Bioreactor Landfills: Issues and Implementation

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1 Bioreactor Landfills: Issues and Implementation Emerging Technologies in Solid Waste Management Conference 2005 March 31, 2005 Debra R. Reinhart, PhD, PE, DEE Civil and Environmental Engineering University of Central Florida

2 Presentation Overview Bioreactor Landfill Introduction Operating and Design Issues Florida Bioreactor Landfill Demonstration Project (if time)

3 Bioreactor Defined a sanitary landfill operated for the purpose of transforming and stabilizing the readily and moderately decomposable organic waste constituents within five to ten years following closure by purposeful control to enhance microbiological processes. The bioreactor landfill significantly increases the extent of waste decomposition, conversion rates and process effectiveness over what would otherwise occur within the landfill.

4 Why Operate a Landfill as a Bioreactor? to increase potential for waste to energy conversion, to store and/or treat leachate, to recover air space, and to ensure sustainability

5 Status less than 20 landfills recirculating leachate ~ 130 landfills recirculating leachate My estimate - > 10% of landfills

6 Regulatory Status EPA permits recirculation of indigenous liquids into landfills with Subtitle D liners Some states more stringent New RD&D rules will allow nonindigenous liquid addition and alternative covers

7 Essential Needs for a Bioreactor Composite liner Efficient leachate collection system Consider hydrodynamics Geotechnical stable design Liquid injection system Adequate storage Active gas collection system Appropriate final cover system Competent landfill operator

8 Methods of Liquid Introduction

9 Design Implications Liquid introduction rates Horizontal injection ( gpm/ft trench) Vertical injection Injection rates of gpm Well specific capacity 10-6 to 10-7 m 3 /sec/m of screen length Location of injection Sufficient distance from side slopes ( ft) Sufficient waste above (~ 20 ft) Spacing of 50 ft common

10 Design Implications - Continued Sufficient leachate storage (3 days) Maximize flexibility with multiple sources and systems Avoid impermeable daily cover Allow for settlement using flexible hose connections Provide cleanout

11 Design Implications Cont d Materials of construction usually HDPE Pipe diameter 3-4 in Trench width 3-5 ft Perforation size 3/8 to ¾ in Bedding materials Chipped tires Stone/gravel Crushed glass

12 External Storage

13 Leachate Storage Impact on Off-site Treatment There is a direct relationship between storage and off site treatment The more storage available the less leachate must be transported off site for treatment

14 Liner Performance

15 Liner System Single composite liner acceptable with downgradient monitoring Double liner is outstanding, with less emphasis on groundwater monitoring

16 Leachate Removal Design High normal stresses (deep wet landfills) may lead to excessive deflection Higher liner temperatures Geonet designs avoid pipe altogether Pipe monitoring and maintenance

17 Gas Collection

18 LFG Generation Curves 25,000,000 Cubic meters LFG 20,000,000 15,000,000 10,000,000 5,000,000 Half-Life = 1.35 yr Half-Life = 3.68 yr Half-Life = 20 yr Year

19 Gas Collection Challenges Higher Gas Temperatures Higher Gas Production Rate (more gas more quickly) Odor Potential Higher Liquid Levels

20 Gas Collection Options Vertical Wells Horizontal Collectors Interconnection with leachate system Common Conduit - HYEX System

21 LFG Collection From Operating Landfills Horizontal Collectors o o Sub-Cap Collector o o o o o Leachate Collection System - LFG Collector Network

22 Terminal end of HYEX conduit with liquid and gas lateral lines and optional CCTV insertion lateral.

23 Cover Issues Waste Height, m Daily Cover Material Horizontal Co-ordinate, m

24 Alternative Daily Cover

25 Final Cover System Design Issues Need to keep gas in and allow controlled infiltration Greater potential for seeps Increased settlement due to increased degradation and higher waste unit weight

26 Leachate Outbreaks

27 Landfill Stability

28 Leachate Influences on Stability Additional moisture increases unit weights, reducing FS value Perched leachate can impose hydrostatic head, reducing FS if intersects a failure plane Leachate head on the liner can impose hydrostatic head, reducing FS if intersects a failure plane Injection of liquid can increase pore pressures, decreases effective stress and mobilizes shear deformation

29 Waste Compaction

30 Recovery of Composted Materials

31 Economic Impacts Benefits Enhanced gas production Recovered space Reduced env. impact Reduced postclosure care Costs Capital costs Operating costs

32 Conclusions Many engineering challenges have been met Regulatory and operational challenges remain Attention to data collection and reporting is essential Research into remaining opportunities available to treat waste components in situ is needed

33 Florida Bioreactor Demonstration Project New River Regional Landfill serving 5 counties, approximately 800 tons/day 19 lined ha, up to 23 m in height Bioreactor ~ 40,000 m 2 ~261,000 Mg of waste Construction cost $US 2,174,798 Design cost $US 639,887

34 Unique Design/Construction Issues Leachate isolation and flow measurement Air introduction Liquid addition Exposed membrane cap Settlement accommodation Gas extraction

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36 Installation of Small Diameter Recirculation Wells: Open Flight Auger

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38 Deploying the Exposed Geomembrane Cap

39 Neoprene Gasket Construction of Expansion Boot Clamp

40 NRRL Gas Extraction System Gas is collected from the horizontal trenches underneath the exposed geomembrane cap Geomembrane Cap Subsurface Collector

41 Vertical Injection Well Clusters Instrumentation Cluster

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43 Resistivity Probe For Moisture Measurements

44 Moisture Distribution 05/30/03 10/01/03 11/01/03 Higher moisture ft ft ft Moisture content obtained from resistance values Lower moisture

45 Multi-level Settlement Settlement (ft) ft Deep Wells 40-ft Deep Wells 20-ft Deep Wells Landfill Surface Time (in days) Day 1 = 06/24/02

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