Global distribution of wastewater treatment plants and their released effluents into rivers and streams

Abstract. The main objective of wastewater treatment plants (WWTPs) is to remove contaminants such as pathogens, nutrients, and organic and other pollutants from wastewaters using physical, biological and/or chemical processes prior to discharge into receiving waterbodies. However, since WWTPs cannot remove all contaminants, they inevitably represent concentrated point sources of residual contaminant loads into surface waters. To understand the severity and extent of the impact of wastewater discharges from such facilities into rivers and lakes, as well as to identify opportunities of improved management, detailed information about WWTPs is required, including (1) their explicit geospatial locations to identify the waterbodies affected; and (2) individual plant characteristics such as population served, flow rate of effluents, and level of treatment of processed wastewaters. These characteristics are especially important for contaminant fate models that are designed to assess the distribution of substances that are not typically included in environmental monitoring programs, such as contaminants of emerging concern. Although there are several regional datasets that provide information on WWTP locations and characteristics, data are still lacking at a global scale, especially in developing countries. Here we introduce HydroWASTE, a location-explicit global database of 58,502 WWTPs and their characteristics. This database was developed by combining national and regional datasets with auxiliary information to derive or complete missing WWTP characteristics, including the amount of people served. A high-resolution river network with streamflow estimates was used to georeference WWTP outfall locations and calculate each plant’s dilution factor (i.e., the ratio of the natural discharge of the receiving waterbody to the WWTP effluent discharge). The utility of this information was demonstrated in an assessment of the distribution of wastewaters at a global scale. Results show that 1.2 million kilometers of the global river network receive wastewater input from upstream WWTPs, of which more than 90,000 km are downstream of WWTPs that offer only primary treatment. Wastewater ratios originating from WWTPs exceed 10 % in over 72,000 km of rivers, mostly in areas of high population densities in Europe, USA, China, India, and South Africa. In addition, 2,533 plants show a dilution factor of less than 10, which represents a common threshold for environmental concern.