微生物固定化のための膜の改質と水処理分野への適用 Surface Modification for Bacterial Immobilization by Radiation-Induced Graft Polymerization and Application to Biological Wastewater Treatment
Most biofilms have redox stratification where aerobic and anaerobic zones are stratified. This inherent property can be potentially applied to removals of persistent organic pollutants and simultaneous carbon and nitrogen. Biofilm reactors, therefore, have been numerously developed; however, their downsides are long-term startup and difficulty to maintain stable reactor performance since the reactor might experience sloughing events. The engineering challenges are to reduce startup time and to create rigid biofilm resistant to such sloughing events. Given that initial bacterial adhesion is an important factor to govern biofilm cohesiveness, enhancement of initial bacterial adhesion to a substratum is required. Here, we applied radiation-induced graft polymerization (RIGP) in terms of modification of a substratum to enhance bacterial adhesion and finally to develop a novel biofilm reactor system. Polyethylene sheets and hollow-fibers were modified with either amino or sulfonic acid groups. RIGP provides precise degree of grafting and density of the functional groups. Bacterial adhesion test on surface-modified membrane has revealed that membrane potential, i.e., electrostatic interaction, mainly governs bacterial adhesion rate, indicating that positivelycharged surfaces are favorable for initial bacterial adhesion. On the contrary, these surfaces potentially decrease bacterial activity, which is probably dependent on cell wall structures of Gram-positive and -negative bacteria. Even though bacteria attaching to the surfaces decrease the activity, flow cell test has demonstrated that these surfaces enhanced and maintained E. coli biofilm growth whereas the biofilm on negatively-charged surfaces did not grow well, paving the way for the effectiveness of the positively charged surfaces for bacterial immobilization carriers. Membrane-aerated biofilm reactors with positively-charged surface have been developed for controllable nitritation (conversion from ammonium to nitrite) and for simultaneous nitrification and denitrification, which achieved high oxygen utilization efficiency and high nitrogen removal rates. Therefore, we conclude that surface-modification by RIGP provides a suitable surface where rigid biofilm grows rapidly, leading to development of the novel biofilm reactor system for wastewater treatment.
膜 33(2), 54-62, 2008-03-01
THE MEMBRANE SOCIETY OF JAPAN