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Thursday, December 29, 2011

METHODS OF SOLID WASTE DISPOSAL

DISPOSAL OF SOLID WASTE

Method of solid waste disposal are as below:
  • Open burning
  • Dumping into the sea
  • Sanitary Landfills
  • Incineration
  • Composting
  • Ploughing in fields
  • Hog feeding
  • Grinding and discharging into sewers
  • Salvaging
  • Fermentation and biological digestion

Open burning

Not an ideal method in the present day context

Dumping into Sea

  • Possible only in coastal cities
  • Refuse shall be taken in barges sufficiently far away from the coast (15-30 km) and dumped there
  • Very costly
  • Not environment friendly

Sanitary Landfilling

  • Simple, cheap, and effective
  • A deep trench (3 to 5 m) is excavated
  • Refuse is laid in layers
  • Layers are compacted with some mechanical equipment and covered with earth, levelled, and compacted
  • With time, the fill would settle
  • Microorganisms act on the organic matter and degrade them
  • Decomposition is similar to that in composting
  • Facultative bacteria hydrolyze complex organic matter into simpler water soluble organics
  • These diffuse through the soil where fungi and other bacteria convert them to carbon dioxide and water under aerobic conditions
  • Aerobic methanogenic bacteria utilize the methane generated and the rest diffuses into the atmosphere
  • Too much refuse shall not be buried – fire hazard
  • Moisture content – not less than 60% for good biodegradation
  • Refuse depth more than 3m – danger of combustion due to compression of bottom layers – hence should be avoided
  • Refuse depth is generally limited to 2m
  • Temperature in the initial stages of decomposition – as high as 70 degree C – then drops
  • Reclaimed areas may be used for other uses

Engineered Landfills

  • Bottom of the trench is lined with impervious material to prevent the leachate from contaminating groundwaters
  • A well designed and laid out leachate collection mechanism is to be provided
  • Leachate so collected is treated and then disposed off



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Components of a Typical Landfill

MSW Landfill Gas

Table: Typical Constituents of municipal solid waste landfill gas
Component
% by volume (dry)
Methane
45 to 60
Carbon dioxide
40 to 60
Nitrogen
2 to 5
Oxygen
0.1 to 1
Ammonia
0.1 to 1
Hydrogen
0 to 0.2

 

Incineration

  • A method suited for combustible refuse
  • Refuse is burnt
  • Suited in crowded cities where sites for land filling are not available
  • High construction and operation costs
  • Sometimes used to reduce the volume of solid wastes for land filling
  • Primary chamber – designed to facilitate rapid descication of moist refuse and complete combustion of refuse and volatile gases
  • A ledge or drying hearth is provided for this purpose
  • Secondary chamber – between the primary chamber and the stack – temperatures above 700 degree C
  • All unburnt and semiburnt material are completely burnt here

Waste to Energy Combustors

  • Incinerators – Refuse was burned without recovering energy – exhaust gas is very hot – exceeds the acceptable inlet temperature for electrostatic precipitators used for particulate emission control
  • Modern combustors – combine solid waste combustion with energy recovery

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Combustors
  • Storage pit – for storing and sorting incoming refuse
  • Crane – for charging the combustion box
  • Combustion chamber consisting of bottom grates on which combustion occurs
  • Grates on which refuse moves
  • Heat recovery system of pipes in which water is turned to steam
  • Ash handling systems
  • Air pollution control systems
  • Grates – Provide turbulence so that the MSW can be thoroughly burned, moves the refuse down, provides underfire air to the refuse through openings in it (to assist in combustion as well as to cool the grates)
  • Operating temperature of combustors ~ 980 to 1090 degree C

Grates
Figure; Grates of MSW combustor. The underfire air is blown through the holes in the drawings show three types grates. (b) reciprocating (c) rocking (d)travelling

Composting

  • Similar to sanitary landfilling
  • Yields a stable end product – good soil conditioner and may be used as a base for fertilizers
  • Popular in developing countries
  • Decomposable organic matter is separated and composted
Methods
  1. Open window composting
  2. Mechanical composting
Open window composting
  • Refuse is placed in piles, about 1.5m high and 2.5m wide at about 60% moisture content
  • Heat build up in the refuse piles due to biological activity – temperature rises to about 70 degree C
  • Pile is turned up for cooling and aeration to avoid anaerobic conditions
  • Moisture content is adjusted to about 60%
  • Piled again – temperature rises to about 70 degree C
  • The above operations are repeated
  • After a few days (~ 7 to 10 weeks) temperature drops to atmospheric temperature – indication of stabilisation of compost
Mechanical composting
  • Process of stabilisation is expedited by mechanical devices of turning the compost
  • Compost is stabilised in about 1 to 2 weeks
  • To enrich compost – night soil, cow dung etc are added to the refuse
  • Usually done in compost pits
  • Arrangements for draining of excess moisture are provided at the base of the pit
  • At the bottom of the pit, a layer of ash, ground limestone, or loamy soil is placed – to neutralise acidity in the compost material and providing an alkaline medium for microorganisms
  • The pit is filled by alternate layers of refuse (laid in layers of depth 30 – 40 cm) and night soil or cow dung (laid over it in a thin layer)
  • Material is turned every 5 days or so
  • After ~ 30 days – it is ready for use
Methods used in India
Indore method – aerobic – brick pits 3 x 3 x 1 m – upto 8-12 weeks materials are turned regularly in the pits and then kept on ground for about 4-6 weeks – 6 to 8 turnings in total
Bangalore method – anaerobic – earthen trenches 10 x 1.5 x 1.5 m – left for decomposition – takes 4 to 5 months

Vermicomposting

  • Ideal for biodegradable wastes from kitchens, hotels etc
  • At household level, a vessel or tray more than 45 cm deep, and 1 x 0.60m may be sufficient
  • A hole shall be provided at one end in the bottom for draining the leachate out into a tray or vessel
  • Lay a 1” thick layer of baby metal or gravel at the bottom of the tray
  • Above that lay an old gunny bag or a piece of thick cloth, a layer of coconut husk upside down over it and above that a 2” thick layer of dry leaves and dry cow dung (powdered)
  • Lay the biodegradable waste over it
  • Introduce good quality earthworms into it (~ 10 g for 0.6 x 0.45 x 0.45 m box)
  • If the waste is dry, sprinkle water over it daily
  • Rainwater should not fall into the tray or vessel or box
  • Keep it closed
  • If the box is kept under bright sun earthworms will go down and compost can be taken from the top
  • Compost can be dried and stored
  • Continue putting waste into the box
  • Add little cow dung at intervals
  • Do not use vermi wash directly. Dilute in the ratio 1:10 before use

Disposal by ploughing into fields

  • Not very commonly used
  • Not environment-friendly in general

Disposal by hog feeding

  • Not common in India
  • Refuse is ground well in grinders and then fed into sewers
  • Disposal of garbage into sewers – BOD and TSS increases by 20-30%
  • Disposal of residual refuse – still a problem

Salvaging

  • Materials like paper, metal, glass, rags, certain types of plastic etc can be salvaged, recycled, and reused

Fermentation or Biological Digestion

  • Biodegradable Waste – convert to compost
  • Recycle whatever is possible
  • Hazardous wastes – dispose of it by suitable methods
  • Landfill or incinerate the rest

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Sanitary Landfill
1. Facilities at Sanitary Landfill

At sanitary landfills, consideration of leachate is of most importance as far as environmental preservation is concerned. Methods of handling leachates consist of liner systems which prevent the leachates from running-off into the groundwater and the river basin: leachate collection systems which collect and discharge the leachates from the site; and leachate treatment equipment which treats the leachates to boring their quality up to water discharge standards (Fig. 1).
 Conceptual Drawing of Sanitary Landfill. க்கான பட முடிவு


Fig 1 Conceptual Drawing of Sanitary Landfill.

Of these techniques, it is the liner system that may present most problems for the locality.

2. Quality of Geosynthetic Materials


Vulcanized rubber materials (EPDM/butyl rubber) and polyvinyl chloride have frequently been used as geosynthetic liners. They have been selected more for reasons of cost than workability, which is determined by their physical properties and heat fusibility.

Recently, there has been a demand for improved geosynthetics as a way to prevent functional disorders due to failure, etc. In reply to this need, a geosynthetic material based on urethane has been developed jointly with Kyowa Hakko Kogyo Co., Ltd. Table 1 is a comparison of typical properties of vulcanized rubber and the urethane.
In addition to its excellent physical properties in the ordinary state compared with conventional vulcanized rubber, the urethane geosynthetic offers the following special features:
1) The material itself contains no component that elutes.
2) Joints can be formed either by bonding using an adhesive or by welding, so repairs are straightforward even if damage occurs.



3. Detection of Failure the Geosynthetic's Cut-off Ability


When laying the geosynthetic, it is difficult to fully check it for functional disorders at the joint, etc. To make matter worse, the geosynthetic is covered with waste as the landfill progresses, preventing visual inspection at a later date.

