
- Qualitative as well as quantitative analysis of metal will be conducted.
Heavy metals which are released in the environment by natural weathering, soil erosion, mining operations, metal plating, pesticides activities and fertilizer and paper industries cause substantial hazards for environment as well as for public health (Morais et al., 2012). The most frequently heavy metals which are found in wastewaters including lead, arsenic, chromium, cadmium, copper, zinc and nickel cause harmful hazards on human health and on environment (Lambert et al., 2000). Because of non-biodegradability of these heavy metal ions, these accumulated in the bodies of living organisms through food chains causing severe toxicity even at low concentration. According to previous research, heavy metal’s binding with DNA as well as nuclear proteins causes oxidative deterioration of macromolecules (Flora et al., 2008). For example, Lead damages the kidney and central as well as peripheral nervous system. It also causes stillbirth and affects the fetus (Deng et al., 2006). Chromium is frequently associated with tumor hemorrhage of digestive tract (Faisal and Hasnain, 2004). Excessive exposure of mercury either in metallic or in molecular form causes brain damage and create problems in kidney as well as in developing fetus (Alina et al., 2012). Major effects of other heavy metals are shown in the table 2.1. International regulations reveals the tolerable limits of various heavy metals. Even though strict regulations are undertook for against disposal of heavy metals in the environment, primarily in USA there are numerous activities including industrial as well as agricultural activities and wastewater irrigation that undergo discharging of heavy metals at hazardous level into environment.
Table 2 Permissible limits as well as effects on health of several heavy metals (Sud et al., 2008).
Abbildung in dieser Leseprobe nicht enthalten
Heavy metals, entering into environment by activities of both natural as well as anthropogenic type. For example, rocks weathering is the cause of naturally produced heavy metals. Petroleum burning as well as non-ferrous metalworking also release the heavy metals into the atmosphere. Effluents discharged from industrial units rises the pollution of heavy metals. Water sources become contaminated through effluents which are released from fertilizer factories as well as paper mills that causes addition of ammonia, cyanides, alkalis and heavy metals. The wastewaters releasing from the pigment and dye industries, metal cleaning, galvanometric industries, electroplating, film and photography, mining and leather industries comprise of large extents of heavy metal ions. According to an estimation, an average of 332,350 tons lead, 131,880 tons zinc and 35,370 tons copper are discharged into atmosphere every year. Moreover, major water polluting sources are wastes of households, steel and manufacturing of iron, metals plating, mining uses and metal smelters. The anthropogenic annual contributions of copper, lead, zinc and nickel into aquatic environments were reported as 112,00 t, 138,000 t, 226,00 t as well as 113,000 t (Nriagu et al., 2004). Ash residues disposal from combustion of coal as well as commercial products disposal on land are main causes of heavy metals into the soils. Average worldwide emission for lead 796,000 t, for copper 954,000 t, nickel 325,000 t and zinc 1,372,000 t in the soils (Nriagu et al., 2004). Heavy metal contamination is significant environment issues of present age. Numerous activities yield & release waste materials comprising of various heavy metals like smelting and mining of metals, industry of surface finishing, manufacturing of fuel and energy, pesticide and fertilizer industry application, iron, metallurgy, steel and iron industry, electrolysis, electroplating, leather working, photography, making of appliance, aerospace, treating of metal surface and installing of atomic energy (Wang and Chen, 2009). Following are considered major significance targets mainly in world of industrialization (Volesky, 2007).
- Acid mines drainage (AMD).
- Waste solutions of industry of electroplating.
- Coal-based power production.
- Generation of Nuclear power.
Almost three types heavy metals are concerning, such as poisonous metals ( Pb, Cr, Hg, Zn, Ni, Cu. Co, Sn, Cd etc.), radionuclides ( U, Ra, Th, Am, etc.), precious metals (such as Pt, Pd, Au, Ag, Ru etc.) (Monitoring, 2002).
Table 3 Common industrial units releasing heavy metals into water sources.
