Treatment performance and macrophytes growth in a restored hybrid constructed wetland for municipal wastewater treatment

- Hybrid constructed wetland represents a valid solution to treat municipal wastewater.
- Horizontal subsurface flow wetland abated nitrate nitrogen, total phosphorus and orthophosphate concentrations.
- Floating treatment wetland reduced water turbidity, chemical oxygen demand and ammonia nitrogen concentrations.
- Iris pseudacorus showed an excellent biomass production in the floating system.
- Phragmites australis well-colonized the horizontal subsurface flow wetland but did not survive in hydroponic conditions.

This work evaluated depuration performance and macrophyte plants growth in a full-scale hybrid-constructed wetland (H-CW) (1000 population equivalent) treating municipal wastewater. The plant was activated in June 2010 after a restoration of an existent H-CW composed of a horizontal subsurface flow (HSSF) bed vegetated with evergreen xerophile species (Prunus laurocerasus, Pittosporum spp., Elaeagnus angustifolia), connected with a sedimentation pond vegetated with Lemna spp. To enhance the depuration performances, in both sections of the plant the original vegetation was removed and the HSSF bed was vegetated with Phragmites australis, whereas in the pond, a floating treatment wetland vegetated with Iris pseudacorus was installed. The depuration performance in treating total nitrogen (TN), nitrate nitrogen (NO3-N), ammonia nitrogen (NH4-N), total phosphorus (TP), orthophosphate (PO4-P) and chemical oxygen demand (COD) was weekly monitored between August 2010 and August 2011. Results indicated median concentration abatements for the entire system of 74.3% for TN, 62.1% for NH4-N, 77.7% for NO3-N, 29.6% for TP, 37.4% for PO4-P, and 46.7% for COD. In addition, at the end of the first growing season (June 2010-November 2010), good adaption to the system was detected for both P. australis and I. pseudacorus, which produced respectively 3.9 ± 2.2 kg m−2 and 3.7 ± 1.0 kg m−2 of above-ground dry biomass, with average above-ground N uptakes of 62.4 ± 35.6 g m−2 and 69.8 ± 19.0 g m−2 and average above-ground P uptakes of 4.6 ± 2.6 g m−2 and 7.8 ± 2.1 g m−2. The results indicate that a H-CW composed of a sequence of HSSF bed and FTW represents an effective application for abating TN, NH4-N, NO3-N and COD concentrations from municipal wastewater.