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MICROBIOLOGICAL SOLUTIONS WORLD PULPPAPER68 one endospore. When environmental conditions become more hostile then the percentage of the population that produce an endospore will increase. The result is that you could kill all of the living bacteria and leave the endospores. Once conditions are again favorable for bacterial growth the same problem will occur. Choosing the right type of control program is important. There are two main types of biocides the organic based and inorganic. The organic products contain an active that is toxic to microbes. It is important to choose the right active for the type of microbe that needs to be controlled. A biocide active that is very effective at reducing an aerobic bacteria population may have little effect in reducing the population of an anaerobic bacteria. Thus it is important to choose the right active or actives for the type of microbe that needs to be controlled. Application program design is also important. Flow rates have to be set so that the kill concentration for that specific active is reached. In addition some actives require more contact time to be effective and this needs to be reflected in the biocide application strategy. One of the downsides in using organic biocides is that they may not penetrate the biofilm to reach the anaerobic population. Also they may not be able to penetrate a pulp build-up at the bottom of a chest. Buckman has the required information for all of the actives in our biocide product line and uses computer models to determine cycling up of the product to ensure that the effective concentration is reached. Inorganic microbicides are mainly in the chlorine family different types include chlorine gas hypochlorite and chlorine dioxide. There are also products such as peracetic acid and peroxide. The chlorine products can be effective but there are limitations especially in a packaging operation. The chlorine products are oxidisers. They will oxidise organic matter inorganic reducing matter and biological matter including bacteria. They have to satisfy the total demand to be effective. For recycled packaging mills the demand will be higher than that found in a 100 virgin bleached kraft fine paper operation. The result is that the traditional inorganic products can be expensive and less than effective. OXAMINE Buckmans Oxamine family of products can be used to control microbes. The Oxamine products are a proprietary mixture of ammonium compounds that when mixed with hypochlorite at precise molar ratios and the correct pH produce the biocidal active. Because Oxamine is already combined it is not affected by the typical oxidant demand of the system. The active itself is biocidal and is able to greatly reduce the population of both aerobic and anaerobic bacteria. The precise mixing of the two components is extremely important to safely produce the required active. If the correct molar ratio is not maintained then other compounds can be produced that are not biocidal. Buckman has developed a PLC controlled sophisticated feed system that maintains the correct ratio to ensure that the biocidal active is produced. In addition it is important that the Oxamine and hypochlorite do not mix together in When environmental conditions become more hostile then the percentage of the population that produce an endospore will increase Figure 1. Oxamine Feed System