greenhouse gas balance for composting operations - sally brown

8122019 Greenhouse Gas Balance for Composting Operations - Sally Brown

httpslidepdfcomreaderfullgreenhouse-gas-balance-for-composting-operations-sally-brown 115

TECHNICAL REPORTS

1396

Te greenhouse gas (GHG) impact of composting a rangeof potential feedstocks was evaluated through a review of theexisting literature with a focus on methane (CH

4) avoidance

by composting and GHG emissions during composting Teprimary carbon credits associated with composting are throughCH

4 avoidance when feedstocks are composted instead of

landfilled (municipal solid waste and biosolids) or lagooned(animal manures) Methane generation potential is given basedon total volatile solids expected volatile solids destruction andCH

4 generation from lab and field incubations For example a

facility that composts an equal mixture of manure newsprint

and food waste could conserve the equivalent of 31 Mg CO2 per 1 dry Mg of feedstocks composted if feedstocks werediverted from anaerobic storage lagoons and landfills with nogas collection mechanisms Te composting process is a sourceof GHG emissions from the use of electricity and fossil fuelsand through GHG emissions during composting Greenhousegas emissions during composting are highest for high-nitrogen materials with high moisture contents Tese debitsare minimal in comparison to avoidance credits and can befurther minimized through the use of higher carbonnitrogenfeedstock mixtures and lower-moisture-content mixturesCompost end use has the potential to generate carbon creditsthrough avoidance and sequestration of carbon however theseare highly project specific and need to be quantified on anindividual project basis

Greenhouse Gas Balance for Composting Operations

Sally Brown University of Washington

Chad Kruger Washington State University

Scott Subler Environmental Credit Corporation

C over climate change as a consequence of therelease of greenhouse gases (GHGs) has resulted in a

range of efforts to regulate and reduce their emissions and toreplenish the stores of fixed carbon (C) on earth As a result ofthese efforts there is now a financial value and internationalmarkets for stored C or CGHGs that are not released into theatmosphere Expected increases in the stringency of regulatoryframeworks will likely lead to increased values for C makingC-offset projects more financially appealing As with other

commodities accounting systems have been developed in anattempt to quantify changes in C emissions associated withdifferent practices Greenhouse gas accounting is done byevaluating the debits and credits associated with a particularpractice Debits are emissions of GHGs into the atmosphereand credits are essentially deposits of C into a fixed stable formTere may also be credits associated with emissions avoidance ofGHGs as a result of a change in standard practice

Considering the GHG impact of a practice that is generallyconsidered environmentally beneficial has the potential to increaseor decrease the benefits associated with the practice Composting isone such practice Composting is an aerobic process that transformsa range of organic substrates into a stable humus-like material

through microbial decomposition Composting can be consideredto be a C-based system categorically similar to reforestation agricul-tural management practices or other waste management industriesUnlike ldquosmoke-stackrdquo industries which are relatively simple todocument biologically based C credits are inherently more variableBecause of this accurate GHG accounting and best managementpractice standards will likely become an important consideration interms of the ldquoqualityrdquo of C credits and market risks and values as-sociated with C trading for these credits Additionally incorporationof the best available information for determining potential creditsassociated with different biologically based C systems will lend cred-ibility to C credits or debits associated with these systems

By most indices including the USEPArsquos evaluation of waste com-posting is considered an environmentally friendly practice (USEPA2002) Te feedstocks used for composing are often residuals or wastesfrom a range of industries that are often diverted from the solid waste

Abbreviations COD chemical oxygen demand GHG greenhouse gas HRT hydraulic

retention time MSW municipal solid waste TVS total volatile solids

S Brown College of Forest Resources Box 352100 Univ of Washington Seattle WA

98195 C Kruger Center for Sustaining Agriculture and Natural Resources Washington

State Univ 1100 North Western Ave Wenatchee WA 98801 S Subler Environmental

Credit Corporation 101 S Fraser St Suite 201 State College PA 16801

Copyright copy 2008 by the American Society of Agronomy Crop Science

Society of America and Soil Science Society of America All rights

reserved No part of this periodical may be reproduced or transmitted

in any form or by any means electronic or mechanical including pho-

tocopying recording or any information storage and retrieval system

without permission in writing from the publisher

Published in J Environ Qual 371396ndash1410 (2008)

doi102134jeq20070453

Received 24 Aug 2007

Corresponding author (slbuwashingtonedu)

copy ASA CSSA SSSA

677 S Segoe Rd Madison WI 53711 USA

REVIEWS AND ANALYSES



Brown et al Greenhouse Gas Balance for Composting Operations 1397

stream Because these feedstocks are part of the short-term C cyclethe CO

2 emissions from decomposing organic matter in compost

piles are not considered as additional GHG emissions In additionby composting these materials a stable reduced pathogen soil con-ditioner that may have nutrient value is produced from materialsthat have potentially been diverted from storage lagoons and land-fills Most composting operations are likely to function as a sourceof GHGs and as a means to avoid GHG release at different stages

of their operations Te stages of a composting operation that havethe potential to affect GHG emissions include selection of feed-stocks transport to and from the compost site energy use duringcomposting gas emissions during composting and end uses ofcompost products Te debited portions of the composting processinclude transport energy use during composting and fugitiveemission of GHGs other than CO

2 from composting operations

Te credited portions of the composting process include diversionof feedstocks from storage or disposal where they would generateCH

4 as well as end use of compost products

Te greenhouse gases that have the potential to be emit-ted by compost operations include CH

4 and N

2O Methane

is formed as a by-product of microbial respiration in severely

anaerobic environments when C is the only electron acceptoravailable Carbon is used as an electron acceptor when othermore energetically favorable electron acceptors includingoxygen nitrogen iron manganese and sulfur have been ex-hausted Because the environments in a waste storage lagoonlandfill or compost pile are not uniform it is also possiblethat different electron acceptors can be used simultaneouslyFor example when sulfur is used as an electron acceptorhighly odorous compounds including dimethyl disulfide andmethyl mercaptan are formed Te presence of these com-pounds can be indicative of the presence of CH

4 A compost

or waste pile that exhibits minimal odors is more likely tohave aerobic conditions throughout than a malodorous pile

Te conditions favorable to the formation of N2O are not as

well understood (Beacuteline et al 1999) Nitrous oxides can be formedduring nitrification (conversion of NH

3 to NO

3minus) and denitrifica-

tion (conversion of NO3minus to N

2) reactions although they are much

more commonly associated with denitrification (Brady and Weil2001) Denitrification involves the following transformations

2 NO3minus rarr 2NO

2minusrarr 2 NO rarr N

2O rarrN

2[1]

In soil systems N2O is much more likely to form and

volatilize when the carbon to nitrogen (CN) ratio of soilorganic matter is low (lt201) and denitrification is muchmore likely to occur under anaerobic conditions (Brady and

Weil 2001 Huang et al 2004 Klemedtsson et al 2005)For some waste storage areas or composting operations theCN ratio of the material is high enough andor the mixtureis dry enough to limit denitrification reactions

A number of recent studies have evaluated the GHG creditsand debits of composting (Clean Development Mechanism 2006Recycled Organics Unit 2006 Smith et al 2001 USEPA 2002Zeman et al 2002) For emissions associated with compostingeach of these considered energy requirements for transport of feed-

stocks to the compost facility and finished product to the end useras debits associated with the process Energy use during compost-ing was also included wo considered a turned windrow compost-ing system for their model whereas Smith et al (2001) also con-sidered closed systems with energy requirements for odor control(Recycled Organics Unit 2006 USEPA 2002) Only Zeman etal (2002) and Clean Development Mechanism (CDM) (2006)considered fugitive emissions of GHG such as CH

4 or N

2O

as debits wo (Recycled Organics Unit 2006 USEPA 2002)used yard waste as the sole feedstock whereas Smith et al (2001)considered organics diverted from municipal solid waste (MSW) which includes food and yard waste For GHG credits associated with composting each of the reviews used different scenarios TeRecycled Organics Unit (2006) and the USEPA (2002) consid-ered different agricultural end uses whereas Smith et al (2001)considered the potential for compost to replace peat for a range ofapplications Te United Nations Framework Convention on Cli-mate Change Clean Development Mechanism (CDM 2006) wasthe only study to include avoidance of methane (CH

4) generation

by the aerobic decomposition of feedstocks in a compost pile incomparison to the anaerobic breakdown of these materials in other

disposal sites in the credits associated with compostingTis review was conducted to quantify potential GHG debits

and credits associated for a wide range of feedstocks and com-posting systems We break the composting process into threedistinct phases (i) the CH

4 generation potential of different com-

post feedstocks (ii) the composting process including energyuse and fugitive emissions during composting and (iii) the enduse of compost Te first phase describes the GHG generationpotential of different feedstocks Tis is pertinent for compostingoperations that divert feedstocks from disposal sites or storagefacilities where they would be expected to generate CH

4 Because

anaerobic digestion is a common practice for municipal biosolidsand is coming to be recognized as a viable stabilization technol-ogy for other types of wastes effi ciencies of digestion and remain-ing CH

4 generation potential post digestion are also examined

Anaerobic digestion with CH4 capture for energy use or flaring

are important techniques for a source of energy and for avoidanceof fugitive GHG release (Matteson and Jenkins 2007) Second we detail the potential for gas generation for during the compost-ing process Te literature on gas emission potential for differentfeedstocks is summarized for storage before composting and dur-ing the composting process Different process variables and theireffect on gas emissions are also discussed Energy requirementsfor different compost systems are summarized Finally potentialend uses of compost and their impact on GHGs are briefly dis-

cussed Complications associated with credits and debits for thisstage of the process are described Te implications of compostend use on GHGs are qualitatively assessed Tis review is in-tended to be suffi ciently detailed so that credits and debits associ-ated with specific composting operations can be determined

Compost FeedstocksMaterials that are commonly used as feedstocks for compost-

ing operations include food paper and yard trimmings that



1398 Journal of Environmental Quality bull Volume 37 bull JulyndashAugust 2008

are separated from the municipal solid waste stream municipalbiosolids and animal manures For each of these materialsconventional disposal practices are associated with the release ofCH

4 into the atmosphere Food paper and yard trimmings are

generally landfilled Biosolids can also be landfilled (often afteranaerobic digestion) Food is landfilled and is also a componentof biosolids through the use of under-sink grinders Emissionsof CH

4 from landfills are expected to increase as the quantity of

waste generated increases with increasing prosperity One esti-mate shows emissions from MSW increasing from 340 Mt CO-

2eq in 1990 to 2900 Mt CO

2eq in 2050 (Bogner et al 2007)

In the USA animal manures are commonly stored in uncoveredlagoons According to a recent United Nations publication stor-age of animal manures in lagoons or liquid holding tanks gener-ates up to 18 million Mg of CH

4 per year (Steinfeld et al 2006)

Te CH4 generation potential of each of the compost feedstocks

is detailed in the next section Tis potential is intended to reflectthe maximum quantity of CH

4 that can be released through

anaerobic decomposition Other site-specific factors may influ-ence the amount of CH

4 that is released into the atmosphere as a

result of decomposition Some examples of these factors include

landfill cover soil oxidation of CH4 and reduced decomposi-tion due to cold temperatures or lack of moisture (Brown andLeonard 2004ab) Some landfills have extensive landfill gascollection systems although there is a great deal of variability inreported collection effi ciencies (Temelis and Ulloa 2007) Tevalues presented in this review can be modified to reflect site-specific conditions

Manures and Biosolids

Methane Generation Potential

For biosolids and manures CH4 generation potential

is generally expressed in relation to the total volatile solids

(VS) content of the feedstock (Metcalf and Eddy 2003IPCC 2006) Te VS is defined as the portion of the car-bonaceous material that volatilize on ignition at 500degC Acertain portion of the VS readily decomposes and formsbiogas under anaerobic conditions Te remainder is gener-ally considered refractory and may decompose under aerobicconditions over time Te portion of the VS that readilydecomposes can be directly related to the CH

4 generation po-

tential of the feedstock An equation was developed to predictthe gases that will evolve from anaerobic decomposition ofdifferent feedstocks based on the chemical composition of thefeedstock (Metcalf and Eddy 2003)

Cv H

w O

x N

y S

z + (V minus w4 + x2 + 3y4 + z2) times H

2O

rarr (v2 + w8 + x4 + 3y8 + z4)CH4

+ (v2 + w8 + x4 + 3y8 + z4)CO2

+ yNH3 + zH

2S [2]

Te Intergovernmental Panel on Climate Change (IPCC) hasidentified values for CH

4 generation based on VS and the

maximum CH4 production capacity for different types of livestock

(IPCC 2006) Here the importance of diet in determining theVS content and the CH4 generation potential of the manure is

emphasized Different values are provided for different continentsand collection of site-specific information is recommended able1 shows volatile solids produced per animal per day the portionof the volatile solids (VS) that are easily decomposed and theresulting energy value or CH

4 generation potential (able 1)

Te table has been expanded to include the CO2 equivalence of

the CH4 per day and per year and comparative values from the

IPCC for animals raised in North America Te values from thispublication are similar to those used for swine feedlot and dairycattle in another study (Garrison and Richard 2005) Te IPCCguidelines specifically recommend the use of locally generated

data because feed type specific breed and local climate factorsaffect CH

4 generation potential of the liquid wastes In this case

the values for dairy cows in Hansen (2004) are higher than theIPCC values whereas the values for poultry are lower than theIPCC values Factors that influence values on a regional levelcan be animal and climate specific Animal breed and diet effect waste properties Cooler ambient temperatures can result in upto a 50 decrease in CH

