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					                                    Lecture No. 9

       Separation and Processing and Transformation of Solid Waste
                             Chapter 9, p. 247
                                  Waste
                                  Generation


                            Waste handling, separation,
                            storage and processing
                            at the source



                                   Collection


             Transfer and                                 Separation and processing
             Transport                                    and transformation of
                                                          solid waste


                                   Disposal

Issues in this lecture:
 Recovery of separated materials.
 Separation and processing of solid waste components
 Transformation processes



1. General

   Methods used to recover source separated material:
- Curbside collection
- Homeowner delivery to drop-off centers
 Further separation of source separated material as well as separation of commingled
    waste
- MRF's Material Recovery Facilities
- MR/TFs Material Recovery/Transfer Facilities, a facility of the future which may
    include:
    -drop-off center
    -materials separation facility
    - composting
    - bioconversion
    - production of refuse derived fuel (DRF)
    - transfer and transport facility
Lecture No. 9: Separation and Processing and Transformation of Solid Waste, Page
                                      No. 2
2. Reuse and Recycling Opportunities

A.      Opportunities for reuse include: (T9-1, p.249)(T9-2)

 Direct reuse as a raw material, 55 gal. drums, furniture, bicycles. Thrift shops.
 Raw material for re manufacturing. Must meet material specifications, e.g.
- glass: color, no label or metal, degree of cleanliness
- plastics: type (PETE/1, HDPE/2 etc.) moisture content
 Feed stock for the production of compost and other processes. If used as an intermediate
    cover the compost can be fairly contaminated. However, compost for sale must be
    free of contaminants.
 Fuel Source: (perhaps the greatest value of MSW)
- Direct burn of the organic fraction. Dirt, ashes, metal, refrigerators will not burn and
    perhaps other constituents such as plastics and tires should not be burned.
- Converting MSW to fuel.
 Land reclamation. Enormous opportunity to reclaim land such as strip-mines or areas
    below sea level as in the Netherlands, or create new green areas such as golf courses,
    ball fields, equestrian centers.

B.      Drop-off, Buy-back Centers

    Drop-off centers may be a wooden bin for newspapers to a thrift shop. Participation
     can be low because the material must be stored by the homeowner and there is not an
     economic incentive. Convenience, next to a supermarket, may be critical.
    Buy-back centers may be a vending type machine in front of Lucky's to a large
     commercial venture, such as the Holt Boulevard operation.


3. Unit Operations for Separation and Processing (T9-3, p.256)

A.      Purpose

    Modify the physical characteristics to facilitate removal of desired component.
    Remove specific components or contaminants.
    Prepare the material for subsequent uses.

B.      Size Reduction

    Size reduction is the process by which as collected materials are mechanically
     reduced in size.
    Object is to obtain a uniform final product that is reduced in size potentially reducing
     storage and shipping course. Size reduction does not necessarily mean volume
     reduction. Shredded paper occupies more space than the parent stock.
Lecture No. 9: Separation and Processing and Transformation of Solid Waste, Page
                                      No. 3
    Shredders include hammer mill, flail mill and shear shredder and usually involve
     metal parts revolving against one another.
    Glass crushers.
    Wood grinders include chippers, such as local tree cutters use, to reduce the branches
     to chips and tub grinders. Once the wood is broken up, the finer pieces can be used as
     raw material for composting and the larger pieces can be used as a fuel.

C.      Screening

   Screening is a unit operation used to separate mixtures of materials of different sizes
    into two or more size fractions by means of screen surfaces.
 Object is to:
- Remove oversized material
- Remove undersized material
- Separate into light (combustible, paper) and heavy (non-combustible, glass) fractions.
- Screening devices include: (Fig. 9-8, p. 260)
    - Vibrating screens
    - Rotary screens
    - Disc screens

D.      Other Processes

- Density Separation (Air Classification) is the unit process used to separate light
materials such as paper and plastic from heavy materials such as metals based on weight
difference in the air stream. In solid waste the light fraction is typically organic while the
heavy fraction is typically inorganic. Used to separate glass from plastic in a commingled
situation.
- Magnetic Separation is the operation by which ferrous metals are separated from the
waste stream utilizing magnetic principals. Used to separate tin cans from aluminum in a
commingled situation.
- Densification (compaction) is a unit operation used to increase the density of the
material so that it can be stored and transported more cheaply and as a means of preparing
densified refuse-derived fuels (dRDR) and include balers and can crushers.


