BIOSORPTION OF DIFFERENT HEAVY METALS FROM WASTEWATER USING NEW FUNGI WASTE MATERIAL

Abstract

6.1.1 Single Component System

• It was found that the low cost W.F. can be successfully used to remove Pb(II), Cu(II), Co(II) and Cd(II) from simulated wastewater using single, binary, ternary and quaternary systems in batch process . • Adsorption/biosorption capacity was found to vary with initial concentration, adsorbent dose, pH and contact time. • To achieve maximum heavy metal ions removal efficiency of adsorbent/biosorbent at 50 mg/L of Pb(II), Cu(II), Cd(II) and Co(II) ions concentration were found to have different optimum conditions of dose, pH, contact time and initial concentration depending on the characteristics of individual adsorbent/biosorbent. • Adsorption/biosorption mechanisms of Pb(II), Cu(II), Cd(II) and Co(II) ions onto the surface of GAC or W.F. are due to the electrostatic attractive interactions between the positive charge of metal ions and the negative surface charge. • It was found that W.F. was more efficient than GAC in adsorbed/biosorbedPb(II), Cu(II), Cd(II) and Co(II) ions. Functional groups of W.F. were responsible for biosorption process which exceeds that GAC. • The results implied that the equilibrium time is strongly dependent on initial concentration, adsorbent dose and pH, where the equilibrium time was found to increase with the increasing the initial concentration, and found to decrease with the increasing adsorbent dose • The optimum pH values was found 4 for Pb(II), Cu(II), Cd(II) and Co(II) ions in adsorption process. While it was 5 for the same heavy metal ions in biosorption process that means the two processes followed values of pH in acidic range (4-5) to give maximum removal. An increase in pH led to a significant increase in adsorption/biosorption heavy metal removal in the range (2-6). • The required contact time to reach the biosorption equilibrium with maximum removal was 30 min using W.F. compared with 60 min. using GAC., that means , the biosorption process was fast and more efficient than adsorption process • Pb(II) ions was the most favourable component rather than Cu(II), Cd(II) and Co(II) due to less solubility and highly molecular weight.Adsorption/biosorption capacity were: Pb(II) > Cu(II) > Cd(II)>Co(II). • The uptake capacity by W.F. was greater than GAC for Pb(II), Cu(II), Cd(II) and Co(II)ions.This difference in behavior due to high affinity between heavy metal ions and W.F. while it is less for GAC • The analysis of F.T.-I.R. showed that carboxylic acid, amide, and amine groups played the most important role in binding the used heavy metal ionson the surface of GAC/W.F. The FT-IR showed that Pb2+ made a greater change in the functional groups of W.F. revealed high affinity of W.F. toward this metal.

• Knowing that the chemical characterization of GAC and W.F. are composed mainly of cellulose, hemicellulose and lignin, which provides binding sites (anionic) for the basic (cationic) metal ions due to the presence of functional groups such as hydroxyl, carboxyl, methoxy, phenols, etc. • Percent removal of lead, copper, cadmium and cobalt ions by W.F. were increased approximately 83.15%, 54.38%, 58.53% and 41.36% higher than removals achieved by GAC for similar equilibrium metal concentrations. • Biosorption capacity of Pb(II), Cu(II), Cd(II) and Co(II) ions were (94.74, 53.12, 56.0, 42.57 mg/g) compared with GAC (15.91, 24.23, 23.22 and 24.96 mg/g), respectively, at concentrations (10 - 200 mg/L). • Eight isotherm models for single isotherm system and four for each of binary, ternary and quaternary isotherm systems were used. R2 values indicated that equilibrium isotherms were well described by the Langmuir model for a single component system, while Extended Langmuir model observed the best fit model for binary, ternary and quaternary systems. • The equilibrium isotherm for each single component onto GAC/W.F. is of a favorable type (since 0 >Rs<1). The maximum adsorption/biosorption capacity took the following sequence: Pb2+> Cu2+ > Cd2+> Co2+. • Lead was shown to be easily displaced than Cu, Cd and Co due in part to properties that are more favourable for binding, such as a higher electronegativity and smaller hydrated radius. • Kinetic study dedicated that pseudo-second order kinetic model was more suitable for adsorption/biosorption of the four heavy metals because of higher correlation coefficients compared with other models. • The maximum adsorption/biosorption capacity of the GAC and W.F. was found to decrease as temperature increase. This indicates that adsorption/biosorption is an exothermic process and physical in nature. However, the heat of adsorption/biosorption was found to be less than 40 KJ/mol, which showed that the adsorption of Pb(II), Cu(II), Cd(II) and Co(II0 onto GAC and W. F. were physical adsorption. • A good matching was found between experimental and predicted data in the experiments for all components. • The studying of intraparticle diffusion model for the adsorption/biosorption of heavy metal ions onto GAC and W.F. indicated that the metal ions uptake process was found to be controlled by external mass transfer at earlier stages and by intraparticle diffusion at later stages. So, the adsorption mechanism was suggested to be complex, consisting of both surface adsorption and pore diffusion.

