Located in the offices of Civil, Architectural and Environmental Engineering Department is a small machine, whose purpose is to use algae to clean wastewater. This bioreactor is the creation of Christopher Sales, an assistant professor in the CAEE department, and Jacob Price, a third-year engineering doctoral candidate. The device uses algae, which can disrupt aquatic environments to nutrients out of wastewater.
“Typically, when [nutrients such as nitrate, phosphorus and ammonia] get into rivers or any body of water, they cause natural algal blooms,” Sales said. Algal blooms can cause illnesses in birds, fish and mammals; for example, Dungeness crabs are currently considered inedible by humans due to concentrations of domoic acid in their bodies.
“The idea is instead of having these algae blooms occur in the environment, why not harness them, why not keep them within the reactor system?” Price explained that humans excrete products such as urea and proteins in their waste. The activated sludge in treatments is designed to oxidize to reduce carbon. The organic carbon is transformed into carbon dioxide and released into the atmosphere. Meanwhile, ammonia-oxidizing and nitrogen-oxygen bacteria can transform reduced nitrogen into nitrite and nitrate. Large wastewater treatment plants take wastewater that has already been treated for organic carbon and place it in a large chamber. The material is oxidized so that the ammonia becomes nitrite and nitrate. In a third chamber, in which there is no aeration, bacteria use the nitrite and nitrate as electron acceptors similar to the way humans use oxygen. The nitrogen gas from the process is released back into the atmosphere. This process is expensive to conduct, so many companies end up releasing the ammonia or nitrate into waterways. This excess nitrogen allows for the development of algae blooms.
“If we were to use this mixed community of algae and bacteria together, before we were to release [the wastewater], the algae and the bacteria in the algae community would be growing in the reactor itself, so what’s leaving is finally cleaner. And once it hits the receiving water, you’re less likely to have those algae blooms,” Price continued.
“When we pass that dirty water through the algae, the whole goal is to have clean water that comes out, so that when we dispense that water into open water bodies, it keeps the quality,” Sales said. The concentration of suspended solids in the bioreactor’s effluent is much less than the maximum limit imposed by the law.
The algae were obtained from a fountain on South Street near the University of Pennsylvania campus. “It’s a natural microbiota, so there are both algae and bacteria in there,” Sales said.
Price estimated that there are between 350 and 400 microbial species in the algae community. In comparison, most photoreactor studies have a much smaller number of species, topping off at about 40 species.
Wastewater treatment is typically conducted using activated sludge. Activated sludge is traditionally composed of heterotrophic bacteria. The activated sludge process takes wastewater influent and mixes it in an aeration vessel. The aeration provides dissolved oxygen to the various bacteria, which use the oxygen to eat the organic carbon and respire carbon dioxide. When the influent leaves the tank, the bacteria is taken to a clarifier and recycled back into the aeration vessel. Meanwhile, the water that goes through the clarifier is relatively clean, though it is often further disinfected afterward.
The machine is based off of designs from previous research of Sales, and it was later designed and built by Price. The bioreactor is powered by two separate pumps. One pump recycles the water; it takes the water from the recycle vessel and pumps it into the bottom of the reactor. The reactor fluid passes through the biomass zone, leaves the reactor through the top port, and returns to the recycle vessel. The second pump takes influent, or feed, from its own vessel and pumps it into the recycle vessel. “Instantaneous mixing occurs because we have aeration there. As that feed vessel pump is pumping the influent into the recycle vessel, it displaces the effluent port on the recycle vessel,” Price explained. “So for one drop that comes in, another has to leave.”
“Before I became an assistant professor here, Mira Olson had already started working on algae a little bit, and her main focus was looking at how algae can treat landfill leachate,” Sales said. “I started working on that for my post-doc, but we didn’t adapt the reactor we had in that paper until [Price] got here when he started about two and a half years ago.”
“The next big step is scaling up the system. So right now we just have the laboratory scale system, and we’ve been able to demonstrate that it works, but to really put it into practice we need to make it a lot larger because the flows of wastewater that go through a wastewater treatment plant are really high, especially for a large city like Philadelphia. It’s on the orders of millions of gallons per day, whereas our reactor is so small we’re actually only putting out [tens of gallons per day],” Sales said.
Price’s current research involves studying the total metabolic capabilities of the bacteria species in the community. “I’m also tracking community and diversity information, so how does the community change over time or in reaction to different influent contents. And then on top of that, I’m not just interested in the community itself, but also what the community is doing,” he said.