The effective removal of heavy metals from wastewater is among the most important issue for many industrialized countries. In this regard, it has been studied that the powder coconut shell was a good biosorbent for the removal of cadmium. In this study, adsorption capacity of biomass was investigated. Kinetic and equilibrium studies, pH and the influence of metal ion concentration were evaluated in this study.[16]
It has been reported that Sugar beet pectin xerogels are the adequate materials for heavy metals recovery from effluents. Xerogels were used as a biosorbent for copper removal using fixed bed column. Feeding system, flow rate, metal concentration and feeding system have been evaluated in this study. The effect of saturation time, amount of adsorbed and treated metal, column performance and metal uptake were studied. Increasing bed height increased saturation time while decreased with increasing feed flow rate and metal concentration. Desorption of copper was carried out using 0.1 M nitric acid.[17]
The biosorption of Cu (×€×€) onto chestnut shell in a batch absorbed has been. Equilibrium isotherms, kinetic data and thermodynamic parameters have been evaluated. Langmuir isotherm and Relich-Peterson isotherm models describes the equilibrium data. At 293 K, adsorption capacity was found to be 12.56 mg/g and the kinetic data follows the pseudo second order model. Gibbs free energy was spontaneous for all interactions and adsorption process exhibited exothermic enthalpy values. It has been shown that chestnut shell was a good biosorbent for Cu (°) removal from aqueous solution.[18]
Comprehensive characterization of parameters indicate that Husk of Bengal gram was an excellent material for biosorption of Cr (ιν) to treat wastewater containing low concentration of metals. In 10 mg/l chromium solution, 99.9% removal has been observed. Optimum pH was 2 and agitation speed was 120 rpm. Adsorption isotherm fitted well with Langmuir and Freundlich models. For Langmuir isotherm calculated adsorption capacity was 91.64 mg Cr (ιν)/g at pH 2 and Fourier Transform infrared Spectroscopy (FTIR) suggested that presence of Cr (ιν) ions affects the bands corresponding to hydroxyl and carboxyl groups.[19]
It has been reported that coconut husk and Rice straw were found to be able to remove significant amount of Cr (ІІІ) ions from aqueous solutions. Its removal is a function of pH and concentration. Optimum pH take is between 4 and 6 for both substrates. The adsorption capacity was found to be 0.55 millimole Cr (°ι)/g for coconut husk and 0.30 millimole Cr (°ι)/g for rice straw. Adsorption kinetics showed that removal process follows first order kinetics.[20]
The biosorption of Cr (°ι) and Cr (vι) using pretreated Roza gruss an teptlitz (red rose) waste biomass was performed. Cr (ι×€×€) and Cr (vι) sorption was found dependent on solution pH, biosorbent dose, biosorbent particles, size, shaking speed, initial concentration of metal ions, temperature and contact time. Kinetic and equilibrium studies were also done. Uptake capacity of biosorbent was affected by pretreatment and it also related to oxidation state of chromium. Cr (°ι) showed best correlation with Langmuir isotherm and Cr (vι) with Freundlich isotherm. Kinetic study follows pseudo second order. Results confirmed that Roza gruss is a potential biosorbent for the removal of Cr (°ι) and Cr (vι) with biosorption capacity of 45.03 mg/g and 48.75 mg/g respectively.[21]
The biosorption characteristics of Cd (°) and Cr (°ι) ions from aqueous solution using the moss (Hylocomium splenders) biomass were investigated in terms of equilibrium, kinetics and thermodynamics. They determined the biosorption conditions as a function of pH, biomass dosage, contact time and temperature. Biosorption isotherms were described by Langmuir, Freundlich and Dubinin-Rsdushkevich D-R models. The maximum biosorption capacity was 32.5 mg/g for Cd (°) ion and 42.1 mg/g for Cr (°) ion. Also thermodynamic parameters, ∆G°, ∆H° and ∆S° were calculated and kinetic study showed that biosorption process followed pseudo second order.[22]
The use of root tissues of two common weeds, Amaranthus spinosis and Solanum nigrum as a biosorbent for the biosorption of copper from aqueous solution has been reported. The continuous adsorption/desorption cycles using packed bed column was studied. The equilibrium level was dependent on pH. Adsorption capacity was decreased with increasing temperature and pH. Adsorption was represented by Langmuir and Freundlich isotherms. This treatment is useful for treating wastewater containing traces of copper.[23]
