Removal of mercury from chloralkali electrolysis wastewater by a mercury-resistant Pseudomonas putida strain

Abstract

A mercury-resistant bacterial strain which is able to reduce ionic mercury to metallic mercury was used to remediate in laboratory columns mercury-containing wastewater produced during electrolytic production of chlorine. Factory effluents from several chloralkali plants in Europe were analyzed, and these effluents contained total mercury concentrations between 1.6 and 7.6 mg/liter and high chloride concentrations (up to 25 g/liter) and had pH values which were either acidic (pH 2.4) or alkaline (pH 13.0). A mercury-resistant bacterial strain, Pseudomonas putida Spi3, was isolated from polluted river sediments. Biofilms of P. putida Spi3 were grown on porous carrier material in laboratory column bioreactors. The bioreactors were continuously fed with sterile synthetic model wastewater or nonsterile, neutralized, aerated chloralkali wastewater. We found that sodium chloride concentrations up to 24 g/liter did not inhibit microbial mercury retention and that mercury concentrations up to 7 mg/liter could be treated with the bacterial biofilm with no loss of activity. When wastewater samples from three different chloralkali plants in Europe were used, levels of mercury retention efficiency between 90 and 98% were obtained. Thus, microbial mercury removal is a potential biological treatment for chloralkali electrolysis wastewater.

FIG. 1

Removal of mercury from model wastewater (containing 1 mg of Hg per liter) in the presence of different concentrations of NaCl by a P. putida biofilm immobilized on Siran beads in an upflow column reactor. l, liter.

FIG. 2

Removal of different concentrations of mercury from model wastewater (containing 10 g of NaCl per liter) by a P. putida Spi3 biofilm immobilized on Siran beads in an upflow column reactor. l, liter.

FIG. 3

Removal of mercury from neutralized, aerated chloralkali electrolysis wastewater samples obtained from three factories (Table 1) by P. putida Spi3 biofilms immobilized on Siran beads (●) and on cellulose fibers (□) in an upflow column reactor. (A) Wastewater A. (B) Wastewater B. (C) Wastewater C. bv, bed volume. l, liter; d, day.

FIG. 4

Design of model bioreactor columns used to remove mercury from industrial effluents. W, wastewater container (1-m³ container for chloralkali wastewater; 1-liter bottle for model wastewater); M, medium (1-liter bottle); B, bioreactor (bed volume, 20 ml); b, bubble trap; p, peristaltic pump. See text for explanation.