Malaysia is a fast developing country that its change from an agro-based to an industrial nation, has led to an increase in the population. Malaysias population increased rapidly from 6 278 800 in 1957 to an estimated 29,179,952 in July 2012. Thus, the amount of solid wastes generated in Malaysia also increases rapidly. Statistic shows that on average, each Malaysian produces 0.8 kg to 1.2 kg of wastes per day (The Star, 2009). About 23,000 tonnes of wastes are produced each day in Malaysia. However, this amount is expected to rise to 30,000 tonnes by the year 2020 (Global Environmental Centre, 2008). The amount of wastes generated continues to increase due to the increasing population and development.
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Problem Statement
There are different alternatives to reduce, treat and dispose the solid wastes. However, landfill is still the most common practice for solid waste management. Sanitary landfill for solid waste management is defined as an engineered method of disposing of solid wastes on land by spreading them in thin layers, compacting them to the smallest practical volume, and covering them with soil each working day in a manner that protects the environment (Brunner and Keller, 1972).
There are 230 official dumping sites in Malaysia, the majority of which are crude landfills, with only 10% providing leachate treatment ponds and gas ventilation systems and with most having no control mechanism and supervision. However, the landfill method causes generation of leachate (Galbrand, 2003). Leachate is defined as a liquid that has percolated through solid waste and has extracted dissolved or suspended materials (EEA, 2005). Leachate occurrence is by far the most significant threat to ground water. Once it reaches the bottom of the landfill or an impermeable layer within the landfill, leachate either travels laterally to a point where it discharges to the ground’s surface as a seep, or it will move through the base of the landfill and into the subsurface formations (El-Fadel et al., 1997). Depending upon the nature of these formations and in the absence of a leachate collection system, leachate has reportedly been associated with the contamination of aquifers underlying landfills which resulted in extensive investigations for the past four decades (Albaiges et al., 1986; Mann and Schmadeke, 1986). Leachate contains high concentration of organic matter, inorganic matter (sodium chloride and carbonate salt) and heavy metal (Trebouet et al., 2001). Organic matter in leachate results in decomposition by microorganisms and causes oxygen depletion in surface water bodies (Schwartz, 2005). This favours anaerobic conditions which are detrimental to the aquatic life. The anaerobic micro flora is responsible for putrefactive processes which are characterized by the production of different types of toxic and noxious compounds (ammonia, hydrogen sulfide and phosphine) as final products of the organic matter degradation. Oxygen deficiency and toxic substance from anaerobic metabolism cause fish death and impairment of aquatic life. Therefore, since leachate can affect aquatic ecosystems and human health, proper leachate treatment is needed before leachate is discharged into receiving water (Paredes, 2003).
Nutrients such as nitrate, ammonia and phosphate (along with co-contaminants such as pathogens, chemicals, and animal pharmaceuticals) are also found in leachate. High levels of nitrate, phosphate and ammonia in our lakes, rivers, streams, and drinking water sources cause the degradation of these water bodies and harm fish, wildlife, and human health. For example, at levels above 10 mg/L maximum contaminant level (MCL) in ground water, nitrates can cause human health effects, such as blue baby syndrome to pregnant woman.
The current conventional leachate treatment systems are physical-chemical treatment, recirculation of leachate through landfill and biological treatment (El-Gendy, 2003). Physical-chemical treatment includes chemical precipitation, chemical oxidation, ion exchange and reverse osmosis, activated carbon adsorption and ammonia stripping (Ehrig, 1989). Precipitation in physical-chemical treatment is based on the addition of any chemicals to remove suspended solids, nitrogen, phosphorus, ammonia and metal. The physical-chemical treatment processes can produce high quality effluents, adapt to wide variations in flow and chemical composition and have the ability to remove toxic substances from leachate (Shams-Khorzani et al., 1994). However, these treatment systems are difficult to operate and require highly skilled labor besides high capital and operating costs. Some of these processes even require extensive pretreatment process (Britz, 1995). As a conclusion, the conventional treatment systems are effective in treating leachate. However, they require highly skilled labour and involve both high capital and operating cost. Therefore, constructed wetland was developed as an alternative to treat leachate in this research since constructed wetland has low cost of construction and maintenance (El-Gendy, 2003). The type of wetland used in this study is a combined system of subsurface flow (SS) and free water surface (FWS) constructed wetland.
1.3 Objectives
The main objectives of this study are;
To determine the nutrients (phosphate, nitrate and ammonia) removal from landfill leachate using combined subsurface and free water surface flow in constructed wetland between planted and control (without plant) system.
To determine the nutrients removal in different hydraulic loading rate (HLR).
To compare the percentage removal between subsurface (SS) and free water surface (FWS) in both planted and control system.
To determine the uptake of nutrients by plants, Limnocharis flava in the subsurface (SS) and Eichhornia crassipes in free water surface (FWS).
1.4 Scope of Study
The scope of this study is leachate treatment by setting up of lab-scaled wetland. The leachate was collected from landfill in Padang Siding and initial concentration of phosphate, nitrate and ammonia were analysed. Then, experiments were conducted with 25% leachate concentration diluted with water in a 60 L container being treated in two different planted and control reactors. Initially, Limnocharis flava plants were planted in the subsurface (SS) tank and Eichhornia crassipes was placed in the free water surface (FWS) tank in planted reactor and left for a few days for acclimatization process while no plant was placed in control reactor. The experiments were conducted with two different hydraulic loading rates which were high hydraulic loading rate (0.55 m/d) and low hydraulic loading rate (0.39 m/d). The efficiency of nutrients removal in leachate was evaluated by few parameters which were phosphate, nitrate and ammonia. The uptake of nutrients by plants in leaf, stem and root was also analysed as well as monitoring the physical plant growth in terms of physical appearance throughout the experiments.
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1.5 Importance of Study
The research was conducted to evaluate the efficiency of nutrient removal from landfill leachate in a combined system of subsurface and free water surface constructed wetland as well as to determine the nutrient uptake by plants. This nutrients removal was done by phytoremediation process by plants. Phytoremediation is the use of plants to clean up or control many kinds of pollutants including metals, pesticides and oil (McCutcheon, 2008). Phytoremediation is a potential method to treat leachate naturally in low cost. It is an environmentally friendly approach to remove pollutants from leachate. Therefore, phytoremediation can be practically used in landfill sites as constructed wetland to remove nutrients from landfill leachate. The plants used in constructed wetland can be Limnocharis flava in the subsurface and Eichhornia crassipes in free water surface.
This research was also conducted to determine the most efficient loading rate for the leachate flow in constructed wetland in removing nutrients effectively. The loading rate plays an important role since the leachate flow also determines the uptake of nutrients by the plants. This research was also conducted to determine the ability of plants, Limnocharis flava and Eichhornia crassipes to uptake nutrients from the leachate.
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