4 production in cooler regions (average

annual temperature le10ndash14degC) Tis decrease is meant for outdoorlagoons where temperature within the lagoon is not controlled TeIPCC guidelines discount the potential for N

2O evolution from

uncovered liquid or slurry storage or liquid waste lagoons Teinformation in able 1 can be used to estimate the maximum CH

4

value (or its CO2 equivalent) for different types of animal manureManures are often stored or lagooned before composting

Decomposition occurs during storage Te IPCC has a protocolfor CH

4 avoidance credits for manure lagoons that are covered

to prevent gas release Te credits are based on the CH4 genera-

tion potential of the manures specific climatic factors and theresidence time for materials in the lagoons (Dong et al 2006)For differences between fresh and stored manure the IPCCguidelines specify appropriate reduction for factors including typeand length of storage (Dong et al 2006) Some of these valuesare based on published literature whereas others are based on the judgment of the authors For example potential CH

4 conversion

factors for uncovered lagoonsrange from 66 to 80 depend-ing on temperature Actual CH

4

evolution from lagoons varies byseason location and lagoon de-sign (DeSutter and Ham 2005Dong et al 2006 Shores et al2005) In lieu of actual data itis also possible to use the defaultvalues provided in the IPCC doc-

Table 1 Volatile solids (VS) produced per 455 kg animal unit per day likely VS destruction total gas CH4

produced (using 224 L per mole of CH4) and CO

2 equivalent for a range of animal wastes (Hansen 2004)

VS per animalper day

Likely VSdestruction

Totalgas CH

4 dminus1

CO2

equivalent IPCC Value

kg m3 dminus1 m3 of CH4

Moles CH4

kg dminus1ndashndashndashndashMg yrminus1

ndashndashndashndash

Beef 268 45 084 050 225 828 302

Dairy 391 48 123 074 33 1214 443 11ndash26

Swine 218 50 081 049 2175 8 292 19ndash43

Poultry layers 427 60 202 121 54 199 725 126ndash147

Poultry broilers 545 60 258 155 69 254 927




ument for appropriate reduction factors In addition a measureof the VS of the lagooned or stored manure may be an indicationof the amount of stabilization that has taken place and the subse-quent loss of CH

4 generation potential

Anaerobic DigestionMunicipal biosolids and animal manures may have under-

gone anaerobic digestion for stabilization and pathogen reduction

(biosolids) or for energy recovery (manures) before compostingFor biosolids retention time in digesters is typically determinedby volatile solids and pathogen reduction Here retention time inthe digester may be less than required for complete CH

4 recovery

In the case of animal manures retention time in digesters is cal-culated to maximize CH

4 generation and minimize storage time

a decision based on economic optimization Tis suggests thatif the manures are returned to piles or lagoons after digestionadditional CH

4 or N

2O can evolve from the storage areas Te

difference between maximum and actual CH4 generation in an-

aerobic digesters can be viewed as the remaining CH4ndashgenerating

potential of the substrate Data from different studies supportthis concept For example Clemens et al (2006) looked at CH

4

generation for raw and anaerobically digested cattle slurry storedin open and closed containers Although CH

4 generation was

highest for the raw slurry (36 kg CO2 eq mminus3) digested slurry (29

d hydraulic retention time [HR] in the digester) also emittedsignificant amounts of CH

4 (15 kg CO

2 eq mminus3)

Tere are several types of anaerobic digesters that are used infarming operations Tese include covered lagoons completemix digesters plug-flow digesters and fixed film digesters Eachof these systems has a different optimal performance potentialCovered lagoons have an average residence time of 40 d and re-quire the least management Complete mix digesters treat ma-nure with total solids content of 3 to 10 and a residence time

of 15 d Plug flow digesters can handle materials with highersolids content (11ndash13) with a moderate retention time usu-ally between 20 and 25 d Fixed-film digesters are appropriatefor material with very low solids content and for short retentiontimes (Kruger 2005) Reported residence times in lagoons andcomplete mix digesters are averages and the actual residencetime of any given substrate sample is highly variable In addi-tion actual CH

4 generation within each type of system is often

significantly different from predicted generation

Factors In1047298uencing Methane GenerationDifferences between predicted and actual performance can

be significant Tis is illustrated with examples from studies

conducted to optimize digester performance Karim et al (2005)looked at different types of mixing in lab-scale digesters com-bined with different solids content of the feedstock Cow manureslurry at 5 solids content released up to 30 more biogas withmixing Mixing can facilitate the distribution of methanogenicbacteria in the digester and may improve the recovery of CH

4

gas bubbles suspended in the substrate Ben-Hasson et al (1985)used manure with a higher solids content and found that mixingdecreased CH

4 production by up to 75 emperature also af-

fects the rate of CH4 production Nielsen et al (2004) compared

two-stage anaerobic digestion with thermophillic temperatureregimes Tey saw up to 8 higher CH

4 yield and 9 greater

VS reduction with the two-stage process compared with diges-tion at a single temperature Bonmati et al (2001) observed a 24to 56 improvement in CH

4 yield with a two-stage temperature

reactor using pig slurry as a feedstockIn a report prepared for the AgSAR program in USEPA the

performance of a mesophilic plug flow digester at a dairy farm was monitored for 1 yr (USEPA 2005) During the course ofthe year the dairy went from 750 head to 860 head Per capitaCH

4 production decreased with the increase in numbers going

from 208 m3 CH4 to 171 m3 CH

4 per animal per day Tis de-

crease shows that the digester effi ciency decreased with increasingnumber of animals due to the reduction in actual residency timecaused by the increase in loading rate It also suggests that theCH

4 generation potential for material coming out of the digester

increased Analysis of the manure from the farm found that 47of the VS were degradable otal volatile solids destruction inthe digester averaged 396 suggesting that the digester oper-ated at 84 effi ciency Te authors note that the digester was

designed for a 22-d retention time Actual retention time duringthe course of the year averaged 29 d Tis extended time in thedigester was partially responsible for the observed effi ciency If re-tention time had been limited to 22 d as specified (which wouldhappen if the dairy further increased its herd size) effi ciency mayhave decreased to only 337 destruction of VS Te authorsreport that a similar study done at another dairy showed only30 destruction of VS Another study reported CH

4 genera-

tion per cow per day in a dairy farm in Minnesota of 146 m3 CH

4 (Goodrich et al 2005) Tis was generated in a plug-flow

digester which serviced 800 head Te digester for this farm wasproducing 30 greater CH

4 than had been predicted otal vola-

tile solids and retention time in the digester were not reportedTese examples support the notion that predicted and

actual performance are generally different Te difference be-tween the estimated portion of the VS in the raw materialthat is decomposable and VS in the digested material can beused as a basis to determine the CH

4 generation potential of

anaerobically digested animal manures

Biosolids Anaerobic digestion is used in municipal wastewater treatment

for stabilization and pathogen destruction (Han et al 1997) Siz-ing of digesters is based on expected solid retention time and HRTese parameters are determined in conjunction with the design

of the remainder of the treatment plant Digesters are generally fedprimary sludge from settling tanks and secondary or waste-activat-ed sludge from biological treatment Te material from biologicaltreatment consists of microbial biomass and can be resistant to de-composition in conventional digesters (Han et al 1997) If a plantis operating at close to design capacity retention time in digesters iskept at the minimum required to meet regulatory requirements As with manure digesters the longer the retention time the higher the destruction of VS and correspondingly the more CH

4 that is




generated during digestion Metcalf and Eddy (2003) give approxi-mate values for volatile solids destruction as a function of digestiontime for high-rate complete-mix mesophilic anaerobic digestion(able 2) Tis paper also reports that retention times normallyrange from 10 to 20 d for high-rate digesters

Volatile solids destruction is also described in Metcalf andEddy (2003) using the following equation

Vd = 137 ln(Solids retention time [days]) + 189 [3]

Using this equation a 100-d retention time would result in82 reduction in VS Tis is an appropriate value to use for

maximum CH4 generation because increased production overthis time frame is minimal Methane generation capacity ofthe sludge can also be estimated If the chemical formula of thevolatile solids into the digester is taken to be C

12H

22O

11 then

the quantity of CH4 will be proportional to the reduction

in VS times volume of decomposable material in the digesterTe concentration of decomposable material in the liquid goinginto the digester depends on the type of wastewater treatmentplant Using the chemical composition of the waste given herethe mass of C converted in relation to the total VS reduction isthen 42 of the total A typical digester produces gas that is 55to 70 CH

4 with the remainder of the C present as CO

2

In acoma Washington sludge at the municipal wastewater

treatment plant is initially treated in an aerobic thermophilic(45ndash65degC) digester and then transferred to an anaerobic meso-philic digester Volatile solids at the beginning of this processare typically 80 Anaerobic digestion eliminates 64 of theVS present at the beginning of the digestion process (DanTompson Environmental Services Wastewater City of a-coma personal communication) At King County Washing-ton the feed into the digester contains about 85 VS Witha retention time of 20 to 30 d generally 65 of the incomingVS are destroyed Te incoming VS and the destruction areconsidered high for what would be typical for the wastewatertreatment industry (John Smyth Wastewater reatment Divi-sion King County WA personal communication) Based on

retention time in digesters and VS reduction such as manuresthe biosolids may have significant CH


As with manures lab studies have confirmed that for biosolidspredicted CH

4 generation potential is not exhausted after standard

retention times in full-scale mesophilic digesters In a laboratorystudy changing the solids retention time from 24 to 40 d in amesophilic digester resulted in an increase in VS reduction from32 to 47 (Han et al 1997) In another study sludges weretaken from mesophilic digesters with retention times of 30 and65 d (Parravicini et al 2006) Tese materials were incubated in

lab-scale anaerobic digesters After 14 d volatile suspended solidsdegradation effi ciency was improved for both materials by 12Changes in digester temperatures may also increase gas generationTe most commonly used digester temperature design is single-stage mesophilic digestion A series of studies found that an initialthermophilic stage combined with mesophilic digestion improvedVS destruction with a subsequent and parallel increase in CH

4

generation (Harris and Dague 1993 Kaiser and Dague 1994

Han et al 1997) Methane production per gram of VS destroyed was almost identical for a single-stage mesophilic and a combinedthermophilic and mesophillic system Tis confirms a relationshipbetween VS destruction and CH

4 generation

Food Paper and Yard TrimmingsFood paper and yard trimmings materials have traditionally

been landfilled as components of MSW (US Congress Offi ce ofechnology Assessment 1989) Tese materials can also be usedas feedstocks for compost Within a landfill food paper and yardtrimmings decompose and generate CH

4 Depending on the rate

of decomposition and the quantity of CH4 associated with the de-

composition it is possible that a high percentage of the CH4

gen-eration potential of the substrate will be exhausted before landfillgas capture systems are put into place Landfills constructed in theUSA after 1991 with total capacities greater than 25 million m3 are required to install gas collection systems to reduce CH

4 emis-

sions (USEPA 1999) Gas collection systems must become opera-tive at active faces of the landfill that have been receiving waste formore than 5 yr Closed areas must have functional collection sys-tems beginning 2 yr after the first waste has been placed in the cell(USEPA 1999) However a recent study showed that CH

4 emis-

sions from the active face of a landfill were 17 higher than fromthe sides of the fill indicating that CH

4 generation commences

before cell closure (Lohila et al 2007) Te USEPA has a model to

assist solid waste professionals in calculating the total GHG emis-sions from decomposition of organics in landfills Te Waste Re-duction Model gives single point values for gas generation potentialthat does not take into account the rate of decomposition of thesubstrate and how that might interface with the gas system require-ments for larger landfills (USEPA 1998b) In a study of the GHGpotential of different end usedisposal options for MSW Smith etal (2001) noted that like USEPA the IPCC treats CH

4 emissions

from landfills as though they are instantaneous However sincethat report was prepared the Clean Development Mechanism hasdeveloped a protocol for compost operations that includes a creditfor CH

4 avoidance (Clean Development Mechanism 2006)

In this model decay rates are based on a first-order decay model

that accounts for different CH4 generation potential as well as thefraction of degradable C for different waste materials Methanegeneration for each material is calculated on a yearly basis until thegas generation potential for the substrate is exhausted Wood andpaper products are classified as slowly degrading non-food organicputrescible garden and park wastes are classified as moderately de-grading and food wastes are considered rapidly degrading

For the organic component of MSW the CH4 generation

potential can be used as a basis for determining the CH4 avoid-

ance credits that would be associated with composting these

Table 2 Volatile solids destruction as a function of digestion time forbiological waste materials undergoing anaerobic digestion atmesophillic temperatures Data are from Metcalf and Eddy (2003)

Digestion time Volatile solids destruction

d

40 694

30 655

20 60

15 56

10 50




materials (IPCC 2006) Values for CH4 generation potential of

these materials in landfill environments and in anaerobic digest-ers has been reported along with approximate time required fordecomposition (eg Eleazer et al 1997) Anaerobic digestionof MSW is an established technology in Europe and is beingrecognized as a viable alternative to landfilling in the USA(DiStefano and Ambulkar 2006 Zhang et al 2007)

