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International Journal of Environmental Research, Vol. 1, No. 2, 2007, pp. 179-187 Technical and Economical Selection of Optimum
Transfer-Transport Method in Solid Waste Management in Metropolitan Cities
Ghiasinejad, H.1* and Abduli, S.2 1Faculty of Environment, University of Tehran, Tehran, Iran Received 12 March 2006; Revised 26 Oct 2006; Accepted 15 Nov 2006 Code Number: er07023 ABSTRACT Transfer-transport of the waste is one of key functional elements in solid waste management from technical and financial viewpoint. Unfortunately very few reach activities has been conducted in this field regarding local characteristic of phenomenon which urges undertaking local surveys and research projects. Tehran Organization of Waste Recycling and Composting has decided to investigate different transfer-transport options for new Tehran landfill in Houshang Site which is located in far distance from Current landfill in Kahrizak. The study surveyed 3 main options comprising of 8 alternatives. This alternatives covered so many aspects of transfer-transport like road or rail transport, compaction of waste, size of containers and system of loading/unloading, The surveyed showed that the two alternative of heavy compaction in 65m3 semi-trailers will be the most economical system that enjoys so many environmental-ecological advantages over current practice. Key words: Solid waste, Transport, Transfer, Management, Optimization, Tehran
INTRODUCTION Transport and transfer of solid waste is a critical part of any solid waste management program. The management of solid waste transfer and transport is most difficult and complex in an urban environment. It is partly due to generation of residential & commercial-industrial solid waste and recyclables takes place in every home, every apartment building and every commercial and industrial facility; as well as in the streets and parks as the patterns of waste generation become more diffuse and the total quantity of waste increase, the logistics of collection and transfer become more complex. Managers must recognize and deal with the concerns of a population paying bills for services that reflect the high cost of fuel and labour. This is also very important from financial point of view. Because a large fraction of the total cost is associated with the transport operation. Thus a small percentage improvement in the transfer-transport operation can affect a significant savings in the overall system cost. (Handbook of Solid Waste Management, 2002). Recently, Tehran Organization of Waste Recycling and Composting has decided to investigate the options of transporting waste to a new landfill site (Houshang site) which is 50 km from south-western boundary of city (BC Berlin, 2003). So a study concerning optimization of waste transport and transfer in the Iran's capital, Tehran, which is a metropolitan area has been done. MATERIALS & METHODS All transfer stations in Tehran were analyzed with respect to their potential for optimization. There are 12 active transfer stations in the Tehran metropolitan area that handle the most part of the household waste generated in the city. A negligible amount of waste is carried directly to the landfill which is currently located in Kahrizak. In table 1 the coding of transfer stations and their distance to the current Tehran landfill is mentioned (OWRC, 2001). As it can be deduced from Table 1 the transfer stations are scattered all over the city and so the distances between transfer stations and the landfill vary a lot (OWRC, 2003). All transfer stations in Tehran except one are classified as large transfer stations according to the amount of waste transferred from each one (EPA, 2000). Current waste turnover of each active transfer station is shown in Table 2. All transfer station in Tehran has a considerable amount of spare capacity. The main point that limits the capacity of current transfer station is the number of semi-trailers available and the absence of waste storage system which increase the waiting time of collection vehicles. The method used in transfer stations is the direct haul method which is based on usage of more semi-trailer than tractors as the storage capacity. No classical compaction is implemented in transfer stations but some manual compaction or using shovels and pushing blade to compact the waste has been observed during site visits. At the landfill the pushing blade method is used by semi-trailers to unload the waste.Management of waste transport is done by private sector contractors and is supervised by the Motor Pool Department. The semi-trailers are owned by the Motor Pool Department and are lent to the contractor under conditions of contract. The circle time varies from each transfer station to another and is highly dependent on the timing of the transportation, technology of tractors and containers and the technology used in transfer stations. Results & Discussions The scenario underlying the transportation study is based on the main assumed scenario for landfill design. In recent years the density of waste in semi-trailers fell to 325 kg/m3, thus proving that the waste density is decreasing in Tehran. This makes the compaction more favorable. In addition the amount of waste is increasing due to increasing in population and public welfare. Because of lack of yearly and continuous data on waste density, it is assumed that with the increasing percentage of non-degradable materials in waste the density of waste in the horizon of study would be 250 Kg/m3 that would mean a middle range, reported for a middle income country (Rudolf, 2000). Transfer station alternatives include an extensive range of facilities from a simple soil platform to a multi-story building with sophisticated instruments. Consequently, the potential technologies used for these transfer stations vary considerably. In Table 3 the advantages/ disadvantages and the common usage of transfer containers are discussed (EPA, 2002). One of the main points that should be considered in waste storage is the leachate generation. In tipping floor and surge pits systems because of significant amount of waste moisture, there would be considerable amount of leachate to collect and treat. This will create substantial cost of leachate treatment in order to release it to the surface water runoff drainage system (Ehrig, 1989). The process of loading transport vehicles is the main issue of waste transfer which has a great effect on the whole transportation system. In Table 4 the advantages, disadvantages and the common usage of various alternatives are discussed