(143f) Symbiotic Hollow Fiber Membrane Photobioreactor for Microalgae Growth and Bacterial Wastewater Treatment

For decades, microalgae have gained much interest for production of high value compounds for food, feed, cosmetic and pharmaceutical products. With rapid depletion of fossil fuels and severe effect of greenhouse gas emissions on global climate change, many microalgae strains are potential sources for biodiesel production. Much attention is now focused on the development of a suitable photobioreactor that can assure mass production of high quality microalgal biomass. One of the crucial factors in designing a photobioreactor is the efficient gaseous transfer of CO₂ supply and O₂ removal.

Symbiotic microalgal-bacterial processes which incorporate microalgae and bacteria in one closed system could provide a potential solution for CO₂ supply and O₂ removal with low energy consumption. In this system, microalgae can produce sufficient O₂ for bacteria to biodegrade organic matter, while bacteria concomitantly release CO₂ for microalgae during photosynthesis. This process, so called photosynthetic oxygenation, is a promising approach to reduce the energy cost for intensive mechanical aeration and potentially eliminate CO₂ emission. For years, photosynthetic oxygenation has been applied not only for economical treatment of wastewater but also for degradation of hazardous contaminants. However, when growing microalgae and bacteria together, slow growth rate of microalgae and unexpected interactions between microalgae and bacteria may result in process failure. More importantly, microalgal biomass from the microalgal-bacteria consortia cannot be used flexibly for the production of food, feed or other high value compounds.

In this research program, we proposed to develop a hollow fiber membrane photobioreactor (HFMP) for symbiotic microalgal growth and bacterial wastewater treatment. In the proposed bioreactor, a gas exchange membrane will be used to physically separate microalgae and bacteria cultures as well as to solely facilitate transfer of CO₂ and O₂. The overall benefits of the proposed membrane bioreactor are to reduce the energy cost for mechanical aeration in an activated sludge process, reduce CO₂ emission to the atmosphere and most importantly, harvest microalgal biomass for extracting other value-added products.

Results obtained from the developed hollow fiber membrane photobioreactor (HFMP) demonstrate a proof-of-concept of the symbiotic relationship that existed between microalgae and activated sludge in wastewater treatment. In the absence of aeration in the synthetic waste water, BOD of synthetic wastewater was completely degraded while microalgae grew continuously in the absence of the external CO₂ supply. This concept hence can be applied for existing activated sludge treatment tanks in order to reduce the demand of aeration energy, and reduce CO₂ emission to the atmosphere. Most importantly, additional produced microalgal biomass can be harvested for other purposes such as for food, feed or biodiesel production.