The effect of re-startup strategies on the recovery of constructed wetlands after long-term resting operation

The objective of this study was to identify the proper re-startup strategies (RSSs) for constructed wetlands (CWs) after long-term resting operation in terms of the recovery of pollutant removal efficiency (RE) and N-cycle gene abundance. The results suggested that backwashing increased the gene abundance without shortening the recovery time of gene abundance. The RSS involving excavation and washing performed better in terms of chemical oxygen demand (COD) RE, especially at the beginning, and performed slightly better or similarly in terms of N-cycle gene abundance and the REs of ammonia nitrogen (NH4+-N) and total nitrogen (TN). The abundance of the Amox gene was 66.1-92.8, 76.3-161.8 and 1550-2492 times larger than that of the napA, narG and amoA genes, respectively, and the anammox process was the dominant N removal pathway. Therefore, excavation and washing is recommended as the RSS for CWs with a long-term rest period.