Effect of Operational Conditions on Pellets Settling Velocity

In pellet flocculation blanket (PFB) process, pellet flocs' settling velocity is an important parameter, hence, it is necessary to investigate it to achieve optimum operation conditions of the process. To evaluate pellets settling behavior under different operational conditions, a dynamic experiment was carried out to concentrate ferric flocs sludge by PFB process with the scale of 0.5~1.2 m3/h. Under different operating conditions such as raw water concentration and up-flow rate, pellet particles were sampled from different locations of the blanket in various operating stages to analyze its setting velocity. Experimental results revealed an approximately linear relationship between the raw sludge concentration and blanket volume concentration, and identified the pellet density was increased along with the increasing of raw sludge concentration. So under the same up-flow rate, agitation intensity and PAM dosage, higher concentration raw water would cause better pellets settling behaviors. While the relationship between the blanket volume concentration and up-flow rate reflected another linear dependence, namely, the blanket volume concentration would decreased linearly as the up-flow rate increased, hence, along with the increase of up-flow rate, pellets settling velocity would decrease due to its lower density.