Comparative environmental analysis of anaerobic mono ‐ digestion and co ‐ digestion of organic waste L. Lijó, N. Voulvoulis, N. Frison , S. González ‐ García, M. T. Moreira and E. Katsou This research was supported by a project granted by the EU project Live ‐ Waste (LIFE 12 ENV/CY/000544) and by the BBVA program “ 2015 edition of the BBVA Foundation Grants for Researchers and Cultural Creators ” (2015 ‐ PO027).
Organic waste management in an Introduction urban context: Anaerobic digestion of sewage sludge and food waste Waste Hierarchy (EC, 2008) Reduce Reuse Organic waste Recycle Cogeneration Biogas Recovery AD Fertilisation Digestate Landfill In line with Circular Economy, anaerobic digestion is able to convert organic waste From the most to the least streams into valuable materials that can find environmentally friendly their way back into the economy.
Introduction Research efforts have been made aiming to boost methane production by means of co- digestion of sewage sludge and food waste Anaerobic mono ‐ digestion Anaerobic co ‐ digestion Sewage sludge Food waste Sewage sludge & food waste Advantages Advantages Advantages ‐ Available infrastructure in ‐ High biogas potential ‐ Improved nutrients balance WWTP ‐ Increased biogas production ‐ Trained technicians in WWTP ‐ Usage of available capacities in WWTP digesters Disadvantages Disadvantages Disadvantages ‐ Low efficiency ‐ Composition variability ‐ Legislative framework in ‐ Low biogas potential ‐ Nutrients imbalance each country (end of waste ‐ High C/N ratio criteria)
Sewage and food waste as a resource
Objectives To evaluate the potential environmental SS FW benefits of sewage sludge and food waste 524 t/d Sewage sludge ‐ co ‐ digestion by comparing different 100% integration rates of food waste within a 35.62 t/d Food waste ‐ 100% WWTP Scheme 2 SS+FW FW • Anaerobic mono ‐ digestion: 524 t/d Scheme 1 separate digestion of each Sewage sludge ‐ 98% substrate 3.85 t/d 31.76 t/d Food waste 2% 100% • Anaerobic co ‐ digestion: on Scheme 2 the basis of surplus capacity of the digester SS+FW • Anaerobic co ‐ digestion : 524t/d introduction of a second Sewage sludge Scheme 3 86% digester to treat all the waste generated 35,62 t/d Food waste 14%
Life Cycle Assessment Methodology Raw materials, Goal and scope Inventory data fossil fuels and water definition collection Interpretation Emissions to air water and soil Conclusions Impact Recommendations Improvement options assessment Inputs from Technosphere Electricity 1000 kWh Identification of Chemicals 50 kg environmental Outputs to Environment Environmental results hotspots CH 4 60 Impact categories Kg A B C Environmental N 2 O Climate change 10 60 ‐ 1 0,1 kg credits Acidification 5 15 ‐ 5 resources recovery Eutrophication 0,8 1 0
Functional unit (FU): Scheme 1 The management of sewage sludge and source ‐ segregated food waste produced by a community of 150,000 PE each day Mono ‐ digestion of sewage sludge Biotrickling Co ‐ generation filter Primary sludge Anaerobic Storage Mixing Thickening Dewatering digestion Secondary sludge Wastewater to Land Pasteurisation WWTP application Mono ‐ digestion of food waste Biotrickling Co ‐ generation filter Water Screening Anaerobic Storage Dilution Dewatering Food waste Shredding digestion Land Pasteurisation application
Functional unit (FU): Scheme 2 The management of sewage sludge and source ‐ segregated food waste produced by a community of 150,000 PE each day Co ‐ digestion of sewage sludge Biotrickling Co ‐ generation filter Screening Food waste Shredding Anaerobic Storage Dewatering Primary co ‐ digestion sludge Mixing Thickening Secondary Land sludge Pasteurisation application Wastewater to WWTP Remaining fraction: Mono ‐ digestion of food waste Biotrickling Co ‐ generation filter Water Screening Anaerobic Storage Dilution Dewatering Food waste Shredding digestion Land Pasteurisation application
Functional unit (FU): Scheme 3 The management of sewage sludge and source ‐ segregated food waste produced by a community of 150,000 PE each day Co ‐ digestion of sewage sludge Biotrickling Co ‐ generation filter Screening 100% Food waste Shredding Anaerobic Storage Dewatering co ‐ digestion 100% Primary Mixing Thickening & secondary sludge Land Pasteurisation application Wastewater to WWTP ‐ Production of inputs and energy : electricity, transport, infrastructure and chemicals. ‐ Direct emissions : biogas losses, CHP, digestate storage, land application. ‐ Waste streams : rejected materials to landfill and wastewater to WWTP. ‐ Environmental credits : electricity and digestate production from organic waste can replace electricity from fossil fuels and mineral fertilisers.
