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Abstract:
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The pulp and paper industry is a dominant sector of the Finnish economy. Nowadays, the most typical operations within the pup and paper industry are Kraft, sulphite and mechanical pulping, papermaking and recovered paper processing. All of them have traditionally been considered as major pollutants. The pulp and paper industry had to reduce its environmental impacts by 80-90% in recent decades. This success was possible due to the development of new technologies relate to pulp and paper processes and the application of end-of-pipe techniques. The pollution of the water bodies is of major concern due to the fact that large volumes of wastewater are generated for each tonne of pulp. Although many mills only used primary treatments to handle effluents until few years ago, secondary treatments are, nowadays, almost indispensable to comply with limitations or recommendations. In this report the most common aerobic and anaerobic treatment systems are studied. The most promising techniques are also introduced.Between aerobic treatments, activated sludge and aerobic lagoons are the most widely used. Results from activated sludge plants and anaerobic lagoons in Finland, Sweden, USA, Canada, etc are reported. New advances in these techniques are also studied, such as suspended carriers in activated sludge or selectors to avoid bulking. Other promising techniques are aerobic biofilters and moving bed biofilm reactors. Anaerobic systems are not as widely used as aerobic techniques, but they have interesting application in combination with them. UASB reactors, anaerobic contact and hybrid systems are the most common unit within the pulp and paper industry. Some full-scale units are studied in this Thesis. A typical problem that is associated with secondary treatments is sludge handling and disposal. The present situation about this subject is explained and future alternatives introduced. Other problems, the impacts of effluents in aquatic enviromnents, such as those of endocrine disrupting substances, coloured compounds, etc, are also described. /Kir10 |