Abstract
Having outstanding settleability, aerobic granular sludge receives increasing attention for wastewater treatment. Washing out undesired sludge (frequently in the form of flocs) is an essential operation condition for developing granules, and thus a high solids concentration is in effluent. However, the properties of effluent solids have not been fully understood. To study the properties of effluent solids could better understand granulation and provide basic information for the followed polish unit design to remove these solids. Results in this study shows that sizes of effluent solids increased with the increase of granule size. The effluent solids exhibited higher EPS (extracellular polymer substances) concentrations but lower fraction of carbohydrate content, and higher fraction of ash solids. The properties of effluent suspended solids and deteriorated granules changed in a similar fashion, suggesting that the effluent solids resulted mainly from the deteriorated granules. It was also found that ash solids buildup was a result of compact structure, which in turn, improved the stability of granules by increasing the settleability.