Technical Bulletin No. 0034: Factors Affecting the Reuse of Board Mill White Waters and Clarifier Underflows

Because of difficulties frequently experienced in re-circulating boxboard machine waters to a high degree, and troubles arising through the reuse in the mill of underflow slurries from clarifiers operating on the "white water", the Rutgers University project of the Council has attempted to determine experimentally the major causes of such difficulties. The experiments described in the attached report indicate that increased concentration of dissolved solids or fines in re-circulated white water have little effect on freeness of the stock. Sliming of the water due to bacterial activity was the only factor observed as having a marked effect on freeness. High temperatures, depressed pH values and germicides were shown to be capable of preventing loss of freeness under the conditions of the experiment, and the addition of substances such as starch and proteins which serve as microbial food accelerated freeness loss. This research emphasizes the paramount importance of slime control in the reuse of board mill white water slurries in re-circulation systems and to some degree contradicts the theory that fines end high dissolved matter concentrations are of controlling importance in the white water system.