In laboratory scale landfills Eleazer et al (1997) measured

CH4 yields for grass leaves branches food scraps and an assort-ment of different paper grades (able 3) Te reaction vessels weremaintained within the mesophilic temperature range and water was added to assure saturation Samples were incubated until con-centrations of CH

4 were below detection limits Observed yields

were 1444 306 626 and 3007 mL CH4 per dry g respectively

for the grass leaves branches and food scraps Methane generationby paper products ranged from 2173 mL CH

4 per dry g for offi ce

paper to 743 mL CH4 per dry g for old newsprint Approximate

time required for decomposition CH4 generated per kg and CO

2

equivalent (Mg CO2 per Mg waste) for each waste material are

shown in able 3 Tese conditions were close to optimal for CH4

generation in an unperturbed system particularly for the drier ma-

terials In an actual landfill moisture content of certain materialssuch as food and yard trimmings are likely to be high enough tofacilitate anaerobic decomposition Other studies have examinedCH

4 yield and decomposition rate of food and yard trimmings

in anaerobic digesters and septic tanks with generally higher ratesof decomposition and CH

4 generation (Luostarinen and Rintala

2007 Maumlhnert et al 2005 Nguyen et al 2007 Zhang et al2007) Methane generation and rate of decomposition for foodscraps in anaerobic digesters are shown in able 4

As was the case with manures and biosolids VS has been usedto predict CH

4 generation potential for decomposition of land-

filled wastes Zhang et al (2007) reported 81 VS destruction offood waste after 28 d in an anaerobic digester with a subsequentCH

4 yield of 435 L CH

4 kg minus1 In another study higher CH

4

yields from anaerobic digestion of food waste (489 L CH4 kg minus1)

were attributed to a higher VS content of the feedstock (Cho andPark 1995) Eleazer et al (1997) reported the VS of the feed-stocks but did not report VS destroyed during the incubationHowever in another study conducted at the same laboratory us-ing food waste the waste (1493 dry g) was mixed with seed ma-terial from a digester (531 dry g) (Wang et al 1997) Te seedmix had VS of 422 and the food waste had VS of 92Te VS of the initial mixture was 53 After incubation VS was reduced to 369 which represents a 30 destruction ofVS However CH

4 generation by the seed mix was only 58 mL

per dry g Tese results indicate close to complete destructionof the VS from the food waste within the 100-d period of theexperiment In a separate study food waste was digested using a

two-stage process to generate hydrogen gas and CH4 (Han and

Shin 2004) In this process 725 of the VS was removed Kay-hanian and chobanoglous (1992) evaluated the degradability offood waste based on lignin content and determined that 82 ofthe VS could be decomposed under anaerobic conditions

Te values for CH4 generation from grasses of 1276 to

1444 L CH4

kg minus1 (or 013ndash014 m3 CH4

kg minus1) observed inEleazer et al (1997) were also lower than values obtained in an-aerobic digesters When based on the VS content of the grasses(87) the values from Eleazer et al (1997) correspond to 015to 017 m3 CH

4 kg minus1 VS Maumlhnert et al (2005) looked at the

CH4 generation potential of three different grass species in a

mesophilic anaerobic digester with an HR of 28 d Biogas yieldsranged between 065 and 086 m3 kg minus1 VS with between 60 and70 of the gas consisting of CH

4 Tis corresponds to 031 to

036 m3 CH4 kg minus1 VS Te authors quote a range of other studies

using different fresh cut grasses or grass silage where biogas produc-tion ranged from 05 m3 kg minus1 VS to 081 m3 kg minus1 VS Methaneyield in other studies ranged from 023 to 05 m3 CH

4 kg minus1 VS

Te low values observed by Eleazer et al (1997) may be related tothe type of grass the lack of mixing or the relatively high loadingrate used

Paper waste is the final component of MSW that has the po-tential to generate significant quantities of CH

4 in a landfill In the

Eleazer et al (1997) study this category of MSW was separatedinto individual components including newsprint coated and cor-rugated paper and offi ce paper Methane generation from theseindividual categories ranged from 743 L CH

4 kg minus1 for old news-

print to 2173 L CH4 kg minus1 for offi ce paper Both materials have a

VS content of 98 Duration of CH4 emissions ranged from 120

d for coated paper to 500 d for offi ce paper Clarkson and Xiao(2000) also looked at the CH

4 generation potential of newsprint

and offi ce paper in bench scale anaerobic reactors Tey foundthat CH

4 generation from offi ce paper was largely complete after

20 d but continued until Day 165 with yield ranging from 71 to

Table 3 Methane yield (in L and mol of CH4) time required for

decomposition and equivalent Mg CO2 for different types of

wastes incubated in a laboratory to simulate decomposition in amunicipal solid waste land1047297ll (Eleazer et al 1997)

Yield Time

L CH4 kgminus1 mol CH

4 kgminus1 Mg CO

2 Mgminus1 waste Days

Grass 1444 64 237 50

Grass-2 1276 57 210 50

Leaves 306 14 050 100

Branch 626 28 103 100Food 3007 134 494 120

Coated paper 844 38 139 150

Old newsprint 7433 33 122 300

Corrugatedcontainers

1523 68 250 400

Offi ce paper 2173 97 357 500

Table 4 Methane generation and CO2 equivalents for food waste that has decomposed in anaerobic digesters or simulated land1047297lls

Source Volatile solids destruction L CH4 kgminus1 mol CH

4 kgminus1 Mg CO


Eleazer et al 1997 simulated land1047297ll 3007 134 494 120

Zhang et al 2007 anaerobic digestion 348 155 572 10

81 435 194 715 28

Nguyen et al 2007 anaerobic digestion 61 260 116 427 60

Cho and Park 1995 anaerobic digestion 489 218 803 40




85 of chemical oxygen demand (COD) and total production ofabout 300 mL CH

4 g minus1 COD In comparison CH

4 conversion

from newsprint ranged from 32 to 41 of total COD for 300 dor about 100 mL CH

4 g minus1 COD Te authors cite previous studies

that showed only a 20 conversion of newsprint COD to CH4

Te lignin content of the newsprint and the association of lignin with cellulose are the reasons given for the slow and limited de-composition of this type of paper Kayhanian and chobanoglous(1992) also used the lignin content of different paper streams as abasis for determining the degradability Degradability was definedas the decomposition under anaerobic conditions for a 30- to 45-dretention time For offi ce paper 82 of the VS was considereddegradable Only 22 of the VS from newsprint was degradabledue to the high lignin content A total of 67 of the VS fraction ofmixed paper was degradable Te values from these studies are notdissimilar and suggest that the CH

4 generation potential predicted

by Kayhanian and chobanoglous (1992) offers a simple means tomeasure the CH

4 generation potential of the paper based on the

initial VS content

SummaryUsing the different values from different reports and research

studies it is possible to summarize the CH4 generation potential

for each type of feedstock considered in this review Tese valuescan be used as a baseline for determining if GHG avoidancecredits are appropriate for composting operations where feed-stocks are composted that otherwise would have been landfilledor stored in anaerobic lagoons without gas capture able 5 sum-marizes the values from the proceeding section Te IPCC hasdiscounted the potential for N

2O from landfills Te small num-

ber of studies suggests that as more data become available thismay be revised (Beacuteline et al 1999 Rinne et al 2005)

Greenhouse Gas Potential from the

Composting ProcessTe composting process has the potential to accrue GHG

debits because of the energy required for the compostingprocess and the unintentional release of GHGs during com-posting Different types of composting operations and energy

requirements for each are detailed herein Te potential forfugitive GHG release before composting when feedstocks arestockpiled and during the composting process is discussed

Feedstock Mixing

In some cases materials to be composted require grinding orsorting before composting Also some high-moisture feedstocks(like biosolids and some manures) require a bulking agent which

may also require size reduction Tis process requires energy In alife cycle analysis of composting of yard wastes a tub grinder run-ning at 1200 HP used 200 L hminus1 of fuel (Recycled Organics Unit2006) During this time the unit was able to grind 60 Mg offeedstock A tub grinder on the market in the USA the VermeerG9000 comes in 800- and 1000-HP units that can grind 50 to100 tons of feedstock per hour (httpwwwvermeercomvcomEnvironmentalEquipmentIndexjspNewsID = 12752) Teseexamples can be used to develop energy estimates for grindingfeedstocks Grinding requires about 33 L of fuel per wet ton At50 moisture this is equivalent to 66 L per dry ton If 1 L offuel weighs 0845 kg and 1 kg of fuel is taken to be the equiva-lent of 328 kg CO

2 mixing 1 dry ton of material has a CO

2

emission cost of 183 kg (Recycled Organics Unit 2006) Teseexamples can be used to develop energy estimates for grindingfeedstocks Te feedstocks that typically need grinding include woody debris and yard waste Nutrient-rich materials includ-ing manures and biosolids or materials coming from anaerobicdigesters are much more homogenous in appearance and do notrequire preparation before composting However some high-moisture feedstocks require bulking agents to provide structureand porosity and other feedstocks (eg food scraps) may requiremechanical mixing before being composted

Composting operations can generally be grouped intothree major categories Tese include windrows static piles with or without forced aeration and mechanized processes(Savage et al 1993 Haug 1993 IPCC 2006) Each of theserequires different amounts of energy to set up and managematerials while they are composting

Composting Process Energy Requirements

Windrow Systems

Windrow composting consists of feedstocks mixed at appropri-ate ratios and set up as long rows that are mechanically turned toaccelerate the composting process Te Recycled Organics Unitof the University of New South Wales (Recycled Organics Unit2006) conducted a life-cycle analysis for windrow composting ofyard wastes that included GHG estimates for the composting pro-cess Teir analysis included transport of materials to the compostfacility shredding and blending feedstocks setting up and turningpiles and transport of the finished product to end users Te esti-mate was based on a facility that processes 40000 Mg of gardenorganics per year With the windrow system this was calculated torequire 200000 L of diesel fuel or 5 L Mg minus1 of feedstock It wasbased on the assumptions that initial mixing would be done witha loader piles would remain on site for 16 wk with turning every3 to 4 wk and material would require shredding before mixing

Table 5 Summary of the maximum potential volatile solids (VS)reduction and CH

4 generation capacity of different feedstocks

that are suitable for stabilization by composting

Feedstock Maximum

destruction VS CH4

Manure

Dairy cow 48 120 g CH4 kgminus1 manure

Swine 50 141 g CH4 kgminus1

Chicken 60 179 g CH4 kgminus1

Municipal biosolids 80 0364 kg CH4 kgminus1 VS

VS destroyedMunicipal solid waste

Food waste 70 190 g CH4 kgminus1

Grass 87 101 g CH4 kgminus1 VS

Paper waste

Newsprint 22 47 g CH4 kgminus1

Offi ce paper 82 138 g CH4 kgminus1

Mixed paper 67 134 g CH4 kgminus1




Te estimate was done for a pile that is 15 to 3 m high 3 to 6 m wide and of indefinite length Estimates of GHG emissions associ-ated with fuel use included production and combustion emissions(total 328times weight of fuel used for CO

2 equivalent) Te estimate

included electricity for operating offi ce facilities and the compostfacility totaling 150000 kW hours (50000 of which were for of-fice operations) Te electricity used on site was for collecting andpumping rain water to keep piles moist Sprinklers were operated

10 h dminus1

for 7 to 10 d during the initial 4 wk of the compostingprocess Tis is equivalent to 4 kW per ton of compost Based onusing coal-fired power plants for electricity each MJ of electricity was equivalent to 028 kg CO

2 Tis equivalence would need to be

adjusted on a facility-specific basis if a portion of the energy used atthe facility came from green sources Because this estimate did notinclude gas emissions during composting the energy used to pro-duce the compost was the most important source of GHG debitsfor the composting process

One of the primary reasons that biosolids are composted isto eliminate pathogens For composting to be used as a mech-anism to destroy pathogens the USEPA has specified a mini-mum temperature and number of turns before the material

can be called ldquoClass Ardquo or pathogen free (USEPA 1993) For windrow compost piles the requirements are for five turnsand maintaining a temperature of 55degC for 72 h between eachturn Tis is within the range of the number of turns outlinedin the Recycled Organics Unit analysis and suggests that en-ergy requirements for windrow compost systems to achieveClass A pathogen reduction requirements in the USA wouldbe similar to the projections by the Recycled Organics Unit

Te USEPA (2002) did an analysis of GHG potential froma windrow compost system and concluded that processing 1Mg of feedstock requires 590 kg of diesel fuel (for materialprocessing and turning) Teir energy cost estimate is expressedas 001 metric tons carbon equivalent of indirect CO

2

emis-sions per ton of material composted with the estimate includ-ing transport of material to a compost facility (363000 Btu)and turning the pile (221000 Btu) Tis estimate is much lessdetailed than the life cycle analysis done by the Recycled Or-ganics Unit It does not include equipment requirements or thenumber of turns required for composting However both esti-mates for fuel use are similar Operations with more frequentturning of piles or with piles of larger or smaller dimensions would require some adjustments to this estimate Based on thedetail provided by the Recycled Organics Unit it should bepossible to alter the estimate with data from specific facilities