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Biosorption is defined a passive uptake of metal by means of certain bio-sorbents, that might be not living (Holan and Volesky, 1994). During recent years, studies on the biosorption mechanisms have become intensified by using biomass to isolate heavy metals by effluents of industries and for recovering valuable metal ions from treating solution (Davis et al., 2003). Foremost adventages of sorption rather than other methods included high efficiency, less cost, minimum production of chemical & biological sludge, probability of metal recovery and biosorbent’s regeneration. This cost advantage of the biosorption technology can facilitate the extensive application and acceptance by heavy metal generating as well as polluting industries (Sud et al., 2008).
A material that has the ability for adsorbing the other materials is recognized as bio-sorbent. Bio-sorbent is material of organic origin that may adsorb certain substances specially pollutant. These products of biological basis have major interest of scientists of environment for eco-friendly cleaning. Chromatography, Adsorption and ion-exchange are procedures of sorption during these methods transferring of some adsorbates occured from one phase to other. Robust bio-sorbents behavior of specific microorganisms for metal ions related to chemical making up of microbial cells. Dead as well as metabolically inactive cells are included in this type of biosorbents (Friis and Myers‐Keith, 1986).
Various laboratories used simply present biomass while some insulated particular microorganisms strains and others processing existing raw formed biomass to a specific extent. Recent experiments on sorption focus their devotion toward wastes materials that are byproducts or wastes of industrial operations of large scale. For example wastes mycelia accessible by process of fermentation, solid residues and oil mills (Pagnanelli et al., 2000), activated slurry disposed by plants of sewage treatments (Zouboulis et al., 1997), bio solids (Norton et al., 2004) and aquaous macro-phytes (Keskinkan et al., 2004).
Other economical biomass source is seaweeds including various kinds of marine algae which are available in oceans in copious amounts. Although, mostly contributions that study the toxic metals uptake by means of living marine algae and smaller degree of freshwater algae had focus metal accumulation, toxicological features as well as indicators of pollution through metabolic active biomass. Mostly natural material of cellulosic type are recommended as bio-sorbents, The sorption is a complex mechanism, generally ionic exchange, sorption by means of physical interactions, chelation and frameing-up in capillaries as well as space of polysaccharide structural networks due to the concentrations gradient & diffusion by cell walls as well as membrane (Argun et al., 2005; Bayramoğlu and Arica, 2008). Numerous chemical groups which could draw and isolate the metal ions in the biomass such as chitin acetamide group, amino & phosphate groups of nucleic acids, structural polysaccharides of fungal species amide, carboxyl & sulfhydryl groups of proteins, hydroxyls in polysaccharide, Phaeophyta, Chlorophyta and Rhodophyta (Chu et al., 2004; Caramalău et al., 2009).
The first main challenge for biosorption process was choosing of more auspicious type of biomass or bio-sorbent from extremely obtainable and low-cost biomaterials. Although numerous materials having biological foundation bind heavy metals biomaterials with adequately great metal binding capability or discernment for heavy metals is suitable for full scale sorption procedure. A large no. of biomass kinds have been scrutinized for their binding aptitude with metals in the presence of several conditions. Biomass may also be derivative of activated slurry as well as fermentation waste of food industries (Alluri et al., 2007).
Moreover, biomass of bacteria is frequently formed as the waste byproduct of industrial fermentation procedures or these might be deliberately grown-up in considerable amounts (Sag and Kutsal, 2001). Numerous species of bacteria e.g. (Pseudomonas, Bacillus, Streptomyces, Micrococus and Escherichia) have been verified for uptake of metal. Algae is recognized very auspicious bio-sorbents since they have noticeable sorption capability and these may be freely obtainable copiously in seas as well as oceans. Unfortunately, algae had been hardly utilizrd as bio-sorbent material rather than fungi and bacteria. From red algae, green algae and brown algae, brown algae has been establish of having improved sorption aptitude (Brinza et al., 2007).
Numerous low cost bio-sorbents, derived by agricultural wastes, industrial byproduct, natural materials, or adapted biopolymers, have newly settled and useful for removing the heavy metals from metals polluted water bodies. Using of activated carbon for treating the wastewaters is concerned with removal of organics (Gomez-Serrano et al., 1998). Discriminating adsorption by red mud (Gupta et al., 2010), photo catalyst beads (Idris et al., 2010), nano particles (Liu et al., 2008), fertilizer wastes of industries, biomass (Sharma, 2009), activated slurry of biomass (Wu et al., 2010), algae (Mane et al., 2011) etc. had produced growing eagerness. Industrialized byproducts like fly ash (Alinnor, 2007) and wastes iron or iron slags (Deliyanni et al., 2007) may be modified chemically to improve its elimination performance for metal removing from wastewaters.
