| At present,the pollution of heavy metals has become one of the severest water pollutions.Hexavalent chromium,one of those poisonous heavy metals,could bring a devastating and permanent contamination to local water area and ecosystem,sequentially would endanger people's health and survival,which mainly ascribes the discharge of wastewater containing large heavy metals from many process industries.The technique of biosorption has been paid more attention by many environmental scholars due to its quick-sorption,low-cost, simple-operation and no-secondary pollution etc.Moreover,it may become a better complementarily for the conventional water disposal technique to completely remove Cr(Ⅵ)at low concentration wastewater (1-100mg/l).In this study,we systemically investigated the biosorption technology for Cr(Ⅵ)by Rhizopus Cohnii and three fermentation industry wastes.The study of packed column experiments with R.Cohnii immobilized on different carriers indicated three carries were fitted to immobilize R.Cohnii.The effect of pretreatment by 1M HCl was obviously superior to other reagents.The removal efficiency of Cr(Ⅵ) strikingly increased by 38%and 44%for living cells immobilized on sawdust and polyurethane foam,and about 21%and 44%for dead cells immobilized on calcium alginate and polyurethane foam,comparing with controls,respectively.The standard Langmuir model was used to describe the process of isothermal adsorption for Cr(Ⅵ).The linear regression analyses showed that r2 were all above 0.99,SD less than 1,which indicated the Langmuir model can well fit the biosorption of Cr(Ⅵ)in packed column with R. Cohnii immobilized on different carriers.The calculated values of RL were from 0 to 1,which revealed all immobilized cells were favorable to sorption of Cr(Ⅵ)in this study.The calculated values of q0 by Thomas model were nearly agreed with the experimental ones in batch experiments as well,and the standard deviation was less 4%.All of these also displayed that the Thomas model can be better used to describe the adsorption column performance in this experiment.The experimental results of Cr(Ⅵ)desorption revealed that 0.1M NaOH solution played greatly on eluting the Cr(Ⅵ)from sorbents than other ones,such as 0.1M NaAC,NaCO3,NaCl and NaNO3 solutions,and approximately 98%Cr(Ⅵ)were eluted from sorbents.The results of 5 cycles for adsorption-desorption displayed that the process of sorption and desorption for Cr(Ⅵ)was reversible,having not almost loss of efficiency.Furthermore,these have shown the better potential for the practical application. The porous magnetic bio-functional magnetic beads were prepared by entrapping powdered R.cohnii and magnetic particles in the matrix of sodium alginate and polyvinyl alcohol(PVA),which were used to adsorb Cr(Ⅵ)in wastewater.The solid-liquid two phases could be separated rapidly under an external magnetic field.The Fe3O4 particles,diameter approximately 20nm,were verified to have paramagnetic properties by the magnetization curve measured with a vibrating sample magnetometer (VSM),in which there was nearly no hysteresis in the magnetization.The performance of these beads were kept in good operating conditions under different pH vales ranging from 1 to 12 at agitation speed 200 rpm and 0-50℃for 96 h.The condition of pH 1,28℃and 100 rpm was better prone to the biosorption of Cr(Ⅵ).The effect of coexistent ions on Cr (Ⅵ)biosorption not only depended on the quantities of coexistent ions and Cr(Ⅵ),but on the values of ions.The sorption of chromium was mainly in form of Cr(Ⅵ)by bio-functional magnetic beads, simultaneously,15%Cr(Ⅵ)was reduced to Cr(Ⅲ)by biosorbents in the process of adsorption.The process of isothermal sorption and kinetics of Cr(Ⅵ)biosorption were fitted well by Langmuir and Lagergren models, respectively.The test results have proved that the bio-functional magnetic beads were simultaneously possessed of the predominance of sorption and separation.In this experiment,a novel applied technique for the removal of Cr (Ⅵ)from wastewater was also developed by combined the magnetic separation technique with the microorganism-immobilizated technique. Three fermentation industry wastes were taken as low-cost sorbents. Meanwhile,the data verified that this technique was rapid and simple in the process of sorption and separation,respectively,which has shown the potential for the practical application.The analysis of FT-IR and RS clearly indicated that the cell component-amidocyanogen was protonated,which played a key role in the process of sorption and removal for Cr(Ⅵ).The acidic solution was advantageous to the protonation of functional groups,such as amidocyanogen.The protonated functional groups rapidly adsorbed the predominant anions,HCrO4- and CrO42-under strongly acid solution and low chromate concentration by electrostatic action.In addition,partial Cr (Ⅵ)was reduced to Cr(Ⅲ).Therefore,two possible mechanisms of sorption and removal for Cr(Ⅵ)were explained well by electrostatic action and Oxidation-reduction. |
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