Pilot scale evaluation on ferric floc sludge concentration with pelleting flocculation blanket process

Pelleting flocculation blanket (PFB) process has been successfully applied to high turbidity suspensions for high efficient solid/liquid separation. In this paper, by using the PFB process, a dynamic experimental study was carried out on concentrating ferric flocs sludge with a scale of 1.3–5.4 m³/h. The pilot experiment aimed to optimize the conditioning system and determine the operational parameters. Under the raw sludge concentrations of 103–1,154 mg/L, the system could achieve ideal conditioning effect with polyacrylamide (PAM) dosages of 0.3–2.7 mg/L, agitation speed of 10 rpm, and water up-flow rates of 18–48 m/h. Under the experimental conditions, the increase of polymer dosage would improve effluent turbidity and pellets settling behaviour, the moderate up-flow rate had no marked effect on treatment results, while too large surface loading could worsen effluent turbidity. The experimental results also revealed that there existed an approximately linear relationship between the raw sludge concentration and optimum PAM dosage, that is, the optimum dosage of PAM increased synchronously as the raw sludge concentration increased. While the relationship between the raw sludge concentration and maximum up-flow rate reflected another linear dependence, namely, the maximum up-flow rate would decreased linearly as the raw sludge concentration increased.