Aerated Static Pile Systems

For aerated static pile systems air needs to be forced throughthe system to maintain aerobic conditions through the pile andto control temperature Te classic aerated static pile systems isknown as the Beltsville static pile because it was developed atthe USDA research facility in Beltsville Maryland (Savage et al1993) Tis system was initially developed for municipal biosol-ids and therefore is suitable for feedstocks with high moisturecontent High-moisture feedstocks are mixed with a bulkingagent to provide structure and porosity Te mix is piled on per-

forated pipes that have been covered with finished compost orthe bulking agent Te pile is similar to that described in the sec-tion on windrow composting Te pile is then generally covered with a layer of finished compost which maintains heat withinthe pile and reduces odor emissions from the pile Air required tomaintain aerobic conditions changes with the specific environ-mental conditions and with the feedstock Air is generally turnedon for set intervals during the composting period Systems can be

controlled automatically based on temperature Air requirementsfor these systems can vary

Savage et al (1993) provide a general guide that blowers needto be suffi ciently powerful to pull 07 to 24 m3 minminus1 air per dryton Haug (1993) modeled a static pile system that consisted of44 dry Mg of municipal biosolids with a solids content of 25 with wood chips added as a bulking agent Tis is equivalentto 176 Mg total weight His calculations include aeration for a21-d period with total air required averaging 0036 m3 of air perminute per 0093 m2 A working guideline is that 0042 m3 of airare required to aerate 0093 m2 of mixture Haug gives the idealmoisture content for a compost feedstock containing biosolids at55 to 60 Tis material would have a density of 08 g cm3 If a

pile were constructed based on the dimensions recommended bySavage et al (1993) (244 times 43 times 21 or 224 m3) the total weightof the pile would be 89 Mg Tis is equivalent to 168 cfm per USton for the composting period Haug (1993) says that althoughstatic pile systems initially supplied with 024 m3 minminus1 tonminus1 drysolids aeration rates have increased and are now approximately094 m3 minminus1 tonminus1 solids Using 024 m3 minminus1 tonminus1 as a lowrange and 094 m3 minminus1 tonminus1 as a high range would seem to be aconservative approach For specific operations the blower capacityand electric requirements can be calculated using these values aslower and upper boundaries Te amount of energy required canbe calculated using a carbon equivalent of 066 kg CO

2 kWhminus1 of

electricity used (Amon et al 2006)In addition to the energy needed to move air the piles also

require energy to set up and break down Te equipment re-quired to do this is similar to that required to set up a compost windrow because the static pile system is essentially a windrowthat is not turned For this the fuel estimate prepared by theRecycled Organics Unit can be adapted to fit a static pile sys-tem In that estimate 5 L of fuel was required to process 1 Mgof feedstock including mixing and setting up turning andbreaking down piles Here mixing setting up and breakingdown piles consume 25 L of fuel for each Mg of feedstock

Mechanical Systems

Mechanical systems are based on the same concepts as wind-row and static pile systems but a portion of the composting pro-cess takes place in an enclosed structure (Haug 1993) Tere area wide range of types of structures that fall into this general cate-gory including vertical flow and horizontal flow systems In bothof these types of systems the mixed feedstock is introduced intoone end of the reactor and is gradually moved through a systemuntil it is suffi ciently stabilized and exits the enclosed system Temovement is generally combined with forced aeration In manycases in addition to the mixing that occurs as the feedstocks are




moved through the system feedstock mixing is accomplishedusing augers Te retention time in these systems is often shortso even though some decomposition occurs within the reactorthe material requires additional curing time in windrows before itis stable enough to be marketed

With the range of different systems available it is out of thescope of this review to detail energy requirements for each indi-vidually Te vast majority of composting systems in the USA

are windrow systems followed distantly by aerated static pilesystems with relatively few proprietary commercial systems inoperation However it is possible to outline general guidelines forevaluating these requirements that can be used for specific sys-tems Each of these systems includes some type of aeration Teyalso involve mechanical moving of feedstocks through the sys-tem from the top down or from the point of entry to the pointof exit Finally they require energy for loading and mixing thesubstrates and energy for setting up the curing piles that the com-posts are put into to stabilize after they are through the reactor

Steve Diddy (personal communication) provided informa-tion on energy requirements for a specific enclosed system thathis company is recommending Te system can handle up to

137 dry Mg of feedstock per day for a 365-d work year or atotal of 50000 dry Mg yrminus1 Te energy requirements for aerat-ing this system average 90 kWh per dry Mg Depending on thesource of electricity in the region where the system is used theenergy costs can be high One source gave a carbon equivalent of066 kg CO

2 kWhminus1 of electricity (Amon et al 2006) Tis is a per

ton electricity cost for aeration of approximately 60 kg CO2 Mg minus1

of material

Greenhouse Gas Emissions During the

Composting Process

Background

Several prior reviews discount the potential for GHG toevolve during the composting process or during storage of feed-stocks before composting (Recycled Organics Unit 2006 Smithet al 2001 USEPA 2002) Tey argue that a well run operationmaintains aerobic conditions to maximize the rate of decomposi-tion Tere are marked differences in decomposition rates in anaerated versus an anaerobic system In one study turning a pilefour times during a 4-mo composting period resulted in a 57plusmn 3 reduction of initial organic matter Te same feedstocksmaintained in a static pile for the same period had a 40 plusmn 5reduction of initial organic matter (Szanto et al 2007) In ad-dition the Recycled Organics Unit (2006) justifies this because

of the low moisture content and low bulk density of yard wastes Although anaerobic conditions may exist in a pile high ammoniaconcentrations within the pile are suffi cient to inhibit methano-genic bacteria An additional safeguard against the release of anyGHGs formed within a pile is the active aerobic microbial com-munity on the surface of the pile Tese organisms oxidize CH

4

before it is released into the environment (Bogner et al 1997)In two of these estimates the focus was on yard waste or mu-

nicipal solid waste including yard wastes for feedstocks (USEPA

2006 Recycled Organics Unit 2006) Another study of gasemissions during composting when using yard waste also foundlow GHG emissions In a lab incubation using yard waste as afeedstock 12 to 114 g N

2OndashN per Mg of feedstock was emitted

over an 89-d period (Hellebrand and Kalk 2001) Yard wastestypically have a lower moisture content lower bulk density anda higher CN ratio than feedstocks such as animal manures andmunicipal biosolids In the case of yard waste composting in Aus-

tralia moisture is commonly limiting Tis is not the case for allcompost facilities or for different feedstocks In situations where wet feedstocks with low CN ratios are used there is a potentialfor CH

4 and N

2O emissions from compost piles Tere is also

the potential for GHGs to volatilize from feedstocks because theyare stored before composting For storage and composting theremay be operational factors that can be modified to reduce the po-tential for GHG evolution Literature on GHG evolution fromfeedstock storage and during composting is summarized below

Other FeedstocksmdashStorage

Although feedstocks such as grass clippings and food waste aregenerally landfilled almost immediately after they are generated

animal manures are often stored before they are used Tere havebeen a number of studies to quantify CH

4 and N

2O emissions

from animal manures Tese studies have included GHG genera-tion of materials that have undergone different types of storageand treatment before storage Results from these studies indicatethat storage of manures can be a significant source of GHGs andthat management practices can be used to reduce these gases

Beacuteline et al (1999) altered the retention time and oxygen flowfor aerobically digested pig manure Tey observed N

2O formation

for all treatments and attributed this to nitrification and denitrifica-tion reactions According to the authors these reactions can occur when oxygen is between 1 and 10 of saturation or conditions aremoderately reducing Although this study was done during treat-ment rather than storage it illustrates the importance of microen-vironments for the generation of N

2O Te importance of low oxy-

gen levels in the formation of N2O has been recognized by other

authors (Wrange et al 2001) Te CN ratio of the feedstock canalso be an important variable In feedstocks with a high CN ratioN is limiting and is more likely to be immobilized than denitri-fied Yamulki (2006) added straw to manure heaps and found thatCH

4 and N

2O emissions were reduced when the CN ratio of the

mixture was increased Reductions as a of loss of N and C asN

2O and CH

4 were from 07 and 006 to 048 and 003 for N

2O

and CH4 respectively Tis was attributed to the reduction in avail-

able N and to the lower moisture content of the mixture Increased

porosity leading to higher O2 diffusion may also have been a factor Although Beacuteline et al (1999) did not report the CN ratio of thepig manure the high N content (3ndash4 g kg minus1) suggests a low CNratio Tey also tested N

2O formation in manure that had been

stored anaerobically in an enclosed space after aerobic digestion Inthe last case N

2O was formed and subsequently transformed into

N2 during storage Amon et al (2006) looked at N

2O and CH

4 from cattle ma-

nure from a dairy operation treated in a variety of ways and thenland applied Te CN ratio of the slurry was 81 reatments




included tank storage separation of liquid and solid phases fol-lowed by composting of solid and land application of liquidanaerobic and aerobic digestion and storage with a 10-cm strawcap Gas emissions during storage and land application weremeasured For all options over 99 of the total CH

4 emissions

occurred during storage of the slurry Te straw cap did notreduce CH

4 emissions from the stored slurry Te majority of

N2O (776ndash913) was also released during storage Clemens et

al (2006) looked at the effect of temperature and storage coveron gas emissions from cattle slurry (able 6) Raw and digestedmanure were tested Methane emissions increased significantly with warmer temperatures Prior anaerobic digestion in combina-tion with a cover decreased CH

4 production In another study

Sommer et al (2004) modeled CH4 and N

2O release from pig

and cattle slurry in house and after field application Tey usedin-house storage for 1 yr with field applications of the slurries in April in Denmark as the basis for their model Methane emis-sions were reduced by increased frequency of washing of manureto outdoor storage areas where cooler temperatures slowed an-aerobic decomposition Nitrous oxide release was modeled onlyfor field application due to the lack of data for stored slurries

Research on gas emissions from stockpiles of other typesof feedstocks is limited Greenhouse gas generation potentialfor stockpiled municipal biosolids is expected to be similarto values observed for anaerobically digested manure becausethe moisture content and CN ratios are similar Hansenet al (2006) measured CH

4 production from anaerobically

digested municipal wastes Tis study was modeled afterpractices in Denmark where wastes are kept in digesters for15 d and then stored for up to 11 mo before a very limitedland application window Methane generation was measuredat several temperatures to mimic conditions in outdoor stor-age tanks at different times of the year Methane produc-tion increased significantly starting at 22degC with a retentiontime of 120 d (gt43 m3 CH

4 Mg minus1 VS) and peaked at 55degC

(gt215 m3 CH4 Mg minus1 VS) Tis is equivalent to 27 kg CH

4

at 22degC and 136 kg CH4 at 55degC Mg minus1 VS Tese results are

similar to those observed for animal slurries in that increasingtemperature is a major factor in determining the quantity ofgas that is released from stockpiled feedstocks

Based on the results of these studies there are several bestmanagement practices that can be adopted to reduce the po-tential for GHG generation from stockpiled feedstocks beforecomposting As the rate of gas production increases with in-creasing temperature reducing storage time during summermonths or in warmer climates limits gas release If material is

stored it should be stored in a covered facility If material is wetand has a low CN ratio a dry carbonaceous feedstock shouldbe incorporated into the material to increase the final CNratio to gt201 to dry the material and reduce the potential fordenitrification If these practices are not adopted stockpiling offeedstocks can result in emissions of CH

4 and N

2O

Composting Process

For feedstocks that are suffi ciently nutrient rich and wetthere are a number of studies in the literature that document

GHG release from compost piles A summary of several stud-ies is presented below and in able 7 It is possible to makegeneralized conclusions from these studies Te summariesbelow are followed by a more specific discussion on the rela-tionship between different variables and GHG emissions

Hao et al (2004) looked at emissions from cattle feedlotmanure composting with straw and wood waste as bulkingagents Manure was set in windrows that were turned eighttimes over a 100-d composting period Air samples were col-lected from the top of the windrows in the morning severaltimes per week during the initial stages of the composting op-eration and then on weekly intervals Methane was detected inboth windrows during the first 60 d of the process with over50 being released by Day 30 Tese results were similar tothose observed in other studies (Fukumoto et al 2003 Lopez-Real and Baptista 1996 Sommer and Moller 2000) Tismakes sense because over time the piles would dry out and be-come more consistently aerobic In the Hao et al (2004) studyN

2O was detected in the early stage of the process and again in

the last 30 d of the process Te authors suggest that this wasthe result of denitrification of NO

3minus otal emissions for each

bulking agent were similar and equaled approximately 892 kgC as CH

4 Mg minus1 dry weight with 008 kg N Mg minus1 as N

2O

In another study Hellebrand and Kalk (2001) observedCH4 (13 kg m2) and N

2O (128 g m2) emissions from windrow

composting of animal manures on an organic farm As in Hao etal (2004) CH

4 evolution was limited to the initial composting

period Nitrous oxide emissions peaked during the third week ofcomposting Data were not given on the gas evolution on a dry- weight basis Analysis of feedstocks and moisture content of thepiles are not reported Fukumoto et al (2003) composted swinemanure in a large and small conical pile to investigate the role ofpile size in quantity of GHG emissions Manure was mixed withsawdust however the CN ratio of the final mixture is not givenotal moisture content of both piles was 65 Methane and N

2O

emissions increased with increased pile size Te authors attribute

this increase to the increased anaerobic sites within the larger pileTey attribute the formation of N

2O to nitrate from the aerobic

portion of the pile being mixed into the anaerobic section A totalof 372 and 465 g N

