Improvements of Microbiological Control in Coled Water Systems for the Paper And Board Industry, 1998 Environmental Conference Proceedings

G LENON,

Centre Technique du Papier

C DESCHAMPS,

Centre Technique du Papier,

L LOUVEL, J MORROS

Rhône Poulenc Industrialisation,

J MORROS

Rhône Poulenc BEVALOID,

J.M. LEBEAULT,

Université de Technologie de Compiègne,

Division des Procédés Biotechnologiques,

Paper manufacturing requires the contribution of an important amount of water. The objective is to attain lower consumption of fresh water by progressively extending the water circuits closure. This is not without repercussions on the development of micro-organisms present in the process waters. The increasing biological activities observed are often a source of bad odours, corrosion problems, slime deposit and consequently, reduced paper machine runnability and product quality. In order to prevent such problems, biocides are increasingly used. The success of their application is not always certain (bacterial stress and / or resistance - higher presence of spore formers). A high microbial load in the water process is not always a sign of slime propensity. Laboratory biofilm experiments emphasize specific adhesion mechanisms of bacterial cells. The assumption is that adhesion is the principle mechanism occurring in slime formation as well as in bacterial contamination of paper. Nevertheless, white water systems are far more complex than the drinking water circuits used to study the behaviour of biofilm (cell aggregates with exopolymers). Actually, the initiation of slime build-up in paper-machine water circuits was often characterized by deposition of insoluble material on surfaces prior to bacterial colonization and exopolymer synthesis. Moreover, it appeared that filamentous bacterial growth was initiated only after formation of exopolymers by primary colonizers. This suggested that postulated specific mechanisms, actually operating in papermaking systems, might not be a determinant factor compared with the non specific ones (sticky effect, entrapment). A simplified process water system allowed the definition of favourable and unfavourable conditions for slime formation and bacterial contamination of paper prior to and after drying. Important bacterial contamination of paper, directly related to the process water micro-organism load, was observed in the wet end. Only spore formers were detected after the drying section. Bacterial contamination of paper was increased with low microbiological load in water favourable for slime development. In this case, the spore formers remaining after the drying section were easily viable.

These observations led to new perspectives in the development of cleaner and environmental friendly technologies in order to decrease or replace biocides in closed water systems slime control and in microbial contamination of paper and board control.