Waste Processing: Size and Volume Reduction

This set of flashcards covers vocabulary and technical definitions related to waste processing techniques including size reduction (comminution), volume reduction (compaction), and the specific industrial equipment used for these processes.

Waste Processing

A process by which the physical property of the waste is altered, essential for subjecting the waste to further treatment.

Segregation (Sorting)

The process by which co-mingled municipal solid waste is separated manually or mechanically into recyclables (paper, glass, plastics) and non-recyclables.

Size Reduction

A process where waste is cut or shredded into small pieces to increase surface area, facilitating better contact with microorganisms during biological treatment.

Volume Reduction

A waste processing technique where waste is compressed into compact bars to facilitate easy transport and storage within landfills.

Comminution

Another term for the size reduction process, also referred to as grinding, involving the use of external forces to reduce particle size to a finer state.

Coarse Size Reduction

A classification of size reduction typically employed for reducing rigid and unevenly formed solids to about $2-96$ inches or higher.

Intermediate Size Reduction

A classification of size reduction used to reduce rigid solids to a size of approximately $1-3$ inches.

Fine Size Reduction

A classification of size reduction employed for reducing rigid solids to about $0.25-0.5$ inches using equipment like ball mills or tube mills.

Moh’s Scale

A random scale of hardness for mineral substances ranging from $1$ (soft, like graphite) to $10$ (hard, like diamond).

Robustness

The toughness of a material which, in some instances of size reduction, is more important than hardness; for example, rubber is harder to fracture than blackboard chalk.

Abrasiveness

A property of hard materials that can limit equipment efficiency and lead to fine particles being polluted with metal from the pulverizing grinder.

Glueyness

The stickiness of a material that cause it to adhere to milling planes or choke screens, especially when heat is produced during size reduction.

Moisture Level (Grinding Criteria)

Substances with less than $5\%$ moisture are fit for dry grinding, while those with more than $50\%$ moisture are suitable for wet grinding.

Reduction Ratio

The ratio of feed particle size to product particle size; it is between $3$ to $7$ for coarse reduction and over $100$ for grinding mills.

Impact

A size reduction mechanism occurring when a solid particle is beaten by a highly accelerated moving substance or hits an immobile surface.

Compression

A size reduction mechanism where a solid particle is disintegrated by two dual rigid forces, similar to a nutcracker.

Shear

A mechanism where a solid particle is squashed between the ends of two rigid surfaces moving tangentially or through rollers.

Attrition

A size reduction mechanism where particles are scrapped against one another, generating forces that shatter the materials.

Hammer Mill

A common shredding device where hammers on a rotor spinning at $8000-15000\,rpm$ hit and shred material introduced into the device.

Flail Mill

A solitary pass shredding equipment similar to a hammer mill but providing only coarse tearing, often used as bag breakers.

Hydropulper

A shredding device that uses a revolving shaft to slice municipal solid waste and water into pulpable products consisting of $2.5$ to $3.5\%$ solid particles.

Glass Crushers

Devices that use compression stress forces applied by rotator wheels or rollers to mash glass vessels and minimize storage costs.

Mechanical Volume Reduction

A process that increases waste density through compaction, typically using compactors.

Thermal Volume Reduction

Reducing waste volume through thermal methods like incineration, combustion, or gasification, converting waste into gas, liquid, or inert residue.

Chemical Volume Reduction

Altering the chemical nature of waste to reduce volume via methods like pyrolysis, hydrolysis, or chemical conversions.

Stationary Compactors

Equipment operated manually or mechanically at fixed locations (residential, commercial, or transfer stations) to load and compress waste into containers.

Low-pressure Compaction

Compaction systems using less than $7\,kg/cm^2$ ($100\,lb/in^2$), typically requiring large containers and used with paper and cardboards.

High-pressure Compaction

Systems using more than $7\,kg/cm^2$ ($100\,lb/in^2$) to minimize waste into small sections, cubes, or bales, with capacities up to $351.5\,kg/cm^2$.

Baling Equipment

Equipment that works under high pressure ($100-200\,lb/in^2$) to generate compact blocks of solid waste or recyclables for transport to 'balefills'.

dRDF (Densified Refuse Derived Fuels)

Dense fuel items generated through cubing and pelleting processes for use in incineration, gasification, or pyrolysis.

Cubing and Pelleting

Processes using extrusion dies and revolving press wheels to create densified fuel; cubes are roughly $3\,in \times 1\,in^2$ and pellets are circular.

Rotary Compactor

A device where a ram for densifying waste is fixed on a revolving platform, commonly used in medium and high-rise apartments for paper or plastic.

Volume Reduction Percentage Formula

$\frac{V_i - V_f}{V_i} \times 100$ where $V_i$ is the initial volume and $V_f$ is the final volume.

Compaction Ratio Formula

$\frac{V_i}{V_f}$ representing the relationship between the volume of waste before and after compaction.