Estimations of municipal point source pollution in the context of river basin management

Abstract

Integrated presentation of total emissions on catchment scale is prerequisite for many tasks in integrated management of point and diffuse sources of pollution. This paper will focus on emissions of nutrients from municipal point sources. Based on calculations of discharges of N, P from households into wastewater and on the detailed evaluation of data from 76 municipal wastewater treatments plants, this paper presents ranges of specific loads of inhabitants and population equivalents in the raw wastewater. In addition data of these treatment plants have been evaluated in respect of the treatment efficiency for nitrogen and phosphorus (average reduction rates) dependent on the design characteristic (with or without nitrification, denitrification or enhanced phosphorus removal). The results of the investigation show that the specific N and P loads from households in Austria lie within the range 1.6–2.0gP/(inhabitant.d) and 11–13gN/(inhabitant.d). The specific contribution of industries to municipal wastewater varies between 0.3 and 2.0gP/(pe.d) and 0 and 13gN/(pe.d) with average values of 1.3gP/(pe.d) and 6.5gN/(population equivalent (pe)/d). As average values for municipal wastewater (contributions from household and industry) this leads to specific influent loads of 1.5gP/(pe.d) and 8.8gN/(pe.d). Average treatment efficiencies of treatment plants are for instance 50% nitrogen removal in treatment plants with nitrification and 80% in treatment plants with nitrification/denitrification. For phosphorus a removal of about 85% can be expected where the treatment plant was designed for enhanced phosphorus removal. Finally a method for load estimations based on standard values as mentioned above was tested for the estimation of emission from municipal point sources of selected regions.