Bioreactor Landfills:Theory and Practice

A Training Course Presented at the MPCA Air, Water and Waste

Conference, 2003February 25

Objective

• Provide overview of bioreactor landfills and their potential use as part of integrated solid waste management systems

Outline

I. Definitions and overviewII. What makes a bioreactor?III. Rules and regulationsIV. Leachate recirculationV. Impact on leachate quality

Outline

VI. Impact on gas productionVII.Operation and monitoringVIII.Other IssuesIX. ClosureX. Summary

About Instructor

• Associate ProfessorDept of Environmental Engineering SciencesUniversity of FloridaGainesville, Florida ttown@ufl.edu

Bioreactor Landfill Research

Polk County

Alachua County

New River Regional Landfill

Alachua County Southwest Landfill

New River Regional Landfill

Installing a well.

• Horizontal injection line installationExcavating:

Polk County NCLF

I. Definitions and Overview

Bioreactor Landfill 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.”

Motivation for Bioreactors

• Despite advances made in recycling, landfills are not going away

• Let’s look at example for Florida

1990 1991 1992 1993 1994 1995 WTE

Recycle

Landfill0

2

4

6

8

10

12

14

16

Tons

MSW

Man

aged

(In

Mill

ions

)Florida MSW Management

1990 1991 1992 1993 1994 1995 1996 1997 1998

WTE

Recycle

Landfill0

2

4

6

8

10

12

14

16

Tons

MSW

Man

aged

(In

Mill

ions

)Florida MSW Management

Motivation for Bioreactors

• If landfills are going to continue to be a major method of managing MSW, how do we operate these landfills better and smarter, with less long term consequences?

Benefits of a Bioreactor

• Rapid decomposition results in additional disposal capacity

Benefits of a Bioreactor

• Rapid decomposition results in additional disposal capacity

• Opportunities for liquids management

Benefits of a Bioreactor

• Rapid decomposition results in additional disposal capacity

• Opportunities for liquids management• Gas recovery is optimized

Benefits of a Bioreactor

• Rapid decomposition results in additional disposal capacity

• Opportunities for liquids management• Gas recovery is optimized• Decrease in active life of landfill may result

in dramatic savings in long-term care

Benefits of a Bioreactor

• Rapid decomposition results in additional disposal capacity

• Opportunities for liquids management• Gas recovery is optimized• Decrease in active life of landfill may result

in dramatic savings in long-term care• Better for the environment

Word of Caution

• If designed or operated poorly, a bioreactor can pose a greater risk to the environment.

Challenges

• Head on Liner• Control of Seeps• Gas Collection• Side Slope Stability• Ease of Construction; Interference with

Operations• Proper Design Procedures

Note

• What is the difference between a bioreactor and leachate recirculation?

II. What Makes a Bioreactor?

Municipal Solid Waste

• MSW contains a relatively large fraction of items that are “biodegradable”– Paper and other paper products– Food waste– Yard trash?– Slowly degradable materials

Municipal Solid Waste in United States1997: Total Weight Generated = 209.7 million

tons

Paper/Paperboard

Glass

Yard Trash

Wood

Food Waste

Metals

Plastics

Misc

9.4%

10.4%

9.9%

7.7%

Source: EPA

38.1%

13.4%5.9%5.2%

Waste Decomposition in Landfills

• Anaerobic bacteria use the biodegradable organic matter in a landfill as “food.”

• Several distinct groups of organisms act to convert large organic compounds (e.g. fats, proteins, starches) to methane and carbon dioxide

Let’s call them Bugs

Anaerobic Digestion(simplified)

Hydrolyzing Bacteria

Acidogenic Bacteria

Acetogenic Bacteria

Methanogenic Bacteria

Anaerobic Decomposition

→+ OHOHC 25106 24 33 COCH +

Creating the Right Conditions

• In a landfill bioreactor, microorganisms that degrade the waste are provided with conditions where their growth thrives.

• How do we provide the conditions that the “bugs” need?

Creating the Right Conditions

• Increase the moisture content• How?

– Recirculate the leachate– Add water– Add other liquid streams?

• Note: It is not just getting it wet, but the movement of water

Creating the Right Conditions

• Other factors– Temperature– Nutrients– pH– Bugs?

III. Rules and Regulations

Subtitle D

• The RCRA Subtitle D regulations govern the siting, design and operation of municipal solid waste landfills.

