A membrane surface monitoring system (MSM) and membrane surface monitoring cell for direct and unambiguous detection of membrane surface fouling and mineral scaling. The system includes a membrane surface monitoring system cell, a control valve, a retentate flow meter/transmitter and a controller. The MSM cell has a visually-observable membrane, an edge-lit light guide, an edge illumination light source, a retentate module, and a permeate module. A pressurized inlet stream is fed into the MSM cell. The feed contacts a membrane sheet, leading to membrane-based separation operation to produce retentate and permeate streams. The MSM cell integrates surface illumination and imaging components to allow direct real-time visualization and spectral imaging of the membrane surface in real time. The pressure on the feed-side of the MSM cells is approximately that of the membrane plant element being monitored such that the plant control system can adjust plant operating conditions.