The National Research Council (NRC) requires an automated compost stirring device to replace the current manual process used in its biodegradability testing of plastics. Lab technicians spend four hours each week manually mixing compost in 48 glass vessels, which is labor-intensive, time-consuming, and causes ergonomic hazards to technicians. The objective of this project is to automate the process by ensuring uniform mixing, reducing labor, and maintaining the integrity of the glass vessels used for testing.

The design combines internal and external mechanisms for effective operation. The internal mechanism features a segmented auger to break compost clumps, a wiper blade to scrape compost from vessel walls, and a grate-holding sleeve to secure the metal grate and prevent scratches on the glass vessel, enabling mixing of compost with varying consistencies. The external mechanism consists of a motor with adjustable speeds, a secure clamping system, and a user-friendly control panel allowing a single operator to set up and mix all 48 vessels in under four hours.

Users set up the device by assembling internal components, placing the vessel in the frame, lowering the motor-lid system, and activating the mixer via a speed-adjustable control, reducing manual effort to a simple, ergonomic process.

The verification process confirmed the design’s success in achieving goals for durability, safety, cost, ease of use, and size. The device operates quietly and supports single operator use, significantly reducing manual effort while meeting key safety and operational requirements. Tests for compost uniformity and spillage tolerance require further evaluation due to clamping challenges at high speeds. This offers areas for engineering recommendations, such as improving automation and user-friendliness. The device improves the efficiency and reliability of biodegradability testing while reducing strain on lab technicians.