Dog faeces, usually viewed as an unpleasant urban waste problem, could have another use — as a potential source of renewable energy. Researchers have found that canine waste can produce biogas through anaerobic digestion, with methane emerging as the main energy-rich fuel.
The study, published in the Biochemical Engineering Journal, examined different methods of processing wet dog faeces to determine whether useful amounts of biohydrogen and methane could be recovered.
Methane delivers most of the energy
Researchers Karla Cruz-Torres, Martín Barragán-Trinidad and Dulce María Arias-Lizárraga tested single-stage anaerobic digestion alongside a two-stage process involving acidogenic fermentation followed by anaerobic digestion.
The two-stage approach was capable of producing both hydrogen and methane. However, hydrogen contributed relatively little to the overall energy recovered.
More than 85% of the recovered energy across the tested approaches came from methane, making it by far the more significant energy product.
Anaerobic digestion uses microorganisms in an oxygen-free environment to break down organic matter, producing biogas consisting mainly of methane and carbon dioxide.
Untreated waste showed strong potential
One of the study’s notable findings was that additional treatment did not necessarily improve the overall process.
Researchers compared untreated wet faeces with dried material and samples subjected to acid hydrolysis. While pretreatment offered certain benefits, it also required additional processing and increased costs.
The study found that single-stage anaerobic digestion using untreated wet dog faeces provided the most favourable balance between energy recovery and economic viability.
From urban waste to useful fuel
The findings do not suggest that dog waste could soon replace conventional fuels. Further research, including life-cycle analysis, is needed to assess its environmental impact and determine how such systems could work on a larger scale.
However, the research points towards a possible circular approach to managing an increasingly common urban waste stream.
Instead of treating collected dog faeces solely as waste, anaerobic digestion could potentially recover some of its stored chemical energy as biogas while leaving digestate behind.
What is normally considered a nuisance on city streets, therefore, may contain a small but useful source of recoverable renewable energy.