Muhammad Juanda1 and Benno Rahardyan2
Environmental Engineering Study Program
Civil and Environmental Engineering Faculty, Bandung Institute of Technology
Ganesha Street No. 10 Bandung 40132
Abstract : Sanitary landfills are necessary for final disposal of the wastes that could not be prevented, reused, recycled or composted. Ideally, sanitary landfills should be used primarily for nonreusable, nonrecyclable and noncompostable residues. Sanitary landfills constitute a dramatic improvement over disposal of wastes in open dumps. Sanitary landfills greatly reduce pollution and risks to human health and the environment compared to open dumping. Landfill design require alternative approach. Waste pretreatment before deposited into landfill with mechanical and biotreatment is one reasonable option because the waste constitutes high biodegradable fraction of more than 50%. The addition recycle facility in waste treatment concept will give benefits that are the recovery valuable waste. The waste reduction from the pretreatment design can reach 90% before dumps into landfill. Approximately 71% waste reduced from biotreatment, 19% recyclable waste will goes to market, and the rest will deposited into the landfill. From leachate generation calculation the ultimate leachate occur in February until May and percolation not take place during May until October. HELP model shows average annual percolation is 42%. Leachate can be controlled by placing liners at the landfill base and installing systems to collect the contaminant before it seeps out of the landfill. The calculation illustrates leachate collection pipes diameter have range between 4 and 10 inch. From the calculation gas generation rate illustrates in year 43 occur degradation gas generation rate since there is no other waste deposits into the landfill. The maximum gas flow rate take place in the last year operation of landfill. The maximum expected gas generation rate used for the gas collection and control system can be determined.
Key words: landfill, pretreatment, leachate, gas generation
Concerning landfilling most Indonesian town face similar problems most landfills are just open dumps. However, landfilling is considered to be the most effective method of solid waste disposal in developing countries if adequate sites are available. Uncontrolled dumping is a serious problem for public health and the environment due to the release of hazardous pollutants such as leachate, which contaminates soil, surface water and groundwater, toxic gases, bad smells, dust and noises, smoke from burning of waste, vermin and other disease carrying organisms, scattered waste by wind and scavenging animals, greenhouse gases (METAP, 2006). The upgrading of existing sites and the sound operation as well maintenance will be major issues of future solid waste management system. The cost associated with landfill construction and operation practiced in developed countries, and indefinite post closure control of gas, and leachate require substantial amount of money and technical skills for post closure activities (Koliopoulos et al, 2006).
The EPA defines a landfill as an engineering method of disposing of solid waste on land. As such, landfills are required to protect the environment by spreading waste into thin layers and compacting them into the smallest practical volume. By day’s end, all waste is then covered with earth (Government Engineering, 2006).
Leuwigajah landfill in Cimahi having wide area of 25.1 hectare ever used for dumping waste by Bandung City, Cimahi City, and Bandung regency. Fig. 1 shows Leuwigajah Landfill location mark with the number 2. Landfilling activity in Leuwigajah started in 1982 with extension and construction in wide area of 12 Ha. In 13 January 1987, Leuwigajah Landfill officially started operation (BPLHD).
The experience gathered from dumping of municipal waste in landfill sites has shown that the deposition of waste that is neither presorted nor treated can lead to considerable environmental pollution through both leachate and gas. Another important point is the high demand on areas used as disposal sites. The use of these areas is not only limited during the active life of the landfill, but will remain limited for many decades after its closure, thus preventing, or making more difficult, any urban planning measures desired. Moreover, disposal sites require regular maintenance and monitoring after depositing has ended. The costs associated with these measures are left to future generations (Damiecky, 2002).
People still assuming waste is an useless goods not as a goods need to exploit. However, the citizens in waste treatment using “end-of-pipe”, that is collect, transport, and throw away to final disposal site. Despite the fact that large volume waste in final disposal site have potential to release methan gas that is cause glass house gas and give contribution to global warning. For waste to degraded in nature required long time and cost substantial amount of money (UU No 18, 2008).
Final disposal of wastes at sanitary landfills is given the lowest priority in an Integrated Waste Management approach. A sanitary landfill is a facility designed specifically for the final disposal of wastes, that minimizes the risks to human health and the environment associated with solid wastes. Sanitary landfills commonly include one, two or three different liners at the bottom and sides of the disposal area, in order to prevent leachates from polluting nearby surface waters or aquifers. Liners also prevent the underground movement of methane. Waste arriving at landfills is compacted and then covered with a layer of earth, usually every day. This prevents animals from having access to the organic matter to feed. Sanitary landfills may also include other pollution control measures, such as collection and treatment of leachate, and venting or flaring of methane. It is possible to produce electricity by burning the methane that landfills generate (Medina, 2003).
