Biological removal of cadmium by Alcaligenes eutrophus CH34

Some bacteria like the heavy metal resistant Alcaligenes eutrophos CH34 strains are able to promote biomineralization, being the biologically induced crystallization of heavy metals. In the presence of heavy metals, this strain may create an alkaline environment in the periplasmic space and outer cell environment appropriate induction of heavy metals resistance mechanisms. In such an environment metal hydroxides are formed together with metal bicarbonates resulting from the carbonates production by the cell. Also metals bind to out cell membrane proteins and the metal hydroxides and bicarbonates precipitate around these nucleation foci inducing further metal crystallization. A pilot-plant was set up in which Alcaligenes eutrophus CH34 were inoculated and reproduced in a composite membrane, based on polysulfone. The membrane is casted on a polyester support. The biological membrane was in continuous contact with nutrients from inside and the other side was in contact with wastewater flow containing 120-mg/l cadmium. Nutrients are used for growth and reproduction of bacteria and for development of bacteria resistance agents against heavy metals. At the effluent side immobilized bacteria induce metal precipitation and metal crystals. A column, which was in continuous contact with treated effluent, was continuously filled with glass bends to which the metal crystals bind and grow. The efficiency for Cd removal was over 99 percent. Cd removal could be recovered from the recuperation column by acid treatment without damaging the bacteria.

Keywords
Alcaligenes eutrophos CH34, cadmium removal, biomineralization, polysulfone membrane, crystallization, industrial wastewater