WETLANDS, CONTRUCTED WETLANDS AND THEIR'S wetlands, ... Wetlands, Contructed Wetlands and ... Proceedings of 7th International Conference on Wetland Systems for Water Pollution Control,
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FACTA UNIVERSITATIS Series: Architecture and Civil Engineering Vol. 7, No 1, 2009, pp. 65 - 82 DOI: 10.2298/FUACE0901065N
WETLANDS, CONTRUCTED WETLANDS AND THEIR'S ROLE IN WASTEWATER TREATMENT WITH PRINCIPLES AND
EXAMPLES OF USING IT IN SERBIA
Vladimir Nikoli1, Dragan Milievi2, Slobodan Milenkovi2
1Erasmus Mundus Stipendist, Euroaquae E-mail: firstname.lastname@example.org 2University of Nis, The Faculty of Civil Engineering and Architecture, Serbia
Abstract. Wetlands protection programs, as a relative new approach in surface water and ground-water protection The types of Wetlands, their's mechanism of removal nutrients and other pollutants from water are shown in this work paper. Wetland restoration, the renewal of natural and historical wetlands that have been lost or degraded, is a growing activity. Constructed wetlands, as treatment systems that use natural processes, are very adequate and highly efficient, low cost way in wastewater treatment for small communities, point pollution sources, depending, of course on conditions and adequate land spaces near those places. Some examples from Serbia of this way and approach are shown.
Key words: Waste water treatment, Wetlands, Constructed wetlands, Macrobiological methods.
Long regarded as Wastelands, Wetlands are now recognized as important features in the Landscape that provide numerous beneficial services for people and for fish and wildlife. Wetlands are among the most productive ecosystems in the world, comparable to rain forests and coral reefs. They provide great volumes of food that attract many animal species.
2. WHAT ARE WETLANDS?
Even though there are many different terms for description of the wetland systems, the most widely accepted definition was developed by the International Union for the Con-servation of Nature and Natural Resources (IUCN) in the Ramsar Convention, in 1980. According to this convention, wetlands were defined as "any areas of swamp, pond, peat, or water, natural or artificial, permanent or temporary, stagnant or flowing water, includ-
Received September 15, 2009
V. NIKOLI, D. MILIEVI, S. MILENKOVI 66
ing estuaries and marine water, the depth of which at low tide does not exceed 6 meters." (Mitsch and Gosselink, 1993).
Wetlands, other than peat bogs, are highly productive systems and support high biodi-versity. Like other ecosystems, wetlands also perform many ecological functions. The hy-drological, biological and biogeochemical functions impart them various values (Sather and Smith, 1984). Some of the values of these wetlands given by Vymazal et. al (1998) and Denny (1997) are summarized below: water quality functions and water quality im-provements, hydrological and hydraulic functions, climatic effects, biodiversity functions, energy production, educational uses, recreational and reclamation uses.
All Wetlands freshwater or salt have one characteristic in common: the presence of surface or near surface water, at least periodically. The hydrology of Wetlands is generally one of slow flows and either shallow or saturated substrates. The slow flows and shallow water depths allow sediments to settle as the water passes through the Wetland. The slow flow also provides prolonged contact time between the water and the surface within the Wetland. The complex mass of organic and inorganic materials and the diverse opportunities for gas/water interchanges foster a diverse community of microorganisms that break down or transform a wide variety of substances.
Wetlands perform many functions that are beneficial to both humans and wildlife. One of the most important is water filtration. As water flows through a Wetland, it slows down and many of the suspended solids become trapped by vegetation and settled out. Other pollutants are transformed to less soluble forms taken up by plants or become inactive. Wetland plants also foster the necessary conditions for microorganisms to live there. Through a series of complex processes, these microorganisms also transform and remove pollutants from the water. Nutrients, such as nitrogen and phosphorus, are deposited into wetlands from storm water runoff, from areas where fertilizers or manure have been ap-plied and from leaking septic fields. These excess nutrients are often absorbed by Wet-land soils and taken up by the plants and microorganisms. For example, Wetland mi-crobes can convert organic nitrogen into useable, inorganic forms (NO3 and NH4) that are necessary for plant growth and into the gasses that escape to the atmosphere.
