Testing Resilience of Microalgae Biofilms When Exposed to Hydrothermal Liquefaction Aqueous Phase

There are a multitude of experimental and processing techniques in the bioenergy field that produce sustainable and carbon negative to carbon neutral methods of converting renewable resources into biologically based hydrocarbons. One example of a process is hydrothermal liquefaction (HTL) which specializes in converting wet biomass into biocrude oil. One reason that these processes are not used outside experimental testing is due to the high cost of performing these processes. There is potential to move these processes to larger scale testing and eventually industrial adaptation if breakthroughs are made to offset the process expenses. There is a waste product produced in this process called the aqueous phase. The hydrothermal liquefaction aqueous phase (HTL-AQ) has no current use, is expensive to dispose of, and consists of high concentrations of nitrogen (N), phosphorus (P), environmental toxins such as phenolic compounds. If HTL-AQ were able to be used to produce value-added products, the value of those products could be used to offset the expenses of the process, thus increasing the likelihood of HTL being used to produce bioenergy in an economically sensible way. Recent research has shown that microalgae biofilms both uptake N and P while also being more resistant to toxins than planktonic or free-floating algae. Since HTL-AQ does contain high concentrations of N and P, this project explores methods to grow microalgae biofilm cultures in dilutions of HTL-AQ. The technology used to cultivate these biofilms is called the rotating algal biofilm reactor (RABR) based on recent studies conducted at Utah State University (USU). Results from this experiment indicate that a 1:3 dilution of HTL-AQ to deionized (DI) water is able to grow microalgae biofilms. This data suggests that there is merit to finding value-added uses to HTL-AQ in ways that can offset HTL expenses, and that further investigation is warranted.