Degradation of phenanthrene and hydraulic characteristics in a constructed wetland

An artificial waste water containing phenanthrene and Tween 80(x) was treated in the horizontal-vertical flow macrophyte-based treatment system. The pilot plant consisted of a cascade of five steel tanks filled with lava, each tank planted with Typha spp, and Scirpus lacustris. The overall removal of phenanthrene in water was about 99.9%. Adsorption of phenanthrene was primarily observed in the upper lava layer. 1-Hydroxy-2-naphthoic acid (HNA) as a bacterial metabolite of phenanthrene was quantified. An MPN(most probable number)-method for the enumeration of phenanthrene-degrading bacteria was modified by staining degradation products formed in the culture media with diazonium salts. The number of phenanthrene-degrading bacteria was highest in the first tank of the cascade. The number of total bacteria remained nearly constant within the cascade. The amount of bacteria in lava exceeded that in water by a factor of 10(3). The number of phenanthrene-degrading bacteria in lava samples in a phenanthrene-loaded tank was approximately 10(6) g(-1), and 10(2) g(-1) in a non-loaded tank. Furthermore, tracer experiments were conducted in 1993 and 1994. The mean residence time was determined to be 1.18 days (1993) and 1.15 days (1994) in the first tank, and 6.66 days (1993) and 6.4 days (1994) in the whole cascade. The experimental values agreed approximately with the theoretical values of 1.27 days and 6.54 days. The Peclet numbers agreed with those of the dispersion characteristic of the lava filling as a porous medium. (C) 1997 Elsevier Science Ltd.