Ni²⁺removal and recovery from electroplating effluent by Pseudomonas putida 5-x cell biomass

Ni2+and Cu2+are the major heavy metal ions in electroplating wastewater of Hong Kong. In the present study, Pseudomonas putida 5-x cell biomass was used to remove Ni2+from electroplating effluent. Ni2+adsorption capacity of P. putida 5-x cell biomass cultured in sulphate-limiting medium was found to be minimum in early logarithmic growth phase, and maximum of 28.1 mg g-1in late stationary growth phase. Pretreated cells by 0.1 mol L-1HCl could greatly enhance the Ni2+adsorption capacity of cell biomass from 28.1 to 36.7 mg g-1and had no significant effect on biomass loss. The adsorption process of P. putida 5-x fresh cells and pretreated cell all could be expressed with Freundlich isotherm. TEM analyses indicated that acidic pretreatment degraded the superficial layer-capsule outside of the fresh cell to improve the adsorption capacity of cell to Ni2+. The Ni2+bound by P. putida 5-x cell biomass could be efficiently recovered using 0.1 mol L-1HCl, and the cell biomass could be reused at least five cycles for Ni2+removal and recovery with 93% above removal efficiency and 98% above recovery rate. Owing to the Cu2+presented in electroplating wastewater inhibiting Ni2+adsorption process by P. putida 5-x cell biomass, two-stage biosorption processes should be designed to remove and recover Cu2+and Ni2+sequentially from electroplating effluent.