Using Kefir to Teach Microbial Kinetics in an Undergraduate Wastewater Treatment Course

As a method of providing hands-on experience in learning reaction kinetics, undergraduate engineering students enrolled in a wastewater treatment course were assigned to characterize the kinetics of kefir production in order to design hypothetical biological reactors. Students designed and implemented experiments investigating parameters including the effects of change in temperature, DO, F:M ratio, pH, the presence of inhibitory substances, and other factors. Kefir is a fermented milk drink that is safe to handle and easy for students to produce, and provides instructional analogies to aspects of biological growth that can be applied when teaching students about wastewater treatment. Student teams were supplied with kefir grains, and were responsible for the ongoing growth and survival of kefir colonies. Changes were made to growth conditions during experimentation (e.g., temperature, oxygen availability, mixing, addition of simple sugars to solution, etc.) in order to observe the effect on kefir production rate, and students measured a variety of indicators of process performance (e.g., pH, degree of carbonation, separation of milk solids, etc.). Students fit data to kinetic models, and derived growth constants that were then used in the design of a scaled kefir production process. Feedback gathered from students indicated enthusiasm with the project and enhanced understanding of reaction kinetics. Gaining independent, self-directed experience in the lab provided students with important opportunities to practice critical thinking and experience the independent reasoning that is required for success beyond graduation.