Effects of vegetation, seasonality, organic and nitrogen loading rates in the performance of Horizontal Subsurface Constructed Wetlands

This thesis aims to contribute for the study of critical factors that influence the removal of organic matter and nitrogen in constructed wetlands with horizontal subsurface flow. It was realized that plants contribute for increasing the removal of organic matter and nitrogen, because they provide oxygen to the rhizosphere and the gowth of roots increases the surface area for biofilm development and uptake nitrogen through the roots. The Phragmites australis releases more oxygen during the daytime, and the oxygen transfer capacity was noted to change between 0.03 and 1.53 gO2.m-2.d-1. There was a positive linear relationship (p<0.05) between the organic removal rate and the influent organic load for the lower load. The removal of the ammonia mass load was not affected (p>0.05) by the respective applied load. The performance evaluation of three full-scale beds showed large fluctuations in organic and solid loads and low nitrogen load. The average removal efficiency (RE) of BOD5 was 88% and for nitrogen was low (<27% NT <30.8% for N-Org. <7% NH4+-N and <18% of NOX-N), although the plants were well developed and the hydraulic retention time was suitable for promoting nitrification. The COD removal ranged between 59% and 76%. There was a significant linear relationship (p<0.05) between the applied load of NT and SST and the respective concentration in the effluent. The effect of seasonal variation in the performance of other full-scale bed has shown that the RE of TSS and BOD5 are not affected (p>0.05) by seasonal periods, while nitrogen and phosphorus are significantly influenced (p<0.05) by the year season. The RE of TSS, COD and BOD5 was not significantly (p>0.05) affected by the income of high hydraulic loads, which shows good resilience of these systems.