4. Facilities for Handling, Moving and Storing MSW

    Conveyors (Fig. 9-14, p.265). Transfer wastes from one location to another and
     include hinge, belt drag and pneumatic. Conveyors are used in the manual sorting of
     MSW. Belt is 4' wide and move at 15-90 ft./min. with a thickness of waste of 6".
Lecture No. 9: Separation and Processing and Transformation of Solid Waste, Page
                                      No. 4
    Example
        Given: A recycling operation of commingled wastes.
        Find: The Chief of Public Works of Pomona wants to know how many sorters, jobs, will be needed
        on the sorting conveyor line. You know the population is 120,000.
        From T6-3, p.138 3.82 lb./capita.day
        Weekly tonnage = 120,000 residents x 3.82 lb./capita.day x days/week x 1 ton/2000 lb.
        Weekly tonnage = 16,044 tons/week
        From T9-4, p.268 2.5 ton/person.hour, Assume a work week of 40 hours
                                                person.hour
        Persons required = 16,044 tons/week x               x 1 week/40 hours
                                                   2.5ton
        Persons required = 160 people not including augmentation because of sickness, vacation, holidays,
        absenteeism etc. An analysis of the economic advantages of the recycling operation seems in
        order.

    Movable Equipment - front end loaders, fork lifts
    Weighing facilities
    Storage facilities


5. Development and Implementation of MRF's

A.      Engineering Considerations

   Function of MRF. Depends on role of MRF, type of materials, how the material will
    be delivered and how it will be presented to the buyer.
 Selection of materials to be separated. Depends on the program set up in the
    community, e.g. commingled, 3 recycle containers and 1 for waste.
 Material specifications.
 Flow diagrams(Fig. 9-20, p. 276). Would consider:
- Characteristics of the waste material to be processed.
- Material specifications.
- Available equipment.
- Example: Refrigerators must be removed, plastic bags must be burst open, brown bags
    are moved from the paper to the cardboard section where they command a higher
    price. Paper may be baled which weigh 1400 lb. and are 30x40x60 inches.
 Example
**Problem 9-6, p. 320
 Estimate Quantities and Loading rates. Mass balance. Usually expressed in tons/hour.
    Based on 1820 operating hours year.


                                             Number of ton/yr (or ton/d)
                      Loading rate, ton/h = 1820 processing h/yr (or h/d)




    Layout and design. Would consider:
Lecture No. 9: Separation and Processing and Transformation of Solid Waste, Page
                                      No. 5
- Waste deliveries, ingress.
- Material delivery rates.
- Loading rates including storage for peak times.
- Material flow and handling patterns
- Performance criteria for equipment selection
 Equipment
 Environmental controls
 Aesthetics


B.      Planning and Design Process for MRF's

   Feasibility analysis. Technical and economic merits.
- The coordination of the MRF into the overall IWM (integrate waste management) plan.
- What kind of MRF and what kind of materials will it process.
- Economics, capital and operating costs. A sensitivity analysis of the effects of
    fluctuating prices is particularly important.
- Ownership and Operation. Public, private, combination.
 Preliminary design.
 Final design.


C.      Issues for MRFs

    Siting. Remote locations, as much buffer as possible, NIMBY inevitable.
    Environmental issues. Traffic, noise, dust, odor, vector control, airborne litter, looks
     terrible.
    Public health and safety. General public and employees. For the employees,
     protective clothing, puncture-proof gloves, air filters, showers, perhaps a radio.
    Economics. Sensitive to market prices. Must be environmentally correct or be shut
     down.

6. Combustion

A.      General

   Object:
- Reduce the volume (85-95% reduction) and weight of wastes.
- Recover conversion products and energy.
 Major concerns:
- Air pollution.
- Siting, NIMBY.



B.      Description of Combustion Process (Fig. 9-31, p. 293)
Lecture No. 9: Separation and Processing and Transformation of Solid Waste, Page
                                      No. 6

- Unload into a storage pit, usually a 2 day volume. The tipping area should minimize
    unloading waiting time with reason.
- An overhead crane drops material into a charging chute which directs the wastes to the
furnace. The operator tries to get an even mix and remove non-combustible items such as
mattresses or engine blocks.
- The waste falls on grates and is mass fired. Air is typically introduced.
- Gases and small particles rise to the combustion chamber and burn at 1600F.
- Heat is recovered from the gases using water-filled tubes in the combustion chamber
and a boiler that produces steam which is converted to electricity in a generator.
- Air pollution is controlled including NOx, SO2 and particulates.
- Clean gases are discharged to the stack.
- Ash and unburned material are quenched (cooled with water). The water and residue
must be properly disposed of. See p.641 for an excellent discussion of air pollution
systems.

