The influence of carrier material on the dominance of polyphosphate-accumulating organism metabolism in the biofilm-based biological phosphorus removal process

This study reveals that the type of carrier material affects the stoichiometry of the anaerobic conversion and the metabolism in cultures enriched with polyphosphate-accumulating organisms (PAOs) and helps increase the biological phosphorus removal performance. PAO-enriched biofilms were cultivated in two identical lab-scale sequencing batch reactors containing different carrier types: a typical moving bed bioreactor carrier (MBBR) and a novel carbon-based moving carrier type (CBMC) coated by activated carbon particles. The experiments were conducted at various influent PO43- concentrations (14, 17, 20 mg-PO43--P/L) and two aeration periods (220 and 460 min) under similar operating conditions. The results showed that due to the particular characteristics of the highly porous CBMC carriers, biomass adhesion increased by approximately 15 % compared to the MBBR carriers. It was also found that the CBMC carrier biofilm relied more on intracellularly stored polyphosphate than glycogen (which could be used by glycogen accumulating organisms (GAO)) as a source of energy for anaerobic uptake of organic substrates, which resulted in a greater dominance of PAO metabolism within the biofilm, especially at lower P concentrations. Conversely, a microbial community with mixed PAO-GAO metabolism was observed within the MBBR carrier biofilm, which changed to PAO dominated metabolism with increasing P concentration. Therefore, a higher specific PO43- uptake rate was obtained for the CBMC reactor (0.072–0.082 P-mol/C-mol.h), indicating a significant enhancement in the range of 13.1–19.6 % compared to the MBBR reactor, depending on the influent P concentration. In addition, better resistance of the CBMC biofilm to prolonged aeration corroborated that although the highly porous structure of the CBMC carriers was effective in achieving a higher P-removal efficiency by 13.5 %, the carrier material still played the major role in PAO metabolism dominance.