Recent research focused on the application of agriculture based by-products as bio-sorbents for elimination of these metals from effluents of industries in biosorption process. Novel resources like hazelnut shell, peanut shells, rice husk, maize cob, jackfruit, rice straws and coconut shells etc. may be utilized as effective sorbent for uptake of heavy metals after conversion or chemical modifications by heating into biochar (Babel and Kurniawan, 2003; Bansode et al., 2003). According to them, the maximum removal of metal occurred by these biomasses is because of having cellulose, silica, lignin and carbohydrates in their adsorbents.
The research for novel techniques concerning toxic metals elimination from wastewater bodies focused devotion toward biosorption, on the base of metals binding abilities of several living materials. Biosorption is well-defined, the capability of biological materials of collecting heavy metals by wastewaters by physical or chemical processes (Mahvi, 2008). Algae, fungi, yeast as well as bacteria confirmed as potential biosorbent for metals (Volesky and Holan, 1995). Main benefits of biosorption as compared to other procedures included (Plazinski and Rudzinski, 2010)
- Cost effective;
- High efficacy;
- Minimum production of biological as well as chemical sludge;
- No requirement of additional nutrient ;
- Renewal of bio-sorbents;
- Probability of metals recovery.
Biosorption method comprises of a solid phase (biosorbent or biological material) as well as a liquid phase i.e. (solvent, usually water) having dissolved species for sorbtion (sorbates or metal ions). Because of higher efficiency of biosorbent for sorbate species, the biosorbent is bound & engrossed by meaning of diverse mechanisms. The process lasts till the equilibrium is achieved between amount of solids bounded sorbate portions that are residual in solutions (Tarley and Arruda, 2004; Igwe et al., 2008).
Faison et al. (1990) investigated that Micrococcus luteus resting cells exhibited more probability to remove strontium ions from aquatic media. Sorption process was considered employing various parameters included time of contact, pH, Initial metals concentration, biomass dose and temperature as well. Optimum pH was considered 7 at which maximum uptake of strontium took place. Loading of about 25 mg of Strontium per gram dry weight of cells was attained by exposing the cells to the solution comprising 50 ppm of Strontium. Binding of strontium happened in absence of nutrient and not need of metabolical activity. Initially, bonding was rather quick (less than 0.5 h), while a deliberate and impulsive discharge of Strontium is perceived. Strontium binding was repressed in existence of polyvalent cations and no with monovalent cations. Strontium was bounded favorably rather other tested cations. Strontium binding action was restricted onto cell envelope which was sensitive to several chemical as well as physical pretreatments. Bound Strontium was evacuated by divalent ions and by protons. Additional monovalent ion was found less operative. Bounded strontium was also detached by numerous chelating agents. It is concluded that binding of strontium by M. luteus is a flexible equilibrium process. Both ion exchange arbitrated by components of acidic cell surfaces or intracellular approval might be elaborate in that activity.
Chen (1997) stated that strontium ions can be adsorbed by powder of root tissues of plant of Amaranthus spinosus which is commonly present weed in the fields. Due to the easily availability and comparatively inexpensive nature of plants, their use as a suitable biosorbents appear to be valuable. A paper stated the opportunity of use of tomato and tobacco roots tissues as appropriate biosorbent for dissolving the strontium (Scott, 1992). Adsorption isotherm was probably fitted to Langmuir and Freundlich model along with maximum sorption capability of being 12.89 mg/g through the Langmuir model of isotherm. The supreme adsorption aptitude of biosorbent decreased by rising of temperature, while pretreatment with alkali material improved the adsorption ability of about 1.9 folds. The alginate beads of gel having 1 mm diameter comprising the powders of root tissues were formed and filled in column for constant sorption and desorption of Strontium from aqueous solutions. Effectual desorption of Strontium might be approved with calcium chloride of about 0.1 M in order to form the concentrated strontium solution by 94% recovery. According to previous investigations, heavy metals have tendency to bind with cellulosic material (Bryant et al., 1992).