Few step require in design sanitary landfill are excavate land, add compacted clay cover or synthetic liner, and install leachate collection system, the next phase are deposit solid waste along with install gas collector pipe. When the landfill fills to capacity, a final stabilizing soil layer is placed over the compacted solid waste (UMUC, 2009).
Designs may vary, but there are three basic methods of building a sanitary landfill: area method, trench method, and ramp method (Government Engineering, 2006).
The area method is best-suited for sites where no natural slopes exist. This method can be adapted, however, to ravines, valleys, quarries, or old surface mines. Disposing of waste in a ravine site requires construction of diversion ditches for runoff water before any waste is received. Here is how the area method works: Waste is pushed into layers, compacted, and adequately covered. A machine, such as a track-type tractor or landfill compactor, spreads and compacts the material. Soil for daily cover must be hauled in from borrow sites using a wheel tractor-scraper or articulated truck.
The trench method is best-suited for flat or gently sloping land where the groundwater table is deep below the surface. The chosen site should have soil that is easy to excavate and suitable for cover. Immediate availability of cover without the need of expensive specialized equipment to haul it long distances can be a major advantage of the trench method. If the landfill is to be brought above ground level, nearby cover material can also be an advantage. The trench does, however, have some disadvantages. If more cover material is excavated than can be used immediately, it will have to be stockpiled and moved again at an additional expense.
The ramp method is a variation of the area and trenching techniques. Waste is spread and compacted on an existing slope. Cover material is excavated directly in front of the waste. It is then spread over the waste and compacted. The excavated area becomes a part of the cell to be worked the following day. Similar to the progressive trench method, the ramp method is considered ideal by some operators because they do not have to haul in cover material (with its extra cost of expensive handling equipment). Because they may handle the cover only once and do not have to prepare the land in advance, they consider this an excellent way to start a landfill with a minimum of equipment. Depth of the water table is another factor, but it is not as critical as with the trench method, which normally requires deeper excavation.
The cell is the basic building block of a sanitary landfill. To build a cell, waste is spread into two-ft layers or less and compacted in thin layers as tightly as practical. At the end of the day, a sufficient amount of cover earth (usually six in.) is spread over waste and compacted. Sometimes an alternative material is approved for daily cover. The compacted waste and soil constitute a cell. A series of cells that adjoin each other make up a lift.
Compaction is the technique to extends the life of the site. Better compaction means packing more waste into less space. Several benefits of compaction are extends the life of the site, decreases settlement, reduces voids, reduces wind-blown litter, discourages insects and rodents, reduces possibility of waste washing away or being exposed during a rain, reduces amount of daily cover needed, reduces leachate and methane migration, provides a more solid travel surface for refuse trucks. Desired density in landfill is 0.56 ton/m3 acquired from 60% – 65% source reduction for normal compacted landfill (Tchobanoglous et al, 1993).
Table 1 represents the waste composition that dump into Leuwigajah Landfill at 2010. Mostly, it constitutes high biodegradable fraction of more than 50%. The moisture content in biodegradable waste is relative high, which is greater than or equal to 50%. In this regard, waste is not suitable for incineration because it requires high-energy input to bring the waste to its ignition level. Nevertheless, landfilling of such waste creates nuisance owing to the generation of highly concentrated leachate, methane gas emission, and quick settlement to waste due to decomposition that eventually affects the stability of landfill. The best disposal solution for this type of waste is the mechanical-biological pre-treatment system. Waste materials potential for recuperation includes mainly paper products, and different types of plastics, little glass, and metals be able to recovered through mechanical processes (Visvanathan et al, 2005).
Table 1 The waste composition that dump into Leuwigajah Landfill at 2010 (BPLHD, 2005)
Recycle facility addition
The addition recycle facility in waste treatment concept will give benefits that is the recovery valuable waste. The recycle facility will require a huge amount of land, equipments and money. Fig. 2 illustrates recycle facility in Switzerland.
The mechanical treatment is a combination of one or several material such as shredder, crusher, and mill: for the reduction of the material size. Bag splitter: a more gentle shredder used to split plastic bags whilst leaving the majority of the waste intact. Trommel and vibrating, star and disc screens: for separating and sizing materials. Ballistic separator: density and elasticity separation for light plastics and paper. Magnet and eddy current separators: for removing ferrous and non ferrous metals. Pelletiser: for improving the handling transportation and feeding of Refuse Derived Fuel. Optic separation (NIR): for the sorting of specific plastic polymers. Water-based separation of differential material densities: light materials as plastics and heavies like stones and glass. Wind shifter that removes light papers and plastics from the main stream. Rotating drum: uses gravity to tumble, mix, and homogenize the wastes (Kallasy et al, 2008).
