MICROBIOLOGICAL TREATMENT OF WATERS FROM PAPER MILLS CIRCUITS

Microbiological aspect of paper making relates to slime issues. They are made of jellylike matter that build-up in process water circuits of paper mills. Water circuit of paper mills provides good conditions of microorganism development (nutritive substances, temperature, pH and oxygen). High contents of microorganisms are noticed on paper circuits that are able to reach up to 107 CFU/mL. The most common microorganisms are bacteria often joined by fungi and yeasts. The signs of infections that frequently occur in a paper mill are the following: a. Formation of slime; Microorganisms tend to attach on water circuit walls as biofilms; b. Felt plugging and foulness; c. Glue and starch damage; d. Stains and coloration; e. Cellulolitic action; f. Localized corrosion and odor (H2S). The first section of the paper shows the physical proprieties of sludge and slime (biological slime, chemical slime, chemical-biological slime). As a general rule, slime that is found in paper machines is a complex, chemical and biological slime. Biofilm deposits on water circuit walls are mainly made of bacteria and extra-cellular polysaccharides (EPS). Bacteria attach to walls, by means of protean filaments. Values of microbiological contamination and efficiency of using various biocides in the alkaline and acid processes are shown. We notice the efficiency of DILURIT 953 biocide, in the alkaline process (pH = 4-8, charge 200 g/ton of paper) that leads to reduction of bacteria number by 82.3%. The activity of DILURIT 953 is extended to all families of contaminants (bacteria, moulds, yeasts, and sulfate reducing bacteria SRB). Paper mills are facing problems not with the number of microorganisms in the system, but with the volume of slime on walls.