Research On Physical And Chemical Property Of Granular Sludge In A Fluidized-pellet-bed Bioreactor

Fluidized pellet bed (FPB) system was originally developed for effective solid/liquid separation in water treatment. It was a new technology which had been applied in the treatment of wastewater. Its characteristic was the organic combination of phsicochemical method and biochemical method. It combined chemical coagulation, particle pelletisation, biological degradation, and separation in one unit. The experimental results showed that FPB bioreactor could successfully remove contaminants from wastewater under the optimal operation. As an independent processing unit, the important issue of FPB bioreactor was the stability and the anti-interferance ability of granular sluge. By laboratory experiment using two sets of FPB columns, this study was thus aimed to investigate the physical and chemical property of granular sludge, the change of particle size distribution and effective density under the periodic influent load. On the base of that result, we evaluated the relationship between property of granular sludge and the remove of contaminants, breakage-recovery characteristics of granular sludge. The conclusions were as follows:(1) Under the standard conditions, it formed good granular sludge in the FPB bioreactor. The particles had very compact structure, the effective density was one order higher than the ordinary flocs. Due to the dynamic balance of growth-breakage of particles and hydraulic stratified, the partical size became small along the bed height. At the height of 10cm,50cm,90cm, the partical size dso were respectively 2.84mm, 2.22mm,1.92mm。(2) Under series operation modes of FPB bioreactor, the second FPB underwent mainly particle breakage. After 12 hours, the partical size of each height became small, and the partical size tended to homogenization, but the particles were still pellet-like. While the second FPB became the first FPB, the partical underwent mainly growth, the broken particles could easily recover their previous state. The experimental results indicated that the granular sludge particles had very good dynamic stability and self recovery.(3) The effective density of the granular sludge did not show a tendency of variation of particle density with particle size as the ordinary flocs. The size-density relation was always within a certain area in the log-log plot and with effective density much higher than the ordinary flocs, indicating that the granular sludge formed by FPB operation possessed a dense structure.(4) Under series operation modes of FPB bioreactor, the change of the first column height had effect on the particle size of the second column, but the regularity was not obvious. That was mainly because there were not coagulant and coagulant aid. It showed that coagulant and coagulant aid were very important for the formation of granular sludge.(5) Under the standard conditions of FPB bioreactor, it could effectively remove TP, NH3-N and COD from wastewater. The rate of removal were respectively 60%, 56.7%,76.7%.(6) The removal to contaminants in the FPB bioreactor, was gradually achieved along the bed height. While the wastewater entered into the column bottom, the concentration of contaminants was decreased obviously, especially TP and COD. That was because of coagulant. While the water was in upflow along the bed height, the contaminants further induced. That was because microorganism degradated the organic compands. Thus, the removal to contaminants was a process which combined chemical coagulation, physical adsorption and biological degradation.