Co-digestion of pig slurry and KOH pre-treated giant reed (Arundo donax L.) enhances methane yield and digestate characteristics

The objectives of this study were: to evaluate the methane yield attainable by co -digestion of pig slurry with thermo-alkaline pre-treated giant reed; to assess the convenience of washing the pre-treated giant reed biomass before anaerobic digestion; to evaluate the composition of the digestate, in the prospect of its possible agronomic use. This study is the first to show a clear advantage in co-digesting potassium hydroxide pre-treated giant reed with pig slurry. In mono-digestion, the maximum methane production per reactor from pre-treated biomass was 263 mL g-1 volatile solids, which was 28% higher than untreated biomass. The co-digestion of pre-treated giant reed biomass with pig slurry increased the volatile solids content by 65% and doubled the methane production per reactor (533 mL); a synergistic effect was also observed (+10%). Washing the biomass after the pre-treatment had a detrimental effect on the overall methane production and also prolonged the anaerobic digestion time both in mono-digestion and in co-digestion. The digestate derived from the pre-treated and unwashed biomass co-digestion has a considerable content of plant nutrients (nitrogen, phosphorous, and potassium) and carbon making it promising for agronomic utilization.(c) 2023 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).