Calculator Tool for Determining Greenhouse Gas Emissions for

Calculator Tool for DeterminingGreenhouse Gas Emissions forBiosolids Processing and End UseS A L L Y B R O W N , † , * N E D B E E C H E R , ‡ A N DA N D R E W C A R P E N T E R §

School of Forest Resources, University of Washington Box352100 Seattle, Washington 98195, United States, North EastBiosolids and Residuals Association, PO Box 422 Tamworth,New Hampshire 03886, United States, Northern Tilth,P.O. Box 361 Belfast, Maine 04915, United States

Received April 15, 2010. Revised manuscript receivedOctober 21, 2010. Accepted October 25, 2010.

A greenhouse gas (GHG) calculator tool (Biosolids EmissionsAssessment Model, BEAM) was developed for the CanadianCouncil of Ministers of the Environment to allow municipalitiesto estimate GHG emissions from biosolids management. Thetool was developed using data from peer reviewed literature andmunicipalities. GHG emissions from biosolids processingthrough final end use/disposal were modeled. Emissions fromnine existing programs in Canada were estimated using themodel. The program that involved dewatering followed bycombustion resulted in the highest GHG emissions (Mg CO2e100 Mg-1 biosolids (dry wt.). The programs that had digestionfollowed by land application resulted in the lowest emissions(-26and-23MgCO2e100Mg-1 biosolids (drywt.).Transportationhad relatively minor effects on overall emissions. The greatestareas of uncertainty in the model include N2O emissionsfrom land application and biosolids processing. The modelsuggests that targeted use of biosolids and optimizing processesto avoid CH4 and N2O emissions can result in significantGHG savings.

Introduction

Wastewater treatment systems often constitute the singlelargest use of electricity within municipal governments with3% of electricity use in the U.S consumed in water andwastewater treatment (1). GHG emissions from wastewatertreatment have been classified as one of the larger minorsources of emissions (2). Energy use is often considered tobe the primary source of GHG emissions related to wastewater(3-6). A recent re-examination of initial estimates resultedin a greater than 100% increase in emissions of N2O and CH4

(7). Biosolids treatment and end use can constitute up to40% of total emissions associated with wastewater treatment(8). A range of different stabilization and end use technologiesare widely available, each with different associated costs andenvironmental impacts (9, 10).

Decisions on end use/disposal of municipal biosolids havetraditionally been based on cost, regulatory, environmental,and public acceptance considerations. Environmental con-

cerns have generally focused on contaminants in the biosolids(11-14). Understanding the GHG emissions associated withdifferent biosolids management practices is likely to influencepublic opinion and municipal decision-making. It can alsobe used as a model for management of other residualsincluding animal manures.

Different biosolids processing technologies require vary-ing energy and chemical inputs. Fugitive emissions of CH4

and N2O during processing and end use of biosolids canresult in significant debits. End use of biosolids may generatecredits, through energy production, as a substitute forsynthetic fertilizers, and through carbon sequestration insoils. These factors have been discussed to varying degreesin previous studies (9, 15-19). The Intergovernmental Panelon Climate Change (IPCC) includes limited discussion ofthese factors in separate sections of the documents on wastemanagement, mitigation, and agriculture (6, 20, 21).

There have been few studies that effectively integratedthe potential emissions/sequestration associated with thefull range of biosolids management options, and those haveoften neglected fugitive emissions or potential credits(4, 5, 9, 22). The goal of the current study was to create a toolfor modeling and calculating GHG emissions from differentbiosolids processing and end use options that includes defaultvalues but also provides for use of site specific data. The toolwas designed to compare the GHG impact of differentbiosolids management options. Data provided by nineparticipating municipalities with different biosolids process-ing and end use programs were put through the model.

Materials and MethodsBiosolids management was divided into categories for solidsprocessing and stabilization, and end use and disposal.Default values for each unit process, including inputs, energyuse, and fugitive gas emissions, were developed based onvalues from published literature and data from individualtreatment facilities. Potential credits for each process werealso described. When multiple values were available for aunit process, preference was given to values from peerreviewed literature or scientific studies. The range of valuesconsidered for each process is shown in the SupportingInformation (SI). Emissions related to electricity productionwere calculated using specific factors for Canadian provinces(23). These ranged from 10 CO2e (g/kWh) in Manitoba,Newfoundland, and Quebec to 926 CO2e (g/kWh) in Alberta.When available, facility-specific data is used in place of defaultvalues. Emissions/credits from each process were classifiedas Scope 1 (direct emissions), Scope 2 (purchased electricity,heat or steam), Scope 1 and 2 combined, or Scope 3 (indirectemissions from production of purchased materials and usesof end products). Carbon dioxide emissions as a result ofaerobic decomposition of biosolids organics were consideredbiogenic in origin and not considered in the model. Calcula-tions were made and are reported on a per dry Mg biosolidsproduced. Individual unit processes and values for munici-palities will be discussed.

Aerobic Digestion. Aerobic digestion (activated sludgetreatment, aerated lagoons, and trickling filters) is unlikelyto be a source of significant CH4 or N2O emissions except forcontrolled nutrient removal via nitrification (6). The modelincludes default values for electricity use for aeration andmixing based on a sludge retention time of 15 days (10).

Storage Lagoons. Anaerobic lagoons storing organicresiduals have been identified as sources of CH4 (6). Bothtemperature and depth of the lagoon will influence the

* Corresponding author phone: (206) 616 1299; fax: (206) 685 3091;e-mail: [email protected].

† University of Washington.‡ North East Biosolids and Residuals Association.§ Northern Tilth.

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potential for CH4 release. Minimal emissions are predictedat temperatures less than 15 °C for nonaerated lagoons.Emissions of 0.12 and 0.40 kg CH4 kg BOD are predicted forlagoons less and greater than 2 m in depth, respectively (6).Aerated lagoons will have minimal CH4 emissions. Emissionsfrom electricity consumption by aeration blowers or me-chanical mixers are included in the model.

