Lesson 3: Solid Waste Collection



 Objective(s): To describe the tasks and logistics of MSW collection, to analyze collection systems, and to become familiar with the principals and theory behind the use of transfer stations

Goals:

  • Understand problems and concerns associated with MSW collection.
  • Compare and contrast privately and publicly operated systems.
  • Understand the types of collection systems
  • To identify the benefits associated with the use of transfer stations
  • To prepare an economic analysis of transfer stations
  • To understand the design issues associated with transfer stations


General Information


Collection accounts for 50-70% of a SW budget!



Types of Collection System

  • Refuse Collection Systems - Household waste removed from the home
  • Commercial Waste Collection - Commercial waste removed primarily using dumpsters
  • Recyclable Material Collection - Collection of recyclable materials separated at the source of generation


Equipment

  • Both Vehicles and Containers are required
  • Average life of vehicles: 5-7 yrs
  • Residential collection vehicles - Packer trucks
    • most have internal compactors
    • Rear loaders - larger hopper not as necessary with the elimination of larger, bulky items
    • Side loaders - 2 person crew (driver and loader)
    • Mechanically loaded
    • Front Loader, residential waste place in bin then cycled (Cal and western states)
  • Commercial waste collection vehicle
    • Front Loader
    • Hoist truck; small operation, few pickup locations, bulky items
    • Tilt frame - large containers, widely used 
    • Trash trailers - heavy rubbish (C/D)
  • Recycling - compartmentalized truck
Automated Collection

         Usually only one driver required works best:

o       without on-street parking, low hanging wires, narrow streets

        Where commitment to preventative maintenance

        Where commitment to educating public

        60-90 gal containers



Collection Options

City-Run Collection

  • More control over collection
  • City owns and operates all equipment
  • City manages personnel
  • Funded from property tax, user fees, or utility bill
  • Advantages
  • Disadvantages
    1. Municipalities tend to be less efficient than private companies
    2. Capital expenditures can be difficult
    3. May require passage of bond
    4. Tendency to minimize short-term spending without considering long-term implications
  • Advantages
    1. Non-profit
    2. Centralized operation
    3. City maintains complete control over waste

Private Collection

         City gives contract to firm(s) as a set fee based on bidding process, users are billed directly

Non-Exclusive Franchises

  • Multiple contractors competing for service in community

Exclusive Franchises

  • One contractor is responsible for a given area

Advantages

  • No capital expenditure for city
  • Long-term lower costs
  • Impose order on collection (exclusive franchise)
  • Regular pickup schedules (exclusive franchise)
  • Trash cans/trucks on street one or two days per week (exclusive franchise)
  • Lower costs due to improved routing and technology (exclusive franchise)

Disadvantages

  • Difficult to compete with large haulers
  • Leads to domination by a few haulers (exclusive franchise)
  • Citizens provide a profit to waste hauler
  • City can become overly dependent
  • Requires oversight by city


Problems and Concerns

Labor

  • Labor intensive
  • Labor unskilled
  • High turn-over rates
  • Few prospects for mechanical replacement of manual labor
  • Injuries and poor working conditions
  • Limited career opportunities

Customer Service

  • Frequency of service
  • Container and storage issues particularly for commercial and industrial
  • Location of pickup
  • Special wastes

Management and Financing Issues

  • Low priority
  • Resistance to change and new technologies
  • Lack of quality management
  • Inflation
  • Changing with new regulations

Technological Issues

  • Collection of multiple streams (recyclables, yard waste, special wastes)
  • Single stream vs. commingled recyclables

         curbside collection costs are $15/ton less for single stream

         sorting costs at MRFs are $10/ton more for single-stream

         paper quality lower for single stream

  • Yard waste containers - bagged material must be debagged prior to composting
  • Automated collection (still requires an operator)
  • Development of efficient routes
  • Vehicle weight restrictions
  • Vehicle turning radius and clearance

Frequency of Collection

Collection frequency has been declining since the 1950s. By the 1970s, once per week (1/wk) collection was common in half of the U.S. This trend continued into the 1980s but at a reduced rate. The south still uses twice a week collection (2/wk) almost exclusively.

 Reasons for declining collection frequency include;

  • Proportion of putrescible waste declined (food grinders)
  • Better design of collection vehicles controls odors and flies
  • Service costs increased
  • Time between collection and disposal decreased
  • Better management

Advantages and Disadvantages of Different Collection Frequencies

Alternative 

Potential Advantages 

Potential Disadvantages 

Favoring Conditions 

Once per week or less 

Less expensive, Requires less fuel 

Improperly stored waste can create odor and vector problems 

Cold to moderate climate 

Twice per week 

Reduces litter, Reduces storage requirements 

More expensive, Requires more fuel 

Warm climate 

More than twice per week 

Reduces litter, Reduces storage requirements 

More expensive, Requires more fuel 

Dense population 



Factors Affecting Decisions and Calculations

Fixed Factors

  • Climate
  • Topography
  • Layout - container access (alley, curbside, rear of house)
  • Available transportation systems, traffic, roads (Venice uses boats)
  • Types of wastes collected
  • Population density

Variable Factors

  • Storage techniques employed
  • Recycling
  • Collection frequency
  • Crew size
  • Equipment


Analysis

1. Analysis of collection time
 

                        Y =  a +  b + c(d) + e + f + g

Where:

