Application of thermal analysis for evaluating the effect of glycerine addition on the digestion of swine manure
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Co-digestion of swine manure with glycerine was studied by thermal analysis (TA) and differential scanning calorimetry (DSC). Co-digestion experiments were performed under batch conditions at different organic loadings by increasing the volumetric percentage of glycerine in the mixture. Batch results were used for evaluating the performance of the process under semi-continuous conditions in an attempt to study the characteristics of the digested material. Batch tests demonstrated a successful digestion at a glycerine volumetric addition of 16% (v/v), whilst failure of the semi-continuous digestion process was reported at 8%. The different operating regimes explained the discrepancy in these outcomes, therefore, indicating that results from batch tests should not be directly extrapolated to estimate continuous performance. The addition of glycerine at high percentage negatively affected the digestion under semi-continuous conditions, resulting in the accumulation of volatile fatty acids and high H2S evolution in biogas. These characteristics were accompanied by a decrease in the conversion of the organic matter as reported from the thermal evaluation of digested samples. TA represents a good indicator of the stabilisation attained when evaluating the fate of complex materials during biological transformations. DSC demonstrated to be a superior tool when evaluating the course of digestion and the quality of the organic material obtained. The failure stage (8% glycerine content) reported a mass change of 25.3 ± 0.5% for the complex materials, which represented an increase of 17% when evaluated against the successful digestion at 4% glycerine content. In this same line, when the enthalpy is considered, these complex materials contribute an increase of 22% in the digested sample of the failure stage. This enthalpy value calculated for the complex materials (temperature region of 370–575 °C) greatly aids in assessing degradation. Therefore, the need of a stabilisation stage for co-digestion systems with a high content of readily degradable material was highly recommended.
KeywordsGlycerine Swine manure Co-digestion Stabilisation Thermal analysis DSC
This research was possible thanks to financial support from Ministerio de Economía y Competitividad and ERDF through project UNLE15-EE-3070.
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