Anaerobic Digestion. Anaerobic digestion is generallyused to meet regulatory requirements for volatile solids (VS)reduction (10). The CH4 generated during digestion can beflared or used to provide heat and power for facilities. In themodel, total CH4 is calculated as a function of the total VSdestruction (10, 24). Biogas yields from VS destruction average0.9 m3/kg VS destroyed (25).

Digesters require energy for heating and operating pumpsand mixers. Default values for electricity requirements andheat loss, based on a typical heat loss of 4.62 m3 of naturalgas/m3 sludge treated (10), are included in the model. Thereare potential fugitive emissions from combustion or flaringof digester gas. A range of values for gas flare efficiency havebeen reported (2, 3). The model uses a default value of 0.3%(26). Emissions of N2O from incomplete combustion areminimal per Mg dry biosolids (between 0.004 and 1.7 g N2O/kg CH4 burned) (3, 6). The model includes default values forVS destruction and composition of biogas and uses U.S. EPAvalues for biogas conversion to electricity.

Thickening, Conditioning, and Dewatering. Emissionsfrom thickening, conditioning, and dewatering includeemissions from polymer production and electricity use.Polymer manufacturing emissions (Scope 3) are approxi-mately 9.0 Mg CO2eq/Mg polymer (27). A default dosage of5 kg of polymer per Mg dry solids was used (23). Centrifugesuse considerably more electricity than belt filter presses.Default values in the model reflect this difference: 101.4 kWhfor centrifuges and 4.9 kWh for presses, per Mg dry sludgetreated (28).

Thermal Drying. Rotary dryers are the most commondrying systems used in North America, generally operatingat 340-370 °C (23). Default electricity for drying was set at214 kWh/Mg dry solids, based on biosolids thermal dryingdata from Windsor, Ontario. Default fuel use for drying wascalculated based on energy required to evaporate water fromsludge and initial and final solids content (10).

Alkaline Stabilization. Lime stabilization is used to meetpathogen reduction prior to land application or landfilldisposal. If the lime is processed specifically for biosolidsstabilization, its production has significant embedded, supplychain (Scope 3) carbon emissions (9). The model uses a supplychain cost of 0.9 Mg CO2e/Mg lime (27). If the liming agentused is a residual from another process, these debits do notapply. Use of lime stabilized biosolids in soils displacesagricultural lime and emissions associated with its use. IPCCestimated emissions of 0.12 Mg CO2e per Mg agriculturallimestone applied to the soil (20). The model includesproduction emissions for total quantity of lime used (9, 28, 29).Credits for displacement of agricultural lime are also included.

Composting. Composting results in emissions fromenergy use and fugitive gas release. Different systems havedifferent energy requirements with lowest requirementsassociated with windrows (5 L of fuel per dry Mg feedstock)and highest for in-vessel systems (90 kWh per dry Mg) (16).The model includes fuel requirements for mixing (18.3 kgCO2e) and turning (14 kg CO2e) per dry Mg feedstock (16, 30).Average energy consumption, including requirements foraeration and odor control across 16 in-vessel compostingfacilities, was 40 kWh per Mg of waste, based on operatingnear full capacity (31, 32). The model also includes aeratedstatic pile and windrow systems.

Methane emissions during composting have been re-ported (16). The Clean Development Mechanism (CDM)

protocol for composting requires oxygen measures to docu-ment the absence of CH4 (33). Studies have shown that CH4

is oxidized in the upper portion of the windrow, with compostused to oxidize CH4 (34). Storage of finished compost releasestrace quantities of CH4 and N2O (35). Regulations forcomposting biosolids require internal pile temperature of 55°C, which is associated with aerobic decomposition.

Nitrous oxide has also been detected during composting(up to 4.6% of total N released as N2O) with increasedemissions resulting from low C:N ratios and high moisturecontent (36, 37). Emissions are reduced by maintaining piletemperature at 55° and by incorporating finished compostinto the pile (36, 38, 39). Default values for N2O and CH4

emissions are provided for piles with excess moisture andlow C:N ratios. The model reduces emissions when a compostcover or biofilter is used.

End Use or DisposalLandfill. In the model, fugitive emissions are the major debitsassociated with landfilling. Landfills are considered a sig-nificant source of CH4 (2, 40). Decomposition rates areaccelerated in sanitary landfills (41-43). Protocols exist fordiversion of biosolids from landfills to composting facilities(6, 33). The decay rate constant for biosolids from the CDMprotocol for CH4 generation in warm wet environments (0.40)was used for default value as these temperatures arecharacteristic of sanitary landfills (33, 41, 42). Default valuesincluded consideration of gas collection efficiency and onsetof collection systems (44-49). Nitrous oxide emissions fromlandfilled biosolids have also been reported (40, 44, 50, 51).The model includes a default debit for N2O emissionsequivalent to emissions from compost. The range of valuesassociated with landfill gas emissions are reported in the SI.Biosolids used as a component of manufactured soil materialfor final landfill cover are considered as an agriculturalapplication and not included in the landfill disposal sectionof the model.

Combustion. There is growing interest in combustion ofbiosolids as a disposal/end use option. Multiple hearth orfluidized bed technologies are the most prevalent, with higherefficiency in fluidized beds (52). There was insufficient dataon pyrolysis/gasification facilities to model emissions fromthese facilities. Because of the high moisture content inbiosolids, combustion operations often require supplementalenergy. Use of waste heat will decrease energy requirements.The model uses the Btu value, percent solids, and the amountof energy required to evaporate water from sludge to calculatea default balance for combustion (10).

