treat commercial food waste?

Transcription

1 What is the most environmentally beneficial way to treat commercial food waste? Supporting Information James W. Levis * and Morton A. Barlaz North Carolina State University, Department of Civil, Construction, and Environmental Engineering, Campus Box 7908, Raleigh, NC Corresponding author. Phone: (919) ; fax: (919) ; jwlevis@ncsu.edu

2 Landfill Model. An estimate of the total global warming potential (GWP), SO x, NO x and net energy attributable to the disposal of materials in a landfill requires consideration of landfill construction, operations, final cover placement, gas and leachate management, and long-term maintenance and monitoring (Eq. 1). Eq. 1 Each of the terms in Eq. 1 are in mass units (kg). GHG emissions associated with all aspects of the landfill except gas management have been shown to be small relative to emissions associated with gas management. As such, the emissions for landfill construction, operations, final cover placement, leachate management and long-term maintenance were adopted from Camobreco et al., and are shown in Table S1. The GHG emissions and sinks associated with gas management and the storage of biogenic carbon were developed in this study with carbon storage factors adopted from Staley and Barlaz, Landfill gas generation was modeled using a first order decay model as in the EPA s LandGEM model. 23 The decay rate (k) is dependent on climate and landfill operation strategy (traditional vs. bioreactor). In contrast to LandGEM, 23 in which MSW is treated as one substrate, the k and methane yield (L 0 ) for food waste and branches were modeled separately to study the influence of biodegradability on methane generation and subsequent collection and emissions. Component-specific decay rates for food waste and branches were calculated as described in De la Cruz and Barlaz, Calculation of component-specific decay rates requires specification of a bulk MSW decay rate, which was 0.04 for the traditional landfills as 0.12 for the bioreactor landfill.

3 For waste in landfills that utilize the methane beneficially, it was necessary to estimate the period over which there was sufficient gas to operate energy recovery equipment. First, it was assumed that all recovered methane is converted to electrical energy although in practice some gas is used directly in industrial boilers along with other beneficial uses. Second, it was assumed that landfills could only generate electricity while the gas flow rate was above m 3 s -1 (500 ft 3 min -1 ) at 50% methane. For both landfill categories, the length of time that the landfill gas flow was above this threshold was determined by modeling methane generation for a 2100 Mg day -1 landfill that accepted waste for 40 years. This resulted in a threshold of 76 years for the traditional landfill and 39 years for the bioreactor landfill. All calculations were based on a 100 year time horizon at which point, food waste and branches will have produced 100 and 78% of their methane in the traditional landfill and 100 and 99% of their methane in a bioreactor. For landfills that utilize the gas for energy, the gas produced at a rate lower than the aforementioned threshold was assumed to be flared between the threshold year and year 100. Landfill gas collection systems are placed based on the age of the landfill cell. This means that waste buried earlier in the cell s life will be under gas collection for less time than waste buried later in the cell s life. It is therefore necessary to temporally average the collection efficiency for each year of cell operation. Gas collection schemes were based on the assumption that a typical cell life is 5 years and that no gas collection is in place for the first two years of cell operation (6 mo for bioreactors). Further, the collection efficiency prior to cell closure and intermediate cover installation is 50% (i.e., years 3 to 5, or 0.5 to 3 yr for a bioreactor). After cell closure at the end of year 5, the collection efficiency is assumed to be 75%. It is further assumed that 10 years after final waste placement (i.e., 15 years after initial waste placement), a final cover is put in place

4 and the gas collection efficiency increases from 75% to 95%. All of the gas collection system default values can be varied in the model. Some fraction of the uncollected methane is oxidized to CO 2 as it passes through the landfill cover. Ten percent oxidation was assumed as recommended in the U.S. EPA s AP-42 database 26 and as used in the U.S. GHG inventory. 24 This value is likely conservative as other studies estimate methane oxidation of 22 to 55%. 27 Table S1. Landfill emissions factors for construction, operations, closure, post-closure, leachate management, and landfill gas treatment. a Construction (kg/mg) Operation (kg/mg) Closure (kg/mg) Post-Closure (kg/mg) Leachate (kg/mg) Flare (kg/m 3 CH4) Turbine (kg/m 3 CH4) GWP (CO 2 e) N/A N/A NO x E E E E-04 SO 2 4.6E E E E E E E-04 TEU (MJ) N/A N/A a. Values are adopted from Camobreco et al.,

