One of the most important chemical contaminants of concern is chromium (Cr), which exists in a series of oxidation states from -2 to +6 valence; the most important stable states are 0 (element metal), +3 (trivalent) and +6 (hexavalent). Cr3+ and Cr6+ are released to the environment primary from stationary point sources resulting from human activities. Contamination of groundwater by Cr at numerous localities primarily resulted from uncontrolled or accidental release of Cr-bearing solutions, used in various industrial applications (metallurgical, chemical, leather tanning, wood processing, textile and refractory), into the subsurface environment. Cr in such solutions mostly occurs as oxyacids and oxyanions of Cr6+ (Mukhopadhyay et al. 2007; Xu and Zhao 2007). It is this oxidation state in which Cr is highly soluble, mobile and toxic.
Cr3+ is an essential dietary mineral in low doses: it is required to potentiate insulin and for normal glucose metabolism. Biocidal properties of chromium salts to aquatic organisms are modified, sometimes by an order of magnitude or more, by a variety of biological and abiotic factors. These include the species, age, and developmental stage of the organism; the temperature, pH, salinity, and alkalinity of the medium; interaction effects of Cr with other contaminants; duration of exposure; and chemical form of Cr tested. For hexavalent chromium, LC50 (96 h) values for sensitive freshwater and marine species were between 445 and 2,000 mg/L. The LC50 value is the concentration of a material in air that will kill 50% of the test subjects (animals, typically mice or rats) when administered as a single exposure. Also called the median lethal concentration and lethal concentration 50, the LC50 value gives an indication of the relative acute toxicity of an inhalable material. For trivalent chromium, LC50 (96 h) concentrations were 2,000-3,200 mg/L for sensitive freshwater organisms and 3,300-7,500 mg/Lfor marine biota. Among warm-blooded organisms, hexavalent chromium was fatal to dogs in 3 months at 100 mg/L in their food and killed most mammalian experimental animals at injected doses of 1-5 mg Cr/kg body weight, but had no measurable effect on chickens at dietary levels of 100 mg/L over a 32-day period. Trivalent chromium compounds were generally less toxic than hexavalent chromium compounds, but significant differences may occur in uptake of anionic and cationic Cr3+ species, and this difference may affect survival.
Acute and chronic adverse effects of chromium to warm-blooded organisms are caused mainly by Cr6+ compounds; there is little conclusive evidence of toxic effects caused by Cr2+ or Cr3+ compounds (Langard and Norseth 1979). Most investigators agree that chromium in biological materials is probably always in the trivalent state, that greatest exposures of Cr3+ in the general human population are through the diet (but no adverse effects have been reported from such exposures), and that no organic trivalent chromium complexes of toxicological importance have been described. Studies with guinea pigs fed Cr3+ for 21 weeks at concentrations up to 50 mg/L dietary Cr3+ showed no adverse effects. Domestic cats were apparently unaffected after exposure to aerosol levels of 80-115 mg Cr3+ /m3 for 1 h daily for 4 months, or after consuming diets with high amounts of chromic (Cr3+) salts over a similar period (Langard and Norseth 1979).
Under laboratory conditions, chromium is mutagenic, carcinogenic, and terato-genic to a wide variety of organisms, and Cr6+ has the greatest biological activity. However, information is lacking on the biological activities of water soluble Cr3+ compounds, organochromium compounds, and their ionic states. Aquatic plants and marine polychaete worms appear to be the most sensitive groups tested. In exposures to Cr6+, growth of algae was inhibited at 10.0 mg/L, and reproduction of worms at 12.5 mg/L. At higher concentrations, Cr)+ is associated with abnormal enzyme activities, altered blood chemistry, lowered resistance to pathogenic organisms, behavioural modifications, disrupted feeding, histopathology, osmoregulatory upset, alterations in population structure and species diversity indices, and inhibition of photosynthesis. Not all sublethal effects observed were permanent, but the potential for acclimatization of organisms to Cr is not well documented. The great variability among species and tissues in the accumulation or concentration of Cr is attributed partly to the route of administration, partly to the concentration of Cr and its chemical species, and partly to numerous biotic and physicochemical modifiers. High accumulations of Cr have been recorded among organisms from the lower trophic levels, but there is little evidence of biomagnification through food chains. Marine bivalve molluscs, for example, accumulated measurable concentrations at ambient water concentrations of 5.0 mg/L of Cr6+, but the significance of Cr residues in molluscs and other organisms is not well understood.
