Process water systems of paper mills producing fluting and liner

With an average specific fresh water consumption of less than 5m(3)/t, paper mills producing fluting and liner have the lowest fresh water consumption compared with papermills producing other paper grades Some papermills even operate with a totally closed water system with zero effluent discharge. Odour and corrosion problems resulting from closing the water circuit could be significantly reduced by the installation of a biological treatment plant which is integrated in the process water system. Such in-line plant concepts are realised in two European paper mills producing fluting and liner. Many producers of these paper grades have efficient anaerobic-aerobic waste water treatment plants. The reasons why the re-use of biologically treated water in such paper mills can still have problems are discussed. Of great significance are the calcium concentrations of the process water and of the treated waste water. An inventory from several German papermills is finally discussed.