5 Table S2. Input parameters and default values for compost model. Parameter Units Windrow ASP Gore In-Vessel Source Time spent at tipping floor Days Active composting time Days Curing time Days a 30 Wet weight moisture content after active composting Wet weight moisture content after curing Grinder power rating. kwh/mg Grinder fuel consumption L/kWh Windrow turner power rating kwh/mg The fuel consumption of a windrow turner L/kWh Turning frequency 1/day Motor efficiency kw-in/kwout Blower power kw Pers. Com. Pers. Blowers required per dry mass compost. 1/Mg Proportion of the time that blowers are on N/A Vessel energy use per wet weight of material kwh/mg Proportion of incoming C emitted Proportion of emitted C emitted as CH Proportion of incoming N emitted Proportion of emitted N emitted as N 2 O Biofilter CH 4 removal efficiency Biofilter N 2 O removal efficiency Percent of carbon in compost remaining after 100 years year carbon storage from humus formation Motor efficiency Com. Pers. Com. kg-c/dry Mg compost kw-in/kwout Odor control air flow required m 3 /hr Time spent under odor control Days Diesel use L/hr Proportion of material that is pulled out N/A Energy required per wet weight of vacummed material kwh/mg Proportion of mass entering pre-screen that is rejected Energy required per wet weight of postscreened material kwh/mg a Compost in the Gore system is cured in large unturned piles for at least 90 days. Pers. Com.

6 Table S2 (continued). Input parameters and default values for compost model. Parameter Units Windrow ASP Gore In-Vessel Source Proportion of mass entering postscreen that is rejected Actual payload of dump trucks filled with screen rejects Mg Empty return of screen reject truck disposal 0/ Frequency of turning during curing phase 1/day Front end loader energy required per wet weight flow of material MJ/Mg Front end loader specific fuel consumption L/kWh Office Area required per ton per day of material m 2 Pers. Com. /Mgpd 7.03E E E E kwh/ m 2 -yr Energy required to power an office Percent phosphorus of dry final compost. % 5.60E E E E-03 5 Percent nitrogen of dry final compost. % 1.85E E E E-02 5 Percent potassium of dry final compost. % 1.32E E E E-02 5 Mineral fertilizer equivalent for nitrogen Mineral fertilizer equivalent for phosphorus Mineral fertilizer equivalent for potassium Ratio of compost required to meet P demand to N demand. 14 Ratio of compost required to meet K demand to N demand Volumetric peat replacement factor Density of peat kg/m General equipment fuel consumption. L/kWh

7 Table S3. Input parameters and default values for AD model. Parameter Units Value Source Daily operating hours hours 8 Annual operating days days 260 Specific electricity usage. kwh/mg Food waste moisture content Yard waste moisture content Carbon content of yard waste % Nitrogen content of yard waste % Reactor moisture content Digestate moisture content after dewatering 0.5 Nitrogen content of digestate kg-n/dry Mg Finished compost moisture content Proportion of incoming waste that is screened out. 0.1 Proportion of food waste in pre-screened mass. 0.1 Density of final compost kg/m Ultimate yield of food waste L/dry kg Proportion of methane in biogas. N/A Heat rate for electrical energy generation. MJ/kWh 12.2 Proportion of gas that is flared w/out electricity generation Methane destruction efficiency 1 Percent of carbon in compost remaining after 100 years % 10 7 kg-c/dry Mg 100 year carbon storage from humus formation compost Front end loader use per facility capacity. kwh/mgd Front end loader specific fuel consumption. L/kWh Screen specific electricity consumption. kwh/kg Proportion of material remaining after post-screening 0.98 Office Area required per ton per day of material M 2 /Mgd Energy required to power an office kwh/m Tub grinder power rating. kwh/mg Tub grinder fuel consumption L/kWh Retention time in windrows Days 30 Windrow turner energy required per ton of compost kwh/mg The fuel consumption of a windrow turner L/kWh Turning frequency 1/day 0.5 Pers. Com.

