A novel CSTR-type of hollow fiber membrane biofilm reactor for consecutive nitrification and denitrification

A continuous stirred tank reactor (CSTR) type of hollow fiber membrane biofilm reactor (HF-MBfR) using composite membranes was investigated for the nitrogen removal in synthetic wastewater. The CSTR-type of HF-MBfR process couples autotrophic biological nitrogen removal reactors with the bubbleless mass transfer of oxygen and hydrogen through hollow fiber membranes. For nitrification, CSTR-type of HF-MBfR was operated over 400 days and for hydrogenotrophic denitrification, CSTR-type of HF-MBfR was operated over 300 days. The maximum + steady-state NH4 -N removal rate achieved was 0.25 kg N/m3 day (2.06 g N/m2 day) and the denitrification rate achieved was 0.22 kg N/m3 day (1.72 g N/m2 day). Consequently, in the HF-MBfRs, biofilms were formed stably on surface of membranes, and nitrification and hydrogenotrophic denitrification were performed successfully during long-term operation.

In this study, by changing a volumetric influent loading rate as NH+-N and NO−-N, nitrogen removal of synthetic wastewater in the absence of organic carbon was evaluated using CSTRtype of HF-MBfR system. The CSTR-type of HF-MBfR contained composite membranes which provide 124 m2/m3 of the specific membrane surface area, and occupied 0.8% of the reactor volume. The nitrification CSTR type of HF-MBfR was operated over 400 day. The maximum steadystate volumetric NH+-N removal rate achieved was 0.25 kg N/m3 day, which corresponded to the membrane specific NH+-N removal rate of 2.06 g N/m2 day. The denitrification CSTR-type of HF-MBfR was operated over 300 days. The maximum steady-state volumetric denitrification rate achieved was 0.22 kg N/m3 day, which corresponded to the membrane specific denitrification rate of 1.72 g N/m2 day. High rates of nitrification and denitrification are achieved by providing slow growing bacteria like as nitrifying bacteria and hydrogenotrophic denitrifying bacteria, large surface area for biofilm attachment. Hollow fiber membranes provide a large surface area for gas transfer and biofilm attachment while occupying a relatively small volume within the bioreactor. Therefore, the high volumetric nitrogen removal rates can be achieved by addition more hollow fibers.