Enhanced Methane Production from Mixed Waste Organic Materials

European Union and United Kingdom have tightened their waste disposal regulations; landfill disposal of waste organic materials will be no longer available after 2020, and so alternatives to waste disposal on landfills are required for a profitable and efficient recycling. EU countries have already agreed on a new renewable energy target of at least 27 % of final energy consumption by 2030, focusing on further development and deployment of second and third generation biofuels. Organic waste management and energy recovery can be effectively combined in the anaerobic digestion process, obtaining a biofuel (biogas) and a by-product (digestate) with an excellent value as fertilizer. Upgraded biogas, named biomethane can substitute natural gas and be injected into the gas grid used as transport fuel.
The principal aim of this research is to improve and optimize the methane production from waste paper and macroalgae through two different technologies: the biomass pretreatment and the co-digestion of two feedstocks. A mechanical pretreatment in a Hollander beater was applied to waste paper and Pelvetia canaliculata macroalgae and both feedstocks were then co-digested at different mixing ratios.
Hollander beater pretreatment increased the methane yield by 21 % in the case of waste paper and by 74 % in the case of macroalgae compared with no pretreated biomass. Longer pretreatment times also increased the biodegradability of the feedstocks. The co-digestion of waste paper and macroalgae resulted in a synergistic effect, increasing the methane yield by 30 % and 22 % compared with the mono-digestion of macroalgae and waste paper respectively. Co-digestion balanced the C/N in the process to an optimum of 26 where a maximum biodegradability index was achieved. Optimized methane production was achieved at low feedstock to inoculum ratios, allowing a better exploitation of the feedstock and ensuring the presence of the groups of microorganisms required for the complete degradation of the biomass.