Paper No: 11 Solid and Hazardous Waste Management Module: 12 Waste Processing – Volume reduction
Development Team
Prof. R.K. Kohli Principal Investigator & Prof. V.K. Garg &Prof.AshokDhawan Co- Principal Investigator Central University of Punjab, Bathinda
Dr. Yogalakshmi K. N., Paper Coordinator Central University of Punjab, Bathinda Dr. Rajesh Banu., Content Writer Anna University Regional Centre Tirunelveli Content Reviewer Dr. Yogalakshmi K. N., Central University of Punjab, Bathinda
Anchor Institute Central University of Punjab 1
Solid and Hazardous Waste Management Environmental Sciences Waste Processing – Volume reduction
Description of Module
Subject Name Environmental Sciences
Paper Name Solid and Hazardous Waste Management
Module Name/Title Waste Processing – Volume reduction
Module Id EVS/SHWM-XI/12
Pre-requisites Basic knowledge on
To minimize the amount of solid waste material to be processed at the dumping site. Objectives To increase the efficiency of collection and disposal of solid wastes. To enhance the durability of dumping sites. Finally, to prepare the economic viability of solid waste management system. Keywords Waste processing, volume reduction, mechanical, compactors, balers, pelletization
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Solid and Hazardous Waste Management Environmental Sciences Waste Processing – Volume reduction
Module 1: Learning Objectives: To minimize the amount of solid waste material to be processed at the dumping site.
To increase the efficiency of collection and disposal of solid wastes.
To enhance the durability of dumping sites.
Finally, to prepare the economic viability of solid waste management system.
Volume reduction
Volume reduction is a type of waste processing where the nature of the waste is altered physically. It is one of the essential steps in waste management system. Proper waste processing will improve the efficiency of solid waste management, facilitate recovery of resources and energy conversion. Volume reduction is defined as handling or processing of waste materials to reduce the volume of the waste. Volume reduction can be achieved by three means. They include
Mechanical volume reduction: By this process the density of the waste is increased through compaction. They are achieved by compaction process.
Thermal Volume reduction: It is a process by which the waste volume is reduced through thermal methods or temperature changes. The solid waste is converted into gas, liquid or inert solid residue. Eg. Incineration, Combustion and Gasification
Chemical Volume reduction: It is done by altering the chemical nature of the waste through the addition of chemicals or temperature changes. Egs. Pyrolysis, hydrolysis and chemical conversions.
Compaction
Waste compaction is the process of compacting waste to reduce its volume and densify the waste. In simple terms it is the process of pressing the waste to compact and increase the density. Compaction is done at three levels, namely in collection vehicles, transfer stations and disposal site. Garbage compactors and waste collection vehicles compress waste so that more waste can be loaded
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Solid and Hazardous Waste Management Environmental Sciences Waste Processing – Volume reduction
within the provided space. At the transfer station they are compacted into bales or cubes or pellets. Waste is also compacted again, more thoroughly, at the landfill to conserve valuable airspace and to extend the landfill's life span.
Benefits of compaction
The benefits of volume reduction by compaction
Reduction in the amount of materials to be handled at the disposal site.
Improved efficiency of collection and disposal of wastes.
Feasibility analysis of waste management system.
Demerits of Compaction
Recyclable material quality will be poor, when solid wastes get compacted.
Once solid waste compacted, the separation or sorting process is too difficult.
Food wastes and organic bio – degradable matters when compacted along with other waste will reduce the recycling value of paper and plastics.
Equipment used for compaction The equipment used for mechanical compaction are classified as follows. Based on the movement: The compactors are categorized into two types based on their movement. Stationary equipment
Stationary equipment is operated either manually or mechanically to collect the solid wastes and load them into the containers. The collection vehicle equipped with compaction mechanisms for compacting the solid wastes is called stationary compactors. Such compactors can be placed in residential, industrial and commercial areas. They are also placed in transfer stations. Stationary compactors can be classified according to their application as (1) light duty - used for residential and commercial solid wastes; (2) commercial or small industries; (3) large industries; (4) transfer station. Movable equipment
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Solid and Hazardous Waste Management Environmental Sciences Waste Processing – Volume reduction
This consists of wheel attached vehicle and tracked equipment used to dump the compacted solid wastes in a sanitary landfill.
Based on the pressure:
The compactors used at transfer stations are classified into 2 major categories based on the pressure used for compaction. They are low pressure (less than 7 kg/cm2 or 100 lb/in2); ii) high pressure (more than 7 kg/cm2 or 100 lb/in2)
Low – pressure (less than 7kg/cm2) compaction
Large sized container is required for low – pressure solid waste compaction. These low pressure compaction systems are used in many industries in association with material recovery such as paper and cardboards.
