What are the important aspects in the implementation of sanitary landfills include?

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

1. Site selection

2. Land filling method and operation

3. Decomposition of the landfill waste

4. Emission from the landfills

5. Leachate movement and its control

1. Site selection

Site selection is perhaps the most difficult obstacle to overcome in the development of a sanitary landfill. While choosing a location for a landfill, the following parameters are taken into consideration:

(i) public opposition

(ii) proximity of major roadways

(iii) available land area

(iv) travel distance

(v) soil condition and topography

(vi) surface water hydrology

(vii) availability of cover material

(viii) climatologic condition

(ix) local environmental condition

(x) ultimate use of site

2. Landfill methods and operations

These are three common structural configurations for landfills:

(i) area method

(ii) ramp method

(iii) trench method

The area method starts with an excavation either naturally occurring or man-made. Solid waste is placed on the ground, spread in layers, and driven over with compaction equipment. A depth of 2-3 m is achieved by successive layering of waste. An intermediate cover material is used at the end of each day, with a complete cover added when the ‘cell is full.

Recommended depths of cover for various exposure periods is given in a profile of a typical landfill is shown

The ramp method is a variation of the area method in which the ground surface is a slope. The trench method utilises successive parallel trenches, with the cover for one trench coming from the excavation of the next trench.

3. Decomposition of land filled waste

After the landfill is closed and capped, decomposition of the waste continues, with some physical as well as chemical changes. Physical changes relate primarily due to compression leading to settling of the landfill. It is estimated that 90% of the settling occurs in the first 5 years, though it may continue for more than 25 years at a slow rate. Landfills with less original compaction tend to settle more.

Bacterial activity also goes on in the landfill. Typically, this activity goes through three different stages. In the first stage there is aerobic decomposition of the waste, with C0₂, water and N0₃ (nitrate) as the primary products when the oxygen supply is depleted, the bacterial activity changes now the facultative and anaerobic microorganisms produce primarily volatile acids and carbon dioxide, resulting in an increase in acidity to a pH of 4-5. Later, methane- producing bacteria begin to predominate, reducing the volatile acids to methane and carbon dioxide and raising the pH to neutral values. The rate of decomposition and therefore the time required for each of these phases depends on a variety of factors including moisture content, temperature, rainfall and permeability of the soil cover, among others. The entire process may take decades to complete.

4. Emission from landfills

Two types of gaseous emissions occur in landfills. Volatiles can permeate out of the landfill either through the cap or along the landfill boundaries through the sides. Methane is the most common component of concern, due to it’s explosively. The other major component of landfill gas is carbon dioxide. In addition to CH₄ and C0₂, minor amounts of nitrogen, hydrogen, hydrogen sulphide and carbon monoxide have been identified in landfill gas.

5. Leach ate movement and its control

Leachate is liquid seepage from landfills. Leachate from landfills is a documented source of ground water pollution. Leachate originates from water percolating through a landfill, picking up soluble constituents. The water that eventually becomes leachate may originate in the waste itself, or from rainwater or other surface water penetrating into the landfill. When the leachate leaves the landfill, it may enter either groundwater or surface water and thus act a vehicle for carrying potentially toxic materials from the landfill to water sources that may be used for human activities. In general, ground water pollution is more serious than pollution of surface water because it is harder to detect and clean up. Surface water has some naturally occurring cleaning mechanisms which groundwater lacks.

Two approaches have been followed for controlling the leachate problem. First, municipal landfills are required to be constructed with the potential for groundwater pollution in mind. This includes provisions for liners at the bottom of the landfill to help prevent leachate seepage, and proper construction and maintenance of landfill caps to prevent the ingress of water. It also includes the consideration of the geological location of the landfill and its proximity to ground and surface water.

The second approach is the regulation of the types of waste which are allowed to enter municipal solid waste landfills. The philosophy is to prevent or at least limit the entry of toxins. A properly designed landfill will prevent leachate contamination of groundwater, in some cases, by collecting and treating the leachate.

Completed sanitary landfill

Completed landfills generally require maintenance because of uneven settling. Maintenance consists primarily of regarding the surface to maintain good drainage and filling in small depressions to prevent and possible subsequent ground water pollution. Completed landfills have been used for recreational purposes such as parks, playgrounds, or golf grounds. Parking and storage areas or botanical gardens are other final uses. In some cases, shops and other light construction have been made as in Mumbai, Kolkata, Surat and few other cities.