Chromium is causally associated with mutations and malignancy (Leonard and Lauwerys 1980; Norseth 1981) . Under appropriate conditions, Cr is a human and animal carcinogenic agent; its biological effects depend on chemical form, solubility, and valence. In general, Cr6+ compounds are hazardous to animals, whereas metallic Cr and Cr3+ are essentially nontoxic (Gale 1978); however, exposure to water solubi-lized Cr3+ has caused cancers and dermatitis in workers, and toxicity in rabbits (Hatherill 1981). In the chromate producing industry workers who developed respiratory cancer had been exposed to 30-1,100 mg/m3 Cr in air for periods of 4-24 years, and workers producing chromate pigment who developed respiratory cancer had been subjected to an estimated Cr6+ exposure of500-1,500 mg/m3 for 6-9 years. Carcinogens released in the chromate manufacturing process have not yet been identified (Post and Campbell 1980). Levels as low as 10 mg/m3 of Cr6+ in air produced strong irritation in nasal membranes, even after short exposures. In some persons whose lower respiratory tissues became Cr-sensitized, asthmatic attacks occurred at levels of Cr6+ as low as 2.5 mg/m3 (Steven et al. 1976). There is no evidence of Cr sensitization in mammals other than humans. In the only animal study demonstrating a carcinogenic effect of an inhaled chromate, adenocarcinomas were reported in the bronchial tree of mice exposed throughout life to CaCrO. dust at 13 mg/m (4,330 mg Cr6+/m3) for 35 h weekly (Langard and Norseth 1979). Trivalent Cr compounds did not produce respiratory cancers (Steven et al. 1976) . In rabbits, both Cr3+ and Cr6+. given 1.7 mg/kg body weight daily for 6 weeks, adversely affected blood and serum chemistry, and both produced significant morphological changes in liver (Tandon et al. 1978); similar results were observed in rats (Laj et al. 1984). Although damage effects and residue accumulations were greater in rabbits treated with Cr6+, water soluble Cr3+ compounds also may have significant biological activity (Tandon et al. 1978).
Hexavalent chromium is present in the effluents produced during the electroplating, leather tanning, cement, mining, dyeing and fertilizer and photography industries and causes severe environmental and public health problems (Demirbas et al. 2004). Its concentrations in industrial wastewaters range from 0.5 to 270 mg/L and the tolerance limit for Cr6+ for discharge into inland surface waters is 0.1 mg/L and in potable water is 0.05 mg/L (EPA 1990). In order to comply with this limit, it is essential that industries treat their effluents to reduce the Cr6+ to acceptable levels. Cr6+ is frequently used in plating process that can discharge wastewater with a concentration as high as 100 g Cr/L. At present the frequently used technology for treating wastewater that contains Cr6 + is to chemically reduce Cr6 + to Cr3+ with NaHSO3, Fe2+ compounds, SO2,and others, followed by pH adjustment with hydroxides of alkaline or alkaline earth metal to pH 10-12 to form Cr(OH)3 suspended particulates. The particulates are subsequently agglomerated and precipitated with introduced agglomerating chemicals. The main shortcomings of this technology are the requirement of a lot of costly chemicals and the generation of vast sludge to be disposed of.