2O kg minus1 N and 1 and 19 g CH

4 kg minus1 OM

were formed from the small and large piles respectively Hellmanet al (1997) observed CH

4 and N

2O release from the surface

of co-composting MSW and yard waste Te moisture contentof the initial pile was 60 and the CN ratio was 261 Gases were collected from the top of the pile at a fixed time of day for

Table 6 Methane and N2O release from digested and raw cattle slurry

The importance of temperature and management options isshown Data are from Clemens et al (2006)

Winter Summer

CH4

N2O CH

4N

2O

ndashndashndashndashndashndashndashndashndashndashndashndashndashg mminus3ndashndashndashndashndashndashndashndashndashndashndashndashndash

Raw-crust 164 44 3590 49

Raw-cover 142 38 3000 57

Digested 111 40 1154 72

Digested-straw 115 40 1192 76Digested-straw-cover 81 41 1021 61




each sampling event Methane release ranged between 05 and15 g C hminus1 Mg minus1 dry weight from Day 10 to Day 28 after whichtime it fell below detection limits Nitrous oxide emissions beganafter Day 30 and ranged from lt50 mg N

2OndashN hminus1 to gt100 mg

N2OndashN hminus1 for the next 30 d Szanto et al (2007) composted pig

manure mixed with straw in astatic pile and a turned pile Te ini-tial CN ratios of the feedstocks ranged from 14 to 7 and moisturecontent of the piles was approximately 70 urning resulted inno emissions of CH

4 for the duration of the composting period

and resulted in lower emissions of N2O

Czepiel et al (1996) measured N2O emissions from com-

posting municipal biosolids and livestock waste Te biosolids were composted in an aerated static pile with wood ash usedas a bulking agent Te manure was composted in windrowsthat consisted of 25 manure and 75 seasoned hay frombedding Only the moisture content of the biosolids is given(75) Nitrous oxide and O

2 content as well as the fraction

of the pore space occupied by water are given for the biosolidscompost at Day 9 and Day 38 As with other studies N

2O

concentration increased with limited but not depleted O2 o-

tal N2O generation capacity for the manure compost pile was

given as 05 g N2OndashN kg of manure or 0125 g N

2OndashN per

dry kg feedstock otal N2O generation capacity for the biosol-ids compost pile was given as 07 g N2O per dry kg biosolids

Te amount of ash included in the mix was not provided Ina lab study using household waste with a CN ratio of 221and total C content of 38 Beck-Friis et al (2001) reportedthat of the 24 to 33 of initial N that was lost during thecomposting process lt2 evolved from the system as N

2OndashN

Tis is equivalent to 01 g N as N2O for each kg of feedstock

or 100 g Mg minus1 of feedstock Moisture content CN ratio andaeration status seem to be key variables in controlling GHG

emissions from compost piles with moisture content perhapsthe most important

Moisture Content

In a general discussion of composting Haug (1993) dis-cusses appropriate moisture contents for different feedstocksand points out that when a feedstock is too wet it is diffi cultto maintain an aerobic environment that is conducive to rapidcomposting (able 8) Ideally a compost pile should not beoxygen or moisture limited Feedstocks that are able to main-tain some structural strength including straw or wood chipscan have higher moisture than others that will subside andeliminate pore spaces Te latter category of materials includesmanures biosolids and wet wastes such as food waste and grassclippings Methane in addition to being a GHG is indicativeof anaerobic conditions that are associated with slower decom-position or composting in comparison to aerobic conditions

In all of the studies where GHG emissions have been detectedfrom the surface of the compost piles the moisture of thefeedstocks has been at or above the maximum levels for appropri-ate aeration Te importance of moisture content in controllingGHG emissions is made clear by the following study Sommer

and Moller (2000) looked at the effect of varying straw contenton GHG emissions from pig litter wo rates of straw addition were used one to bring the bulk density of the mixture to 023g cm3 and the other to to bring the bulk density to 044 g cm3Te dry matter content and CN ratio of the piles also differed236 (DM) and 1276 (CN) for the low-straw and 652and 1627 for the high-straw piles No CH

4 and minimal N

2O

(01ndash05 g N m2 minminus1 for approximately 3 d at the beginningof the composting period) were emitted from the dryer pile Tedenser pile had significantly higher emissions of both gases Te

Table 7 A summary of research reporting N2O and CH

4 emissions from composting operations The citation feedstocks used type of compost

system moisture content and quantity of gas evolved are shown

Reference Feedstock System Moisture CH4 loss N

2O loss

Hao et al 2004 cattle feedlot manure + straw windrow 60 892 kg C per Mg manure

25 of initial C

0077 kg N Mg manure

038 of initial N

cattle feedlot manure + wood chips windrow 60 893 kg C Mg

19 of initial C

0084 kg N Mg manure

06 of initial N

Hao et al 2001 cattle manure and straw bedding static pile 70 63 kg CH4ndashC Mgminus1 manure 011 kg N

2OndashN Mgminus1 manure

windrow 70 81 kg CH4ndashC Mgminus1 manure 019 kg N


Fukumoto et al 2003 swine manure + sawdust static pilendash noaeration 68 19 kg Mgminus1

OM(05 of initial C) 465 kg N Mgminus1

N46 of initial N

Lopez-Real and Bapatista 1996 cattle manure + straw windrow 75 background not measured

aerated static pile 75 background

static pile 75 48675 ppm per volume

Sommer and Moller 2000 pig litter low straw static pile 76 1916 g C02 of initial C

586 g N08 of initial N

pig litter high straw 35 BDdagger BD

Hellebrand and Kalk 2001 cattle pig manures + straw windrow 13 kg mminus2 128 g mminus2

Hellman et al 1997 yard waste + MSW windrow 60 252 g CndashCH4

54 g NndashN2O

He et al 2001 food waste aerated static pile 65 not measured 4 microL Lminus1 for 60 d

Czepiel et al 1996 biosolids + wood ash aerated static pile 75 not measured 05 kg N2O Mgminus1 dry

feedstock (13 of initial N)

manure + seasoned hay windrows not reported not measured 0125 kg N2O Mgminus1 dry

feedstock

Beck-Friis et al 2001 food waste aerated static pile 65 not measured lt07 of initial NKuroda et al 1996 swine manure + cardboard windrow 65 very low 01 of initial N

dagger BD below detection




authors attribute this difference to higher O2 content measured

in the less dense pile In addition the convection of hot air fromthe interior of the pile drove off ammonia which restricted forma-tion of N

2O in the less dense pile Te results of this study were

mirrored in a comparative study of three composting systems forcattle manure (Lopez-Real and Baptista 1996) Here a mixtureof cattle manure (cong70) and straw were composted using threesystems windrow forced aeration and static pile with no aeration

or turning Te moisture content of the feedstocks was about 75for all piles Although CH

4 concentrations in the piles where air

was incorporated were similar to background concentrations thosefrom the wet static pile were three orders of magnitude higher forseveral weeks

Te IPCC has published default values for CH4 and N

2O

emissions for different types of composting operations usingswine and cattle manures as feedstocks (IPCC 2006) Differentparameters including moisture content and CN ratio are notincluded in these estimates Te CH

4 estimates were based on the

best judgment of the authors and include a reference to a singlepublished study Methane conversion factor estimates range from05 for in-vessel composting under all temperature regimes to

15 for passive and intensive windrow composting operationsEstimates for N

2O emissions from composting animal manures

range from 0006 to 01 kg N2OndashN kg minus1 N excreted for static

pile and intensive windrow systems respectively Tese estimatesare based on the judgment of the IPCC group rather than a re-view of the existing literature

Pile Surface Reactions

Te previous section detailed the importance of feedstockvariables including CN ratio and solids in controlling fugi-tive GHG emissions from compost operations Emissions ofGHGs can be controlled by the active microbial community onthe surface of the piles that oxidize (CH

4

) or reduce (N2

O) gasesbefore they are emitted (USEPA 2002) Tere is evidence forthis in the literature Hao et al (2001) measured gas concentra-tions at a range of depths from windrowed manure compostpiles One of the piles was turned and the other was left to cure without turning Te feedstock used for both piles was relatively wet with a solids content of 30 Both CH

4 and N

2O were de-

tected in the piles during the 90 d that the piles were monitoredCH

4 consistently and N

2O periodically over the course of the

composting period Concentrations of both gases were highestbelow the pile surface Te highest CH

4 concentrations (lt15 of

gas collected) in the turned pile were found at the bottom of the windrow with concentrations in the top 46 cm ranging from 0

to 3 for the entire composting period Concentrations of N2O were detectible in the turned pile only at 71d and 84ndash90dTe highest measured concentration was between 20 and 550 μLLminus1 However this concentration was only observed at the 30- to107-cm depth Concentrations in the upper portion of the pile were at the detection limits Tis pattern was also observed in thestatic pile with higher concentrations of both gases throughoutthe composting period

Kuroda et al (1996) measured emissions of odorous com-pounds and GHG from windrowed swine manure mixed with

corrugated cardboard to bring the moisture content to 65Methane was only detected in the first day of the composting pro-cess Nitrous oxides and odorous compounds (methyl mercaptandimethyl sulfide and dimethyl disulfide) were detected in gradual-ly decreasing concentrations through the first 28 d of the compost-ing process For each of these (less pronounced for dimethyl disul-fide) emissions peaked immediately after the pile was turned andthen sharply decreased until the next turn Tis pattern suggeststhat the gases were present in the interior of the piles and were re-leased as the material from the interior was brought to the surface When not being turned diffusion of these gases to the atmospherethrough the pile was limited by decomposition of the compoundsin the aerated surface section of the pile otal release of N

2O in

this study was 01 of total initial N Tis figure is consistent withother research In a cattle manurestraw static pile system Lopez-Real and Baptista (1996) observed CH

4 concentrations in the pile

of up to 48675 mg kg minus1 per volume whereas concentrations onthe surface of the pile were 2620 mg kg minus1 per volume

Other researchers have used finished compost as a means tooxidize CH

4 from landfills before it is released to the atmosphere

Compost has also been used to construct biofilters to oxidize CH4

(Mor et al 2006) Termophilic methanotrophs have been identi-fied in compost piles that oxidize CH

4 before it is released to the

atmosphere (Jaumlckel et al 2005) Finished compost as a surfaceto active compost windrows has also been used to reduce VOCemissions from the windrows (Fatih Buyuksonmez personal com-munication) Tese data suggest that the microbial community ina compost pile is active enough to prevent or reduce the release ofGHGs from the interior of the pile to the atmosphere It also sug-gests that controls to reduce odor emissions from composting pilesincluding biofilters and capping piles with finished compost canalso reduce GHG emissions from piles

From the data presented in this discussion there seem tobe particular characteristics of compost feedstocks and com-posting operations that can be used to determine the potentialfor GHG release during the composting process

If feedstocks are low in nutrient content (CN gt301) andbull

or moisture content ( moisture lt55) then the potentialfor GHG release during composting can be discountedMaterials such as yard waste certain agricultural wastes andmixed MSW can be included in this category

If feedstocks include nutrient-rich and wet materialsbull

(including animal manures municipal biosolids food wastes and grass clippings) there is a potential that they will release GHGs when they are composting

Table 8 Maximum recommended moisture content for variouscomposting materials (from Haug 1993)

Type of waste Moisture content

of total weight

Straw 75ndash85

Wood (sawdust small chips) 75ndash90

Rice hulls 75ndash85

Municipal solid waste 55ndash65

Manures 55ndash65

Digested or raw sludge 55ndash60Wet wastes (grass clippings food waste etc ) 50ndash55




If a bulking agent is added to bring the moisture contentbull

to lt55 andor the CN ratio to gt301 andor sometype of aeration system is included as a part of thecomposting process (windrow or aerated static pile) thispotential can be discounted

If this is not the case a debit can be taken in relationbull

to the total C and N concentrations of the feedstock A conservative value for this is 25 of initial C and

15 of initial N Tese values are in agreement with theupper-end values provided by the IPCC (2006)

If the facility has an odor-control mechanism in placebull

including scrubbers that oxidize reduced sulfur compoundsor a biofilter debits for CH

4 can be eliminated If it is a

static pile system and the composting feedstocks are coveredby a layer of finished compost that is kept moist the gasemission potential can be cut by 50 for CH

4

End Use of CompostsTe benefits associated with compost use in relation to

GHG emissions were considered by the USEPA (2002) Re-

cycled Organics Unit (Recycled Organics Unit 2006) andSmith et al (2001) in their calculations Te EPA estimateand Recycled Organics Unit based their calculations on spe-cific end-use cases Smith et al (2001) based their calculationson more general properties of compost and the potential forcompost to replace peat for a range of end uses

For their estimate the Recycled Organics Unit modeled twotypes of end use for compost (i) as a soil conditioner for cot-ton with an application rate of 12 Mg ha minus1 and (ii) as a mulchfor grapes with an application of 75 Mg ha minus1 every 3 yr Fac-tors that were considered included increased soil C reduced water usage fertilizer value and reduced use of herbicides Te Australian regulations have product quality criteria for mulch

and soil conditioners with nutrient concentration being aprimary determinant Te soil conditioner is a nutrient-richproduct with total N of 1 to 2 and a water-holding capacityof 50 to 60 It contains 55 to 75 organic matter As a soilconditioner the potential C credits or benefits associated withcompost use were

