Vermiculite as a potential functional additive for water treatment bioreactors inhibiting toxic action of heavy metal cations upsetting the microbial balance.

A new adsorbent that combines mineral vermiculite with the yeast Saccharomyces cerevisiae, was used for Cd removal. The influence of vermiculite presence on the toxic effects of Cd to Saccharomyces cerevisiae yeast was evaluated as a function of the microorganisms' respiratory activity (CO production). The Cd toxicity increased with prolonged exposure time reaching the LC value of 857 and 489 mg L after 30 and 120 min, respectively. The yeast managed to bioaccumulate 25.0 ± 0.6 mg g of Cd at the initial Cd concentration of 741.9 mg L; the maximum Cd adsorption capacity of vermiculite reached 25 ± 5 mg g. The addition of the mineral decreased the cations toxic effect; the LC value in vermiculite absence attained approximately 200 mg L after 30 min and decreased to 80 mg L after 2 h, while in the bio-mineral system it was at the level of 435 ± 50 mg L without a significant change in time. The mineral provided a superior living environment for the yeast by removing part of the cations, releasing essential microelements and providing a protective, clay hutch-like habitat for the cells.