A potential alternative to remove heavy metals from wastewater is to use naturally-occurring humic substances as sorbent due to their richness in organic functional groups such as carboxylic acid, and others. Chromium can be removed from water with both aquatic plants and dead biomasses, or humic substances. Vegetable-based waste materials have been used as natural adsorbent for Cr6+: coirpith (Sumathi et al. 2005) , sawdust (Acar and Malkoc 2004) , rice husk and rice husk carbon (Bishnoi et al. 2004) , hazelnut shell carbon (Kobya 2004) and debris of aquatic plants (Hu et al. 2003). Batch tests on gravel, compost, sterilized compost and mixture of gravel + compost formerly carried out by the authors proved that the gravel contribution to the Cr6+ removal is quite negligible. Besides, the removal observed was predominantly due to the biomass activity, which converted Cr6+ into Cr3+ under a stable form, such as Cr(OH)3. The Freundlich isotherm has been particularly used to model the data of chromium sorption by the kitchen waste compost. It results in the following "K" values: 0.261 g Cr3+/kg and 0.105 g Cr6+/kg. The "n" is 1.56 in the Cr3+ sorption and 1.35 in the Cr6+ sorption. The "K" values indicate that the capacity of kitchen waste compost for sorbing Cr3+ is greater than that for sorbing Cr6+. Both "n" values in this study are greater than unity, therefore sorption of Cr3+ and Cr6+is favorable. In addition, the sorption affinities to Cr3+ and to Cr6+ are similar. X-ray absorption near-edge structure spectroscopic simulation has indicated that the Cr species distribution is estimated to be about: 54.1-61.0% Cr)(OH)2 (OOCCH3)7 + 39.0-45.9% Cr(NO3)3 in all compost samples sorbing Cr from Cr)+ solutions; and 54.5-69.0% Cr)(OH)2(OOCCH3)7 + 18.0-24.9% Cr(OH)3 + 6.1-28.5% CrO3 in the samples from Cr6+solutions. No Cr(OH)3 is expected in the Cr(NO3)3-sorbing compost samples due to the low solution pH. In contrast, the solution pH after the CrO3-sorption experiments is always greater than 5.9, that confirms the formation of Cr(OH)3 precipitate on the compost after the chemical reduction of Cr6+ to Cr3+ by the compost.
As a corollary, compost derived from cellulosic materials or kitchen wastes is effective as a biosorbent in removing Cr from water (Wei et al. 2005). Over the past years, various materials have been used by several researchers to remove chromium and results have been also very encouraging. The trend has now been set for adsorption of Cr using low cost biometarials. Table 10.5 summarizes the use, testing and removal performance of some biomaterials and biosorbents for the removal of chromium species from chromium-laden waters.
Copper, one of the most widely used heavy metals, is mainly employed in electrical and electroplating industries, and in larger amounts is extremely toxic to living organisms. The presence of copper (II) ions cause serious toxicological concerns, it is usually known to deposit in brain, skin, liver, pancreas and myocardium
Table 10.5 Biosorbents used for chromium removal from Cr-laden aqueous media
Green algae spirogyra species
Neurospora crassa fungal biomass
Composite chitosan biosorbent prepared by coating chitosan, a glucosamine biopolymer, onto ceramic alumina Mucilaginous seeds of Ocimum basilicum
Sargassum sp. algae
Palm flower (Borassus aethiopum)
Maximum removal of Cr6+ was around
14.7 x 103 mg metal/kg of dry weight biomass at a pH of 2.0 in 120 min with 5 mg/L of initial concentration Biosorption capacity of acetic acid pretreated biomass was found to be 15.85 ± 0.94 mg/g biomass under optimum conditions. The adsorption constants were found from the Freundlich isotherm model at 25°C. The biosorbent was regenerated using 10 mM NaOH solution with up to 95% recovery and reused five times in biosorption-desorption cycles successively Experimental equilibrium data to Langmuir and Freundlich adsorption isotherms and ultimate capacity obtained from the Langmuir model was 153.85 mg Cr6+/g chitosan
Seeds boiled in water were found to be superior in terms of mechanical stability and exhibited fairly optimal Cr6+ uptake kinetics. Maximum adsorption capacity from Langmuir isotherm was 205 mg Cr/g dry seeds
Freundlich isotherm was found to represent the measured sorption data well. Fourier transform infrared spectrometry showed that the hydroxyl group was the chromium-binding site within pH range (pH 1-5) where chromium does not precipitate. Results indicated that the biomass of E. Crassipes is suitable for development of efficient biosorbent for the removal of chromium from wastewater of chemical and allied process industries
Capacity of removal obtained at optimum conditions was 19.06 mg of metal/g biosorbent
For Cr3+, maximum adsorption capacity was
6.24 mg/g by raw adsorbent and 1.41 mg/g by acid treated adsorbent. For Cr6+, raw adsorbent exhibited a maximum adsorption capacity of 4.9 mg/g, whereas the maximum adsorption capacity for acid treated adsorbent was 7.13 mg/g. There was a significant difference in the concentrations of Cr6+ and total chromium removed by palm flower
Tunali et al.