To overcome this problem, a method of checking for leakage based on electrical prospecting techniques has been developed. This supplied as the"Geosynthetic Liner Leakage Position Detection System".
Geosynthetics are normally electrical insulators, so no current flows from within the landfill site, which is enclosed by the geosynthetic, to the surrounding soil. However, if a functional failure of the cut-off ability occurs, a current will flow. The detection system is based on this fact.
Figure 2(a) shows how electrodes (A and B) are placed within the landfill side and outside it to set up an electrical current. Then, by placing further electrodes (S and D) between points A and B, the electrical potential can be measured. Lines of equal potential can then be traced by moving electrode S, as shown in Fig. 2(b), thereby locating the position of any functional disorder in the geosynthetic.
This system offers the following special features:
1) Inspections can be carried out without removing any waste.
2) Once installed, constant monitoring for functional disorders can be carried out.


Sanitary Landfill Design Procedures
..................................

When designing a sanitary landfill, your objectives are to provide long -term environmental protection, ensure regulatory compliance, and achieve cost -effective utilization of manpower, equipment, and space. This lesson and Lesson 7 will present a design methodology to achieve these objectives.
The site selected for a sanitary landfill ordinarily has certain characteristic that are less than ideal. During landfill design, engineering techniques are used to overcome the site limitation and to meet design goals.
The design process is summarized in Table 1. Data collected during site selection will be incorporated into the site design, but changing conditions and the need for more detail may require re-evaluation and additions to previously collected data.

Environment regulations

Federal, state, and local government standards generally are of two types: engineering design standards and performance standards and performance standards.
Engineering design standards are essentially building codes which describe how the facility must be built: for example, a requirement that a new landfill have a six-foot-high fence -surrounding the facility. Compliance with these standards is evaluated by agency review of the building plans and on-site inspection of the landfill during construction.
Performance standards applicable over a facility’s life, and specify that a certain level of environmental control be achieved. For example, the state agency regulating groundwater quality may specify the maximum allowable concentration of a contaminant which may be present in the groundwater below or adjacent to the site. The site operator must incorporate the necessary control systems to achieve compliance with the groundwater standard. If the features initially designed do not achieve compliance, then the operator must install additional protective systems.
The U.S. Environmental Protection Agency, under the authority of the Resource Conservation and Recovery Act (RCRA), has regulations regarding: floodplains; disturbance of endangered species; surface water discharges; groundwater contamination; prevention of disease transmission; air pollution control; and safety concerns.
State regulations vary widely, but usually landfill engineering plans are submitted for review and approval. State standards are ordinarily more extensive than RCRA standards and address concerns that are specific to a particular geographic region.
Procurement of the various permits that may be required to open and operate a landfill may take several years, especially if there is public controversy regarding the site. State or local governments may require a Solid Waste Landfill Plan Approval, Zoning, Conditional Use Zoning Permit, Highway Department Permit for entrances on public roads and increased traffic volume, Construction Permit for landfill site preparation, Operation Permit for on-going landfill operation, Mining Permit for excavations, NPDES Permit for runoff discharge, Building Permit to construct buildings on the landfill site, Fugitive Dust Permit, Air Emission Permit, and Closure Permit (Conrad et al., 1981).
The regulatory standards should be viewed only as minimum requirements which specify a baseline standard of design and performance. Waste disposal facility owners are being held responsible for environmental damage and cleanup many years after the disposal site became operational, and even following closure. Claiming compliance with regulatory standards has not been an effective defense against pollution damage claims. Consequently, the landfill developer may find it a good strategy for build a facility that in some aspects exceeds the regulatory requirements. This may also be necessary in order to achieve public acceptanc

Identification of goals

The landfill project's goals should be decided upon with input from the site owner and operator, potential landfill users, regulatory authorities, and residents or land owners near the site. Design goals for sanitary landfill could include:
.To protect groundwater quality by limiting the discharge of leachate;
.To protect air quality and conserve energy by installing a landfill gas recovery system;
.To minimize impact on adjacent wetlands by controlling and impounding surface runoff;
.To minimize dumping time for site users;
.To use the landfill space efficiently and extend site life as much as is practical; and .To provide for maximum use of land upon site completion.

Consideration of final site use

The final use of the landfill must be considered during the design phase in order to provide for the best use of the property. Good planning at the earliest possible stage will minimize costs and maximize the site's usefulness after closure.
A landfill's final use should be compatible with nearby land use as well as the limitations of the landfill to support structures. Most full landfills are used for recreational purposes, such as golf courses, nature preserves, or ski hills. Consideration must also be given to compatibility with existing land forms, settlement allowances, and drainage patterns.

Waste characteristics

Waste characteristics provide important design information for determining operating procedures; the waste type affects the handling techniques and waste quantity determines site lifetime, daily operating procedures, and cover requirements. A waste characterization study should precede the landfill siting work, but additional information may be needed while the facility is being designed. For example, certain waste types may be used as daily cover or on-site road base.
When preparing a profile of the wastes which will be received at the new landfill, special attention should be given to sources which may be unknowingly mixing hazardous waste with solid waste. In suspicious cases, hazardous waste testing procedures may be needed. Systematic load checking during site operation should also be planned.
The types and number of vehicles which will transport the solid waste to site should be tabulated also. Traffic information will be useful for later analysis of roadways and access points.

Sanitary Landfill Design Steps

1. Determination of solid waste quantities and characteristics
a. Existing
b. Projected
2. Compilation of information for potential sites
a. Performance of boundary and topographic surveys
b. Preparation of base maps of existing conditions on and near sites - Property boundaries, topography and slopes, surface water, wetlands, utilities roads, structures, residences, land use
c. Compilation of hydrogeological information and preparation of location map
- Soils (depth, texture, structure bulk density, porosity, permeability, moisture, ease of excavation, stability, pH, CATION exchange capacity), bedrock (depth, type, presence of fractures, location of surface outcrops), groundwater (average depth, seasonal fluctuations, hydraulic gradient and direction of flow, rate of flow, quality, uses)
d. Compilation of climatological data
- Precipitation, evaporation, temperature, number of freezing days, wind direction
e. Identification of regulations (federal, state, local) and design standards
- Loading rates, frequency of cover, distances to residences, roads, surface water and airports, monitoring, groundwater quality standards, roads, building codes, contents of application for permit
3. Design of filling area
a. Selection of landfilling method based on:
- Site topography, site soils, site bedrock, site groundwater
b. Specification of design dimensions
- Cell width, depth, length, fill depth, liner thickness, interim cover soil thickness, final soil cover thickness
c. Specification of operational features
- Use of cover soil, method of cover application, need for imported soil, equipment requirements, personnel requirements
4. Design features
a. Leachate controls -
b. Gas controls
c. Surface water controls
d. Access roads
e. Special working areas
f. Special waste handling
g. Structures
h. Utilities
i. Recycling drop-off
j. Fencing
k. Lighting
l. Washracks
m. Monitoring wells
n. Landscaping
5. Preparation of design package
a. Development of preliminary site plan of fill areas
b. Development of landfill contour plans
- Excavation plans (including benches), sequential fill plans, - completed fill plans, fire, litter, vector, odor and noise controls
c. Computation of solid waste storage volume, soil requirement volumes, and site life
d. Development of final site plan showing:
- Normal fill areas, special working areas, leachate controls, gas controls, surface water controls, access roads, structures, utilities, fencing, lighting, washracks, monitoring wells, landscaping
e. Preparation of elevation plans with cross-sections of:
- Excavated fill, completed fill, phase development of fill al interim points
f. Preparation of construction detalls
- Leachate controls, gas controls, surface water controls, access roads, structures, monitoring wells
g. Preparation of ultimate land use plan
h. Preparation of cost estimate
i. Preparation of design report
j. Preparation of environmental impact assessment
k. Submission of application and obtaining required permits
l. Preparation of operator's rnanual
Source: Conrad, et al - 1981, with additions by the authors
the solid waste to the site should be tabulated also. Traffic information will be useful for later analysis of roadways and access points.


Specifying design basis

The design basis is a tabulation of the general performance requirements that the new facility must satisfy in order to achieve project goals. It includes the facility's capacity, waste flow rates, traffic counts, and principal environmental controls. Tabulating the design basis in this manner communicates to the project design team end others, such a regulatory review specialists, the nature and size of the proposed Iandfill. An example is shown in Table 2.
The design basis may require later revision if unforeseen circumstances cause a significant change in the landfill plan.

Data for site layout

Geotechnical information is used to begin the site layout. Geotechnical data includes information on the geology, hydrology and soils at and around the site. The data is usually collected during the site selection process, then supplemented during subsequent site investigations. The number,
Table 2

Example Landfill Design Basis

ItemQuantity/Standard
Receive Waste 10 hours/day, 6 days/week




Operating Schedule Average (TPD) Maximum (TPD)
Municipal Solid Waste
Industrial, non-hazardous sludges,.........................
450
525
50% moisture ..................
55
75
Demolition Materials...........
10
150
Projected Total Quantities .
515
950
160,680 tons/year
(Note: Maximum waste loads for different waste types not expected to occur on same day.)



