Pilot Study Of Control Parameters And Characteristics Of Fluidized-pellet-bed Bioreactor In Municipal Wastewater Treatment

Fluidized-pellet-bed bioreactor is a new wastewater process developed from fluidized pellet bed, which achieves high rate of solid/liquid separation. This process is applied for domestic wastewater treatment in one unit by combining fluidized pellet bed technique and activated sludge process perfectly. On the base of the former research findings, the experiment directed at the influence of control parameters, including the height of granular sludge layer, dosages of flocculant PAC and promoter PAM, stirring rotational speed and up-flow rate to the performance and microbes of FPB bioreactor; besides, the characteristic of FPB bioreactor in treating municipal wastewater, the analyzing of mass-balance and the COD equivalents of granular sludge layer. The following conclusions can be drawn:(1) In the range of 1100mm-1100mm heights in this experiment, the FPB obtains higher remove rate of the contaminants and more microbes are observed when the higher granular sludge layer is adopted, especially for the remove of NH3-N and the observation of ammonificator counts.(2) The deficient or excessive dosage of PAC will influence the state of granular sludge and the outflow water, and the excessive dosage of PAM will agglomerate granular sludge on the spindle of the blender. The optimum dosage of PAC and PAM is 48 mg/L and 4.0 mg/L.(3) The rotations of impellers and the upward flow maintain hydraulic conditions required by pelleting process and fluidized state in the column. The optimum rotational speed is 8r/min-12r/min and the up-flow velocity should not exceed 6.5m/h.(4) Removal of contaminants at 100mm has almost reached FPB bioreactor's entire value. The removal are persisted but nor much at higher position and the value of BOD₅/COD are enhanced a little. (5) In FPB bioreactor, average total aerobic bacteria counts per one gram dry granular sludge approach 10⁸, and total aerobic bacteria counts per unit volume are 4-8 times that of conventional wastewater treatment reactor. The content of volatile solids of granular sludge of FPB bioreactor is 56%. This content of chemical sludge of Chemical Enhanced Primary Treatment is about 30%, and the content of conventional activated sludge is 60～80%. Time required for completely replacement of granular sludge in FPB bioreactor is 13.6h by mass balance calculation, which match the actual measured SRT. It turns out that,for the granular sludge in the column, the COD equivalent is 1.88g COD/g MLVSS. As a comparison, the COD equivalent of C₅H₇O₂N which represents microbes ofconventional activated sludge treatment is 1.42 g COD/g MLVSS, and the COD equivalent of C₁₀H₁₉O₃N which presents organic substances in municipal wastewateris 1.99g COD/g MLVSS.