Towards intensified preservation technology of anammox granular sludge: Insights into the role of energy support

Anammox is an advanced biotechnology for nitrogen removal and has been widely applied in wastewater treatment. Preservation of anammox granular sludge (AnGS) is an essential approach to support the sustainable development of anammox processes. In this study, the activity descent and its mechanism of AnGS during long-term cryopreservation were investigated. The results showed that the cryopreservation process of AnGS could be divided into plummeting stage, maintaining stage and descending stage in terms of activity index, namely three-stage activity descent. A significant positive correlation was observed between the ATP pool and the three-stage activity descent (by hzo-mRNA/hzo-gene ratio) of AnGS (R2 = 0.944). The ATP pool was found to be replenished by the sequential consumption of endogenous energy substances, leading to the stationary activity of AnGS. The consumption of essential cell components as an energy source was revealed to cause damage and even death of functional bacteria, and the energy stress could be mitigated by the regular exogenous substrate supply. Consequently, the energy support in terms of ATP could be a feasible way to innovate the preservation tech-nology and promote the sustainable development of anammox processes.