Biosorption Of Heavy Metal Ions In Liquid By Magnetotactic Bacteria

Huge amount of heavy metal ion retained in the environment, e.g. Au, Cu, Ni, Cd, Hg, which is originated from its wide application in smelting, chemical industry, papermaking, electronic industry and mining especially, is harmful to our body. These ions can exist for a long time in the body after entering the human circulatory system, which make the body of certain metabolic pathways blocked and cause great harm to human health. So the governance of heavy metal pollution has become a very important environmental issue in recent years.Magnetotactic bacteria are motile, mostly aquatic prokaryotes that swim along geomagnetic field lines. Their highly nutritional and environmental requirements make it very difficult Purification. The orientational behavior in magnetic field make them play an important role in the treatment of waste water containing heavy metals. Papers have mentioned that magnetic field-magnetotactic bacteria compound technology is effective on the removal of heavy metals in waste water, which makes the study of magnetotactic bacteria's biosorption is of great significance.In this study, I got microorganism from the sewage treatment plant and used special traps for collecting after 20 days of enrichment culture. The magnetotactic bacteria collected are used for single colony separation in the aerobic and micro-aerobic conditions. As a result, three aerobic bacteria M1, M2, M3 and one micro-aerobic bacteria M4 were obtained. The four bacteria are used in adsroption of heavy metals in water after large-scale cultivation of liquid, and strain M3 was selected as a model organism for follow-up research because of its good effect in biosorption.The study on adsorption characteristics of heavy metals by strain M3 found that, the optimum status of biomass for biosorption is original bacteria, the optimum adsorption pH for Au³⁺, Cu²⁺, Ni²⁺ are pH2～3, pH5, pH5 respectively; optimum temperature is 30℃; the optimum biomss for Au³⁺, Cu²⁺, Ni²⁺ are 1.19g/L, 1.54g/L, 1.22g/L respectively; adsorption can be basically completed within one hour through kinetic experiment of biosorption; batch adsorption isotherm experiments found that Freundlich model can be better in fitting the adsorption curve than Langmuir model; desorption experiments were carried out with four different desorbent, finding that thiourea is effective in desorption of Au³⁺ and EDTA is a good desorbent for Cu²⁺ and Ni²⁺. Finally, the preliminary research in adsorption mechanism of heavy metals by strain M3 is carried on. We found that ion exchange exists in the biosorption, but the amount is small and contribute little to the adsorption. Through comparison of infrared spectrum of strain M3 before and after biosorption of heavy metals, we found that carboxyl, amine, hydroxyl, phosphate play an important role in the course of adsorption. Adsorption capacity has decreased in varying degrees after chemical modification of a certain group mentioned above, the more biosorption amount decrease, the more important the group is in biosorption. It can be inferred that phosphate and hydroxyl, carboxyl and amino groups, hydroxyl and amino groups play a major role in the adsorption of Au³⁺, Cu²⁺, Ni²⁺ respectively. XRD and XPS analysis of bacteria after adsorption of Au³⁺ show that Au³⁺ is reduced into Au0 by a certain group on the cell wall.