I In nf fl lu ue en nc ce e o of f b be ed d m me ed di ia a c ch ha ar ra ac ct te er ri is st ti ic cs s o on n a am mm mo on ni ia a a an nd d n ni it tr ra at te e r re em mo ov va al l i in n s sh ha al ll lo ow w h ho or ri iz zo on nt ta al l s su ub bs su ur rf fa ac ce e f fl lo ow w c co on ns st tr ru uc ct te ed d w we et tl la an nd ds s Abstract Two 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 nitrificationdenitrification. 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.

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a b s t r a c tThis study investigated the effects of reed and willow on bioremediation of landfill leachate in comparison with an unplanted control by measuring redox potential levels in the rhizosphere of microcosm systems in a greenhouse. Plants had a significant influence on redox potential relative to the plant-less system. Redox potential in the reed rhizosphere was anoxic (mean À102 AE 85 mV), but it was the least negative, being significantly higher than in the willow (mean À286 AE 118 mV), which had the lowest Eh. Redox potential fluctuated significantly in the willow rhizosphere during daylight hours, with large decreases in the morning. Levels of NH 4 þ decreased significantly in the first day of the experiment and remained at similar low levels in all three variants for the next four weeks of the experiment. Following this removal of ammonia significant peaks in NO 2 À occurred in the control and reed tanks on the 1st day, and again on 14th day in the control tank up to 13 mg/dm 3 . In the willow tank there was also one significant peak of NO 2 À in the first week, but only up to 0.5 mg/dm 3 . Significant accumulation, within 21 days of NO 3 À in all variants was observed, but in tanks with reed and willow the concentration of NO 3 À remained significantly lower (<4 mg/dm 3 ) than in the unplanted tank (w35 mg/dm 3 ). Final levels of total-nitrogen, nitrate and chemical oxygen demand were considerably lower in the reed and willow tank than in the unplanted tank.

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