Presentation on theme: "By: Audella Eid Advisor: Dr. R. Zurayk Constructed Wetlands for Wastewater treatment."— Presentation transcript:
By: Audella Eid Advisor: Dr. R. Zurayk Constructed Wetlands for Wastewater treatment
What are constructed wetlands ? CW are complex, integrated systems in which water, plants, microorganisms, and the environment all interact to improve water quality. CW have been used in Europe since the 1960’s.
Municipal wastewater treatment Acid mine drainage Agricultural point and non-point discharges Storm water treatment Usage of CW
Important Characteristics of CW Inexpensive Low-maintenance Easy operation High removal efficiencies under various temp, pH, hydraulic and biological loading rates.
Are earthen basins or channels filled with shallow water and emergent vegetation. Wastewater is exposed to the atmosphere. Recommended for lower strength wastewater, stormwater treatment or where nitrogen removal is required. Free-water surface (FWS)
Subsurface Flow wetland (SF) Is composed of a cement cell filled with a porous media such as rock or gravel. Wastewater percolated through a porous medium that supports the root system of the vegetation. Water flows below the porous surface and is not exposed to the environment.
Recommended for residential homes, schools and other areas where the exposed wastewater treatment site may not be suitable. Decrease chance of exposure, odor and insect vectors. SF ( cont’d)
Treatment of wastewater CW treat wastewater using the following processes: Filtration Sedimentation Physical or chemical immobilization Chemical and biological decomposition Absorption and assimilation of excess nutrient by plants
In each of the two systems march plants aid in: the treatment of water by improving conditions for the microorganisms living in the cells. and by acting as a filter to absorb some trace metals.
How do they operate? Plants and microorganisms play a key function in the cleaning of the wastewater. Plant roots transpire oxygen and thus aerate the water.
Large populations of aerobic and anaerobic bacteria grow within the rhizosphere (which is the small area surrounding the root zone). These microbes are the primary source of treatment, breaking down the complex dissolved organic and nutrient pollutants into simpler forms that the plants use as food. How do they operate?(cont’d 1 )
Aerobic conditions in the root zones of the plants also facilitates growth of large microorganisms (protozoa) that are essential to the removal of bacteria, such as fecal coliforms. The most common plant used for subsurface flow is the common reed (Phragmites australis). How do they operate?(cont’d 2 )
The Gharzouz Reed Bed The choice of using a constructed wetland for wastewater treatment was based on: m environmental feasibility m social acceptance m economic feasibility m previous removal efficiencies
Environmental feasibility The place is relatively isolated with a lot of land around it and a large area for the wetland construction. The possibility of using the effluent in irrigating of the olive and other trees that is present in the area.
Social acceptance The community is a relatively very small ranging from 15 to 50 people at different times. They accepted the implication of this technique
Economic feasibility The budget available for wastewater treatment is not very high. The difference in costs between construction of a wetland and using a mechanical method.
Previous removal efficiency Previous studies that showed high reduction rates of BOD, SS and nitrates. The previous pilot tests that were done on this system (in AUB and other places in Lebanon) and proved to be efficient in reducing BOD and other measures.
Characteristics of the gravel bed t= V*Porosity of the gravel bed (assumed to be 35%)/Q & BOD loading rate =Co(avg)*Q /A
Methodology 15 samples of wastewater were collected from June 1999 till March 2000. Analysis was carried out using standard method for COD, BOD, TSS, TDS, Nitrates, Ammonia, Phosphates, Sulfates, conductivity, pH, Fecal coliforms, Total Coliforms
Limitations Large land area requirements. Lack of a consensus on design specifications. Long term effectiveness is not known. Wetland aging may contribute to a decrease in contaminant removal rates over time.
When metals are key contaminant, CW do not destroy them; but only restrict their mobility. Performance may be more variable and less predictable than other treatment methods. Limitations (Cont’d)