Enhanced resuscitation of anammox granular sludge by adding folate: A perspective from the growth factor

Quick resuscitation of preserved anammox granular sludge (AnGS) is crucial for its engineering applications. In this study, the stimulation effect and its mechanism of folate addition on resuscitation of AnGS after the long-term cryopreservation were investigated. The folate addition was found to enhance the recovery of AnGS activity to 76.4% of the original level on the 8th day, which was 28.1% higher than the folate-free group (CK). The folate addition could also promote the community recovery of AnGS, in which the live cells and abundance of anammox bacteria (AnAOB) were 10.2% and 14.0% higher than those in the CK in the early phase of resuscitation. Besides, the folate addition was revealed to stimulate the AnAOB recovery of AnGS, with higher activity and cell number by 58.7% and 40.9% than those in the CK. Furthermore, the mechanism of folate stimulation was proposed on the resuscitation of preserved AnGS. The exogenous folate addition could enhance the CO2 fixation capacity of AnAOB, which further accelerated both activity and cell number recovery of AnAOB, leading to the strong stimulation effect on the resuscitation of AnGS. These findings could offer valuable insights for optimizing and innovating the preservation technology of AnGS.