Melo and D'Souza (2004)
Mohanty et al. (2006)
Vieira et al. (2008)
Elangovan et al. (2008)
Table 10.5 (continued)
Shells of Walnut (WNS) (Juglans regia), Hazelnut (HNS) (Corylus avellana) and Almond (AS) (Prunus dulcis) Cassia fistula biomass
Crushed eggshells possess relatively high sorption Chojnacka (2005) capacity, when comparing with other sorbents that was evaluated as 21-160 mg/g. Eggshells were able to remove the concentration of Cr3+ ions below the acceptable level, i.e. at 40°C, at the initial concentration of metal ions 100 mg/ kg, at sorbent concentration 15 g/L
Langmuir isotherm with maximum Cr6+ion Pehlivan and sorption capacities of 8.01, 8.28, and 3.40 mg Altun (2008) g-1 for WNS, HNS and AS, respectively. Percentage removal by WNS, HNS and AS was 85.32%, 88.46% and 55.00%, respectively at a concentration of 0.5 mmol/L
Adsorption capacity of biomass for Cr3+and Abbas et al. (2008)
Cr6+was found to be significantly improved by the treatments of gluteraldehyde (95.41 and 96.21 mg/g) and benzene (85.71 and 90.81 mg/g) respectively
Biosorption was found to be a quick process. The Chojnacka (2006) equilibrium was reached within 10-20 min. Biosorption capacity of the studied sorbents was intermediate when compared with other sorbents of plant origin ca. 20 mg Cr3+/g, but since these materials are commonly abundant and of minimal cost, it is possible to improve wastewater treatment efficiency by increasing the concentration of the sorbent
Brown seaweed (Turbinaria spp) was pre-treated Aravindhan et al. with sulfuric acid, calcium chloride and (2004)
magnesium chloride and tested for its ability to remove chromium from tannery wastewater. urbinaria weed exhibited maximum uptake of about 31 mg of chromium for one gram of seaweed at an initial concentration of 1,000 mg/L of chromium. Freundlich and Langmuir adsorption isotherm models were used to describe the biosorption of Cr3+ by Turbinaria spp.
Maximum adsorption was observed in the acidic Garg et al. (2007) medium at pH 2 with a contact time of 60 min at 250 rpm stirring speed. Jatropha oil cake had better adsorption capacity than sugarcane bagasse and maize corn cob under identical experimental conditions. The results showed that studied adsorbents can be an attractive low cost alternative for the treatment of wastewaters in batched or stirred mode reactors containing lower concentrations of chromium
Turbinaria ornata seaweed
Sugarcane bagasse, maize corn cob and Jatropha oil cake
Helianthus annuus (sunflower) stem waste pre-consumer processing agricultural waste: Rice husk
Low cost activated carbon (ATFAC) was prepared from coconut shell fibers (an agricultural waste)+A commercially available activated carbon fabric cloth (ACF) (control) Japanese cedar (Cryptomeria japonica) bark
Natural biosorbents tested: Natural sediment, chitin chitosan,
Aspergillus flavus I-V, Aspergillus fumigatus I—ll, Helmintosporium sp, Cladosporium sp, Mucor rouxii mutant, M. rouxii IM—80, Mucor sp-I and 2, Candida albicans and Cryptococcus neoformans
Maximum metal removal was observed at pH 2.0. Jain et al. (2009) The efficiencies of boiled sunflower stem absorbent and formaldehyde-treated sunflower stem absorbent for the removal of Cr6+ were 81.7% and 76.5%, respectively for dilute solutions at 4.0 g/L adsorbent dose Maximum metal removal was observed at pH 2.0. Bansal et al. The efficiencies of boiled and formaldehyde (2009)
