The University of Kentucky Center for Applied Energy Research (UK CAER) recently demonstrated a pilot scale photobioreactor that converts CO2 in flue gas to algal biomass via photosynthesis to U.S. Congressman Thomas Massie of Kentucky’s 4th Congressional District. (See Congressman Massie’s Facebook post on the visit.) The algae demo is a joint project between UK CAER and Duke Energy’s East Bend Power Station in Boone County, Kentucky.

Members of UK CAER Biofuels and Environmental Catalysis research group were on hand to explain the process and equipment to the Congressman. UK CAER Associate Director Mark Crocker outlined the project’s origins and goals, and summarized the various steps involved in cultivating and harvesting algae, as well as processing algae biomass into useful products.

Ms. Stephanie Kesner, UK CAER, is a biological scientist who takes care of the algae organisms. The project specifically works with microalgae, which are single celled organisms around 5 microns in size. Though they do photosynthesize, though they are not plants. Even though they have moving parts, they are not animals nor bacteria. Algae are in their own taxonomic classification, and are actually one of the fastest growing organism on the planet with the ability to double their mass in a day. The particular species of alga we have in our reactor is called Scenedesmus Acutus, a local freshwater species of microalgae which can withstand pretty harsh environmental conditions while utilizing CO2 from flue gas to photosynthesize and grow.

According to Michael Wilson, UK CAER Engineer and project manager, the cyclic flow photobioreactor was developed at the Center for Applied Energy Research to create an optimum, controlled growth environment for microalgae while minimizing energy consumption required. The reactor is composed of off-the-shelf parts including 8’ long, 3.5 inch diameter clear PETG (coke bottle material) tubes integrated with PVC pipe fittings and arranged to maximize photon collection needed to drive photosynthesis. Flue gas is introduced to the bottom of the tubes and sparged for 20 seconds every minute in order to ensure good mixing for mass transfer and increase CO2 conversion efficiency. Periodically, 6 times per day, the tube banks are drained back to a main feed tank, mixed, and sent back out to the phototube array to continue normal operation. This ‘cyclic’ operation ensures limited exposure to dead zones in the reactor (dark zones, places with suboptimal gas introduction, etc) while also preventing biofilm formation. So far this iteration of photobioreactor has outperformed all before it in terms of operational stability, performance, and biomass productivity. The faster the algae grows, the more CO2 is consumed.

UK CAER group member and engineer Daniel Mohler talked about the field analytical equipment used in mass balance experiments in order to determine CO2and NOx reduction. These molecular species are measured in the gas going into the reactor then measured again in the gas coming out of the reactor, allowing for calculations of CO2 and NOx reduction.

The algae need to be harvested regularly as the culture grows and becomes more dense, thus limiting light penetration according to UK CAER Engineer Jack Groppo. To harvest the algae, roughly 80% of the culture volume is diverted into a thickener where the algae cells are flocculated and settled. Clarified water containing soluble nutrients are decanted from the thickener, sterilized with UV light and recycled back into the system to dilute the remaining 20% of the culture volume for another growth cycle. Settled algae is then filtered for utilization as feedstock for bioplastic manufacture and biofuel production. Other products from algae could include livestock feed (as it can be up to 30% protein); dietary supplements and neutraceuticals since it contains Omega 3 fatty acids and carbohydrates.

The UK CAER team is excited about the future possibilities this project presents in developing algae's unique ability to beneficially re-use greenhouse gas emissions. This technology has the potential to drive economic growth, enable food and energy security, while reducing the impact of industrial emissions.

The UK CAER Biofuels and Environmental Catalysis Algae Research Team (L to R): Daniel Mohler, Jack Groppo, Stephanie Kesner, Mike Wilson and Mark Crocker.