Biotreatment facility addition
For biological treatment two methods are available: aerobic processes (composting/rotting) and anaerobic processes (Soyez et al, 2002). Anaerobic digestion is one form of the naturally occurring processes of decomposition and decay, by which organic matter is broken down to its simpler chemical constituents in the absence of dissolved oxygen. During decomposition anaerobic bacteria convert organic molecules into methane and carbon dioxide. Anaerobic processes tend to be classified as high-tech plants. When considering the general conditions in Indonesia, low-tech plants are the obvious choice for implementation (Christopoulos, 2005).
The main goals of biological waste treatment before deposit in landfills are (Fricke et al, 2008):
- Reduction of waste volume to be deposited by means of decomposition of biologically degradable components.
- Reduction of leachate volume and its contaminant loading through biodegradation of organic matter, contaminants are fixed and immobilized within the stabilized waste.
- Reduction of the gas formation potential by 80 to 90%.
- Stabilization of the waste to be safely deposited, thus decrease of the landfill settling process and reduction of malodor emissions.
There are three main types of composting: windrows, aerated static piles and in-vessel systems, as represented in Fig. 3.
Waste treatment design concept
Wastes firstly will be check by truck scale. Afterwards wastes enter into mechanical treatment facility. In mechanical treatment facility wastes sorted by their type. Organic waste goes into biotreatment facility. Approximately 19% recyclable waste will send into the market. The other wastes dump into the landfill. Fig. 4 illustrates treatment method and Fig. 5 illustrates material flow. Landfill scenario limited the waste input up to 138 ton/day. 71% waste contain organic and paper goes into biotreatment facility. 27-ton recyclable waste obtained daily from mechanical treatment. 13.36-ton wastes will be deposited into landfill.
Mechanical treatment facility design
The scale capacity should be able to hold waste truck weight. Scale capacity used in design is 30 ton (Peer Consultans, 1991).
Storage yard unit
Mechanical treatment facility operated at 06:00 – 18:00. Storage yard designed for anticipated material loading stack before treatment. From 12-hour operation, material loading peak take place near daytime. Assumption material loading peak occur at 09:00 – 13:00 four times fold. Thus, mechanical treatment facility has capacity 880.57 m3/hour (396.26 ton/hour).
Fig. 6 shows mechanical treatment capacity at operation time. At 9 until 12 operation time the waste input exceeding mechanical treatment facility capacity. Thus the wastes should be able to stock in storage yard unit.
Sorting unit begin from distribution followed by transportation to baller. Manual assortment unit has velocity 3-4 hour/person/m3 (prabaharyaka, 2007), using conveyor belt with length 48 m, and 48 conveyor unit, conveyor belt has speed 0.167 m/s, sorting area a person is 1 m2. The sorting capacity from calculation is 7570.29 m3/day.
Biotreatment facility design
Selected biotreatment is self-aerated windrow system (Fig. 2). The intention using this method is simple and effective waste treatment, which is inexpensive to apply and still provides for adequate environmental protection. Aerobic process occurs in this treatment system.
Self-aerated windrow system was developed at the Leichtweiss-Institute several years ago, and has been implemented with great success in various plants in Germany. Experience in Germany has shown that emissions from landfills after treatment of the waste are reduced by approximately 90% (Munnich et al, 2005).
450 windrows, each with a surface of approximately 10 x 5 m and a waste tipping height of approximately 2 m were constructed on sealed surface. Drainage ditch installed encircling each windrow. Altogether approximately 32.7 ton of wastes were tipped into each windrow. The treatment processes has a duration between 16 – 20 weeks (Kuehle, 2005).
The waste should be ground, mixed beforehand in a homogenization drum, and moistened with additional water to produce optimum water content for biological decomposition. Afterwards the waste covered with a layer of shredded bark approximately 30 cm high after tipping into the windrow. This biofilter had the following effects (Munnich et al, 2005): eliminating odors from wastes, eliminating flies and vultures, moreover the filter stores precipitation. It thus impairs excessive dehydration of the waste, which hinders the biological processes. The filter also causes more even distribution of the volume of water entering the waste in periods of high precipitation.
The windrows outfitted with data collection equipment in order to observe the biological processes by means of temperature and gas measurements, and to be able to intervene if necessary. In order to ensure adequate water content in long dry periods, a sprinkler system will installed to moisten the windrows.
Three windrows will be use daily. The biological treatment facility designed for 5 months treatment although the treatment processes take place for 4 months is to provide safety factor time.
