Long-term Operation of a Microbiological Pilot Plant for Clean-up of Mercury Contaminated Wastewater at Electrolysis Factories in Europe
Johannes Leonhäuser, Harald von Canstein, Wolf-Dieter Deckwer and Irene Wagner-Döbler
from: Bioremediation of Mercury: Current Research and Industrial Applications (Edited by: Irene Wagner-Döbler). Caister Academic Press, U.K. (2013)
A plant for BIOlogical MERcury Remediation (BIOMER) based on mercury resistant bacteria was operated for three years at a chlor-alkali factory in technical scale. Here we report on the performance of the plant and on the technical problems that had to be solved until a stable and continuous operation could be guaranteed. One basic improvement was the installation of a pre-treatment unit. Basic process characteristics were determined during long-term operation. The BIOMER plant could treat wastewater with up to 10 mg/L of mercury. The optimal operation temperature was between 25-35°C. A salt concentration of up to 40 g/L of chloride could be tolerated by the microbes, but the fluctuations should be as small as possible. The bioreactor has to be operated at a pH of 7.0 ± 1.0. A space velocity of up to 4 h-1 could be obtained. The wastewater flow rate should be constant to avoid export of fine particles. Finally a space time yield of 1 kg mercury per day and m3 bed volume corresponding to 100 m3 wastewater per day is possible. The biological system showed a high capacity for self-regeneration. Interruptions of the water inflow for up to 12 hours and of the medium supply over several days were tolerated. Toxic shocks loads of high concentrations of chlorine or mercury chloride also caused only a transient reduction of the microbial activity. The plant was able to quickly return to normal operation with high mercury retention efficiency after such stresses. The results from the long-term operation show that a process can be scaled up from laboratory tests to an industrial plant without any serious engineering problems. It was demonstrated that the BIOMER plant is able to work under industrial conditions at two different chlor-alkali electrolysis factories in Europe read more ...