Solid Waste Treatment

Resource Recovery and Processing

• partial solid waste disposal• to achieve about 60% reductions in future

landfill volume • Resource recovery and processing is a

complex, economical and technical system with social and political implications

Products To Be Recycled

1. Plastic : It is synthesized from petrochemicals to create a long, complicated chain of atoms called polymers.

• Bacteria and fungi that would usually live on the decaying waste of natural food, and flora cannot digest these recovery polymers.

• plastic is one of the most common non-biodegradable wastes• They create great decomposition problems eg . are diapers,

grocery• bags and balloons. • Today only 3% of all plastic containers are recycled.• Marine mammals and birds have suffocated, strangled, and been

poisoned by the plastic waste

2. Tires : Discarded tires pose two particular vector health threats to a community: rats and mosquitoes. • Tires create an excellent breeding place for rats and

mosquitoes, which in turn carry diseases to human. • An automobile tire contains about 10 liters of oil, which has• the potential to produce enough electricity to serve a small

town• Although 15 million old tires are recycled each year, the

number of recycled tires is actually going down each year as new blends of rubber and steel-belted tires cannot use recycled tires

3. Paper : Paper is the single most frequently seen item in most landfills, taking up more land space. • It accounts for more than 40% of a landfill's

contents. • Newspapers alone may take up as much as 13

to 30% of the space in landfills• Paper may be one of the most recyclable waste

products

The sources and uses of recycled paper. ( World HealthOrganization (1999) Safe Management of Wastes From Health CareActivities.)

Obstacles to resource recovery

• heterogeneity of the waste• location of the waste• low value of product• uncertainty of supply• unproven technology• administrative and industrial constraints

Techniques involved in resource recovery

1. compaction2. incineration3. mechanical size reduction4. screening /component sorting

Compaction

• reducing the wastes size. • Garbage compactors and waste collection vehicles compress

waste so that more of it can be stored in the same space. Waste is compacted again, more thoroughly, at the landfill to conserve valuable airspace and to extend the landfills life span

• Radioactive solid waste is generated during various processes and operations. These compactable solid wastes include air filters and other materials like mops, clothing, papers, plastics etc.

• Compaction technique leads to safe disposal of lower volumes of waste.

PELLETISATION FOR COMPACTABLE SOLID WASTE• A hydraulic compactor of 200 tonn capacity • The waste is compacted along with the metallic

drum and reduction in volume of 4-5 times is achieved.

• The final pelletized product is achieved employing three-stage

• compaction. This ensures safe and control release of contaminated entrapped air & water.

• On an average 1500 drums and 1200 filters are compacted annually.

Incineration

• Combustion of organic substances contained in waste materials.

• Incineration and other high-temperature waste treatment systems are described as "thermal treatment".

• Incineration of waste materials converts the waste into ash, flue gas, and heat.

• Incineration with energy recovery is one of several waste-to-energy (WtE) technologies such as gasification, pyrolysis and anaerobic digestion

• Incineration removes water from hazardous sludge, reduces its mass and/or volume, and converts it to a non-burnable ash that can be safely disposed of on land, in some waters, or in undergroundpits. However, it is a highly contentious method because incomplete incineration can produce carbon monoxide gas, gaseous dioxins, and/or other harmful substances.

Mechanical Separation the use of different sorting or separation aggregates to recover single materials for reuse from the waste stream of municipal solid waste.

Size Reduction • Size reduction is the transfer of objects, in this case waste, into smaller

particles. Every process of size reduction helps to increase the specific surface of the particle, but there is some information necessary to choose the right aggregate for the size reduction:

• The physical characteristics of the material to be reduced (e.g. particle size, structure, hardness, brittleness and fissionability), • The future usage of the material (e.g. is there a following physical or chemical processing of the material) and • The required properties of the final material (e.g. particle size, particle size distribution and average particle size)

Hammer Mills • Basically, hammer mills only vary in

the construction of the rotor of the mill.

• to minimize scrap automobiles, construction, commercial and paper waste.

Impact Crushers• Impact crushers are made up of multisectional

body and breaker plates. A rapidly rotating roller is equipped with exchangeable hammers.

Screening

• Screening of material is a segregation of various sizes into specific particle size categories. This process can also called classification.

• Waste can be screened according to particle size and also at the same time separated into different material characteristics, assuming that the material remain in the same particle size range.

• If the particles are smaller than the openings, they fall through the moving screen and become a part of the fine fraction. The other part of the material contained above the screen is considered the oversize fraction.

• The efficiency of the screening is based on the relationship between the fine fraction which passes the screen openings and the fine fraction which in the initial feed.

• Fine grained, damp and sticky material can clog the screen surfaces. In these cases the opening areas are reduced and the screen output decrease.

• To reduce the clogging it is possible to add screening aids including brushes, chains, screen heaters, air blasts or adding water to increase the capillary pressure between the sticking parts.

Air classifier• The classifier separates according to the falling

velocity of the particles. The falling velocity depends on particle form and the specific gravity.

• The design of an air classifier requires calculation of the waste-loading rate in kg/m or the reciprocal value Also all the parameters like apparent density, moisture content, waste composition, agglomeration tendency of the waste and any previous size reduction have an influence on the efficiency of the classifier.

• Two types of classifier are in use for waste processing: the zig-zag air classifier and the rotation air classifier.

Eddy Current Separation• The edge current separator provides a mechanism for

sorting a waste mixture of similar density grades. • This technology relies on the induction of eddy currents

in metal objects in response to an electromagnetic field. Eddy currents are created when conductive objects are located in or exposed to a spatially or temporally alternating magnetic field.

• According to Lenz’s law, the induced electric current produces a magnetic field opposite of the field to which it is exposed. A force is produced against the conductive object which trusts the object out of the magnetic field.

• Less conductive objects require less force.

Density Sorting• The source of this technology

was the ore industry. They developed a fluid medium for the density sorting. This technology was also tried for sorting waste components, nonferrous metals, glass, plastics and contaminants. Today density sorting is often used for sorting plastics.

• There are two types for the density sorting with fluid mediums: Float-sink method and Hydrocyclones

Manual separation• The application of manual separation can take place

to sort different qualities of wastepaper, colour specific glass, clear and coloured polyethylene foil or remove contaminating materials out of household or industrial waste streams

• It is possible to increase the effectiveness and minimize the costs for manual sorting by including mechanical sorting. Therefore magnetic separators, blowers, inclined conveyors and screens prepare the waste stream for the manual separation and help to raise the efficiency rating of sorting personnel.

• The manual separation can distinguish between positive and negative sorting. Positive sorting

• involves hand removal of the recyclables from the waste stream and placement into appropriate bins.

• The negative sorting means the removal of the discards out of the waste stream.

• On the basis of this property it is possible to achieve higher collections rates with the negative sorting, but with lower qualities. Positive sorting causes a material with a higher quality, but with a slower collection rate.