As the global population rises and water scarcity becomes an increasingly relevant problem, the need for an efficient, cost-effective process of sewage treatment becomes even more pressing. Wastewater treatment plants currently in use are costly and difficult to maintain. Consequently, our team researched ways to improve treatment plant operations so that they are more efficient, making them cheaper to maintain.

Although the wastewater treatment process varies by facility, every facility has three main treatment steps: primary, secondary, and tertiary. The primary step removes solid objects such as twigs or trash from water by passing the water through a screen. In the secondary step, bacteria work to break down organic matter. Finally, in the tertiary step, bacteria remove nitrogen and phosphorus to further purify the water. Excess nutrients remaining in the purified water have disrupted the natural ecosystems into which the water is released. This contamination has proven a big issue in such important waterways as the Chesapeake Bay. After investigating further into wastewater treatment processes, we saw an opportunity to make the tertiary process more manageable and energy efficient.¹

During the tertiary step of the wastewater treatment process, nutrients such as nitrogen and phosphorus are removed by employing an activated sludge process. Activated sludge contains a multi-culture of bacteria that facilitate the nitrification-denitrification process responsible for the removal of ammonia. Some types of bacteria perform a nitrification process while others perform a denitrification process.

We specifically examined a co-culture consisting of Nitrosomonas europaea and Paracoccus denitrificans ² because they are two of the most commonly used species in activated sludge. In this particular co-culture system, maintaining a consistent level of N. europaea is difficult because P. denitrificans, a facultative anaerobe, can outcompete N. europaea in aerobic environments. A fluctuation of the ratio of nitrifiers to denitrifiers results from this competition. Additionally, N. europaea cannot thrive in hypoxic conditions. To ensure the maintenance of N. europaea at optimal levels, treatment plants must expend more energy for aeration.

Our solution is to eliminate the need for a co-culture and unite the functions of nitrification and denitrification in a single chassis. We will express the nitrification pathway from N. europaea in P. denitrificans. This solution will eliminate the competition in a co-culture, simplifying the management of bacteria cultures. This system will be more energy-efficient due to less oxygenation of the water being required.

References

1. https://www3.epa.gov/region9/water/recycling/ ↩

2. Uemoto, H., and H. Saiki. “Nitrogen Removal by Tubular Gel Containing Nitrosomonas Europaea and Paracoccus Denitrificans.” Applied and Environmental Microbiology 62, no. 11 (November 1996): 4224–28 ↩