Study of magnetite-immobilized bacterial cell system for removal and recovery of heavy metals from electroplating effluent

Cu2+ and Ni2+ are the major heavy metal ions in electroplating wastewater of Hong Kong. The present study was conducted to investigate the removal and recovery of Cu2+ and Ni2+ from electroplating wastewater by bacterial cell biomass.; A gram-negative bacterium Pseudomonas putida with high Cu2+ and Ni2+ accumulating capability was isolated from local electroplating effluent. P. putida 5-x cells cultured in sulfate limiting medium was found of obviously high Cu2+ and Ni2+ adsorption capacity compared with those cultured in other media. Higher incubation temperature had a negative effect on Cu2+ and Ni2+ adsorption of P. putida 5-x cell, with effect particularly obvious at the logarithmic growth phase. The bacterial cells harvested in 34∼38h and 28–30h had maximum Cu2+ and Ni 2+ adsorption capacity, respectively.; The adsorption process of Cu2+ and Ni2+ by fresh cell consisted of two phases, namely a rapid, metabolism-independent metal ions adsorption phase (biosorption) followed by a slow metabolism-dependent bioaccumulation phase, while pretreated cell only consisted of a rapid, metabolism-independent adsorption phase. About 80% of the total Cu2+ and Ni 2+ taken up by the fresh bacterial cells were removed within the rapid adsorption phase. The adsorption capacity of P. putida 5-x cell was obviously affected by changes of pH. The high the pH, the high the Cu2+ and Ni2+ adsorption capacities.; Under suitable conditions, 0.1∼0.3 M HCl could effective recover Cu2+ and Ni2+ from loaded cell biomass with less biomass loss rate. The desorption process was quite rapid, with 95% Cu 2+ and 99% Ni2+ being desorbed in the first 5 minutes. P. putida 5-x cell as biosorbent could be effectively regenerated and reused at least five cycles for removing and recovering Cu2+ or Ni2+.; The adsorption capacity of magnetite immobilized P. putida 5-x cell to Cu2+ and Ni2+ appeared to be much higher than using magnetite alone. The Cu2+ and Ni2+ adsorption by both magnetite alone and magnetite immobilized cells obeyed the Freundlich isotherms of Q_M-Cu = 2.1 C_e-Cu 0.68, Q_Im-Cu = 11.9 Ce_-Cu0.74 and Q_M-Ni = 0.78 C_e-Ni0.79, Q_M-Ni = 9.7, C_e-Ni0.21.; The capsules outside the fresh cell of P. putida 5-x reduced the adsorption capacity to Cu2+ due to the Cu 2+-bridging formed by binding divalent Cu2+ on electronegative groups in the capsule, which might induce a conformation change within the capsule, and thus resulted in some metal-binding sites on the cell outer membrane or PEG layer becoming inaccessible for Cu2+ binding. (Abstract shortened by UMI.)...