Fugitive Emissions. The IPCC default value of 4.85 × 10-5

kg CH4 emitted/dry kg wastewater solids burned, was usedin this model (6). Combustion temperature is the primaryvariable controlling N2O emissions, with higher emissionsobserved at lower temperatures. The IPCC default value forN2O release from combustion is based on moisture contentwith limited information provided on percent solids for eachcategory and limited data forming the basis for the values(6, 53, 54). A study of emissions from fluidized bed combus-tion facilities for monoincineration using continuous moni-toring showed significantly higher emissions factors rangingfrom 1520-6400 g N per dry Mg biosolids (19). The emissionswere described as a function of total N in the material usingthe equation:

where η is the % of total N that is volatilized as N2O, and Tf

is the average highest freeboard temperature from thefluidized bed facilities. There is limited published data oncocombustion of coal or MSW and biosolids (54). There wasno published data for emissions from multiple hearth

η ) 161.3 - 0.140Tf

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furnaces. These facilities have more frequent start-up andshut-down with associated temperature fluctuations (52).For this study, no distinction is made between mono- andcocombustion of biosolids or types of facilities. Nitrous oxideemissions are calculated using the equation presented abovewith reduction factors for drier biosolids. The model emis-sions factors for combustion at 850 °C, are similar to emissionsfrom the IPCC default. The ash resulting from combustioncan be used as a soil amendment or for cement manufacture.Beneficial use of ash is given a credit based on the quantityof lime or phosphorus it displaces (9).

Direct Land ApplicationThe model includes CO2 emissions debits for transport andland application.

Fugitive Emissions. Biosolids are generally applied toaerobic soils to meet the N requirements of a crop. Previouswork has shown minimal CH4 release, even in poorly drainedsoils (15, 55). The model includes CH4 emissions for storageprior to land application. A number of studies have quantifiedN2O release from soils, with higher emissions on poorly

drained soils in warmer climates (56-59). A majority ofemissions associated with the production of agronomic cropshas been attributed to N2O release (60). The IPCC defaultfactor for N2O emissions for fertilizer, compost and biosolidsuse are 1% of the total N added. Published literature generallyreports lower emissions for biosolids compared to fertilizer(15, 57, 61, 62). The range of emissions is shown in the SI.The current model considers N2O emissions from biosolidsas equivalent to synthetic fertilizer for biosolids applied asa fertilizer replacement.

Offsets from Land Application. Using biosolids in lieu ofsynthetic fertilizers results in avoidance of Scope 3 emissionsdue to energy use from production of synthetic fertilizers.Different values for emissions have been reported (9, 30).For this model, we used default values of 4 and 2 kg CO2e/kgfor N and P respectively, with no distinction made betweentotal and available nutrients (30, 63, 64). As biosolids supplyadditional macro- and micronutrients, default values wereconsidered conservative. Offsets associated with increasedsoil organic matter are included in the model. Increases insoil carbon have been observed in biosolids amended soils

TABLE 1. Data from Nine Municipalities Used to Model Greenhouse Gas Emissions

municipalitypopulation

served

wastewatertreated(MLD)

weighted GHGemissions for

electricitygeneration

g CO2e/kWh treatment processes end use/disposal

GHG emissionsMg CO2e/100

Mg drysolids

TB, Ontario 100 000 70 181

• anaerobic digestion• centrifuge dewatering

biosolids/soil landfill cover 46

AN, Quebec 330 000 295 10• rotary press dewatering

• incineration/heat recovery• ash recycling

148LA, Quebec 271 600 254 10 • rotary press dewatering

• rotary drum hightemperature drying

• landfilling dewatered cake• cement kiln incineration

49

WI, Ontario 181 350 161 181 • centrifuge dewatering• rotary drum high

temperature drying

agricultural land application 10

MO, NewBrunswick

125 000 79 352 • centrifuge dewatering• polymer addition• alkaline stabilization• composting

land application 5

VA, BritishColumbia

980 000 436 20 • gravity thickening• dissolved air• floatation thickening• anaerobic digestion• centrifuge dewatering

restoration land application -23

HX, NovaScotia 54 000 27 733

• anaerobic digestion• Fournier press dewatering• alkaline stabilization

agricultural application 28NA, British

Columbia25 000 10 20 • gravity thickening

• aerobic digestion• centrifuge dewatering

silvicultural land application 12

HA, Ontario 165 000 96 181 • dissolved airfloatation thickening

• anaerobic digestion• polymer addition• belt filter press

dewatering

liquid and dewatered biosolidsagricultural application

-26

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(18, 65, 66). The current model provides a default credit of25 Mg CO2e 100 Mg-1 biosolids (dry wt.). The range of reportedvalues for fertilizer offsets and soil carbon sequestration areprovided in the SI.

Applying the Model. Data from nine wastewater treatmentfacilities across Canada was applied to the spreadsheet. Thefacilities were selected to represent different treatmentprocesses and end use/disposal programs. This enabled adirect comparison of different biosolids management sce-narios with regard to GHG emissions. The programs evalu-ated, treatment and end use for biosolids, and associatedGHG emissions are shown in Table 1.

Total GHG emissions per dry Mg of biosolids ranged froma low of -26 Mg CO2e 100 Mg-1 biosolids (dry wt.) for HA(anerobic digestion, polymer addition, belt filter pressdewatering followed by liquid and dewatered land applica-tion) to 144 Mg CO2e 100 Mg-1 biosolids (dry wt.) for AN(rotary press dewatering followed by incineration with heatrecovery and ash recycling). This difference was observeddespite the fact that emissions associated with electricity

use in HA were significantly higher (181 g CO2e kWh-1) thanthose in AN (10 g CO2e kWh-1).

The bulk of emissions and credits for the differentprograms were associated with indirect factors. This illustratesthe importance of considering a full range of potential GHGimpacts when evaluating different biosolids treatment andend use options. Emissions associated with energy andtransport are shown in Figure 1a. Emissions associated withfugitive gas release, credits from soil carbon sequestration,use of ash, fertilizer offset credits, or credits for heat recoveryare shown in Figure 1b.

The wide range of GHG costs associated with electricityuse across Canada shows the importance of consideringprovince specific factors as well as future power needs whenconsidering the benefits of an anaerobic digestion facilitywith energy capture. For provinces with low GHG costs forelectricity, use of heat for drying to offset transport emissionscould be preferable to generating electricity.

