Towards mainstream partial nitritation/anammox in four seasons: Feasibility of bioaugmentation with stored summer sludge for winter anammox assistance

The strong effect of low temperatures on anammox challenges its mainstream application over the winter in temperate climates. Winter bioaugmentation with stored summer surplus sludge is a potential solution to guarantee sufficient nitrogen removal in winter. Firstly, the systems for which nitrogen removal deteriorated by the temperature decrease (25 degrees C -> 20 degrees C) could be fully restored bioaugmenting with granules resp. flocs stored for 6 months at 118 resp. 220% of the initial biomass levels. Secondly, the reactivation of these stored sludges was tested in lower temperature systems (15.3 +/- 0.4/10.4 +/- 0.4 degrees C). Compared to the activity before storage, between 56% and 41% of the activity of granules was restored within one month, and 41%-32% for flocs. Additionally, 85-87% of granules and 50-53% of flocs were retained in the systems. After reactivation (15.3 +/- 0.4/10.4 +/- 0.4 degrees C), a more specialized community was formed (diversity decreased) with Candidatus Brocadia still dominant in terms of relative abundance. Capital and operating expenditures (CAPEX, OPEX) were negligible, representing only 0.19-0.36% of sewage treatment costs.

Automated summary

The strong effect of low temperatures on anammox limits its use in temperate climates during winter. Winter bioaugmentation with stored summer surplus sludge is a potential solution to ensure sufficient nitrogen removal. The study found that the deteriorated nitrogen removal in systems due to temperature decrease could be fully restored by bioaugmentation with stored granules or flocs. Additionally, the reactivation of stored sludges in lower temperature systems resulted in partial activity restoration and the formation of a more specialized bacterial community.