Fast start-up and reactivation of anammox process using polyurethane sponge

Anammox is a novel and efficient nitrogen removal technique, while the long start-up time limits its industrial application, thus carriers are always utilized to accelerate its start-ups. Meanwhile, the preservation of anammox bacteria is a key element in its application. Therefore, it is also quite significant to evaluate the effect of carriers in reactivation of the anammox process after preservation. Through addition of polyurethane sponge in the upflow anaerobic sludge blanket (UASB) reactor (R1), comparing with the one without polyurethane sponge addition (R2), the time for anammox start-up was shorten by 28%, and the reactivation time was reduced by 50%. The preservation in 4 ℃ did not significantly affect the survival of anammox bacteria, but significantly decreased their nitrogen removal rate (NRR). Moreover, during the preservation, the decomposed EPS in R1 (44%) was less compared to that in R2 (66%). It took 36 days for R1 to recover the NRR (0.084 kg·N·m-3·d-1), but took 60 days for R2. At the end of reactivation, the abundance of Candidatus (Ca.) Brocadia and Ca. Kuenenia (both are anammox bacteria) was 4.5% and 2.7%, respectively, in R1, whereas there was no identified Ca. Kuenenia and the Ca. Brocadia was only 0.2% in R2. Therefore, the addition of polyurethane sponge could short the start-up and reactivation time for anammox process by retaining more anammox bacteria in the reactor. [Display omitted] •Polyurethane sponge reduced start-up time by 28%.•Reactivation time was also reduced by 50%.•Preservation in 4 ℃ decreased NRR significantly.•Both Candidatus Brocadia (4.5%) and Candidatus Kuenenia (2.7%) were in R1.•Only Candidatus Brocadia (0.2%) was in R2.