A sensitivity analysis was conducted for two municipalitiesto see how the range of reported factors would influence theoutcomes of this analysis. Midrange values were used for themodel as a means to show general trends while remainingconservative considering the high level of uncertainty (Figure2). Transport and electricity use were not included in thisestimate. Uncertainties related to soil carbon sequestrationand N2O emissions were associated with the largest differ-ences in end values. The range in reported values weresufficient to alter the net balance in the VA program from anet credit per dry 100 Mg biosolids of 293 Mg CO2e (low endfactors) to a net emitter of 53 Mg CO2e 100 Mg-1 biosolids(dry wt.) (high range emissions factors). The default valuesfor VA resulted in a net credit of 42 Mg CO2e 100 Mg-1 biosolids(dry wt.). For landfilled biosolids, the high-end emissionsscenario used high decomposition rates with midrange gascapture efficiency. The low end coupled slower decomposi-tion with more effective gas collection. As collection systemsare not required for the first three years after material isdeposited, these changes had a low impact on total emissions[range from 32-53 Mg CO2e 100 Mg-1 biosolids (dry wt.)].

A side-by-side comparison of two of the Canadianprograms illustrates the importance of fugitive emissions,energy, minimal impact of transport, and the importance ofScope 3 factors in determining the potential GHG impactsof different biosolids management options (Table 2). VA, amunicipality that uses anaerobic digestion followed by land

FIGURE 1. Greenhouse gas emissions or credits associated with(a) electricity, fuel and transport and (b) fugitive gas emissions,carbon sequestration, and fertilizer offsets for nine biosolidsprograms in Canada. Emissions include province-specificweighting factors for electricity.

FIGURE 2. High, low, and default emissions factors for VAshowing range of reported values for fertilizer offsets, soil carbonsequestration, CH4 emissions from flaring biogas, and N2Oemissions following land application. Transport and electricity useare not included.

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application, and AN, an incineration facility, were used forthis comparison. These programs feature very different enduse options and represent the highest emissions (AN) andclose to the lowest emissions of the programs modeled inthis exercise. The CO2e for electricity in both provinces arealso similar at 20 and 10 g CO2e kWh-1, respectively.

Data from 1 of 5 treatment plants operated by VA wasused for this model. The plant treats an average of 436megaliters per day (MLD). Primary solids are gravity thickenedand secondary solids are thickened by dissolved air floatation.Thickened solids are fed to thermophilic anaerobic digesters.Digester gas is burned for heat alone (18%) and heat pluselectricity (60%), generating 61 MJ/yr of heat or 20 × 106

kWh/yr of electricity. A portion (22%) of the gas is flared.Biosolids are dewatered to 31% solids using polymer andcentrifuges. Approximately 40 000 wet Mg of biosolids aregenerated and land applied with round trip distance toprojects of 520-875 km.

At AN, the treatment plant services approximately 330 000people with total inflow of 295 MLD. Sludge is dewateredusing chemical mixing, flocculation, and settling. It isconcentrated in thickening tanks and dewatered using rotarypresses and polymer. The dewatered sludge is incineratedin a fluidized bed monocombustion facility at 760 °C. Processheat is used for process and facility heating. Externalelectricity and fuel are also required. The ash (8 Mg per day)is used for cement production at a cement kiln 35 km fromthe treatment plant.

Emissions per dry Mg biosolids were similar for bothmunicipalities for conditioning, dewatering, and thickening.Transport emissions were higher in VA [12.5 Mg CO2e 100Mg-1 biosolids (dry wt.)] in comparison to AN [0.2 Mg CO2e100 Mg-1 biosolids (dry wt.)]. VA derives a negative net GHGbalance of -303 Mg CO2e 100 Mg-1 biosolids (dry wt.) fromanaerobic digestion with heat and electricity generation and-48 Mg CO2e 100 Mg-1 biosolids (dry wt.) from landapplication of the biosolids for fertilizer replacement andsoil carbon sequestration. This credit has the potential toincrease with use of all digester gas for electricity generation.Decreasing transport distances would also decrease emissions.

Using the model, biosolids programs for both munici-palities were optimized to reduce emissions and maximizecredits. Results from this optimization are compared tocurrent estimated emissions in Table 2. GHG credits relatedto net electricity use and generation were increased 40% forthe VA program by expanding electricity production to

include use of all CH4. Reducing the one-way haul distanceto 100 km resulted in a reduction of transport GHG emissionsby 83%. These two optimization steps resulted in net negativeGHG emissions (credits) for VA’s biosolids program increasingfrom -23 to -34 Mg CO2e 100 Mg-1 biosolids (dry wt.).

Nitrous oxide was the primary emission associated withthe combustion facility, result in a debit of 163 Mg CO2e 100Mg-1 biosolids (dry wt.). According to the model, increasingthe combustion temperature to 880 °C effectively eliminatedN2O. This temperature increase was estimated to require anadditional energy input of 54 GJ/day. This municipalityreported using a portion of heat from the combustion processfor heating buildings and reducing energy requirements forcombustion. The theoretical optimization included increas-ing the fraction of waste heat used for combustion andincreasing combustion temperature to eliminate N2O emis-sions. This resulted in emissions per dry 100 Mg biosolidsdecreasing from 144 to -4 Mg CO2e. As a result of this study,the municipality has increased the burn temperature at itsfacility to minimize N2O emissions.

The BEAM spreadsheet tool provides a means for mu-nicipalities to evaluate GHG emissions associated withbiosolids treatment and end use, considering both directand indirect emissions. Because of their high CO2e, emissionsof CH4 and N2O have the potential to negate benefitsassociated with biosolids use or disposal. Focusing solely onCO2e emissions related to energy use results in an incompleteunderstanding of net GHG emissions. Similarly, the highemissions and/or offset potentials associated with indirect(Scope 3) factors should be considered. The results from thisstudy suggest that limiting considerations of emissions toScope 1 and 2 factors has a high potential for generatingmisleading GHG estimates.

