Background/Question/Methods Numerous interacting factors influence the proper functioning of aeration tanks in wastewater treatment plants, which mimics natural systems, offering an excellent learning model for ecological systems. For the past two years, environmental science classes at Carthage College have been working with the Kenosha Wastewater Treatment Facility (KWWTF) to research how to lower filamentous bacterial growth at dissolved oxygen levels of 1-2 ppm. This DO level is the operating norm for other, nearby treatment facilities, but the Kenosha plant was finding that filamentous organisms would take over at this level. As a result, the KWWTF was using additional energy to operate their aeration process at a higher DO of 5-6 ppm. Based on conversations with operators of the KWWTF, the students tested four different hypotheses related to potential limiting factors that could influence how much oxygen the organisms use: (1) that the microbes in the aeration tank were limited by phosphorus, (2) that they were limited by nitrogen, (3) that the pH was not optimal, and (4) that the ferrous chloride that they were using to bind phosphorus was using up oxygen and they could potentially benefit by switching to a different chemical.

Results/Conclusions Based on their manipulations of these factors and cultures grown in the lab, students found that the number of filamentous organisms significantly decreased (resulting in a higher overall diversity and a more operational tank) if ferric chloride was used to bind to phosphorus rather than ferrous chloride. This suggests that the use of ferrous chloride lowers oxygen availability, which limits aerobic bacteria and allows filamentous organisms to thrive. An additional result of this study was that while the students learned about the process of treating wastewater and about basic ecology and chemistry, the plant benefitted from these results as well. Based on these findings, the KWWTF has now switched from ferrous chloride to ferric chloride on a trial basis, and data from the first few months of this trial suggest that this new method of phosphorus removal may be more efficient. By giving students the opportunity to work on a real-world, local scenario, all participants have benefitted.