Increased soil water-holding capacity of 24 tobull

3 resulting in reduced irrigation of 013 to016 mL H

2O ha minus1 in irrigated cotton (reduced energy

requirements for irrigation)

Fertilizer equivalent of 34 to 68 kg N 29 to 57 kg P andbull

24 to 48 kg K ha minus1 for the first year (reduced energy from

avoidance of synthetic fertilizers)Sequestering 29 to 59 Mg C ha bullminus1 after 10 yr

Mulch is categorized as a low-nutrient mixture made fromgarden wastes with 75 to 95 organic matter and total N of02 to 04 Te water-holding capacity of the mulch is 10 to20 Te benefits associated with use of compost as a mulch were detailed as follows

Increased soil water-holding capacity of soils by 98 withbull

total savings of 095 mL H2O ha minus1 for irrigated viticulture


72 to 108 kg K ha minus1 for the first year

Herbicide replacement of 2 to 6 L ha bullminus1

Carbon sequestration of 116 Mg C ha bullminus1 after 10 yr

Other studies have also shown the ability of compost to increase water-holding capacity and total soil organic matter For example Aggelides and Londra (2001) saw improvement in water-holdingcapacity and other soil physical properties after application of 75

150 and 300 m3 ha minus1 of a finished compost Improvements wereproportional to application rate Albiach et al (2001) noted in-creases in soil organic matter after application of 98 to 122 Mg ha minus1 of compost Soil type and local climactic conditions also influencethe extent of benefits after compost application

Te USEPA (2002) discussion considered application of13 to 32 wet tons (29ndash72 Mg ha minus1) of compost to field corn Although this estimate included some discussion of the fertil-izer value of compost and changes in soil properties associated with compost use these variables were not included in any typeof quantitative estimate As a result of this and of the low ap-plication rates benefits from land application of compost wereminimal Te different conclusions reached by scenarios modeledby the Recycled Organics Unit and the USEPA illustrate theimportance of the type of end use for compost in quantifying thebenefits associated with that end use Tese differing conclusionssuggest that quantifying benefits with regard to GHG and enduse of compost will be possible only on a case-by-case basis

Smith et al (2001) used a different approach in an attempt tobe less case specific Te authors attempted to identify the portionof the C in the compost that would persist for gt100 yr Tey notethat C dynamics vary by soil type and climate and attempt to iden-tify the fraction of the added organic matter that is likely to persistunder a range of scenarios Tey also consider likely climate chang-es in Europe as a result of global warming and their effect on soil

C dynamics in their estimate Te fraction that will persist is takento be 82 of the added C or 22 kg CO2 per wet Mg of feedstock

Tis estimate does not consider the potential for added C to restoresoil tilth which would subsequently allow the soil system to main-tain a higher level of C based on increased annual inputs related toimproved plant vigor and soil microfauna

Smith et al (2001) also consider direct replacement ofpeat by compost as an additional source of C credits for useof compost Here they calculate the quantity of peat used byhome gardeners and factor the portion of that that could bereplaced by compost For this estimate they consider only theC content of the peat and do not factor in emissions whenpeat bogs are harvested or when peat is transported to end-

use sites Credits for this end use are 29 kg CO2 per Mg offeedstock Tis type of credit may be valid for compost that isused as a peat replacement Te small quantity of credits as-sociated with this end use suggests that actual accounting togain these credits may be limited

ConclusionsTis estimate has focused primarily on GHG avoidance for

compost feedstocks where compost is chosen as a recycling option




rather than landfilling or lagoon storage Against this the potentialrelease of GHGs during the composting process were calculatedTese include emissions from stockpiles of feedstocks before activecomposting energy costs for different compost systems and GHGemissions from actively composting feedstocks At this point in theprocess the cured composts are ready to be marketed Althoughthe USEPA and the Recycled Organics Unit estimates included thepotential credits associated with compost use it is not clear if these

benefits are appropriate to consider in this estimate Te very dif-ferent scenarios used by each group resulted in different end cred-its Te way that both groups went about calculating these benefits were centered on different end uses rather than inherent propertiesof the materials Neither estimate considered landscaping uses ofcompost which are common near urban centers that producemuch of the feedstocks (MSW food waste and municipal biosol-ids) that are commonly used for composting End use of compostis diffi cult to monitor therefore it may be more appropriate toallocate any GHG credits to the end user who is able to documenthow the material was applied and the resulting savings Tis is alsothe approach taken by the CDM (2006)

Te majority of C credits for composting different feedstocks

are related to avoidance or prevention of CH4 release Compostingoperations can also be considered to be sources of GHGs for theenergy requirements for composting and for fugitive gas emissionsduring the composting process Even in a worst-case scenariohowever these emissions are minimal in comparison to the benefitsassociated with avoidance credits It is also possible to significantlyreduce emissions from compost piles by an increase in the solidscontent of the feedstocks and by an increase in the CN ratio Tisreview confirms that composting in addition to other environ-mental benefits associated with this practice can be an effectivemeans to reduce GHG emissions from a range of waste materials

Acknowledgments

Te authors would like to acknowledge Ron Macdonald andHerschel Elliot for their comments and edits to the manuscript

References Aggelides SM and PA Londra 2001 Effects of compost produced from town

wastes and sewage sludge on the physical properties of a loamy and a clay soilBioresour echnol 71253ndash259

Albiach R R Canet F Pomares and F Ingelmo 2001 Organic mattercomponents and aggregate stability after the application of differentamendments to a horticultural soil Bioresour echnol 76125ndash129

Amon B V Kryvoruchko Amon and S Zechmeister-Boltenstern 2006Methane nitrous oxide and ammonia emissions during storage and afterapplication of dairy cattle slurry and influence of slurry treatment AgricEcosyst Environ 112153ndash162

Beck-Friis B S Smaringrs H Joumlnsson and H Kirchmann 2001 Gaseous emissionsof carbon dioxide ammonia and nitrous oxide from organic household waste in a compost reactor under different temperature regimes J AgricEng Res 78423ndash430

Beacuteline F J Martinez D Chadwick F Guiziou and C-MCoste 1999 Factorsaffecting nitrogen transformations and related nitrous oxide emissions fromaerobically treated piggery slurry J Agric Eng Res 73235ndash243

Ben-Hasson RM AE Ghaly and RK Singh 1985 Design and evaluation ofno-mix energy effi cient anaerobic digester Proceedings Annual MeetingCanadian Society of Agricultural Engineering 23ndash27 June CharlottetownPrince Edward Island Canada

Bogner J M Abdelrafie Ahmed C Diaz A Faaij Q Gao S Hashimoto K

Mareckova R Pipatti and Zhang 2007 Waste management In B Metzet al (ed) Climate change 2007 Mitigation Contribution of WorkingGroup III to the Fourth Assessment Report of the Intergovernmental Panelon Climate Change Cambridge Univ Press Cambridge United Kingdomand New York

Bogner JE KA Spokas and EA Burton 1997 Kinetics of methane oxidationin a landfill cover soil emporal variations a whole-landfill oxidationexperiment and modeling of new CH

4 emissions Environ Sci echnol

312504ndash2514

Bonmati A L Flotats L Mateu and E Campos 2001 Study of thermalhydrolysis as a pretreatment to mesophilic anaerobic digestion of pig slurry

Water Sci echnol 44109ndash116Brady N and R Weil 2001 Te nature and properties of soils Prentice Hall

New York

Brown S and P Leonard 2004a Biosolids and global warming Evaluating themanagement impacts Biocycle 4554ndash56 58ndash61

Brown S and P Leonard 2004b Building carbon credits with biosolids recyclingPart II Biocycle 4525ndash29

Cho JK and SC Park 1995 Biochemical methane potential and solid stateanaerobic digestion of Korean food wastes Bioresour echnol 52245ndash253

Clarkson WW and W Xiao 2000 Bench-scale anaeraobic bioconversion ofnewsprint and offi ce paper Water Sci echnol 41393ndash100

Clean Development Mechanism 2006 ype III Other Project Activities IIIF Avoidance of methane production from biomass decay through compostingUnited Nations Framework Convention on Climate Change Available athttpcdmunfcccintmethodologiesSSCmethodologiesapprovedhtml(verified 5 Mar 2008)

Clemens J M rimborn P Weiland and B Amon 2006 Mitigation ofgreenhouse gas emissions by anaeraobic digestion of cattle slurry AgricEcosyst Environ 112171ndash177

Czepiel P E Douglas R Harriss and P Crill 1996 Measurement of N2O from

composted organic wastes Environ Sci echnol 30 2519ndash2525DeSutter M and JM Ham 2005 Lagoon-biogas emissions and carbon balance

estimates of a swine production facility J Environ Qual 34198ndash206DiStefano D and A Ambulkar 2006 Methane production and solids

destruction in an anaerobic solid waste reactor due to post-reactor caustic andheat treatment Water Sci echnol 5333ndash41

Dong H J Mangino McAllister JL Hatfield DE Johnson KRLassey M Aparecida de Lima and A Romanovskaya 2006 Emissionsfrom livestock and manure management In S Eggleston et al (ed)Intergovernmental Panel on Climate Change 2006 IPCC guidelines fornational greenhouse gas inventories Vol 4 Agriculture forestry and otherland use Available at httpwwwipcc-nggipigesorjppublic2006glvol4

htm (verified 5 Mar 2008)Eleazer WE WS Odle Y Wang and MA Barlaz 1997 Biodegradability ofmunicipal solid waste components in laboratory-scale landfills Environ Sciechnol 31911ndash918

Fukumoto Y Osada D Hanajima and K Haga 2003 Patterns and quantitiesof NH

3 N

2O and CH

4 emissions during swine manure composting without

forced aeration Effect of compost pile scale Bioresour echnol 89109ndash114

Garrison MV and L Richard 2005 Methane and manure Feasibility analysisof price and policy alternatives rans ASAE 481287ndash1294

Goodrich P D Schmidt and D Haubenschild 2005 Anaerobic digestion forenergy and pollution control Agric Eng International Te CIGR EjournalVol VII Available at httpcigr-ejournaltamueduvolume7html (verified 5Mar 2008)

Han SK and HS Shin 2004 Performance of an innovative two-stage processconverting food waste to hydrogen and methane J Air Waste Manage Assoc54242ndash249

Han Y S Sung and RR Dague 1997 emperature-phased anaerobic digestion

of wastewater sludges Water Sci echnol 36367ndash374Hansen RW 2004 Methane generation from livestock wastes Colorado State

University Cooperative extension bulletin No 5002 Available at http wwwextcolostateedupubsfarmmgt05002html (verified 5 Mar 2008)

Hansen L SG Sommer S Gabriel and H Christensen 2006 Methaneproduction during storage of anaerobically digested municipal organic waste

J Environ Qual 35830ndash836

Hao X C Chang and FJ Larney 2004 Carbon nitrogen balances andgreenhouse gas emissions during cattle feedlot manure composting JEnviron Qual 3337ndash44

Hao X C Chang F Larney and GR ravis 2001 Greenhouse gas emissionsduring cattle feedlot manure composting J Environ Qual 30376ndash386




Harris WL and RR Dague 1993 Comparataive performance of anaerobicfilters at mesophilic and thermophilic temperatures Water Environ Res65764ndash771

Haug R 1993 Te practical handbook of compost engineering Lewis PublBoca Raton FL

He Y Y Inamori M Mizuochi H Kong N Iwami and Sun 2001 Nitrousoxide emissions from aerated composting of organic waste Environ Sciechnol 352347ndash2351

Hellebrand HJ and WD Kalk 2001 Emission of methane nitrous oxide andammonia from dung windrows Nutr Cycling Agroecosyst 6083ndash87

Hellman B L Zelles A Palojaumlrvi and Q Bai 1997 Emission of climate-relevanttrace gases and succession of microbial communities during open-windrowcomposting Appl Environ Microbiol 631011ndash1018

Huang Y J Zou X Zheng Y Wang and X Xu 2004 Nitrous oxide emissionsas influenced by amendment of plant residues with different CN ratios SoilBiol Biochem 36973ndash981

IPCC 2006 2006 IPCC guidelines for national greenhouse gas inventories In SEggleston et al (ed) Vol 5 Waste Available at httpwwwipcc-nggipigesorjppublic2006glvol4htm (verified 5 Mar 2008)

Jaumlckel U K Tummes and P Kaumlmpfer 2005 Termophilic methane productionand oxidation in compost Microbiol Ecol 52175ndash184

Kaiser SK and RR Dague 1994 Te temperature-phased anaerobic biofilterprocess Water Sci echnol 29213ndash223

Karim K R Hoffmann K Klasson and MH Al-Dahhan 2005 Anaerobicdigestion of animal waste Effect of mode of mixing Water Res393597ndash3606

Kayhanian M and G chobanoglous 1992 Computation of CN ratios for

various organic fractions Biocycle 3358ndash60Klemedtsson L K Von Arnold P Weslien and P Gundersen 2005 Soil CN

ratio as a scalar parameter to predict nitrous oxide emissions Global ChangeBiol 111142ndash1147

Kruger C 2005 Anaerobic digestion Climate Friendly Farming Research BriefNo 1 Washington State Univ Center for Sustaining Agriculture and NaturalResources Available at httpcffwsuedu (verified 5 Mar 2008)

