The biomethanization of sewage sludge has several disadvantages such as low methane yield, poor biodegradability andnutrient imbalance. In this paper, a sewage sludge and strawberry extrudate mixture in a proportion of 40:60 (wet weight) isproposed to improve the viability of the process. The addition of an easily biodegradable co-substrate enhanced the nutrientbalance and diluted the heavy metals and inhibitors from sewage sludge. Two different experimental set-ups at lab and semi-pilot scalewere employed in order to ensure the reproducibility and significance of the obtained values.Co-digestion improvedthe stability of the process by decreasing the alkalinity to a mean value of 3215 ± 190mg CaCO3/L, while maintaining thepH within the optimal range for anaerobic digestion. The methane yield coefficient and biodegradability were 176 L/kgVS(total volatile solids) (0◦C, 1 atm) and 81% (VS), respectively. Kinetic parameters decreased at the highest loads, suggestingthe occurrence of a slowing down phenomenon. A quality organic amendment with a heavy metal content lower than thelimits established under European legislation for agricultural applications was obtained from the digestate of the proposedtreatment.
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