The value of anaerobic purification for pulp and paper mill effluents
In comparison to the food industry, anaerobic treatment had a later and a slower start in the pulp & paper industry. The first plants were installed in the beginning of the eighties and at the moment the number of projects that has been counted is approximately 140. Many of these plants have been installed as a pre-treatment stage before an activated sludge plant and reduce at least 80% of the energy consumption and the waste activated sludge yield. In return the produced biogas gives a positive energy balance of approximately 347 MJ/ton of packaging paper produced, which is, in the example of this publication, 4.6% of the total energy required to produce the paper. It is shown in graphs that anaerobic treatment is quite popular within the recycled paper and board sector. Furthermore there is a growing interest from the pulp mill sector, especially sulphite mills, TMP/CTMP mills and kraft mills. The majority of all projects are in Europe, with the peak in Germany, where 25 % of all realized projects can be found. The developments in North America are very slow. It is expected that the Far East will be developing more quickly in the coming years. Closed circuit operation and recovery of effluent is getting more and more popular among the users of anaerobic treatment. This positive development can be the spin-off of a better and more constant treated effluent quality, as well as the achievement of lower salt levels.