We aimed to evaluate the efficiency of six different horizontal subsurface flow constructed wetlands (HSSF-CWs), with different substrates (gravel and crushed PET bottles), which also varied in relation to the presence and arrangement of plant species (elephant grass and Tifton 85 bermudagrass) in the removal of pollutants from a bulk milk cooling tank (MTWW). Each bed was fed at a flow rate of 0.18 m 3 d -1 and average organic load rate (OLR) of 318 kg ha -1 d -1 of BOD5, with hydraulic detention time (HRT) of 1.84 days in the gravel-filled HSSF-CWs (CWS-G) and 2.97 days in the PET-filled HSSF-CWs (CWs-P). The CWs-P were as efficient as the CWs-G in the removal of BOD5, COD, Total-P, and K-Total, being in some cases even more effective (turbidity, TS, TSS and Na). The gravel, on the other hand, provided greater removals of Total-N from the MTWW. In the non-cultivated CWs and those cultivated with elephant grass, in its first half and Tifton 85 grass in its second half, there were higher average efficiencies in COD and TSS removal sand, in the latter, the highest average removal of Total-N.

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A B S T R A C TDenitrification and uptake by plants in constructed wetlands (CWs) were studied. Nitrate was applied in CWs operated in batch mode. The systems received 50 g m −3 NO À 3 -N, and among six units, three received ethanol as carbon source. The experiment consisted of two main stages, with each one cycle time (t c ) of 3 and 1 d. In an extra stage, the decay values of water variables were assessed. The range of nitrate-nitrogen removal (stage I) was 11.7-54.8% for CWs without ethanol and 98.0-99.9% for CWs receiving the external carbon source. During stage II, NO À 3 -Nremovals were 3.6-15.7% for CWs without ethanol and 94.7-97.5% for CWs with ethanol addition. CWs were effective for removing nitrate, especially the planted systems. CWs cultivated with vetiver showed the best results in nitrogen removal. The addition of ethanol increased the denitrification efficiency, but increasing nitrite concentrations in the CWs should also be considered.

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This study aimed to characterize the material composition responsible for clogging the porous medium of horizontal subsurface flow constructed wetland (HSSF-CW) systems, which is detrimental to a proper system operation. Six completely clogged HSSF-CWs were used after treatment of swine wastewater. Operating conditions of these systems were named CW-C (HSSF-CW 1 and HSSF-CW 4, non-cultivated, i.e. controls), CW-T (HSSF-CW 2 and HSSF-CW 5, cultivated with Tifton 85 (Cynodon spp.)), and CW-A (HSSF-CW 3 and HSSF-CW 6, cultivated with alligator weed (Alternanthera philoxeroides)). The results showed that most of the clogging material was composed of total fixed solids (95, 84, and 82% in CW-C, CW-T, and CW-A, respectively). However, total volatile solids (TVS) mostly affected pore clogging. The larger accumulations and productions of TVS in CWs might have originated from dead plants.

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