Characterization of humic acid extracted from solid fermentation of rice straw using Trichoderma viride and Phanerochaete chrysosporium

M.S. Umi Kalsom and D. Noor Shita

Abstract

The basidiomycetes, Phanerochaete chrysosporium and ascomycetes, Trichoderma viride decompose rice straw in solid state fermentation. Degradation of rice straw by these fungi resulted in the formation of humic acid (HA). The HA extracted from two fermentations using P. chrysosporium (HAP) and T. viride (HAT) were characterized using i) elemental analysis ii) fourier transform infrared (FTIR) and iii) solid state cross polarization magic angle spinning carbon-13 nuclear magnetic resonance (CP/MAS 13C NMR) spectroscopy. From elemental analysis it was shown that, HAP has a lower C/N ratio (13.9) as compared to HAT (16.2). The O/C ratio was higher in HAP (0.6) than in HAT (0.5). Result of CP/MAS 13C NMR analysis showed that 27.2% of the total component of HAT was made up of aliphatic alkyl groups, 24.7% N-alkyl, 33.4% O-alkyl, 6.1% aromatic, 1.1% phenolic and 7.5% carboxylic. On the other hand, 24.6% of the total component of HAP was made up of aliphatic alkyl groups, 17.8% N-alkyl, 33.9% O-alkyl, 5.2% aromatic, 1.4% phenolic and 17.1% carboxylic. The FTIR spectra of both HAT and HAP contained all the major characteristic absorption peaks of humic acid which indicate the presence of the major structural elements of HA namely phenolic- OH, CH2, CH3, and aromatic ring. Results from both elemental and spectroscopic analysis suggest that HAP has a higher degree of humification as compared to HAT.

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