• Subtitle D promotes the operation of dry landfills

• There is specific language regarding leachate recirculation

§ 258.28 Liquids restrictions. (a) Bulk or noncontainerized liquid waste may not be

placed in MSWLF units unless: • (1) The waste is household waste other than

septic waste; • (2) The waste is leachate or gas condensate

derived from the MSWLF unit and the MSWLF unit, whether it is a new or existing MSWLF, or lateral expansion, is designed with a composite liner and leachate collection system as described in § 258.40(a)(2) of this part. The owner or operator must place the demonstration in the operating record and notify the State Director that it has been placed in the operating record; or

• (3) The MSWLF unit is a Project XL MSWLF and meets the applicable requirements of § 258.41.

Landfill Gas Issues

• New landfill gas rules specifically address bioreactors

State Rules

• States may have specific rules• Need to get a permit• What are greatest hurdles that have to be

overcome?

IV. Leachate Recirculation

Leachate Recirculation

• Leachate recirculation, sometimes known as leachate recycle.

• Several different methods can be used.• The choice of method depends on several

factors:– When you are constructing– Infrastructure at site– Degree of operator involvement desired– Design and regulatory constraints

Leachate Recirculation Methods

• Wetting working face• Surface ponds• Horizontal trenches

– Surface trenches– Buried trenches

• Vertical well– Large diameter– Small diameter

Wetting of the Working Face

Wetting the Working Face

• Advantages– Good potential for thorough moisture

distribution– Easy

• Disadvantages– Working conditions– Limiting in wet weather– Concerns over worker exposure

Infiltration Ponds

Surface Infiltration Ponds

• Advantages– Relatively easy– Good distribution underneath pond

• Disadvantages– Limited area– Floating garbage– Stormwater issues

Horizontal Trenches

Horizontal Trenches

• The most popular method currently• Two approaches:

– Buried trenches within the waste; Can be operated under pressure.

– Trenches on the surface of the landfill; Gravity infiltration only.

Buried Trench

Cover or Cap

Waste

Leachate Collection System

Surface Trench

Cover or Cap

Waste

Leachate Collection System

Construction Materials

• HDPE pipe is preferred

• PVC has been successfully used, however

Drainage Media

• Rock/gravel• Shredded tires• Other?• None?

Horizontal Trenches at ACSWL

Horizontal Injection Leachate Recycle at ACSWL

• A total of 16 injection lines were constructed from 1992 through 1994.

• Leachate recycle began in 1993.

• From February 1993 through August 1994, a total of 7,900,000 gallons of leachate were recycled to the landfill by horizontal injection.

Horizontal Trenches at Polk County NCLF

NCLF Phase II

• Leachate injection lines are installed in the waste as the landfill is filled up.

Digging

First Two Injection Lines

Surveying – “As-Built”

Shredded Tires

Placing First Line in Trench

Hands-on Training

Filling in Trench

Vertical Injection Wells

• Two major types– Large diameter wells– Small diameter wells

• Many of the early leachate recirculation attempts used large diameter wells

• Most new designs use small diameter wells

Why Use Vertical Wells?

• Can be applied to retrofit landfills, i.e., those landfills that have already been filled but still want to recirculate leachate

• Minimizes the involvement of the landfill operations crew. Allows for the entire system to be installed by an outside contractor.

Large DiameterVertical LeachateInjection Well

Potential Disadvantage of Vertical Wells

• The greatest hydraulic pressure will be at the bottom of the well

• This might result in more leachate distribution on the bottom of the landfill

• Potential method to address this: cluster wells

Top of Landfill

Top of Sand DrainageBlanket

10 ft

Vertical Injection Cluster Wells

Methods of Installation

• Auger drill rig• Push technology

Drill rig sets up and begins drilling. First well cluster: CN2.

Installing a well.

Additional pipe sections were threaded into place as the pipe was pushed into the hole. For the most part, all wells were able to be installed to the drilled hole depth.

The landfilled waste tended to expand around the pipe shortly after placement. A bentonite plug was placed in the annulus between the pipe and the waste.

The thermocouple leads were placed within the pipe and a cap was placed on the pipe. This is temporary condition.

Catch of the day – a mattress (with one of the drillers). Auger bits were changed while drilling resumed.

