Rapid Achievement of Nitritation Using Aerobic Starvation

Rapid start-up of partial nitrification is of great significance for subsequent denitrification and the anammox process; however, slow nitritation hinders the application of these processes. The current study presents a novel strategy for achieving nitritation using aerobic starvation and controlling sludge retention time (SRT). Activated sludge with a high level of complete nitrification was introduced into an aerated reactor without feeding to start the aerobic starvation. The results showed that nitritation was rapidly achieved, while the shorter SRT (15 days) guaranteed the stability of nitritation with an average nitrite accumulation ratio (NAR) of more than 95%. The activity recovery rates of ammonium-oxidizing bacteria (AOB; from 0.20 ± 0.00 d^-1 to 0.29 ± 0.08 d^-1) were higher than those of nitrite-oxidizing bacteria (NOB; -0.11 ± 0.02 d^-1 to 0.16 ± 0.05 d^-1) during the reactivation periods. Furthermore, the transcriptional responses of amoA and hao mRNA after aerobic starvation were faster than that of the nxrB gene, which explained the fast occurrence of nitritation after the aerobic starvation period. The quantitative real-time PCR (qPCR) analysis showed that the cell number of nitrifying bacteria remained stable during the starvation process, whereas the AOB population gradually became dominant over that of NOB in the reactivation period. These observations strongly supported the feasibility of accelerating the establishment of nitritation using aerobic starvation.