Shaukat et al. (2005) worked on Pakistani coal powder in order to eliminate the strontium ions from aquatic media. They studied sorption process by scrutinizing pH, shaking times, amount of adsorbent and Sr2+ ions concentration. Samples of coal were collected from Sangardh District of Province Sindh, Pakistan. Conditions for maximum sorption of strontium have been recognized. Results disclose the diffusion of sr2+ ions into pores of powder happens during process of adsorption and kinetics of process is controlled by the intra-particle diffusion. They employed adsorption measurements through batch method at room temperature (24±1 ). Optimum speed of rotation was found to be 100 rpm. Langmuir as well as D-R equations of adsorption are effective over the complete range of calculated concentration. The impact of numerous anions on adsorption behavior of strontium ions was considered. The influence of the several anions including acetate, hypophosphate, phosphate, thiosulphate, nitrite, chloride and EDTA on sorption of strontium ions was examined below optimal conditions. On the basis of results, it is determined that the sorption of strontium onto Pakistani coal powders follows the Langmuir as well as the Dubinin-Raduskevich isothermal equations under investigated concentration ranges. Maximum sorption take place at pH of 11. Equilibrium is achieved during 60 minutes. Adsorption energy to sorb the strontium onto coal is calculated as 9.63 kJ/mol.
Chakraborty et al. (2007) used Ocimum basilicum mucilaginous seeds in order to uptake the strontium-90. Results displayed the dependent of metal uptake on structural veracity of mucilage fibrils. The water swallowed seeds exhibited advanced sorption of strontium-90 in contrast to seeds pretreated with sodium hydroxide, hydro chloric acid and sodium period ate solutions. The uptake is depending on pH while several divalent ions had slight harmful effect. The alkali metal’s ions Li+, K+ and Na+ reduced the uptake. The maximum sorption capability was found to be 247 mg strontium per g of dry mass of seed. These seeds are cheap and easily obtainable in countries like India. While using as biosorbant O. basilicum seeds deliberated the benefits in terms of their capability to adsorb strontium-90 providing a normal organized bases, which was considered a main cost issue in this process (Fahn and Werker, 1972; Ryding, 1992) The carboxylic group and lone pairs of electron existing on the oxygen may elaborate in the strontium binding. The existence of numerous of these groups of mucilage polysaccharides can be facilitated for biosorption of strontium ions. Protons concentration has strong effect in uptake of strontium with maximum at pH of about 7. Increase in uptake may be because decreasing of protons concentration that facilitates 90Sr binding by COOH, or with lone pairs present on oxygen in mucilage polysaccharide. Biosorption studies for cadmium employing O. basilicum seeds exhibited an opposite correlation (Melo and D’souza, 2004).
Dabbagh et al. (2007) studied the capability of living cells of Oscillatoria homogenea to isolated the stable strontium as well as 90Sr from aqueous medium. Ramsar was selected as great level natural area of radiation in order to isolate the cyanobacteria (Ghiassi-Nejad et al., 2002). On basis of these filamentous cells bio-volume, the removal was estimated as 43.79 n M.ml and 3129.49 m Bq.ml during incubation time of 240 hours. The optimal pH to adsorb the strontium is calculated as 9±0.3. The growing bio-volume of blue green algae uplifts the sorption process. Liquid culture, comprising 21.2 mm3.ml–1 of filament cells as well as 1000 nM.ml–1 initial conc. of strontium and the extreme removal of strontium was estimated as 455.34 nM.ml (mm3)–1. At 1200 illumination, the great elimination value was estimated as 58.62 nM.ml (mm3)–1 having initial conc. of strontium 6590 nM.ml-1 and of removal 235.40 nM.ml (mm3)–1 was detected. Langmuir isothermal model probably explains the data of experiment. Results displayed that O. homogenea filament of the blue green algae has great tendency for sorption of 90Sr. The separated cyanobacterium might be cultured into water bodies which are polluted with radioactive strontium. Cyanobacteria are usually present in water bodies having pH values above of 8. Moreover, activity of photosynthesis causes the depletion of dissolving CO2 in pool that results in the increase of pH value. Hence, O.homogenea may accumulate substantial amount of 90Sr into natural environment of water. It might be probable to remove the radionuclides from the wastewater bodies of nuclear facilities. (Chegrouche et al., 2009)
