The Metro Colombo Solid Waste Management (MCSWM) project consists of four components; the loading station in Kelaniya, the unloading station, construction of the sanitary landfill in Aruwakkalu, and improvements in rail transportation with necessary equipment and machines.
The unloading station and the landfill site will be located 170km away, in Aruwakkalu in the Puttalam District in the North Western Province. Nearly 1,200 MT/day of Municipal Solid Waste(MSW) will be transferred to 20feet-sealed containers with necessary compaction and will be transported to Aruwakkalu by two specially-made trains, using the existing railway lines from Kelaniya to Aruwakkalu via Puttalam. The waste containers will be unloaded in Aruwakkalu unloading station and transferred to the sanitary landfill site.
All environmental precautions and necessary wastewater treatment systems will be set up both in Kelaniya Transfer Station, and Aruwakkalu Transfer Station and Sanitary Landfill Site to ensure that leachate and wastewater will be treated to the standards being enforced by the respective environmental authorities.
ABOUT THE PROJECT
Kelaniya Transfer Station
The proposed transfer station is to be set up in a plot of land belongs to the Sri Lanka Land Reclamation and Development Corporation (SLLRDC) located in Kelaniya, bordered by the Colombo railway mainline and the exit road of the Colombo-Kandy highway. It is adjoined to the current dumping site operated by the Kelaniya Pradeshiya Sabha.
Following activities and related constructions will be carried out at Kelaniya site:
* Access roads for the arrival of RCV (Refuse Collecting Vehicles)
* Receiving and tipping of MSW on to a platform
* Compaction and loading into sealed containers
* Loading the sealed containers to low-bed rail carriages using transfer crane
* Connectivity to the main rail transportation system
* Control system for the operation and monitoring of the station
* Miscellaneous facilities such as workers and wastewater treatment system
Rail transportation
The existing railway infrastructure will be used for the transport of waste from Kelaniya to Aruwakkalu and total length is approximately 170km.
Sanitary landfill site
The proposed Aruwakkalu Landfill Site includes an unloading station and a sanitary landfill. Under the MCSWM project, the government envisages implementing a sanitary landfill using the abandoned and worked-out limestone quarry pits in Aruwakkalu, Puttalam to dispose about 1200 MT/day of MSW for which the approval of the Cabinet of Ministers has been already granted and necessary financial support guaranteed.
Accordingly, a site for Aruwakkalu Transfer Station and Aruwakkalu Landfill was identified adjacent to the railhead of lime quarrying facility operated by the INSEE Cement of Siam City Cement (Lanka) Ltd. The area under the landfill will be about 46ha and the land is primarily the areas mined for lime extractions. Some of the mine areas are deep pits partially filled with overburden soil which are now grown with forest plantations.
Intended activities to be performed at Aruwakkalu Transfer Station (ATS):
* Receiving MSW-compacted and loaded containers by trains using cranes;
* Transferring of the MSW-loaded containers to special tipping trailers;
* Emptying of the waste containers on trailers at the sanitary landfill;
* Washing of containers and a wastewater treatment system;
* Re-load the empty containers to the train using cranes; and
* Ancillary facilities needed for operation and maintenance of the site.
SANITARY LANDFILL TECHNOLOGY
Sanitary landfillis a method of controlled disposal of municipal solid waste (refuse) on land. The method was introduced in England in 1912 (where it is called controlled tipping). Waste is deposited in thin layers (up to 1 metre or 3 feet) and promptly compacted by heavy machinery (e.g., bulldozers); several layers are placed and compacted on top of each other to form a refuse cell (up to 3 metres, or 10 feet, thick). At the end of each day, the compacted refuse cell is covered with a layer of compacted soil to prevent odours and windblown debris.
All modern landfill sites are carefully selected and prepared (e.g., sealed with impermeable synthetic bottom liners) to prevent pollution of groundwater or other environmental problems. When the landfill is completed, it is capped with a layer of clay or a synthetic liner in order to prevent water from entering. A final topsoil cover is placed, compacted, and graded, and various forms of vegetation may be planted in order to reclaim otherwise useless land (e.g., to fill declivities to levels convenient for building parks, golf courses, or other suitable public projects).
