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

Abstract

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 degrees 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 x 10(-6)cm(2)s(-1)and 29.35 m(2)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. (c) 2020 Society of Chemical Industry