Effect of granular activated carbon on the aerobic granulation of sludge and its mechanism

- GAC accelerated the granulation of activated sludge under EBPR conditions.
- GAC had no obvious effect on the bacterial community structure of granules.
- A mechanism for GAC effect on granulation was proposed.
- Simultaneous removal of COD, nitrogen and phosphorus in aerobic granules system.

The granulation of activated sludge and effect of granular activated carbon (GAC) was investigated under the alternative anaerobic and aerobic conditions. The results showed that GAC accelerated the granulation, but had no obvious effect on the bacterial community structure of granules. The whole granulation process could be categorized into three phases, i.e. lag, granulation and granule maturation phase. During lag period GAC provided nuclei for sludge to attach, and thus enhanced the morphological regularization of sludge. During granulation period the granule size increased significantly due to the growth of bacteria in granules. GAC reduced the compression caused by the inter-particle collisions and thus accelerate the granulation. GAC has no negative effect on the performance of SBR, and thus efficient simultaneous removal of COD, nitrogen and phosphorus were obtained during most of the operating time.