Removal of nutrients in various types of constructed wetlands
Introduction
Constructed wetlands are engineered systems that have been designed and constructed to utilize the natural processes involving wetland vegetation, soils, and their associated microbial assemblages to assist in treating wastewater. They are designed to take advantage of many of the processes that occur in natural wetlands, but do so within a more controlled environment (Hammer and Bastian, 1989). Synonymous terms to “constructed” include “man-made”, “engineered” or “artificial” wetlands. The basic classification is based on the type of macrophytic growth, further classification is usually based on the water flow regime (Fig. 1). The paper deals only with constructed wetlands with free-floating plants (FFP), free water surface CWs with emergent plants (FWS) and sub-surface CWs with horizontal (HSSF or HF) and vertical (VSSF or VF) flows (Fig. 2) as data on CWs with floating leaved plants and submerged plants are still not abundant, and therefore it is not possible to make sound evaluations.
Section snippets
Nitrogen
Nitrogen has a complex biogeochemical cycle with multiple biotic/abiotic transformations involving seven valence states (+ 5 to − 3). The compounds include a variety of inorganic and organic nitrogen forms that are essential for all biological life. The most important inorganic form of nitrogen in wetlands are ammonium (NH4+), nitrite (NO2−) and nitrate (NO3−). Gaseous nitrogen may exist as dinitrogen (N2), nitrous oxide (N2O), nitric oxide (NO2 and N2O4) and ammonia (NH3).
Phosphorus
Phosphorus in wetlands occurs as phosphate in organic and inorganic compounds. Free orthophosphate is the only form of phosphorus believed to be utilized directly by algae and macrophytes and thus represents a major link between organic and inorganic phosphorus cycling in wetlands. Another group of inorganic phosphorus compounds are polyphosphates linearly condensed and cyclic. Organically-bound phosphorus is present e.g., in phospholipids, nucleic acids, nucleoproteins, phosphorylated sugars
Conclusions
Removal of total nitrogen in studied types of constructed wetlands varied between 40 and 50% with removed load ranging between 250 and 630 g N m− 2 yr− 1 depending on CWs type and inflow loading. However, the processes responsible for the removal may differ in magnitude among systems. Single-stage constructed wetlands cannot achieve high removal of total nitrogen due to their inability to provide both aerobic and anaerobic conditions at the same time. Vertical-flow constructed wetlands remove
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