Postconsumption Sewage Treatment in Environmental Systems Analysis of Foods: A Method for Including Potential Eutrophication

Food in general has a high nutrient content, which essentially passes through the human organism and ends up in the sewage system. This high nutrient content in sewage, however, is rarely included in environmental systems analyses of food products or production systems. At the same time, several studies on sewage systems have shown the significance of plant nutrients in sewage system outlets. This means that important environmental effects may be neglected in environmental systems studies of food. We present a method for including emissions that occur after food consumption in environmental systems analyses of foods. The method uses easily accessible input data to calculate the postconsumption emissions caused by certain food products. The method was tested by completing the results for eutrophication from seven life‐cycle assessments (LCAs) on food products with the corresponding emissions caused by outlets from a sewage plant. The results showed that postconsumption eutrophication was a significant part of the products' total life‐cycle impact, ranging from 5.5% (beef) to 86% (apples). The conclusion is that including postconsumption emissions is important for studies aiming at mapping a product's life cycle to find the most environmentally relevant parts, as well as for eco‐labeling purposes. If the purpose of the study is decision support, the postconsumption phase should be included where the decision affects this part of the system, otherwise not. When products are compared, postconsumption emissions should be included if their nutrient contents differ.