8 Table S3 (continued). Input parameters and default values for AD model. Parameter Units Value Source Leachate density kg/l 1 20 Mass of sludge per BOD removed. kg sludge/kg BOD Electricity used per pound of BOD removed. kwh/kg Amount of BOD in leachate kg/l BOD removal efficiency Mass of biomass CO 2 emitted per pound of BOD removed kg CO 2 /kg BOD Haul distance to treatment facility. km Empty return from treatment facility. 0/ Percent phosphorus of dry final compost. % Percent nitrogen of dry final compost. % Percent potassium of dry final compost. % Mineral fertilizer equivalent for nitrogen Mineral fertilizer equivalent for phosphorous 1 5 Mineral fertilizer equivalent for potassium 1 5 Ratio of compost required to meet P demand to N demand Ratio of compost required to meet K demand to N demand Aerobic activity left in digestate 0.25 Proportion of incoming C emitted Proportion of emitted C emitted as CH Proportion of incoming N emitted Proportion of emitted N emitted as N 2 O Biofilter CH 4 removal efficiency Biofilter N 2 O removal efficiency 0 Haul distance to the landfill. km 32.2 Empty return from landfill. 0/1 1 General equipment fuel consumption. L/kWh Volumetric peat replacement factor 1 18 Density of peat kg/m

9 Table S4. Windrow composting process emissions a Yard Waste Shredding Active Windrow Turning Screen and Front End Emission Reject Mngt Curing Loaders GWP (kg CO 2 e) SO 2 (kg) E E-04 0 NO x (kg) TEU (MJ) Biodegra dation Emission Electricity Use Peat Offset Fertilizer Offset Soil Carbon Storage Gross Emissions Peat Net Fertilizer Net GWP (kg CO 2 e) SO 2 (kg) 1.45E NO x (kg) 6.8E TEU (MJ) a. The net emissions include either peat or fertilizer as the beneficial use of compost, but not both. Hence, two results are presented.

10 Table S5. ASP composting process emissions a Emission Yard Waste Shredding Electricity Use Screen and Reject Mngt Curing Front End Loaders Biodegradation GWP (kg CO 2 e) SO 2 (kg) E E-04 0 NO x (kg) TEU (MJ) Emission Peat Offset Fertilizer Offset Soil Carbon Storage Gross Emissions Peat Net Fertilizer Net GWP (kg CO 2 e) SO 2 (kg) NO x (kg) TEU (MJ) a. The net emissions include either peat or fertilizer as the beneficial use of compost, but not both. Hence, two results are presented.

11 Table S6. Gore composting process emissions a Emission Yard Waste Shredding Electricity Use Screen and Reject Mngt Front End Loaders Biodegradation GWP (kg CO 2 e) SO 2 (kg) E-04 0 NO x (kg) TEU (MJ) Emission Peat Offset Fertilizer Offset Soil Carbon Storage Gross Emissions Peat Net Fertilizer Net GWP (kg CO 2 e) SO 2 (kg) NO x (kg) TEU (MJ) a. The net emissions include either peat or fertilizer as the beneficial use of compost, but not both. Hence, two results are presented.

12 Table S7. In-Vessel composting process emissions a Yard Waste Shredding Screen and Reject Management Electricity Front End Emission Use Curing Loaders GWP (kg CO 2 e) SO 2 (kg) E E-04 0 NO x (kg) TEU (MJ) Biodegradation Emission Peat Offset Fertilizer Offset Soil Carbon Storage Gross Emissions Peat Net Emissions Fertilizer Net Emissions GWP (kg CO 2 e) SO 2 (kg) NO x (kg) TEU (MJ) a. The net emissions include either peat or fertilizer as the beneficial use of compost, but not both. Hence, two results are presented.

