Calculating expected effects of treatment effectivity and river flow rates on the contribution of WWTP effluent to the ARG load of a receiving river

Carsten Ulrich Schwermer,Wolfgang Uhl

doi:10.1016/j.jenvman.2021.112445

Abstract

Concentrations of genetic markers for antibiotic resistance genes (ARGs) were measured in the effluents of three Norwegian wastewater treatment plants (WWTPs) and in a receiving river upstream and downstream of the discharge point of one WWTP. Calculations based on mass balances were carried out to evaluate the impact of river flow rates and treatment effectivity on the WWTP's contribution to the load of genetic markers in the river. At average river flow rates, the WWTP effluent contributes 5–15% to the genetic marker load of the respective river. However, at minimum river flow rates, the WWTP effluent contributes 22–55% to the loads of different genetic markers. Scenarios of an improved or worsened removal of genetic markers in the WWTP showed that a further 1-log removal using additional treatment would be sufficient to improve considerably the river water quality with respect to genetic markers. Then, at an average flow rate, the contribution of the WWTP effluent to the load of the river would be less than 2%. However, in the case of low treatment effectivity or malfunction of the WWTP, the marker load of the river would increase dramatically. Even at average flow rate, 75–92% of the marker load would then originate from the WWTP. The results demonstrate the importance of considering the flow rates and hydrologic characteristics of the recipient water body when deciding on priorities regarding the upgrade of WWTPs for further removal of ARGs.

Highlights

The global dissemination of antimicrobial resistance (AMR), one of today’s major health challenges, is mainly due to the emission to the environment of antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs) and antimicrobials contained in human and animal wastes
The threat of AMR in environmental settings is due mainly to envi ronmental bacteria that contribute to the development of antimicrobial resistance in clinically associated bacteria through the mobilisation of novel ARGs and the transmission back to commensals and pathogens in humans and animals
The extent of ARG dissemination in environmental bacteria, how this is influenced by anthropogenic inputs, and how ARGs are shared between human-associated and environ mental bacteria, is currently unknown

Summary

Introduction

The global dissemination of antimicrobial resistance (AMR), one of today’s major health challenges, is mainly due to the emission to the environment of antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs) and antimicrobials contained in human and animal wastes. The extent of ARG dissemination in environmental bacteria, how this is influenced by anthropogenic inputs, and how ARGs are shared between human-associated and environ mental bacteria, is currently unknown. In addition to this indirect pathway, AMR may pose health risks in humans and animals through direct exposure to ARB and ARGs contained in food and water (Leonard et al, 2015; Wellington et al, 2013). Anthropogenic inputs to the environment in the form of discharge from urban wastewater treatment plants (WWTPs), hospitals, industries and application of manure to the land, in addition to inputs from diffuse pollution such as agricultural run-off, are thought to be the major streams influencing this process (Amos et al, 2014a, 2014b)

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