Abstract
Effects of upflow velocity on the biofilm physical properties in items of biofilm thickness, biofilm density and biomass per unit surface area of support particles were investigated by using lab-scale anaerobic fluidized bed reactors fed with a synthetic wastewater (a mixture of skimmilk and sucrose ; 2,000 mg-COD·l-1). Four identical reactors were operated for a period of 100 days in parallel at different upflow velocities, i. e., 4, 7, 14 and 25m·hr-1. The initial biofilm formation process was categorized into three types.
For the runs at 14 and 25m·hr-1, direct adhesion of inoculum sludge onto the carrier surface took place promptly, and the biofilm thickness developed up to 200 μm within only 1 to 2 days, and then decreased eventually to 100 μm. On the contrary the biofilm density increased consistently up to 10.2 mg·cm-3 and 4.4, respectively.
As for the run at 7m·hr-1, the biofilm thickness increased gradually to 100 μm with an increase in the biofilm density up to 14.4mg·cm-3. Granulated sludge in the size ranging 1 to 5mm and containing several carriers was formed at the lowest upflow velocity of 4m·hr-1.
The occurrence of initial adhesion led to shorten the period for which the biomass per unit surface attained the saturation values. The biofilm density was a more useful factor to determine the biomass per unit surface.
