Converting Municipal Waste to Energy through the Biomass Chain, a Key Technology for Environmental Issues in (Smart) Cities
2. Background Information and Context
2.1. European Context
2.2. Current Situation in Romania
2.3. Related Works
3. MSW to Biogas Production Technologies
3.1. Biogas Conversion Facilities—Overviews
- The amount of organic waste to be used;
- The ratio with which household waste is collected;
- The type of the organic waste (later on the article, a table with the most common biomass constituents of MSW are provided—Table 3);
- Local demand of the biogas—assuming that the plant is only feeding local needs and does not serve as a national or international source of biogas;
- The climate in the region throughout the different seasons.
- = bioreactor volume (m3)
- = biomass volume to be used daily (m3 * day−1)
- = retention time (days)
- = gas space—about 10% from the total volume of (the place where the biogas accumulates).
3.2. Municipal Solid Waste Supply Chains (MSWSCs)
- Waste generation is forecasted with high probability rates for the entire scheduling periods;
- Waste generated in cities is collected by the city collection station;
- All costs related to waste collection, transportation as well as other operational costs are linear functions.
|MSW Biomass Constituents||Biogas over Biomass Constituents (L kg−1, Dry Weight)||Methane (%)||Energy MJ **||Energy KWh ***|
|Column 1 (C1)||Column 2 (C2)||Column 3 (C3)||Column 4 (C4)||Column 5 (C5)|
|Leather * ||25–77||34||0.0208–0.0639||0.0019–0.0059|
|Cotton and wool * ||25–77||65||0.0397–0.1222||0.0037–0.0113|
- (rho) = density of methane (CH4), 46.5 kg/m3 
- = value of energy (heat) for methane (CH4), 50–55 MJ/kg
- (eta) = efficiency (MJ to KWh converted at 33% efficiency is 0.0926) .
- The capacity of each storage station; this should equalize the amount left from the previous period plus the waste collected the period taken into consideration;
- = capacity of a storage station (m3);
- = time;
- = waste collection ratio;
- = quantity/volume of waste collected;
- Transportation limits; clearly, the total waste transported from the city to distribution centers and further on the supply chain cannot exceed the transport capacity.
- = transportation mean (vehicle);
- = the total number of vehicles available for MSW transportation;
- = the volume (or quantity) of MSW transported by each unit/vehicle;
4.1. Bergen Example
4.2. Tønsberg Example
4.3. London Example
4.4. Barcelona Example
- Energy prices;
- Tax concessions, if any;
- Land prices;
- Labor costs;
- Construction and material costs;
- Prices and markets for biofertilizer;
- Quality of both the biogas produced and biofertilizer.
- The complexity of the whole system. Establishing a self-sustaining institutional system is a complex activity that may require many resources, capability and initiative. In this regard, the author considers that private–public partnerships are a great way to deal with this new perspective of transforming MSW into biogas—Bergen is one of the most convincing cases of huge scale complexity.
- Individual behavior and waste cycles. The daily behavior of individuals cannot be precisely predicted (only their aggregation can); in fact, the volume of waste, as well as its type, are very particular. As such, it is not an easy task to do any prior calculation of inputs to properly understand the expected outputs. Introducing Smart Metering may help, but the costs associated with it would be added to the whole project.
- (Technical) acceptance by officials. Introduction and use of biogas require a huge change in the actual waste collection and deposit. The benefits must be fully observed and understood by the officials, as well as by citizens, in order for them to accept the investments. Barriers as management failures and organizational inflexibility are difficult to overcome [85,86]. Therefore, extra efforts should be made in this regard.
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
- Official Journal of the European Union. Directive 2009/29/EC of The European Parliament and of The Council, of 23 April 2009, amending Directive 2003/87/EC so as to Improve and Extend the Greenhouse Gas Emission Allowance Trading Scheme of the Community. Available online: https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2009:140:0063:0087:en:PDF (accessed on 22 November 2019).
