David Ravnjak, Janja Zule, and Adolf Može
Pulp and paper institute, Bogišičeva 8, 1000 Ljubljana, Slovenia

Abstract
Detrimental substances are a group of various dissolved and colloidal anionic olygomers or polymers and non-ionic hydrocolloids in papermaking waters, which negatively affect the papermaking process during the reusal of process water. They can be removed from the process water by the use of fixing agents (chemicals with high surface charge density). In our work we investigated the efficiency of detrimental substances removal by the use of Al-salt, combined with a polyelectrolyte. The results showed that in this way the detrimentals could be removed quite well. Also it was found, that the removal efficiency is not dependent only on fixing agent concentration, but also on other factors.