Review Articles Constructed Wetlands
109 ecomed publishers, D-86899 Landsberg, Germany and Ft. Worth/TX Tokyo Mumbai Seoul Victoria ParisJSS J Soils & Sediments 33333 (2) 109 124 (2003)
Review Article with Case Studies
Constructed Wetlands for the Treatment of Organic PollutantsRaimund Haberl1, Stefano Grego2, Gnter Langergraber 1 (*), Robert H. Kadlec3, Anna-Rita Cicalini4,Susete Martins Dias5, Julio M. Novais5, Sylvie Aubert6, Andre Gerth7, Hartmut Thomas7 and Anja Hebner7
1 IWGA-SIG - Department for Sanitary Engineering and Water Pollution Control, BOKU University of Natural Resources andApplied Life Sciences, Vienna, Muthgasse 18, A-1190 Vienna, Austria
2 Dipartimento di Agrobiologica ed Agrochimica, Universit della Tuscia, Via S. G. Decollato 1, I-01100 Viterbo, Italy3 University of Michigan and Wetland Management Services, Chelsea, Michigan, USA4 Dipartimento Biologica e Ambiente, ISRIM, I-05100 Terni, Italy5 Instituto Superior Tcnico, Centre for Biological and Chemical Engineering, Av. Rovisco Pais, P-1049-001 Lisboa, Portugal6 Laboratory for Environmental Biotechnology (LBE), Swiss Federal Institute of Technology Lausanne (EPFL), CH-1015 Lausanne, Switzerland7 BioPlanta GmbH, Benndhorfer Landstrasse 2, D-04509 Delitzsch, Germany
* Corresponding author: Gnter Langergraber ([email protected])
Introduction
Wetlands are transitional environments between dry landand open water. In an ecological context, wetlands are in-termediate between terrestrial and aquatic ecosystems. Wet-lands can be defined as ecosystems that depending on con-stant or recurrent, shallow inundation or saturation at ornear the surface of the substrate (Lewis 1995, in: Vymazalet al. 1998). The major wetland components are: Vegetation. The prevalent vegetation consists of macro-
phytes that are typically adapted to areas heaving hydro-logic and soil conditions described in the definition.
Soil. Soils are present and have been classified as hydric,or they posses characteristics that are associated withreducing soil conditions.
Hydrology. The area is inundated either permanently orperiodically at mean water depth of 2 m, or the soil issaturated to the surface at some time during the growingseason of the prevalent vegetation.
Compared with the vegetation of well-drained soils, wetlandplants have a world-wide similarity which over-rides climateand is imposed by the common characteristics of a free wa-ter supply and the abnormally hostile chemical environmentwhich plant roots must endure (Etherington 1983, in: Vyma-zal et al. 1998). Wetland plants have elaborated structuralmechanisms to avoid root anoxia. The main strategy hasbeen the evolution of air spaces (aerenchyma) in roots andstems that allow the diffusion of oxygen from the aerialportions of the plant into the roots (e.g. Armstrong and Arm-strong 1990). The magnitude of oxygen diffusion throughmany wetland plants into the roots is apparently large enoughnot only to supply the roots but also to diffuse out and oxi-dize the adjacent soil (Teal and Kanwisher 1966, and Howeset al. 1981, in: Vymazal et al. 1998).Four groups of aquatic macrophytes can be distinguishedon a basis of morphology and physiology (Wetzel 1983, in:Vymazal et al. 1998):
1. Emergent macrophytes grow on water saturated or submersedsoil from where the water table is about 0.5 m below the soilsurface to where the sediment is covered with approximately1.5 m of water (e.g. Acorus calamus, Carex rostrata, Phrag-mites australis, Scirpus lacustris, Typha latifolia).