It has been evaluated that the biomass of nonliving green algae (Cladophora albida) was useful for the removal of Cr (ιν) from wastewater. The influence of pH, algal dosage, initial Cr (ιv) concentration, temperature and co- existing anions on removal efficiencies of C. albida biomass. Optimum pH was chosen in the range of 1.0-3.0 and by the variation of pH removal process was influenced. 2 g/L of the algal dose was used and in the first 60 min the rate of removal of copper was fast but after that it was decreased gradually. In the removal of copper, bioreduction and biosorption processes involved.[24]
Removal of cadmium, lead and nickel was investigated by using tea waste. Tea waste was found to be an efficient adsorbent for heavy metal removal from industrial wastewater. The analysis has performed by using different amounts of adsorbents in solution with 5 different concentration of each metal and in mixed combination. By using 0.5 g and 1.5 g adsorbent having 5 and 10 mg/L concentration Pb, 94 and 100% removal of lead was achieved. However, for 5 mg/L of nickel and cadmium solution using 1.5 g tea waste can treat nickel and cadmium with an efficiency of 85.7% and 77.2%. Similarly, for mixed solution of 5 mg/L with 0.5 g adsorbent, 3.5% and 13.2% decrease efficiency in lead and nickel was shown.[25]
Adsorption of hexavalent chromium from aqueous solution by Wheat Bran was evaluated. They investigate the chromium adsorption from aqueous solution. The influence of pH, time, adsorbent dosage and initial Cr concentration was determined. Adsorption isotherms and kinetic parameters were studied. Higher chromium adsorption was observed at lower pH and maximum chromium removal obtained at pH of 2. Kinetics of adsorption isotherm follows pseudo second order with rate constant value of 0.131 g/mg.min. Adsorption of chromium follows Langmuir isotherm with 0.997 correlation coefficient.[26]
The use of locally available fish (Labeo rohita) scales for the removal of Pb (°) from aqueous solutions was analyzed. Pb (°) sorption was found to be Ph, dose, initial metal concentration, contact time and shaking speed dependent while particle time independent. This study was designed to evaluate the effect of physical and chemical pretreatments on surface properties of scales by Fourier Transform infrared Spectroscopy (FTIR). This analysis shows that in Pb (°) biosorption, there was an involvement of amino, carboxylic, phosphate and carbonyl groups. Acidic pretreatments results in degeneration of functional groups whereas there was no effect of alkaline pretreatments. The adsorption isotherm fitted well with Freundlich isotherm.[27]
Barley straws showed potential as an adsorbent for removal of nickel from wastewater containing nickel sulphate generated by nickel plating industry. The present work deals with the biosorption of nickel by barley straws. The nickel biosorption isotherm fitted well with Langmuir isotherm. Nickel uptake at room temperature was very sensitive to solution pH showing better uptake value of nickel at pH of 4.85±0.10. When ionic strength was increased from 0.02-0.6 M, the uptake of nickel was reduced to 12%.[28]
Tobacco dust was investigated for its heavy metal binding efficiency. It has been studied that Tobacco dust exhibited a strong capacity for heavy metals such as Pb (°), Cu (°), Cd (°), Zn (°), and Ni (°) with equilibrium loading of 39.6, 36.0, 29.6, 25.1, and 24.5 mg of metal per g of sorbent respectively. Moreover, the heavy metals loaded onto the adsorbent could be released easily with a dilute HCl solution. Tobacco dust was negatively charged over a ph range (pH>2) with a strong acidity and high OH¯ adsorption capacity. Fourier Transform infrared Spectroscopy (FTIR) showed that when tobacco dust is subjected to biosorption, there was no change in chemical structure of tobacco dust. Metal-H ion exchange also interpreted the heavy metal uptake.[29]
