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- Effect of vegetation on the performance of horizontal subsurface flow constructed wetlands with lightweight expanded clay aggregatesPublication . Mesquita, Maria da Conceição; Albuquerque, Antonio; Amaral, Leonor; Nogueira, ReginaThis research evaluates the effect of both organic and ammonia loading rates and the presence of plants on the removal of chemical oxygen demand and ammonia nitrogen in horizontal subsurface flow constructed wetlands, 2 years after the start-up. Two sets of experiments were carried out in two mesocosms at different organic and ammonia loading rates (the loads were doubled); one without plants (control bed), the other colonized with Phragmites australis. Regardless of the organic loading rate, the organic mass removal rate was improved in the presence of plants (93.4 % higher for the lower loading rate, and 56 % higher for the higher loading rate). Similar results were observed for the ammonia mass removal rate (117 % higher for the lower loading rate, and 61.3 % higher for the higher loading rate). A significant linear relationship was observed between the organic loading rate and the respective removal rates in both beds for loads between 10 and 13 g m(-2) day(-1). The presence of plants markedly increase removal of organic matter and ammonia, as a result of the role of roots and rhizomes in providing oxygen for aerobic removal pathways, a higher surface area for the adhesion and development of biofilm and nitrogen uptake by roots.
- Influence of bed media characteristics on ammonia and nitrate removal in shallow horizontal subsurface flow constructed wetlandsPublication . Albuquerque, Antonio; Oliveira, José; Semitela, Sabrina; Amaral, LeonorTwo bed media were tested (gravel and Filtralite) in shallow horizontal subsurface flow (HSSF) constructed wetlands in order to evaluate the removal of ammonia and nitrate for different types of wastewater (acetate-based and domestic wastewater) and different COD/N ratios. The use of Filtralite allowed both higher mass removal rates (1.1 g NH4–N m−2 d−1 and 3 g NO3–N m−2 d−1) and removal efficiencies (>62% for ammonia, 90–100% for nitrate), in less than 2 weeks, when compared to the ones observed with gravel. The COD/N ratio seems to have no significant influence on nitrate removal and the removal of both ammonia and nitrate seems to have involved not only the conventional pathways of nitrification–denitrification. The nitrogen loading rate of both ammonia (0.8–2.4 g NH4–N m−2 d−1) and nitrate (0.6–3.2 g NO3–N m−2 d−1) seem to have influenced the respective removal rates.