Abstract
The characteristics of granular anammox sludge were studied through long-term continuous cultivation in a stirred tank reactor. The reactor was operated steadily with stirring speeds of 70–120 rpm. A maximum nitrogen loading rate of 9.52 kg/m3/d was obtained after 318 days of continuous treatment. The particle size of anammox granules ranged primarily from 2.0–4.0 mm, the wet density was 1.04 g/ml, and the settling velocity was 152.7 m/h, indicating satisfactory settling of the granules. The sludge contained high amounts of organic matter with a volatile to total solids mass percent of 0.91. Observations by scanning electron and stereo microscopy showed that the anammox granules were relatively regular in shape and had a very clear outline. Furthermore, the bacterial composition of the mature community was investigated by amplifying the 16S rRNA sequences by PCR. Results showed that Planctomycete KSU–1 was dominant in the reactor and played a significant role in the anammox process.
