Denitrifierande bioreaktorer: rening av kväve i lakvatten
Ammonium nitrate-based explosives are the most commonly used explosives in various industries today, including mining, rock quarrying, and tunnel excavation for roads. Studies from the mining industry have, however, shown that up to 28% of the explosives remain undetonated. These undetonated explosives dissolve in water and eventually discharge to nearby surface water and groundwater recipients, primarily in the form of nitrate (NO3-). A denitrifying bioreactor is a passive and cost-effective technique for reducing NO3-concentrations in leachate from piles of excavated rock, and have been built and evaluated at several sites in Sweden since 2015. A bioreactor is a simple construction and consists of an excavation that is filled with a reactive organic material, such as woodchips. Water with high concentrations of NO3- flows horizontally through the reactive material and the inflowing NO3- is transformed to N2 by the process of microbial denitrification. This paper provides a summary of the denitrifying bioreactor technique as a potential method for reducing nitrate concentrations in leachate from rock piles, with focus on design and operation criteria for optimal performance. A case study from a rock quarry in Kalmar County is presented, where the bioreactor has been in operation for four years with an average nitrate removal of 90 %.