Lesson 7: Transfer Stations

Goals:

• 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
• To become aware of other waste transportation issues such as interstate transport and flow control

Review: MSW On-Line Learning Tool: Transfer Stations (pay particular attention to the example problem)

Introduction

Alternative to direct haul, justified when:

• the cost of direct transport (trip from waste collection sites to disposal site) is greater than
• the cost of transport from waste collection sites to a transfer station plus the cost of a larger vehicle hauling the waste from the transfer station to disposal site

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 drive the decision making process:

Compare direct haul and transfer operation costs

Economic 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

Tractor Trailers

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

Railcars

• Generally > 50 mi. haul distance
• Replaces truck hauling
• 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, Md, 20mi 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
• Spill concerns limit size

Types of Transfer Stations

• Direct discharge
• Storage pit
• Combined
• Compaction (with or without?)

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

 

Interstate Transport (1990-1991)

• 15x10⁶ tons/year shipped via interstate (NY/NJ 53%)
• All but 12 states are importer/exporters, 30 are both
• Legislative roadblocks are being attempted to slow influx to states,
  • The U.S. constitution protects interstate transport  as a form of interstate commerce
  • Federal legislation to either ban or impose export fees on out of state waste transport have been considered
• Economics impact transport as much as land scarcity or NIMBY, NIMTOO, etc.
• Moral Dilemma:
  • NorthEast serves entire country industrially , perhaps only fair to distribute resulting waste
• California building mega landfills (>20,000 tpd) for larger regions

Flow Control

• Review: Flow Control Page at the EPA
• Review: Waste 360 - Traveling Trash (Stephen Ursery | Feb 01, 2006)
• Review: Waste 360 - A New Era (Stephen Ursery | Jun 01, 2007)

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 onstructing and operating a transfer station as well as hauling the waste with tractor trailers.

The cost equation for either direct haul or transfer operations will plot as a straight line (y=mx+b).

Fixed Costs (b, $/ton)

• 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 and crews required which may have to be accounted for.
• The capital costs (trucks, vehicles, equipment, facilities, etc.) are amortized over a return period typically 10 or 20 years using a capital recover factor (CRF) and then normalized by the amount of waste processed in a year

• Capital Recovery Factor, CRF

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

Variable Costs (mx, $/ton)

• 'm' is the variable cost associated with hauling waste and includes labor, maintenance, fuel, etc. ($/ton/mile, $/ton/hr)
• 'x' is the round trip hauling distance or time (miles or hours)

Solution

• A graph is developed with the X-axis representing distance or time and the Y-axis having units of or $/ton.  The point where the plots of direct haul and transfer operation costs intersect is the break even point.
• Alternatively, the two equations can be set equal and solved for x. (ydirect.haul=ytransfer.op)