The recycling effect in the nitrification-denitrification process in vertical flow constructed wetlands

Abstract

Uncontrolled discharge of nutrient rich wastewater to the environment is a common source of pollution and it is partly responsible for the eutrophication of surface water, as well as degradation of the quality of groundwater. Constructed wetlands have proven to be an effective and affordable alternative to reduce BOD, suspended solids and even to reduce the concentration of nutrients from domestic wastewater, if the design, operation and establishment of the system meet certain conditions. Two of the most important nutrients are nitrogen and phosphorus. To remove nitrogen it is necessary that first nitrification and then denitrification occurred. The first process is aerobic and autotrophic bacteria carry it out whereas denitrification happens in anoxic conditions by heterotrophic bacteria. Phosphorus is removed basically by precipitation with aluminium, iron and calcium. This paper shows the removal processes of these nutrients as well as the removal of undesirable wastewater parameters through a system made up of the following components: (i) a 2-m3 three chamber sedimentation tank; (ii) a first stage 10-m2 vertical flow constructed wetland; (iii) three P-filter units; and (iv) a second stage 5-m2 vertical flow CW. The pilot plant is placed in the vicinity of Århus (Østjylland, Denmark), and the study took place between October 2002 and January 2003. Furthermore, these results have been validated in an operational single household autonomous system.