The present disclosure generally relates to a system for monitoring and/or controlling one or more agents, such as cleaning agents, in a wastewater treatment system. The system comprises a bio-electrochemical sensor for monitoring metabolic activity of a population of exo-electrogenic bacteria and providing an electrical output corresponding with the metabolic activity, where the bio-electrochemical sensor comprises an electrode pair and a power source for delivering a voltage across the electrode pair, and an electrical output analyzer for analyzing the electrical output and correlating the electrical output with the one or more agents in the wastewater treatment system. a change in electrical output beyond a threshold indicates that an adjustment in the delivery of the one or more agents is needed. a method and sensor for monitoring and/or controlling a cleaning process in a wastewater treatment system are also provided. The system, method, and sensor disclosed herein are particularly useful for cleaning membranes incorporated in a wastewater treatment process.