Accumulation Effect Of Heavy Metal Cadmium By Immobilization Microorganism

With the rapid development of modern industry, lots of heavy metals entered into our environments.Air, water and soil have been all polluted by heavy metals.Cadmium is considered as the most hazardous heavy metal with abroad applications.Cadmium left in environments can get into the body's blood circulation system, and exist in the body for a long time,which could obstruct certain metabolic pathway, and then damage human health. Hence, more attention has been paid to the waste water disposal in the environments.Biosorption method is one method using organisms or its derivatives to absorb metal ions in the environments.Compared to traditional methods, biosorption treatment showed high efficiency, low costs,wide range of pH values and temperature adaption.Moreover, it works more efficiently when wastewater has lower concentrations of heavy metals.The immobilized microorganism can improve the stability and mechanical strength of biological organisms. For example, the stability and mechanical strength improve, the size and shape are easy to control,in the continuous reactor the treatment would not cause blocking again, would make solid-liquid separation more easy thus simplifying the process.In addition,if immobilized organisms were not damaged, they would be reused.The microorganisms which live in the cadmium-rich environment, such as battery factory wastewater, can be induced to produce tolerance and resistance to cadmium.Therefore,to separate and study the cadmium-resistant microorganisms is very important to concentrate cadmium in water so as to control pollution.In this study,5 cadmium-resistant bacterial strains were separated from the environment polluted with cadmium.The strains can grow in beef-protein medium agar with cadmium(100-200 mg/L).The high tolerance microorganisms were immobilized by using sodium alginate-gelatin embedding method,and used for Cd adsorption.The optimum conditions for Cd absorption were selected from pH (pH 1.0-10.0), duration time(1-24 h), temperature (20,30 and 40),rotate speed(100 and 200 rpm), Cd original concentration (6.16,12.32,20.00 and 50.00 mg/L), nutritional substances, microorganisms concentration and immobilized microorganism concentration.The results showed that the enrichment effect of J2 strain is relatively high and stable under selected conditions.For J2 strain, the optimum adsorption conditions were as follows: bacteria cells,250 g/L in immobilization mixture;immobilized cells,0.20 g/ml;temperature,30℃; pH 6.0;duration,1 h; initial Cd concentration, 20.00 mg/L,and the highest enrichment rate was 75.90%.