Nitrogen removal performance and membrane fouling in a microalgae-bacteria dynamic membrane system

As an innovative wastewater treatment technology, the microalgae-bacteria coupled dynamic membrane bioreactor (DMBR) is expected to enhance biomass retention and mitigate membrane fouling. The research established a microalgae-bacteria partial nitrification/anammox dynamic membrane system by utilizing Chlorella sp. (R1) and Navicula sp. (R2), respectively, aiming to investigate the impacts on nitrogen removal efficiency and membrane fouling characteristics. The results indicated that at the influent NH₄⁺-N concentration of 70 mg/L, R1 showed the best total nitrogen removal efficiency of 81.5 %, surpassing the efficiency of 66.9 % in R2. Chlorella sp. formed a looser layer, facilitating better effluent and supporting anoxic zones for anammox activity. In contrast, the denser membrane formed by Navicula sp. hindered these conditions. R1 exhibited faster transmembrane pressure growth (11.33 kPa/d), attributed to the smaller size (typically 4-6 μm) and higher protein (Pn) release of Chlorella sp. Conversely, Navicula sp. mitigated membrane fouling in R2 owing to the length (typically 20-30 μm) and lower protein/polysaccharide ratio in the extracellular polymers. When the influent NH₄⁺-N concentration increased to 100 mg/L, the relative abundance of Nitrospira in R2 rose to 5.28 %, surpassing that of R1 (1.02 %). This phenomenon may be attributed to silicate or polysaccharide release promoting nitrite-oxidizing bacteria growth, thus further reducing TNRE. These findings offered insights into selecting optimal algal species for enhanced nitrogen removal and membrane performance in DMBR systems.