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MICROBIOLOGICAL SOLUTIONS WORLD PULPPAPER66 INTRODUCTION All grades of paper can have a problem with odour. The problem can be in the paper or as part of the operation. The cause of odour problems fall into two main groups chemical and microbiological. The microbiologically- caused problems occur more often than the chemical- and this is especially so with recycled packaging grades. When investigating an odour problem an understanding of the possible causes is important. There are various lab methods to identify the odour forming gas. Identifying the source of the odour is an important first step in the problem solving process. Once the source has been identified then a solution can be implemented. The solution can include process changes as well as a treatment program. This article focuses on volatile fatty acids VFAs and the issues they can cause in recycled packaging grades. RECYCLING PACKAGING When looking at the packaging industry as a whole VFAs are more of a problem in 100 recycled operations. If you think about the pulps used in virgin packaging such as unbleached kraft NSSC and sulphite it is clear that the pH and temperatures that are used in these processes result in good microbial control. With old corrugated containers OCC you have a number Identifying the source of the odour is an important first step in the problem solving process. Once the source has been identified then a solution can be implemented of factors that result in more microbial contamination. These include outdoor storage and single stream recycling. With single stream recycling there is more chance of the recovered board to be contaminated with food matter. The food matter will contain microorganisms and also serve as food for the microbes. The other factor that has led to more VFA issues is the tightening or closing up of water systems in packaging mills. As packaging companies look to reduce fresh water use save energy and reduce effluent there is less and less opportunity to remove or wash out undesirable compounds. This is a factor that affects all types and grades of pulp and paper. VOLATILE FATTY ACIDS What are VFAs and where do they come from VFAs are fatty acids with an aliphatic tail of less than six carbon atoms. Table 1 lists the various VFAs and the odours they produce. The most common types of VFAs found in recycled packaging operations would be acetic propionic and butyric. Many different types of bacteria can produce VFAs these include both facultative and strict anaerobic bacteria. Facultative anaerobic bacteria can survive with or without oxygen while strict anaerobes thrive in no or low oxygen conditions. One example of a VFA producing bacteria is the Clostridium genus. These are obligate anaerobes meaning that oxygen is toxic to them. They are also endospore formers. Some bacteria form an endospore this is a spore that is formed inside the bacterial cell that contains the genetic material. This spore is released when the cell dies and is very resistant to hostile environmental conditions. They will survive prolonged boiling for example. Once conditions are again favorable to the bacterias growth the spores wake up and start to grow. The presence of endospore forming bacteria is a factor that needs to be considered in a control program. What are the issues that can be caused by VFAs These fall into a few areas the first is odour which can be in the final product or in an area. There can be complaints from neighbours or from the workers in the mill. Odour in the final product can be a very serious issue that can lead to loss of business and can put a mills future in jeopardy. Some packaging customers have limits on the VFA level in the sheet that need to be met by the board producer. DIAGNOSTIC METHODS In problem solving any odour issue you first need to determine the type of gas or gases that are producing the odour. There are various tests that can be done By David R Jones Industry Specialist Buckman Solving Volatile Fatty Acids Issues in Recycled Packaging Operations