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 (R-1), comparing with the one without polyurethane sponge addition (R-2), the time for anammox start-up was shorten by 28%, and the reactivation time was reduced by 50%. The preservation in 4 degrees C 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 R-1 (44%) was less compared to that in R-2 (66%). It took 36 days for R-1 to recover the NRR (0.084 kg.N.m(-3).d(-1)), but took 60 days for R-2. 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 R-1, whereas there was no identified Ca. Kuenenia and the Ca. Brocadia was only 0.2% in R-2. 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.