Constructed wetland

Research on the topic Constructed wetland " Waste Water Treatment Plant" . Among the topics of Sanitary Engineering

1. Constructed Wetlands : A low Cost Waste Water Treatment System BAGHDAD UNIVERSITY SANITARY ENGINEERING DEPARTMENT M.Sc. student : Marwa Mohammed

2. Constructed wetlands offer several advantages over tradition water treatment systems: Wetlands are less expensive to build and operate than mechanical systems. There is no energy required to operate a wetland. Wetlands are passive systems requiring little maintenance. Normally, the only maintenance required is monitoring of the water level and rinsing the media every few years to remove solids and restore adsorption capacity. Wetlands can also provide wildlife habitat and be more aesthetically pleasing than other water treatment options. Subsurface wetlands produce no biosolids or sludge that requires disposal.

3. What are Constructed wetlands ? Constructed wetlands are small artificial wastewater treatment systems consisting of one or more shallow treatment cells, with herbaceous vegetation that flourish in saturated or flooded cells. They are usually more suitable to warmer climates. In these systems wastewater is treated by the processes of sedimentation, filtration, digestion, oxidation, reduction, adsorption and precipitation . The constructed wetlands generally consist of six chambers Each chamber consists of four cells: Within each cell are water hyacinth plants The constructed wetland removes solids, dissolved solids, nutrients, and pathogens.

4. 4. Perforated drains, drain rock, texture transition and sand filter 1. Excavation and Forming 2. Waterproofing: Base, geo-textile membrane 3. Distribution piping CONSTRUCTION & INSTALLATION

5. Types of constructed wetlands Surface flow FWS (Free Water Surface) Subsurface flow VSB (Vegetated Submerged Beds) Vertical flow

6. 1. Free water surface(FWS) wetlands, like most natural wetlands are those where the water surface is exposed to the atmosphere. Water flows over soil media . A channel (flow bed) is dug and lined with an impermeable barrier such as clay or geo- textile. The flow bed is then covered with rocks, gravel and soil. Vegetation is also planted. It is better to have plants that are native to the area. After that the wastewater is let into the flow bed by an inlet pipe. The usual depth of the wastewater is 10 to 45cm above ground level. As the water slowly flows through the wetland, simultaneous processes clean the wastewater and the cleaned water is released through the outlet pipe.

7. Surface Flow Wetlands

8. Surface Flow Wetlands

9. In this, Water flows below media. No water on soil surface but subsoil is saturated 2. Subsurface wetlands , where the water surface is below ground level. The use of subsurface constructed wetlands for water treatment began in Western Europe in the 1960’s and in the U.S. in the 1980’s.

10. Horizontal Subsurface Flow Wetlands

11. Vertical Flow Wetland

12. Q   KA dh dl The basis for the hydraulic design of the system is Darcy’s Law, W he r e, Q = Flow rate in volume per unit time. K = Hydraulic conductivity of the media. A = Cross-sectional area of the bed perpendicular to the flow. dh/dl = The hydraulic gradient.

13. Typical SubsurfaceWetland System consists of : Liner Inlet structure Bed (including media and plants) Outlet structure Slope Systems have been designed with bed slopes of as much 8 percent to achieve the hydraulic gradient. Newer systems have used a flat bottom or slight slope and have employed an adjustable outlet to achieve the hydraulic gradient . Aspect Ratio The aspect ratio (length/width) is also important. Ratios of around 4:1 are preferable. Longer beds have an inadequate hydraulic gradient and tend to result in water above the bed surface.

14. Filtration and sedimentation – Larger particles are trapped in the media or settle to the bottom of the bed as water flows through. Because these systems are normally used with a pretreatment system, such as a septic tank or detention pond, this is a small part of the treatment. The main treatment processes are, The breakdown and transformation by the microbial population clinging to the surface of the media and plant roots The adsorption of materials and ion exchange at the media and plant surfaces. The plants in the bed also provide oxygen and nutrients to promote microbial growth. The rest of the bed is assumed to be anaerobic. Wetlands treat water in the following ways

15. The Subsurface Wetlands have proved to be effective at greatly reducing concentrations of following parameters : 5-day biochemical oxygen demand (BOD 5 ) Total suspended solids (TSS) Nitrogen Phosphorus Fecal Coliforms Wetlands have also shown the ability for reductions in metals and organic pollutants.

16. Plants in FWS Wetlands (Macrophytes) In the past monocultures or a combination of two species were used Currently more diverse representative of natural ecosystem plantings occur The presence of macrophytes is one of the most conspicuous features of wetlands and their presence distinguishes constructed wetlands from unplanted soil filters or lagoons. The macrophytes growing in constructed wetlands have several properties in relation to the treatment process that make them an essential component of the design (Brix, 1997). The type of plant does not matter because primary role is providing structure for enhancing flocculation, sedimentation, and filtration of suspended solids Even though plant type does not matter much, there are some common varieties-

17. Sedges, Water Hyacinth , Common Cattail , Duckweed, Spatterdock , Waterweed

18. Advantages of Subsurface Wetland(SSW) over Free Water Surface wetland(FWS) No exposed water surface to attract mosquitoes or for people to come in contact with. Fewer odors. Due to the greater surface area in contact with the water and greater root penetration of the plants, subsurface systems can be significantly smaller. Although the media cost can be expensive, it is usually offset by the smaller land area required, resulting in a lower cost for the subsurface system. Better performance in colder climates due to the insulating effect of the upper media layer.

19.  Increase water quality  stop pollution  think for a solution  Bring out a revolution  constructed wetlands are referred as kidneys of mother land. Conclusion :