Determining the Carbon Footprint of Biogas Production from Sewage Sludge

Barber, W.P.F.

Joint Conference: Residuals & Biosolids and Innovations in Treatment Technology, 2025

Introduction

It has eventually and sometimes reluctantly, become understood that climate change is directly influenced by the anthropogenic release of what are known as “Green House Gases – GHGs”. Their release into the earth’s atmosphere has been correlated with an increase in global temperature which in turn, has been linked to weather change with potentially catastrophic impacts (IPCC, 2001). With such significant global impacts expected, it is therefore no surprise that a great deal of interest is being shown by industry and the media alike on highlighting the issues and also proposing methods of reducing the generation of GHGs.

Methane is a potent greenhouse gas. Based on current methodology, one tonne of methane released is equivalent to releasing 30 tonnes of carbon dioxide to the atmosphere over a 100 years. As methane has a shorter atmospheric lifetime compared to carbon dioxide, it’s global warming potential increases significantly to 86 times higher than carbon dioxide when considered over a 20-year time frame (IPPC, 2024). According to the IPPC (2024), methane is
responsible for approximately a third of current global warming. The wastewater sector is a major source of these methane emissions, contirbuting to 5-8% of global anthropogenic methane emissions, just following livestock (32%), oil and gas (25%), landfills (13%), and coal mining (11%) (Ocko et al., 2021). Methane emissions from wastewater treatment come from a variety of sources including: sludge and wastewater storage, leaks from digesters – especially floating roof – and biogas infrastructure, incomplete combustion of biogas in combined heat and power plants and even from treated biosolids (Brower, 2025). Now, with modern measuring techniques becoming more available, recent studies have found that methane emissions from wastewater treatment works are approximately twice as high as previously thought (Song et al., 2023; Moore et al., 2024).

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