The impact of low COD/N ratio on denitrification performance and microbial community in an intermittent aeration moving bed membrane bioreactor

Abstract

Conventional biological nutrient removal (BNR) processes for treating wastewater from ionic rare earth mining areas with low COD/N ratios typically require a significant supply of organic carbon sources. To overcome this limitation, an intermittently aerated moving bed membrane bioreactor (MBMBR) was utilized to facilitate simultaneous partial nitrification and denitrification (SPND) under low COD/N conditions. At a mixing-to-aeration duration of 30 min:20 min, and a COD/N ratio of 3.5, removal rates of 99.88 % for NH₄⁺-N, 86.14 % for TN, and 91.62 % for COD were achieved. 16S rRNA sequencing revealed a significant impact of COD/N ratio on the microbial community structure. Notably, at a COD/N ratio of 3.5, SM1A02, known for its nitrification and anaerobic ammonium oxidation capabilities, was identified with a relative abundance of 10.32 %. With the further reduction of the COD/N ratio, the abundance of SM1A02 showed a progressive decline. Fluorescence analysis of extracellular polymeric substances (EPS) from both the mixed liquor and membrane surface sludge revealed that proteins and humic acids were the predominant components of EPS, with proteins identified as the primary contributors to membrane fouling. Meanwhile, a reduction in the COD concentration was found to mitigate membrane fouling. This study offers key strategies for minimizing energy consumption and controlling membrane fouling during the treatment of low COD/N ratio wastewater through the application of MBMBR technology.