Comparative study of domestic wastewater treatment by mature vertical-flow constructed wetlands and artificial ponds

- Five-years old wetlands greatly improved COD, BOD, NH4−N and SS outflows over time.
- Wetlands with doubled COD loading rate resulted in better COD, BOD and SS outflows.
- COD and SS removals were significantly higher in wetlands if compared to ponds.
- Aerated and planted ponds removed NH4-N and PO4-P significantly the best.
- Regardless of contact times tested, wetlands were higher in BOD removal than ponds.

This study compares the performance, design and operation variables of two wetland technologies treating domestic wastewater: an experimental artificial pond system and a mature experimental vertical-flow constructed wetland system. The wetland system planted with Phragmites australis (Cav.) Trin. ex Steud. (common reeds) was operated between June 2011 and October 2015, while the pond system was only operated between July 2015 and October 2015. Three different types of ponds were compared: ponds with wastewater; ponds with wastewater and reeds; and ponds with wastewater, reeds and aeration. Findings regarding the performances of mature wetlands showed that the wetland systems improved the water quality except for ortho-phosphate-phosphorus (PO4−P), where the treatment performance reduced slightly over time. In general, the aerated pond systems showed better treatment performances in terms of ammonia-nitrogen (NH4−N) and PO4−P‎. Both systems were linked with medium to high levels of five-day biochemical oxygen demand (BOD) removal. The highest COD and SS removals were observed for wetlands in comparison to ponds. Moreover, mature wetlands were better in removing NH4−N and PO4−P than ponds unless the ponds were aerated. The nitrate-nitrogen (NO3−N) concentration increased in the aerated ponds reflecting the high oxygen availability.

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