Vehicle Count 40 Trucks/Day 50 Trucks/Day
Compacted waste density
1,000 pounds/cubic yard
Waste to dally soil cover ratio
4 cubic yards waste to 1 cubic yard dally cover
Minimum final cover thickness
2 feet of clay
Minimum separation distance landfill base to ground water
8 feet
Minimum distance to water supply wells
500 feet
Maximum methane gas
1.25%
Minimum distance to homes
500 feet
Estimated site life
12 years - final estimate will depend on site layout
location, and depth of soil borings are determined by regulations and by the geological conditions at the site, with more borings needed, at sites with irregular formations.
Soil boring logs, as well as other data describing subsurface formations and groundwater conditions, are diagrammed to present a picture of the underground conditions at the planned landfill site. Figure 1 shows a diagram of subsurface conditions that exist at a landfill under development. The soil boring logs are shown and the extent of each formation is extrapolated between the boreholes. The depths to bedrock and the groundwater table are also shown.
Using this data, the landfill designer can determine the suitability of the various soil layer for landfill construction and the eventual landfill cross - section. Of particular concern are the potential for gas and leachate migration and the suitability of the soil for landfill base and cover material.
Four types of commonly encountered geologic conditions are diagrammed in Figure 2. The landfill’s layout will be strongly influenced by the geology. The formation in Type A are moderately impermeable and the water table is deep. Therefore, the primary concern is preventing excessive drainage of leachate form the landfill base in order to reduce its permeability.
If leachate accumulates at the landfill base, it can be removed with leachate recovery collection lines. A major asset of this type of site is the attenuative capacity of underlying soils which reduce the potential for groundwater contamination.
Type B conditions are similar to Tupe A but the water table is shallo. The landfill may be constructed above ground in a manner similar to Type D or a zones of saturation landfill may be constructed (as illustrated). The natural soils are used for final cover but the botton of the landfill is placed below the water table and the base soils are not compacted. Leachate in controlled by using drain tiles to induce groundwater flow into the site where the groundwater and any leachate are collected for disposal.

Varying conditions

Construction below the water table is possible because the impermeable soil conditions prevent rapid drainage of groundwater into the excavation, These types of sites are best suited for groundwater discharge areas to ensure proper leachate removal and to limit groundwater contamination.
The primary concerns at sites with moderately permeable soils and deep groundwater tables (Type C) are the restriction of excessive infiltration through the landfill cover, and the need to install a liner to afford more protection of groundwater. Since many permeable soils will not provide a high degree of protection, importation of clay soil or the use of a geosynthetic cover or liner may be necessary. These soils will often be good-quality construction materials upon which to place the landfill base and liner material.
Constructing a landfill on Type D sites will be more difficult because they are moderately permeable and have shallow water tables which have the potential for rapid leachate movement. This necessitates controlling drainage from the landfill. Soils available at the site are probably not suitable for controlling cover infiltration or liner construction. The permeable formulation will restrict construction below the water table. If a site of this type must be utilized, the usual approach is to build the site almost entirely above the original ground surface and to import cover and liner materials. Soils required for intermediate cover and utility purposes such as roads can hopefully be obtained at or near the site.
Other conditions may exist at proposed landfill sites. The presence of bedrock can impede excavation and further complicate groundwater protection, Sites with multiple soil layers and formations will require careful assessment when designing time landfill. Many other site layout strategies have been proposed to overcome soil and ground water limitations.

Leachate control system design

The leachate control system elements are the landfill cover, surface water control structures which prevent water from running into the site and, if installed the landfill liner, collection pipes, leachate detection systems, and leachate disposal system.
Percolation through the proposed cover is estimated with the water balance equation (see Lesson 4).
Selection of the best alternative can be based on the cost and availability of the cover materials, the potential detrimental effect of leachate that drains from the base of the landfill, and leachate treatment cost. Regulatory constraints will also influence the alternative selected.
The slope and soil characteristics of the cover will establish the runoff characteristics of the site. Runoff quantities and peak flows can be predicted with standard drainage calculation techniques ("Urban Hydrology for Small Watersheds," 1975).
Water that percolates through the landfill cover is assumed to eventually reach the base of the landfill as leachate. A variety of decisions is necessary on how to best handle this leachate.
A small amount of leachate may not have a significant potential effect on groundwater. Making this determination is difficult; however, groundwater computer models are available to predict leachate flow and contaminant migration patterns. The difficulty arises in selecting the model's input parameters for leachate chemical characteristics, and in predicting the chemical reactions that will occur as the leachate moves through the soil.
The amount of leachate that drains from the base of the landfill will depend upon the type of liner, how successfully the liner is installed, and the procedures employed for removing leachate from the landfill. For soil liners, a liner efficiency can be calculated if data regarding soil permeabilities ms available. Am example of the results of a liner efficiency calculation, for a clay liner, is shown in Figure 3.
The projected liner efficiency of 81% indicates that 19% of the leachate will eventually drain through the liner. If this quantity is determined to be potentially detrimental to groundwater quality, then a more efficient liner can be designed. One possibility would be to incorporate a geosynthetic membrane into the liner system. Implicit in the design of the soil liner with the efficiency calculation is the slope of the soil liner at the base of the landfill and the spacing of leachate collection lines. The leachate retained by the liner must be removed for treatment or a portion recycled.
Geosynthetic liners may complement or be used in place of clay liners. The typical geosynthetic lining material is 40-to 80-thousandths-of-an-inch-thick flexible sheets which can be bonded to adjacent sheets with thermal or chemical bonding equipment. Many configurations are available for installing geosynthetic liners. Composite liners utilize a combination of geosynthetic and clay liners. The geosynthetic liner is placed immediately on top of the clay liner. Sand above the geosynthetic liner carries leachate to time collection system. Alternately the sand may be replaced by high-strength geosynthetic grid or mesh material which is less than one-half-inch thick and capable of transmitting large quantities of leachate to the collection pipes.
Double geosynthetic lined landfills utilize two layers of liners and leachate collection systems. The upper layer is the leachate collection liner. The lower layer acts as a leak detection liner, should the upper liner develop a hole.
Liner systems, clay, geosynthetic. or combination, cost hundreds of thousands of dollars per acre. An interesting design consideration is the reduced volume that a geosynthetic liner system occupies within the increased volume of the landfill, A 367-foot-thick clay liner system may, depending on regulatory controls, be replaced by a geosynthetic liner system that is less than one foot thick. The geosynthetic liner system will cost more per acre but the added cost may be more than offset by the additional revenue which results from having a larger volume available for landfilling. Similar considerations apply to landfill covers constructed with geosynthetics.
When the design concepts for the leachate control system are completed, laying out the landfill on maps and engineering plan-sheets can begin. .


Develop detailed design

Preparation of the first map usually shows the landfill location in relation to surrounding communities, roads and other features. A topographic map of the area published by time U.S.
Geological Survey can be used as a base map. Note, however, that some features such as buildings, roads, and stream Iocations may have changed since this map was produced. A recent air photo, which may be obtained from a state or local zoning, transportation, or other agency, will help to update these maps.
Next, a detailed site map with a scale of one inch equaling 200 feet is prepared. Contour lines are drawn at two- or five-foot intervals, the property Iine is determined accurately, easements and rights-of-way are indicated. Utility corridors, buildings, wells, roads and other features are located, drainageways are marked, and neighboring property ownership and land use are shown.
Detailed design follows with the selection of landfill base elevations, top elevations, and slopes. Development is usually planned so that the landfill can be constructed and operated in phases. T he site plans should describe landfill development in sequence, showing the chronological order in which the features are to be developed (Figure 4). Dividing the project into phases minimizes the amount of open landfill surface, thus reducing the potential for the accumulation of rainwater within the site that would require special handling. As each phase is completed, that portion of the landfill can be closed and final cover placed over the waste.
A final advantage of phasing is that premature closure of the landfill is more practical and economical in the event of an environmental problem. In a well-planned phase development, the landfill's end use can be implemented in the completed sections while other areas are still being utilized for disposal purposes.
Some regulatory agencies will mandate the construction of screening berms or fences around the active areas of the landfill. The extra soil needed for berm construction must be accounted for when planning excavation work. The height of time berms will depend upon the lines of sight into the landfill from adjacent areas.
Concurrent with the development of plans for liners, covers, service roads, and embankments soil cut and fill balances must be calculated. The best designs provide for earth-moving procedures that minimize soil movement. Substantial volumes of earth will be required for cover and possibly liners. When practical, the phases should be laid out so that earth excavated is immediately used as cover. When stockpiling is necessary, the work should be organized so that stockpiled soil may be heft undisturbed until needed.
After the completion of the phasing diagrams and earthwork balances, a table is prepared which summarizes the waste each phase of the landfill.







