UN Sustainable Development Goal 13: Take urgent action to combat climate change and its impacts
UNFCCC COP21 commitments: In December 2015, 195 countries adopted the UNFCCC Paris Agreement and thereby agreed to a global action plan to keep global warming to well below 2⁰C with an aim to limit the increase to 1.5⁰C. The need for peak global emissions to be reached soon and thereafter rapidly reduced has been recognised. In addition to nationally determined targets, commitments from cities, regions, local authorities and the private sector have been invited (European Commission, 2016). The greenhouse gas (GHG) emission reduction benefits of anaerobic digestion can play a role in achieving these targets by abating emissions related to energy production, agriculture and waste management.
Fossil fuel substitution and CO2 emissions reduction: Globally, heat and electricity production is fuelled primarily by coal, natural gas and petroleum products. Carbon dioxide emissions from consumption of the energy thus produced account for 25% of total anthropogenic GHG emissions (IPCC, 2014). Renewable energy derived from biogas produced from organic wastes and agricultural by-products not only substitutes fossil fuels but also reduces carbon dioxide emissions by completing the carbon cycle.
Methane and nitrous oxide from livestock manures: Livestock emissions account for 14.5% of total anthropogenic GHG emissions, mainly in the form of carbon dioxide, methane and nitrous oxide (Gerber, et al., 2013). Methane (CH4) and nitrous oxide (N2O) are greenhouse gases that are 21 and 310 times more damaging than CO2. Treating manures through anaerobic digestion reduces the formation of nitrous oxide and captures the methane as biogas, which can be used for energy generation. This has the multiple benefits of reduced GHG emissions from farms and energy generation, the substitution of fossil fuels and production of nutrient rich digestate biofertiliser.
Emissions from landfills: While increasing numbers of countries and cities are separately collecting the organic fraction of municipal solid waste, landfills globally still account for 700 million tonnes of methane emissions annually (US EPA, 2012). Extraction of landfill gas from operating and closed landfills and diversion of additional organic waste to AD will lead to reduced emissions, recirculation of nutrients via digestate and use of biogas to generate energy.
Domestic fuel substitution: Globally, an estimated 1.6 million deaths are attributed to indoor air pollution – caused largely by use of firewood, crop residues, dried animal dung and crop waste as domestic fuel (Berkeley Air Monitoring Group, 2015). Additionally, use of firewood is one of the leading causes of deforestation, which in turn contributes to the build-up of greenhouse gases. The use of biogas produced externally from the digestion of household and agricultural wastes as a cooking fuel can mitigate indoor air pollution and abate deforestation.
Transport sector: The transport sector is fuelled 95% by petroleum based fossil fuels and accounted for 14% of all anthropogenic GHG emissions in 2010. The use of crop and organic waste-derived biogas upgraded to biomethane as vehicular fuel completes the carbon cycle rather than adding further fossil fuel/sequestered carbon into the atmosphere.
Ratchaburi Farms Biogas Project at NongBua Farm, Thailand:
- Digests swine barn flushing wastewater
- Reduces emissions by 13,150 t CO2 eq. per annum (CDM registered and verified)
- Replaces fossil-derived imported grid electricity
- Biofertiliser from the wastewater replaces commercial fertilisers in local farms and school (UNFCCC, 2008)
Exploitation of the biogas from Controlled Landfill in Solid Waste Management Central – CTRS / BR.040, Belo Horizonte, Brazil
- Landfill gas generated from 17.4million m3 of solid urban waste collected over 32 years.
- The landfill gas, primarily methane, is collected and used to power a 4.278MW installed capacity electricity generation plant. The electricity produced is fed into the national grid, substituting fossil fuel based energy.
- Greenhouse gas emissions equivalent to 134,160 metric tonnes of CO2 eq. are offset on an annual basis, in the form of emissions avoided by the capture of landfill gas as well as the generation of renewable energy.