Microbial community and N removal of aerobic granular sludge at high COD and N loading rates.

An aerobic granular sludge, cultivated with modified piggery wastewater, was capable of simultaneously removing COD and N at high COD and N loading rates. Confirmed to be identical with the DGGE band B9, isolate Thauera strain TN9 was the most dominant microorganism in the granular sludge. NirS and NosZ gene were amplified and sequenced from strain TN9 suggested it is crucial to N removal. Some other dominant DGGE bands belonged to Zoogloea and TM7, might play important roles in the formation and the stabilization of the granules. Meanwhile, no AOA amoA or anammox bacterium hzo gene was detected in the granules. All amoA clone libraries of AOB were clustered to Nitrosomonas. Yet those AOB were not present in DGGE dominant bands. Therefore, the heterotrophic nitrification and autotrophic nitrification coexist in the granules, the heterotrophic nitrification might contribute more to the N removal at high COD and N loading rates.