Wetland processes: water retains more days sedimentation its cleaned by plants and microorganisms
reduction of nitrogen, phosphorus substances, heavy metals and other toxic compounds and bacteria
plants under the surface of device provide oxygen
an area rich with oxygen is created around the roots
cleaning is effective
Fig. 1 How wetlands work
Wetlands, Contructed Wetlands and their's Role in Wastewater Treatment... 67
Wetlands are one of the most valuable and fragile components of a watershed, but for many years they were filled and drained for agriculture and development. Now we are learning that wetlands are crucial to the health of our waters and wildlife. Wetland resto-ration, the renewal of natural and historical wetlands that have been lost or degraded, is a growing activity. It can improve water quality and wildlife habitat across the world. When high concentration of nutrients enter water as a result of human activities, often occurs Hypoxia. Hypoxia is the condition in which dissolved oxygen is below the level necessary to sustain most animal life. For many members of aquatic community, hypoxia is like drowning, because life giving dissolved oxygen levels in a body of water drop much lower than normal.
There is growing interest and expertise in the field of Wetland restoration. This trend is a good news for hypoxia affected waters since some Wetlands can significantly reduce the amount of nutrients reaching our inland and coastal waters. Restoring the lost and de-graded Wetlands to their natural state is essential to ensure the health of watersheds. Restoration is a complex process that requires expertise, resources, and commitment from many different stakeholders. All restoration projects require planning, implementation, monitoring and management. Many projects require a team with expertise in ecology, hy-drology, engineering, and environmental planning. Getting local experts and community involved gives the project local ownership, which is important for restoration success.
Nutrient removals from several specific natural wetlands projects are presented in Table 1.
Table 1. Nutrient removals from several specific natural wetlands projects
4. CONSTRUCTED WETLANDS FOR WASTEWATER TREATMENT
As a result of the exponentially increasing demands of human expansion and resource exploitation, it has been recognized that natural wetland ecosystems cannot always func-tion efficiently for desired objectives and stringent water quality standards. These and many other factors have led to the rapid development of "constructed wetlands" for wastewater treatment (Wetzel, 1993).
Because natural systems can improve water quality and filter pollutants from water that flows through on its way to receiving lakes, streams and oceans, engineers and scien-
V. NIKOLI, D. MILIEVI, S. MILENKOVI 68
tists construct system that replicate the functions of natural wetlands. So, Constructed wetland treatment systems are engineered systems that have been designed and con-structed to utilize the natural processes involving wetland vegetation, soils, and their as-sociated 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. Synonymous terms to constructed include manmade, engi-neered or artificial wetlands.
What Constructed Wetlands can provide: water quality improvement flood storage and the desynchronization of storm rainfall and surface runoff cycling of nutrients and other materials habitat for fish and wildlife passive recreation, such as bird watching and photography active recreation, such as hunting education and research aesthetics and landscape enhancement
When properly designed, constructed wetlands offer a number of advantages, includ-ing low cost, simplicity of operation, and effective removal of BOD5 and TSS (table 2). When sized adequately, constructed wetlands are also tolerant of fluctuating flows and variable water quality.
Constructed wetland treatment is constrained by a number of limitations, including relatively large land requirements and a degree of uncertainty not found in more conven-tional approaches (table. 2).
Table 2. Advantages and limitations of constructed wetland treatment of domestic wastewater
Excellent removal of BOD5 and TSS Good removal of nutrients, depending on system design Ability to handle daily or seasonally variable loads Low energy and maintenance requirements Simplicity of operation
Variable treatment efficiencies due to the effects of season and weather Uncertainty as to treatment effectiveness under all conditions Sensitivity to high ammonia levels Larger land area requirement than for conventional treatment Potential for mosquito production
The use of constructed wetlands for sewage treatment at different levels is commonly well known. However, they have also been applied for the treatment purpose of different types of wastewater. Some of these applications include treatment of wastewater origi-nating from several industries, agricultural activities, landfills, surface runoff, acid mine drainage, sludge dewatering, etc. In order to understand the current trend for constructed wetlands, the current literature has been reviewed and classified according to the type of treated wastewater (Table 3).
