Glass Tumbling for Safe Waste Glass Disposal in Cape Maclear, Malawi

Glass waste is an increasing environmental challenge, particularly in communities with limited waste management infrastructure. In Cape Maclear, Malawi, rapid growth in tourism has caused a sharp rise in imported glass bottles, which are often discarded without treatment. Broken glass persists in the environment for long periods, creating ongoing safety hazards for residents, waste workers, and visitors. Conventional approaches, such as bottle crushing, have proven difficult to operate on a larger scale and often produce fragments that remain hazardous to handle. This research therefore aimed to investigate whether tumbling, a process commonly employed in industrial finishing and mineral processing, could offer a simple, low-tech solution for rendering glass waste safe. A prototype tumbling machine was designed, constructed, and tested, emphasizing simplicity, affordability, and the use of widely available or repurposed materials. The machine comprises rotating drums made from repurposed gas cylinders, supported by parallel shafts and driven by a salvaged electric motor. The prototype was tested with waste glass collected from discarded bottles, broken into fragments, and subjected to multiple tumbling cycles. During testing, glass fragment sharpness was assessed through tactile and visual inspection, while fragment size distribution and machine performance, including energy consumption, were also monitored. Results indicated that tumbling effectively dulls sharp glass edges, with most transformation occurring within the first hour of operation. Larger fragments dulled more quickly, whereas fragments smaller than ten millimeters required several hours of tumbling to reach comparable safety levels. Operating speed was identified as a critical parameter: moderate speeds minimized the occurrence of new fractures and the formation of fresh sharp edges. Contrary to expectations, tumbling did not consistently reduce the size of large fragments, indicating that complementary methods would be necessary if size reduction is also a goal. Finally, the machine design proved robust, although improvements were noted primarily in vibration control and in the selection of structural and mechanical construction materials.