It must be emphasized that default factors used in themodel for each unit process vary dramatically with regardsto level of uncertainty. Factors used in the model range fromthose that can be predicted with a relatively high degree ofaccuracy (transport related emissions) to those with a greaterdegree of uncertainty (soil carbon credits and N2O emissions).The factors with the greatest potential impact on netemissions include all sources of N2O.

Results from applications of the BEAM model suggestthat maximizing potential offsets, including energy captureand fertilizer and carbon sequestration value, while mini-mizing fugitive CH4 and N2O emissions associated withbiosolids management practices such as landfilling, low

TABLE 2. Existing and Optimized GHG Emissions/Credits for the VA (Anaerobic Digestion Followed by Land Application) and AN(Dewatering, Combustion with Ash Use in Cement Production) Programs

VA AN

existing optimized existing optimized

kWh Mg-1 biosolids (dry wt.)conditioning

kWh Mg-1 biosolids(dry wt.)

5 5 5 5anaerobic digestion -1658 -2333 0 0dewatering 171 171 11 11combustion 0 0 1113 716total electricity use -1482 -2157 1129 732

Mg CO2e 100 Mg-1 biosolids (dry wt.)

electricity Mg CO2e 100 Mg-1

biosolids (dry wt.)-3 -4.3 1.1 0.7

polymer 5 5 5 5fuel/not transport 0.6 0.6 -25 -10fuel/transport 12.5 2 0.2 0.2CH4 emissions 7 7 0 0N2O emissions 3 3 163 0carbon sequestration -25 -25 0 0ash use 0 0 -0.1 -0.1fertilizer offset -23 -23 0 0total emissions -23 -34 144 -4

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temperature combustion, or poor compost management,can significantly decrease the GHG emissions from biosolidsmanagement programs. The end use options associated withthe highest credits were also those with the lowest capitolcosts, suggesting a cost-effective means for wastewatertreatment agencies to lower their GHG footprints withoutincreasing capitol expenditures (11).

AcknowledgmentsFunding for this work was provided by the Canadian Councilof Ministers of the Environment.

Supporting Information AvailableAdditional information including the calculator spreadsheets,tables summarizing the literature for the range of reportedvalues for different parameters, and a flow diagram for thewastewater treatment process. This material is available freeof charge via the Internet at http://pubs.acs.org.

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(45) Lohila, A.; Laurila, T.; Tuovinen, J.; Aurela, M.; Hatakka, J.; Thum,T.; Pihlatie, M.; Rinne, J.; Vesala, T. Micrometeorologicalmeasurements of methane and carbon dioxide fluxes at amunicipal landfill. Environ. Sci. Technol. 2007, 41, 2717–2722.

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(57) Jones, S. K.; Rees, R. M.; Skiba, U. M.; Ball, B. C. Influence oforganic and mineral N fertiliser on N2O fluxes from a temperategrassland. Agric. Ecosys Environ. 2007, 121, 74–83.

(58) Peterson, S. O. Nitrous oxide emissions from manure andinorganic fertilizers applied to spring barley. J. Environ. Qual.1999, 28, 1610–1618.

(59) Rochette, P.; Angers, D. A.; Chantigny, M. H.; Bertrand, N. Nitrousoxide emissions respond differently to no-till in a loam and aheavy clay soil. Soil Sci. Soc Am. J. 2008, 72, 1363–1369.

(60) Kim, S.; Dale, B. E. Effects of nitrogen fertilizer application ongreenhouse gas emissions and economics of corn production.Environ. Sci. Technol. 2008, 42, 6028–6033.

(61) Goodroad, L. L.; Keeney, D. R.; Peterson, L. A. Nitrous oxideemissions from agricultural soils in Wisconsin. J. Environ. Qual.1984, 13, 557–561.

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ES101210K

VOL. xxx, NO. xx, XXXX / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 G

Supporting Information

A calculator tool for determining greenhouse gas emissions for biosolids processing and end use

Sally Brown†*, Ned Beecher‡ and Andrew Carpenter§

School of Forest Resources, University of Washington Box 352100 Seattle, WA 98195, North East Biosolids and Residuals

Association, PO Box 422 Tamworth, NH 03886, Northern Tilth, P.O. Box 361 Belfast, Maine 04915

List of Tables

Spreadsheet for all systems processes for wastewater treatment including default values and range of reported values for

different parameters

Table S1 Reported values for landfill gas capture efficiency, cover soil CH4 oxidation rates, N2O emissions, and internal landfill

environment

Table S2 Reported values for soil carbon sequestration following land application of municipal biosolids

Table S3 Reported values for soil N2O emissions following land application of biosolids

Table S4 Reported values for energy required to produce, transport and apply synthetic fertilizers

List of Figures

Figure S1. Process flow diagram, wastewater treatment process

Table S1 Factors Relating to Emissions from Landfills - Data Sources

Landfill Climate

Author(s) / Date Title Journal

Waste Quantity (Mg) Temperature % Moisture

CH4 onset

Bäumler, R. and I. Kögel-Knabner. 2008.

Spectroscopic and wet chemical characterization of solid waste organic matter of different age in landfill sites, Southern Germany

J. Environ. Qual. 37:146-153

893 000 20° C at surface 50 °C at depth

0.6-42%, primarily 10-35%

Gholamifard, S., R. Eymard, and C. Duquennoi. 2008.

Modeling anaerobic bioreactor landfills in methanogenic phase: Long term and short term behaviors

Water Research 42:5061-5071

35- 40 °C average temperature at depths greater than 3 m, 15-20 °C at shallower depths for landfills in France

Lefebvre, X., S. Lanini, and D. Houi. 2000

The role of aerobic activity on refuse temperature rise, I. Landfill experimental study

Waste Manage. Res. 18:444-452

200 000 40 °C 20-50% Day 20

Zhao, X., R. Musleh, S. Maher, M. V. Khire, T.C. voice and S.A. Hashsham. 2008.

