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Control of Micro-organisms in Paper Production: An Overview

In the Pulp and Paper Industry, the microbiological population being dealt with is dynamic, so any treatment program must maintain a flexibility capable of handling production or seasonal changes that may be reflected in the nature or severity of the slime problems encountered. A good microbiological control program will extend the time of high operating efficiency and produce a high-grade finished product. Cesco Solutions, Inc.’s ACT (Advanced Control Technology) Team will provide local experts in the area of microbiology, surface and colloidal chemistry, engineering/application technology, safety and regulatory compliance to support our microbiological control programs. Our commitment is to provide the right expertise to the mill on a 24-hour basis to ensure the success of our microbiological control programs.


Controlling micro-organisms on a paper machine may seem a costly proposition, especially on a modern alkaline fine paper machine. However, the cost of not controlling micro-organisms can be much higher. Micro-organisms, if left uncontrolled, will generally lead to the production of slime. Slime-related problems are a large economic drain. The Institute of Paper Chemistry estimates that slime-related problems cost the United States paper industry upwards of $100 million per year. The cost could be as high as ten times that without biological control systems or chemicals. Microbiological growth in a paper mill can lead to the following problems:

  1. Loss of Production. Breaks, unscheduled boil-outs, and wash-ups.
  2. Reduction in Quality. Slime spots, holes, odors in product.
  3. Microbiological Corrosion. Damage to metals, including stainless steel.
  4. Loss of Additives. Micro-organisms can grow in any of the following and plug lines, cause odor, reduce the effect of the additive, or cause slime growth on the machine: coatings, broke, filler, wet lap, alum, retention aid, size, or starch (cooked or uncooked).
  5. Production of Dangerous Gases. Hydrogen, hydrogen sulfide, or methane can be produced by bacteria, creating the potential for explosions.
  6. Off-spec and Rejected Product. Cost of segregating and repulping broke, cost of customer claims, loss of customers.

The control of micro-organisms is 60% housekeeping, 20% flow design, and 20% chemical program. A mill can troubleshoot for biological problems before they cause problems and effect profits. A routine survey for micro-organisms can identify potential problems and lead to a program to control microbiological deposits. An effective program is more than just adding chemicals. One can usually reduce costs by considering a couple of basic ideas.

First is to reduce contamination. A very important part of controlling slime is minimizing the amount of trouble-causing organisms entering the system. This is called good housekeeping. Maintain the machine in as clean a condition as possible, from the entrance of raw materials through the machine to the reel and converting. Washups are an integral part of controlling contamination. Water hoses should be employed to spray areas prone to buildup of stock or deposits during down time of machine due to break, boilout, or grade changes. Control of other deposit type on the machine is also related to good housekeeping. Pitch or stickies, scale, fiber or filler deposits provide an ideal place for microorganisms to grow. Probably the most important part of a microbiological program is a proper boil-out. The frequency of boil-outs is often closely related to the use of biocides.

Second is the selection of microbiological control chemicals. A biological control program is all encompassing, including a complete system survey: Make certain that the problem is indeed a microbiological slime problem; select the correct biocide; decide how and where to apply the biocide in the system (feed system, monitoring, and control of biocide); and assess the service capabilities of the chemical supplier. Cesco’s ACT Team can perform this survey, and help to determine the best control program for your plant and it’s changing needs.

The overall aim of a microbiological control program in a paper mill is to keep the machine system clean and free from any build-up of slime related deposits. Effective microbiological control calls for a highly systematic approach, due to the multitude of factors that must be considered and appraised when setting up the treatment program. Cesco’s microbiologists, chemists, and engineers are highly trained and experienced, and can help your plant achieve measurable economic benefit from an effective microbiological control program.

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