(255d) Submerged Hollow Fiber Membrane Bioreactor for Symbiotic Microalgal Growth and Bacterial Wastewater Treatment

Activated-sludge process is the most widely used biological method for the treatment of domestic wastewater. However, a main disadvantage of this process is the high energy cost for the mechanical aeration, which accounts for 45 – 75% of the plant energy consumption. The symbiotic microalgal-bacterial process, which incorporates microalgae and bacteria in one closed system, is a potential approach to solve this problem: in the presence of light microalgae can produce sufficient O₂ for bacteria to biodegrade organic matters in wastewater, while bacteria release CO₂ for microalgal photosynthesis. In order to efficiently apply this symbiotic microalgal-bacterial process to current activated sludge tank, a novel submerged hollow fiber membrane bioreactor (SHFMB) for symbiotic bacterial wastewater treatment and microalgal production has been developed. In this SHFMB, a microalgae tank is built above bacteria tank for effective light penetration, and the microalgal culture is circulated through hollow fiber membranes immerged in the bacteria tank. These hollow fiber membranes are used to isolate the bacteria from the microalgae, and for CO₂ and O₂ exchanges in both the microalgal and bacterial growth. Results showed that through the photosynthetic oxygenation, the BOD content of the synthetic wastewater was completely degraded, while the microalgae grew effectively in the absence of the external CO₂ supply. It is also feasible to operate the SHFMB in continuous mode. Hence, the developed SHFMB could be applied for existing activated sludge treatment process as it allows reduced energy cost for mechanical aeration and eliminates atmospheric CO₂ emission, while less or no additional land area for the construction of microalgal photobioreactor is required. Especially, the microalgal biomass obtained from the SHFMB could be used as sources of food, feed or other high-value compounds.