Research On Characteristics Of Contaminants Removal In A Fluidized-pellet-bed Bioreactor Under 2-stage Serial Operation

In order to understand the removal of organic matter in the fluidized pellet bed (FPB) bioreactor by extending hydraulic retention time (HRT), Two identical devices were investigated by laboratory experiment using two sets of FPB columns under parallel and series operation modes. a 2-stage serial FPB bioreactor was used for laboratory experiment. Under a condition of changing the sequence of the two reactor columns every 12 hours, Using activated-sludge at the end of oxidation ditch of Xi'an Beishiqiao sewage treatment plant to inoculation our biological fluidized pellet bed, the water quality, biological culture conditions and physical characteristics of particles were regularly tested.The research shows that:(1) A biomass concentration of 108ind./g could be maintained and the sludge particles could keep good granular shape in both columns.(2) The removal of COD and consumption of DO showed a continuity in the two columns. The first order kinetic relationship could be found for COD in both columns with quite similar kinetic coefficients.(3) By the exchange of the two columns in series order, fluidized bed particles experienced growth-broken-growth process. When it changed to the secondary column, it would underwent the decrease of sludge particle size. But the sludge particles could gradually grow and eventually return to the original level when it became to the first grade. Granular sludge in the fluidized pellet bed showed obvious periodicity.(4) The results indicated that the granular sludge in the FPB had very good dynamic stability, and the 2-stage serial FPB operation could provide an effective way to extend HRT and to improve the efficiency of pollutant removal.(5) The using of 2-stage serial FPB bioreactor, the hydraulic detention time was extended, doubling the effective height of sludge treatment, pollutant removal in a fluidized bed in effect could be strengthened. For the removal of organic pollutants, the first grade column could be 46.4%, and the secondary column based on the further could degradate 27.9%. Removal of ammonia nitrogen in the first grade column was 28.7%, and the secondary column based on the further could degradate 12.1%. Phosphorus removal was mainly by chemical precipitation.Contaminants from liquid to solid could be achieved by coagulation granulation process, the initial formation of granular sludge microorganisms were able to provide substantial adhesion and propagation of solid surface. From the perspective of microbial growth, fluidized pellet bed operation was similar to the pre-biological fluidized bed unit plus carrier later. In order to satisfy the condition of dissolved oxygen in FPB, there was an aeration device before water pumped to the fluidized pellet bed, equivalent to traditional wastewater treatment process in extended aeration units, the organic particles mainly removed by the biochemical role of aeration device. The removal of pollutants might include coagulation itself (the direct transfering of contaminants which can be condensed) and as well as physical absorption, bio-absorption, and biodegradation.