- Romanian Government Official Gazette. Hotărârea nr. 1844/2005 Privind Promovarea Utilizării Biocarburanților și a Altor Carburanți Regenerabili Pentru Transport (Decision no. 1844/2005 on Promoting the Use of Biofuels and Other Renewable Fuels for Transport). Available online: https://lege5.ro/Gratuit/hazdmnbz/hotararea-nr-1844-2005-privind-promovarea-utilizarii-biocarburantilor-si-a-altor-carburanti-regenerabili-pentru-transport (accessed on 22 November 2019). (In Romanian)
- European Commission. Directive 2008/98/EC on Waste (Waste Framework Directive). Available online: https://ec.europa.eu/environment/waste/framework/ (accessed on 22 November 2019).
- Gusmerotti, N.M.; Corsini, F.; Borghini, A. Assessing the role of preparation for reuse in waste-prevention strategies by analytical hierarchical process: Suggestions for an optimal implementation in waste management supply chain. Environ. Dev. Sustain. 2019, 21, 2773–2792. [Google Scholar] [CrossRef]
- Eurostat. Municipal Waste Statistics. Available online: https://ec.europa.eu/eurostat/statistics-explained/index.php/Municipal_waste_statistics (accessed on 23 November 2019).
- OECT.Stat. Municipal Waste, Generation and Treatment. Available online: https://stats.oecd.org/Index.aspx?DataSetCode=MUNW (accessed on 22 November 2019).
- EU (2006) Directive 2006/12/CE of the European Parliament and of the Council of 5 April 2006 on Waste. Available online: https://eur-lex.europa.eu/eli/dir/2006/12/oj (accessed on 24 January 2020).
- EU (2014) Directive 2014/94/UE of the European Parliament and of the Council of 22 October 2014 on the Deployment of Alternative Fuels Infrastructure. Available online: https://eur-lex.europa.eu/eli/dir/2014/94/oj (accessed on 24 January 2020).
- Bucharest Master Plan for the Integrated Waste Management System at the Level of Bucharest Municipality. Available online: https://www3.pmb.ro/storage/proiecte/1541510102master-plan.pdf (accessed on 24 January 2020).
- Sennes, V.; Gombert-Courvoisier, S.; Robeyre, F.; Felonneau, M.L. Citizens’ environmental awareness and responsibility at local level. Int. J. Urban. Sustain. Dev. 2012, 4, 186–197. [Google Scholar] [CrossRef]
- Tampakis, S.; Tsantopoulos, G.; Arabatzis, G.; Rerras, I. Citizens’ views on various forms of energy and their contribution to the environment. Renew. Sustain. Energy Rev. 2013, 20, 473–482. [Google Scholar] [CrossRef]
- Anagnostopoulos, T.; Zaslavsy, A.; Medvedev, A.; Khoruzhnicov, S. Top—k Query Based Dynamic Scheduling for IoT-enabled Smart City Waste Collection. In Proceedings of the 16th IEEE International Conference on Mobile Data Management, Pittsburgh, PA, USA, 15–18 June 2015; pp. 50–55. [Google Scholar] [CrossRef]
- Jaydeep, L.; Venkata, R.M.; Xuan, Z. Solid waste collection/transport optimization and vegetation land cover estimation using Geographic Information System (GIS): A case study of a proposed smart-city. Sustain. Cities Soc. 2017, 35, 336–349. [Google Scholar] [CrossRef]
- Scholwin, F. Energy flows in biogas plants: Analysis and implications for plant design. In The Biogas Handbook; Woodhead Publishing Series in Energy: Cambridge, UK, 2013; pp. 212–227. [Google Scholar]
- Bachmann, N. Design and engineering of biogas plants. In The Biogas Handbook; Woodhead Publishing Series in Energy: Cambridge, UK, 2013; pp. 191–211. [Google Scholar]
- Abbasi, T.; Tauseef, S.M.; Abbasi, S.A. Biogas Capture from Solid Waste. In Biogas Energy; Springer Briefs in Environmental Science: Berlin/Heidelberg, Germany, 2011; Volume 2, pp. 105–143. [Google Scholar]
- Scheper, T. Advances in Biochemical Engineering/Biotechnology. In Biogas Science and Technology; Springer International Publishing: Cham, Switzerland, 2015; p. 5. [Google Scholar]
- Makádi, M.; Tomócsik, A.; Orosz, V. Digestate: A New Nutrient Source—Review. In Biogas; IntechOpen: Rjeka, Croatia, 2012. [Google Scholar] [CrossRef]
- United Nation Framework Convention on Climate Change (UNFCCC). Kyoto Protocol Reference Manual on Accounting of Emissions and Assigned Amount. Available online: https://unfccc.int/resource/docs/publications/08_unfccc_kp_ref_manual.pdf (accessed on 22 November 2019).
