Two Stage Membrane Biofilm Reactors for Nitrification and Hydrogenotrophic Denitrification.

摘要

Membrane biofilm reactors (MBfR) utilize membrane fibers for bubble-less transfer of gas by diffusion and provide a surface for biofilm development. Nitrogen removal was attempted using MBfR in various configurations - nitrification, denitrification and consecutive nitrification and denitrification.;Effects of mineral precipitation, dissolved oxygen and temperature on hydrogenotrophic denitrification were investigated in a stand-alone denitrifying MBfR. Mineral precipitation, caused by intended pH control, caused the deterioration of denitrification performance by inhibiting the diffusion of hydrogen and nitrate. Operating reactor in various dissolved oxygen conditions showed that the denitrification performance was not affected by dissolved oxygen in MBfR. Optimum temperature of the hydrogenotrophic denitrification system was around 28°C.;Total nitrogen removal in a two-step MBfR system incorporating sequential nitrification and hydrogen-driven autotrophic denitrification was investigated in order to achieve nitrogen removal by autotrophic bacteria alone. Long-term stable operation, which proved difficult in previous studies due to excessive biofilm accumulation in autotrophic denitrification systems, was attempted by biofilm control. Average specific nitrification rate of 1.87 g N/m 2d was achieved and the performance was very stable throughout the experimental periods over 200 days. Performance of autotrophic denitrification was maintained stably throughout the experimental periods, however biofilm control by nitrogen sparging was required for process stability. The average specific denitrification rate increased from 1.50 g N/m2d to 1.92 g N/m2d with nitrogen sparging, over J90 days thus demonstrating the feasibility of stable long-term operation. Biofilm thickness was also stably maintained at an average of 270 mum by the gas sparging biofilm control. Maximum achievable nitrogen removal rate in consecutive operation turned out to be 6 g N/m2d.;According to the cost analysis of denitrifying MBfR, hydrogenotrophic denitrification can be an economical tertiary treatment option compared to conventional denitrifying filter although its economic feasibility highly depends on the cost of hydrogen gas.;Effects of loading rate and dissolved oxygen on nitrification performance were primarily investigated in a stand-alone nitrifying MBfR. Specific nitrification rate increased linearly with specific loading rate, up to the load of 3.5 g N/m2d. Beyond that load, substrate diffusion limitation inhibited further increase of specific nitrification rate. 100% oxygen utilization was achievable under limited oxygen supply condition.;Although this study was conducted in a lab-scale, the findings from this study can be a valuable stepping stone for larger scale application and open the door for system modifications in future.