The issue of waste is arguably one of the most significant problems facing society today. Landfills are filling rapidly as there are fewer and fewer places to put waste. Meanwhile, there are many resources within this waste that could have been reused. As resource conservation and the dwindling supply of natural resources become larger issues, recycling part of this waste takes on more significance. A good part of the waste ending up in landfills is food waste, accounting for 21% of the total waste stream. Composting, on the other hand, has experienced a recent surge in interest on both a municipal and household scale due to its ability to divert this organic waste from the landfill. However, many are still misinformed about the composting process and believe that it is too hard or smells too much. Some products have been developed to address these complaints, but many are either poorly designed or too expensive to be considered by the average household user. Therefore, I hope to build the TerraPreta, a compost system that will be both cheap and easy to use, while fitting conveniently underneath one's kitchen sink.
Through the Explore grant, I will purchase materials in order to build a prototype of the TerraPreta. Materials include polycarbonate sheet, a stainless steel shaft, a motor, among other raw materials. I have already designed the TerraPreta in CAD and will make the prototype to test the concept. The goal is to have a working prototype by April 15. A testing process will be performed on the prototype to determine throughput for different food scraps, optimal running characteristics, and overall yield. If successful, additional prototypes and testing will be performed.
The project will be evaluated based on the completion of a prototype and the testing process. It will be successful if the prototype can take a mixture of food waste and transform it into a compost-like soil based on a detailed set of scientific specifications that were outlined in the design report completed last fall in an independent study. For more information, and to view my progress, please visit terrapretacompost.wordpress.com.
Explore Grant Report:
The TerraPreta is a mechanical compost system designed to turn household food waste into finished soil without ever leaving the kitchen. The final product will be installed under a kitchen sink and will convert all food waste (excluding large bones) into compost-like material that can be used in the garden or on houseplants. Users would put their food waste down their sink, and the TerraPreta would pulverize the waste in an upper processor and then send it to a lower hopper chamber for composting, all while extracting and removing liquids from the waste. The Explore Grant was used to build a prototype of the hopper chamber of the TerraPreta.
Thus, the grant was used to purchase materials to construct the prototype. The hopper consists of three sub-assemblies: the mechanical system, the heating system, and the aeration system. The hopper container was built out of clear polycarbonate sheeting and the bottom was lined with perforated stainless steel mesh. The mesh holds the food waste until it is sufficiently composted to pass through and into a final holding cabinet. The mechanical system was designed to turn the food waste and incorporate oxygen into the material. This would be done with a set of blades, consisting of a stainless steel shaft and aluminum plates, attached to a motor. The shaft was centered in the polycarbonate chamber using bronze bearings and connected to a motor using a flexible shaft coupling. The motor was mounted on the exterior of the chamber for powering. Additionally, a silicone rubber heating pad was attached on the inside of the chamber to provide the high temperatures necessary for composting. Finally, a fan was placed on top of the chamber to draw oxygen into the system and create an aerobic environment for the microorganisms. Overall, by incorporating oxygen, turning the food waste, and adding heat, the TerraPreta was designed and built to provide the ideal characteristics for composting. While challenges were faced throughout the manufacturing process, ultimately it was a great learning experience in product design and creation.
Upon completing the prototype, the testing process began by creating a representative mix of food waste to add to the chamber. Various fruits and vegetables, including apples, pears, carrots, and potatoes, were juiced and processed. The pulp from the produce was combined with other compostable material, like coffee grounds, and a small amount of finished compost, to provide the bacteria necessary to initiate the decomposition process. This mixture was placed in the hopper chamber and was turned, heated, and aerated. The testing process is currently ongoing, although initial results showed that all sub-systems functioned as expected. Smaller particles began to pass through the mesh and minimal odor was emitted. The moisture content, pH, and temperature are recorded throughout the process to quantify the characteristics of the compost. Next steps include testing a larger and more diverse array of food waste in the system to determine the viability of the system as a whole.