Performance and microbial community of MBBRs under three maintenance strategies for intermittent stormwater treatment.

Maintaining microbial activities is a critical problem for biological treatment processes of stormwater runoff because of its intermittent nature. In this study, the suitability of the moving bed biofilm reactor (MBBR) was assessed for stormwater treatment by long-term dry - rainy alternation operation. Three strategies to maintain microbial activities during the dry period, including keeping idle (MBBRI), introducing river water throughout the period (MBBRC), and ahead of a rainy day (MBBRM), were investigated. COD and NH4+-N removal efficiencies declined linearly from 94.2 % and 94.7 % to 51.7 % and 64.6 %, respectively, after the 61-day operation with microbial activity and biomass decreased. Introducing river water adversely affected the process performance as MBBRC presented the highest declining rates of COD and NH4+-N removal efficiencies. Most genera in MBBRs decayed and their microbial communities developed towards individualization, especially in MBBRM because of its highest environmental variability. Keeping idle slightly alleviated the performance decline and formed a more stable microbial community structure. However, significantly deteriorating performance in all MBBRs after the long-term operation indicated that MBBRs were unsuitable for treating stormwater independently of intermittent nature.