Freezing of aerobic granules for storage and subsequent recovery

Aerobic granules stored in liquid medium can lose structural integrity during storage. Freezing and thawing is applied for disintegrating and then compacting sludge flocs into pellets. This study stored aerobic granules cultivated by seeding activated sludge into column-type sequential batch reactors and fed with synthetic wastewater at organic loading rate of 1.5kg/(m³d) at -20°C for 40 days, and then thawed and recovered the frozen granules in 1 day. The present granules have a resilient granule matrix that can resist engulfing of freezing front in freezing. The microbial communities of the frozen and re-cultivated granules were probed using polymerase chain reaction-denaturing gradient gel electrophoresis technique. The family Xanthomonadaceae and the genus Comamonas can survive during freezing and thawing and could contribute to maintain structural integrity in re-cultivation stage. © 2013 Taiwan Institute of Chemical Engineers.