Injection Well Cluster

Injection Well Cluster

Compacting Soil around Injection Wells

Wells Under Liner

Location of Injection Well Under GeomembraneGeomembrane will later be cut and a boot will be installed

Solid Wasteand Daily

Cover

Soil

2-inch PVC injection wells TemporaryCaps

Thermocouple Wire

Process of Constructing EGC

over Injection Wells

VFPE Geomembrane Placed on Surface of Landfill

Process of Constructing EGC

over Injection Wells

Geomembrane Cut Around Wells

Process of Constructing EGC

over Injection Wells

Geomembrane Cut Around Wells

Process of Constructing EGC

over Injection Wells

Extrusion Weld Boots

Process of Constructing EGC

over Injection Wells

As soon as geomembraneis pulled over wells, locationis marked.

At a later time, the geomembrane is cut aroundwell.

Temporary Well Boots

Temporary Well Boots

Temporary Well Boots after Well Extension

Permanent Well Expansion Boots

Construction of Expansion Boot: 1 Note: Geomembrane used

for boot is illustratedin red for clarity.

Note: Boots are prefabricatedon site.Geomembrane Collar Around Well

Construction of Expansion Boot: 2 Note: Geomembrane used

for boot is illustratedin red for clarity.

Note: Boots are prefabricatedon site.

Boot Base Sheet

Extrusion Weld

Construction of Expansion Boot:3 Note: Geomembrane used

for boot is illustratedin red for clarity.

Note: Boots are prefabricatedon site.

Note: Boot Collar is Shownslightly expanded for clarity.

Boot Bellows

Extrusion Weld

Construction of Expansion Boot: 4 Note: Geomembrane used

for boot is illustratedin red for clarity.

Note: Boots are prefabricatedon site.

Note: Boot Collar is Shownslightly expanded for clarity.

Neoprene Gasket

Clamp

How Does Expansion Boot Work?

Initial Condition

How Does Expansion Boot Work?

Landfill Settles

How Does Expansion Boot Work?

Adjust Collar

Where Does the Leachate Go?

• While we can design and systems to recirculate leachate, we are not quite as sure where the water in the landfill goes.

• Several methods have been used to predict the distribution of leachate

Ymax

Xmax

x

y

Boundary ofSaturated

Zone

Xwell

InjectionWell

Flow System for Horizontal Injection Well

y = - infinity

maxY = q2 k kx yπ

maxX = q2 k y

qwell

yX =

4 k

Equations for a Saturated Zone Surrounding a Horizontal Injection Well

x = q2 k

[ xy

kk

]y

-1 y

xπtan

Effect of Anisotropy on Saturated ZoneSurrounding Horizontal Injection Well

InjectionWell

kk

x

y

=

kk

x

y

=

kk

x

y

=

kk

x

y

=

1

5

2

20

Numerical Modeling

• A saturated/unsaturated numerical model was developed by McCreanor

• Looked at many different scenarios

Landfill Heterogeneities

• The presence of cover soil and the natural heterogeneity of compacted MSW will result in deviations from ideal scenarios

Cover Problems

-8 -6 -4 -2 0 2 4 6 8Horizontal Co-ordinate, m

0

2

4

6

8

10

12

14

Waste

Heigh

t, m

DailyMaterialCover

How Much Water You Add?

• Need to get waste to at least field capacity.

• How do you now much of the waste is at field capacity?

V. Impact on Leachate Quality

Impact on Leachate

• Early research found that leachate recirculation had a positive impact on leachate quality

• The was primarily observed with a reduction in organic strength of the leachate (e.g. BOD, COD)

• High organic strength is a result of the acids produced by the bugs in the decomposition process

Leachate Strength

0

5

10

15

20

25

30

35

Chem

ical O

xygen

Demand

, mg/L

Thousa

nds

1983198519861987198819891990199119921993Year

Closure

Note

• There may be a time when you will see the leachate strength increase

Impact on Other Parameters

• Some parameters will tend to increase over time– Salts– Ammonia

Impact of Other Parameters

• Organic compounds and trace metals– Both of these are relatively low in leachate

regardless• Most organic trace compounds should be

biodegraded over time by organisms in the landfill

• Many heavy metals will be reduced in the anaerobic environment of the landfill

Question

• Can you recirculate leachate forever?

• Do you need other forms of leachate management?

VI. Impact on Gas Production

Gas Production

• An end product of rapid waste decomposition is gas production

• The total amount of gas produced from the landfill should be the same, but the time during which it is produced is condensed

Anaerobic Decomposition

→+ OHOHC 25106 24 33 COCH +

Year

0

5,000,000

10,000,000

15,000,000

20,000,000

25,000,000 C

ubic

met

ers

LFG

0 10 20 30 40 50

LFG Generation Curves

Half-Life = 1.35 yr

Half-Life = 3.68 yr

Half-Life = 20 yr

Gas Collection from a Bioreactor

• Because of the large amount of gas produced from a bioreactor and the wet nature of the waste, gas collection is a challenge.