Start-up performance of a full-scale bioreactor landfill cell under cold-climate conditions

Waste Management 28:2623-2634

32 400 ambient 25-60 Day 70

N2O Emissions

Author(s) / Date Title Journal N2O Emissions Comments

Börjesson, G., Samuelsson, J., and J. Chanton. 2007.

Methane oxidation in Swedish landfills quantified with the stable carbon isotope technique in combination with an optical method for emitted methane

Environ Sci. Tech 2007 41, 6684-6690

Emissions of -0.011-35.7 mg N2O-N m-2 h-1

High N2O emissions observed when biosolids were used as cover material

Rinne, J., M. Pihlatie, A. Lohila, T. Thum, M. Aurela, J. Tuovinen, T. Laurila, and T. Vesala. 2005.

Nitrous oxide emissions from a municipal landfill

Environ. Sci. Tech. 39:7790-7793

2.7 mg N m-2 h-1 Eddy covariance measure

Rinne, J., M. Pihlatie, A. Lohila, T. Thum, M. Aurela, J. Tuovinen, T. Laurila, and T. Vesala. 2005.

Nitrous oxide emissions from a municipal landfill

Environ. Sci. Tech. 39:7790-7794

6.0 mg N m-2h-1

Closed chamber both measures made at open face of landfill, cover material 20-40% organic, remainder mineral soil

Zhang, H. P. He, and L. Shao. 2009.

N2O emissions at municipal solid waste landfill sites: Effects of CH4 emissions and cover soil

Atmospheric Environment 43:2623-2631

Emissions of -0.1-2.48 mg N2O-N m-2h-1

Measured at 3 locations at a landfill, emissions similar across open face and sites with operating gas collection systems and high clay covers

Landfill gas capture efficiency/cover oxidation rate

Author(s) / Date Title Journal Collection efficiency

Notes Cover Soil Oxidation Rate

US EPA. 1998. Greenhouse gas emissions from management of selected materials in municipal solid waste

EPA530-R-98-013. Online Waste Reduction Model (Warm). USEPA, Washington, DC.

75%

Assumes a constant rate of gas capture across the life of the landfill. This is being revised to include different capture efficiencies for the different stages of landfill life, including low capture efficiency prior to operation of gas capture systems, high efficiency while capture systems are operational, and lower efficiencies after required time for gas capture has ended

10%

US EPA. 1999.

Municipal solid waste landfills, Volume 1: Summary of the requirements for the new source performance standards and emission guidelines for municipal solid waste landfills

EPA-453-R/96-004. USEPA, Washington, DC

IPCC. 2006 Chapter 3 Solid Waste Disposal. IPCC Guidelines for Solid Waste Inventories

20%

Note a wide range in gas capture efficiency when collection systems are operational

10%

Themelis, N.J. and P.A. Ulloa. 2007.

Methane generation in landfills Renewable Energy 32:1243-1257

34%

compared predicted to actual gas capture at 25 landfills in California and calculated a 34% capture efficiency

Chanton, J.P., D.K. Powelson, and R.B. Green. 2009.

Methane oxidation in landfill cover soils, is a 10% default value reasonable?


Based on review of literature. This value does not consider differences in oxidation efficiency based on location in the land fill- open and active face versus under final cover

25%

Börjesson, G., Samuelsson, J., and J. Chanton. 2007.

Methane oxidation in Swedish landfills quantified with the stable carbon isotope technique in combination with an optical method for emitted methane

Environ Sci. Tech 41, 6684-6690

Measured CH4 emissions from 6 landfills at both active faces and closed portions. Found much lower oxidation rates at open faces in comparison to areas under final cover

38-42% and 4.6-15%

Table S2 Reported values for soil carbon sequestration following land application of municipal biosolids

Author(s) / Date Title Journal Land use Summary Comments Change in soil C storage per Mg biosolids

Kurtz, K. 2010.

Quantification of the long-term effects of organic soil amendment use: carbon, nitrogen, bulk density, and water-holding capacity

MS Thesis, Univ. of Washington, College of Forest Resources

Dryland wheat, conventional tillage

Cumlative loading rate of 18-40 Mg ha

-1.

Site 14 years old

Replicated field trial

1.25-1.6 Mg CO2 per dry Mg biosolids

Kurtz, K. 2010.



Surface application to fescue

Annual application from 1993-2000, sampled in 2008, cumulative loading rates 67-201 Mg ha

-1


0.15 to 0.3 Mg CO2

per dry Mg

biosolids

Kurtz, K. 2010.



Roadside, incorporated

Single 147 Mg ha-1

application 2 years prior to sampling


1.74 Mg CO2 per dry Mg biosolids

Tian, G., T.C. Granato, A.E. Cox, R.I. Pietz, C.R. Carlson and Z. Abedin. 2009.

Soil carbon sequestration resulting from long-term application of biosolids for land reclamation

Journal of Environmental Quality 38: 61-74

Agriculture and restoration

data from 41 sites. Biosolids applied at cumulative rates from 455 to 1654 dry Mg ha

-1 from 1972-2004

All sites now used for agronomic crops. No information on tillage practices


Trilca, A. 2010.

Mitigation of climate change through land reclamation with biosolids: Carbon storage in reclaimed mine soils, life cycle analysis of biosolids reclamation, and ecosystem services with reforestation


Coal mine, WA state

Single 560 Mg ha-1

application 20 years prior to sampling,

Large scale reclamation

0.11 MgCO2 per dry Mg biosolids

Trilca, A. 2010.



Cu mine, British Columbia

Single 133-138 Mg ha

-1 application 4-8

years prior to sampling


Trilca, A. 2010.



Coal mine, Pennsylvania

Single 128-337 Mg ha

-1 application 7 to

27 years prior to sampling

Large scale reclamation

0.85 CO2 per dry Mg biosolids

Trilca, A. 2010.



Gravel mine, British Columbia

Single and multiple 50-102 Mg ha

-1

biosolids application 8-9 years prior to sampling

Large scale reclamation, pulp and paper sludge used with biosolids in one site

1.15 CO2 per dry Mg biosolids

Table S3 Reported values for soil N2O emissions following land application of biosolids

Author(s) / Date

Title Journal N Source Summary Comments % N lost as N2O

Calderón, G.W. McCarty, J.A. Van Kessel and J. B. Reeves III. 2004.