Kuroda K Osada M Yonaga A Kanematu Nitta S Mouri and Kojima1996 Emissions of malodorous compounds and greenhouse gases fromcomposting swine feces Bioresour echnol 56265ndash271

Lohila A Laurila J-P uovinen M Aurela J Hatakka Tum M Pihlatie J Rinne and Vesala 2007 Micrometeorological measurements ofmethane and carbon dioxide fluxes at a municipal landfill Environ Sciechnol 412717ndash2722

Lopez-Real J and M Baptista 1996 A preliminary comparative study of threemanure composting systems and their influence on process parameters and

methane emissions Compost Sci Util 471ndash82Luostarinen S and J Rintala 2007 Anaerobic on-site treatment of kitchen waste

in combination with black water in UASB-septic tanks at low temperaturesBioresour echnol 981734ndash1740

Maumlhnert P M Heiermann and B Linke 2005 Batch- and semi-continuousbiogas production from different grass species Ag Eng International CIGREjournal VII Available at httpcigr-ejournaltamueduvolume7html(verified 5 Mar 2008)

Matteson GC and BM Jenkins 2007 Food and processing residues inCalifornia Resource assessment and potential for power generationBioresour echnol 983098ndash3105

Metcalf amp Eddy chobanoglous G FL Burton HD Stensel 2003 Wastewaterengineering treatment and reuse McGraw-Hill Boston MA

Mor S A De Visscher K Ravinda RP Dahiya A Chandra and O VanCleemput 2006 Induction of enhanced methane oxidation in compostemperature and moisture response Waste Manage 26381ndash388

Nguyen PHL P Kuruparan and C Visvanathan 2007 Anaerobic digestionof municipal solid waste as a treatment prior to landfill Bioresour echnol98380ndash387

Nielsen HB Z Mladenovska P Westermann and BK Ahring 2004Comparison of two-stage thermophilic (68degC55degC) anaerobic digestion

with one-stage thermophilic (55degC) digestion of cattle manure BiotechnolBioeng 863291ndash300

Parravicini V E Smidt K Svardal and H Kroiss 2006 Evaluating thestabilization degree of digested sewage sludge Investigations at four municipal

wastewater treatment plants Water Sci echnol 5381ndash90

Recycled Organics Unit 2006 Life cycle inventory and life cycle assessment for windrow composting systems Te Univ of New South Wales Sydney Australia Available at httpwwwrecycledorganicscompublicationsreportslcalcahtm (verified 5 Mar 2008)

Rinne J M Pihlatie A Lohila Tum M Aurela J-P uovinen Laurilaand Vesala 2005 Nitrous oxide emissions from a municipal landfillEnviron Sci echnol 397790ndash7793

Savage GM LL Eggerth CG Golueke and LF Diaz 1993 Composting andrecycling municipal solid waste Lewis Publ Boca Raton FL

Shores RC DB Harris EL Tompson CA Vogel D Natschke RAHashmonay KR Wagoner and M Modrak 2005 Plane-integrated open-path fourier transform infrared spectrometry methodology for anaerobicswine lagoon emission measurements Appl Eng Agric 21487ndash492

Smith A K Brown S Ogilvie K Rushton and J Bates 2001 Wastemanagement options and climate change Final report to the EuropeanCommission DG Environment Available at httpeceuropaeuenvironmentwastestudiesclimate_changehtm (verified 5 Mar 2008)

Sommer SG and HB Moller 2000 Emission of greenhouse gases duringcomposting of deep litter from pig production Effect of straw content J

Agric Sci 134327ndash335Sommer SG SO Peterson and HB Moller 2004 Algorithms for calculating

methane and nitrous oxide emissions from manure management NutrCycling Agroecosyst 69143ndash154

Steinfeld H P Gerber Wassenaar V Castel M Rosales and C de Haan2006 Livestocks long shadow Environmental issues and options Food and

Agriculture Organization of the United Nations (FAO) Rome Italy

Szanto GL HVM Hamelers WH Rulkens and AHM Veeken 2007 NH3N

2O and CH

4 emissions during passively aerated composting of straw-rich

pig manure Bioresour echnol 982659ndash2670Temelis NJ and PA Ulloa 2007 Methane generation in landfills Renewable

Energy 321243ndash1257US Congress Offi ce of echnology Assessment 1989 Facing Americarsquos trash

What next for municipal solid waste OA-O-424 US Gov Print Offi ce Washington DC Available at httpwwwblackvaultcomdocumentsotaOta_2DAA19898915PDF (verified 5 Mar 2008)

USEPA 1993 Standards for the use or disposal of sewage sludge Fed Register589387ndash9415 USEPA Washington DC

USEPA 2006 Greenhouse gas emissions from management of selected materialsin municipal solid waste USEPA Washington DC Available at http

wwwepagovclimatechangewycdwasteSWMGHGreporthtml (verified3 Apr 2008)

USEPA 1999 Municipal solid waste landfills Volume 1 Summary of the

requirements for the new source performance standards and emissionguidelines for municipal solid waste landfills EPA-453-R96-004 USEPA Washington DC

USEPA 2002 Solid waste management and greenhouse gases A life-cycleassessment of emission and sinks EPA530-R-02ndash006 EnvironmentalProtection Agency USA httpepagovclimatechangewycdwastedownloadsEnergy20Savingspdf

USEPA 2005 An evaluation of a mesophilic modified plug flow anaerobicdigester for dairy cattle manure USEPA AgSAR Program WashingtonDC

Wang Y W Odle WE Eleazer and MA Barlaz 1997 Methane potential offood waste and anaerobic toxicity of leachate produced during food wastedecomposition Waste Manage Res 15149ndash167

Wrange N GL Velthof ML van Beusichem and O Oenema 2001 Role ofnitrifier denitrification in the production of nitrous oxide Soil Biol Biochem331723ndash1732

Yamulki S 2006 Effect of straw addition on nitrous oxide and methane emissions

from stored farmyard manures Agric Ecosyst Environ 112140ndash145Zeman C D Depken and M Rich 2002 Research on how the composting

process impacts greenhouse gas emissions and global warming Compost SciUtil 1072ndash86

Zhang R HM El-Mashad K Hartman F Wang G Lui C Choate and PGamble 2007 Characterization of food waste as a feedstock for anaerobicdigestion Bioresour echnol 98929ndash935




stream Because these feedstocks are part of the short-term C cyclethe CO

2 emissions from decomposing organic matter in compost

piles are not considered as additional GHG emissions In additionby composting these materials a stable reduced pathogen soil con-ditioner that may have nutrient value is produced from materialsthat have potentially been diverted from storage lagoons and land-fills Most composting operations are likely to function as a sourceof GHGs and as a means to avoid GHG release at different stages

of their operations Te stages of a composting operation that havethe potential to affect GHG emissions include selection of feed-stocks transport to and from the compost site energy use duringcomposting gas emissions during composting and end uses ofcompost products Te debited portions of the composting processinclude transport energy use during composting and fugitiveemission of GHGs other than CO

2 from composting operations

Te credited portions of the composting process include diversionof feedstocks from storage or disposal where they would generateCH

4 as well as end use of compost products

Te greenhouse gases that have the potential to be emit-ted by compost operations include CH

4 and N

2O Methane

is formed as a by-product of microbial respiration in severely

anaerobic environments when C is the only electron acceptoravailable Carbon is used as an electron acceptor when othermore energetically favorable electron acceptors includingoxygen nitrogen iron manganese and sulfur have been ex-hausted Because the environments in a waste storage lagoonlandfill or compost pile are not uniform it is also possiblethat different electron acceptors can be used simultaneouslyFor example when sulfur is used as an electron acceptorhighly odorous compounds including dimethyl disulfide andmethyl mercaptan are formed Te presence of these com-pounds can be indicative of the presence of CH

4 A compost

or waste pile that exhibits minimal odors is more likely tohave aerobic conditions throughout than a malodorous pile

Te conditions favorable to the formation of N2O are not as

well understood (Beacuteline et al 1999) Nitrous oxides can be formedduring nitrification (conversion of NH

3 to NO

3minus) and denitrifica-

tion (conversion of NO3minus to N

2) reactions although they are much

more commonly associated with denitrification (Brady and Weil2001) Denitrification involves the following transformations

2 NO3minus rarr 2NO

2minusrarr 2 NO rarr N

2O rarrN

2[1]

In soil systems N2O is much more likely to form and

volatilize when the carbon to nitrogen (CN) ratio of soilorganic matter is low (lt201) and denitrification is muchmore likely to occur under anaerobic conditions (Brady and

Weil 2001 Huang et al 2004 Klemedtsson et al 2005)For some waste storage areas or composting operations theCN ratio of the material is high enough andor the mixtureis dry enough to limit denitrification reactions

A number of recent studies have evaluated the GHG creditsand debits of composting (Clean Development Mechanism 2006Recycled Organics Unit 2006 Smith et al 2001 USEPA 2002Zeman et al 2002) For emissions associated with compostingeach of these considered energy requirements for transport of feed-

stocks to the compost facility and finished product to the end useras debits associated with the process Energy use during compost-ing was also included wo considered a turned windrow compost-ing system for their model whereas Smith et al (2001) also con-sidered closed systems with energy requirements for odor control(Recycled Organics Unit 2006 USEPA 2002) Only Zeman etal (2002) and Clean Development Mechanism (CDM) (2006)considered fugitive emissions of GHG such as CH

4 or N

2O

as debits wo (Recycled Organics Unit 2006 USEPA 2002)used yard waste as the sole feedstock whereas Smith et al (2001)considered organics diverted from municipal solid waste (MSW) which includes food and yard waste For GHG credits associated with composting each of the reviews used different scenarios TeRecycled Organics Unit (2006) and the USEPA (2002) consid-ered different agricultural end uses whereas Smith et al (2001)considered the potential for compost to replace peat for a range ofapplications Te United Nations Framework Convention on Cli-mate Change Clean Development Mechanism (CDM 2006) wasthe only study to include avoidance of methane (CH

4) generation

by the aerobic decomposition of feedstocks in a compost pile incomparison to the anaerobic breakdown of these materials in other

disposal sites in the credits associated with compostingTis review was conducted to quantify potential GHG debits

and credits associated for a wide range of feedstocks and com-posting systems We break the composting process into threedistinct phases (i) the CH

4 generation potential of different com-

post feedstocks (ii) the composting process including energyuse and fugitive emissions during composting and (iii) the enduse of compost Te first phase describes the GHG generationpotential of different feedstocks Tis is pertinent for compostingoperations that divert feedstocks from disposal sites or storagefacilities where they would be expected to generate CH

4 Because

anaerobic digestion is a common practice for municipal biosolidsand is coming to be recognized as a viable stabilization technol-ogy for other types of wastes effi ciencies of digestion and remain-ing CH

4 generation potential post digestion are also examined

Anaerobic digestion with CH4 capture for energy use or flaring

are important techniques for a source of energy and for avoidanceof fugitive GHG release (Matteson and Jenkins 2007) Second we detail the potential for gas generation for during the compost-ing process Te literature on gas emission potential for differentfeedstocks is summarized for storage before composting and dur-ing the composting process Different process variables and theireffect on gas emissions are also discussed Energy requirementsfor different compost systems are summarized Finally potentialend uses of compost and their impact on GHGs are briefly dis-

cussed Complications associated with credits and debits for thisstage of the process are described Te implications of compostend use on GHGs are qualitatively assessed Tis review is in-tended to be suffi ciently detailed so that credits and debits associ-ated with specific composting operations can be determined

Compost FeedstocksMaterials that are commonly used as feedstocks for compost-

ing operations include food paper and yard trimmings that

























4 generation po-


Cv H

w O

x N

y S


2O

rarr (v2 + w8 + x4 + 3y8 + z4)CH4

+ (v2 + w8 + x4 + 3y8 + z4)CO2

+ yNH3 + zH

2S [2]















2O evolution from


4






4 conversion


4







Totalgas CH

4 dminus1

CO2



Moles CH4



Beef 268 45 084 050 225 828 302

Dairy 391 48 123 074 33 1214 443 11ndash26

Swine 218 50 081 049 2175 8 292 19ndash43











4 recovery




4 or N





4


4 generation was



4 (15 kg CO

2 eq mminus3)








4

















4 genera-












4 that is









12H

22O

11 then




2









4



4 generation







4 emis-


4 emis-





4 emissions










d

40 694

30 655

20 60

15 56

10 50














2












4 yield of 435 L CH


4








1444 L CH4









4 kg minus1 VS
















Yield Time


4 kgminus1 Mg CO


Grass 1444 64 237 50

Grass-2 1276 57 210 50

Leaves 306 14 050 100

Branch 626 28 103 100Food 3007 134 494 120




1523 68 250 400

Offi ce paper 2173 97 357 500



4 kgminus1 Mg CO




81 435 194 715 28








4 conversion








initial VS content










Feedstock Mixing




2




Windrow Systems





Feedstock Maximum

destruction VS CH4

Manure








Paper waste










10 h dminus1







2








2 kWhminus1 of



Mechanical Systems












of material


Composting Process

Background



4







4 and N






4 and N

2O emissions



2O formation





4 and N



2O and CH


2O








2O and CH

4 from cattle ma-






4 emissions







2O release from pig







4





4 and N

2O

Composting Process









2O






2O






4 kg minus1 OM


4 and N





Winter Summer

CH4

N2O CH

4N

2O


Raw-crust 164 44 3590 49

Raw-cover 142 38 3000 57

Digested 111 40 1154 72















2O




2OndashN per



2OndashN




Moisture Content




4 and minimal N

2O






2O loss


25 of initial C

0077 kg N Mg manure

038 of initial N


19 of initial C

0084 kg N Mg manure

06 of initial N







N46 of initial N









54 g NndashN2O





feedstock














2O










4

) or reduce (N2


4 and N

2O were de-










2O in

















of total weight

Straw 75ndash85




Manures 55ndash65














4





































Acknowledgments













312504ndash2514



New York














3 N

2O and CH























































2O and CH










































4 generation po-


Cv H

w O

x N

y S


2O

rarr (v2 + w8 + x4 + 3y8 + z4)CH4

+ (v2 + w8 + x4 + 3y8 + z4)CO2

+ yNH3 + zH

2S [2]















