For the purpose of reducing the anaerobic fluidized-bed reactor start-up period by increasing the initial biomass concentration, the operational conditions and mechanism of the pelletizing seed sludge were investigated by using laboratory- and bench-scale equipments.
It has been revealed that the factors that affect the pelletization process are the concentration of the recycled sludge, the upflow rate of the sludge recycle in the reactor and the distribution of the carrier material diameter. In addition, it has been found that the pellets (2 to 5 mm in diameter) can be formed within several tens of hours by limiting these factors within an appropriate range. During the pelletization process, the needle-shaped matter was first formed with the sludge adhering in a broom shape to the upper side of each carrier, and then they were merged and rolled while incorporating the recycled sludge. The pelletization process took place physically rather than by biomass growth.
The initial biomass concentration in the reactor could be made to be 4,000 to 8,000 mg VSS·l-1, due to pellet formation.