The Davao City P268 million Sanitary Landfill


A legacy to healthy living


By ROGER M. BALANZA

“Our focus on the environment and natural resources will be principally directed on ecological solid waste management, watershed rehabilitation and coastal resource management. We will continue to pursue the path to sustainable development of our city.”


In December last year, Mayor Rodrigo Duterte gave the Dabawenyos the biggest gift of all: the P268-million ultra-modern Sanitary Landfill in Barangay New Carmen, Tugbok District.



Built on a 3.8-hectare property, the landfill, in compliance with Republic Act 9003 or the Ecological Solid Waste Management Act of 2000, has a capacity of 1.2 metric tons of residual garbage and a life span of eight to ten years.


With the project, Davao City is among few local government units which complied with RA 9003, which poised administrative charges against local officials failing to establish sanitary landfills five years after the approval of RA 9003.


RA 9003 is also known as “An Act Providing for an Ecological Solid Waste Management Program, Creating the Necessary Institutional Mechanisms and Incentives, Declaring Certain Acts Prohibited and Providing Penalties, Appropriating Funds, therefore, and for other purposes,” mandates for all LGUs to be at the frontline in the implementation of the mandatory segregation of biodegradable, non-biodegradable and special wastes, recycling and composting and the establishment of a materials recovery facility (MRF).”


The ultimate aim of RA 9003 is to reduce garbage volume starting at home, with the community joining hands in segregation and recycling.


Davao City has long practised throwing the nearly half a million tons of annual garbage volume churned out by its 1.4 million inhabitants into open dumpsites which is now outlawed by RA 9003.


In compliance with RA 9003, the landfill operates through the principle of waste segregation starting from the homes to the site to reduce waste to a few tons of residual waste.


At the landfill, engineering designs prevent leachate from seeping into water tables, thus protect the city’s water resources.


Recycling transforms residual waste into bricks and tiles. Chemicals convert soft garbage through the process of decomposition using biologically-friendly processes to produce solid, liquid, and gaseous products.


The operation of the Sanitary Landfill as provided in the city’s Ecological Solid Waste Management Program has four components: public awareness campaign; waste segregation into biodegradable, recyclable, and residual components; recycling and composting of recyclable and biodegradable components; and landfilling of residual solid waste.


While the last is in full operation, sanitary personnel have yet to set into place the three others, particularly on the manner of segregation at the homes.


Nevertheless, the education, information campaign tapping barangays which are given responsibility to be active players in the solid waste management program are on stream. Some barangays have institutionalized the Materials Recovery Facility (MRF), also mandated by RA 9003, which is the second step to recycling at home to reduce residual waste destined for the Sanitary Landfill.


The 3.8-hectare facility meets the standards of the National Solid Management Waste Commission Technical Guidelines for Sanitary Landfill Design and Operation.


It was designed by IPM Construction and Development Corporation and conforms to international standards on sanitary landfills, with lycheate retention pond, monitoring wells, drainage system, and gas vents. Mayor Duterte admitted garbage disposal is a major problem and the Sanitary Landfill is in reponse to this concern.


Mayor Duterte said a major focus of his administration is the preservation of the environment and public health through ecological solid waste management, watershed rehabilitation and coastal resource management.


The buck however does not stop at the Sanitary Landfill, whose three support components are still to be perfected.


“We will continue to pursue the path to sustainable development of our city,” Duterte said. 

Establishment of Bayawan City's Waste Management and Ecology Center: An Environmental Milestone
ByJouke D. Boorsma, German Development Service & Ion T. Bollos, Eric O Torres, and Antonio S. Aguilar. Bayawan City, Negros Oriental
Date Released: May 20, 2009

To enhance its local solid waste management system and to implement the legal prescriptions of RA 9003 the Local Government Unit (LGU) Bayawan City established a new 10-Year Solid Waste Management (SWM) Plan in 2004, which also proposed to implement a city Waste Management and Ecology Center. Based on the outline of the SWM Plan, the LGU conducted a site selection survey, prepared the needed planning documents and gained an Environmental Compliance Certificate from the Environmental Management Bureau in June 2008. Since then various construction works are conducted at site to establish the first fill unit of the clay-lined landfill, a composting plant, a material recovery facility, a septage treatment facility and a wastewater treatment facility to treat the leachate from the landfill and the supernatant from the septage treatment. The project focuses on the application of appropriate technologies and utilizes local equipment, local expertise and local materials to reduce project cost as far as possible.

The evaluation of local waste characterization data was the main initial consideration to outline the city solid waste management system. The results illustrate the actual composition of waste generated (biodegradable, recyclable, residual and special waste) within the collection area and provide a basis for its projection in the whole LGU, whereas the quantity of wastes determines the following:

  1. Land area requirement for a sanitary landfill;
  2. Type and specifications of collection trucks;
  3. Frequency of waste collection activities;
  4. Area requirement for material recovery (MRF) and composting facilities.

Outline of the Bayawan Waste Management and Ecology Center (BSWMEC) The following sketch shows the general site development plan of the Bayawan Waste Management and Ecology Center (BCWMEC), which comprises 26 hectares. After designing the general site development plan, the task of the involved Bayawan City engineers was to identify and establish the detailed engineering components for project implementation. The first and most challenging part was to plan out   the   first   fill    unit   (waste disposal cell) of the Sanitary Landfill (SLF) component.

Establishment of base liner technology for the landfill component The following figure shows the details of the dimensions and outlay of waste disposal cell 1. The planning followed the legal prescriptions of RA 9003 and applicable technical standards. The City decided to use bentonite as a clay additive instead of a synthetic liner to reduce material cost since HDPE liner is rather costly. Initially it was proposed that a 20 - 80 mixture (20% bentonite clay/80% host clay) should be used. However, hauling cost to bring in bentonite clay was too expensive, since the bentonite
clay source is located at the other side of Negros Island more than 200 km away from Bayawan City. Hence, the viability to further reduce bentonite content to 10% of the base liner was explored. To safeguard the quality of the clay liner and to especially check whether the permeability coefficient meets the standards set by RA 9003, several samples were sent to the Department of Science and Technology (DOST). The outcome of the sampling for the 10-90 mixture (10 percent bentonite/90 percent host clay) was 3.44x10"10 m/sec, which confirmed the use of the mixture as liner, having exceeded the permeability coefficient of 1.10"8 m/sec set by RA 9003 for a category 2 landfill. The optimized clay liner mixture translates to cost savings of approximately 1 million pesos for the City.

Sanitary Landfill under construction

Directly after the issuance of the Environmental Compliance Certificate, the LGU Bayawan City started with site development, construction of access road, site fencing, excavation works at the fill unit 1 and the base liner construction. As elaborated during a landfill construction workshop organized by GTZ/AHT in February 2009, working with clay is a challenging job. In order to reach maximum compaction, the mixture should be compacted at around a moisture content of 26 %. Preferably, the compaction should take place at the wet side (a little bit above 26 percent). Instead of being a summer month as expected, April 2009 turned out to be rather wet and brought a total of 14 rainy days with a corresponding 173 mm ample rainfall. Data from the city's weather station showed a maximum rainfall intensity of 140 liters per square meter per hour. Consequently, the construction of the sanitary landfill faced an unexpected delay due to the changing weather patterns.

In order to extend the lifespan of the landfill, a Materials Recovery Facility (MRF) will be constructed to recover recyclables and to prevent disposal of biodegradable waste into the cell. According to the local waste characterization study conducted in 2003, the LGU collects approximately 6 tons of residual, 4 tons of recyclables and 8 tons of biodegradable waste every day. Assuming that only 6 tons residuals arrive at the landfill and the SLF operation is able to attain a compaction rate of 350 kg/m3, the lifespan of the landfill unit 1 will be in the magnitude of 9 to 10 years.


However, with the extensive information and education campaign (IEC) conducted in line with the implementation of a fee system for the collection of both biodegradable and non-biodegradable waste, it is likely that the current waste management practices may render the 2003 data inapplicable. To verify changes in waste generation a follow up waste analysis and characterization study was recently conducted, which will be finalized in June 2009. The study may also assist to adjust the planning of detailed components for composting and material recovery at the BCWMEC as well. Besides, the results will also clarify if the projected lifespan of the sanitary landfill is sufficient to accommodate residual waste from neighboring municipalities later on.


In addition to the landfill and the MRF component, the LGU decided to integrate a sludge treatment facility to enhance the liquid waste management as well. With this, the City goes one step further to utilize the project and to add initiatives to maintain a clean environment. The system consists of two storage tanks connected to drying beds. Recently the City acquired two declogger trucks which will be used to collect septage from households in the city. The collected septage will be stored for approximately 30 days in the storage tanks and subsequently emptied into the drying beds. The whole system is connected to a waste water treatment system in which the leachate from the landfill is treated as well. The outlined project is a further pioneering effort of Bayawan City to show the way in implementing environmental laws and to likewise provide the needed infrastructure to perform environmental duties and to safeguard a sustainable local development with environmental preparedness.

