in Svenljunga together with municipal wastewater from Svenljunga. This situation was a barrier for the tannery to increase the leather production, and furthermore the environmental authorities in Sweden were pressing the tannery to reduce the nitrogen pollution. The reduction of the nitrogen discharge to rivers and lakes has been a very high priority in Sweden for several years. The tannery started planning for the construction of a new treatment plant in 2002, with a clear goal that the amount of nitrogen removed should be high ( more than 80%) and stable. The nitrogen removal should not be affected by changes in the composition of the wastewater, nor by the harsh winter conditions in Svenljunga where temperatures of - 20 ° C are not uncommon. Selection of technology The project started with an extensive survey of results from other wastewater treatment plants. The study showed that the nitrification and denitrification of tannery wastewater to reduce the nitrogen content in the wastewater has gradually been discussed as an option in countries with strict nitrogen discharge limits. However, due to severe difficulties in controlling the process and odour problems, the process has not been introduced or considered possible for the treatment of tannery wastewater. One of the major suppliers of nitrification/ denitrification systems in Europe performed laboratory trials for a total of eight months on the use of nitrification/ denitrification " The reduction of the nitrogen discharge to rivers and lakes has been a very high priority in Sweden for several years"
technology on tannery wastewater with Elmo Leather. These trials were very successful and the results from the trials were used for upscaling to demonstrate that the technology can be used on wastewater from tanneries. Examples of important factors needed to obtain a stable cleaning process are: the plant has a strict process control ( pH and balance of nutrients is especially important); the plant is a two- step plant ( toxic compounds degraded in the first step) and the plant has the possibility of hydraulic equalization ( in order to avoid fluctuations in, for example, chloride concentration). Technical description An overview of the plant is given below and followed by a description of the plant. The principle of the WWTP ( wastewater treatment plant) is as follows: The wastewater flows from the tannery to the new inlet pumping station through a 2mm screen. The wastewater is then pumped to biological treatment.