Study On Biosorption Of Chromium-containing Wastewater By Candida Lipolytica

The biosorption of chromium-containing wastewater was studied comprehensively in the research, including capacity of biosorption by Candida lipolytica, mechanism of biosorption, the capacity of biosorption column by immobilized biomass, salt effect of biosorption, the preparation of biosorbent and removal of chromium from industrial wastewater.The biosorption capacity and sorption kinetics of chromium by Candida lipolytica were investigated. After 2 hours of adsorption more than 95% chromium were removed when chromium concentration and the strain dosage were 20 mg/L, 10.0 g/L (wet weight), respectively. The kinetics analysis of chromium onto the Candida lipolytica revealed that the biosorption process followed the pseudo second-order reaction kinetics. The sorption processes within 20~50 mg/L were in accordance with Freundlich isotherms.The experiment of heavy metal tolerance of Candida lipolytica indicated that chromium had the highest toxicity. The analysis of IR indicated that amido and carboxyl were the main active functional groups for biosorption. The experiments of Atomic Force Microscope (Abbreviated as AFM) showed that there were no evident changes on the cell wall before and after adsorption. X ray analysis indicated that the structure of the strain was not destroyed after biosorption of chromium.The influence of different concentrations of NaCl, MgCl2, AlCl3, NaNO3, Na2SO4 and NaBr electrolytes on the biosorption of chromium by Candida lipolytica was studied experimentally. The result indicated that Na+ and Mg2+ in lower concentration had positive effect on biosorption. With the same kind of cations, only Cl- in lower concentration can stimulate the biosorption. The salt effect of biosorption process might be related with the radii of cations and the stability of chelates, maybe also related to the interaction between anions and functional groups which had positive charge.Candida lipolytica was immobilized on wood crumbs and the immobilized biomass was packed in a glass column. The results indicated that the biosorption column had high efficiency of removing chromium from aqueous solution. More than 80% of chromium could be removed up to 6 038 mL when the bed depth and chromium concentration were 500 mm, 50 mg/L, respectively. The higher the concentration was, the shorter the breakthrough time was. The breakthrough time for 50 mg/L chromium was 4.5 times longer than that for 200 mg/L chromium. The analysis of the biosorption column showed that thebehavior of the column could be described by Thomas model.The preparation and capability of biosorption of chromium by Candida lipolytica-wood crumbs-activated sludge were investigated. It was found that the biosorbent which consisted of 80 g/L activated sludge, 10 g/L wood crumbs and Candida lipolytic had high efficiency to remove chromium from aqueous solution, the ratio of removal of 50 mg/L chromium was 93.2%. The result of different conservation methods indicated that the biosorbent could stabilize for 15-30 days. And the biosorbent was innoxious and safe.pH was one of the most crucial factors for the removal of chromium by biosorbent. The optimal pH was 1 ~3. The experimental results showed that the removal efficiency was lower when dealing with electroplating wastewater. It may be due to the complex compositions of the wastewater. The existed ions and the organic matters competed with the chromium ions.