Biosorption of Cd (°) and Pb (°) from aqueous solution using oyster mushroom (Pleurotus platypus), button mushroom (Agaricus bisporus) and milky mushroom (Calocybe indica) were performed. Optimum conditions re studied for each metal separately. Desired pH for Cd (°) and Pb (°) was 6.0 and 5.0 respectively and percent removal of both metals increase with increasing biosorbent dosage and contact time. Langmuir adsorption model was better suitable for the biosorption of Cadmium and lead by mushrooms. Highest metal uptake potential of cadmium (q max 34.96 mg/g) was showed by P. platypus whereas A. bisporus showed maximum potential for lead (q max 33.78 mg/g). For both of the metals, lowest efficiency was shown by milky mushrooms This study confirms that mushrooms may be used as efficient biosorbent for removal of both metals.[30]
The litter of natural trembling poplar (Populus tremula) forest was used for the biosorption of Cu (°). The sorption process was dependent on pH, particle size, agitating speed, initial concentration, temperature and adsorbent concentration. With decrease of particle size and initial concentration and increase in pH, temperature, agitating speed and adsorbent concentration, efficiency of copper uptake increases. Thermodynamic parameters, ∆G°, ∆H° and ∆S° were calculated and adsorption isotherm fitted well with Langmuir isotherm. The pseudo second order was found to be best fit the kinetic data. 94% of copper removal occurred within 5 min and equilibrium was reached after 30 min.[31]
The removal of arsenate present in industrial water was studied by using acid washed crab shells. These shells were very sensitive to pH greatly increased at 3.44±0.07 to 2.51±0.02 but reduced at 1.99±0.01. Arsenic uptake was affected by ionic strength of solution. At 0.1 M ionic strength, arsenic uptake was seriously depressed. In aqueous solution, acid washed crab shells have a dense structure and low extent of swelling.[32]
Utilization of straw and bran from Triticum aestivum (wheat) for the removal of metal ions from water. High efficiency, high biosorption capacity, cost effectiveness and renewability of wheat were the important parameters for metal removal. The biosorption has been found to be quite complex. Equilibrium and kinetic studies and effect of different parameters were evaluated.[33]
The biosorption of Zinc ions from aqueous solution was evaluated using Azadiracta indica. The biosorption studies were carried out as a function of pH, concentration, contact time, biosorbent size and dosage. The maximum biosorption took place at pH 6 and increase with biosorbent dosage. Isothermal data well interpreted by Langmuir model with biosorption capacity of 33.49 mg/g of zinc ions and kinetic study properly fitted with pseudo second order.[34]
The biosorption of hexavalent and trivalent chromium by palm flower was presented. Both Cr (°×€) and Cr (ν×€) adsorption followed second order kinetics. Maximum adsorption capacity for Cr (°ι) was 6.24 mg/g by raw adsorbent and 1.41 mg/g by acid treated adsorbent and for Cr (νι) raw adsorbent exhibited 4.9 mg/g and acid treated adsorbent capacity was 7.13 mg/g. Acid treatment increased Cr (νι) adsorption capacity whereas alkali treatment reduced the capacity. However, acid treatment decreased Cr (ιι) adsorption capacity whereas alkali treatment increased the capacity.[35]
The process of cadmium biosorption on NaOH pretreated Aspergillus niger was investigated. Effect of three parameters pH (1.3-8.7), biomass dosage (0.1-7.5 g/l) and initial cadmium concentration (0.5-37.5 mg/l) were determined and then optimized by response surface methodology. At 1440 min contact time, the optimum values of variables were found to be 5.96, 30.0 mg/l and 1.6 g/l for pH, initial cadmium concentration and biomass dosage respectively. 82.2% Cd (°) efficiency was observed at biosorption capacity of 10.14 mg Cd (°)/g. A. niger was proved as an effective biosorbent for heavy metal removal from industrial wastewater.[36]
The adsorption capacity of wheat shell for Cu (°) was studied at pH (2-7), agitation speed (50-250 rpm), and initial metal concentration (Co, from 10-250 mg/L). Maximum adsorption occurs at pH 5 and 6 and agitation speed of 240 rpm. The biosorption values were increased with increasing pH from 2-5 and decreasing copper/wheat shell (x/m) ratios from 0.83-10.84 mg Cu (°)/g wheat shell. Efficiency of biosorption wee 99% and 52% at the end of contact time of 120 min. The equilibrium and kinetic studies were obtained at 298 K. This study revealed that Wheat shell was a suitable biosorbent for Copper removal from aqueous solutions.[37]