• When do you collect?

• How do you collect?

When to Collect?

• It is not really a bioreactor if you are not collecting and managing the gas. TT

• Do you wait until the landfill is closed to start collecting the gas?

• How do you collect the gas as you go?

LFG Collection From Operating Landfills

HorizontalCollectors

Sub-Cap Collector

Leachate Collection System - LFG Collector Network

o

o

o

o

o

oo

0

5

10

15

20

25

30

-0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30 0.40

Pressure (m water column)

Land

fill E

leva

tion

(m)

Pressure Distribution within a Landfill

VII. Operation and Monitoring

Operations

• It is important to have a good operations plan and a trained set of operators

• The systems can be the best designed in the world, but if it is not operated correctly, trouble can happen

Operations

• Think of the bioreactor as being a treatment system like a wastewater treatment plant; it needs an operator

Operations

• Operating the system– How much?– Where?– How long?

• Monitoring and inspecting• Recording information

Monitoring the Bioreactor

• Leachate production and quality• Gas production and quality• Landfill settlement• Waste quality• In-situ instrumentation

– Moisture sensors– Temperature

Leachate

Leachate Meter Manholes

pH

5.5

6

6.5

7

7.5

8

pH

Manhole

TDS

0

2000

4000

6000

8000

10000

12000

14000

MH-1 MH-2 MH-3 MH-4 MH-5 MH-6 MH-7 MH-8 MH-9

Manhole

TD

S (m

g/l)

Typical Temperature Profile

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60

Dep

th fr

om th

e to

p su

rface

(ft)

5/11/01 12/18/01 4/4/02 6/25/02 7/22/02 8/13/02 10/1/02 11/18/02

Temperature ( C)

In addition to leachate/air injection wells, the researchers will also be installing instrumentation within the landfill to measure Moisture, Temperature and Gas composition. Future updates will discuss the operation of these MTGsensors in more detail. In short, these gravel-packed slotted PVC cylinders contain a device for sensing the degree of moisture present, as well as a temperature thermocouple and a tube for collecting gas samples.

-4-202468101214161820222426283032343638404244464850High Resistivity

(Low Moisture)

Low Resistivity(High Moisture)

Surface ofBioreactor

20 feet deep

60 feet deep

40 feet deep

Resistivity distribution inside NRRL Bioreactor, 12/18/02

High Temperature (degree C)

Low Temperature(degree C)

Surface ofBioreactor

20 feet deep

60 feet deep

40 feet deep

Temperature distribution inside NRRL Bioreactor, 12/18/02

25

30

35

40

45

50

55

60

65

BMP results

Methane Yield (L / g VS added)

0~0.05 0.05~0.10 0.10~0.15 0.15~0.20 0.20~0.25 0.25~0.30 0.30~0.35

Num

ber o

f sam

ples

0

2

4

6

8

10

12

14

16

VIII. Other Issues

Landfill Settlement

• Bioreactor landfills will settle more rapidly; the design must accomodate

Slope Stability

• The presence of “ponded” water within the landfill can reduce the “strength” of the waste (or the strength at the interface of waste and other materials)

• This can possible result in slope failures

Addition of Other Liquids

Aerobic Bioreactors

Aerobic Decomposition

→+ 25106 6OOHC OHCO 22 56 +

Aerobic Bioreactors

• Offers potential for very rapid degradation.• May degrade some components that are

otherwise recalcitrant under anaerobic conditions.

Aerobic Bioreactor

• Rapid stabilization of waste• Enhanced settlement• Evaporation of moisture• Degradation of organics which are

recalcitrant under anaerobic conditions• Reduction of methane emissions

Aerobic Bioreactor - Issues and Concerns

• Potential for waste combustion• Nature of air emissions• Cost• Technological feasibility in deep landfill• Waste density effects• Efficiency of air distribution

Types

• Aerobic

• Semi-aerobic

Aerobic Landfill

Permanent Well Expansion Boots

02468

10121416182022

0 5 10 15 20 25% Methane

% O

xyge

nMixtures that can

not be formed

ExplosiveRange

Not capable offorming flammablemixtures with air

Capable of forming flammablemixtures with air (contains too

much methane to be in explosive range)

Recovery of Composted Materials

IX. Closure

Closure

• When are you able to close the landfill?– 30 years?

• Can you close early if you are bioreactor?

X. Summary