Waste management options and climate change - the case of biowaste Keith A Brown AEA Technology Workshop Biological treatment of biodegradable waste - Technical aspects Brussels - 8th-10th April, 2002
Policy context Improve sustainability - reduce reliance on landfill (Landfill Directive targets) Alternatives for biowaste: prevention, reduction & avoidance of contamination re-use (eg paper and cardboard) recycle to replace virgin materials produce compost for high quality use use MBT for stabilising residual wastes prior to landfill use biowaste for energy recovery Does the study support this hierarchy?
Terms of Reference Climate change impacts only - as greenhouse gas fluxes Policy / planning level: EU Time frame: 2000-2020 Geography: EU-15 Focus on options for municipal solid waste (MSW)
Approach Methodology Characterise GHG climate impacts Characterise the waste stream Characterise treatment options Results Evaluate options Compare options for bulk and segregated wastes Conclusions
Methodology - Greenhouse gases Greenhouse gas Global Warming Potential (100 y) Emission Storage Fossil CO 2 +1 0 Short-cycle CO 2 0-1 Methane CH 4 21 n/a Nitrous oxide N 2 O 310 n/a The Global Warming Potential (GWP) allows all GHG fluxes to be expressed in terms of CO2 equivalents
Methodology - Waste characterisation MSW composition and quantities MSW:- waste from households, as well as waste, which, because of its nature or composition, is similar to wastes from households OECD 1999 data / national sources Data quality often poor Total arisings in 2000 for EU-15: ~172Mt Textiles and other 15% Metal 5% Glass 11% Plastics 8% Food and garden 32% Paper and board 29% biowaste
Methodology - Treatment options LANDFILL Options for bulk or residual wastes MSW INCIN MBT RECYCLING Separated wastes Options for clean segregated wastes COMPOSTING & AD
Landfill GHG fluxes Degradable carbon breaks down to methane and carbon dioxide in landfills Methane emission calculated according to IPCC methodology Gas can be collected and used Big differences in gas collection C not released is assumed to be sequestered for >100y.
Results - landfill (base case - kg CO2 eq / tonne MSW) 1000 800 Paper Putrescibles Raw MSW 600 400 Methane C sequest 200 0-200 -400-600 Paper Putrescible R aw MSW CH4 298 323 712 carbon sequestered -227-86 -371 transport CO2 2 2 7 avoided energy and materials -9-10 -22 energy use CO2 0 0 1 Net flux 65 230 328
Results - landfill (kg CO2 eq / tonne MSW) 1000 800 EU average Limited collection 600 Exc sequestration 400 Inc 200 sequestration Best practice Best practice + restoration layer 0-200 -400 EU-average Limited collection Best practice R estoration layer Net flux 328 462-121 -299 Net flux exc seq 699 833 250 72
Incineration GHG fluxes Main GHG flux is fossil CO2 from plastics Focus on mass-burn incineration Energy recovered replaces other energy sources GHG fluxes calculated from waste properties, process characteristics & GHG emission factors of replaced energy source Baseline assumes average energy is replaced - half power only, half CHP Ferrous metal also recovered for recycling
Results - incineration (Average energy mix - kg CO2 eq / tonne MSW) 400 200 0 Process CO2-200 -400 Avoided emissions -600-800 -1000 No energy recovered MSW incin no energy recovery Electricity only MSW incin electricity only MSW incin CHP N2O 15 15 15 transport CO2 8 8 8 avoided energy and materials -72-262 -601 process CO 2 230 230 230 Net flux 181-10 -348 CHP
MBT GHG fluxes Whole waste composting - produces stabilised residue for landfilling Metals (Al + Fe) removed for recycling 20% of paper and all plastics assumed to be removed for landfilling or incineration before processing GHG flux landfilled residue depend on stability of compost and treatment in landfill - 3 alternative cases considered
MBT GHG fluxes Case 1: Highly stabilised compost landfilled at high compaction. Zero methane emission - high sequestration Case 2: As case 1, but less highly stabilised, slight methane escape - high sequestration Case 3: Compost used for landfill site restoration. Decays aerobically - no methane formed - little sequestration
