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 °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 °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 °C (R 3 ) exhibited a better recovery performance than those preserved at 20 °C (R 2 ), −30 °C (R 4 ), and 35 °C (R 1 ). The comprehensive comparison indicated that 4 °C is the optimal storage temperature for anammox granular sludge because it promotes improved maintenance and recovery performance properties.