6.1.2 Multi-Component System

• For each binary, ternary and quaternary component systems, extended Langmuir Isotherm and the combination of Langmuir-Freundlich model give the best fit for the experimental data. The behaviour of the equilibrium isotherm is of the favourable type. • Due to the competitive effect of four metal mixtures to occupy the available sites of the A.C. and W.F., Pb2+ions offer the strongest component followed by Cu2+and Cd2+ions while Co2+was the weakest adsorbed component. • Compared with their adsorption in single component system the adsorption capacity and percentage removal of all four metals shows obvious decreases both in the binary, ternary and quaternary systems. This is because of more than one component was found which enhance the competitive struggling race for occupying a certain site • Lead is still most adsorbed component rather than copper, cadmium, and cobalt.

6.2 Fixed Bed columns The effects of flow rate, bed height and metal ions concentrations in column reactors was also investigated because column reactors appear to be the most appropriate form in which biosorbent technology for remediation is best applied in industry, as opposed to batch reactors. 6.2.1 Single Component System • Thomas model which includes external mass transfer and coefficient pore diffusion resistance provides a good description of the adsorption/biosorption process for single, binary, ternary and quaternary than second order reversible reaction model, homogenous surface diffusion model and quasichmical kinetic model for Pb(II), Cu(II), Cd(II) and Co(II) ions. • Thomas model shows excellent fitting for all examined range of breakthrough curves. Therefore, the Thomas model was used in simulations of breakthrough curves. Results show very good agreement of simulated and experimentally performed curves. • Thomas model has been found to be the most suitable one for mathematical description and modeling of lead, copper, cadmium and cobalt removal on a fixed bed on GAC/W.F. • The experimental data are in good agreement with theoretical results. • The breakpoint time decreases with increasing the flow rate, initial concentration and decreasing the bed height. • The breakthrough curves were plotted for each metal, Pb2+was the largest breakthrough time compared with other metals demonstrating high affinity, while Co2+had the shortest breakthrough time. • In fixed bed system, Thomas model gives a good description of the adsorption/biosorption process for single and competitive multicomponent system. • The breakthrough curve was more flat for Pb2+ and the breakpoint appeared later than that for Cu2+, Cd2+ and Co2+. • The time for reaching breakpoint (Ce/Co=0.05) for lead, copper, cadmium and cobaltions were found to be 24000, 15600, 13091 and 5400 s, respectively when using W.F. and 3000, 1800, 600, 351s respectively using GAC.

6.2.2 Multi-Component System • As the initial concentration of weak solutes increased, its breakthrough curves become flat and its breakpoint appear early, this may explained by the fact that the driving force for mass transfer increased with the increase of concentration of solute and resulting in lowering the competitive adsorption rate. • The biosorption capacity order for the quaternary system is: Pb2+>Cu2+>Cd2+>Co2+. • The breakpoint of cobalt cations is the lowest values followed by cadmium, copper and lead in binary, ternary and quaternary systems. • Overshooting, Ct/Co>1 appeared in breakthrough curve of the weak component in quaternary system and disappeared in the strongest component, Pb2+ ions. . • The regeneration studies with fungal biomass were encouraging, increasing the possible economic benefits of its application in bioremediation processes. • Scanning electron microscopy, although not conclusive, showed no apparent break-down in the physical structure of the W.F. with repeated adsorption and desorption cycles • The fixed bed adsorption system was found to perform better with lower inlet concentration, lower feed flow rate and higher bed height.