Potassium assisted pyrolysis of Chinese Baijiu distillers' grains to prepare biochar as controlled-release K fertilizer

Distillery-Waste-Derived C-SiO2 Catalyst Support Reinforces Phenol Adsorption and Selective Hydrogenation

Selective hydrogenation of lignin-derived phenolic compounds is an essential process for developing the sustainable chemical industry and reducing dependence on nonrenewable resources. Herein, a composite C-SiO2 material (DGC) was prepared via the stepwise pyrolysis and steam activation of the distiller's grains, a fermentation solid waste from the Chinese liquor industry. After Ru loading, Ru/DGC was used for the catalytic hydrogenation of phenol to cyclohexanol. Steam activation remarkably increased the hydrophilicity and specific surface area of DGC, introducing oxygen-containing functional groups on the surface of DGC, thereby promoting the adsorption of Ru3+ and phenol. Additionally, the large specific surface area facilitated the dispersion of the active metal. Furthermore, the steam activation of DGC promoted the graphitization of the carbon matrix and formed Si-H/Si-OH bonds on the SiO2 surface. The benzene ring of phenol interacted with the carbon matrix via π-π stacking, and the hydroxyl group of phenol interacted with SiO2 via hydrogen bonding. The synergistic interactions of phenol at the C-SiO2 interface enhanced phenol adsorption to promote the hydrogenation. Consequently, 100 % of phenol was hydrogenated to cyclohexanol at 60 °C within 30 min. Furthermore, the optimized catalyst exhibited high activity for phenol hydrogenation even after four reuse cycles. The outstanding stability of the catalyst and its requirement for mild reaction conditions favor its large-scale industrial applications.

Unraveling the synergistic effect of biochar and potassium solubilizing bacteria on potassium availability and rapeseed growth in acidic soil

Potassium (K) is an essential macronutrient for plant growth. However, its bioavailability is low in acidic soils. Excessive K fertilization deteriorates the soil health, thus highlighting the need for sustainable alternatives. In previous studies, biochar application has been proven to be an effective amendment. Meanwhile, various potassium solubilizing bacteria (KSB) have been identified in soil that contributes to K bioavailability. However, their interaction under combine (co) application in acidic soil and its effects on K availability remain poorly understood. Therefore, a pot experiment was conducted to investigate the synergistic effect of co-application of rice straw biochar (BC) and KSB consortium on K availability to promote rapeseed growth. The treatment plan consisted of CK (control), recommended K fertilizer, 2 % BC (2 % w/w), KSB consortium, KSB consortium + 2 % BC (2 % w/w). Results of soil analysis conducted after crop maturity showed that co-application of 2 % BC and KSB consortium significantly improved the soil pH and organic matter contents by 0.62 and 12.52 units respectively, relative to CK. Meanwhile, soil available nutrients were greatly enhanced, as available K content increased by 52.1 %, which indicated that co-application of 2 % BC and KSB consortium could facilitate the better conversion of different forms of soil K and make it available for plant uptake. Furthermore, it also improved extracellular enzymatic activities (26.7-71.6 %) and soil bacterial community (Actinobacteriota and Firmicutes). These improvements greatly enhanced plant biomass (46 %) and yield (31 %). Overall results proved that co-application of 2 % BC and KSB effectively enhanced K availability for sustainable plant growth. Still, there is a need to identify the most efficient KSB strains that, in conjugation with BC, reduce the K fertilizer usage.

Valorization of food waste to biofertilizer and carbon source for denitrification with assistance of plant ash and biochar toward zero solid discharge

This study developed a novel strategy for food waste (FW) valorization through incorporating plant ash and biochar into enzymatic hydrolysis of FW. After 12-h hydrolysis of FW with fungal mash, the solid and soluble products were separated and harvested as solid biofertilizer and carbon source for denitrification respectively. Soluble COD produced from plant ash and biochar mediated FW hydrolysis could reach approximately 170 g/L on average, which showed a specific denitrification rate of 26.23-31.33 mg N/g MLVSS/h higher than that with commercial glucose (i.e. 25.92 mg N/g MLVSS/h). The applicability of solid biofertilizers produced from plant ash- or biochar-assisted hydrolysis of FW was evidenced by the higher germination rate of 138-166 % against that without exogeneous additives (122 %). It is expected that the proposed approach can offer an effective solution for upgrading FW into value-added products, while realizing a complete resource recycle with no wastes discharged.

Artificial humic acid produced from wet distillers grains in a microwave-assisted hydrothermal process: Physicochemical characteristics and stimulation to plant growth

Wet distillers grains, as a waste biomass with a large annual output, pose a threat to the environment and food industry. Herein, artificial humic acid (AHA) was first produced from wet distillers grains in a dual-stage microwave-assisted hydrothermal process. The influence of temperature on AHA's characteristics was investigated and compared with natural humic acid (NHA) and standard humic acid (SHA). A high yield of AHA at 20.6% was obtained at 200 °C with a total reaction time of 1 h, which is 1.8-3.1 times that obtained in traditional single-stage hydrothermal process. Increasing the reaction temperature induced the formation of phenolic hydroxyl in AHA. AHA was rich in aromaticity and carboxylic acid structure, showing similar spectral characteristics to NHA. The distribution of molecular weight of AHA was mostly 5797 Da, which decreased by 15% compared to SHA. The optimal concentration of AHA to promote seedling growth was 0.2 g/L, and the root length was 2.0 times that of the control. The microwave hydrothermal process is a facile and efficient approach to preparing AHA from waste biomass with high moisture content.