13 Table S8. AD process emissions a Front End Loader Yard Waste Shredding Windrow Turner Electricity Use Postscreening Office Leachate Transport Leachate Treatment Landfill Transport GWP (kg CO 2 e) SO 2 (kg) E E E-04 NO x (kg) E TEU (MJ) Landfill Curing Biogas Combustion Soil Storage Gross Emissions Elec. Offset Fertilizer Offset Peat Offset Fertilizer Net Peat Net GWP (kg CO 2 e) SO 2 (kg) E NO x (kg) TEU (MJ) a. The net emissions include either peat or fertilizer as the beneficial use of compost, but not both. Hence, two results are presented.

14 Figure S1. Mass flow diagram for composting processes. All weights are wet mass.

15 Figure S2. Process flow diagram for a process to treat food waste by anaerobic digestion. All weights are wet mass.

16 Figure S3. Sensitivity results for SO 2 from composting alternatives. The x-axis shows percent distance between the minimum and maximum values for each parameter (Table 4). MC: moisture content, %N in FC is the nitrogen content of the final compost product. The MFE for nitrogen was also tested. The line was directly under the %N in FC line because both control the same offset mechanism and were varied by the same relative amount.

17 Figure S4. Sensitivity results for NO x from composting alternatives. The x-axis shows percent distance between the minimum and maximum values for each parameter (Table 4). MC: moisture content, %N in FC is the nitrogen content of the final compost product. The MFE for nitrogen was also tested. The line was directly under the %N in FC line because both control the same offset mechanism and were varied by the same relative amount.

18 Figure S5. Sensitivity results for TEU from composting alternatives. The x-axis shows percent distance between the minimum and maximum values for each parameter (Table 4). MC: moisture content, %N in FC is the nitrogen content of the final compost product. The MFE for nitrogen was also tested. The line was directly under the %N in FC line because both control the same offset mechanism and were varied by the same relative amount.

19 Figure S6. Sensitivity results for SO 2 emissions from anaerobic digestion and landfilling alternatives. The x-axis shows percent distance between the minimum and maximum values of the parameter (Table 4). MC: moisture content, MYFW: methane yield of food waste, HR: heat rate of gas turbine, DRFW: decay rate of food waste, CSFB: carbon storage factor of branches, %coal: % coal included in electricity offsets, ColEf: Methane collection efficiency after final cover is in place.

20 Figure S7. Sensitivity results for NO x from anaerobic digestion and landfilling alternatives. The x-axis shows percent distance between the minimum and maximum values of the parameter (Table 4). MC: moisture content, MYFW: methane yield of food waste, HR: heat rate of gas turbine, DRFW: decay rate of food waste, CSFB: carbon storage factor of branches, %coal: % coal included in electricity offsets, ColEf: Methane collection efficiency after final cover is in place.

21 Figure S8. Sensitivity results for TEU from anaerobic digestion and landfilling alternatives. The x-axis shows percent distance between the minimum and maximum values of the parameter (Table 4). MC: moisture content, MYFW: methane yield of food waste, HR: heat rate of gas turbine, DRFW: decay rate of food waste, CSFB: carbon storage factor of branches, %coal: % coal included in electricity offsets, ColEf: Methane collection efficiency after final cover is in place.

22 (1) Diamond Z Manufacturing Horizontal Grinder Sales Literature. Accessed November 11, (2) Backhaus Ecoengineers Windrow Turners Sales Literature eddownload&tx_abdownloads_pi1[uid]=10&chash=6225a1805d March 26, (3) New York Blower Co. Series 20 General Industrial Blower sales literature. March 26, (4) Wright Environmental Management In-Vessel Composting System Specifications Retrieved from Accessed April 18,2008. (5) Boldrin, A.; Andersen, J.K.; Moller, J.; Christensen, T.H.; Favoino, E. Composting and compost utilization: accounting of greenhouse gases and global warming contributions Waste Manage. Res., 2009, 27 (8), (6) Amlinger, F.; Peyr, S.; and Cuhls, C. Greenhouse gas emissions from composting and mechanical biological treatment Waste Manage. Res., 2008, 26 (1) (7) Bruun, S.; Hansen, T.L.; Christensen, T.H.; Magid, J.; Jensen, L.S. Application of processed organic municipal solid waste on agricultural land: a scenario analysis. Environ. Model. Assess., 2006, 11, (8) U.S. Environmental Protection Agency. Solid Waste Management and Greenhouse Gases, EPA 530-R , Office of Solid Waste and Emergency Response, Washington, D.C., 2006.

