Components of MSW compression at varying states of decomposition

1
Relative Contributions of Physical and
Biological/Chemical Processes on Compression of
Municipal Solid Waste in Bioreactor Landfills
Christopher A. Bareither1, Ronald J. Breitmeyer1,
Craig H. Benson1, Tuncer B. Edil1, and Morton A.
Barlaz2
1University of Wisconsin-Madison 2North Carolina
State University
ESD/MWIA 19th Annual Solid Waste Technical
Conference 18 March 2009
2
Background Motivation

• Impacts landfill air-space utilization and
  integrity of the final cover
• Maximize landfill capacity
• Economics
• Vertical expansions
• Expand capacity of present landfills vs.
  establishing new landfills
• Bioreactor/recirculation landfills
• Influences integrity/life-span of leachate and
  gas lines

3
Background Motivation

• MSW compresses due to physical and
  biological/chemical processes
• Total compression 25-50 of initial landfill
  thickness
• Approximately 15 due to biodegradation of
  degradable organic matter
• Vertical expansions and/or bioreactor technology
  requires estimation of future compression
• Physical and biological/chemical processes
• Temporal behavior of each process

Yolo County Pilot Project
Control Cell
Bioreactor Cell
4
MSW Compression

• Physical mechanical yielding and reorientation
  of MSW constituents
• Biological/Chemical weakening and degradation
  of MSW conversion of solids to gas (anaerobic)

Strain (e)
? Increasing
log(time)
5
Experiment Objective

• Separate physical and biological/chemical impacts
  on secondary MSW compression
• Physical Moisture induced softening due to
  liquid addition
• Biological/Chemical Waste decomposition due to
  biological activity

6
Experimental Design

• Three reactors
• Dry no liquid addition
• Biological leachate recirculation
• DI water added initially
• Leachate buffering with NaOH when pH lt 7
• Non-Biological deionized water biocide
• Fresh mixture used for each addition
• Monitoring
• Settlement
• Influent and effluent volumes
• pH, EC, Redox, COD, Alkalinity
• Gas composition and production

7
Experimental Design
8
MSW Composition

• Initial degradable fractions
• Cellulose 54.4
• Hemicellulose 9.8
• Lignin 34.2
• (CH)/L 1.88

• From North Carolina transfer station
• Shredded to maximum lengths 100 mm
• Blended for specimen preparation

9
Complete Compression Data
Incremental stress 1 kPa every 30 min. to
achieve 8 kPa Daily measurements of vertical
strain Cc' 0.13 0.17 End of primary
strain Dry 24 Non-Biological 18 Biological
23
10
Secondary Compression
Liquid Added No bio 8,712 L/Mg Bio 8,528
L/Mg Range in practice 0-1300 L/Mg Liquid
Retained Non biological 17.9 L Dw
55 Biological 18.9 L Dw 58 Compression
due to water addition 1.5 mm (0.006 strain)
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Gas Composition and Production

• Monitoring gas production since day 255
• Negligible gas production in dry and
  non-biological reactors limited biodegradation
• 38 L-CH4/dry-kg (m3/Mg) generated in biological
  reactor

12
Leachate Chemistry

• Similar compression behavior from onset of liquid
  addition to Day 180
• Acid accumulation in biological cell
• Stabilization of pH above 7 reduction in COD ?
  Biodegradation

13
Temperature Effect
Temporal changes in Ca' and CH4 flow rate
influenced by laboratory temperature Feb. 1 2008
day 291 May 1, 2008 day 381 Cold spikes
open window in adjacent room
14
Temperature Effect
15
Observations Settlement Experiment

• Liquid addition increases Ca'
• MSW constituent softening
• Lubrication of particle contacts
• Biocide has inhibited biological activity
• No methane detected, and no gas production
• Biological activity increases Ca'
• Increase correlates with period of maximum solids
  decomposition
• Temperature fluctuations affect physical and
  biological/chemical processes

16
Conclusions and Recommendations

• Can separate moisture and biological impacts on
  MSW compression
• Moisture initially increases compression rate
• Biodegradation has significant impact on rate and
  magnitude of MSW compression (10 strain)
• Secondary compression index (Ca') is variable
• May not be appropriate to use single Ca'
• Mechanical creep physical processes dominate,
  Ca' 0.005 to 0.09, average 0.04
• Biodegradation-induced compression
  biological/chemical processes dominate,
  Ca' 0.14 to 0.58, average 0.30

17
Moving Forward
18
Acknowledgements

• Bioreactor Partnership
• Waste Industry
• Allied Waste Services
• Republic Services
• Veolia Environmental Services
• Waste Management
• Waste Connections
• Buncombe County, NC
• Delaware Solid Waste Authority
• Yolo County, CA
• National Science Foundation

• Engineering Firms
• CH2MHill
• Geosyntec Consultants
• Regulatory Agencies
• US EPA
• New York Dept. of Envr. Conservation
• Wisconsin DNR
• Industry Associates
• Environmental Research and Education Foundation
• National Council of Air and Stream Improvement

Thanks to Brian Ezyk, Adam Larky, and Tim Walker
with Engineering Society of Detroit