| Summary: | The objective of this study was to verify the effect of kraft lignin as a microbial carrier on biogas/methane yield. An anaerobic co-digestion test process was carried out, in which confectionery waste was used with sewage sludge. At the first stage of the study pure lignin and lignin combined with polyvinylpyrrolidone (PVP) were subjected to an extensive physicochemical analysis. Their morphology, dispersion and adsorption properties were determined. The two materials were also subjected to thermal, spectroscopic and elementary analysis. The anaerobic digestion of the two substrates was carried out with and without the addition of the carrier, under mesophilic conditions and in periodic operation. The monitoring and analysis of the two essential parameters, i.e., pH and volatile fatty acids/total alkalinity (VFA/TA) ratio, revealed that the process was stable in both tests. Microbial and biochemical analyses showed intensified proliferation of eubacteria and increased dehydrogenase activity in samples prepared with the lignin + PVP material. The cell count increased by 46% in the stuffed wafers (WAF) + sewage sludge (SS) variant with the carrier, whereas the enzyme activity increased by 43%. Cell immobilisation noticeably improved the process efficiency. The biogas production increased from 722 m<sup>3</sup> Mg<sup>−1</sup> VS to 850 m<sup>3</sup> Mg<sup>−1</sup> VS (VS ⁻ volatile solids), whereas the methane production increased from 428 m<sup>3</sup> Mg<sup>−1</sup> VS to 503 m<sup>3</sup> Mg<sup>−1</sup> VS (by about 18%). The research proved that lignin could be used as a very effective microbial carrier in anaerobic digestion (AD).
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