The use of regional material balances in water quality management

Results of a material balance for nitrogen and phosphorus for Austria will be shown as one example for the use of regional material balances in water quality management. Nutrients in wastewater stem from food and thus from agricultural production to a high extent. The use of sewage sludge from wastewater treatment plants recirculates a part of these nutrients into agriculture. Phosphorus removal at treatment plants is an important step for the improvement of sludge quality. Problems with the reuse of sewage sludge are related to the content of potentially hazardous substances (e.g., heavy metals) in the sludge. Strategies for reduction of heavy metal loadings of sewage sludge have to consider all different sources. As shown in a second example diffuse sources (e.g., corrosion of roofings) highly influence the heavy metal contents of sewage sludge. Additionally, the input of heavy metals via coagulants for phosphorus precipitation must be considered.