and evaluated (EPA, 2002) . Baling will not be considered further, because of unstable bales due to large amounts of high density and moist organic waste, high capital and operational costs for balers in transfer stations and the need of a totally new technical and operational system to unload bales. Top loading into semi-trailers is the method which is currently in practice and the introduction of any alternative will need significant amounts of capital investment. With a longer distance to the new landfill than to the Kahrizak landfill, the option of minimization of volume of waste has to be Each bale of approximately 1 ton of weight should be unloaded and stapled in the landfill. This would result in 8000 bales a day to be stapled in the landfill which is not feasible. Compaction directly into containers is a rarely applied practice for transfer stations and is not recommended for Tehran. Press water will remain in the containers and the container is especially enforced to absorb the direct pressing power. The only alternative to the currently successfully applied system is the pre-load compaction into containers. This study will, in addition to the current system, describe different container types and sizes for both rail and road transport. The unloading procedure is highly dependent on the technology in use and the type of container to be used. There are four options to unload vehicles. In Table 5 the advantages, disadvantages and the common usage of varoius alternatives are discussed. Among all alternatives the trailer tippers is used in current situation and will have less needed capital cost to modify present system. It is also compatible for container-type railway transfer. If there would be operation problems due to short tipping front to cause some delays for transport trailers open top railcar tippers would be considered. From the Table 5, two possible options derivs: either the trailer tipper, for smaller containers (e.g. 30 m³) by a hook-lift system, or the push-out blade for larger containers (up to 65 m³). Both options will be compared and described in the text. In order to select the best Transfer-Transport method for the city, technical and economical characteristics of the systems must be taken into consideration. Option 1: Open semi trailer and sample of methodology used In the case of current way of transportation to the landfill with some minor changes (Top closing, cleaner transfer…), the available transfer stations will be used further on, without building a new one. The same trailers and tractors as currently used will transport the waste and therefore no compaction is possible, at least not to an efficient level. The only system which could be considered for open trailers in this respect is the power roller. The investment costs for this system is around US$ 20,000 and the compaction rate is only significant for light densities such as packaging and paper. So with no recycling it is not recommended to use this approach. Because of the longer distance to the new landfill the cycle times will increase and additional vehicles will be necessary. Accordingly more drivers will be needed. The vehicles will also have a higher rate of wear and will not last as long as the currently used vehicles. In Table 6 a sample methodology used to calculate investment costs and required fleet for transport of waste is mentioned. In other alternatives the same methodology is used. Option 2: Container with compaction on road In this option, the waste is compacted before loading into containers. The objective is to reduce the size of the transportation fleet, which in turn means reduction of the number of trips and overall investment. The option works with using sticks to the present way of waste delivery to the landfill using the road. The preload compaction system can compress the waste in range of 400-500 kg per cubic meter. If compared to the 300 kg/m3 average current waste density increase the capacity of containers to about 30-40%. Option 2a: 50 m³ containers on semi-trailers The containers of 50 m³ volume are put on semi-trailers, the loading is via the compaction unit (Chapter 5), the unloading via push-out blade. Compaction of waste is performed by installation of compactors at the existing transfer stations. Option 2b: Two 30 m³ flexible containers This option is increasing the transported amount of waste by using two 30 m³ containers: one each on the chassis and the trailer. Loading and un-loading will be done with the help of a hook-lift. The hook lift will also be used to lift the container from the trailer and to empty it too. Option 2c: 65m³ containers on semi-trailers This option is the continuation of option 1 after addition of compaction facilities at the existing transfer stations. Also, it utilizes 65 m³ fully closed containers fixed on semi-trailers which are filled with compacted waste at the transfer stations and pulled to the landfill by tractors. The process of unloading waste at the landfill is made through installation of push-out blades at each container. At the new transfer station (with railway connection) compactors will be installed. The delivered waste is tipped into the compaction hopper and pressed into enclosed 30-ft container. The delivery from nearer districts is directly done by collection vehicles, from far-away districts the existing transport vehicles transport from the existing transfer station to the new one. In this mode a part of the existing transfer stations can be closed to save space and personnel. The full container is removed from the compactor and an empty one is linked by an automatic container change system. For continuous work of the compactors a container stock is necessary to have empty containers available in time when no train is at the station. The containers are loaded on the train by movable cranes or stationary cranes with automatically moving locomotives to tug the train and position the wagons under the crane. The train transports the container to the landfill station, where other cranes lift the container onto semi-trailers. Semi-trailers are tugged to the deposit site by tractor units with installed hydraulic equipment to unload the container by pressing the front shield through it. The empty container is brought back to the station and loaded on the train again by crane. This variant is similar to the transfer station in Berlin-Gradestraße which is one of several transfer stations in the world which transport the waste via rail. Option 3a: 50 m³ containers on semi-trailers This option builds on the characteristics of option 2a for deliveries to the rail transfer