Competitive Adsorption Among Dyes Or Heavy Metal Ion And Electrochemical Oxidation Or Photocatalytic Degradation Of Dyes

Industrial developments in recent years have left their impression on theenvironmental society. Many industries like the textile industry used dyes to color theirproducts and thus produce wastewater containing organics with a strong color. Theremoval of color from waste effluents becomes environmentally important because evena small q uantity of dye in water can be toxic and highly visible. Since the removal ofdyes from wastewater is considered an environmental challenge and governmentlegislation requires textile wastewater to be treated, therefore there is a constant need tohave an effective process that can efficiently remove these dyes. With the rapiddevelopment of industries such as metal plating facilities, mining operations, fertilizerindustries, tanneries, batteries, paper industries and pesticides, etc., heavy metalswastewaters are directly or indirectly discharged into the environment increasingly,especially in developing countries. Unlike organic contaminants, heavy metals are notbiodegradable and tend to accumulate in living organisms and many heavy metal ionsare known to be toxic or carcinogenic. Toxic heavy metals of particular concern intreatment of industrial wastewaters include, copper, nickel, mercury, cadmium,chromium and lead.In this thesis, the adsorption of anionic dye onto chemically cross-linked chitosanbeads, and heavy metal ions on bentonite, was investigated. The competitive adsorptionbehavour among adsorbates was tested as a function of dosage of adsorbent. Theoxidation of dye in simulated wastewaters using a three-dimensional electrode reactorand photocatalytic degradation was performed.1. Adsorption of anionic dyes onto chemically cross-linked chitosan beads fromsingle and mixed dye solutions. The performance of chemically cross-linkedchitosan-epichlorohydrin beads as an adsorbent to adsorb anionic dyes from single, binary and ternary dye solutions was investigated. Acid Scarlet （AS）, Direct Fast Scarlet（DFS） and Reactive Violet （RV） were used as the model dyes. For the adsorption fromsingle dye solutions, the isotherms follow the Langmuir equation and the adsorptionkinetics obeys the pseudo-second-order model. The adsorption equilibrium constantsonto chitosan-ECH beads were in the order of RV>AS>DFS. The saturated amounts ofadsorption are70357、57246and41131mol/g for AS, DFS and RV respectively.For the adsorption from mixed dye solutions, the isotherm of each individual dye hasdifferent shape. The dye with higher affinity toward the adsorbent was preferentiallyadsorbed. The reduction in uptake of the dye with increasing equilibrium dyeconcentration in the isotherms and desorption in the kinetic curves were observed forthe dye with lower affinity. The total amounts of dyes adsorbed versus the totalequilibrium dye concentrations were fitted well by the Langmuir isotherm model. Thekinetics of the total adsorbed amount of dyes followed the pseudo-second-order kineticmodel. The effect of the dosage of adsorbent on color removal efficiency and adsorptionkinetics was investigated. The utilization efficiency of cross-linked chitosan is improvedin a two steps adsorption method.2. Competitive adsorption behaviour of Cu（II）,Cd（II），Hg（II） and Pb（II） ontobentonite. The adsorption of four heavy metal ions, Cu（II）,Cd（II），Hg（II） and Pb（II）,onto bentonite was studied. The adsorption isotherms follow the Langmuir equation andthe adsorption kinetics obeys the pseudo-second-order model. The adsorptionequilibrium constants onto bentonite were in the order of Pb（II）>Hg（II）>Cu（II）> Cd（II）.The saturated amounts of adsorption are284.1,563.8,371.2,409.3mol/g for Cd（II）,Cu（II）, Hg（II）, Pb（II）, respectively. The competitive adsorption among the four ionswere tested as a function of dosage of adsorbent. It was shown that the equilibriumconstant dominates the adsorption of heary ions in solution of mixed ions. In the case ofinsufficient of bentonite，the adsorption of ion with less equilibrium constant isrestrained. A desorption was observation in the adsorption kinetics process. Under ourexperimental conditions, the relation of total amount adsorbed versus total equilibriumconcentration was fitted well by a Langmuir isotherm model. The total amount adsorbedfollows the the pseudo-second-order kinetic model. The removal efficiency is improvedin two steps adsorption and sequent addition of adsorbent. 3. Electrolytic treatment of Isatin in simulated wastewater using a three-dimensional electrode reactor. A model dye wastewater of Isatin was treated by athree-dimensional electrode reactor equipped with granular activated carbon as particleelectrode and stainless steel electrodes as the anode and cathode. Under the influence ofan electric field with an appropriate voltage，activated carbon particles can be polarizedto form charged microelectrodes. In comparison to the two-dimensional electrodereactor,the three-dimensional method offers the advantages of higherarea-volume-ratio，shorter transfer distance between the reactant and the electrode.Hence，the current efficiency for electrolytic treatment ofwastewater is improved. In thiswork， the influence of the way to prepare particle electrode, current density,concentration of Fe²⁺and salt on the color removal efficiency was investigated.4. Photocatalytic degradation of Malachite green and OP-10by PdO-TiO₂catalyst.The photocatalytic degradation of cationic dye （Malachite green） and nonionicsurfactant （OP-10） was carried out in the presence of PdO-TiO₂catalyst,which wasprepared by photochemically deposition of PdO onto commercial TiO₂nanoparticles.The prepared PdO-TiO₂nanocomposites showed a more effectivephotocatalytic activities for Malachite green and OP-10than unmodified TiO₂nanoparticles. In the mixture of Malachite green and OP-10, the removal effectivity forMalachite green or OP-10is less than that in a single solute solution of the sameconcentration. But the total removal effectivity is greater than that inn a single solutesolution of the same concentration.