Background Pickling of stainless steel is a chemical process in which strong acids, mainly nitric acid, are used to remove oxides from the steel surface. The effluent from this process is an acidic stream contaminated with metals. Both the acid and metals in the effluent are environmentally problematic. When nitric acid is used the effluent also contains nitric compounds, which can cause eutrophication when the effluent is discharged into watercourses. Effluent from pickling facilities is usually treated and purified and only small amounts of metals and acids are found in the effluent released from these facilities. The waste acid is neutralised with lime, a process which reduces the metal and fluoride content by precipitation. The nitrates from the nitric acid however cannot be treated efficiently and are therefore discharged (in the case of the beneficiary, to Lake Mälaren, the third largest lake in Sweden). The aims of this project is therefore to develop a proces for the removal of these nitric compounds. The proposed process would result in a reduction in the consumption of fresh nitric acid, which would not only have a positive environmental impact, but would also have a positive economic impact. Objectives The objective of this project was to demonstarte a new clean technology which would reduce the discharge of nitrates from the stainless steel industry by nitric acid recycling. The process to be used is called electrodialysis. This is a membrane filtration process, which with the help of ion selective membranes and an electric field is able to recycle nitric acid from a waste acid stream and concentrate the recycled acid to a concentration reusable in the pickling process. The aim was to reduce the discharge of nitrate-nitrogen (N-NO3-) from 250 to around 120 tons per year. The project would involve the construction of a full-scale electrodialysis plant which would be used to recycle nitrates. The plant would be fully integrated into the normal acid handling process. This type of facility would also be promoted in several other plants run by the beneficiary company. Pilot plant experiments showed that it is possible to reduce the emissions of nitrates by up to 85% with this type of technology. The process to be developed had a target for total nitrite effluent reduction of about 60% at the pickling facilities. The plant was to be located at the beneficiary company's pickling facility in Torshälla, Sweden. Results The project demonstrated that the introduction of electrodialysis for mixed pickling acid recycling functiond as envisaged. The installation led to a 55% reduction in the discharge of nitrates. The need for a precipitation agent in the neutralisation step and the land-filling of sludge were also reduced. The integration of the equipment into the pickling process is a vital part of AvestaPolarit acid management system and this has brought the Nyby plant a step closer to the desired closed loop system. This process is considered a “Best available technology,” as stated in the EC´s directive on integrated pollution prevention and control (IPPC). Apart from the obvious environmental benefits, the cost reduction is also considered to be an added bonus. Although the system still has to prove itself over a longer period, the results show that such a system can generate about a 10% return on investment per year. This Life demonstration project has attracted alot of attention from Swedish and International stainless steel producers and environmental authorities. With increasing pressure to reduce the discharge of nitrates this process, which has shown high transferability, has considerable potential for reproduction elsewhere. Further installations throughout Europe would increase production efficiency and would also create new employment opportunities. . In an interview published in the LIFE Focus publication, “Industrial pollution, European solutions: clean technologies” (2004), the beneficiary reported nitric acid recycling through electrodialysis would soon be adopted at other units within the Nyby steel group. A major German producer has also expressed interest in the process. Furthermore, the project results have been presented at seminars and other international meetings.