Waste Not, Want Not: Fungi as Decomposers




Certain species of fungi and bacteria are the engines of the process of decomposition. When plants grow and produce new leaves, fruits, and stem wood, they use scarce nutrients like nitrogen to make the new tissues. Over time, without decomposition, so much nitrogen would be locked up in leaves and other tissues that there would not be enough nitrogen available for the plant to make new leaves, stems and wood. The surface of the ground would also be buried by dead leaves and wood lying forever where they fell.

Fungi and bacteria are the major organisms decomposing dead leaves and other organic matter. Here, we do not use the word "organic" in the same way it is used by the food industry. In Biology and Chemistry, "organic" describes any material made up of molecules containing carbon and hydrogen atoms. All living things, and a few other surprising substances, are considered organic. Decomposition is a complex process. Organic matter is broken down into carbon dioxide and the mineral forms of nutrients like nitrogen. It is also converted into fungi and bacteria through these organisms feeding on the organic material and reproducing. Scientists call the organisms that decompose organic matter decomposers, saprobes or saprotrophs.

Decomposition is made up of a number of subprocesses. Consider the decomposition of leaves. Earthworms and other soil animals break the leaves into smaller pieces in a process called fragmentation. This is an important step, because smaller fragments have more surface area to support the growth of bacteria and fungi. Bacterial growth is especially affected by fragment size, since fungi can penetrate substances more easily than bacteria. Rainwater percolates through the leaves, dissolving and carrying away some of the chemicals in the leaves in a process called "leaching". The movements of earthworms and other soil animals stir the leaf fragments and mineral soil particles together in a process called "mixing". The result of the interaction of these processes can be seen in the changes in the leaves. The fallen leaves started out whole, and were green, yellow or red. They were reduced to small dark brown shreds as their fragments became heavily colonized by fungi. Finally, at the end of the processes of decomposition, they have become fine black particles of soil organic matter, and their original shape no longer exists.

The speed at which the decomposition occurs, called the "rate of decomposition", depends on the temperature, moisture and chemical composition of the organic matter. If the temperature is too low, or too high, fungi and bacteria cannot grow and the rate of decomposition is slow. If the leaves have a low nitrogen content, the rate of decomposition is slowed because fungi and bacteria can not extract enough nitrogen to make proteins they need for growth. The oxygen level is another important factor, since fungi require oxygen for growth. In lakes and other low oxygen environments, fungal growth will be slower and thus decomposition will be slow.

If decomposition could not occur, the nitrogen in dead organic matter would remain locked up. Plant growth would decrease over time as the nitrogen the plants took from the soil was not replaced. This would be a catastrophe, because plant growth supplies all of our food. We need it to feed ourselves directly in the form of grain, fruits and vegetables, and to raise the animals we eat. By understanding the factors controlling decomposition we can protect our food supply, and increase plant growth.

Fungi and bacteria are not restricted to decomposing leaves and other plant materials. They will decompose any dead organic matter, whether it is a cardboard box, paint, glue, pair of jeans, a leather jacket or jet fuel. Jet fuel? Yes! — remember that jet fuel is made from petroleum, which is made of decomposed microscopic creatures from the oceans of the Mesozoic Era.

Decomposition can be a problem on a large and small scale. The U.S. military wouldn't want fungi to decompose uniforms and tents in a wet environment, or dissolve the glue holding the lenses in a pair of binoculars. Wooden buildings need regular attention to prevent their wood from being invaded by rot. In our own homes, we don't want our food to become moldy. Many times, we want to stop decomposition.

The enormous amount of organic matter produced by decomposition creates problems of storage and disposal. In nature, a forest produces about a pound of dead leaves and wood per square yard every year. This may not sound like much material, but consider the amount that would fall on an area the size of a football field or soccer field. An American high school football field, including end zones, covers 6400 square yards (120 by 53.3 yards wide). A football field-sized area in a forest would be covered by 6400 pounds, or 3.2 tons, of dead organic matter per year. A soccer field covers 8800 square yards (110 by 80 yards wide). An area this size in a forest would be covered by 4.4 tons of dead organic matter. To give an idea of how much material this is, remember that an average-sized car weighs only 1.5 tons.

American cities produce even more organic waste (garbage) than forests, and very little of it decomposes and becomes recycled into new plant growth by natural processes. Every resident of Los Angeles produces 7 pounds of garbage per day! This is equal to one ton of garbage per year per person. The disposal and recycling of nutrients in garbage is a large problem because of the huge amount of garbage produced every day. Sanitary landfills are the current solution to the garbage problem.

The first modern sanitary landfill was built in Champaign, Illinois in 1904. The phrase "sanitary landfill" was invented in the 1930s by Jean Vinenz, the commissioner of public works of Fresno, California. By 1945, about 100 American cities had sanitary landfills; by 1960 there were 1400. Before sanitary landfills were invented "dumps" were used to dispose of garbage. Dumps were open, the garbage was not covered, and the garbage was often burned. Dumps smell terrible, are often surrounded by blowing paper, attract flies and provide food for large populations of rodents. Sanitary landfills have less odor, there is no black smoke from burning tires and garbage, and the number of flies and rodents is greatly reduced, hence the term "sanitary".

The largest American sanitary landfill is the Fresh Kills Landfill on Staten Island, New York. It opened in 1948 and covers 3,000 acres, a rectangular area roughly 3 by 4 miles. When it reached full capacity and closed in 2001, its estimated height was 505 feet. If it had been allowed to get any taller, it would have interefered with air traffic.



Landfills are usually lined with several feet of dense clay and then sealed with thick layers of plastic to prevent leaks of hazardous chemicals. The garbage is dumped in rows or piles from 10 to 20 feet high. Bulldozers are used push the garbage into rows and squash large objects. Compactors with 5 foot wide studded rollers are also used to squash the garbage. Squashed garbage takes up less space extending the life of the landfill. Each day, soil, glass, or plastic foam pellets is spread over a landfill to reduce odors and pests. The soil covering also reduces the amount of rainwater that seeps in. Invading rainwater carries water-soluble chemicals out of the garbage to form liquids called leachates. When leachates pool in the bottom of the landfill, they are pumped out, collected and treated. The treated leachate is handled like sewage. The particles, called sludge, are separated from the liquid and burned, or used as fertilizer, or dumped in the ocean or back into the landfill. If the sludge is considered hazardous, it is shipped to a hazardous waste disposal site.

Landfills also produce methane gas. Once landfills are full, they are often capped with a layer of clay. The cap excludes water, reducing the danger of chemicals leaching from the landfill into the surrounding soil and groundwater. The cap also greatly slows the movement of oxygen from the atmosphere to the buried garbage. When the oxygen available below ground is used up by fungi and bacteria, their decomposing activity stops. Easily decomposed organic substances will continue to be broken down by anaerobic bacteria, which can live where no oxygen exists. Methane gas is one of the products of their decomposing activity. The anaerobic condition (very low to no oxygen) and low moisture level in the garbage stops or greatly slows decomposition. The garbage is essentially "mummified" in this stable environment. Newspapers that have been buried in landfills can still be read 20 years later. Only one-third to one-half of even easily decomposed materials such as lawn, garden and food waste is decomposed after 20 years.

The newest landfills contain a system of perforated pipes to collect methane gas. Methane is one of the main ingredients of natural gas, and is dangerous because it is explosive in high concentration. In April, 2000, a house in Michigan was destroyed when methane seeped from an old nearby landfill into its basement and then exploded. To dispose of methane, it is sometimes released into the air or burned, but it can also be purified and used as fuel. Releasing methane into the atmosphere is not recommended because it is a potent "greenhouse gas". Methane and other greenhouse gases are responsible for destroying part of the ozone layer in our atmosphere, which protects us from harmful solar radiation.

Landfills are expensive to build and run. The cost of landfills can be reduced by making them last longer, which means filling them more slowly. One way to reduce the amount of garbage being deposited in landfills is for homeowners to compost lawn, garden and food waste.

Homeowners usually construct a compost heap from a mixture of lawn and garden waste (grass clippings, leaves, branches) and garbage. Paper and cardboard are sometimes added, but they take longer to decompose. The resulting compost is a soil which contains a high percentage of fine organic matter whose nitrogen and other nutrients can be easily used by plants. Compost can be used to pot plants, or enrich the soil in vegetable and flower beds. By using what we know about decomposition, homeowners can adjust the rate at which the compost heap decays. The rate of decomposition can be increased by adding earthworms, mixing the contents occasionally, adding chemical fertilizer, and the keeping the heap moist. Chemical fertilizer is added when the organic material has low nitrogen levels, because fungi and bacteria also need nitrogen to grow. Mixing the compost is probably the hardest step, because a cubic yard of compost weighs about a ton.


Ants may have discovered composting before us. Fungus growing ants collect leaves and inoculate them with a fungus that decomposes the leaves. The ants harvest the fungus for food and discard the decayed leaves.





