Microalgae Cultivation in Closed-Loop Photobioreactors: Biofilm Characterization, Prevention and Removal

Given the negative environmental effects of carbon dioxide and the finite nature of fossil fuel reserves, there is a need to both mitigate carbon dioxide emissions and develop sustainable fuels.  Microalgae offer a potential solution to both problems in that they are the fastest growing photosynthetically active organisms on the planet and are rich in lipids which can be upgraded into liquid fuels. While open ponds represent the lowest cost option for algae cultivation, geographic and climatic constraints can limit their application. In these cases closed-loop photobioreactors (PBRs) provide a viable alternative. Carbon capture using PBRs requires that a viable alga culture be maintained for considerable lengths of time. However, at long cultivation times (>1 month) the formation of an organic film on the interior surface of reactor tubes is often observed. This biofilm traps algae that would otherwise remain in solution and progressively increases in size, becoming thicker and covering a significant area of the reactor tubes. If left untreated, the biofilm will eventually become light impenetrable and the culture will die. In an attempt to better understand the origin of biofilm formation, a study was undertaken to characterize the adhered biofilm using elemental analysis, thermogravimetry, pyrolysis-GC/MS and optical microscopy. In this contribution the results of this study are presented, and potential prevention and removal techniques are discussed.