Reactivation characteristics of stored aerobic nitrifying granules

A sequencing batch airlift reactor(SBAR) was conducted to study the performance of physical characteristics and respirometric activities during reactivation of aerobic granules after a 2-month storage time.Results showed that the color of the aerobic granules had completely become dark,the size and settleability did hardly change during the storage period.The color turned to be brownish-yellowish when the reactor was restarted for 2 weeks.The MLSS,granule size,and settleability increased rapidly along with reactivation.The heterotrophic activity resumed 86% within 1 day and was fully reactivated after 5 days.Then the COD removal rate was stabilized above 80%.Higher aeration rate and longer cycle time facilitated the reactivation of nitrifiers.When aeration rate was increased from 0.05(m~3·h~(-1)) to 0.10(m~3·h~(-1)) at 41th day,activities of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were improved from 88% and 82% to 122% and 92%,respectively.The removal rate of ammonium-nitrogen promptly reached above 96%.Nitrite-oxidizing bacteria were fully reactivated after the cycle time was prolonged from 4 h to 6 h.