High – pressure (more than 7kg/cm2) compaction
In high – pressure compaction systems, specialized compactors systems are used to minimize the volume of solid wastes into small sections, cubes or bales of various sizes. Pulverized or shredded waste can be compacted to form logs or bales. The nature of waste determines the use of high – pressure compaction equipment. High pressure compacvtion units possess a capacity to compact waste upto 351.5 kg/cm2 or 5000 lb/in2 and the reduction range may vary from about 3 to 1 through 8 to 1.
Bailing equipment
Bales are another substitute to compaction equipment. It works under huge pressure, mostly 100 to 200 lb/in2. Through this equipment relatively low, compact bales of solid waste or recycled materials are generated. Bale size ranges from 48 x 30 x 42 in. up to 72 x 30 x 44 in. Likewise, the weight of the bales varies based on the solid waste composition and ranges between 1150 to 1800 lb for the light and high bales of crumpled cardboard. Moreover, baled solid wastes should be landfilled in “balefills”. Practically all kind of recycled materials like cardboard, paper, plastic, PETE bottles and aluminium cans be baled and sent to recycling industries. These kind of baled materials are easily load with the help of forklifts and can be economically shipped due to its large bulk density. Balers can be of two types: vertical and
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Solid and Hazardous Waste Management Environmental Sciences Waste Processing – Volume reduction
horizontal. Vertical balers are used in small scale operations and horizontal balers are used for large scale operations.
Cubing and pelleting equipment
Cubing and pelleting is a process that can be used to generate densified refuse derived fuels (dRDF) for combustion in incineration, gasification or pyrolysis techniques. The expenditure of the process can vary according to the following features namely when the dRDF has to be exported to a long distance, stocked or stored for more periods, or fired in existing boilers made for coal or wood. Cubing and pelleting equipment were operated under same principle. Waste paper RDF is ejecting through extrusion dies with an eccentric revolving press wheel (Figure 1). An entire cubing or pelleting techniques demands a shredder, a conveyor and a moisture control system (Figure 2). The cubes or pellets are joined by heat due to friction as the cubes or pellets are ejects. The cubes and pellets stored in dry condition, dRDF can be kept for months without decay. Normal cubes are almost 3 in by 1 in2. Pellets are circular, basically 0.5 to 0.75 in diameter by 0.5 to 1 in long.
Figure 2. Cubing (densification system) 6
Solid and Hazardous Waste Management Environmental Sciences Waste Processing – Volume reduction
Table 1 summarizes the various types of compaction equipments used in different locations
Table 1. Compaction equipment used at different locations Location or Type of Compactor Remarks Operation Stationary/residential Vertical The equipment provides a perpendicular compaction using a ram in perpendicular direction
It may be operated automatically or hydraulically
They are usually hand-fed
Wastes compacted into corrugated box vessels or paper or plastic bags Popularly used in medium and high-rise flats. Solid waste Rotary The Ram device used for generation points densifying the waste is fixed on a revolving platform.
Hammer mechanism used to
thicken waste The platform rotates as containers are filled with waste They used to densify paper or plastic bags Used in medium and high-rise apartments Bag or extruder Compactor can be chute fed Both perpendicular and horizontal rams are used Densification is done for both single and multi-bags
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Solid and Hazardous Waste Management Environmental Sciences Waste Processing – Volume reduction
Used in medium and high-rise flats. Figure 2 depicts bag or extruder type compactors. The revolving press at the center compact the solid waste and forces it through the extrusion dies. Through the opening the waste comes out as cubes. Under counter They are small compactors Used in individual houses and apartment units Wastes is dropped into bags through a panel door, then it is compacted into paper bags The odour released is controlled by odour controller sprays Stationary/commercial The compaction takes place in steel vessels fixed with ram The ram can be vertical and horizontal The compressed wastes are physically tied and removed Used in low, medium and high- rise flats, commercial and industrial services Collection Stationary/packers Solid gathering vehicles armed with compaction mechanism. Stationary/transfer Trailers used for transport are fitted trailer with compactors Transfer and/or Stationary low Wastes are compacted into large pressure containers.
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Solid and Hazardous Waste Management Environmental Sciences Waste Processing – Volume reduction
processing station Stationary high Wastes are compacted into solid pressure bales or other forms. Movable wheeled or Particularly designed to achieve Disposal site tracted equipment extreme compaction of wastes. Stationary/track High-pressure transportable mounted motionless compactors used for volume reduction at a discarding site.
Figure 2. Bag or extruder
Criteria for the selection of compaction equipment
To confirm active processing, the following factors should be considered while choosing compaction equipment.
1. Characteristics of solid waste: Size, composition, bulk density and moisture content of the solid waste to be compacted.