DOI: http://dx.doi.org/10.1065/jss2003.03.70
Abstract
Background. Constructed wetlands (wetland treatment systems)are wetlands designed to improve water quality. They use thesame processes that occur in natural wetlands but have the flex-ibility of being constructed. As in natural wetlands vegetation,soil and hydrology are the major components. Different soiltypes and plant species are used in constructed wetlands. Re-garding hydrology surface flow and subsurface flow constructedwetlands are the main types. Subsurface flow constructedwetlands are further subdivided into horizontal or vertical flow.Many constructed wetlands deal with domestic wastewaterwhere BOD and COD (Biochemical and Chemical Oxygen De-mand respectively) are used as a sum parameter for organic mat-ter. However, also special organic compounds can be removed.Objective. The objectives are to summarise the state-of-the-arton constructed wetlands for treatment of specific organic com-pounds, to the present the lack of knowledge, and to derivefuture research needs.Methods. Case studies in combination with a literature revieware used to summarise the available knowledge on removal proc-esses for specific organic compounds.Results and Discussion. Case studies are presented for the treat-ment of wastewaters contaminated with aromatic organic com-pounds, and sulphonated anthraquinones, olive mill wastewater,landfill leachate, and groundwater contaminated with hydro-carbons, cyanides, chlorinated volatile organics, and explosives.In general the removal efficiency for organic contaminants ishigh in all presented studies.Conclusion. Constructed wetlands are an effective and low costway to treat water polluted with organic compounds. There is alack of knowledge on the detailed removal pathways for most ofthe contaminants. Removal rates as well as optimal plant speciesare substance-specific, and also typically not available. If a con-structed wetland provides different environmental conditions anduses different plant species the treatment efficiency can be improved.Recommendations and Outlook. There is a great need to lightenthe black box 'constructed wetland' to obtain performance datafor both microbial activity and the contribution of the plants tothe overall removal process. Also genetic modified plants shouldbe considered to enhance the treatment performance of con-structed wetlands for specific compounds.
Keywords: Constructed wetlands; groundwater; organic con-taminants; wastewater; water treatment
Constructed Wetlands Review Articles
110 JSS J Soils & Sediments 33333 (2) 2003
2. Floating-leaved macrophytes are rooted in submersedsediments in water depths of approximately 0.5 to 3 mand posses either floating or slightly aerial leaves (e.g.Nymphaea odorata, Nuphar lutea).
3. Submerged macrophytes occur at all depths within thephotic zone. Vascular angiosperms (e.g. Myriophyllumspicatum, Ceratophyllum demersum) can occur in wa-ter up to 10 m deep (1 atm hydrostatic pressure) but nonvascular macro-algae can occur to the lower limit of thephotic zone (up to 200 m, e.g. Rhodophyceaered algae).
4. Freely floating macrophytes are not rooted to the substra-tum; they float freely on or in the water column and areusually restricted to nonturbulent, protected areas (e.g.Lemna minor, Spirodela polyrhiza, Eichhornia crassipes).
1 Wetlands for Water Treatment (Constructed wetlands,Wetland treatment systems)
Natural wetlands have been used for wastewater treatmentfor centuries. In many cases, however, the reasoning behindthis use was disposal, rather than treatment and the wetlandsimply served as a convenient recipient that was closer thanthe nearest river or other waterway (Reddy and Smith 1987).
Naturals wetlands are still used for wastewater treatment (e.g.Kadlec and Tiltion 1979), but since 10 to 20 years the use ofconstructed wetlands has become more popular and effectivearound the world (e.g. Reddy and Smith 1987; Kadlec andKnight 1996; Cooper et al. 1996). Constructed wetland treat-ment systems are engineered systems designed and constructedto utilize the natural processes involving wetland vegetation,soils, and their associated microbial assemblages to assist intreating wastewater. They are designed to take advantage ofmany of the same processes that occur in natural wetlands,but do so within a more controlled environment.
Constructed wetlands for wastewater treatment may be clas-sified according to Brix (1994) to the life form of the domi-nating macrophytes into1. Free-floating macrophyte-based systems,2. Submerged macrophyte-based systems, and3. Rooted emergent macrophyte-based systems.
and according to the water flow different rooted emergentsystems are distinguished into surface flow systems, horizontal subsurface flow systems, and vertical subsurface flow systems.
Surface flow wetlands (SF) are densely vegetated by a varietyof plant species and typically have water depths less than 0.4 m.Open water areas can be incorporated into a design to pro-vide for the optimisation of hydraulics and for wildlife habitatenhancement. Typical hydraulic loading rates are between 0.7and 5.0 cm.d1 (between 2 and 14 ha.1000 m3.d1) in con-structed surface flow treatment wetlands.
The subsurface flow wetland (SSF) technology is based onthe work of Seidel (1967). Since then the technology hasgrown in many European countries and is nowadays world-wide applied. Subsurface flow wetlands use a bed of soil orgravel as a substrate for the growth of rooted emergent wetland
plants. Mechanically pre-treated wastewater flows by gravity,horizontally or vertically, through the bed substrate, where itcontacts a mixture of facultative microbes living in associa-tion with the substrate and plant roots. The bed depth in SSFwetlands is typically between 0.6 and 1.0 m, and the bottomof the bed is sloped to minimize overland water flow.
1.1 Elimination principles
1.1.1 General
The elimination principles are similar for all systems. Rawor pre-treated waste water flows through the constructedwetland. The elimination processes take place during thispassage; they are based on various complex physical, chemi-cal and biological processes within the association ofsubstrate, macrophytes and microorganisms