C.      Types of Combustors

     Mass fired. Use unseparated, commingled MSW. Predominate in US, 68%. Pick out
     the bicycles and refrigerators, burn the rest. The energy content is probably extremely
     variable.
     RDF (Refuse Derived Fuel) fired. 23%. Produced from the organic fraction and can
     be made with consistency to meet energy, moisture, ash content specifications. Forms
     include: shredded, fluff, pellets or cubes. Also, since metals, plastics etc. are not
     burned, air emissions are cleaner.

D.      Volume Reduction (T9-8, p.299)

    Typically 90% volume reduction of the materials that were combusted. Demolition
     wastes, white goods, cars etc. were never considered.
    Always a residue and ash left over after combustion consisting of glass, tin cans, iron
     and steel.

E.      Issues With Combustion Facilities

    Siting. As with MRF's, a remote location with plenty of buffer zone.
    Air Emissions. May exceed the cost of the combustion facilities. Most pressing issue
     in the LA area. Important consideration in the decision between mass-fired and RDF
     systems.
    Disposal of residues, bottom ash, fly ash, scrubber product. Typically disposed of in
     land fill.
    Liquid Emissions. Sources: ash removal, wet scrubbers.
    Economics. Standardized life cycle costing.
Lecture No. 9: Separation and Processing and Transformation of Solid Waste, Page
                                      No. 7
F.      Example Problem

**Problem 9-16, p. 321

7. Composting

A.      General

    The organic fraction of MSW (less plastic, rubber and leather) is converted into an
     earthy, humus-like, material by the action of bacteria and other microbes.


                   Proteins
                   Amino acids
                   Lipids
                   Carbos     + O2 +Nutrients+MOs   Compost + New Cells + Dead Cells +
                   Cellulose
                   Lignin                            CO2 + H20 + NO3 + SO4 +heat
                   Ash


   Objectives:
- Convert the MSW into a biologically stable material which is reduced in volume.
- Destroy unwanted biologicals: pathogens, weeds, insect eggs.
- Retain the maximum nutrient (N, K, pH).
- To produce a valuable, soil amendment product. Not a fertilizer. Lousy C:N ratio.

B.      Process Description

   Howard et al in India in 1930.
   Three basic steps:
- Preprocessing MSW
    - Segregating degradable matter, removing engine blocks, tin cans.
    - moisture content.
    - fertilizer content perhaps by adding sewer sludge
- Decomposition
    - windrow
    - static pile
    - in-vessel
- Preparation for market.
    - grinding
    - screening
    - blending
    - additives
    - bagging
Lecture No. 9: Separation and Processing and Transformation of Solid Waste, Page
                                      No. 8
C.      Design and Control

- Particle size
- Seeding, mixing and turning
- Oxygen requirement (aerobic process)
- Moisture content
- C:N ratio

D.      Composting Techniques

   Agitated and Static. With agitated, the material is turned; with static, air is blown
    through the material.
 Windrow composting.
- Most common agitated method.
- The material to be composted is shredded into 1-3" pieces and the moisture is adjusted
    between 50-60%.
-The material is formed into triangular shapes called windrows which may be 6-7' high
    and 1`4-16' at the base.
- The windrows are tuned twice a week to maintain aerobic decomposition and the
    temperature is maintained at 131F (55C).
- Takes 3-4 weeks and cured for an additional 3-4 weeks without turning.
 Aerated Static Pile (Fig. 9-40, p. 307) (also Beltville or ARS process)
- MSW is placeed on top of exhaust piping in mounds 7'-8' high.
- Each pile has its own blower to deliver air, oxygen.
- 3-4 weeks of processing with an equal period for curing.
 In-Vessel. Inside an enclosed vessel. Proprietary.(Fig. 9-41, p. 309)
- Plug flow and dynamic systems.
- Takes 1-2 weeks and 4-12 weeks of curing.

