Seed sludge was obtained from a hydrolysis acidification tankof the refinery wastewater treatment plant of the Liaohe Petro-chemical Company (Liaoning province, China). It showed goodsettleability and a dark brown color, with 17.23 g/L of mixed liquorsuspended solids (MLSS) and 8.74 g/L of mixed liquor volatile sus-pended solids (MLVSS), respectively.