Nutrient removal in gravel- and soil-based wetland microcosms with and without vegetation

In this study, four lab-scale microcosms, including gravel-beds with and wi thout plants, and soil-beds with and without plants, were used to conduct t he nutrient removal tests. The influent used in the tests is primary treate d sewage, while the plant selected was Napier grass (Pennisetum purpureum). The purpose of this study is to compare the removal efficiencies of nitrog enous and phosphorus nutrients among these four microcosm wetland systems b ased on statistical analyses. Three factors, namely, with/without vegetatio n (F-1), medium types of gravel/soil (F-2), and time period for the test ru n of first/second stage (F-3), and four combined effects of factors, F-1 by F-2 (F-1,F-2), F-1 by F-3 (F-1,F-3), F-2 by F-3 (F-2,F-3), and F-1 by F-2 by F-3 (F-1,F-2,F-3), were run by an ANOVA model to analyze the relationshi ps between the amounts of nutrient removed from the wetland systems and the se seven factors. We found that the removals of ammonia (NH3-N), nitrate (N O3--N), and soluble reactive phosphorus (SRP) were related to these factors and combined effects of the factors. It was found that the main removal me chanism for NH3-N was nitrification, which could be enhanced by the root zo ne effect in the vegetated gravel-bed wetland systems, while NO3--N was rem oved mainly by denitrification and plant uptake in vegetated systems. Howev er, the main removal mechanism for SRP was chemical adsorption in the unsat urated soil-bed systems. The effect of plant litter was also a significant mechanism affecting nutrient removal in the surface flow pattern soil-bed w etland systems without harvest. (C) 2001 Elsevier Science BY. All rights re served.