A system for determining operating conditions of a rotating biological contactor includes a sensor including a first end coupleable to the gearbox assembly of the rotating biological contactor at a radial distance from a rotation axis of a rotatable shaft. The rotatable shaft rotates a plurality of media elements about the rotation axis to treat water within a basin of the rotating biological contactor. The sensor also includes a second end coupleable to a brace to prevent rotation of the sensor and the gearbox assembly when the rotatable shaft is rotated. The sensor further includes a body extending between the first end and the second end. The sensor is configured to detect a load on the body when the rotatable shaft is rotated. The system further includes a controller communicatively coupled to the sensor. The controller is configured to determine a torque of the rotatable shaft based on the load detected by the sensor.