Wetlands, Contructed Wetlands and their's Role in Wastewater Treatment... 69
Table 3. Distribution and percentage of the studies on constructed wetlands used for several purposes (1994-2000)
Type of Treated Wastewater in Constructed Wetlands Number of Studies
Municipal 106 31.5 Leachate 12 3.6 Acid Mine Drainage 8 2.4 Surface Runoff 24 8.1 Sludge Dewatering 5 1.5 Industrial 35 10.5 Restoration and Rehabilitation, Prevention of Eutrophication 42 12.5 Agro-Industrial 38 11.3 Reviews, Suggestions, Design Criteria 64 19.1
References: Water Science and Technology, Vol: 35(5) 1997 and Vol: 40(3) 1999; Proceedings of 7th International Conference on Wetland Systems for Water Pollution Control, Florida, 2000.
5. CLASSIFICATION OF CONSTRUCTED WETLANDS
Constructed wetlands could be classified according to the various parameters but two most important criteria are water flow regime (surface and sub-surface) and the type of macrophytic growth (Fig. 2). Different hybrid or combined systems in order to exploit the specific advantages of the different systems.
Sub-surface flowSurface flowEmergent plants
Free floating plants
Tidal Fig. 2 Basic types of Constructed Wetlands
Constructed wetlands with surface flow (= free water surface, FWS) consist of basins or channels, with soil or another suitable medium to support the rooted vegetation (if pre-sent) and water at a low flow velocity, and presence of the plant stalks and litter regulate water flow and, especially in long, narrow channels, ensure plug-flow conditions (Reed et al., 1988). One of their primary design purposes is to contact wastewater with reactive biological surfaces (Kadlec and Knight, 1996). The FWS CWs can be classified accord-ing to the type of macrophytes (Fig. 2).
V. NIKOLI, D. MILIEVI, S. MILENKOVI 70
Fig. 3 A surface flow wetland consists of a shallow basin, soil or other meddium to
support the roots of vegetation, and a water control structure that maintains a shallow depth of water.
A subsurface flow (= subsurface flow system, SFS) constructed wetland consists of a sealed basin with a porous substrate of rock or gravel. The water level is designed to re-main below the top of the substrate. Constructed wetlands with sub-surface flow may be classified according to the direction of flow into horizontal (HF or SSF-H) and vertical (VF or SSF-V) (Fig. 2).
Fig. 4 Constructed Wetlands with rooted vegetation and horizontal (left) or vertical
flow of the water (right)
Various types of constructed wetlands may be combined in order to achieve higher treatment effect, especially for nitrogen. There has been a growing demand in achieving fully-nitrified effluents but secondary treatment HF systems cannot do this because of their limited oxygen transfer capacity (Cooper et al., 1996; Vymazal et al., 1998a). VF systems have a much greater oxygen transport capacity and, therefore, provide much better condi-tions for nitrification.
Fig. 5 Schematic arrangement of the HF-VF hybrid system
according to Brix and Johansen
Hybrid systems used to comprise most frequently VF and HF systems arranged in a staged manner, however, all types of constructed wetlands could be combined. In hybrid systems, the advantages of various systems can be combined to complement each other. It is possible to produce an effluent low in BOD, which is fully-nitrified and partly denitri-fied and hence has much lower total-N concentrations (Cooper 1999, 2001).
Wetlands, Contructed Wetlands and their's Role in Wastewater Treatment... 71
6. CONSTRUCTED WETLANDS DESIGNING
Constructed wetlands are ecological systems that combine physical, chemical, and biological processes in an engineered and managed system. Successful construction and operation of an ecological system for wastewater treatment requires a basic knowledge and understanding of the components and the interrelationships that compose the system. A Constructed Wetland consists of a properly designed basin that contains water, a sub-strate, and, most commonly, vascular plants. Other important components of Wetlands, such as the communities of microbes and aquatic invertebrates, develop naturally.
Suggestions for creating an effective constructed wetland are given in table 4. Since the objective of using a constructed wetland is to simplify the handling of wastewater, the system should be made as easy to operate as possible while ensuring reliable treatment. Building a slightly larger system may be more expensive to construct but may be more reliable and less costly to operate than a smaller system. Attention to several factors will help to ensure successful wetland treatment:
Adequate pre-treatment. Pol...