One containerboard mill was operating closed water circuit for several decades. This situation was born from the fact that there is no river discharge point and the COD load is far beyond the capacity of the local municipal sewage treatment plant.
The mill uses 100% waste paper as raw material and as starch content in the recycled paper had increased, the process water became contaminated and started fauling. Unfortunately this was also noticeable in the surrounding and in the product.
An inline process water treatment plant consisting of an anaerobic and an aerobic stage was installed and the return of treated water brought the process water in the mill back to the qualities that are normal for an open water circuit.