Waste management options and climate change - the case of biowaste

Transcription

1 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

2 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?

3 Terms of Reference Climate change impacts only - as greenhouse gas fluxes Policy / planning level: EU Time frame: Geography: EU-15 Focus on options for municipal solid waste (MSW)

4 Approach Methodology Characterise GHG climate impacts Characterise the waste stream Characterise treatment options Results Evaluate options Compare options for bulk and segregated wastes Conclusions

5 Methodology - Greenhouse gases Greenhouse gas Global Warming Potential (100 y) Emission Storage Fossil CO Short-cycle CO 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

6 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

7 Methodology - Treatment options LANDFILL Options for bulk or residual wastes MSW INCIN MBT RECYCLING Separated wastes Options for clean segregated wastes COMPOSTING & AD

8 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.

9 Results - landfill (base case - kg CO2 eq / tonne MSW) Paper Putrescibles Raw MSW Methane C sequest Paper Putrescible R aw MSW CH carbon sequestered transport CO avoided energy and materials energy use CO Net flux

10 Results - landfill (kg CO2 eq / tonne MSW) EU average Limited collection 600 Exc sequestration 400 Inc 200 sequestration Best practice Best practice + restoration layer EU-average Limited collection Best practice R estoration layer Net flux Net flux exc seq

11 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

12 Results - incineration (Average energy mix - kg CO2 eq / tonne MSW) Process CO Avoided emissions No energy recovered MSW incin no energy recovery Electricity only MSW incin electricity only MSW incin CHP N2O transport CO avoided energy and materials process CO Net flux CHP

13 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

14 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

15 Methane Avoided C Sequest 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 CH carbon sequestered transport CO avoided energy and materials energy use CO process CO Net flux

16 Results MBT (rejects to incineration - kg CO 2 eq /tonne MSW 400 Methane Process Avoided C Sequest Case 1 Case 2 Case 3 Av 1 & 2 Case 1 Case 2 Case 3 Mean 1 & 2 N2O CH carbon sequestered transport CO avoided energy and materials energy use CO process CO Net flux

17 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

18 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.

19 Results - Composting / AD (kg CO 2 eq /tonne MSW Transport Open compost Closed compost Home compost AD elec only AD CHP Comp / AD Process 0 Avoided C Sequest Open composting Closed composting Home composting AD-power only AD-CHP Mean comp/ AD carbon sequestered transport CO avoided energy and materials energy use CO Net flux

20 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

21 Results - Recycling (kg CO 2 eq /tonne MSW Glass Plastic Fe metal Textiles Al Paper Total Glass Plastic (HDPE) Ferrous metal Textiles Aluminium Paper Total recycling Net flux

22 Results - overall (base case LFG collection & energy, kg CO 2 eq /tonne MSW ) Bulk options Source segregated Landfill Incin MBT/ LF MBT/ Incin Comp/ AD/recyc Landfill raw waste Mass burn R DF-FBC MBT landfill MBT incin R ecycling, compost & AD Net flux Net flux excluding sequestration

23 Results - overall (best LFG collection, base case energy, kg CO 2 eq /tonne MSW ) Bulk options Source segregated Landfill Incin MBT/ LF MBT/ Incin Comp/ AD/recyc Landfill raw waste Mass burn R DF-FBC MBT landfill MBT incin R ecycling, compost & AD Net flux Net flux excluding sequestration

24 Results - diversion from landfill to composting & recycling (base case LFG collection kg CO 2 eq /tonne MSW) Exc sequestration Inc sequestration Comp /AD Glass Plastic Fe Textiles Al Paper -200 Mean comp/ AD Glass Plastic (HDPE) Ferrous metal Textiles Aluminium Paper Net flux Net flux exc seq

25 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

26 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.