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Abatement of VOC load from waste water treatment in mechanical pulping (VOCless waste water)
Start date: Oct 1, 2010, End date: Sep 30, 2013 PROJECT  FINISHED 

Background In 2007, some 43 million tonnes of wood pulp was produced for papermaking in Europe, representing some 20% of the total world supply. The main grades of wood pulp for papermaking in Europe in 2008 were sulphate pulp (62%), mechanical and semi-chemical pulp (33%) and sulphite pulp (5%). Between 1991 and 2007, while pulp production in Europe increased the number of pulp mills in operation declined. There are now approximately 200 mills in Europe with a production capacity of 200 000 tonnes/yr or more. Volatile organic compound (VOC) emissions are between 0.1-1.0 kg/tonne of pulp produced, being highest in the mechanical pulping process. The data imply that the contribution of the mechanical and semi-chemical pulping to total VOC emissions in Europe is significant. VOC emissions from mechanical pulping processes are recognised as the most significant air emission from pulping, accounting for 2-3% of European non-methane VOC emissions. VOCs are the main contributors to the formation of photochemical oxidants. An important by-product of the degradation of VOC is ozone, an extremely toxic agent, which affects eco-systems e.g. human health, the growth of plants, and materials e.g. plastics. VOCs from pulping also cause significant odour problems. Objectives The VOCless waste water project aimed to reduce emissions of VOCs from mechanical pulping processes, thereby reducing their contribution to smog formation and odour problems. The project would specifically target VOCs in wastewater from the mechanical pulping. It would demonstrate the viability of VOC and odour abatement systems in conditions characterised by fumes with high humidity, varying VOC concentrations, low oxygen content, the possible presence of sulphur compounds and large air-flows. It would seek to determine how plant design for pulp processing and wastewater treatment could be altered to minimise the VOC load. This would help to create a healthier working environment for pulp mill workers and a cleaner environment for people living in the vicinity of these plants. The main expected results were the development and testing of three prototype technologies (UV-filtration, bio-filtration and catalytic incineration), as an alternative to thermal treatment, to lower the emission of VOCs from the wastewaters in pulping; and, as a support measure to develop valid and reliable method(s) to measure the emissions at the wastewater treatment plants emitting VOCs. Results The different technologies (i.e. UV-filtration, bio-filtration and catalytic incineration) were developed and tested at the aerobic wastewater treatment plants in Anjalankoski and Kotka, and at the anaerobic wastewater treatment plant in Kotka, Finland. The preliminary results indicated that the VOC emissions can be measured and/or quantified to a reasonable degree: The comparison and testing data provided new information about the potential of the technologies under two different types of treatment systems (aerobic and anaerobic). In total, six separate, parallel pilot operations were carried out. VOC measurements were carried out, ahead of the pilot abatement tests. These indicated that the VOCs are literally volatile: the emission concentrations vary within short time periods, and, in general, the emissions are higher than expected, usually at concentrations of more than 50 mg/m3. The aerobic treatment process was found to be more stable than the anaerobic concerning emissions. But, both remain very volatile. The pilot tests indicated that all three technologies lower emissions, but that the ultraviolet technology is overly-dependent on the VOC concentration in the air and performs well only in low concentrations. The project concluded, therefore, that the ultraviolet technology was not feasible at this stage of development. The catalytic and bio-filtration abatement technologies performed in general, better and similarly. But, the costs of bio-filtration are slightly lower than for catalytic incineration – representing 0.1 - 0.2 % of the market price of the pulp. Finally, the future sustainability of the project results depends very much of the regulatory framework and e.g. more detailed, quantified emission limits that will dictate the applicability of the developed methods. The findings could, however, be utilised in the local implementation of the IPPC directive, as well as in the further development of the best available technology (BAT) reference document in the pulp and paper industry. Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).

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