Background Most pulp bleaching processes use hydrogen peroxide as the main bleaching chemical. Bleaching processes are sensitive to metal ions, which negatively affect the final result. Therefore, substances such as EDTA (ethylene diamine tetracetic acid) are used to collect the metal ions, in order to prevent deterioration. In Western Europe, 35 000 tonnes of EDTA are used every year, and 3 800 tonnes of this amount is used within the pulp industry. (The largest sectors for EDTA in Western Europe are: industrial detergents (30%), agriculture (18%), pulp and paper industry (11%) and photochemicals (10%).) EDTA is a hydrophilic, chelating agent used for its abilities to form complexes with metal ions in the pulp suspension and to be washed out prior to bleaching. The metals would otherwise catalyze degradation of the bleaching chemicals. By using EDTA in the pulping process the beneficiary can increase the efficiency of every kilogram of hydrogen peroxide by 50%. However, EDTA-complexes are stable and not degraded biologically. EDTA’s ability to form metal complexes leads to harmful remobilisation of metals. EDTA also causes de-loading of useful metals in the sediments and suspended particles, leading to an increase of metals in the water phase. Objectives The project aimed to demonstrate the new BIORED concept based on a Multistage Biological Reduction process, designed for biological treatment of EDTA in pulp mills. This was to be done by Nordic Paper Seffle AB at the sulphite pulp mill in Säffle, Sweden. The experience gained during the demonstration phase was expected to provide an important reference for the European pulp and paper industry. To this aim, the project was to be divided into seven tasks: a planning and preparation phase (task 1) to be able to perform optimisation and construction at the mill (task 2); installation of the new and innovative BIORED system (task 3); testing of the system in full-scale production during a full year after installation (task 4); preparation and production of an analytic report during the final evaluation process to illuminate the effectiveness (task 5); dissemination of the results to all interested parties (task 6); and ensuring high quality and structure during project implementation by a sound and efficient project management (task 7). Results The BIORED-project has met the objectives and achieved the expected results. It demonstrated a new concept, decreasing the discharge of EDTA in effluents from pulp and paper mills through Multistage Biological Reduction. The innovative aspect of the BIORED concept has been the highly elaborated degree of segregation of the various microbial populations in the food chain. The project delivered a renewed wood handling process reducing water use as well as improving mechanical treatment and wood chips screening, which resulted in a reduced need to use EDTA chemical in bleaching. In addition, the project designed and constructed a water treatment plant based on a biological process to degrade the EDTA in the wastewater from the pulping process in several Moving Bed Biofilm Reactors in series (applying the MBBR™ biofilm technology). Each reactor contained a separate and specialised micro-flora, removing different fractions of the wastewater. In the bioreactors, the micro-organisms were growing on the surfaces of innovatively designed plastic carrier elements which entailed an extremely large surface area for microbial growth. A reduction of the EDTA dosage to the pulp has been achieved because of more effective complex formation due to the increased reaction time in the Q-stage (acid stage where chelating agent is used to remove metals) tower and the optimisation of the bleaching process. The installation of the biological wastewater treatment plant resulted in a degradation of about 40% of the EDTA in influent water to the wastewater treatment plant. In all, discharges of EDTA to the recipient water bodies have been decreased by some 60% and were expected to decrease more after the full optimisation of the biological treatment. The Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) in the wastewater were reduced by 92% and 40-50%, respectively. Due to the technical content of the project, the results of wastewater treatment process and impact in the recipient water bodies could not be verified in detailed quantitative terms during the course of the project. The developed process takes a longer time to become optimised and stabilised. For that reason, the project beneficiary continues the dissemination of the results after the project's end. A Reference Group of vital stakeholders (pulp mill, branch organisation, technical expert and research institute) was closely connected to the project, thus ensuring validation of project results and reproduction potential. EDTA reduction with MBBR™ biofilm technology can be applied to the treatment of other kinds of wastewaters in various industries. The only requirement is a continuous wastewater flow with enough concentration of EDTA to stimulate the adaptation process for the microbial degradation.