Volume and size reduction is an important factor in the development and operation of any SWM system. The main purpose is to reduce the volume (amount) and size of waste, as compared to its original form, and produce waste of uniform size.

Some of the benefits of compaction include:

• reduction in the quantity of materials to be handled at the disposal site
• improved efficiency of collection and disposal of wastes;
• increased life of landfills
• economically viable waste management system

Volume reduction of solid waste mainly occurs in the following three ways:

1. Mechanical Volume Reduction

Mechanical volume reduction is perhaps the most important factor in the development and operation of solid waste management systems. Vehicles equipped with compaction mechanisms are used for the collection of most municipal solid wastes.

To increase the useful life of landfills, wastes are compacted. When compacting a broad range of municipal solid wastes, it has been found that the final density is essentially the same regardless of the starting density and applied pressure.

This fact is important in evaluating the claims made by manufacturers of compacting equipment.

1.1. Stationary equipment:

Equipment in which wastes are brought to and loaded into either manually or mechanically.

According to their application, stationary compactors can be described as light duty, commercial or light industrial, heavy industrial, and transfer station compactors.

Large stationary compactors are necessary when wastes are to be compressed into steel containers, or transport vehicles directly.

1.2. Movable equipment:

This represents the wheeled and tracked equipment used to place and compact solid wastes as in a sanitary landfill.

2. Shredding

This is required to convert large-sized wastes (as they are collected) into smaller pieces. Size reduction helps in obtaining the final product in a reasonably uniform and considerably reduced size in comparison to the original form.

It is noted that Size reduction does not necessarily imply volume reduction and this must be factored into the design and operation of SWM systems as well as in the recovery of materials for reuse and conversion to energy.

In the overall process of waste treatment and disposal, size reduction is implemented ahead of:

• land filling to provide a more homogeneous product. This may require less cover material and less frequent covering than that without shredding. This can be of economic importance, where cover material is scarce or needs to be brought to the landfill site from some distance.
• recovering materials from the waste stream for recycling.
• baling the wastes: a process sometimes used ahead of long distance transport of solid wastes – to achieve a greater density.
• making the waste a better fuel for incineration waste energy recovery facilities. (The size reduction techniques, coupled with separation techniques such as screening, result in a more homogeneous mixture of relatively uniform size, moisture content and heating value and thereby improving the steps of incineration and energy recovery)
• reducing moisture, i.e., drying and dewatering of wastes

3. Chemical volume reduction

Chemical volume reduction is a method, wherein volume reduction occurs through chemical changes brought within the waste either through addition of chemicals or changes in temperature.

Incineration is the most common method used to reduce the volume of waste chemically and is used both for volume reduction and power production. These other chemical methods used to reduce volume of waste chemically include pyrolysis, hydrolysis, and chemical conversions.

4. Thermal Volume Reduction:

The volume of municipal wastes can be reduced by more than 90% by incineration. In the past, incineration was quite common.

However with more restrictive air pollution control requirements necessitating the use of expensive cleanup equipment only a limited number of municipal incinerators are currently in operation.

More recently, increased haul distances to available landfill sites and increased fuel cost has brought about a renewed interest in incineration and a number of new incinerator projects are now on the drawing boards.