Design and Experimental Evaluation of a BLDC Motor– Magnetic Gear Drive for a Rotating Biological Contactor

Rotating biological contactors (RBCs) are recognized for their small footprint, reliability, and low energy demand. RBCs are a potential option for compact decentralized wastewater treatment systems, but pose scalability challenges and mechanical constraints. We present, as a proof-of-concept, design modifications to the RBC drive system that use an innerrotor brushless direct current (BLDC) motor and a waterproof magnetic gearbox (MG) to drive rotating disks at low speeds (<1 rpm) while isolating electrical components from water. We assess 1) the magnetic air gap inside the sealed rim of the rotor, which can impair efficient torque transfer, and 2) the maximum output torque of the MG limited by the strength of the magnets and the air gap flux. Our results show that the BLDC's performance is adequate even with a large radial air gap, but the electronic overhead significantly reduces overall efficiency in a small system. Also, the MG's torque capacity is sufficient to maintain the system's rotation.