treated rice husk for Cr6+ removal were 71.0% and 76.5% respectively for dilute solutions at 20 g/L adsorbent dose. The experimental data fitted with Freundlich and Dubinin-Radushkevich isotherm models The maximum adsorption capacities of ATFAC Mohan et al. and ACF at 25°C are 12.2 and 39.56 mg/g, (2006)
respectively. Cr3+ adsorption increased with an increase in temperature (10°C: ATFAC— 10.97 mg/g, ACF—36.05 mg/g; 40°C: ATFAC—16.10 mg/g, ACF—40.29 mg/g). sorption capacity of activated carbon (ATFAC) and activated carbon fabric cloth is comparable to many other adsorbents/carbons/biosorbents utilized for the removal of trivalent chromium from water/wastewater The equilibrium data at different temperatures fit Aoyama et al. well in the Langmuir isotherm model. The (2004)
endothermic nature of the adsorption was confirmed by the positive value of enthalpy change (18.9 kJ/mo1). The positive value of entropy change (65.2 J/mol.K) suggested the increased randomness at the solid-solution interface during the adsorption. The studies showed that Japanese cedar bark can be used as a cost-effective adsorbent for the removal of Cr6+ from wastewater C. neoformans, natural sediment, Ismael Acosta
Helmintosporium sp and chitosan was more et al. (2004)
efficient to remove Cr6+ achieving the following percentage of removals: 98%, 98% and 63%, respectively.
(Davis et al. 2000). Copper toxicity is a much overlooked contributor to many health problems; including anorexia, fatigue, premenstrual syndrome, depression, anxiety, migraine headaches, allergies, childhood hyperactivity and learning disorders. The involvement of copper toxicity and bio-unavailability in such a wide range of health conditions may seem unusual.
Copper is an essential nutrient in humans, and has not been shown to be carcinogenic in animals or humans. However, young children, and infants in particular, appear to be especially susceptible to the effects of excess copper. Case reports have attributed adverse effects (diarrhea and weight loss) in infants to rather low levels of copper in drinking water, estimated as 0.22-1.0 mg/L or 1.0-6.5 mg Cu/L. High levels of copper in tap water in homes with copper plumbing have been linked to childhood cirrhosis in Germany. In other studies, consumption by adults of drinking water containing > 3 mg/L ionized copper was associated with a significant increase in nausea, abdominal pain or vomiting.
Copper is a component of many naturally occurring minerals and is extensively used in industry and household products. Copper is also found in surface water, groundwater, seawater and drinking water. Surface water concentrations of copper range from 0.5 to 1,000 mg/L. Most of the copper tends to be bound to sediments. Urban runoff often contains elevated concentrations of copper due to household and industrial uses of water. Sewage is also a major source of copper input to rivers and streams, although some is removed in treatment plants because of its sediment binding properties. Copper in surface water is a well-known environmental hazard, associated with toxicity to a variety of aquatic organisms. The concentration of copper in drinking water can vary widely, depending on variations in acidity/alkalinity (pH), mineral content (hardness), and copper availability in the distribution system. Results from studies in the U.S., Europe and Canada indicate that copper levels in drinking water can range from < 0.005 to > 30 mg/L, with the corrosion of copper pipes serving as the most frequent cause of copper contamination.
