Machine learning in wastewater: opportunities and challenges - "not everything is a nail!"

This paper highlights the potential of machine learning (ML) for wastewater applications, with a focus on key applications and considerations. It underscores the need for simplicity in ML models to ensure their interpretability and trustworthiness, cautioning against the use of overly complex 'black box' models unless absolutely necessary, especially with limited data. Not all modelling problems should be considered nails for which the ML hammer is the best-available tool. We emphasise the critical role of thorough data collection, including metadata, given its scarcity in some areas. Future research is encouraged to develop benchmark hybrid models to bridge the educational gap for environmental engineers and to establish best practices for managing data and model metadata, thereby improving ML's accessibility and utility in wastewater applications.