Effect of temperature decrease on anammox granular sludge: Shock and adaptation

Cryopreservation is one of the effective methods for the preservation of anammox granular sludge (AnGS). How-ever, the effects of cooling pretreatment on AnGS are still unclear. In this study, the effects of temperature decrease on AnGS property were investigated by designing different cooling modes: constant at room tempera -ture 20-25 degrees C (CK), sharp cooling to 4 degrees C (S4), -20 degrees C (S20) and stepwise cooling to 4 degrees C (A4), -20 degrees C (A20). The results showed that compared with CK, the cooling modes in S4, S20, A4 and A20 improved the physical preserv-ability of AnGS, slowing down the changes of color, shape and structure; and elevated the preservation rate of functional bacteria Planctomycetes (phylum level) and Candidatus Brocadia (genus level). The preservation rate of live cells in different experimental groups was 48.4 +/- 1.8%(CK), 61.1 +/- 3.3%(S4), 37.8 +/- 0.8%(S20), 81.7 +/- 4.8%(A4), 61.9 +/- 3.1%(A20), respectively. The Anaerobic Ammonium Oxidation Bacteria (AnAOB) in the stepwise cooling mode (A4 and A20) were found to enter the dormant state and form dormant zoogloea, while the AnAOB in the sharp cooling mode (S4 and S20) were observed to enter the shock state with a little change. The findings in this work (especially the dormant state of AnAOB) are helpful to understand the effect of temper-ature decrease on AnGS and to promote the development of AnGS preservation technology. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study investigated the effects of different cooling modes on the properties of anammox granular sludge, finding that temperature decrease can improve its physical preservability and impact the preservation rate of functional bacteria. The findings, especially the induction of dormancy in AnAOB, contribute to understanding the effect of temperature decrease on AnGS and promoting the development of preservation technology for AnGS.