Web Resources and Further Reading

  • Cornell Composting - Everything you wanted to know about composting. Includes projects.
  • Introduction to the Mesozoic Era from the Museum of Paleontology at the University of California, Berkeley -- an illustrated introduction to the era that gave us our fossil fuels.
  • Fresh Kills lifescape: Introduction & objectives - Photos of the landfill, and the natural areas that have been established there. The word "kill", as used here, is a Dutch word for a stream or creek. It is common as part of place names in areas of North America, like the New York area, that were first settled by the Dutch.
  • Dickinson, C. H. and G. J. F. Pugh. 1974. Biology of plant litter decomposition. 2 volumes. Academic Press, New York. ISBN 0-1221-5001-5.
  • Mason, C. F. 1976. Decomposition. Edward Arnold Publ. Ltd, Southampton. ISBN 0-7131-2589-6.
  • Rathje, W. and C. Murphy. 2001. Rubbish: The archeology of garbage. University of Arizona Press, Tucson. ISBN 0-8165-2143-3.
  • Trautmann, N. and M. Krasny. 1997. Composting in the Classroom: Scientific Inquiry for High School Students. A comprehensive guide for teachers. ISBN 0-7872-4433-3.

 

Sanitary Landfill Operation

 Equipment,
safety, operational strategies, and operator training..


Operating procedures at a sanitary landfill are determined by many factors, which vary from site. The landfill operational plan prepared as a part of the desing procedure serves as the primary resource document, providing the technical details of the landfill and procedures for constructing tre various engineered elements.

Since a landfill is constructed and operated over number of years, it is important that personnel continually consult the plan to assure conformance with the plan okver the long term. If operating produceres must be noted so that an accurate record is maintained. Changes in operating procedures often need regulatory agency approval, and careful planing is necessary to make a smooth transition to a revised operating plan.
After receiving the required site desing approvals from the appropriate authorities, preparation and construction of the site can begin. Table 1 lists the steps to be completed for site preparation and construction. However , at a given site, the steps may not necessarily follow the exact order shown.T

Site Preparation and Construction Steps
  1. clear site.
  2. Remove and stockpile topsoil.
  3. construct berms.
  4. Install drainage improvements
  5. excavate fill areas.
  6. stockpile daily cover materials.
  7. install environmental protection facilities (as needed) : 
    a. landfill liner with leachate collection system, 
    b.groundwater monitoring system, gas control equipment and gas monitoring equipment.
  8. Prepare access roads.
  9. construct support facilities: 
    a. Service building, 
    b. Employee facilites, 
    c.Weigh scale, and 
    d.Fueling facilities.
  10. Install utilities:
    a.Electricity
    b.Water
    c.Sewage, and
    d.Telephone
  11. Construct fencing:
    a.Perimeter
    b.Entrance
    c.Gate and entrance sing, and
    d.Litter control
  12. Prepare construction documentation (continuosly during construction)

Development of the complete landfill may be divided into stages, some of which are completed many years after the opening of the site. As with other construction projects, all the work should be documented. While commonly overlooked in landfill construction, documentation can be invaluable when questions arise in the future regarding the adequacy of site construction. Documentation is important for proving to regulatory authorities and local committees of concerned citizens that design standards are actually being implemented. Also, good documentation can case repairs if they become necessary.

Guidelines shown in Table 2 list important considerations when placing the landfill into operation.


Landfill equipment use


Equipment at sanitary landfills falls into five functional categories: site construction, waste movement and compaction, cover transport, placement and compaction, and support functions.

Landfill site construction is often done by contractors employed by the site developer. Whether the work is done by contractors or site personnel, good construction management and coordination of equipment is essential. Conventional earth moving equipment, including scrapers, bulldozers, excavators, trucks, and graders, is usually employed. Specialized equipment is needed for the installation of geosynthetic Tabl


Twelve Suggested Rules to Guide Landfill Operation

  1. Start landfilling on high ground and work toward low ground.
  2. First fill on the windward side of the site.
  3. Spread each load of waste and thoroughly compact it using a heavy, wheel-type landfill compactor, if available.
  4. Never deposit wastes against the advancing wall of the excavation.
  5. Once a load of soil has been picked up by an earth-moving machine, do not put it down until it is in its final resting place in the landfill.
  6. Keep the active area as small as possible and fill upward to final grade as directly as possible.
  7. Use the proper equipment and use it well within its capabilities.
  8. Build interior haul roads high and drain them well.
  9. Put interior haul roads on top of completed areas.
  10. Keep intermediate waste slopes three horizontal to one vertical.
  11. Keep surface and groundwater away from waste.
  12. Keep trucks and equipment off all inactive areas.

and soil liners. This includes specially adapted tractors and cranes for moving synthetic liner material and compaction equipment for placement of soil liners at the desired permeability.

Waste movement is usually confined to the spreading of wastes on the working face with compactors or dozers after the wastes are deposited by the truck. Movement over long distances is inefficient with this equipment.
Figure 1 shows a typical operation. Periodically, usually daily, the compacted waste is covered with earth and a new cell is started. An alternative to soil cover is the use of manufactured foams or temporary blankets. Foams require specialized application equipment to spray the material onto the compacted waste. Blankets can be lifted into place with a crane, or specially equipped tracked excavator, and then removed the following day before waste placement begins.
At some sites, wastes may be deposited at the top of the working face, making it easier to spread the wastes over the face. Litter control nay be more of a problem when this procedure is used.


Landfill equipment selection

Selection of type, size, quantity, and combination of machines required to spread, compact, and cover waste depends on the following factors:
  • Amount and type of waste to be handled;
  • Amount and type of soil cover to be handled;
  • Distance cover material is to be transported;
  • Weather conditions;
  • Compaction requirements;
  • Landfill method utilized;
  • Site and soil conditions such as topography, soil moisture, and difficulty in excavation; and
  • Supplemental tasks such as maintaining roads, assisting in vehicle unloading, and moving other materials and equipment around the site.

The amount of waste produced by a community is the major variable in selecting the appropriate size machine. Table 3 shows equipment needs by population and waste generation amounts. 

The type of waste to be handled strongly influences the machines to be used. Proper machines can be selected after identifying major solid waste components for a community. For example, at a site receiving a high proportion of hard-to-compact, heavy industrial waste (bricks and concrete), a compactor might not achieve normal compaction densities and the pushing and gripping ability of a track-type tractor may be needed.


However, a small track-type tractor has more difficulty compacting bulky wastes than a landfill compactor. Landfills accepting only shredded wastes are operated much like landfills handling unprocessed wastes, although there may be less need for daily soil cover, and there will usually be less trouble with waste compaction. Landfills handling baled wastes have substantially different operating procedures and requirements. Not only are soil cover requirements often less stringent, but the bales can be handled with forklifts or similar types of equipment, without the need for compaction equipment.


Compaction requirements


Degree of compaction is a critical parameter for extending the useful life of a landfill. For achieving high in-place waste densities, a compactor may be necessary. A minimun in-place compaction density of 1,000 pounds per cubic yard is recommended.

The number of passes that the machine should make over the wastes to achieve optimum compaction depends upon machine wheel pressure, waste compressibility, land and fuel requirements, labor costs, and work load. Generally, three to five passes are recommended to achieve optimum inplace waste densities.
Although additional passes will compact the waste to a greater extent, the return on the effort diminishes beyond six passes. An experienced operator will know if additional passes will result in greater compaction.
The graphs in Figure 2 show the relationship between waste layer thickness, number of passes, and the compacted waste density found in a field test for a particular type of machine and operating procedure. Each landfill will have different results, but the shape of the curves will he similar.
Note the rapid decrease in density after a thickness of about 1 1/2 feet. Thus, the most efficient solid waste compaction should be in a number of thin layers up to the total cell thickness and not in layers greater than two feet thick.
The working face slope will also affect the degree of compaction achieved. As the slope increases, vertical compaction pressure decreases. The highest degree of compaction is achieved at the grade with the least slope However, the feasibility of flat working face grades has to be weighed against the larger area over which the solid wastes must be spread.


Landfill equipment


Steel-wheeled compactors are designed specifically for compacting solid wastes. Wheels are studded with load concentrators of various designs. This equipment gives maximum compaction of solid wastes. Steel-wheeled compactors are best suited to medium or large sanitary landfills.

