Wim De Windt

Bio-deposition of a calcium carbonate layer on degraded limestone by Bacillus species

To obtain a restoring and protective calcite layer on degraded limestone, five different strains of the Bacillus sphaericus group and one strain of Bacillus lentus were tested for their ureolytic driven calcium carbonate precipitation. Although all the Bacillus strains were capable of depositing calcium carbonate, differences occurred in the amount of precipitated calcium carbonate on agar plate colonies. Seven parameters involved in the process were examined: calcite deposition on limestone cubes, pH increase, urea degrading capacity, extracellular polymeric substances (EPS)-production, biofilm formation, ζ-potential and deposition of dense crystal layers. The strain selection for optimal deposition of a dense CaCO3 layer on limestone, was based on decrease in water absorption rate by treated limestone. Not all of the bacterial strains were effective in the restoration of deteriorated Euville limestone. The best calcite precipitating strains were characterised by high ureolytic efficiency, homogeneous calcite deposition on limestone cubes and a very negative ζ-potential.

Biocatalytic dechlorination of trichloroethylene with bio‐palladium in a pilot‐scale membrane reactor

Trichloroethylene (TCE) is a toxic and recalcitrant groundwater pollutant. An innovative technology using microbial produced Pd(0) nanoparticles for the remediation of TCE contaminated groundwater was developed. The nanoscale bio‐Pd particles were precipitated on the biomass of Shewanella oneidensis and hydrogen gas, formate, or formic acid were used as hydrogen donors. Ethane turned out to be the only organic degradation product and no intermediate chlorinated reaction products were detected. Subsequently bio‐Pd was implemented in a plate membrane reactor (MR) for the treatment of water containing TCE. In a continuous MR system, containing 50 mg L−1 bio‐Pd, removal rates up to 2,515 mg TCE day−1 g−1 Pd were achieved with H2 gas as hydrogen donor. The measured chloride mass balance confirmed the removal rates. This work shows that a complete, efficient and rapid removal of TCE was achieved with bio‐Pd and that a MR system containing bio‐Pd and supplied with hydrogen gas offers an alternative for the current remediation technologies of water contaminated with TCE. Biotechnol. Bioeng. 2009;102: 995–1002.