Study On Mathematical Model Of Activated Sludge Granulation

Compared with the conventional activated sludge, aerobic granular sludge has many advantages, such as compacte structure, good settling performance, strong impact resistance, etc. It could be operated at high organic loading.In addition, it could realize simultaneous nitrification and denitrification in waste water treatment. However, it is always companied by floc-like sludge. This coexistence and competition are directly related to granulation process of sludge. The existence of toxic refractory material has an impact on the competition between aerobic granular sludge and floc-like sludge. This experiment systematically simulate the granulation process of activated sludge. Considering the diffusion and mass transfer effect, and introduct competitive inhibition and noncompetitive inhibition, the one-dimensioned radial growth model was established based on the no.1activated sludge mathematical model. Breakup model and settlement model were established based on population balance equation.The simulation results show that the increase of particle size go against the substrate competition of granular sludge,but is beneficial to it’s denitrification. Low DO concentration go against the COD removal of granular sludge, but it’s denitrification was promoted. High DO concentration could promote the COD removal of granular sludge, but the denitrification of granular sludge and floc-like sludge was suppressed.Granular sludge could buffer the inhibition of Cu2+. When the concentration of Cu2+is small, the inhibition of Cu2+to Granular sludge is weak. So the buffer action of granular sludge may seem relatively large. The removal quantity and rate of COD and NH4+-N, and the growth quantity and rate of XA and XB in granular sludge were higher than that in floc-like sludge. When copper ion concentration increases more than10mg/L, the inhibition of Cu2+is strong. It leads the buffer action of granular sludge to smaller. Because of no mass transfer limit, the growth of floc-like sludge has the advantage. With the increase of Cu2+concentration, the inhibition to heterotrophic bacteria in particle was increased. N2generation quantity and rate become smaller too. However the generation quantity and rate in granular sludge were always greater than that in floc-like sludge.Granular sludge could buffer the inhibition of phenol, and is good for the growth of phenol degradation bacteria. The increase of phenol concentration is advantageous to the amount accumulation of phenol degradation bacteria but not conducive to its rapid growth. In a cycle, the amount of heterotrophic bacteria in the outer is less than which inside the particles, amount of heterotrophic bacteria. The quantity of autotrophic bacteria in Each part of the particles were less, the amount in the outer of particles is slightly less than which inside the particles. Phenol degradation bacteria were mainly in the outer layer which is located in the1.2to1.8mm from the center of a particle.When the flow velocity gradient value is10s-1, the particle size after the collapse was mainly distributed in0.25to1.75mm. When the flow velocity gradient value is25s-1, it was distributed in0.1to1.2mm. When the flow velocity gradient value is75s-1, it was distributed in0.05to0.6mm. With the increase of velocity gradient value, the disintegration rate of particle is faster. The smaller velocity gradient value lead to larger particle, but not stable. The bigger particle size granular sludge has the better settling performance, the higher sludge concentration is unfavorable to the settlement of granular sludge.