The objectives of this study are to investigate the effects of acidification and alkalization on volume/solid reduction, dewaterability, and coagulant recovery from textile chemical sludge. The results indicate that solid reduction by acidification and alkalization was mainly due to the dissolution of Al. The best conditions for acidification and alkalization are pH = 2 and pH = 12, respectively, both exceeding 60% in AI(III) recovery efficiency. However, organic matters dissolved along with Al(III) dissolution by alkalization have detrimental effects on the usability of recovered Al. Thus, acidification was a better process for recovering coagulants than alkalization. In the meantime, only acidification could decrease both the capillary suction time (CST) and specific resistance value (SRF), indicating that only the acidification can improve the dewaterability of sludge. (C) 2004 Elsevier B.V. All rights reserved.