A variety of attachments may be added to give the versatility required in small one-machine operations. This equipment is best used on level or gently sloping surfaces, and will not perform as well as tracked equipment on steep slopes or under wet conditions.
A loader-type front-end blade can add to the versatility of these machines. This attachment will allow excavation and carrying of soil for cover material. Cover material can be moved distances of up to 300 feet economically.
Track-type tractors may be used for site preparation as well as road construction and maintenance. Ripper attachments are available and can increase usefulness in frost conditions or unconsolidated soil. These machines work well in wet conditions due to high traction.
Track-type loaders are designed similarly to track-type tractors.. Instead of a push blade, they are equipped with a bucket for digging and carrying materials. Track-type loaders are similar to track-type dozers in versatility; they have the added ability of lifting and carrying soil without losing excavating and spreading ability. These machines are not equipped to pull scrapers, limiting hauling to short distances.
Rubber-tired scrapers are efficient for excavating and transporting soil for cover when the cover soil is greater than 1,000 feet from the working face. Where the soil is hard to excavate (e.g., clay or frozen soil), scrapers can be pushed with a bulldozer. Rubber-tired compactors may be needed for clay liner compaction.
Some site operators are replacing their scrapers with trucks, using them in combination with excavators or end loaders. In their opinion, this equipment is better suited to move large quantities of soil greater distances than a scraper. For large projects, off-road trucks with 30-yard capacities are used.
Backhoes are best employed for small, specialized excavation at the landfill, such as leachate collection system excavation. Dump trucks can be useful at landfills for the transportation of cover material in conjunction with other equipment to excavate the earth.
Draglines are also efficient earth movers, but are only able to deposit soil within the area reached by the boom and are not suitable for transporting cover material. They can be used in combination with other pieces of equipment, including loaders and trucks. Draglines are especially efficient at trench-type landfills, where the entire trench is often constructed prior to being used for waste disposal.
Motor graders are useful for road construction and maintenance, construction of berms and drainage ways, and landscaping.
Equipment maintenance is clearly an important task. Regular maintenance can reduce repair problems before more costly and time-consuming repairs are needed. Equipment manufacturers provide instructions for periodic maintenance and will provide assistance with equipment maintenance and repairs. It is imperative that a periodic preventive maintenance program be implemented and supported by a well-equipped maintenance shop.
Cold weather brings many problems in starting and operating machinery, keeping employees comfortable, and obtaining cover material. Equipment manufacturers can offer recommendations for cold weather starting and operating. Cabs, proper clothing, and employee facilities will help improve employee comfort.
Wet weather problems are especially serious with soils that have high silt or clay content. When wet, these soils become very muddy, and provision should be made to continue operation in areas of the fill that are less susceptible to problems.
Wet weather plans should include measures to reduce tracking of mud from the landfill onto the road system and provisions for cleaning trucks.


Litter and fire control


Litter does not seriously damage the environment, yet it is perhaps the most persistent operational problem cited by surveys. lts seriousness is due, in part, to bad public image.

Waste discharging procedures, orientation of the working face to the wind, existence or absence of nearby wind shielding features, and waste type and preparation all play a role in solving the litter control problem. Unloading wastes at the bottom of the working face can help. Here the wind cannot pick up materials as easily as when wastes are deposited at the top of the working face.
If the trench method is used, it is often recommended that the trench be at right angles to the wind. An open landscape will allow the wind to blow unimpeded, thereby increasing the likelihood of litter. Planting trees or constructing berms can reduce the wind velocity and, hence, litter problems. Portable fences are often used to catch the litter, followed by manual cleaning of the litter fence and the area downwind of the working face. The fence should be cleaned at least daily.
An alternative approach, which has been particularly effective at small sites, is to require all wastes to be bagged for pickup.
Dust can also be a nuisance at landfills, both to employees and neighbors. Water wagons can be used to control dust. Calcium chloride is also used for dust control, since it absorbs moisture from the air.
Fires within the waste are best controlled by digging out the combusting material and covering it with dirt. Each equipment operator should have a fire extinguisher readily available. Expensive pieces of equipment should be protected with automatic fire detection and suppression equipment.
Water wagon equipment can be used for fire control. Also, arrangements should be made with local fire-fighters to establish procedures for extinguishing landfill fires.


Hiring and training


To maintain an efficient landfill operation, employees must be carefully selected, trained, and supervised. Proper landfill operation depends on good employees.

Along with equipment operators, other necessary employees may include maintenance personnel, a scale operator, laborers, and a supervisor. People will also be needed to keep financial and operating records.
The landfill manager should have experience in operation of an advanced technology landfill and, in addition, receive technical and managerial training. Several institutions and associations conduct training courses for landfill operators. Some state agencies require that the landfill's manager participate in a training program and successfully complete an exam. In addition to several states, the Solid Waste Association of North America conducts courses and offers a certification exam.


Accidents are preventable


Accidents are expensive, with hidden costs often several times more than the readily apparent costs. Solid waste personnel work in all types of weather situations, with many different types of heavy equipment, with a variety of materials presenting diverse hazards, and in many different types of settings.

The types of accidents possible at landfills include direct injury from explosion or fire; inhalation of contaminants and dust; asphyxiation due to workers. entering a poorly vented leachate collection system, manhole, or tank; falls from vehicles; accidents associated with the operation of heavy earth-moving equipment; attempting to repair equipment while the engine is operating; exposure to extreme cold or heat; or traffic accidents at or near the site.
Safety guidelines specific to the operation of the landfill equipment are shown in Table 4. Educational films and written material on safety at the landfill are available from the federal government as well as equipment manufacturers.
Assistance in setting up a safety program is available from insurance companies with workers' compensation programs, the National Safety Council, safety consultants, and federal and state safety programs.


Quality control and record keeping


During site construction, a quality control program should be followed to assure the landfill is built in accordance with the design plans. An inspector should be on-site to approve construction work as each structure is completed. Compliance with specifications should be checked by soil tests before waste is placed over the liner. Grades and elevations can be measured with surveying equipment to document the as-built features of the landfill.

Some operational records that should be maintained include: waste quantity by tons or, preferably, by volume, since landfill capacity is by volume; cover material used and available; equipment operation and maintenance statistics; landfill costs; labor requirements; safety statistics.; and environmental monitoring data. Data op waste loading with allow the site operator to predict the useful remaining site life of special equipment or personnel requiremets. Financial records are especially important to ensure that the operation is sound.



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Protective Liner Uses and Landfill Application

 

INTRODUCTION

With the increase of industrialization, companies are producing more wastes that need to be treated proir to being released into the environment. When residual or solid wastes are produced from municipal authorities or from mills as slag, a hazardous leachate usually results from the exposure to weather. A liner system is installed to prevent the contamination of the soil or groundwater by the hazardous leachate. Lining systems can be utilized in the application of leachate collection ponds, subsurface wall barriers, and to create landfill cells. The majority of the lining systems being installed today are for solid waste landfill cells. Due to the differences among industries, many chemicals must be treated from these leachates. This variation forces liner companies to produce a wide variety of liners that are chemical resistant. The installation process and the specific types of liners that can be used will be discussed in the further sections.




LINER TYPES AND USES

  • GEOMEMBRANE: Geomembrane liners are made of high-density polyethene to ensure maximum security of the solid waste contaminant. There are a variety of choices of geomembrane liners that the liner companies manufacture to suit the needs of the lining system. The simplest difference that is offered are geomembranes which are textured or smooth. A smooth geomembrane liner is normally used for collection ponds since they are not covered with soil or other liners. Collection ponds also do not have steep side slopes which results in minimal slipping if additional liners are placed. A textured geomembrane is typically used for mining and solid waste landfills. This creates a surface for additional layers such as geocomposite or soil to adhere to and releases pressure from the seams of the liner. Other types of geomembrane liners that are available are white geomembranes, which will cut back on thermal expansion and also create a cooler environment for the workers due to light reflection. This type of geomembrane is typically used in solid waste landfills. A flame retardent geomembrane is available from certain companies. It can be used in areas such as nuclear facilities and petrochemical applications. Finally, there is a conductive geomembrane that has been made available by the GSE Lining Company. This liner can be used for a collection pond and provides a simple procedure to test for damages. This is accomplished by using a unique type of spark testing. This was constructed for collection ponds that are exposed to the elements and have increased chances for damage. The primary use of the geomembrane liner is to contain the contaminants of solid waste.


  • GEOCOMPOSITE:Geocomposite is a combination of two types of liners. The first and main component is a geonet. The geonet is a high density polyethylene net that is usually placed either above or below the geomembrane liner. This net is used as a collection system for the leachate produced by the solid waste. The second component that makes up the geocomposite liner is a nonwoven geotextile. This geotextile is bonded to the geonet either on one side or both. The purpose of the geotextile is to prevent any soil from clogging the geonet. This ensures proper collection of the contaminant. The geotextile, when layed over a textured geomembrane, acts as a adherent preventing the geocomposite liner from slippping on the steep slopes of the landfill cell. The geocomposite leads to the final step of the lining system.

