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BACTERIAL CONTROL MEASURES WORLD PULPPAPER58 One of our key findings is that the total quantity of vegetative cells and spore counts do not directly correlate machines. One of our key findings is that the total quantity of vegetative cells and spore counts do not directly correlate. Some process tanks can contain higher bacterial counts but not spores whereas another tank that may look fine based on low total bacteria count is really surprisingly high in spore content. RUNNING CLOSE TO THE EDGE Based on the experience and knowledge gained through both RD studies and numerous mill trials we are now confident that we have good solutions that can control hygiene issues. We have worked in many mills that having experienced hygiene troubles had tried and failed with other biocide solutions before we got involved. When we came in and worked closely with the mill team we were able to get them comfortably and consistently within specifications. Figure 2 below gives a typical before and after picture regarding spores. We have also observed many machines that run barely within specifications or put simply close to the edge. This leads to a fairly nervous situation for the mill management operations and sales teams. Achieving superior hygiene on a board machine requires complete cooperation between the mill and the partner taking care of dosing and monitoring of microbe control products ensuring that problems are anticipated and dealt with in a proactive way. Success also requires careful monitoring of all raw materials coming into the process including pulp and all chemicals. It may seem like an excessive amount of initial hard work but the payback to the mill in terms of reduced lost tonnage is very significant. In addition the mysterious and frustrating outbreaks of spores are reduced leading to improved peace of mind for the mill management. CORROSION RISKS OF INTENSIVE BIOCIDE PROGRAMS Another issue that unfortunately does not receive much attention until it is sometimes too late is the corrosion of machinery and components. We know of over 30 paper and board machines that have experienced dangerous and costly corrosion issues due to intense use of biocides. Machine corrosion due to biocides is a very real risk especially in food packaging board machines which are often using biocide-intensive control strategies due to the hygiene requirements. It is thus extremely important to understand and mitigate any potential corrosion risks especially when applying an intensive biocide program. We have conducted basic research on vapour phase corrosion mechanisms in paper machines to improve both understanding and control. Like hygiene corrosion on paper machines is very complex. In all of our laboratory studies steel plates were located above containers of flowing white water in a manner that only vapour phase contact occurred. Different oxidising biocides were then dosed at equal total active chlorine concentration and the subsequent corrosion of the steel coupons was measured. There were two key Figure 2. Development of bacterial spore content in finished board during a period of correcting the hygiene situation green line by applying a new control philosophy