Carbon and nitrogen dynamics during incubation of manured soil

Soil Sci Soc. Am. J. 68:1592-1599

Dairy manure

Tested >100 manures on an ultisol. Saw mineralization on manures with C:N<16:1, about 75% of demineralized N evolved as N2 gas, with average losses of N about 5% of added N N2O evollution limited to first 3 weeks of study

0.8% of 265 kg N ha Manure 0.8% of 265 kg N ha Manure

Fine, P., U. Mingelgrin and A. Feigin. 1989.

Incubation studies of the fate of organic nitrogen in soils amended with activated sludge

Soil Sci. Soc. Am. J. 53:444-450.

Biosolids

Formation of NH4 peaks by day 20 with NO3 and also potential demineralization beginning at day 20-30 and growing over time

Only monitored denitrification to day 26. Saw measurable N2O formation in the clay soil with sludge added at 10%, 6.5 mg N2O-N kg d

-1 at day

26

one time measure

Huang, Y., J. Zou, X. Zheng, Y. Wang, and X. Xu. 2004.

Nitrous oxide emissions as influenced by amendment of plant residues with different C:N ratios

Soil Biol. Biochem. 973-981

Plant matter

Measured N2O emissions from a high clay (51% clay, 45% silt) soil amended with plant material with C:N ratios varying from 116-8/ added at 4 Mg ha

-1

N2O release from 8:1 amendment was 568 ng g

-1,

for 118:1 amendment was 384 ng g

-1, 37:1 was 476 ng

g-1

. Some effect of C:N ratio observed

Stuczynski, T.. and G. McCarty. 2007.

Assessing the potential for greenhouse gas emissions from sewage sludge.

Poster presented at the Soil Science Society of America annual meetings, New Orleans, LA, Nov

Biosolids

Used reclamation rates of biosolids (10% dry weight to an ultisol) range of biosolids tested included anaerobically digested and aerobically stabilized. Kept wet and dark in lab incubation no plants

Saw relationship between C:N ratio and N2O emissions, with emissions decreasing at higher C:N ratios/ average emission 0.021% of total N applied

0.21% of total N

Zaman, M., M. Matsushima, S.X. Chang, K. Inubushi, L. Nguyen, S. Goto, F. Kaneko, and T. Yoneyama. 2004.

Nitrogen mineralization, N2O production and soil microbiological properties as affected by long-term applications of sewage sludge composts.

Biol. Fertil Soils 40:101-109

Biosolids compost Fertilizer

Incubated soils collected from the field for 6 weeks, measured N2O every week, compost soils higher than fertilizer with increased emissions in week 3-4. As controlled incubation, not clear on field implications

applied 240 kg N ha-1

as biosolids compost since 1978 to andisol silt loam- N2O emissions ranged from 3-8 ug N kg

-1 dry soil

Kim, S. and B.E. Dale. 2008.

Effects of nitrogen fertilizer application on greenhouse gas emissions and economics of corn production.

Environ. Sci. Tech 42:6028-6033

Synthetic fertilizer

Use Daycent model to calculate when yield increases and resultant carbon are high enough to compensate for emissions associated with N application- determine an optimum fertilizer rate re GHG. Emissions for corn range from 227 to 518 g CO2 per dry kg grain

N2O emissions from soil accont from 31-59% of total GHG emissions from crop (88-284 g CO2 kg

-1 grain. N

fertilizer associated with grain 63-97 g CO2e kg

-1 grain or 17-

28% total emissions

4% for 50 kg N ha

-1 8% for 260

kg N ha-1

Rochette, P., D.A. Angers, M.H. Chantigny, and N. Bertrand. 2008.

Nitrous oxide emissions respond differently to no-till in a loam and a heavy clay soil.

Soil Sci. Soc Am. J. 72:5:1363-1369

Synthetic fertilizer

High clay soils with high organic matter release significantly more N2O than coarser textured soils under no till (Canadian study)

In clay soil, no-till doubled N2O emissions in comparison to plow. In loam soil emissions were similar under no-till and plow

12-45 kg N2O ha

-1 year

-1 in

clay, 0.6-1.5 kg N2O ha

-1 yr

-1 in

loam

Scott, A., B.C. Ball, I.J. Crichton, and M.N. Aitken. 2000.

Nitrous oxide and carbon dioxide emissions from grassland amended with sewage sludge

Soil Use Manage 16:36-41

Biosolids and synthetic fertilizer

Up to 1% of total N added evolved as N2O in poorly drained, high rainfall in Scotland, in the range of emissions for mineral fertilizers

100-150 kg N ha-1

, for 6 months total N loss was 23 kg N ha

-1 in wet soils/sandy clay

loam with imperfect drainage/ plot had received 185 dry Mg biosolids ha

-1 for 3 previous

years Total N applied = 2500 kg N ha

-1 yr

-1 with 30% of total

considered available

0.3-0.8% of biosolids N, 0.2% of fertilizer N

Jones, S.K., R.M. Rees, U.M. Skiba, and B.C. Ball. 2007.

Influence of organic and mineral N fertiliser on N2O fluxes from a temperate grassland

Agric. Ecosys Environ. 121:74-83.

Synthetic fertilizer, poultry manure, dairy manure, pellitized biosolids

300 kg available N applied to a grassland in Scotland for 2 years as synthetic fertilizer, poultry manure, dairy manure and pelletized biosolids Much higher N2O release from biosolids amended soil as a % of N applied, however application rates were significantly higher in biosolids so difficult to determine what release would be on agronomic rates

Total N applied per year for dairy 500 kg ha

-1, 2486 kg ha

-

1 for poultry and 3066 kg ha

-1

for biosolids

Urea 0.1-0.4% Ammonia nitrate 0.1-1.4%, Cattle slurry0.2-0.5%, Poulrtry 0.5-2.6%, biosolids 1.3-4.3%

Ball, B.C., I.P. McTaggart and A. Scott. 2004.

