Increasing environmental demands and needs to reduce water and energy consumption have lead to more closed process systems. In certain process steps the oxalic acid, present in the wood and also formed during pulp bleaching, forms an only slightly soluble precipitation with calcium. This is why many pulp mills experience problems due to calcium oxalate precipitation in tubes, heat exchangers and washing filters.Karlstad University, Domsjö Fabriker, EKA Chemicals, Holmen, M-real and Novozymes have participated in the project ”Control of oxalic acid in pulp manufacturing” SCA, Stora Enso and Södra have supported the research.78 pulp mills in Europe, America, Asia and Africa participated in a study, which showed that 29 mills had problems due to calcium oxalate precipitation. Eleven mills had precipitation of other compositions.The project has given both suppliers and mills an increased knowledge of how the oxalate problem can be reduced. /AA