EnE 301: ENVIRONMENTAL ENGINEERINGEnE 301: ENVIRONMENTAL ENGINEERING

3.0 Solid Waste Management3.0 Solid Waste Management

3.1 Overview of Solid Waste Management

3.2 Collection of Solid Wastes

3.3 Disposal by Sanitary Landfill

3.4 Resource Conservation and Recovery

3.5 Ecological Solid Waste Management Act of 2000-

RA9003

Disposal by Sanitary LandfillDisposal by Sanitary Landfill

• A sanitary landfill is defined as a land disposal site employing an engineered method of disposing of solid wastes on land in a manner that minimizes environmental hazards by spreading the solid wastes to the smallest practical volume, and applying and compacting cover material at the end of each day.

1) Public opposition

2) Proximity of major roadways.

3) Speed limits

4) Load limits on roadways

5) Bridge capacities

• Site location is perhaps the most difficult obstacle to overcome in the development of sanitary landfill. Opposition by local citizens eliminates many potential sites.

• In choosing a location for a landfill, consideration should be given to the following variables:

Site SelectionSite Selection

6) Traffic patterns and congestion

7) Hydrology

8) Availability of cover material

9) Climate (i.e. foods, mud slides, etc.)

10) Zoning requirements

• The plans and specifications for a sanitary landfill should require that certain steps be carried out before operations begin. These steps include:

Site PreparationSite Preparation

1) Grading the site area

2) Constructing access roads and fences

3) Installing signs, utilities, and operating facilities

• Two operating methods are employed at sanitary landfills, namely, the area method and the trench method.

OperationOperation

1. Area Method

• In the area method, the solid waste is deposited on the surface, compacted, then covered with a layer of compacted soil at the end of the working day.• Use of the area method is seldom restricted by topography; flat rolling terrain, canyon and other types of depressions are all acceptable.• The cover material may come from the site.

2. Trench Method

• Trench method is used on level or gently sloping land where the water table is low.• In this method, a trench is excavated, the solid waste is placed in it and compacted, and the soil that was taken from the trench is then laid on the waste and compacted.• The advantage of the trench is that the cover material is readily available as a result of trench excavation.

• Burning, which may cause air pollution is never permitted at a sanitary landfill.

• Odors can be controlled by covering the wastes quickly and carefully, and by sealing any cracks that may develop in the cover.

• Methane and carbon dioxide are the principal gaseous products emitted from landfill as a result of microbial decomposition.

• Leachate is the liquid that passes through the landfill and that has extracted dissolved and suspended matter. The liquid enters the landfill from external sources such as rainfall, surface drainage, groundwater, and the liquid in and produced from the decomposition of the waste.

Environmental ConsiderationsEnvironmental Considerations

• The design of the landfill has many components including site preparation, buildings, monitoring wells, size, liners, leachate collection system, final cover, and gas collection system.

Landfill DesignLandfill Design

• To estimate the volume required for landfill, it is necessary to know the amount of refuse being produced and the density of the in-place, compacted refuse. Compacted solid waste densities vary from 300 to 700 kg/m3.

• In order to prevent groundwater contamination, strict leachate control measures are required.

• The specified liner system includes a synthetic membrane (geomembrane) at least 0.75 mm thick supported by a compacted soil liner at least 0.6 m thick. The soil liner must have a hydraulic conductivity of no more than 1 x 10-7 cm/s. Flexible membrane liners consisting of high-density polyethylene (HDPE) must be at least 1.5 mm thick.

• The leachate collection system must be designed so that the depth of leachate above the liner does not exceed 0.3 m. The leachate collection system is designed by sloping the floor of the landfill to a grid of underdrain pipes that are placed above the geomembrane.

• The major function of the final cover is to prevent moisture from entering the finished landfill. If no moisture enters, then at some point in time the leachate production will reach minimal proportions and the chance of groundwater contamination will be minimized.