Effects of biocarrier type and size on the performance of nitrification and simultaneous nitrification and denitrification

Abstract

Four soft polyurethane biocarriers with different sizes and a hard polypropylene biocarrier were selected to evaluate the effects of material type and size on the nitrification and simultaneous nitrification and denitrification (SND) performance of the aerobic moving bed biofilm reactors (MBBR) in treating synthetic coking wastewater under different organic loading rates (OLR, 0.95, 0.65, 0.49 kg COD m−3 day−1). The attached biomass concentrations of the polyurethane biocarriers were 1.65 ± 0.15 g L−1, almost twice that of the polypropylene one (0.76 ± 0.05 g L−1), while the differences in the suspended biomass concentrations were relatively small (1.48 ± 0.18 g L−1 and 1.28 ± 0.06 g L−1, respectively). The SND efficiency of 32.43% ± 5.15% for all five MBBRs was achieved at an OLR of 0.95 kg COD m−3 d−1, which decreased to 8.48% ± 5.25% and 4.35% ± 2.99%, respectively, at lower OLRs. It was clear that OLR was an important factor affecting the SND performance. The MBBR using the smallest polyurethane biocarrier (10 mm × 10 mm × 10 mm) achieved complete nitrification at an OLR of 0.65 kg COD m−3 day−1, while the other ones achieved it at a lower OLR (0.49 kg COD m−3 day−1). The smallest polyurethane biocarrier exhibited a higher specific ammonium oxidizing rate (SAOR, 0.071 ± 0.007 g NH4+-N g−1 VSS day−1) than the other ones (0.045–0.050 g NH4+-N g−1 VSS day−1 for the larger size polyurethane ones and 0.023 ± 0.002 g NH4+-N g−1 VSS day−1 for the polypropylene one). Miseq analysis revealed that Nitrosomonas and Nitrospira were respectively the dominant AOB and NOB in all MBBRs. The polyurethane biocarriers enriched AOB and NOB in the biofilms as much as 14.6 and 9.7 times, while the polyethylene one only enriched them 3.8 and 2.2 times. Thus, the polyurethane biocarrier with smaller size was advantageous for improving nitrification capacity.