Integrated global assessment of Escherichia coli emissions from wastewater treatment plants

Wastewater treatment plants (WWTPs) are critical for mitigating anthropogenic contaminants, yet their effectiveness in controlling waterborne pathogens has not been assessed globally. This study presents the first global assessment of Escherichia coli (E. coli) emissions from 58,502 WWTPs across 188 countries and territories, utilizing a CatBoost machine learning model based on actual data from 230 facilities. Our results reveal pervasive E. coli contamination in global WWTP effluents, with a median concentration of 3.83 log Most Probable Number (MPN)/100 mL (range: 0-5.86 log MPN/100 mL), and 78.3% of WWTPs exceeding 3 log MPN/100 mL, particularly in Africa, South America, and Southeast Asia. The primary driver of this contamination is insufficient disinfection coverage, which is closely linked to the lack of enforceable microbial discharge standards rather than the development level alone. Furthermore, E. coli emissions from WWTPs compromise the microbial quality of downstream drinking and recreational waters, posing serious public health threats. To address this gap, we propose Human Development Index (HDI)-stratified E. coli discharge standards based on reverse risk modeling aligned with WHO health-based targets. Scenario analyses indicate that combining these risk-informed thresholds with targeted disinfection upgrades could reduce global non-compliance of WWTPs by 47% for drinking water and 58% for recreational water exposure, with the greatest benefits in regions with limited infrastructure. This study provides the first global, health-based framework for microbial water quality management in WWTPs, offering actionable guidance to reduce inequities in waterborne disease risk and improve global water safety.