3 Biotech (2018) 8:258
Bioconversion of lignite humic acid by white-rot fungi
and characterization of products
· Yunyun Li
· Yuansong Liao
· Huirong Ma
· Jianjun Wu
· Yixin Zhang
· Jinghua Yao
Received: 6 January 2018 / Accepted: 7 May 2018 / Published online: 14 May 2018
© Springer-Verlag GmbH Germany, part of Springer Nature 2018
Lignite humic acids (LHAs) were sequentially separated from lignite with aqueous NaOH and HCl and biotreated by an
isolated fungus WF8. The liquid product (LP), residues (RS) and LHAs were analyzed using a Fourier transform infrared
spectrometer (FTIR) and a proton nuclear magnetic resonance (
H NMR). Three main enzymes in WF8 (i.e., lignin peroxi-
dase, manganese peroxidase and laccase) were also measured and analyzed with and without LHAs. The results show that
LHAs can induce the ligninolytic enzymes. The oxidation and hydrogenation reactions proceeded to some extent, aromatic-
ity in LHAs and carboxyl in LP decreased, and LHAs were converted into simpler LP via biochemical reactions by WF8.
Keywords Lignite humic acids · Fungus · Bioconversion · Products analysis
LHAs Lignite humic acids
LP Liquid product
FTIR Fourier transform infrared
NMR Nuclear magnetic resonance
LiP Lignin peroxidase
MnP Manganese peroxidase
ABTS 2,2-Azinobis (3-ethylbenzthiazoline-6-sulfonate)
DMSO Dimethyl sulfoxide-d
Lignite reserves in China are about 130 billion tons,
accounting for 12.4% of lignite reserves worldwide (Yao
et al. 2015). However, lignite hasn’t been utilized eﬃciently
and is also a potential threat to the environment (Xiao et al.
2010; Yu et al. 2013; Zhang et al. 2015). Lignite contains
up to 30–80% of humic acids. To better utilize lignite, it has
been proposed to convert humic acids to chemical products
with higher added values (Willmann and Fakoussa 1997).
However, the application of lignite-based humic acids is lim-
ited by its high molecular weight, low solubility in water,
poor activity and safety concerns. To expand the application
range and increase its added value and activity, lignite humic
acids (LHAs) can be converted into some simpler products,
such as fulvic acids.
Currently, compared to the other conventional conversion
procedures, biodegradation/bioconversion is safe, environ-
mentally friendly and energy eﬃcient (Fakoussa and Frost
1999; Gramss et al. 1999; Steﬀen et al. 2002; Yao et al.
2015; Zavarzina et al. 2004; Ziegenhagen and Hofrichter
1998). Separated from lignite, LHAs are simpler than lig-
nite and have more similarities to lignite than other model
compounds (e.g., benzoic acid, phenol, pyrrole, etc.). Thus,
bioconversion of LHAs can not only provide useful informa-
tion for lignite bioconversion, but also have the capability of
producing soluble active low-molecular materials.
LHAs are complex mixtures of polydisperse, polyelectro-
lyte-like molecules with irregular structures (Grinhut et al.
2011). LHAs are hard to be degraded by microorganisms,
and the products are diﬃcult to analyze. Currently, system-
atic studies on LHAs bioconversion mechanism is still lack-
ing, therefore, not fully understood.
In the present investigation, we separated LHAs from lig-
nite, biotreated LHAs using an isolated fungus and examined
the bioconversion of LHAs.
* Jinghua Yao
Key laboratory of Coal Processing and Eﬃcient Utilization,
Ministry of Education, China University of Mining
and Technology, 1 University Road, Xuzhou 221116, China