Seasonal and annual performance of a full-scale constructed wetland system for sewage treatment in China

A full-scale constructed wetlands system with a total area of 80 ha and treatment capability of 2.0 × 104 m3 d−1 was completed in October 1998 in Rongcheng, Shandong Province, China. To evaluate wastewater treatment effectiveness and seasonal performance of the system, water samples were collected and analyzed from January 1999 to December 2004. Comparison of mean inlet and outlet concentrations showed that the constructed wetland system could effectively reduce the output of SS (71.8 ± 8.4%), BOD5 (70.4 ± 9.6%), COD (62.2 ± 10.1%), total coliform (99.7%) and fecal coliform (99.6%). However, the percent reduction of ammonia nitrogen was relatively low (40.6 ± 15.3%), and total phosphorus showed the least efficient reduction (29.6 ± 12.8%). BOD5, COD, ammonia nitrogen, and total phosphorus removal efficiencies displayed seasonal variations. BOD5 and COD removal was more efficient in spring and summer than in autumn and winter whereas ammonia nitrogen and total phosphorus removal was more efficient in summer and autumn than in spring and winter. Annual variation analysis shows that COD, BOD5, and ammonia nitrogen reduction efficiencies increased from 1999 to 2004. In contrast, mean total phosphorus reduction efficiency did not change from 2001 to 2002 and began to decrease from 2003 onwards.