Long term performance of a constructed wetland planted with Typha angustifolia

Abstract

Constructed wetlands are often utilized for wastewater treatment' including removal of metals. The removal mechanism is phytoremeditation, in which plants are manipulated to immobilize the pollutants. Physico-chemical properties of substrate and its potential tor removal of pollutants also effects the performance of constructed wetlands. Many engineering studies of treatment by wetlands use a black box approach.This paper discusses the Zn uptake by Tvpha angustifoha and its distribution within the shoot (leaves and stem) and root. This was investigated by introducing different operation conditions to the constructed wetland during acclimatization with nutrients, and gradual variation of Zn loading with incremental increases. The relative changes in the substrate (clay tile) were also investigated by means of XRD, FT-IR and SEM analysis. The results revealed that the clay tile is a promising adsorption material for Zn. In addition,Typha angustifolia is found to contribute to metal trapping into the senescing plants via rhizodeposition and act as a catalyst for biochemical reactions. The interesting feature noted in the wetland was that after nearly two years of operation, almost all clay tiles around the rhizosphere of Typha angustifolia were disintegrated completely, back to the original clay, suggesting that nature helps to sustain the plants by providing an environment with less toxicity. lt could be concluded that the long term adaptation of wetland plants to heavy-metal rich environments would not help the sequestration process, and they cannot be considered to be heavy metal sinks in the aquatic system once this stage is reached.