An optimal magnetite immobilized Pseudomonas putida 5-x cell system was developed to remove Cu2+ from industrial waste effluent. Cu2+ adsorption capacity of P. putida 5-x cultured in sulphate-limiting medium (SLM) was minimum in early log growth phase, and reached maximum in late stationary growth phase or early death phase. Pretreated cells by 0.6 N HCl could greatly enhance the adsorption capacity of biomass up to 85.6 mg/g and had no significant effect for the loss of P. putida 5-x cells during the pretreatment. In a semi-continuous biosorption system, the removal efficiency of Cu2+ from wastewater reached 96%, and recovery efficiency of Cu2+ was 95%, and the concentration in the recovery solution was 1.4 g/L using 0.6 N HCl as eluant. The mechanism of Cu2+ adsorption by this type of biomass was studied by using the technique of transmission electron microscopy (TEM). Degradation of a peptidoglycan layer on the cell surface was observed after acidic pretreatment, but no further degradation appeared after the adsorption-desorption cycle. TEM and X-ray analysis also showed that Cu2+ was mainly accumulated on the cell surface, so it was effectively desorpted by acidic treatment in the desorption process. The process of adsorption obeyed the Freundlich isotherm.

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