2O evolution from


4






4 conversion


4







Totalgas CH

4 dminus1

CO2



Moles CH4



Beef 268 45 084 050 225 828 302

Dairy 391 48 123 074 33 1214 443 11ndash26

Swine 218 50 081 049 2175 8 292 19ndash43











4 recovery




4 or N





4


4 generation was



4 (15 kg CO

2 eq mminus3)








4

















4 genera-












4 that is









12H

22O

11 then




2









4



4 generation







4 emis-


4 emis-





4 emissions










d

40 694

30 655

20 60

15 56

10 50














2












4 yield of 435 L CH


4








1444 L CH4









4 kg minus1 VS
















Yield Time


4 kgminus1 Mg CO


Grass 1444 64 237 50

Grass-2 1276 57 210 50

Leaves 306 14 050 100

Branch 626 28 103 100Food 3007 134 494 120




1523 68 250 400

Offi ce paper 2173 97 357 500



4 kgminus1 Mg CO




81 435 194 715 28








4 conversion








initial VS content










Feedstock Mixing




2




Windrow Systems





Feedstock Maximum

destruction VS CH4

Manure








Paper waste










10 h dminus1







2








2 kWhminus1 of



Mechanical Systems












of material


Composting Process

Background



4







4 and N






4 and N

2O emissions



2O formation





4 and N



2O and CH


2O








2O and CH

4 from cattle ma-






4 emissions







2O release from pig







4





4 and N

2O

Composting Process









2O






2O






4 kg minus1 OM


4 and N





Winter Summer

CH4

N2O CH

4N

2O


Raw-crust 164 44 3590 49

Raw-cover 142 38 3000 57

Digested 111 40 1154 72















2O




2OndashN per



2OndashN




Moisture Content




4 and minimal N

2O






2O loss


25 of initial C

0077 kg N Mg manure

038 of initial N


19 of initial C

0084 kg N Mg manure

06 of initial N







N46 of initial N









54 g NndashN2O





feedstock














2O










4

) or reduce (N2


4 and N

2O were de-










2O in

















of total weight

Straw 75ndash85




Manures 55ndash65














4





































Acknowledgments













312504ndash2514



New York














3 N

2O and CH























































2O and CH


























4 recovery




4 or N





4


4 generation was



4 (15 kg CO

2 eq mminus3)








4

















4 genera-












4 that is









12H

22O

11 then




2









4



4 generation







4 emis-


4 emis-





4 emissions










d

40 694

30 655

20 60

15 56

10 50














2












4 yield of 435 L CH


4








1444 L CH4









4 kg minus1 VS
















Yield Time


4 kgminus1 Mg CO


Grass 1444 64 237 50

Grass-2 1276 57 210 50

Leaves 306 14 050 100

Branch 626 28 103 100Food 3007 134 494 120




1523 68 250 400

Offi ce paper 2173 97 357 500



4 kgminus1 Mg CO




81 435 194 715 28








4 conversion








initial VS content










Feedstock Mixing




2




Windrow Systems





Feedstock Maximum

destruction VS CH4

Manure








Paper waste










10 h dminus1







2








2 kWhminus1 of



Mechanical Systems












of material


Composting Process

Background



4







4 and N






4 and N

2O emissions



2O formation





4 and N



2O and CH


2O








2O and CH

4 from cattle ma-






4 emissions







2O release from pig







4





4 and N

2O

Composting Process









2O






2O






4 kg minus1 OM


4 and N





Winter Summer

CH4

N2O CH

4N

2O


Raw-crust 164 44 3590 49

Raw-cover 142 38 3000 57

Digested 111 40 1154 72















2O




2OndashN per



2OndashN




Moisture Content




4 and minimal N

2O






2O loss


25 of initial C

0077 kg N Mg manure

038 of initial N


19 of initial C

0084 kg N Mg manure

06 of initial N







N46 of initial N









54 g NndashN2O





feedstock














2O










4

) or reduce (N2


4 and N

2O were de-










2O in

















of total weight

Straw 75ndash85




Manures 55ndash65














4





































Acknowledgments













312504ndash2514



New York














3 N

2O and CH























































2O and CH


























12H

22O

11 then




2









4



4 generation







4 emis-


4 emis-





4 emissions










d

40 694

30 655

20 60

15 56

10 50














2












4 yield of 435 L CH


4








1444 L CH4









4 kg minus1 VS
















Yield Time


4 kgminus1 Mg CO


Grass 1444 64 237 50

Grass-2 1276 57 210 50

Leaves 306 14 050 100

Branch 626 28 103 100Food 3007 134 494 120




1523 68 250 400

Offi ce paper 2173 97 357 500



4 kgminus1 Mg CO




81 435 194 715 28








4 conversion








initial VS content










Feedstock Mixing




2




Windrow Systems





Feedstock Maximum

destruction VS CH4

Manure








Paper waste










10 h dminus1







2








2 kWhminus1 of



Mechanical Systems












of material


Composting Process

Background



4







4 and N






4 and N

2O emissions



2O formation





4 and N



2O and CH


2O








2O and CH

4 from cattle ma-






4 emissions







2O release from pig







4





4 and N

2O

Composting Process









2O






2O






4 kg minus1 OM


4 and N





Winter Summer

CH4

N2O CH

4N

2O


Raw-crust 164 44 3590 49

Raw-cover 142 38 3000 57

Digested 111 40 1154 72















2O




2OndashN per



2OndashN




Moisture Content




4 and minimal N

2O






2O loss


25 of initial C

0077 kg N Mg manure

038 of initial N


19 of initial C

0084 kg N Mg manure

06 of initial N







N46 of initial N









54 g NndashN2O





feedstock














2O










4

) or reduce (N2


4 and N

2O were de-










2O in

















of total weight

Straw 75ndash85




Manures 55ndash65














4





































Acknowledgments













312504ndash2514



New York














3 N

2O and CH























































2O and CH































2












4 yield of 435 L CH


4








1444 L CH4









4 kg minus1 VS
















Yield Time


4 kgminus1 Mg CO


Grass 1444 64 237 50

Grass-2 1276 57 210 50

Leaves 306 14 050 100

Branch 626 28 103 100Food 3007 134 494 120




1523 68 250 400

Offi ce paper 2173 97 357 500



4 kgminus1 Mg CO




81 435 194 715 28








4 conversion








initial VS content










Feedstock Mixing




2




Windrow Systems





Feedstock Maximum

destruction VS CH4

Manure








Paper waste










10 h dminus1







2








2 kWhminus1 of



Mechanical Systems












of material


Composting Process

Background



4







4 and N






4 and N

2O emissions



2O formation





4 and N



2O and CH


2O








2O and CH

4 from cattle ma-






4 emissions







2O release from pig







4





4 and N

2O

Composting Process









2O






2O






4 kg minus1 OM


4 and N





Winter Summer

CH4

N2O CH

4N

2O


Raw-crust 164 44 3590 49

Raw-cover 142 38 3000 57

Digested 111 40 1154 72















2O




2OndashN per



2OndashN




Moisture Content




4 and minimal N

2O






2O loss


25 of initial C

0077 kg N Mg manure

038 of initial N


19 of initial C

0084 kg N Mg manure

06 of initial N







N46 of initial N









54 g NndashN2O





feedstock














2O










4

) or reduce (N2


4 and N

2O were de-










2O in

















of total weight

Straw 75ndash85




Manures 55ndash65














4





































Acknowledgments













312504ndash2514



New York














3 N

2O and CH























































2O and CH























4 conversion








initial VS content










Feedstock Mixing




2




Windrow Systems





Feedstock Maximum

destruction VS CH4

Manure








Paper waste










10 h dminus1







2








2 kWhminus1 of



Mechanical Systems












of material


Composting Process

Background



4







4 and N






4 and N

2O emissions



2O formation





4 and N



2O and CH


2O








2O and CH

4 from cattle ma-






4 emissions







2O release from pig







4





4 and N

2O

Composting Process









2O






2O






4 kg minus1 OM


4 and N





Winter Summer

CH4

N2O CH

4N

2O


Raw-crust 164 44 3590 49

Raw-cover 142 38 3000 57

Digested 111 40 1154 72















2O




2OndashN per



2OndashN




Moisture Content




4 and minimal N

2O






2O loss


25 of initial C

0077 kg N Mg manure

038 of initial N


19 of initial C

0084 kg N Mg manure

06 of initial N







N46 of initial N









54 g NndashN2O





feedstock














2O










4

) or reduce (N2


4 and N

2O were de-










2O in

















of total weight

Straw 75ndash85




Manures 55ndash65














4





































Acknowledgments













312504ndash2514



New York














3 N

2O and CH























































2O and CH
























10 h dminus1







2








2 kWhminus1 of



Mechanical Systems












of material


Composting Process

Background



4







4 and N






4 and N

2O emissions



2O formation





4 and N



2O and CH


2O








2O and CH

4 from cattle ma-






4 emissions







2O release from pig







4





4 and N

2O

Composting Process









2O






2O






4 kg minus1 OM


4 and N





Winter Summer

CH4

N2O CH

4N

2O


Raw-crust 164 44 3590 49

Raw-cover 142 38 3000 57

Digested 111 40 1154 72















2O




2OndashN per



2OndashN




Moisture Content




4 and minimal N

2O






2O loss


25 of initial C

0077 kg N Mg manure

038 of initial N


19 of initial C

0084 kg N Mg manure

06 of initial N







N46 of initial N









54 g NndashN2O





feedstock














2O










4

) or reduce (N2


4 and N

2O were de-










2O in

















of total weight

Straw 75ndash85




Manures 55ndash65














4





































Acknowledgments













312504ndash2514



New York














3 N

2O and CH























































2O and CH




























of material


Composting Process

Background



4







4 and N






4 and N

2O emissions



2O formation





4 and N



2O and CH


2O








2O and CH

4 from cattle ma-






4 emissions







2O release from pig







4





4 and N

2O

Composting Process









2O






2O






4 kg minus1 OM


4 and N





Winter Summer

CH4

N2O CH

4N

2O


Raw-crust 164 44 3590 49

Raw-cover 142 38 3000 57

Digested 111 40 1154 72















2O




2OndashN per



2OndashN




Moisture Content




4 and minimal N

2O






2O loss


25 of initial C

0077 kg N Mg manure

038 of initial N


19 of initial C

0084 kg N Mg manure

06 of initial N







N46 of initial N









54 g NndashN2O





feedstock














2O










4

) or reduce (N2


4 and N

2O were de-










2O in

















of total weight

Straw 75ndash85




Manures 55ndash65














4





































Acknowledgments













312504ndash2514



New York














3 N

2O and CH























































2O and CH






















4 emissions







2O release from pig







4





4 and N

2O

Composting Process









2O






2O






4 kg minus1 OM


4 and N





Winter Summer

CH4

N2O CH

4N

2O


Raw-crust 164 44 3590 49

Raw-cover 142 38 3000 57

Digested 111 40 1154 72















2O




2OndashN per



2OndashN




Moisture Content




4 and minimal N

2O






2O loss


25 of initial C

0077 kg N Mg manure

038 of initial N


19 of initial C

0084 kg N Mg manure

06 of initial N







N46 of initial N









54 g NndashN2O





feedstock














2O










4

) or reduce (N2


4 and N

2O were de-










2O in

















of total weight

Straw 75ndash85




Manures 55ndash65














4





































Acknowledgments













312504ndash2514



New York














3 N

2O and CH























































2O and CH































2O




2OndashN per



2OndashN




Moisture Content




4 and minimal N

2O






2O loss


25 of initial C

0077 kg N Mg manure

038 of initial N


19 of initial C

0084 kg N Mg manure

06 of initial N







N46 of initial N









54 g NndashN2O





feedstock














2O










4

) or reduce (N2


4 and N

2O were de-










2O in

















of total weight

Straw 75ndash85




Manures 55ndash65














4





































Acknowledgments













312504ndash2514



New York














3 N

2O and CH























































2O and CH





























2O










4

) or reduce (N2


4 and N

2O were de-










2O in

















of total weight

Straw 75ndash85




Manures 55ndash65














4





































Acknowledgments













312504ndash2514



New York














3 N

2O and CH























































2O and CH






























4





































Acknowledgments













312504ndash2514



New York














3 N

2O and CH























































2O and CH

























Acknowledgments













312504ndash2514



New York














3 N

2O and CH























































2O and CH




























































2O and CH


















greenhouse gas balance for composting operations - sally brown

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