Setting of Optimal Dosage of Polymer Flocculant in Centrifugal Dewatering Process for Digested Sewage Sludge

In the present study, we investigated the relationship between 11 properties of digested sludge and the optimal dosage ratio of polymer flocculant, assuming a conditioning process for sludge fed into a dewatering centrifuge. Furthermore, the study was focused on the supernatant phase （ mixed phase of colloidal matter and dissolved matter ） obtained by centrifugal separation of sludge, and a list of the properties of the supernatant phase was created. We then attempted to identify the properties that govern the optimal dosage. As a result, no correlation between total solids and the optimal injection ratio was observed. Therefore, the dosage was defined as the absolute quantity of polymer flocculant per 100 grams of sludge （ g/100 g sludge = % per sludge weight ） . As a result of examining its relationship with various properties, the strongest correlation was observed between the anion concentration of the supernatant phase and the optimal quantity of polymer flocculant, with r=0.73. A correlation was also found between the optimal quantity of polymer flocculant and the turbidity of the supernatant phase （ r=0.68 ） . We thus found that the optimal quantity of polymer flocculant can be predicted simply by centrifuging the raw sludge and measuring the turbidity of the supernatant phase.