Wagner-Döbler I: Long-term performance of bioreactors cleaning mercury-contaminated wastewater and their response to temperature and mercury stress and mechanical perturbation. Biotechnol Bioeng 2001

Abstract: The long-term performance of bioreactors re-taining mercury from contaminated industrial wastewa-ter was analyzed at the laboratory scale, and its response to mechanical perturbations (gas bubbles and shaking) as well as to physical (increased temperature and hy-draulic load) and chemical stresses (increased mercury concentration) likely to occur during on site operation was studied. Two packed-bed bioreactors with 80-cm3 lava chips as biofilm carrier were inoculated with nine Hg(II)-resistant natural isolates of a- and g-proteobacte-ria. Chloralkali wastewater containing ionic mercury (3.0 to 9.7 mg/L Hg2+), amended with sucrose and yeast ex-tract, flowed through the bioreactors at 160 mL/h. During the 16-month investigation the bioreactors showed no sign of depleted performance in terms of mercury-retaining capacity. After 16 months, both bioreactors still retained 96 % of the mercury load. The performance of the bioreactors was sensitive to mechanical perturba-tions (e.g., sheer forces of gas bubbles). Shifts to higher Hg2+ inflow concentrations initially decreased the mer-cury retention efficacy slightly. However, the bioreactors could adapt to Hg2+ concentrations of up to 7.6 mg/L within several days. Old biofilms were less affected than the younger ones. The performance of the bioreactors was not affected by an increase in temperature up to 41°C and an increased volumetric load (up to 240 mL/h). The bioreactors regained activity spontaneously after the stress had stopped. Recovery could be accelerated by increased nutrient concentration, although this may lead to blocking of the packed bed. © 2001 John Wiley & Sons