E. What Can Be Composted (Applications)

    Yard wastes T9-9, T9-10 and T9-11, p. 310. Ranges from minimal which may take 3
     years to high level in container which can be done in several weeks.
    MSW (organic fraction). Metals or household hazardous waste can easily contaminate
     the compost. If a high quality product is desired, source separation is a must.
    MSW (commingled, partially processed). Not suitable as a gardener's compost; use as
     an intermediate cover if allowed.
    MSW (with sewer sludge). May avoid sludge dewatering. Increases the nutrient and
     moisture contents of the mix; may also contain heavy metals. A 2:1, MSW: sludge is
     recommended as a starting point.
Lecture No. 9: Separation and Processing and Transformation of Solid Waste, Page
                                      No. 9
F.     Issues With Composting Facilities

   Odors. Usually caused by:
- Low C:N ratios
- Poor temperature control
- Excessive moisture
- Poor mixing
- Can be controlled with various towers and facilities and odor-masking agents and
    enzymes.
 Pathogens. Usually destroyed by normal composting parameters of 55C for 15-20
    days
 Heavy metals. Particles are created when the waste is shredded and these particles
    may become attached to the lighter fractions.
 Definition of acceptable compost


G.     Example Problem

**Problem 9-18, p. 322

8. Impact of Source Reduction and Recycling on Combustion and
Composting

see example 9-4, p. 318

EXAMPLES
9-6, 9-16, 9-18

HOMEWORK
Read Chapter 9, Separation and Processing and Transformation of Solid Waste, PP. 247-
323
Problems, p. 320, 9-2, 9-8, 9-13, 9-17, 9-20
Lecture No. 9: Separation and Processing and Transformation of Solid Waste, Page
                                     No. 10


LECTURE NO. 9 .......................................................................................................................................... 1

SEPARATION AND PROCESSING AND TRANSFORMATION OF SOLID WASTE...................... 1

1. GENERAL ................................................................................................................................................ 1

2. REUSE AND RECYCLING OPPORTUNITIES .................................................................................. 2
    A.       OPPORTUNITIES FOR REUSE INCLUDE: (T9-1, P.249)(T9-2) ............................................................... 2
    B.       DROP-OFF, BUY-BACK CENTERS ....................................................................................................... 2
3. UNIT OPERATIONS FOR SEPARATION AND PROCESSING (T9-3, P.256) ............................... 2
    A.       PURPOSE ........................................................................................................................................... 2
    B.       SIZE REDUCTION ............................................................................................................................... 2
    C.       SCREENING ....................................................................................................................................... 3
    D.       OTHER PROCESSES............................................................................................................................ 3
4. FACILITIES FOR HANDLING, MOVING AND STORING MSW .................................................. 3

5. DEVELOPMENT AND IMPLEMENTATION OF MRF'S ................................................................ 4
    A.       ENGINEERING CONSIDERATIONS ....................................................................................................... 4
    B.       PLANNING AND DESIGN PROCESS FOR MRF'S ................................................................................... 5
    C.       ISSUES FOR MRFS ............................................................................................................................. 5
6. COMBUSTION ........................................................................................................................................ 5
    A.       GENERAL .......................................................................................................................................... 5
    B.       DESCRIPTION OF COMBUSTION PROCESS (FIG. 9-31, P. 293) ............................................................. 5
    C.       TYPES OF COMBUSTORS.................................................................................................................... 6
    D.       VOLUME REDUCTION (T9-8, P.299) .................................................................................................. 6
    E.       ISSUES WITH COMBUSTION FACILITIES ............................................................................................. 6
    F.       EXAMPLE PROBLEM .......................................................................................................................... 7
7. COMPOSTING ........................................................................................................................................ 7
    A. GENERAL .......................................................................................................................................... 7
    B. PROCESS DESCRIPTION ..................................................................................................................... 7
    C. DESIGN AND CONTROL...................................................................................................................... 8
    D. COMPOSTING TECHNIQUES ............................................................................................................... 8
    E. WHAT CAN BE COMPOSTED (APPLICATIONS) ........................................................................................ 8
    F.  ISSUES WITH COMPOSTING FACILITIES ............................................................................................. 9
    G. EXAMPLE PROBLEM .......................................................................................................................... 9
8. IMPACT OF SOURCE REDUCTION AND RECYCLING ON COMBUSTION AND
COMPOSTING ............................................................................................................................................ 9

				
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