Results Scheme 1 Scheme 2 Scheme 3 Parameter Unit SS FW SS+FW FW SS+FW Primary sludge t/d 183 183 183 Secondary sludge t/d 341 341 341 Food waste t/d 35.62 3.85 31.76 35.62 SGP m 3 /kg TVS fed 0.35 0.7 0.40 0.7 0.54 TVS degraded % 37 74 42 74 43.5 Biogas production m 3 /d 2,855 5,281 3,598 4,710 8,543 rate Sludge produced t/d 30.22 9.45 30.59 8.43 38.13
Results Specific biogas production (m 3 /d) 10000 x 3.0 8000 6000 x 1.3 4000 2000 0 Scheme 1 Scheme 2 Scheme 3 FW SS Heat and Electricity: Scheme 1 4.2 GWh/yr Scheme 2 5.2 GWh/yr Scheme 3 12.5 GWh/yr
Results Impact categories: • Climate change (CC): GHG emissions (e.g. CH 4 , N 2 O) ReCiPe Midpoint • Terrestrial acidification (TA): acidifying emissions (e.g. SO 2 , NH 3 ) methodology 3 ‐ ) • Freshwater eutrophication (FE): P ‐ based compounds to water (e.g. PO 4 ‐ ) • Marine eutrophication (ME): N ‐ based compounds to water (e.g. NO 3 • Environmental credits 100% Avoided electricity production and 75% Comparative results mineral fertilisation 50% 25% • Environmental burdens 0% ‒ Phosphate and nitrate leachates to ‐ 25% water resulting from land application of ‐ 50% digestate ‐ 75% ‒ Reject water recirculation to WWTP ‐ 100% CC TA FE ME • Mono ‐ digestion VS Co ‐ digestion Scheme 1 Scheme 2 Scheme 3 Posi � ve synerge � c e ff ects: ↑ biogas yield ↑ environmental credits
Policy context Source ‐ segregated biodegradable waste and sewage sludge fall into different regulatory regimes in the UK Digestate from source ‐ segregated biodegradable waste is classified as a waste until it meets PAS 110 and Quality Protocol standards . The Quality Protocol for anaerobic digestate establishes the end ‐ of ‐ waste criteria then: it is no longer classified as a waste, waste management control is not required. Digestate from sewage sludge is controlled under the Sludge (Use in Agriculture) Regulations . Digestate from co ‐ digestion it is not covered by an approved quality protocol and expensive environmental permits may be required
Conclusions Co ‐ digestion of sewage sludge and food waste achieved better environmental results of all the evaluated environmental impact categories higher biogas production and lower digestate production. An integrated and holistic approach for organic waste management enhanced the environmental profile of the applied management practice. Economic and social constrains and benefits will be integrated in the sustainability assessment (future work). For its implantation, it is essential that the regulatory policy stimulates the development of a suitable market for the co ‐ digestate.
Comparative environmental analysis of anaerobic mono ‐ digestion and co ‐ digestion of organic waste L. Lijó, N. Voulvoulis, N. Frison , S. González ‐ García, M. T. Moreira and E. Katsou This research was supported by a project granted by the EU project Live ‐ Waste (LIFE 12 ENV/CY/000544) and by the BBVA program “ 2015 edition of the BBVA Foundation Grants for Researchers and Cultural Creators ” (2015 ‐ PO027).
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