Bioreactor Landfills –Objectives and Fundamentals

Topics Covered

Bioreactor landfill definition and statusBiological processesLeachate impactsGas impactsTypes of bioreactor landfillsEconomic issues

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.”

Bioreactor Landfill Definition –EPA NESHAP Rule

…MSW landfill or portion of a MSW landfill where any liquid other than leachate …is added in a controlled fashion into the waste mass (often in combination with recirculating leachate) to reach a minimum average moisture content of a least 40 % by weight to accelerate or enhance the anaerobic …biodegradation of the waste…

Chronology of “Bioreactor” Implementation

1970’s: Laboratory/Pilot studies1980’s: First generation full-scale application1990’s: Second generation full-scale application2000’s: Technology Implementation

US Bioreactor Status

1993 - less than 20 landfills recirculating leachate1997 - ~ 130 landfills recirculating leachateMy estimate - > 10 % of landfills

Why Operate a Landfill as a Bioreactor?

to increase potential for waste to energyconversion,to store and/or treat leachate,to recover air space, andto ensure sustainability

Essential Needs for a Bioreactor

Composite linerEfficient leachate collection systemConsider hydrodynamicsGeotechnical stable designLeachate recirculation systemAdequate storageActive gas collection systemAppropriate final cover systemCompetent landfill operator

MSW Landfill Bioreactor Control Opportunities

CompositionRedox conditionsMoisture ContentOther Environmental ConditionsPhysical Waste Properties

Advantages of Moisture Addition

Distribution of nutrients and enzymespH bufferingDilution of inhibitory compoundsRecycling and distribution of methanogensLeachate treatmentLiquid storageEvaporation opportunities

StorageIn SituEx Situ

Storage

Blow Down

To Ex Situ Treatment

Recirculation

Leachate

Landfill

PrecipitationEvaporation

Runoff

Temperature Control

Gas

Liquids, Nutrient, Inoculum, Buffer Addition

Infiltration

Moisture Control

Anaerobic Pathway

Degradable particulate organic material (Proteins Carbohydrates and Lipids)

Inert Soluble

Amino Acids & Sugars Long chain fattyacids

Valerate, Butyrate,& Propionate

Acetate Hydrogen

Methane

Hydrolysis

Fermentation ofAmino acids &

Sugars

AnaerobicOxidation of

LCFA

Acetotrophicmethanogenesis

Hydrogenotrophicmethanogenesis

AnaerobicOxidation of

Acids

Anaerobic Decomposition

→+ OHOHC 25106

24 33 COCH +

Aerobic Decomposition

→+ 25106 6OOHC

OHCO 22 56 +

Moisture Balance

Moisture, gpm/acre

Aerobic Anaerobic

Loss/Gain – Biodegradation

-0.51 0.24

Removed in Exhaust Gas

1.16 0.21

Required Input 0.65 0.45

Waste Degradation – Impact of MC

Leachate and Gas

Leachate COD

Leachate Constituents

Parameter Conventional* Recirculating

Iron, mg/l 20 - 2100 4 - 1095

BOD, mg/l 20 - 40,000 12 - 28,000

COD, mg/l 500 - 60,000 20 - 34,560

Ammonia, mg/l 30 - 3000 6 - 1850

Chloride, mg/l 100 - 5000 9 - 1884

Zinc, mg/l 6 - 370 0.1 - 66

*Pohland and Harper, 1986

Leachate Constituents

Contaminants do not extensively concentrate in leachateLeachate characteristics follow similar pattern to that of conventional landfills over a compressed time period

LFG Generation Curves

Year

25,000,000

0

5,000,000

10,000,000

15,000,000

20,000,000

Cub

ic m

eter

s LF

G

0 10 20 30 40 50

Half-Life = 1.35 yr

Half-Life = 3.68 yr

Half-Life = 20 yr

Gas Production

0

10

20

30

40

50

60

70

0 2 4 6 8 10

Time, years

Sp

ecif

ic F

low

Rat

e, m

3/M

g-y

r

Wet Cell Curve (shifted)

Conventional Cell Curve

Operational Schemes

AnaerobicAerobicHybridFacultative

Anaerobic Bioreactor

Source: www.wastemanagement.com

Aerobic Bioreactor

Source: www.wastemanagement.com

Facultative Bioreactor

Source: www.wastemanagement.com

Nitrification of leachate

Recycled leachate has high NO3

-

concentrations

Hybrid Bioreactor

Source: www.wastemanagement.com

Air is switched on and off

Economic Impacts

BenefitsEnhanced gas productionRecovered spaceReduced environment impactReduced post-closure care

CostsCapital costsOperating costs