Utformning av en driftstrategi för Löt lakvattenreningsanläggning

Söderhalls renhållningsverk AB’s (SÖRAB) waste facility have an active landfill where they previously have been deposited organic waste. This landfill generates leachate that contains high levels of ammonium. To treat the ammonium rich leachate SÖRAB has built a continuous biological treatment plant (KBR). The KBR uses nitrification and denitrification to transform ammonium to nitrogen. Together with a wetland it constitutes SÖRAB’s treatment for leachate. This project aimed at creating a strategy to ensure that nutrient limits given by Miljödomstolen are not exceeded. SÖRAB wished for the KBR to be emptied yearly, a consequence of this is that the treatment period is paused for 4-5 months. While investigating the recipient it was found that the outflow from the treatment plant cannot be larger than the flow in the recipient. In cases where the outflow was larger internal nutrient limits were exceeded. With these demands and by evaluating the efficiency of the treatment steps and modelling the leachate formation an operational strategy of how the leachate treatment should be operated during the year was created. The evaluation showed that the denitrification process in the KBR needs additional phosphorus to perform satisfactory. Phosphorus cannot be added without taking the risk of exceeding the limits in the recipient. During the warm season the wetland performed denitrification adequately, though it decreased with the temperature. Therefore the most suitable time for emptying the KBR and pausing the treatment is the cold season. The KBR is optimally emptied during the fourth quarter, it will then be functioning again during the second quarter. Modelling the leachate volume showed that the outflow was greater than the recipient runoff during the third quarter. During this time water needs to be stored within the treatment plan, the wetland was considered the most suitable pond for storage. To enable capacity for the excess volume the level in the wetland needs to be lowered during the first quarter, when the flow in the recipient is high due to the spring flood. The outflow is then higher than the actual runoff from the treatment plant. During the third quarter the water level in the wetland is increased to allow for the treated water to be stored