Long-term starvation and subsequent reactivation of anaerobic ammonium oxidation (anammox) granules

• The effect of long-term starvation on anammox granules properties was evaluated.
• The influence of starvation temperature was examined.
• The reactivation characterization of anammox granules was investigated.
• The properties of anammox granules can be restored after starvation up to 50 days.
• Starvation at 4 °C was more suitable for the reactivation of anammox granules than that at 20 °C.

Starvation of biomass is common in the biological wastewater industries. To investigate the influence of starvation on the sludge characteristics and reactivation performance of the anaerobic ammonium oxidation (anammox) process, the starvation process of high-activity anammox granules over 50 days and the subsequent reactivation characterization of the granules were evaluated in two upflow anaerobic sludge blanket (UASB) reactors at 20 °C and 4 °C, respectively. The results showed that the starvation temperature had a significant impact on the morphological and physical properties. Anammox granules stored at 4 °C achieved a relatively low decay rate, excellent nitrogen removal capacity, and a low protein-to-polysaccharide (PN/PS) ratio after reactivation. Those results demonstrated that 4 °C was more suitable for the maintenance of structural integrity and granule stability during long-term starvation. The nitrogen removal performance of anammox granules after starvation could be recovered after 4 days of operation, and the anammox activity could be fully restored within 8 days. Furthermore, anammox granules preserved at 4 °C obtained a better recovery performance than those at 20 °C. In summary, anammox granules could be stored up to 50 days without running the risk of losing the integrity of the granules and metabolic potentials. And anammox performance after prolonged starvation could be fully revived.

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