Pan et al. (2009) investigated characteristics of strontium sorption employing fungus Aspergillus terreus as biosorbent. The adsorption behavior studied functions of numerous parameters including pH, primary concentration of metal, time of contact and temperature. Fungus A. terreus displayed the chief strontium uptake capability at 15°C of temperature employing initial Sr2+ ions concentration of about 876 mg L-1 and initial value of pH is 9. Biosorption aptitude improved from 219mg g-1 to 308 mg g−1 by decreasing temperature values by 45°C to 15°C. The equilibrium data probably fitted to Langmuir model of adsorption within concentration ranges of Sr2+ ions at all examined temperatures. The probability of the first as well as second order dynamical equations for the sorption of strontium ions by fungus A. terreus were deliberated. Estimation of concerned experiment data regarding biosorption dynamics exhibited that sorption of Sr2+ by fungus was monitored by the pseudo second order dynamics in a better way. The estimated parameters of thermodynamics such as Δ G °, Δ H ° and Δ S ° indicated the spontaneous, feasible and exothermic nature of adsorption of Sr2+ ions at temperature ranges values between 15 to 45°C. Batch system was utilized in order to investigate the capabilities of fungus A. terreus. It is observed that pH level, temperature, time, and initial metal ion concentrations greatly influence the biosorption capability of sorbent. The maximum strontium sorption yield is attained at pH of 9. Biosorption aptitude increased as conc. of metal ion is increased and temperature is decreased.
Chegrouche et al. (2009) stated the sorption of Sr2+ ions from aquatic medium on activate carbon. Numerous factors including pH, particle size, initial conc. of strontium and temperature were also measured. Optimum conditions attained in order to adsorb the strontium were pH value of 4.0, particle size of 270 μm and 293.15 K temperature employing 100mg g-1 of initial metal concentration although equilibrium was achieved within 8 hours. Strontium (II) adsorption by activated carbon monitors the pseudo first-order and activation energies E a was found as 3.042 kJ/mol which is calculated by means of Arrehenius equation. Adsorption isotherms were probably fitted to the Langmuir kinetic model along with supreme uptake capacity Qo of 5.07×10–4 mol/g at temperature of about 293.16 K. A non-dimensional factor of separation RL is utilized for evaluation the satisfactory sorption. The values of mass transfer coefficient β L (cm/s) at dissimilar temperatures specified that the mass transfer velocity of strontium ions by activated carbon is a slow process. The mechanism of intra-particle diffusion is of vital importance to determine the inclusive ratio of removal. According to the negative entropy Δ S# value of about 145.13 kJ/mol, there is no noteworthy change in internal structure of this biosorbent during strontium adsorption. The values of Gibbs free energy Δ G ads ranges between –36.61 kJ/mol and –41.75 kJ/mol at temperature of 293.15 to 333.15 K, which illustrates the properties of physical adsorption of activated carbon as well as specify the validity and probability of that procedure (Humelnicu et al., 2006; Mellah et al., 2006).
Ji et al. (2010) considered the sorption as well as subsequent desorption of Sr+2 ions from aqueous medium onto cells of fodder yeast of magnetically modified (Kluyveromyces fragilis). Results exposed that adsorption of strontium is improved by enhancing the initial conc. of metal, reaching plateau at around about of 80mgl-1 at 20 °C temperature and pH of 7. The biosorption of strontium increased by increasing the pH as well. The process of biosorption is slightly affected by changes in temperature also. The value of sorption were 19.5 mgg-1 on 10mg/L and 40 mg/L solution of strontium respectively at pH higher than 4 after 20 min time of incubation. Equilibrium was attained after 20 minutes. Langmuir model of isotherm was properly fitted in order to explain the experiment data. Under optimized conditions, maximum uptake of metal was estimated to be 140mgg-1. About 0.1 mol/L of nitric acid can desorbed the 80% of adsorbed strontium. By using the permanent magnet, magnetic modification of yeast cells made their removal easy from suspensions. The results indicated that fodder yeast show super-paramegntic behavior as the particles exhibited properties of magnetism by placing in magnetic field (Safarik et al., 2007).
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