23 (9) Airlift AL2000D compost vacuum specs. Retrieved from Accessed on 3 August (10) Diaz, L.F.; Savage, G.; Golueke, G. Resource Recovery from Municipal Solid Wastes: Volume 1, Primary Processing, CRC Press, Inc., Boca Raton, FL, (11) Komilis, D.P.; Ham, R.K. Life-Cycle inventory of municipal solid waste and yard waste windrow composting in the United Stated. J. Environ. Eng., 2004, 130 (11), (12) U.S. Environmental Protection Agency. Exhaust and crankcase emission factors for nonroad engine modeling - compression-ignition, EPA420-P , Office of Air and Radiation, Washington, D.C (13) U.S. Department of Energy. Commercial Buildings Energy Consumption and Expenditures 1992, Energy Information Administration, DOE/EIA-0318(92)/2, Department of Energy, Washington, D.C (14) Levis, J. W. A life-cycle analysis of alternatives for the management of waste hot-mix asphalt, commercial food waste, and construction and demolition waste. Master s Thesis, Raleigh, North Carolina: Department of Civil, Construction and Environmental Engineering, North Carolina State University, (15) DRANCO Brecht II DRANCO Anaerobic Digestion Facility (Belgium) Retrieved from Accessed 3 August (16) Tchobanoglous, G.; Theisen, H.; and Vigil, S. Integrated Solid Waste Management: Engineering Principles and Management Issues. McGraw-Hill, Inc., New York, 1993.

24 (17) Hansen, T.L.; Gurbakhash, B.S.; Christensen, T.H. (2006) Life cycle modelling of environmental impacts of application of processed organic municipal solid waste on agricultural land (EASEWASTE). Waste Manage. Res., 2006, 24 (2) (18) Boldrin, A.; Hartling, K.R.; Laugen, M.; Christensen, T.H. Environmental inventory modelling of the use of compost and peat in growth media, Resour. Conserv. Recycl., 2010, 54 (10), (19) Eleazer, W.E,; Odie, W.S.; Wang, Y.S.; Barlaz, M.A. Biodegradability of municipal solid waste components in laboratory-scale landfills. Envir. Sci. Technol., 1997, 31 (3), (20) Sich, B.; Barlaz, M. A. Process model documentation: Calculation of the cost and life-cycle inventory for waste disposal in traditional, bioreactor and ash landfills. Internal Report, Dept. of Civil Engineering, North Carolina State Univ., Raleigh, N.C, Camobreco, V.; Ham, R.; Barlaz, M.; Repa, E.; Felker, M.; Rousseau, C.; Rathle, J. Lifecycle inventory of a modern municipal solid waste landfill. Waste Manage. Res. 1999, 17, Staley, B.F. and Barlaz, M.A. Composition of Municipal Solid Waste in the United States and Implications for Carbon Sequestration and Methane Yield. J. Environ. Eng. -ASCE 2009, 135, Landfill Gas Emissions Model (LandGEM) Version 3.02 User s Guide; EPA-600/R-05/047; U.S. EPA, Office of Research and Development: Washington, DC, 2005; Retrieved: November 11, 2010.

25 24. Inventory of U.S. Greenhouse Gas Emissions and Sinks: ; EPA 430-R ; U.S. EPA: Washington, DC, 2010; _Report.pdf. 25. De la Cruz, F.B. and Barlaz, M.A. Estimation of Waste Component-Specific Landfill Decay Rates Using Laboratory-Scale Decomposition Data. Environ. Sci. Technol. 2010, 44, AP 42, Fifth Edition, Volume I Chapter 2: Solid Waste Disposal; U.S. EPA, Office of Resource Conservation and Recovery: Washington, DC, 1998; Retrieved: November 11, Chanton, J.R.; Powelson, D.K.; Green, R.B. Methane Oxidation in Landfill Cover Soils, is a 10% Default Value Reasonable? J. Environ. Qual. 2009, 38,