[Fast Start-up of Shortcut Nitrification in a CSTR and an MBR].

In order to achieve fast start-up of shortcut nitrification, a continuous stirred tank reactor (CSTR) and a membrane bioreactor (MBR) were selected for a comparative study about the start-up characteristic of shortcut nitrification. The differences in three aspects of the two reactors were investigated, namely start-up time, nitrogen transformation, and sludge performance. The results showed that the start-up of shortcut nitrification was successfully achieved in the CSTR and MBR after 44 and 56 days of operation, respectively, with influent C/N=1, temperature around 30℃±1℃, pH of 7.5-8.0, and dissolved oxygen (DO) of 0.6-1.0 mg·L, as well as combining anoxic/aerobic ratio 1:3 (15 min:45 min) with shortened hydraulic retention time (HRT). The start-up period of the MBR was shorter. On the 14th, 28th, and 56th day, the average nitrite accumulation efficiencies in the CSTR were 51%, 66%, and 89%, respectively, and 50%, 71%, and 93% in the MBR, and nitrate formation rates of the CSTR was successively 7.4, 4.0, and 1.7 mg·(g·h) (NO-N/MLVSS), respectively, and 7.6, 3.5, and 1.0 mg·(g·h) (NO-N/MLVSS) for the MBR. A higher nitrite accumulation efficiency and a lower nitrate formation rate were detected in the MBR on the 28th and 56th day, respectively, which could be beneficial to the fast start-up of shortcut nitrification. During the operation period, the shortcut nitrification sludge in the two reactors was yellow, the sludge volume index (SVI) was between 55 and 110 mL·g, and the mixed liquor volatile suspended solids (MLVSS)/mixed liquor suspended solids (MLSS) ratio was around 0.6-0.8. The good sludge performance created favorable conditions for the fast start-up of shortcut nitrification in both the CSTR and MBR. In conclusion, the MBR exhibited better performance in the fast start-up of shortcut nitrification.