Co-composting of lignin to build up humic substances—Strategies in waste management to improve compost quality

Co-composting of different lignin sources with biogenic waste from the separate collection in Vienna was carried out in lab-scale experiments to promote humification as lignin is known to be a precursor molecule of humic substances. Humification is a target to be reached by composting due to the favorable properties for soils and plants. Extractable humic acids have been proved to be a suitable parameter to assess humification. Biogenic waste was used as a reference and basic material for co-composting of lignin. Lignin from different origins and composition was added: microbiologically degraded wood and lignin powder from industrial processes. Preliminary results show that addition of 2–5% of lignin powder could improve humic acid formation. Microbiologically degraded wood did not effect higher humic acid contents within the short time of lab-scale composting.Humic acid determination is based on photometrical investigations. To ensure that humic acid contents were not pretended by the presence of lignin, quality control was carried out using FT-IR spectroscopy and thermal analysis. The results obtained showed that lignin had been integrated in the humic acid molecule.