Microorganisms common to papermaking systems

This section describes the four main groups of microorganisms that colonise papermaking systems and their significance. 

1 Bacteria. Bacteria are the most numerous microorganisms in mill systems, with populations typically ranging from 1,000 to 100,000,000 colony forming units (CFU) per ml of stock or additives. 

Aerobic bacteria. In a typical, well-agitated paper system many of the bacteria grow aerobically and utilise oxygen for growth. Pseudomonas species are common rod-shaped bacteria frequently found in the bulk fluids 

A coliform not common in papermaking systems is Escherichia coli. E. coli is closely associated with fecal contamination. If E. coli is found in the paper system, it indicates that sewer lines are entering process waters, or that faecal waste from birds or other animals contaminates the system. 

Anaerobic bacteria. Anaerobic bacteria do not use oxygen and may be harmed by it. Anaerobes thrive in poorly agitated chests, and in areas of deposits in well-aerated chests where oxygen has become depleted. Biofilms are several hundred cells thick, and the microorganisms in the outer layers rapidly use up available oxygen. This results in anaerobic conditions within the biofilm that will favour the growth of strict anaerobes. 

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