Mitigation of greenhouse gas emissions from soil under silage production by use of organic manures or slow-release fertilizer

Soil Use Manage 20:287-295

Synthetic N, cattle slurry, pelletized, liquid and composted biosolids

Field trial conducted in Scotland on a poorly drained soil, synthetic N, cattle slurry, pelletized, digested liquid and composted biosolids were all applied to give 150 kg available N per year, Not clear if wet or dry application rates are provided

Loss of N ranged from 0.2% for dried pellets to 5.5% for cattle slurry. Dryer materials had generally lower emissions. Total emissions highest from NPK, 26.4 kg N ha

-1, cattle slurry 15.3 kg N

ha-1

, biosolids compost 10.3 kg N ha

-1, liquid 10.3kg N ha

-1

and pellets 8.0 kg N ha-1

over 3 years

NPK- 5.8%, Cattle slurry -1.2%, Compost -0.4%, Pellets- 0.3%, liquid biosolids -1.5%

Peterson, S.O. 1999.

Nitrous oxide emissions from manure and inorganic fertilizers applied to spring barley


Digested and liquid manure, synthetic fertilizer

Experiment on an ultisol with 77% sand/ spring barley in Denmark Found that digested slurry was similar to fertiizer re N2O emissions. Total emissions over all trts ranged from 0.14-0.64% of total N added

Results from this study using IPCC guidelines suggest that digestion of slurry prior to land ap could reduce N2O emissions by 1.2-2.5%

0.14-0.34% N for digested manure and fertilizer, 0.35 -0.64% for liquid manure

Grant, R.F., E. Pattey, T.W. Goddard, L.M. Kryzanowski and H. Puurveen. 2006.

Modeling the effects of fertilizer application rate on nitrous oxide emissions

Soil Sci. Soc Am. J. 70:235-248

Fertilizer

IPCC uses a default of 1.25+-1 of N applied as N2O for organic and synthetic N, majority of differences come from site specific factors including % time soil moisture is >60%, clay content and topography

Modeled N2O flux at two stations in CA, one in Alberta and one in Ontario to see if cooler and dryer reduced N2O and they did, Emissions much higher in sites with higher fertilization.

0.3% in dry year, 2.4% in wet year in Alberta on silt loam, 0.1-1.83% in Ontario on clay loam, higher with higher rates

Rochette, P. E. van Bochove, D. Prévost, D.A. Angers, D. Côté and N. Betrand. 2000.

Soil carbon and nitrogen dynamics following application of pig slurry for the 19th consecutive year:II Nitrous oxide fluxes and mineral nitrogen

Soil Sci. Soc. Am. J. 64:1396-1403

Pig slurry synthetic fertilizer

Studied site where pig slurry had been applied for 19 years near Quebec. High 120 Mg ha

-1, low 60 Mg ha

-1 slurry,

and 150 kg ha-1

N were treatments. N2O emissions totaled 1.65, 1.23 and 0.62 % of total N applied for each treatment, in line with IPCC values

Sampled in the pig slurry treatments above the banded application area- cumulative emissions per ha were 0.93 kg ha control, 1.55 in PS60 and 4.16 in PS120- no measures of total soil C or N given

Fertilizer 0.62% total N, Slurry@60 Mg ha 1.23% total N, Slurry @120 Mg ha 1.65% total N

Goodroad, L.L., Keeney, D.R. and Peterson, L.A. 1984.

Nitrous oxide emissions from agricultural soils in Wisconsin


Biosolids, dairy manure

Measured N2O emissions from biosolids and manre amended fields over two growing seasons. Biosolids were applied each year at 22 Mg ha

-1 (440 kg N ha

-1).

Manure was applied at 33 Mg ha

-1 (330 kg N ha

-1)

Gas samples collected weekly using a flux chamber during the growing season

Biosolids 0.2- 1.6 kg N2O-N ha

-1 total per

season(0.05-0.4%), manure emissions were 1.2-6.1 kg N2O-N ha

-1 (0.4-

1.9%)

Table S4 Reported values for energy required to produce, transport and apply synthetic fertilizers

Author Title Journal Nitrogen Phosphorus Comments

Brown, S. and P. Leonard. 2004.

Biosolids and global warming: Evaluating the management impacts

BioCycle, August. 3 g CO2 per g P

Used Sitting 1979 to calculate energy required for P production, and IPCC factor used for N for multiplier to take into account transport and production inefficiencies

Murray, A., A. Horvath, and K.L. Nelson. 2008.

Hybrid life cycle environmental and cost inventory of sewage sludge treatment and end-use scenarios: a case study from China

Enivon. Sci. Tech. Published online 3/20/08

3.6 g CO2 per g N 4.86 g CO2 per g P

Kim, S. and B.E. Dale. 2008.

Effects of nitrogen fertilizer application on greenhouse gas emissions and economics of corn production

Environ. Sci. Tech 42:6028-6033

3.1-4.7 g of CO2 per g N

Total emissions from all other fertilizer use (P, K, S, lime, pesticides and herbicides) similar to N fertilizer emission

Intergovernmental Panel on Climate Change (IPCC). 2006.

Guidelines for National Greenhouse Gas Inventories

Available at http://www.ipcc-nggip.iges.or.jp/public/2006gl/index.html

1.3 g of CO2 per g N Manufacture only

Recycled Organics Unit. 2006.

Life cycle inventory and life cycle assessment for windrow composting systems

Univ. of New South Wales, Sydney, Australia. Available at http://www.recycledorganics.com/p

3.96 g of CO2 per g N 1.76 g of CO2 per g P

Potassium, factor of 1.36 given

ublications/reports/lca/lca.htm

Schlesinger, W. H. 1999.

Carbon sequestration in soils: some cautions amidst optimism

Agriculture, Ecosystems and Environ. 82: 121-127

4.5 g CO2 per g N 1.436 moles of CO2-C per mole of N

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