**6.1.2 Waste stabilization ponds (WSP) / surface flow wetlands (SFW)**

*Design:* In the period between 2000 and 2003, a pilot SFW and a pilot WSP were constructed at the outlet of wastewater treatment plant (WWTP). The SFW was planted with *Phragmites australis* and *Eichhornia crassipes*, while in the WSP development of algae was spontaneous.

*Monitoring:* The systems were monitored under the same operating conditions. The efficiency was evaluated by means of physical and chemical parameters in the inflow and outflow water, by plant productivity and by the analysis of N and P contents in biomass.

*Results and Discussion:* The SFW proved more efficient in the elimination of suspended solids (64.6 %), settleable solids (91.8 %), organic N (59.3 %), total N (38 %), COD (67.2 %) and BOD5 (72.1 %) than the WSP. The WSP was more efficient in the treatment of ammonia nitrogen (48.9 %) and orthophosphate (43.9 %). The difference in treatment efficiency between the systems most probably originates from different primary producers (macrophytes vs. algae) and consequent food webs established. The results of this study provide data of help in optimising combinations of SFW and WSP (Šajn-Slak et. al., 2005).
