Real-time carbon monitoring at water resource recovery facilities (WRRFs) is of growing importance as it relates to plant-wide energy balances, efficacy of biological nutrient removal processes, and detection of process upset events. Bio-electrochemical technologies convert organic matter to electrical current, creating the potential to provide real-time amperometric sensory data of soluble carbon concentrations. Additionally, the amperometric signal generated by electroactive biofilms provides an online biometric to monitor metabolic activity and detect toxic shocks or overloading in real-time. Recent case studies indicate the potential benefits of bio-electrochemical sensing (BES) for real-time carbon monitoring; however, there is a need to develop mechanistic insights into sensor structure and function, models that account for environmental factors, and guidance documents for application under diverse conditions at WRRFs. This project seeks to fill this gap by developing mechanistic insights into BES biofilm structure and function, evaluating BES sensitivity to environmental factors under field conditions, and establishing best practices for BES monitoring of carbon and metabolic activity.