Input of copper into aquatic ecosystems increased sharply during the past century and includes inputs from waste discharges into saline waters, industrial discharges into freshwater, and leaching of antifouling marine paints and wood preservatives. Many industries include copper in their processes and discharge it in wastewater streams. These industries include tanning, mining, metal processing and finishing, electroplating, the automobile industry, and the pharmaceutical industry to name a few. World production of copper amounts to 13 million tons a year, and is still rising. Present anthropogenic inputs of copper are two to five times higher than natural loadings; the atmosphere is a primary recipient of these inputs. In mining and industrial areas, precipitation of atmospheric fallout is a significant source of copper to the aquatic environment. In surface water copper can travel great distances and it strongly attaches to organic matter and minerals. It does not break down in the environment and thus accumulates in plants and animals. In copper-rich soil only a small number of plants can survive. This is why there is not much plant diversity near copper-disposing factories and it is a serious threat to farmlands. It negatively influences the activity of microorganisms and earthworms and thus seriously slows the decomposition of organic matter. Another important factor in decreasing the copper in industrial waste streams is the possibility of reclamation of copper. Waste stream concentrations can range up to several thousand mg/L for copper plating bath waste where the EPA's recommended limit is 1.3 mg/L. Industries already must lower their copper limits to meet their local legal guidelines and recycling the metal these companies are throwing away provides extra financial incentive for them to do so through continuous research and development in this direction.
Adsorption and biosorption technology have consequently both gained great concern in research over the last 15 years for the removal of copper (Cu2 +) ions from wastewaters. Stylianou et al. (2007) have studied the ability of natural zeolite (clinop-tilolite) and exfoliated vermiculite to remove copper from aqueous solutions in fixed bed column and batch reactors. The effect of agitation speed (0, 100, 200, 400 rpm), temperature (25°C, 45°C, 60°C), and particle size [2.5-5.0 mm, dust (< 0.25 mm)] and solution pH (1.00-4.00) on the removal of heavy metals was studied. Fixed bed experiments were conducted, using three different volumetric flow rates of 5-7-10BV (Bed Volumes)/h, under an initial normality of 0.01 N (317.7 mg/L), at initial pH of 4.00 and ambient temperature (25°C). Stylianou et al. (2007) found that vermiculite was more effective for the removal of copper in batch mode reactors under all the tested conditions, while the removal efficiency follows the order: vermiculite > clinop-tilolite dust > clinoptilolite 2.5-5.0 mm. Kaewsarn (2002) has reported the biomass of marine algae to have high uptake capacities for a number of heavy metal ions. Kaewsarn (2002) investigated the adsorption properties of a pre-treated biomass of marine algae Padina sp. for Cu2+. It was found that biosorption capacities were solution pH dependent and the maximum capacity obtained was 0.80 mmol/g at a solution pH of about 5. The biosorption kinetics was found to be fast, with 90% of adsorption within 15 min and equilibrium being reached at 30 min. The study of Kaewsarn (2002) demonstrated that the pre-treated biomass of Padina sp. could be used as an effective biosorbent for the treatment of Cu2+ containing wastewater streams. Later, Basci et al. (2004) studied the adsorption capacity of wheat shell for copper (II) at various pH (2-7), agitation speeds (50-250 rpm) and initial metal ion concentrations (10-250 mg/L). The maximum biosorption of copper onto wheat shell occurred at 240 rpm agitation speed and at pH between 5 and 6 and the biosorption values of Cu2+ were increased with increasing pH from 2 to 5 and decreased with increasing copper/ wheat shell ratios from 0.83 to 10.84 mg Cu2+/g wheat shell. Basci et al. (2004) concluded that wheat shell was a suitable biosorbent for removing Ctf + from aqueous solutions.
Recently, Vilar et al. (2008) have studied the biosorption of copper ions by an industrial algal waste, from agar extraction industry in a batch system. The latter biosorbent was compared with the algae Gelidium itself, which is the raw material for agar extraction, and the industrial waste immobilized with polyacrylonitrile (composite material). Earlier, Cho and Jian (1998) have investigated the adsorption of copper(II) in aqueous solutions by living mycelium pellets of Phanerochaete chrysosporium. The maximum copper adsorption capacity of the fungal mycelium estimated with the Langmuir model was 3.9 mmol Cu per gram of dry mycelium compared with 1.04 mmol Cu/g of a strong acidic ion-exchange resin. The living mycelium also showed a high affinity to copper in diluted solutions.
Table 10.6 presents a summary of the Cu2+ removal performance of some recently studied biosorbents and low cost waste materials. It is brought to the attention of the reader that Table 10.6 (and similar tables) is not exhaustive but an attempt for reasonably representative listing of the results of research studies for Cu2+ removal by biosorption.
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