Vertical flow treatment wetlands have been developed as very useful tools for treatment of combined sewage overflow. Several systems have been in operation for over 15 years. Based on recent research work, new technical guidelines now recommend systems with a drained filter of sand 0/2 mm and a throttled outflow. COD, NH4-N and SS removal rates of 85–99% can be expected from this type of filter. SS loadings that are too high and very long or frequent inundation affect the performance adversely. Information for successful long-term operation were derived from various existing plants.

Combined sewer overflow, constructed wetlands, enhanced treatment, operation, planning, receiving water
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