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Food waste is typically sent to landfills, where it decomposes and releases methane into the environment, causing a serious pollution issue. Mabee Dining Hall’s previous solution to this problem, the Earth Tub Composting Tank, became inoperative after 11 years of service. The team was tasked with developing an alternative solution. Based on the constraints imposed by the location and the project sponsor’s stipulations, such as low odor emission and ease of use, the team decided that the solution would consist of an in-vessel composting system. The container, a 6-gallon HDPE tank, is set up in a horizontal configuration suspended by two A-frames and an internal rod with aeration spikes. These aeration spikes prevent the process from going anaerobic and thus minimizing the odor produced in the composting process.
During the development of the prototype, the team conducted a series of empirical tests to determine, (1) the ideal amount and type of bulking agents that would allow the pre-consumer food waste to compost within a four to six week time frame, and (2) to identify the degree to which aeration affects overall composting time and the odor produced by the pile. All tests were performed under a controlled environment in two fume hoods provided by Dr. Hunsicker-Wang and Dr. Uddin. The results suggested that, among the tested food waste to bulking agents, the most effective ratio with regards to fastest composting time and least odor production is 4:1:2 (food waste:hay:wood shavings). Additionally, the aeration test demonstrated that when the pile is properly aerated, the smell of the compost pile is negligible.
Throughout the duration of the project, the team was able to suggest a composting method based on the limiting factors of Trinity University campus, recommend the type and amount of bulking agents that would satisfy ideal conditions of the composting process, create a CAD drawing and an instruction manual, and construct a physical prototype. However, due to delays caused by COVID-19 and the winter storm, several aspects of the project had to be modified. As a result, the team developed a smaller-scale prototype than initially stipulated, and did not get to test it after its completion. However, several recommendations and improvements have been determined using the empirical tests presented in this report.
During the empirical tests, the team failed to obtain suitable compost within the predicted four to six week time frame. The reason for this could be that the sizes of the piles were small (3.5 total pounds of food waste and bulking agents), which affects the ability of the microbes to retain heat. To accommodate this realization, the team added insulation around the pails mid-test. However, the team suspects that too much time had already passed and the majority of the microbes had died. Thus, one of the team’s proposals is that the Composting Time Test and the Aeration Test be repeated with insulation added on day one to ensure that the piles are able to complete the composting process without heat loss. Additionally, testing the actual prototype to analyze the results and make the pertaining modifications would be an important improvement.
Hippensteel, Mary; Rodriguez, Armando; and Willis, Matthew, "Mabee Waste Solution Final Project Report" (2021). Engineering Senior Design Reports. 47.