Biofilm Performance in an Aerobic Fluidized Bed Reactor During the Start-Up Period

This study investigated the performance of an aerobic fluidized-bed biofilm reactor (AFBBR) at the start-up stage. By means of cultivating bacteria naturally in a growth culture medium that has similar ingredients as the feed water for the AFBBR reactor, the seeding bacteria solution with sufficient amount of lively and well-acclimated bacteria and very low suspended solid was obtained after 4 days cultivation and acclimation. AFBBR was quickly started up in 14 days after bacteria solution was seeded, achieving a COD removal efficiency of 82.3% for a synthetic wastewater of 220 mg/L influent COD at Hydraulic Rentention Time (HRT) of 45 min. Growth of biofilm thickness was tracked and the film thickness stabilized at 24plusmn2 mum under steady state operating conditions. The course of biofilms formation was observed by an optical microscope. At the beginning, biofilm formed when some microorganisms attached onto the activated carbon particles irreversibly. As the biofilm grew and more metabolite accumulated on the particle surface, the whole particle became covered by the biofilm. Finally, mature biofilm formed and biofilm thickness growth slowed down due to the shear stress of flowing liquid. Both low liquid velocity and decreased nutrient concentration with bed height contributed to the variation of biofilm thickness of bioparticles. Bacillus was found to densely pack on the surface of the activated carbon particles, observed by SEM.