Development and Evaluation of Low-Cost Incubator for Testing Microbial Contamination of Private Well Water (2023)

Undergraduate: Zachary Mangel

Faculty Advisor: Amanda Northcorss
Department: Environmental Science and Engineering

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This project was carried out with the goal of creating an accessible low-cost incubator that can be implemented outdoors in low-income K-12 schools and maintain a temperature of 30-44.5°C. Incubation in this range is necessary for 18-24 hours to test water samples for fecal indicator bacteria, Escherichia coli. A need for this project arises due to the elevated costs of commercial incubators and the financial burden of testing private wells on low-income users. In this study, a 40W incandescent light bulb was used to heat a Styrofoam cooler containing data-logging thermocouples and ten plastic bags with 100 mL of water (which mimicked the thermal properties of ten E. coli compartment bag tests). Using a thermostat under constant ambient conditions, a mathematical model was created to predict the amount of heat loss from the incubator given any temperature gradient (difference in temperature inside and outside the incubator). A low-cost outlet timer was then used with settings predicted by the model to impose a relatively steady-state amount of heat in the incubator for a 24-hr period. The incubator, using the timer and under the prediction of the model, was able to maintain the desired temperature range over 94% of the time, as well as produced similar results when tested against a commercial incubator with compartment bag tests. These results indicate that simultaneous incubation of up to ten low-cost compartment bag tests is achievable with an estimated build cost of just $25.

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