The treatment of spent cooking liquor is critical for
clean production
of pulp and paper industry. There is a compelling need to develop
a cost-effective and green technology for reuse of organic matter
in spent cooking liquor to mitigate the negative impacts on the environment.
The objective of this study is to examine the chemical structure of
fulvic acid-like substances extracted from spent cooking liquor (PFA)
and their relationship with bioactivity in plant growth. Compared
with the benchmark Pahokee peat fulvic acid (PPFA), PFA has less aromatic
structure, but higher content of lignin, carbohydrates, and amino
acid. After fractionation, protein/amino proportion decreased with
increasing molecular weight, but the aromaticity increased. Under
salt stress, rice seedling growth was promoted by PFA with low molecular
weight (<5 kDa), but inhibited by fraction with high molecular
weight (>10 kDa). Principal component analysis suggested that promoted
growth was more related with chemical structure (O- and N-alkyl moieties)
than with molecular weight. This study provided the theoretical basis
for development of an innovative green technology of sustainable reuse
of spent cooking liquor in agriculture.
Although
solid-phase activation of lignite using a nanocatalyst
has great potential in producing low-cost and sustainable humic acid,
the large-scale application of this technology still faces challenges
because of the high price and toxicity of the nanocatalyst. Additionally,
the specific molecular components of humic acid in activated lignite
remain unknown. In this work, a multifunctional molybdate-phosphorus
hierarchical hollow nanosphere (Mo-P-HH) catalyst was successfully
manufactured by a simple way followed by phosphorization. In comparison
with a commercial Pd/C catalyst, the multifunctional Mo-P-HH catalyst
was more effective in producing water-soluble humic acid with small
molecular functional groups from lignite via solid-phase activation.
Moreover, Fourier transform ion cyclotron resonance mass spectrometry
revealed the molecular compositions of humic acid in activated lignite.
Compared with that from raw lignite, the humic acid after Mo-P-HH
activation had less aromatic structure but higher content of lipids,
proteins, amino sugar, and carbohydrates. In addition, the activated
humic acid simulated seed germination and seedling growth. Therefore,
this study provided a high-performance hierarchical hollow nanocatalyst
for activation of humic acid and also offered the theoretical basis
for the application of humic acid in agriculture.
The complex synthesis process, low utilization, and single
function
of fungicides have seriously hindered the development of fungicides
in resistance to rice sheath blight. Here, an inexpensive and multifunctional Cu(II)-based water-dispersible
humic acid (Cu-WH) fungicide with growth-promoting ability was developed
with a simple method. A 3D molybdate carbon hierarchical nanosphere
(MoO2-C-HN) catalyst was successfully synthesized using
a green route and applied in a solid-phase activation of lignite to
obtain water-dispersible humic acid. Cu(II)-based water-dispersible
humic acid (Cu-WH) was then formed through a simple reaction of Cu(II)
and the humic acid. The resultant Cu-WH showed strong antifungal performance
against Rhizoctonia solani in laboratory incubation
experiments. After being treated with Cu3-WH (0.1 mg L–1), the control efficiency of rice sheath blight at 1, 3, and 5 days
after infection was 90.54%, 78.96%, and 66.31%, respectively. It also
enhanced the water-holding capacity of the substrate and thus effectively
improved the growth of rice seedlings. In comparison to commercial
rice seedling substrate, the substrate treated with 8 wt % of Cu3-WH
increased plant height, stem diameter, fresh weight, and chlorophyll
content by 19.23%, 35.91%, 14.52%, and 42.85%, respectively. The newly
developed Cu-WH thus can be used as a novel low-cost efficient fungicide
and growth stimulator to treat rice sheath blight as well as to increase
rice production.
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