- Abbasi, T.; Tauseef, S.M.; Abbasi, S.A. Biogas and Global Warming. Biogas Energy 2012. [Google Scholar] [CrossRef]
- Scarlat, N.; Dallemand, J.F.; Fahl, F. Biogas: Developments and perspectives in Europe. Renew. Energy 2018, 129, 457–472. [Google Scholar] [CrossRef]
- Official Website of the European Union. Renewable Energy Directive. Available online: https://ec.europa.eu/energy/topics/renewable-energy/renewable-energy-directive/overview_en (accessed on 9 April 2021).
- Michelini, G.; Moraes, R.N.; Cunha, R.N.; Costa, J.M.H.; Ometto, A.R. From Linear to Circular Economy: PSS Conducting the Transition. CIRP IPSS 2017, 64, 2–6. [Google Scholar] [CrossRef]
- Ciuta, S.; Apostol, T.; Rusu, V. Urban and Rural MSW Stream Characterization for Separate Collection Improvement. Sustainability 2015, 7, 916–931. [Google Scholar] [CrossRef][Green Version]
- Mutz, D.; Hengevoss, D.; Hugi, C.; Gross, T. Waste-to-Energy Options in Municipal Solid Waste Management, Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH, Eschborn, 2017; pp. 10–19. Available online: https://www.giz.de/en/downloads/GIZ_WasteToEnergy_Guidelines_2017.pdf (accessed on 16 January 2020).
- BP. BP Statistical Review of World Energy; BP: London, UK, 2019; Volume 68, pp. 8–10. [Google Scholar]
- REN21. Renewables Now; Global Status Report; REN21: Paris, France, 2019; p. 71. [Google Scholar]
- Mahajan, J.; Vakharia, A.J. Waste Management: A Reverse Supply Chain Perspective. VIKALPA 2016, 41, 1–12. [Google Scholar] [CrossRef]
- European Biogas Association (EBA). EBA Statistical Report 2018. 2019. Available online: https://www.europeanbiogas.eu/wp-content/uploads/2019/05/EBA_Statistical-Report-2018_AbrigedPublic_web.pdf (accessed on 2 December 2019).
- European Parliament News Portal. What is Carbon Neutrality and How Can It Be Achieved by 2050? Available online: https://www.europarl.europa.eu/news/en/headlines/society/20190926STO62270/what-is-carbon-neutrality-and-how-can-it-be-achieved-by-2050 (accessed on 31 March 2021).
- Wüstenhagen, R.; Bilharz, M. Green Energy Market Development in Germany: Effective Public Policy and Emerging Customer Demand. Energy Policy 2006, 34, 1681–1696. [Google Scholar] [CrossRef][Green Version]
- Roberts, P. Energy Is Power. In The End of Oil: On the Edge of a Perilous New World, 1st ed.; Houghton Mifflin: Boston, MA, USA, 2004; pp. 91–115. [Google Scholar]
- French Institute of International Relations (IFRI); Eyl-Mazzega, M.A.; Mathieu, C. Biogas and Biomethane in Europe: Lessons from Denmark, Germany and Italy; IFRI: Paris, France, 2019; Available online: https://www.ifri.org/sites/default/files/atoms/files/mathieu_eyl-mazzega_biomethane_2019.pdf (accessed on 31 March 2021).
- Lyng, K.A.; Skovsgaard, L.; Jacobsen, H.K.; Hanssen, O.J. The implications of economic instruments on biogas value chains: A case study comparison between Norway and Denmark. Environ. Dev. Sustain. 2020, 22, 7125–7152. [Google Scholar] [CrossRef]
- Global Methane Initiative (GMI). Official Web Site. Available online: https://www.globalmethane.org/resources/index.aspx?sector=Municipal+Solid+Waste (accessed on 24 March 2021).
