Abstract: Effect of immobilized Rhodopseudomonas sphaeroides treating cadmium (Cd) and chromium (Cr) containing wastewater was investigated and technological conditions for the immobilized bacteria to adsorb Cd and Cr ions were optimized in treating electroplanting wastewater continuously in a bioreactor. Results show that the bacteria immobilized in gel complex with 20 g·kg^-1 of zeolite and 20 g·L^-1 of sodium alginate were significantly better than free bacteria in removing Cd and Cr from the wastewater. Orthogonal experiments were conducted to optimize technological conditions for wastewater treatment.It was found that pH of the wastewater and inoculation rate of the bacteria were two major factors affecting heavy metals rermoving efficiency. When pH of the wastewater containing 40.00 mg·L^-1 Cd to be treated was 6.0 and inoculation rate of the bacteria 10.00 g·L^-1, Cd removing rate reached 96.68%. Results of four cycles of sorption-desorption reveal that immobilized bacteria could last three cycles. Its Cd removing rate might still come up to 51.20% in the third cycle. In the bioreactor,immobilized R.sphaeroides was used to treat electroplating wastewater containing 92.61 mg·L^-1 Cd. Three hours of treatment removed 98.80% of the Cd in the wastewater and over 90.00% of other heavy metals (Cu, Au and Ni) as well.

Key words: Rhodopseudomonas sphaeroides, immobilization, heavy metal wastewater, bioreactor