Hybrid Silica-Microbial Materials for Bioremediation Applications

The research presented here is focused on developing an advanced bioremediation technique to remove environmental pollutants by integrating microbial biodegradation and material science. The research is based on microbial enzymes used in combination with a silica support material to metabolize s-trazine ring compounds and aromatic hydrocarbons for applications in environmental cleanup and biotechnology. A genetically-engineered bacterium expressing atrazine chlorohydrolase was encapsulated into novel silica gel compositions. The biodegradation ability of the developed hybrid material was tested in a continuous-flow bioreactor filtration system for atrazine removal in wastewater. The materials-biocatalyst hybrid was further applied to a different enzyme system and a different chemical to expand the scope of applications. Cyanuric acid was chosen because there is no current remediation method available although there is a need for such method. Three different bacterial cyanuric acid hydrolases were compared with respect to stability and effectiveness in the silica matrix. Cyanuric acid hydrolase from a thermophilic bacterium was further investigated in a simulated bioactive filter system using a solution prepared in the laboratory as well as actual water samples. The results from both experiments showed the efficacy of the process. The materials-biocatalyst also was investigated to create a synthetic ecosystem consisting of two distinct bacterial species to degrade aromatic hydrocarbons. In this system, heterotrophic bacteria performed aerobic biodegradation requiring a high oxygen level, while phototrophic bacteria produced oxygen via photosynthesis. Experimental results showed the system was more effective for oxygenation than external supplementation. The materials-biocatalyst was further modified to be applied for bioremediation of atrazine spills. In order to treat high concentration of waste chemicals, hydrophobic silica materials were used to allow rapid adsorption of the chemical prior to biodegradation. The hydrophobic materials-biocatalyst was characterized in terms of mechanical properties and biodegradation ability. The study showed that the hydrophobic silica with cells adsorb chemicals selectively, releasing biodegradation products, which makes the material self-regenerating.