Abstract
Abstract. The main objective of wastewater treatment plants (WWTPs) is to remove pathogens, nutrients, organics, and other pollutants from wastewater. After these contaminants are partially or fully removed through physical, biological, and/or chemical processes, the treated effluents are discharged into receiving waterbodies. However, since WWTPs cannot remove all contaminants, especially those of emerging concern, they inevitably represent concentrated point sources of residual contaminant loads into surface waters. To understand the severity and extent of the impact of treated-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 the population served, flow rate of effluents, and level of treatment of processed wastewater. 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. 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 a spatially explicit global database, termed HydroWASTE, containing 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 number 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 treated wastewater at a global scale. Results show that 1 200 000 km of the global river network receives wastewater input from upstream WWTPs, of which more than 90 000 km is 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, the USA, China, India, and South Africa. In addition, 2533 plants show a dilution factor of less than 10, which represents a common threshold for environmental concern. HydroWASTE can be accessed at https://doi.org/10.6084/m9.figshare.14847786.v1 (Ehalt Macedo et al., 2021).
Highlights
In all inhabited regions of the world, the water quality of rivers, lakes, and the ocean depends on how wastewater produced from human activities in upstream areas, especially those that are densely populated, is processed and disposed
To assign the estimated effluent outfall location of each wastewater treatment plants (WWTPs), various raster and vector layers representing the river network and catchment boundaries were obtained from a global hydrographic database termed HydroSHEDS (Lehner et al, 2008), which was derived from digital elevation data provided by NASA’s Shuttle Radar Topography Mission (SRTM) at 90 m (3 arcsec) resolution
The remaining 224 WWTPs were not linked to the river network, as they were located on small islands or in small coastal basins and are assumed to discharge directly to the ocean
Summary
In all inhabited regions of the world, the water quality of rivers, lakes, and the ocean depends on how wastewater produced from human activities in upstream areas, especially those that are densely populated, is processed and disposed. Robust estimates of current and future changes in water quality are needed to support global environmental and health risk decision making and to sustainably manage water resources to ensure clean and accessible water for all, as required by SDG 6 (Van Vliet et al, 2019; Tang et al, 2019; Strokal et al, 2019) To achieve this goal, global water quality assessments must be spatially consistent and comparable to be able to identify hotspots of contamination and trends in water pollution over time and across large regions. Calculations are typically based on the fractions of population connected to sewage systems per country To address this important shortcoming, the objective of the presented study is to develop a novel global database of WWTPs as a means for estimating the distribution of treated wastewater in the global river network at high spatial resolution. The database, termed HydroWASTE, includes the explicit geospatial locations of WWTPs, their main characteristics, and their linkages to the global river and lake network
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