    Y    =     total collection time
    a     =     garage to route time
    b     =     actual time collecting waste
    c     =     number of trips to disposal site
    d     =     time to drive fully loaded truck to disposal facility, unload and return to collection area
    e     =     time to drive to garage at the end of the trip
    f     =     official breaks, including bathroom visits
    g     =     other lost time such as traffic jams, breakdowns

f  + g   =     off route time, usually a fraction of Y
 

  • a, d, and e are a function of distance and speed
  • b is a function of the number of customers, time per customer, number of loads (full or partial)
  • c is a function of the capacity of the vehicle and its compaction ratio

2. Analysis of number of vehicles required

                            N = SF/XW

Where:

    N    =     number of vehicles required
    S     =     total number of customers served per week
    F     =     collection frequency
    X    =      number of customers truck can serve per day
   W    =      number of work days per week



Transfer Stations - Introduction

Alternative to direct haul, justified when transport cost (route to disposal site) is greater than transport from route to transfer station plus haul to disposal site by larger vehicle



Benefits

  • Large transfer trailers replace several collection vehicles for the hauling of waste to the disposal site
  • Collection vehicles are rapidly routed back to work, at-site or turn-around time is reduced compared to the normal time associated with disposal
  • Paved roads/tipping surfaces at transfer station reduce maintenance costs
  • Disposal facilities can be located far from populated areas which may diffuse local siting opposition
  • Waste stream inspection opportunity when unloading onto tipping floor or into compactors - spotters remove hazardous wastes
  • Provides another opportunity for recycling, compaction, and/or baling
  • Easy use of multiple disposal sites

Need for a transfer station is indicated by the following

  • Presence of illegal dumps and litter
  • Remote disposal sites (> 10 miles)
  • Small capacity collection vehicles (< 20 yd3)
  • Low density residential areas
  • Widespread use of medium sized commercial containers


Economics
    Compare direct haul and transfer costs

Considerations:

  • Cost of disposal
  • Fixed transfer station costs - cost to build, own, operate, and maintain
  • Transport cost - cost/ton/min of transport time
  • Plot cost/ton vs. difference between round trip to transfer station and disposal site


Transport Equipment

Tractor Trailers

  • Compaction vs. Open top
  • Tractor trailers restriction of highway access due to wt limits (~40 ton)

Railcars

  • Generally > 50 mi. haul distance
  • Replaces truck hauling as fuel costs increase rail becomes more cost effective
  • Paper Train - hauls paper from New England Area (30 loc) to Chicago hub from there to West coast and/or Mexico, 2000 tons/day
  • 60 box car 90 tons, Seattle and Vancouver, WA
    • Seattle to Oregon LF, 325miles
  • South Cal 16-20,000 tpd to 3 LF in Mojave Desert
  • Montgomery County, Maryland, 20 mi one way
    • Waste processed at a modified transfer station then hauled to WTE
    • Processing includes separation of recyclables, scrap, and compost
    • Residual waste compacted into 30 ton, 37 foot logs and placed in sealed containers
    • Ash from WTE backhauled to transfer station and disposed at Oaks Landfill
    • Hauling cost: $5/ton waste and $2.5/ton ash

Barges

  • Common in Europe
  • Fresh Kills Landfill, NY - 680 tons/barge (prior to closure)
  • Spill concerns limit size


Design Considerations

Types of Transfer Stations

  • Direct discharge
  • Storage pit (with or without compaction)

Station Equipment

  • Fixed equipment
    • Scales
    • Hoppers
    • Hydraulic push pits
    • Bridge crane with clamshell bucket
    • Stationary Compactors
  • Mobile Equipment -
    • Front end loaders
    • Clamshell dozers (push and break up waste, load transport vehicles)

Site Layout

  • Size unloading area, access, storage for peak volumes, surges occur at 10 am, 4 pm
  • Provide for expansion - economies of scale exist for capital and operational costs

Location

  • Near center of collection area
  • Convenient to good haul routes
  • An area zoned industrial or commercial
  • Min. public objections
  • Costs of land and construction
  • Avoid flood plains, historical/archeological sites, wildlife habitats
  • Closed landfills or incinerators are good sites


Problem Solving

Transfer station problems involve determining whether it is cheaper to haul waste to the disposal site with the collection vehicles or with separate larger capacity tractor-trailers.

The cost of hauling directly to the disposal site is compared to the cost of constructing and operating a transfer station as well as hauling the waste with tractor-trailers.

  • The waste must be collected in either case so, the cost of collection is not included however, the decision to use a transfer station may effect the number of collection vehicles required which may have to be accounted for.
  • The capital costs associated with the transfer station are amortized over a return period typically 10 or 20 years and divided by some amount of waste typically the amount of waste processed over some unit time (week, month, year, etc.)
  • A graph or equations are developed to determine the break even haul time or distance with the X-axis representing distance or time and the Y-axis having units of $/yd3 or $/ton

Capital Recovery Factor, CRF

        CRF={i(1+i)n}/{(i+1)n-1}
where:
        n=number of years
        i=interest rate

Example Problem:

Determine the break-even haul time between a direct haul truck and a transfer station operation with the following properties:
            - Direct haul uses a 10 yd3 container
            - Direct haul cost = $20/hr
            - The transfer trailer has a capacity of 100 yd3
            - Tractor- trailer haul cost = $40/hr
            - Transfer station operation cost = $525,000/year
            - Waste processed at transfer station = 300,000 yd3/yr
The break-even haul time should be 1.1 hours.



Page last updated July 2004 by Dr. Reinhart