Landfills are often the most cost-efficient way to dispose of waste. While resource recovery and incineration both require extensive investments in infrastructure, material recovery also requires extensive manpower to maintain, landfills have fewer fixed or ongoing costs, allowing them to compete favourably. In addition, landfill gas, primarily of methane, a leading contributor to global warming, can be flared or upgraded to natural gas. Another advantage is having a specific location for disposal that can be monitored, where waste can be processed to remove all recyclable materials before tipping.
Components of a typical landfill
1. Bottom and sidewall liners
2. Leachate collecting pipes
3. Leachate treatment plant
4. Stormwater drainage facilities
5. Gas collecting pipes
6. Tyre washing bay
7. Weighbridge
8. Protective fence
9. Groundwater monitoring well
Bottom and sidewall liners
A landfill liner or composite liner is intended to be a low-permeable barrier which is laid down under engineered landfill sites. Until it deteriorates, the liner retards the migration of leachate and its toxic constituents into underlying aquifers or nearby rivers causing spoliation of the local water.
Modern landfills generally require a combination of different types of synthetic liners sandwiched into a layer of compacted clay with a minimum required thickness and a maximum allowable hydraulic conductivity, overlaid by a high-density polyethylene (HDPE) geomembrane.
Content of the bottom liner
Modern landfills generally require a combination of different types of synthetic liners sandwiched into a layer of compacted clay with a minimum required thickness and a maximum allowable hydraulic conductivity, overlaid by a high-density polyethene (The bottom of the landfill is formed by applying several layers in sequential order starting from the existing compacted soil surface, as follows,
* Groundwater collecting pipes
* 30cm aggregate (metal) layer
* Geotextile liner (1000g/m3)
* 30cm thick Bentonite clay layer
* 1.5mm thick HDPE (High-Density Poly Ethylene) layer
* Geotextile liner (1000g/ m3)
* Leachate collecting Pipes
* 30 cm aggregate (metal) layerHDPE) geomembrane.
Leachate collecting pipes
A network of leachate (black colour liquid wastewater that is formed by the decaying of waste) collecting perforated pipes will be laid down towards the bottom of the landfill to collect the leachate passing through the masses of waste. The collected leachate will then be piped out of the landfill for treatment at a wastewater treatment facility.
Leachate treatment plant
There are many components in a leachate collection system including pumps, manholes, discharge lines and liquid level monitors. However, there are four main components which govern the overall efficiency of the system. These four elements are liners, filters, pumps and sumps.
Sequencing batch reactors or sequential batch reactors (SBR) are a type of activated sludge process for the treatment of wastewater. SBR reactors treat wastewater such as sewage or output from anaerobic digesters or mechanical biological treatment facilities in batches. Oxygen is bubbled through the mixture of wastewater and activated sludge reduces the organic matter (measured as biochemical oxygen demand (BOD) and chemical oxygen demand (COD)). The treated effluent may be suitable for the discharge to surface waters or possibly for use on land. Wastewater will be treated to meet the treated effluent wastewater standards stipulated under the National Environmental Act (Gazetted Extra Ordinary 1534/18 dated February 1, 2008) for inland waters, then it is suitable for discharge to inland water bodies.
One additional method of leachate management more common in uncontained sites is leachate re-circulation, in which leachate is collected and re-injected into the waste masses. This process greatly accelerates decomposition thereby increasing the gas production. This will have an impact of converting some leachate volume into landfill gas and reducing the overall volume of leachate for disposal. However, it tends to substantially increase the concentration of contaminated materials which might make it more difficult to treat as waste.
Stormwater drain system
A stormwater drain is designed to drain excess rainwater from roofs, buildings, and other open areas of the sanitary landfill site. The stormwater drain is essential in a landfill to avoid mixing of freely flowing drain water with the leachate generating in the working cells of a landfill thereby the reducing the quantity of wastewater destined for treatment.
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