Approaching method to measures leachate generation from landfill are Thornwaite method and HELP Model (USEPA)
Thorntwaite method uses conservation of mass, by first determining the major segments of precipitation that detract from percolation. The method accounts for precipitation after it strikes the ground. The incident precipitation can form surface water runoff, evaporate directly to the atmosphere, transpire to the atmosphere through vegetation surfaces, or infiltrate into the cover soils and refuse at the surface of the landfill (McBean et al, 1995)
The HELP model is a quasi-two-dimensional, deterministic, water routing model for determining water balances. The model was adapted from the Hydrologic Simulation Model for Estimating Percolation at Solid Waste Disposal Sites of the U.S. EPA. The HELP Model requires general climate data for computing potential evapotranspiration, daily climatologic data, soil characteristics, and design specifications to perform the analysis (Schroeder et al, 1994). The required general climate data include growing season, average annual wind speed, average quarterly relative humidities, normal mean monthly temperature, maximum leaf area index, evaporative zone depth, and latitude.
Some organics in wastes can serve as a source of food for bacteria will, in a landfill environment, produce methane and CO2 (landfill gas). Landfills will also release a number of other volatile chemicals, including highly hazardous VOCs and odorous compounds, which are a threat to the health and welfare of those within the sphere of influence of the landfill. This sphere can extend for several miles, depending on the topography of the area and the tendency for atmospheric inversions to take place (Fred Lee et al, 2004).
For the purposes of determining the maximum expected gas generation flow rate from the landfill, the total gas generation from the landfill for each year during either active period or closure period should be calculated based on each year’s waste mass and waste age. Then, the maximum annual gas generation rate can be found by comparing each year’s amount of gas generation.
RESULTS AND DISCUSSION
Leachate quantity depend in water infiltration, part of it comes from rain, beside affected by operational aspect such as cover soil, slope surface, and climate conditions. The soil and waste ability to kept water then evaporate it cause leachate generation hard to calculate (Damanhuri, 2008). The design using Thorntwaite water model and HELP model from USEPA. Fig. 7 illustrates Leuwigajah landfill design and Fig. 8 shows the results of calculation water balance method Thorntwaite model.
From October to February, the infiltration through the cover is larger than the actual evapotranspiration. Thus, the difference goes into storage in the surface layer. However, at the end of February, the storage capacity in the surface layer is reached.
From February until May, the infiltration continues to be larger than the actual evapotranspiration, yet the surface layer is at field capacity. Therefore, additional water contributions create percolation (and ultimate leachate).
Commencing in May, the evapotranspiration exceeds filtration. To meet this demand (for evapotranspiration), water comes out of surficial storage. The increasing depletion of the soil moisture continues until October, when once again, infiltration rates exceed evapotranspiration rates. Table 2 represents output HELP Model.
Table 2 Average annual HELP output model
Fig. 9 shows gas generation rate year-to-year and maximum gas generation rate is in the year 42 the last year landfill operating time. Thus, starting in year 43 occur degradation gas generation rate since no waste deposit into the landfill. The maximum expected gas generation rate used for the gas collection and control system can be determined.
Leachate can be controlled by placing liners at the landfill base and installing systems to collect the contaminant before it seeps out of the landfill. Fig. 10b illustrates design leachate collection pipe.
The main goal of a gas collection piping line is to transport gas from extraction wells or horizontal collectors to gas treatment devices (flare stations or gas-to-electricity power plant) in an efficient steady-state manner (Qian et al, 2002). Fig. 10a illustrates design gas collector pipe.
Landfill gas collection pipe designed to include vertical and horizontal pipe. Gas collection pipe designed part from leachate collection pipe system. Vertical pipe gas constructed in all leachate collection pipe connection.
Determine spacing gas extraction well is important phase in design gas collection system. Spacing for collector gas pipe with clay layer is 100 ft and goemembran layer is 150 – 200 ft (Tchobanoglous et al, 1999). Spacing gas collector pipe design basically in landfill layout. Vertical pipe design having influence radius 100 m basis the waste already treat by pretreatment facility
Sanitary landfills are necessary for final disposal of the wastes that could not be prevented, reused, recycled or composted. Ideally, sanitary landfills should be used primarily for nonreusable, nonrecyclable and noncompostable residues. Sanitary landfills constitute a dramatic improvement over disposal of wastes in open dumps. Sanitary landfills greatly reduce pollution and risks to human health and the environment compared to open dumping (Medina, 2003).
From leachate generation calculation obtained in February until May occur ultimate leachate (percolation) and leachate not occur during May until October. HELP model shows average annual leachate generation is 42%.
Leachate can be controlled by placing liners at the landfill base and installing systems to collect the contaminant before it seeps out of the landfill. The calculation explain leachate collection pipe diameter have variation 4 until 10 inch.
The calculation gas generation rate year-to-year shows maximum gas generation rate take place in the year 42 the last year landfill operating time. Thus, starting in year 43 occur degradation gas generation rate since no waste deposit into the landfill. The maximum expected gas generation rate used for the gas collection and control system can be determined.
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This Paper presented at the Environmental Engineering Undergraduate ITB Seminar in August 2009. Bandung. Indonesia