Traditional wastewater treatment infrastructure, heavily reliant on aerobic processes like activated sludge, operates as a significant net energy sink, consuming approximately 1–3% of global electricity production primarily for mechanical aeration. This operational model overlooks the substantial chemical energy (~16.1 kJ/g COD) embedded within organic pollutants. Microbial Electrochemical Systems (MESs) including Microbial Fuel Cells (MFCs) and Microbial Electrolysis Cells (MECs) represent a foundational shift in environmental biotechnology by leveraging electrochemically active bacteria (EAB) for extracellular electron transfer (EET) directly to solid-state electrodes. This article provides a comprehensive academic review of MES principles, evaluating fundamental thermodynamics, advancements in electrode material engineering, and diverse resource recovery pathways, including direct electricity generation, biohydrogen production, and targeted nutrient mining (e.g., struvite precipitation). Key bottlenecks limiting real-world scalability, such as high internal ohmic resistance, mass-transfer constraints, and capital expenditures, are critically analyzed. We propose a framework for integrating MESs into hybrid treatment trains to achieve process intensification, establishing a pathway for transitioning wastewater management facilities into circular bio-economy "resource mines."