Combining anaerobic digestion slurry and different biochars to develop a biochar-based slow-release NPK fertilizer

In this research, we developed a biochar-based fertilizer using biogas slurry and biochar derived from lignocellulosic agro-residues. Biogas slurry was obtained through the anaerobic digestion of the organic fraction of municipal solid waste (fresh vegetable biomass and/or prepared food), while biochars were derived from residues from quinoa, maize, rice, and sugarcane. The biochar-based fertilizers were prepared using an impregnation process, where the biogas slurry was mixed with each of the raw biochars. Subsequently, we characterized the N, P and K concentrations of the obtained biochar-based fertilizers. Additionally, we analyzed their surface properties using SEM/EDS and FTIR and conducted a slow-release test on these biochar-based fertilizers to assess their capability to gradually release nutrients. Lastly, a bioassay using cucumber plants was conducted to determine the N, P, and K bioavailability. Our findings revealed a significant correlation (r > 0.67) between the atomic O/C ratio, H/C ratio, cation exchange capacity, surface area, and the base cations concentration with N, P, and/or K adsorption on biochar. These properties, in turn, were linked to the capability of the biochar-based fertilizer to release nutrients in a controlled manner. The biochar-based fertilizer derived from corn residues showed <15 % release of N, P and K at 24 h. Utilization of these biochar-based fertilizers had a positive impact on the mineral nutrition of cucumber plants, resulting in an average increase of 61 % in N, 32 % in P, and 19 % in K concentrations. Our results underscore the potential of biochar-based fertilizers in controlled nutrient release and enhanced plant nutrition. Integration of biochar and biogas slurry offers a promising and sustainable approach for NPK recovery and fertilizer production in agriculture. This study presents an innovative and sustainable approach combining the use of biochar for NPK recovery from biogas slurry and its use as a biochar-based fertilizer in agriculture.

The fate and supply capacity of potassium in biochar used in agriculture

We used chemical extraction, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) to study the potassium (K) in biochar prepared from corn straw at different temperatures (300 °C, 500 °C, 700 °C and 900 °C). The characteristics of biochar were analyzed through Fourier transform infrared spectroscopy (FTIR) and specific surface area analysis. We found that the potassium in biochar can be divided into water soluble potassium, exchangeable potassium, non-exchangeable potassium, and insoluble potassium according to the availability of agricultural potassium. The fate of potassium in straw changed as follows: with increasing pyrolysis temperature, the proportion of the sum of exchangeable and non-exchangeable potassium decreased, and the proportions of insoluble and lost potassium increased. The total, water soluble and exchangeable potassium contents in biochar were highest at 700 °C. The non-exchangeable and insoluble potassium contents were highest at 300 °C and 900 °C, respectively. Kinetics experiments were conducted to determine the different fates of potassium released from biochar at different temperatures; pot experiments were also undertaken. The release of different forms of potassium in biochar at different temperatures is mainly dominated by heterogeneous diffusion. Biochar increased not only the content of different forms of potassium in soil but also the potassium content of soybean stems and leaves. We calculated the potassium supply capacity of biochar by two strategies, measurements of the potassium content in biochar and the conversion rate of potassium in straw during pyrolysis. The most active and efficient potassium supply capacities were 33.60 g·kg-1 and 9.53 g·kg-1 at 700 °C and 300 °C, respectively. Biochar provides readily available (water soluble and exchangeable) potassium and a long-term (non-exchangeable) potassium supply to soil.

Effects of acid modified biochar on potassium uptake, leaching and balance in an alternate wetting and drying paddy ecosystem

Straw biochar amended soils reduce fertilizer losses and alleviate soil K-exhaustion, while decrease grain yield due to its high pH. H2SO4-modified biochar has been studied as a means to enhance the advantages of biochar and address yield decrease. However, little information is available on its effects on aboveground K uptake, soil K fixation, K leaching, and utilization in paddy rice systems, especially under water stress. A 3-year field experiment was conducted with two irrigation regimes (continuously flooded irrigation, ICF and alternate wetting and drying irrigation, IAWD) as main plots and 0 (control), 20 t ha-1 biochar (B20), and 20 t ha-1 acid-modified biochar (B20A-M) as subplots. The results showed that IAWD significantly decreased water percolation by 9.26 %-14.74 % but increased K leaching by 10.84 %-15.66 %. Compared to B0, B20 and B20A-M significantly increased K leaching by 32.40 % and 30.42 % in 2019, while decreased it by 11.60 %-14.01 % in 2020 and 2021. Both B20 and B20A-M significantly improved aboveground K uptake by 3.45 %-6.71 % throughout the three years. B20 reduced grain yield in 2019 and increased it in 2020 and 2021, while B20A-M increased grain yield throughout the three years. Apparent K balance (AKB) from pre-transplanting to post-harvest over the three years suggested that IAWD significantly increased the risk of soil K depletion but B20 and B20A-M significantly increased AKB, thereby addressing the depletion of it. IAWDB20A-M have a comparable AKB with ICFB20A-M, but had up to 18.3 % and 21.61 % higher AKB than IAWDB20 and ICFB20. Therefore, the use of H2SO4 modified biochar could produce higher grain yield with lower K leaching for addition in IAWD paddy systems, which is beneficial to mitigate soil K depletion and ensure a sustainable agricultural production.