- Treichel, H.; Alves, S.L.J.; Müller, C.; Fongaro, G. An Overview About of Limitations and Avenues to Improve Biogas Production. Biofuel Biorefinery Technol. 2019, 9, 289–304. [Google Scholar]
- Anaokar, G.S.; Khambete, A.K.; Christian, R.A. Biogas modeling by fuzzy comprehensive index of municipal wastewater and sludge. Environ. Prog. Sustain. Energy 2021, 40, e13502. [Google Scholar] [CrossRef]
- The Barcelona Website|Barcelona City Council. Available online: https://ajuntament.barcelona.cat/ecologiaurbana/en/services/the-city-works/maintenance-of-public-areas/waste-management-and-cleaning-services/household-waste-collection (accessed on 14 February 2021).
- SEAT Official Web Page. Available online: https://www.seat.com/company/news/company/seat-turns-organic-waste-into-fuel.html (accessed on 14 February 2021).
- European Commission. Estimates of European Food Waste Levels. Available online: https://ec.europa.eu/food/safety/food_waste_en (accessed on 5 December 2019).
- Eurostat. Waste Generated by Households by Year and Waste Category. Available online: https://ec.europa.eu/eurostat/tgm/table.do?tab=table&init=1&language=en&pcode=ten00110&plugin=1 (accessed on 5 December 2019).
- European Commission, Statistical Office. Portrait of the Regions—Romania; European Commission: Brussels, Belgium, 2011; Volume 11, Available online: https://insse.ro/cms/files/publicatii/Statistica%20teritoriala/Portrait%20of%20the%20regions_Romania_volume%2011.pdf (accessed on 23 March 2021).
- DIGI 24 News Channel, Article: Toate Gropile de Gunoi ale Bucureștiului, în Afara Legii (All the Landfills of Bucharest, Outside the Law). Available online: https://www.digi24.ro/stiri/actualitate/social/toate-gropile-de-gunoi-din-bucuresti-in-afara-legii-824826 (accessed on 18 March 2021).
- European Commission, Directorate-General for Internal Market, Industry, Entrepreneurship and SMEs. Country Report, Romania, Legal Assistance on the Application of Public Procurement Rules in the Waste Sector; Ramboll: Copenhagen, Denmark, 2016. [Google Scholar]
- National Statistics Institute, Metadata [O4_9]. Available online: http://www.insse.ro/cms/files/Web_IDD_BD_ro/ob4.htm (accessed on 19 March 2021).
- Pfau, S.F.; Hagens, J.E.; Dankbaar, B. Biogas between renewable energy and bio-economy policies—Opportunities and constraints resulting from a dual role. Energy Sustain. Soc. 2017, 7, 7–17. [Google Scholar] [CrossRef][Green Version]
- Holm-Nielsen, J.B.; Oleskowicz-Popiel, P. Process control in biogas plants. In The Biogas Handbook; Woodhead Publishing Series in Energy: Cambridge, UK, 2013; pp. 228–247. [Google Scholar]
- Al Seadi, T.; Rutz, D.; Janssen, R.; Drosg, B. Biomass resources for biogas production. In The Biogas Handbook; Woodhead Publishing Series in Energy: Cambridge, UK, 2013; pp. 19–51. [Google Scholar]
- Beil, M.; Beyrich, W. Biogas upgrading to biomethane. In The Biogas Handbook; Woodhead Publishing Series in Energy: Cambridge, UK, 2013; pp. 342–377. [Google Scholar]
- Iakovou, E.; Karagiannidis, A.; Vlachos, D.; Toka, A.; Malamakis, A. Waste biomass-to-energy supply chain management: A critical synthesis. Waste Manag. 2010, 30, 1861–1870. [Google Scholar] [CrossRef] [PubMed]
- Kerroum, D.; Mossaab, B.; Hassen, M.A. Production of Biogas from Sludge Waste and Organic Fraction of Municipal Solid Waste. Biogas 2011. [Google Scholar] [CrossRef][Green Version]
- Gomez, C. Biogas as an energy option: An overview. In The Biogas Handbook; Woodhead Publishing Series in Energy: Cambridge, UK, 2013; pp. 1–16. [Google Scholar]
- Viancelli, A.; Michelon, W.; ElMahdy, M. Current Efforts for the Production and Use of Biogas Around the World. Biofuel Biorefinery Technol. 2019, 9, 277–287. [Google Scholar]
- Svensson, M. Biomethane for transport applications. In The Biogas Handbook; Woodhead Publishing Series in Energy: Cambridge, UK, 2013; pp. 428–443. [Google Scholar]
- Folk, E. BioEnergy Consult, Insights into MSW-to-Energy. 2019. Available online: https://www.bioenergyconsult.com/msw-to-energy/ (accessed on 16 January 2020).
