Studies On Treatment Of Lead－bearing Wastewater By Immobilized

Fundamental and technological studies on treatment of lead-bearing wastewater by immobilized Rhizopus oligosporus were carried on. The main subjects in this dissertation are as follows.Factors affecting growth and propagation of Rhizopus oligosporus, temperature and pH value, were discussed. A new cultivation was developed, which offers several advantages over traditional cultivation, such as simple operation, time saving and low cost. Rhizopus oligosporus grows fast on the new culture medium, with the growth rate constant being 0.1685 h-1, and a large-scale culture can be proceeded.The characteristics of three gelatinous materials, namely calcium alginate, zinc alginate and aluminum alginate were evaluated for immobilizing biomass of the common mycete, Rhizopus oligosporus. And calcium alginate was found to be the most ideal matrix. The microbeads in which nonliving Rhizopus oligosporus cells were immobilized possess favorable properties with a potential for industrial use, such as adsorption rate, mechanical property and endurance for acid and base. The optimized conditions for preparing biosorbents based on the immobilization of nonliving Rhizopus oligosporus were obtained, i.e., the concentration of imbedding agent sodium alginate is 4%, the concentration of cross-linker CaCb is 3% and the time of cross linkage is 24 hours. Application of the Langmuir isotherm to the system yields the maximum sorption capacity of 42.918 mg Pb( II ) per gram biosorbent.Basic physicochemical parameters, significantly influencing bioremoval of Pb( II ), such as pH value, temperature and interfering cations, were investigated. The results show that the process can be proceeded at room temperature, with the pH value being controlled in the range of 2-5. The immobilized Rhizopus oligosporus accumulates less Pb( II ) when interfering cations exist in the lead-bearing wastewater, and the copper ion has the obvious effect on decreasingthe adsorption amount of Pb( II ) by the biosorbent.The kinetics on biosorption of Pb( II ) by immobilized Rhizopus oligosporus was studied. An initial rapid step of lead binding to Rhizopus oligosporus cell walls is followed by a subsequent slow phase of ions diffusion in the microbeads. The processfor adsorbing Pb(II ) to suspended cells can be described by Bangham model. At initial Pb( II ) concentration of 200 mg / L the adsorption rate constant was calculated to be 0.8775 min-1 according to the model. The diffusion of lead ion in the pellet is intrapartically controlled and the transfer coefficient De was assessed to be 1.31 X 10"10 m2/s. By analyzing the IR spectrograms of several pretreated biomass, the main mechanism on accumulation of Pb( II ) by nonliving Rhizopus oligosporus cells was regarded as chelation between metal cations and amino groups of chitoson.Immobilized systems are well suit for non-destructive recycling. Elution by citrate acid of 0.3 mol / L was found to be the best for Pb(II) desorption over 98%. The biosorbed immobilization Rhizopus oligosporus was regenerated by contacting with a solution containing 0.01 mol / L K\ Ca2+ and Mg2+ ions before further adsorption. With five cycles of biosorption-elution-regeneration the microbeads still keep high lead biosorption capacity. In addition, a series of flow studies was carried out using columns containing biosorbents. The results indicated that the saturation biosorption capacity reaches 48 mg Pb( II ) per gram biosorbent. The study provides an important base for the commercial application of the immobilized nonliving Rhizopus oligosporus in the removal of lead ions from wastewater.