station. The rail transport cannot take place from each transfer station, and the waste needs to be transported to and from the two rail-container terminals. Option 3b: 30 m³ flexible containers This option builds on characteristics of option 2b for deliveries to the rail transfer station. In this case, the containers are transported by heavy-duty lifters instead of cranes. Option 3c: 65 m³ containers fixed on semi-trailers This option builds on characteristics of option 2c for deliveries to and from the rail transfer station. Option 4: Open semi-trailer on rail In this option the waste transport vehicles drive on the railway wagons (railway- owned wagons) via a ramp. When the whole train is loaded it is driven to the landfill. At the landfill other drivers take over the vehicles and drive from the station to the deposit site, unload the vehicles and bring back the empty vehicles to the railway wagons which are driven back to the loading station where the regular drivers take back the vehicles. In this option the working times of the drivers for the transportation period are saved and only loading and unloading stations without further equipment are needed. The benefit of railroad transport is generally the less environmental impact by reducing noise and pollution and the saving of traffic movements.But the numbers of vehicles increases as well as the number of drivers and the transportation of vehicles cause a loss of payload on the railway wagons. The comparison of costs will consider not only the investment costs but also the operating costs and other preferences such as ecological reasons. Therefore an enormous amount of information is required to cover the local situation as exactly as possible and to proof the conditions for each individual transportation system. If options No. 1 or No. 2 is considered to be implemented, a bypass of approximately 3 km will be needed to avoid crossing small towns in the road. The investment cost of this bypass is estimated at US$ 1,100,000. Table 7, shows the comparison of costs in 2019 in US$ for different variants. The implementation of a successful waste reduction strategy by 25% would result in • 20% less investment costs and a 10% increase of the costs per Mg for the transportation system with compaction; • 25% less investment costs and a 5% increase of the costs per Mg for the road transportation system without compaction, and • 10% less investment costs and a 5% increase of the costs per Mg for the transportation system by rail The differences can easily be explained by the different impact of the reduction on the investments and the related operation. CONCLUSION As a result of the comparative transfer analysis the current option should be phased out. The current system does create pollution on the way due to the open semi-trailers, and causes the highest number of vehicle movements through the city It has also been shown that the railway option is not recommendable. Firstly, expensive new tracks towards the landfill should be planned. Secondly the transport is several times broken, since waste is to be transported from the transfer stations to a rail terminal by truck and also from the final terminal at the landfill towards the dumping site. Two additional transfer stations with container movement facilities are needed and the need of more containers as buffer or while in the train. This requirement increases the price for the rail option significantly. Finally, the rent for the rail wagons adds up to the higher price of the railroad option. The transportation by road has as described above has several environmental and social impacts. Those impacts can be reduced by reducing the number of daily trips for the transportation of the waste to the landfill.This will be achieved by compacting the waste prior to loading. The direct compaction into the containers is not recommended since the amount of liquid as a result from the pressing can not be collected externally and has to remain in the container. From the three researched options, two 30 m³container on a truck and a trailer are considered as less favourable: Firstly, the system is less efficient due to higher investment costs and longer loading and unloading procedures. Secondly, this system is different to the existing equipment. As Fig. 3 and the related tables demonstrate, due to the greater distance from the new landfill to the transfer stations the compaction system is more effective in both terms of capital and operation costs. The lower numbers of vehicles for the compaction alternative and especially the container system result in even less capital costs. Consequently, the most preferred option is the 65 m³ closed container system attached to semi-trailers with push out blade and pre-load compaction. In the same way, the 50 m³ container system might be considered as neither the operation nor the cost does not differ significantly. The final price can be determined by the tendering procedure. If the compactors are all of the same made all type of containers should be compatible to the compaction unit. This will, however, depend on the supplier of the material. The costs for pre-load compaction are estimated at 10 to 15 % of the total investment sum, while the resulting reduction in transportation equipment will be more than 20 to 40 %. The study in Tehran shows that in the larg cities as the landfills are located in remote areas, optimization of the transport/transfer system can make a great change in the investment and operation costs of the system and it is feasible to introduce innovative technologies for transporting the waste. On the other hand it has been shown that if the transfer stations are so spatially dispersed and there is limited number of railway stations in dense urban areas, it will not be feasible to use railway transport even for very distant landfills. The study shows that implementation of a compaction system would be potentially beneficial to decrease the costs and environmental impacts in such situation. Acknowledgement It is necessary to specially thank Tehran Organization of Waste Recycling and Composting (OWRC) for her great deal of cooperation & allowing us to use its wide range of information & publications. Also we thank BC-Berlin for her great conduction of this research which hopefully be used in further national studies. REFERENCES
The following images related to this document are available:Photo images[er07023t7.jpg] [er07023t3.jpg] [er07023t2.jpg] [er07023t5.jpg] [er07023f3.jpg] [er07023t4.jpg] [er07023f1.jpg] [er07023t1.jpg] [er07023t6.jpg] |
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