Problem or Resource - Why It Is Important For the Environment to Keep Track of Nitrogen, Phosphorus and Carbon in Wastewater and Sludge Management

Magdalena Svanström, G

Abstract

This paper discusses how the fate of nitrogen, phosphorus and carbon in wastewater and sludge management affects the environmental performance as it may easily be shifted from a resource to a problem and vice versa. The paper explores the impact of some variations in wastewater treatment technology with resulting shifts of elements between forms and media. To this end, life cycle assessment (LCA) results were calculated for a model municipal wastewater treatment plant with primary settling and secondary treatment, and anaerobic digestion of mixed primary and secondary sludge and subsequent use of the sludge in agriculture (baseline scenario). The effect of changing plant operation to increase nitrogen removal and to add also phosphorus control was studied, using data from mass and energy balances. Further, the paper shows that how data for many flows containing nitrogen, phosphorus and carbon is selected in LCA within ranges found in literature may have a large influence on the results. This effect was studied by varying the flows in the baseline scenario between high and low values found in literature. It was shown that LCA results are considerably affected by both considered operational changes and by assumptions on the magnitudes of some flows. The paper argues that more careful consideration of flows of these elements should be made in the operation of wastewater treatment plants and in selection of data in life cycle assessment (LCA) studies.