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Solid and Hazardous Waste Management Environmental Sciences Waste Processing – Volume reduction
2. Method of transporting, handling and feeding of solid wastes to the compactor equipment 3. Possible usages of compacted solid waste materials. 4. Design features such as the size of filling chamber, compaction pressure, compaction ratio, etc. 5. Operative characteristics such as energy requirements, maintenance requirement, ease of operation, reliability, noise output, air and water contamination regulator requirement.
Table 2. Factors governing selection of densification equipment
Factor Comment
Scope of densification Compaction system for processing of solid wastes, bailing for handling recyclables and solid wastes
Characteristics of material to be Particle size, shape, water content, processed composition, specific weight
Transfer technique for materials to and Conveyor characteristics and specifications, from the densification system forklifts used to handling purpose
Equipment design parameters Unit capacity, power demand, compaction ratio, operating pressure
Operational condition Energy demands, maintenance, complexity of operation, noise and air emissions
Site factors Floor level and vertical space availability, approach.
Compaction ratio: The compaction ratio and the volume reduced during compaction are calculated as per the equation 1 and 2.
푉푖−푉푓 Volume reduction (%) = x100 Equation 1 푣푖 10
Solid and Hazardous Waste Management Environmental Sciences Waste Processing – Volume reduction
The compaction ration of the waste by equation 2, given below:
푉푖 Compaction ratio = Equation 2 푣푓
3 3 where Vi = volume of waste before compaction, m and Vf = volume of waste after compaction, m .
The relationship among the compaction ratio and the percent of volume reduction is depicted in Figure 3. Upto 80% volume reduction, the compaction ratio increase is very slow and gradual. Above which a gradual increase in compaction ratio occurs. To secure an increase from 80 to 90 %, an increase in compaction ratio from 5 to 10 is required. This analysis was important to assess the tradeoff analysis among compaction ratio and overall compaction ratio.
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8 Compaction Compaction ratio
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0 0 20 40 60 80 100 Volume reduction (%)
Figure 3. Compaction ratio vs volume reduction
Another imperative factor that should be concluded is the final specific weight (density in metric units) of the waste after compaction. Some regular curves for raw solid waste are presented in Figure 4 the asymptotic value used in expanding these curves in 1800 lb/yd3, which is steady with values attained by using high pressure compactors. As a point of reference, the specific weight of water is 1685 lb/yd3.
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Solid and Hazardous Waste Management Environmental Sciences Waste Processing – Volume reduction
When shredded wastes are compacted under the same scenario, the density may be up to 35 percent greater than that of raw wastes, up to an induced pressure of 100 lb/in2. The higher specific weight obtained under the applied pressure greater than 100 lb/in2 is not changed significantly by shredding.
Perhaps the most significant fact to be noted in Figure 4 is that the primary raise in specific weight brought about by the application of pressure are mostly dependent on the initial specific weight of the waste to be compacted. This case is relevant when claims made by producers of compaction machinery are examined. The moisture content, which changes with region, is another variable that has a huge reaction on the degree of compaction obtained. In some stationary compactors, arrangement is made to introduce moisture, basically in the form of water, during the compaction mechanism.
For cubing and pelleting equipment, the two imperative achieved characteristics are the unit and bulk specific weights of the cubes and pellets. The unit specific weight is the specific weight of an individual cube or pellet. The bulk specific weight is an analysis of a permanent volume of cubes or pellets and is suggestive of the specific weight of cubes or pellets in the presence or absence of movement because it incorporate the void space caused by randomly packing cubes in a container. The cubing system has obtained unit specific weights of 1750 lb/yd3 for shredded newsprint. However, the bulk specific weight of the cubes was only 814 lb/yd3.
2000 ) 3 1500
1000
500 Specific weight Specific weight (lb/yd
0 0 50 100 150 200 Applied load (lb/in2)
Figure 4. Specific weight of solid wastes vs applied load
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Solid and Hazardous Waste Management Environmental Sciences Waste Processing – Volume reduction
To made a trade – off analysis among compaction ratio and cost of compacted solids, the relationship between the percent of volume reduction and compaction ratio is very important. Moisture is another important parameter that needs to be considered. The moisture content will vary with respect to location. In certain cases, addition of moisture in the form of water to stationary compactors becomes essential while under processing.
Summary
In this lecture we learnt about mechanical volume reduction as an important step in waste processing. A complete coverage on classification of compactors, types of compactors and selection criteria for choosing a best compactor has been provided. The significance and relation between volume reduction and compaction ratio has also been studied.
References
George Tchobanoglous, Hilary Theisen, Samuel Vigil, “Integrated Solid Waste Management Engineering Principles and Management Issues”, (1993), referred page 570 – 577.
http://nptel.ac.in/courses/120108005/module5/lecture5.pdf
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Solid and Hazardous Waste Management Environmental Sciences Waste Processing – Volume reduction