In order to study the effect of different volumetric exchange rates (VER) on the granulation and stable operation of SNAD sludge

two lab-scale SBR reactors

with a 37.5% VER (R1) and 75% VER (R2)

were comparably analyzed. Experimental results demonstrated that the granulation of R1 could be achieved in 36 days

was 12 days faster than R2. Meanwhile

a relatively lower sludge loss rate of R1 was obtained. The nitrogen removal rate (RNR)

RAO and RAN in R1 were 0.356 g·L-1·d-1

0.113 0 and 0.080 9 g·g-1·d-1

respectively; while that of R2 was 0.248 g·L-1·d-1

0.093 6 and 0.070 5 g·g-1·d-1

respectively. This confirmed that a lower VER reduced the loss of floc sludge

and further declined the granulation period. Moreover

a lower VER not only enhanced the activity of ammonia-oxidizing and anaerobic ammonia-oxidizing bacteria

but also suppressed nitrite-oxidizing bacteria

was benefit for a stable and efficient removal performance of the SNAD granular sludge.