In an energy constrained world, anaerobic digestion (AD) of organic fraction of municipal solid waste (OFMSW) i.e. food residues and green waste, offers a high potential of clean and renewable energy. OFMSW is highly biodegradable in nature, and a high biogas recovery up to 200 m3(≈ 400 kWh of power) per ton of waste treated is achievable, which may reduce the CO2emissions by 200-300 kg CO2/t of bio-waste (Bolzonella et al., 2006)., if used (power and heat) instead of fossil fuels.
However, OFMSW lacks certain characteristics that may be a limiting factor in proving its actual efficacy to produce the biogas. Sewage sludge, animal waste and other organic wastes inherit such characteristics that can synergize the biogas potential of OFMSW when it is co-digested. AcoD of OFMSW with sewage sludge could provide the economic benefits from the surplus renewable energy produced in the form of methane as well as costs savings by means of sharing the treatment infrastructure i.e. use of common facilities. The digestate from co-digestion can be recycled as a fertilizer at a reasonable price.
Several full-scale application of AcoD of OFMSW has been reported in Finland (1400 m3); at two Italian WWTP, Viareggio and Treviso, where inclusion of OFMSW co-digestion step costs approximate €1.5 million, with a payback period of 3.5 years (Cavinato et al., 2013); 22 full scale centralized plants in Denmark; and in Velenje, Slovenia. However, there is a limited industrial application of co-digestion i.e. only 9.7% of the overall anaerobic digestion of the OFMSW capacity is at present co-digested.
Lack of design and operational experience, impacts of co-digestion on downstream processing of biosolids and biogas, waste collection and handling, lack of biogas utilization options and inadequate financial incentives were considered the key bottlenecks in the integration of co-digestion to existing WWTP facilities (Nghiem et al. 2017). Complex synergies among the administrative bodies responsible for wastewater and solid waste management have been identified to hamper the development and wide application of the co-digestion approach.
OFMSW offers a renewable, abundantly available, and low-cost source of raw material for the production of several value-added products including biofuels (methane, hydrogen, ethanol), bio-plastic, bio-pesticides, organic acids, chemicals (acetone and butanol, glycerol), and enzymes (lipase, amylase, and pectinases). The recovery of these value-added products from AcoD of OFMSW is the domain of current research, which needs more work in order to realize the potential of technology and further translation to the real scale.
More techno-economic and energy efficiency studies are needed under different sets of conditions in order to realize the true benefits of AcoD. A socio-economic study considering the stakeholders’ preferences towards sustainability of a biomass to bioenergy approach and perception of the households towards biogas as an alternative source of energy over conventional sources of energy can be a valuable addition. It can also provide the insight on the social acceptance of installing a biogas facility and net benefit accrued by the society.
An integrated management system involving OFMSW and other organic wastes co-digestion resulting in renewable energy generation, reduced GHG emission, sustainable bio-waste recycling, nutrients recycling, and an economically-feasible option for waste management.
These findings are described in the article entitled Anaerobic co-digestion of organic fraction of municipal solid waste (OFMSW): Progress and challenges, recently published in the journal Renewable and Sustainable Energy Reviews. This work was conducted by Vinay Kumar Tyagi from Nanyang Technological University and the Indian Institute of Technology Roorkee, L.A. Fdez-Güelfo, C.J.Álvarez-Gallego, and L.I. Romero Garcia from the University of Cadiz, and Yan Zhou and Wu Jern Ng from Nanyang Technological University.
References
- Bolzonella D, Pavan P, Mace S, Cecchi F. Dry anaerobic digestion of differently sorted organic municipal solid waste: a full-scale experience. Water Sci Technol 2006; 53: 23-32.
- Nghiem LD, Koch K, Bolzonella D, Drewes JE. Full-scale co-digestion of wastewater sludge and food waste: Bottlenecks and possibilities. Renew Sustain Energy Rev 2017; 72: 354–62.