Drying and re-cultivation of aerobic granules

Aerobic granules stored in liquid medium can lose structural integrity during storage. This study demonstrated that the aerobic granules cultivated by seeding activated sludge into column-type sequential batch reactors and fed with synthetic wastewater at organic loading rate of 1.5 kg/m3-d can be dried by acetone gradient method to moisture content less than 1%. Then, the dried granules can be reactivated through a re-cultivation process to recover their organic degradation capacity in 12 h, or their appearance in 5 d. During the drying and recovery, the granules experienced volume and weight losses by >80% and >85%, respectively, with minimal loss in structural integrity. The microbial communities of the dried and re-cultivated granules were probed using polymerase chain reaction-denaturing gradient gel electrophoresis technique. The family Xanthomonadaceae and the family Comamonas can survive in dried granules and could contribute to maintain structural integrity in re-cultivation stage.