  • GEOSYNTHETIC CLAY LINER:The geosynthetic clay liner(GCL) acts as a substitute for a compacted layer of bentonite clay that is usually placed over the geocomposite to complete the lining system. The GCL, with its easy deployment, gives the contractor the ease of rolling out a clay layer that would normally have to be placed and compacted by heavy machinery, adding risk to damaging the liner system. The GCL can be used as a protective cap to cover the landfill as well. (GSE Lining Technology,1996)




LINER APPLICATION OF SOLID WASTE LANDFILL

The liner installation process for a solid waste landfill is a process that takes several weeks due to the precautions that need to be taken. These precautions help to ensure damage free installation. It is up to the design engineer and the engineer of the company having the liner installed to decide what type of liner should be used. Most primary liners used today are made of high density polyethylene (HDPE) with a minimum of 60 mil (1.5 mm) thickness; HDPE liners can be smooth or textured. With the way landfills are being constructed today, to optimize space and revenue, the sidewalls of the cell tend to be very steep. Having steep side slopes can sometimes cause the cover soil to slide and create added stress to the seams of the liner and the liner itself. This is why companies have designed the textured liners to optimize friction control and keep the liner and cover soil in place during its operation. These primary liners are used in the cell to contain hazardous leachates and protect the groundwater surrounding it. The second most important part of the liner system is the geocomposite. The geocomposite lining is an HDPE net that provides a high in-plane flow for the leachate. The geocomposite lining acts as a a leachate collection system that has relatively high resistance to chemicals. Since this geonet is placed directly on top of the primary liner there is usually a geotextile that is bonded to it to prevent clogging from the cover soil. Most systems that use the textured geomembrane will also use the double bonded geocomposite. A secondary lining system is usually installed because of requirements for leak detection systems.
This secondary system is to monitor the primary liner on a regular basis. The secondary system is the same as the primary system consisting of a layer of geomembrane and either geocomposite or geonet. The use of any of these layers is dependent on whether a clay layer is used under the primary liner. This two liner system containing the primary and secondary systems is becoming the most widely used in order to ensure complete protection. Once the underlying system is complete a protective cover goes over the primary liner. This protective cover is usually a 18-36 inch compacted clay cover. The clay cover is placed at a specified moisture content to achieve ultimate compaction and protection of the primary liner. (GSE Lining Technology,1996)
The final stage in completing a landfill liner system is the landfill cover itself. Once the cell is filled with waste it must be covered to eliminate problems such as odor, litter, and most of all leachate production; leachate in a solid waste landfill is a result from precipitation. In order to contain the waste a flexable geomembrane cover is installed. It is crucial that the protective cover be able to contain hazardous methane gas production from the decomposition of waste. The decomposition and shifting of waste is the primary reason for a flexible cover. The liner system does not involve a complicated set up; however the precautions that have to be taken are never ending. Successful installation of a lining system can ensure the proper protection from hazardous leachates entering the groundwater or soil. (GSE Lining Technology, 1996)
Schematic of Liner System


LINER TESTING AND WELDING METHODS

Laboratory Testing : There are several tests performed on the geomembrane liners in the laboratory and they all follow the guidelines of the American Society for Testing Materials (ASTM). Some of these tests include Tensile, Stess Cracking, Multi-Axial, Density, and Melt Flow Index testing.


  • Tensile Testing (ASTM D638): Is the measure of the greatest tension the geomembrane can handle without tearing. In this test a liner specimen is placed in a machine and stretched until it breaks. This is recorded on a tensometer and sent to the engineer in charge.
  • Stress Cracking Test (ASTM D1693): This test is to find out how susceptable the geomembrane is to cracking when exposed to the environment. These stress cracks are less than tensile strengths and are caused by exposure to the environment. For this test a bend speciman is placed in a test vessel and submerged in a surface-active agent. After a given time interval the speciman is analyzed for cracks. Ideally the liner needs to be impervious to stress cracking.
  • Multi-Axial Testing (GM 4): Is a test that gives a more accurate representation of field performance of the liner. The liner is stretched 360 degrees all at once in a pressure vessel. This test lets there be no exposed edges as would be in the field. The peak deflection point is measured and recorded.
  • Density Testing (ASTM D1505): The determination of the density of liner through this test identifies certain properties that can predict chemical resistance, and some other physical properties. This density is determined by how far a sample will sink in a water/alcohol liquid column.
  • Melt Flow Index Test (ASTM D1238): This test gives the lab technician an idea of the polymer's molecular weight, viscosity, and processability. This test will help find uniformities in other polymer properties.

Welding Techniques:
  • Hot Wedge Weld : This welding technique allows the worker to guide the welder along the length of the liner fusing two liners together to create a leak proof seal. The hot wedge welder is self propelled and is capable of welding up to 15 feet/ minute. The hot wedge welder leaves a small gap between the two sealed liner sides. this gap enables the workers to use an air test to test the seam quality. The air test is a field test in which a needle and gauge are placed at one end of the seam and then pressurized. The seam, which can be up to 500 feet long, has to remain under pressure for 5 minutes. After the 5 minutes has passed and the seam passed the test, the needle is then removed and an extrusion weld is placed over the needle hole.


  • Extrusion Weld : This welding technique is used for placing patches that may be in the middle of a liner section, for welding boots around piping, and just fixing penetrations of the liner. The weld is different from the hot wedge weld because it leaves an extrudate on the top of the liner being welded. In this case an air test will not work so another field test known as the vacuum box test is used. The vacuum box test consist of placing a soapy solution all over the extrusion weld, then a box with a plexiglass top is then put on the weld. The weld then receives a 5 psi vacuum from the box and a visual inspection of the weld is performed. If the seam fails there will be noticable air bubbles forming from the soap.
  • Schematic of weld types




    LEACHATE COLLECTION AND CONTROL

    With the increase in solid waste that municipalities are generating (almost 200 million tons/ year) the solid waste collection and disposal constituants are growing fast. In the United States the most popular method for solid waste disposal is sanitary landfills. Many of the solid waste landfills that were developoed before 1988 had to either be shut down of reconstructed due to Subtitle D of the Resource Conservation and Recovery Act (RCRA) going into effect in the later part of 1993. Under Subtitle D leachate management must be properly implemented. The previously discussed landfill lining system prevents the leachate from seeping into the groundwater. The Subtitle D allows for the treatment of the leachate collected to be mandated by the states. One rule that must be followed by all states is that the leachate collected must be treated as industrial waste. Publicly owned treatment works have to be sure the leachate does not interfere with other treatment processes or sludge quality. 
    Production of leachate from sanitary landfills is an environmental hazard. There are several factors that influence the generation of leachate. Some of these are precipitation, runoff, evaporation, waste density, and depth of the landfill. It is said that not much leachate is produced until the landfill is fully saturated. The leachate that is generated comes from the decomposition of the landfill waste. This occurs in three possible stages: First aerobic decomposition dominates , in this phase the temperatures raise well above ambient temperatures and produce leachates mainly of soluble salts. The second stage is believed to be anaerobic decomposition. The first part of this decomposition produces large amounts of volatile fatty acids and carbon dioxide. The facultative bacteria then get taken over by the methane producing bacteria. These mathane producing bacteria, which require neutral pH, convert the facultative anaerobes into methane and carbon dioxide. The decomposition process eventually decreases with landfill age due to substrate depletion. Through all the decomposition processes and the water that percolates through from precipitation carries these contaminants to the bottom of the landfill producing the leachate. The liquid state leachate is not the only contaminant that must be regulated. Over time the decomposition process produces gases that may be emitted to the atmosphere. These gases also have to be regulated. As for the liquid leachate once it has been collected into the sump from the bottom of the landfill it must then undergo treatment before it can be distributed into receiving waters. 
    Treatment of landfill leachate is a difficult task due to the nature of the leachate. A typical landfill leachate usually starts out as a high-strength wastewater, having low pH, high biochemical oxygen demand (BOD) and chemical oxygen demand (COD), and the presence of toxic chemicals. This wastewater profile can change from landfill to landfill as well as within the same landfill as it ages. Due to the changes of the wastewater composition over time, sometimes 30 years, the conventional biological waste treatment and chemical treatment processes seperately do not achieve high removal efficiency in the effluent. When it comes to the design of treatment facilities factors that influence the design are leachate characteristics, effluent discharge regulations, costs, and permit requirements. Some of the common waste treatment processes that have been applied to the landfill leachates are Activated Sludge, Waste Stabilization Ponds, Aerated Lagoons, Trickling Filters, Rotating Biological Contactor, and Anaerobic Digestion.(Qasim and Chiang, 1994)
    Leachate Collection Process




    CONCLUSION

    For solid waste the future brings about a large emphasis on resource recovery and solid waste reduction. There will be less landfills and more innovative ways of disposing solid waste. One way will be through incineration with some sort of energy recovery system. Even though there will be less landfills in the future they will still play a major role in solid waste and residual disposal. Each year the design of the landfills and leachate control strategies will become more and more strict in order to protect the groundwater. So when the permit application is submitted by the municipality to the state, these applications will be looked at very closely to be sure the design engineer has properly designed the landfill. Desinging a landfill is not just the application of the liner system, there are issues of proper slopes for runoff, there has to be a sophisticated monitoring well system around the landfill, and most important the leachate must receive proper treatment before discharge. Under Subtitle D of RCRA all of these regulations are mandated and inforced through each state to ensure the safety of the soil and groundwater to be free from any solid waste contaminants 

    Acknowledgments

    • Tom Eld, Construction Quality Engineer at Almes & Associates
    • All photographs were provided and used with permission from Almes & Associates

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