Waste Management and Landfills

American residents and businesses may rent a dumpster at times when they need some junk disposal work done or if they are in the middle of a contruction project or renovation. This way their junk is easily discarded and sent to the nearest landfill. But what happens after the dumpster truck downloads all that junk at the landfill site?

At the entrance of a landfill, the permanent presence of a guard is an important element of security, in addition to the passive security provided by the fence. Outside operating hours, only authorized persons and vehicles (security, control of purification facilities, etc.) are likely to enter the site. During operating hours, the checkpoint registers vehicles entering and leaving the site and ensures the weighing and quality control of the waste introduced.

Knowledge of the waste brought by dumpsters in terms of quantity and composition is an essential element for any future management program, in particular for estimating recoverable biogas production. In this sense, a weighing station is a valuable tool as well as the recording of the coordinates of the carrier, origin and types of waste, etc., and possibly the approximate place where they were buried (especially if it is is specific waste and in large quantities).

As a landfill generally consists of several cells to which are associated independent leachate and gas collection networks, the filling of the landfill will be done cell by cell. This will also make it possible to separate waste of very different natures. For example, organic waste can be grouped together to optimize methanization while keeping non-organic waste such as incineration bottom ash, specific industrial waste, plastics, etc., isolated.

Each day, an activity zone is defined on which spills will be carried out. The width of the landfill zone is linked in particular to the quantity of waste dumped, and the number of compactors, in order to induce methanogenic biological activity as quickly as possible. The slope of the landfill work area may not exceed 1:4 (vertical: horizontal) for reasons of stability of the machinery maneuvering there and efficiency of compaction.

After the dumping by the dumpster truck generally comes the summary spreading followed by the compaction. These activities are carried out successively by the bulldozer and/or by the compactor at sheep’s feet equipped with a front blade. The objective of compaction is to guarantee a good density over the entire cell and thus avoid the formation of gas pockets. The final density depends on six parameters: the weight and the number of passes of the compacting equipment, the thickness and the slope of the layers, the size and the nature of the waste (sparse plastics, very dense metals, etc.) .

The size parameter is important to consider particularly if bulky items are part of the frequently dumped waste. These objects are characterized by a large size and rigidity as well as a low density, biodegradability and rate of biodegradation. The waste manager will therefore take care to arrange, break or crush them in such a way as to limit the significant differential settlements between zones with or without this type of waste.

This problem ruled out, in general, 4 to 6 passages of the heavy machine (15 to 30 tons) will give a high degree of compaction of a layer of waste of one meter. It should be noted that a density greater than 0.7 makes it possible to reduce leachate production by 40 to 75% compared to a lower density.

At the end of the day, the activity zone can reach between 2 and 4 meters in height. A lower height can accelerate the methanisation phase and limit the risk of fire, but increases the cover layer/waste ratio. Conversely, a greater height can delay methanization. After a final series of passages of the compactor, a layer of soil of about 15 cm is put in place to prevent the spread of fresh waste odors, the flight of light waste and the attraction of rodents or birds. When the availability of cover soil is low, this is sometimes replaced by a film of permeable and moistened textile material (possibly with the addition of fragrant products such as plant extracts, etc.) after laying in order to limit the odor fumes.

The problem of odors is indeed a source of conflict with neighbors as much as flying waste. To remedy this, operators are invited to place screens or nets in the direction of the prevailing winds downstream of the active areas and, in some cases, to add misting screens containing odorous products to mask the smells of fresh waste, particularly unpleasant.

We should also remember the additional precautions both to cover by means of a minimum width of the daily front, for a single compactor, depending on the quantity of waste dumped in a tarpaulin or net the vehicles transporting the waste in order to avoid accidental losses, and the washing of wheels when leaving the site.

Some of the main equipment needed to run a landfill include bulldozers, compactors and loaders, as well as dumpster trucks. Waste management research presents some characteristic values ​​of these gears. Bulldozers are used in site preparation and to spread the cover layers. They are equipped with tracks of variable widths (460, 510, or 610 mm). The pressure exerted on the waste is achieved by distributing the weight of the machine on the contact surface. However, these machines are not very effective in compaction because of the low pressure exerted. Sheep’s foot compactors are used to spread and compact waste.

The wheels are equipped with inverted V-shaped teeth allowing the weight of the machine to be concentrated on a small contact surface and therefore exerting significant pressure on the mass of waste. With a width of more than 3m, they can compact around 75 tons of waste per hour and bring the density to more than 0.7 ton/m3. They are usually equipped with turbo-diesel engines and are more maneuverable and faster than bulldozers.

The loaders (loaders) are used for the excavations of weak ground, to load the cuttings in the trucks and for the transport of materials on a short distance (50 to 60 meters). They are usually equipped with diesel engines and have four-wheel drive. They can be equipped with solid or inflatable tires. The type of tires used depends on the job and the ground conditions.

Proper waste management of a landfill also requires qualified personnel: qualified workers to operate heavy machinery, administrative agents to ensure recordings and checks, technicians to take charge of tests, managers to organize cells, depots, ancillary facilities, mechanics and electricians for the maintenance of installations and vehicles, etc.