Mass transfer efficiency inside the polyvinyl alcohol‐sodium alginate carriers: kinetic changes of immobilized anammox bacteria

BACKGROUND Mass transfer inside the plain polyvinyl alcohol (PVA)‐sodium alginate (SA) carriers was determined to correlate with nitrogen removal by anaerobic ammonium‐oxidation (anammox) bacteria in this study. The anammox bacteria immobilized by the PVA‐SA material for nitrogen removal were inoculated into a sequencing batch reactor (SBR) operated at a hydraulic retention time of 4 days and a temperature of 35 ± 1 °C while another identical reactor inoculated with the un‐immobilized biomass was run for comparison. RESULTS Results show that the total nitrogen removals were 81 and 92% for the immobilized and un‐immobilized biomass, respectively, when the ammonium‐ and nitrite‐nitrogen, both at 200 mg N L−1, were fed into the SBRs. The poorer performance observed from the immobilized biomass was due to the lower mass transfer efficiency. The obtained diffusion coefficient of the ammonium‐nitrogen and specific surface area were 15.2 × 10−6 cm2 s−1 and 29.35 m2 g−1 gel beads, respectively. In addition, the mass transfer efficiency influenced the kinetics of the immobilized anammox bacteria. Results indicate that the ammonium‐nitrogen removal rate of the un‐immobilized biomass was 28 to 34% greater than that of the immobilized biomass, while the nitrite‐nitrogen removal rate was greater by 9 to 24% for the un‐immobilized biomass. This influence was more significant at high levels of ammonium‐ and nitrite‐nitrogen concentrations. CONCLUSION Increasing the mass transfer efficiency inside the plain PVA‐SA carriers was needed before using the PVA‐SA carriers to immobilize anammox bacteria. © 2020 Society of Chemical Industry