Sustainable Water Resources Management using Floating Treatment Wetland
by Mohd Hafiyyan bin Mahmud & Dr. Lee Khai Ern
Water is absolutely essential for the survival of every living thing on Earth including plants, animals and humans. Water is used for various activities throughout human daily life from domestic to industrial purposes. However, there are several causes of the deterioration of water quality. Natural phenomenon such as flood and soil erosion, as well as anthropogenic sources such as agriculture and industry wastes, are the main causes of water pollution. There is a high demand for clean water to satisfy the needs of rapid development and increasing human population. Therefore, water resources need to be well conserved and managed to ensure sustainable development.
The Malaysian effluent limitation standard of Environmental Quality (Industrial Effluent) Regulation 2009 specifies that any type of industrial wastewater needs to be treated before being discharged into the environment to prevent pollution of water resources. Extensive research has been conducted in treating water and wastewater to ensure water resources are clean and safe. Polluted waters can be treated with different processes depending on the nature of the water. Physical treatment can be used to separate suspended particles that are visible to naked eyes, through filtration, gravitational settling, sedimentation and floatation. Physico-chemical and chemical treatments separate colloidal and dissolved solids through coagulation-flocculationa, adsorption, oxidation, etc. These processes are widely used worldwide because of their effectiveness and cheap maintenance cost. However, treating wastewater on-site from a conventional waterway system would lead to major geomorphological and hydrological changes due to the construction of treatment plant. A large area of land may be needed to treat wastewater on-site before releasing it to the environment. Space constraints also apply in building water treatment systems in congested areas such as urban or industrial sites. Furthermore, chemicals used in these treatment processes could create secondary pollution which may harm human and environmental health.
a Coagulation is a process of overcoming the inter-particle repulsive energy barrier by simply increasing its ionic strength. Flocculation is a process involves the addition of floc-forming chemical reagent usually after coagulation to agglomerate non-settable and slow-settling colloidal solid .
Natural biological treatment system, which utilises plants and algae to remove pollutants from water, is an alternative without secondary pollution. A retrofitted Floating Treatment Wetland (FTW) has the potential to be a sustainable solution to manage water resources effectively in space constrained areas. FTWs are man-made wetlands created using floating rafts which allow plants to grow on top of it hydroponically (Figure 1). Numerous plant species can be used in FTW to remove pollutants from water, namely sharp dock (Polygonum amphibium L.), duck weed (Lemna minor L.), water hyacinth (Eichhornia crassipes), water lettuce (P. stratiotes), water dropwort [Oenathe javanica (BL) DC], calamus (Lepironia articulate), pennywort (Hydrocotyle umbellate L.) [1-2]. FTW is easy to use, sustainable and economically feasible. Besides providing flexibility in design, the raft floats on any surface water such as on existing wet pond, natural or concrete stream, lake or wetland. FTW is able to withstand water depth fluctuation or deep water bodies as it is anchored to the bottom or tethered to the shoreline, preventing from damage or loss during the treatment process.
Figure 1 shows the FTW floating on the water body whereby it is able to uptake and remove almost all pollutants from water through biosorptionb process [3-5]. The fate of pollutants is illustrated in Figure 2. Nutrients, heavy metals and suspended solids can be captured by the plant roots and stored as biomass in plant tissues. The plant roots below the floating raft serves many purposes. First, it provides a large surface area for the assimilation of nutrients for the microbial biofilm from the water body which breaks down pollutants such as organic matter, nitrogen and reduces biological oxygen demand. The plant roots help shelter algae settling and solids that are settling below the raft from water turbulence. Additionally, they filter the sediment by entrapping fine suspended solid and enhancing the settling time for the suspended solids and phosphorus. The plant biomass production can be controlled through mechanical harvesting and converting into biochar that can be used for carbon sequestration. FTW also mimics natural wetlands by providing habitats for fishes, and nesting and protection for reptiles, amphibians and aquatic birds. Additionally, the FTW could be effectively marketed for tourism industries whereby it enhances aesthetic value by creating a healthy ecosystem for animal to live in.
b Biosorption for metal is a passive process of metal uptake and sequestering is understood whereby the metal is sequestered by chemical site naturally present and functional even when the biomass is dead .
The Institute for Environment and Development (LESTARI) at the Universiti Kebangsaan Malaysia (UKM) is currently developing FTW as a sustainable management solution for integrated stormwater management. FTW represents a relatively low cost and sustainable engineering technique to reduce pollution of nutrients loading, metals-contained stormwater and surface runoff. The tolerance of deep and fluctuating water levels enables this new ecologically engineered treatment system to be feasible in any surface water, including ponds, lakes, dams, reservoirs, estuaries and slow-flowing waters. As such, FTW has a huge potential to be widely applied in sustainable water resources management.
About the Author
Mohd Hafiyyan bin Mahmud is a Ph.D. candidate and a Research Assistant at the Institute for Environment and Development (LESTARI), Universiti Kebangsaan Malaysia.
Dr. Lee Khai Ern is a Senior Lecturer and a Research Fellow at the Institute for Environment and Development (LESTARI), Universiti Kebangsaan Malaysia. He is also the project leader for the Floating Treatment Wetland project (TD-2014-015).
Find out more about
- Dr. Lee Khai Ern at http://www.scientificmalaysian.com/members/khaiernlee/
- Mohd Hafiyyan Mahmud at http://www.scientificmalaysian.com/members/rageqint/
This article first appeared in the Scientific Malaysian Magazine Issue 11. Check out other articles in Issue 11 by downloading the PDF version for free here: Scientific Malaysian Magazine Issue 11 (PDF version)
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