BOOK OF ABSTRACTS 233 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Hall A Poster Session / Environment, Agriculture, and Forestry P4.11 Monitoring of Humification And Humification Degree Of Products Derived From Pulp And Paper Industry Residues Deborah P Dick1,2; Gabriela Koetz2; Valentina Becker1; Ana Julia R Almeida1 1 Federal University of Rio Grande do Sul (UFRGS), Institute of Chemistry. Av. Bento Gonçalves, 9500.91501-970. Porto Alegre, RS, Brazil, deborah.dick@ufrgs.br 2 UFRGS, Post-Graduation course in Soil Science, Agronomy Faculty, Av. Bento Gonçalves, 7712. 91540-000. Porto Alegre, Brazil Currently, Brazil is the world‘s largest producer and exporter of pulp, with a projected production of 29.4 million tons in 2025. Approximately 14.2 million tons of waste are associated with this production, and waste management focuses on modern sustainability practices in production and on the circular economy. This study aimed to evaluate the humification process of residues from a pulp and paper industry in South Brazil as well as the humification degree of the resulting composts, over time. The waste materials, including decomposing biological sludge from trenches (LBV), biological sludge from biodigesters (LBB), and eucalyptus bark compost (CCE), were supplied by the waste management company VIDA, located in Guaíba, RS, Brazil. Humic substances (HS), namely Humic Acids (HA) and Fulvic Acids (FA) were extracted and quantified [1] over time (12 months for LBV and 21 months for CCE) and the following proxies were calculated: HS proportion (%), humification index (HI): AH %/AF %; and HA proportion (HP): (AH / SH) x 100. Sludges and compost materials, and their purified HS were analyzed by elemental analyses, and HA and FA were characterized by FTIR and TGA. LBV presented a low initial C/N ratio (13) which tended to decrease over time (10). Humification indicators in LBV were relatively high at the beginning of decomposition (14% HS, 1.7% HI, 62% HP), peaked in the 4th month in the trench, and subsequently decreased. The LBB sample showed humification degree comparable to that of LBV samples, suggesting that sludge biodigestion for 45 days is an alternative for its maturation with the aim of using it in the soil. In contrast, the composting of CCE for 21 months was accompanied by a gradual decrease in the C/N ratio (83 to 50) and a concomitant increase in humification proxies: HS from 5 to 25 %; HI from 0.76 to 1.24; HP from 43 to 55%. In fact, the monthly increase of HA and of FA in CEE within 21 months was 0.55 % and 0.38 %, respectively. The chemical–molecular characterization of HA from LBV by FTIR revealed a reduction in carbohydratelike structures and an increase in carboxylic groups over time, reflecting the degradation of more labile structures and the increase in functionalization. For
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