Comparative Study on the Ni2+ Biosorption Capacity and Properties of Living and Dead Pseudomonas putida Cells

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Microbial cells have been successfully used as biosorbents to remove heavy metals from wastewater. In some cases, dead cells appear to offer more advantages than living cells in the removal and recovery of heavy metal ions from industrial wastewater. Maintaining higher biosorption capability and understanding the biosorption properties of dead cells are the keys to heavy metal removal and recovery from wastewater using dead cells as biosorbents. The present experiment showed that the dead Pseudomonas putida 5-x cells killed by dilute HCl had a higher Ni2+ biosorption capacity due to the retention of a complete cell structure during the acid treatment process. The biosorption process of the dead cells was faster than that of the living cells. Metabolic-independent physical adsorption played a major role in the Ni2+ sorption by the dead cells.The pH obviously affected the biosorption capacity of the dead cells, because of the variation of the hydrogen ion concentration and cell surface property, as well as occurrence of micro-precipitation along with the change of solution pH. Considering both biosorption capacity and desorption efficiency, pH 6.5-7.0 is a suitable condition for Ni2+ biosorption by dead P. putida 5-x cells killed with dilute HCl.