Effects of physicochemical properties of poly-epsilon-caprolactone on nitrate removal efficiency during solid-phase denitrification

Laboratory-scale batch and continuous flow solid-phase denitrification reactors for nitrogen removal were constructed by acclimating activated sludge with poly-e-caprolactone (PCL) with weight-average molecular weights (M-W) of 60,000 (PCL-1), 80,000 (PCL-2), and 140,000 (PCL-3, PCL-4) g mol(-1). The biodegradability and denitrification rate of PCL in batch tests increased with decreasing molecular weight. However, PCL-4 showed higher nitrate removal efficiency than the other PCL carriers under high shear forces in batch and continuous tests, suggesting that the rough surface and pore structure of PCL-4, which was beneficial to the attachment of denitrifying bacteria, may play a more important role than M-W in biological denitrification during the solid-phase denitrification process. Environmental scanning electron microscope (ESEM) observations demonstrated the firm attachment of biofilm on PCL-4 and microbial utilization of all the PCL carriers, and the Fourier Transform Infrared Spectrometer (FTIR) analysis indicated that biological utilization of PCL carriers on the surface did not significantly change the chemical structure of PCL carriers, regardless of the M-W. Microbial community analysis showed that Myxobacterium (Deltaproteobacteria) and Thauera, Rubriyivax, and Comamonas (Betaproteobacteria) were the dominant microbial genus and played a primary role in PCL degradation and denitrification in the PCL-4-acclimation packed-bed reactor. (C) 2015 Elsevier B.V. All rights reserved.