Modification of a tumbler machine that transforms organic waste into compost

Abstract

The rapid accumulation of organic waste in urban centers, particularly Kampala, poses significant environmental and public health challenges. This project aimed to design, fabricate, and test a modified tumbler composting machine to efficiently convert organic waste into nutrient-rich compost while addressing key limitations of existing systems, such as poor aeration, weather sensitivity, and lack of particle size reduction mechanisms. The methodology was structured around three key objectives: design, fabrication, and performance evaluation. The composter was designed using engineering principles including volume estimation, thermal insulation analysis, and torsional stress testing. A double-walled cylindrical drum insulated with fiberglass was modeled in SolidWorks, and the prototype was fabricated using mild steel, UCP bearings, and a manually operated rotating shaft. For testing, a 14-day composting cycle was conducted using shredded organic waste sourced from Gayaza market. Parameters such as temperature, pH, and moisture content were monitored to assess composting performance. Results showed that the composting system attained a thermophilic phase (peak core temperature of 58.6°C) by Day 6 and stabilized to ambient temperature by Day 14. The pH shifted from 6.2 to 7.0, indicating successful microbial succession and compost maturity. A 60% mass reduction was observed, and the final compost exhibited desirable qualities: dark color, fine texture, and earthy smell. The study concluded that the modified tumbler design significantly improved composting efficiency by enabling optimal aeration, temperature retention, and mixing. The design successfully reduced composting time to 14 days, well below that of traditional methods. It was recommended that future iterations incorporate automated rotation, real-time monitoring sensors, improved moisture control, and more durable materials to enhance scalability, user-friendliness, and long-term performance. This project demonstrates the viability of decentralized, small-to-medium scale composting solutions for sustainable urban waste management and soil fertility enhancement.