- Frombo, F.; Minciardi, R.; Robba, M.; Rosso, F.; Sacile, R. Planning woody biomass logistics for energy production: A strategic decision model. Biomass Bioenergy 2009, 33, 372–383. [Google Scholar] [CrossRef]
- Dornburg, V.; Faaij, A. Efficiency and economy of woodfired biomass energy systems in relation to scale regarding heat and power generation using combustion and gasification technologies. Biomass Biomass Energy 2001, 21, 91–108. [Google Scholar] [CrossRef]
- Taifouris, M.S.; Martín, M. Multiscale scheme for the optimal use of residues for the production of biogas across Castile and Leon. J. Clean. Prod. 2018, 185, 239–251. [Google Scholar] [CrossRef]
- Malmberg, Insights, The Magic Factory, A Real Win-Win Situation. Available online: https://www.malmberg.se/en-us/Insights/The-Magic-Factory (accessed on 16 January 2020).
- Den Magiske Fabrikken. Available online: https://kampanje.vesar.no/den-magiske-fabrikken/ (accessed on 13 February 2021).
- Samer, M. Biogas Plant Constructions. In Biogas; InTech: Rijeka, Croatia, 2012; pp. 343–369. [Google Scholar]
- Zhang, Y.; Huang, G.H.; He, L. A multi-echelon supply chain model for municipal solid waste management system. Waste Manag. 2014, 34, 553–561. [Google Scholar] [CrossRef]
- Themelis, N.J.; Ulloa, P.A. Methane generation in landfills. Renew. Energy 2007, 32, 1243–1257. [Google Scholar] [CrossRef]
- Mustafa, M.Y.; Calay, R.K.; Román, E. Biogas from Organic Waste—A Case Study. Procedia Eng. 2016, 146, 310–317. [Google Scholar] [CrossRef][Green Version]
- Roddy, D.J. Biomass in a petrochemical world. Interface Focus 2013, 3, 20120038. [Google Scholar] [CrossRef][Green Version]
- Ofoefule, A.U.; Nwankwo, J.I.; Ibeto, C.N. Biogas Production from Paper Waste and its blend with Cow dung. Adv. Appl. Sci. Res. 2010, 1, 1–8. [Google Scholar]
- Salehian, P.; Keikhosro, K.; Zilouei, H.; Jeihanipour, A. Improvement of biogas production from pine wood by alkali pretreatment. Fuel 2012, 106, 484–489. [Google Scholar] [CrossRef]
- Leather International, Tannery Waste to Biogas—Industry Report. 2016. Available online: http://www.leathermag.com/features/featuretannery-waste-to-biogas-industry-report-4995410/ (accessed on 21 December 2019).
- Rajendran, K.; Balasubramanian, G. High-Rate Biogas Production from Waste Textiles. Master’s Thesis, University of Borås, Industrial Biotechnology, Borås, Sweden, 2011. Available online: https://www.researchgate.net/publication/232285480_High_rate_biogas_production_from_waste_textiles (accessed on 21 December 2019).
- Ramasamy, E.V.; Gajalaksl, S.; Sanjeevi, R.; Jithesh, M.N.; Abbasi, S. Feasibility studies on the treatment of dairy wastewaters with up flow anaerobic sludge blanket reactors. Bioresour. Technol. 2004, 93, 209–212. [Google Scholar] [CrossRef] [PubMed]
- Endmemo. Methane Mass Volume Converter. Available online: www.endmemo.com/chem/massvolume.php?q=Methane (accessed on 21 December 2019).
- World Nuclear Association. Heat Values of Various Fuels. Available online: https://www.world-nuclear.org/information-library/facts-and-figures/heat-values-of-various-fuels.aspx (accessed on 21 December 2019).
