Evaluation of batch mesophilic anaerobic digestion of waste Euro banknotes for methane Production: Preliminary studies and kinetic approach

The European Central Bank is striving to find environmentally friendly alternative methods of waste disposal. In 2020, it decided to end the disposal of Waste Euro Banknotes (WeuroB) in landfills and planned to use them for recycling and/or energy recovery. Despite being recognized as an effective tool in a circular economy model, there are no reported studies on the use of WeuroB as a substrate in anaerobic digestion (AD). Thus, the aim of this research was to assess the viability of WeuroB to be converted into high-value-added energy products (mainly methane) through AD. WeuroB (euro10 and euro20 denominations) provided by the Bank of Spain were used. Biochemical methane potential (BMP) tests of pre-treated (grinded) and untreated WeuroB were assessed at mesophilic temperature. The ultimate methane yield was considerably higher for pre-treated WeuroB (334 +/- 23 NmL CH4 g VS-1 added) than for untreated WeuroB (297 +/- 14 NmL CH4 g VS-1 added). The Logistic or Sigmoidal kinetic model adequately fit the experimental data and allowed for obtaining the kinetic parameters of each case studied. In this sense, an increase of 22.4 % in the maximum methane production rate (Rmax) was observed for the pre-treated WeuroB (52.5 +/- 0.9 mL CH4 (g VS center dot d)-1 compared to the untreated WeuroB (16.2 +/- 1.8 mL CH4 (g VS center dot d)-1). According to the obtained results, AD may be a good alternative for the energetic valorization and recycling of WeuroB.