Vertical flow-constructed wetlands for domestic wastewater treatment under tropical conditions: effect of different design and operational parameters

This study assessed the treatment of domestic wastewater to find the optimum vertical flow-constructed wetland (VFCW) configuration under tropical conditions. Eight pilot-scale configurations units were studied to compare between fine sand and medium gravel used as substrate, two feeding frequencies (20 pulses d(-1) and 10 pulses d(-1)), and the presence or absence of tropical plants (Heliconia psittacorum). The results showed that the sand beds were significantly more efficient in the removal of organic matter, ammonia nitrogen, and total suspended solids than gravel beds, presenting average removal rates of 48 and 24 g m(-2) d(-1) of COD; 35 and 16 g m(-2) d(-1) of BOD5; 7 and 4 g m(-2) d(-1) of NH4+ -N; 9 and 0 g m(-2) d(-1) for sand and gravel, respectively. The oxygen consumption rates were calculated and a value of 65 g m(-2) d(-1) was obtained for sand beds while for the gravel beds the consumption rate was 30 g m(-2) d(-1). The assessment of different kinds of nitrogen showed interesting dynamics in the nitrification processes. The presence of H. psittacorum showed positive effects in the total nitrogen (TN) removal. The different loading frequencies applied did not show significant statistical differences in the removal of the tested contaminants. Preliminary results were found in the pathogen removal, where the sand is favorable as the substrate. This work represents the first step in the research of optimum VFWC design and operation parameters for Colombia as well as the use of plants of the genus Heliconia.