Including oxidisation of ammonia in the eutrophication impact category

Oxygen depletion of lake and seawater is a serious condition with large implications for biodiversity. Therefore, in LCA, the potential oxygen demand of water emissions is estimated under the label eutrophication impact category. This impact category should contain the impact of water emissions on the total oxygen consumption in the receiving water. This means that it should include both primary and secondary oxygen consumption. In spite of this, the oxygen needed to oxidise ammonia has normally not been taken into account when quantifying the eutrophication impact category. In this paper, weighting factors for ammonium/ammonia are suggested for the eutrophication impact category. It is shown that, for treated wastewater, the amount of oxygen needed for nitrification of ammonia is important when compared to the potential eutrophication calculated using the current recommended weighting factors. These weighting factors take into account oxygen needed to oxidise the organic matter in the wastewater emission and that needed to degrade the algae potentially grown due to the emission of nutrients.