- Wen, X.Y. City intelligent life: A case study on Shenzhen city intelligent classification of domestic waste. SCRD Smart Cities Reg. Dev. J. 2021, 27–30. [Google Scholar]
- Infrastructure Intelligence Official Web Page. Available online: http://www.infrastructure-intelligence.com/article/nov-2016/world%E2%80%99s-largest-automated-vacuum-waste-collection-system-set-bergen (accessed on 14 February 2021).
- ENVAC Official Web Page. Available online: https://www.envacgroup.com/project/bergen/ (accessed on 14 February 2021).
- Bugge, M.M.; Fevolden, A.M.; Klitkou, A. Governance for system optimization and system change: The case of urban waste. Res. Policy 2019, 48, 1076–1090. [Google Scholar] [CrossRef]
- London’s Global University. Available online: https://www.ucl.ac.uk/circular-economy-lab/Past_events/teg_visit (accessed on 14 February 2021).
- L’àrea Metropolitana de Barcelona Official Web Page. Available online: https://www.amb.cat/en/web/ecologia/residus/instalacions-i-equipaments/detall/-/Equipament/ecoparc-montcada-i-reixac/352170/11818 (accessed on 14 February 2021).
- London Municipality Official Web Page. Available online: https://www.london.gov.uk/about-us/london-assembly/london-assembly-publications/energy-waste (accessed on 14 February 2021).
- Kok, S.W.; Irene, M.C.L. A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong. Waste Manag. 2016, 47, 3–10. [Google Scholar] [CrossRef]
- Tavares, G.; Zsigraiova, Z.; Semiao, V.; Carvalho, M.G. Optimization of MSW collection routes for minimum fuel consumption using 3D GIS modelling. Waste Manag. 2009, 29, 1176–1185. [Google Scholar] [CrossRef] [PubMed]
- Mustafa, A.; Kaur, C.R.; Mohamad, Y.M. A Techno-economic Study of a Biomass Gasification Plant for the Production of Transport Biofuel for Small Communities. Energy Procedia 2017, 112, 529–536. [Google Scholar] [CrossRef]
- Winquist, E.; Van Galen, M.; Zielonka, S.; Rikkonen, P.; Oudendag, D.; Zhou, L.; Greijdanus, A. Expert Views on the Future Development of Biogas Business Branch in Germany, The Netherlands, and Finland until 2030. Sustainability 2021, 13, 1148. [Google Scholar] [CrossRef]
- Dahlgren, S.; Ammenberg, J. Sustainability Assessment of Public Transport, Part II—Applying a Multi-Criteria Assessment Method to Compare Different Bus Technologies. Sustainability 2021, 13, 1273. [Google Scholar] [CrossRef]
- Vrabie, C. Elemente de E-Guvernare (Elements of E-Government); Pro Universitaria Publishing House: Bucharest, Romania, 2016; pp. 33–53. [Google Scholar]
- Solutions for eGovernment. Deliverable 3 for the EC-funded Project ‘Breaking Barriers to eGovernment’. Breaking Barriers to eGovernment. Overcoming Obstacles to Improving European Public Services; Modinis Study; 2007. eGovernment Unit, DG Information Society and Media, European Commission. Available online: https://www.oii.ox.ac.uk/archive/downloads/research/egovbarriers/deliverables/solutions_report/Solutions_for_eGovernment.pdf (accessed on 17 February 2021).
|Waste Categories||Estimated Composition (Average) %|
|Cotton and wool||3.7|
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Vrabie, C. Converting Municipal Waste to Energy through the Biomass Chain, a Key Technology for Environmental Issues in (Smart) Cities. Sustainability 2021, 13, 4633. https://doi.org/10.3390/su13094633
Vrabie C. Converting Municipal Waste to Energy through the Biomass Chain, a Key Technology for Environmental Issues in (Smart) Cities. Sustainability. 2021; 13(9):4633. https://doi.org/10.3390/su13094633Chicago/Turabian Style
Vrabie, Catalin. 2021. "Converting Municipal Waste to Energy through the Biomass Chain, a Key Technology for Environmental Issues in (Smart) Cities" Sustainability 13, no. 9: 4633. https://doi.org/10.3390/su13094633