Methane Avoided C Sequest 400 300 200 100 0-100 -200-300 -400-500 -600-700 Results MBT (rejects to landfill - kg CO 2 eq /tonne MSW Case 1 Case 2 Case 3 Av 1 & 2 Case 1 Case 2 Case 3 Mean 1 & 2 N2O 0 0 0 0 CH4 97 171 97 134 carbon sequestered -364-364 -99-364 transport CO2 5 5 5 5 avoided energy and materials -162-162 -162-162 energy use CO 2 22 22 22 22 process CO 2 0 0 0 0 Net flux -403-329 -137-366
Results MBT (rejects to incineration - kg CO 2 eq /tonne MSW 400 Methane Process Avoided C Sequest 300 200 100 0-100 -200-300 -400-500 -600-700 Case 1 Case 2 Case 3 Av 1 & 2 Case 1 Case 2 Case 3 Mean 1 & 2 N2O 3 3 3 3 CH4 0 74 0 37 carbon sequestered -289-289 -23-289 transport CO2 5 5 5 5 avoided energy and materials -241-241 -241-241 energy use CO 2 22 22 22 22 process CO 2 205 205 205 205 Net flux -295-221 -30-258
Composting / AD GHG fluxes About 64% of biodegradable C is converted to CO2 during composting or to CO2 + CH4 in AD The biogas from AD is used for energy recovery and replaces energy recovered from other sources The compost is used in agriculture (50%), horticulture (20%) and land restoration / gardening (30%) Nutrients in the compost avoid emissions from manufacturing an equivalent amount of mineral fertilisers for agriculture
Composting / AD GHG fluxes Compost used in horticulture avoids emissions of fossil CO2 from the peat it replaces Compost degrades aerobically in soil limiting the scope for sequestration. 8% of compost carbon assumed to be sequestered in the soil for >100y - based on literature survey.
Results - Composting / AD (kg CO 2 eq /tonne MSW Transport 20 10 Open compost Closed compost Home compost AD elec only AD CHP Comp / AD Process 0 Avoided -10-20 C Sequest -30-40 -50-60 -70 Open composting Closed composting Home composting AD-power only AD-CHP Mean comp/ AD carbon sequestered -7-7 -7-7 -7-7 transport CO2 2 2 0 2 2 2 avoided energy and materials -11-11 -11-28 -54-23 energy use CO2 4 6 0 0 0 2 Net flux -12-10 -18-33 -58-26
Recycling GHG fluxes Recycling avoids emissions from manufacture of product from virgin materials Net effect = emissions from recycling minus emissions from virgin manufacture Data from published LCA studies
Results - Recycling (kg CO 2 eq /tonne MSW 0-50 -100-150 -200-250 -300-350 -400-450 -500 Glass Plastic Fe metal Textiles Al Paper Total Glass Plastic (HDPE) Ferrous metal Textiles Aluminium Paper Total recycling Net flux -30-41 -63-60 -95-177 -467
Results - overall (base case LFG collection & energy, kg CO 2 eq /tonne MSW ) 800 600 Bulk options Source segregated 400 200 Landfill Incin MBT/ LF MBT/ Incin Comp/ AD/recyc 0-200 -400-600 Landfill raw waste Mass burn R DF-FBC MBT landfill MBT incin R ecycling, compost & AD Net flux 328-179 177-366 -258-461 Net flux excluding sequestration 699-179 312-2 31-406
Results - overall (best LFG collection, base case energy, kg CO 2 eq /tonne MSW ) 800 600 Bulk options Source segregated 400 200 Landfill Incin MBT/ LF MBT/ Incin Comp/ AD/recyc 0-200 -400-600 Landfill raw waste Mass burn R DF-FBC MBT landfill MBT incin R ecycling, compost & AD Net flux -299-179 -178-451 -258-533 Net flux excluding sequestration 72-179 -44-87 31-478
Results - diversion from landfill to composting & recycling (base case LFG collection kg CO 2 eq /tonne MSW) 600 500 400 Exc sequestration Inc sequestration 300 200 100 0-100 Comp /AD Glass Plastic Fe Textiles Al Paper -200 Mean comp/ AD Glass Plastic (HDPE) Ferrous metal Textiles Aluminium Paper Net flux 256 31 42 63 61 95 242 Net flux exc seq 335 31 42 63 70 95 469
Conclusions - 1 Paper & putrescibles account for nearly all of the GHG emissions from landfills Landfills also act as a sink for carbon For bulk wastes, incineration and MBT offer major GHG flux reductions GHG benefits of incineration depend on energy recovery (power/chp) and source of displaced power MBT benefits highly if C sequestration is taken into account
Conclusions - 2 Overall, source separation of biowaste followed by composting / AD and recycling offer the greatest GHG reductions on landfilling Major reductions could also come from improving landfill management to minimise gas emissions - end of pipe solution Overall, the study supports the policy hierarchy BUT is concerned only with climate change impacts.