Influence of preservation temperature on the characteristics of anaerobic ammonium oxidation (anammox) granular sludge

Preserving active anaerobic ammonium oxidation (anammox) biomass is a potential method for securing sufficient seeding biomass for the rapid start-up of full-scale anammox processes. In this study, anammox granules were cultured in an upflow anaerobic sludge blanket (UASB) reactor (R-0), and then the enriched anammox granules were preserved at 35, 20, 4, and -30 A degrees C. The subsequent reactivation characteristics of the granules were evaluated in four UASB reactors (denoted R-1, R-2, R-3, and R-4, respectively) to investigate the effect of preservation temperature on the characteristics of anammox granules and their reactivation performance. The results demonstrated that 4 A degrees C was the optimal preservation temperature for maintaining the biomass, activity, settleability, and integrity of the anammox granules and their cellular structures. During the preservation period, a first-order exponential decay model may be used to simulate the decay of anammox biomass and activity. The protein-to-polysaccharide ratio in the extracellular polymeric substances and the heme c content could not effectively indicate the changes in settleability and activity of the anammox granules, respectively, and a loss of bioactivity was positively associated with the degree of anaerobic ammonium-oxidizing bacteria cell lysis. After 42 days of storage, the anammox granules preserved at 4 A degrees C (R-3) exhibited a better recovery performance than those preserved at 20 A degrees C (R-2), -30 A degrees C (R-4), and 35 A degrees C (R-1). The comprehensive comparison indicated that 4 A degrees C is the optimal storage temperature for anammox granular sludge because it promotes improved maintenance and recovery performance properties.