Low-temperature torrefaction assisted with solid-state KOH/urea pretreatment for accelerated methane production in wheat straw anaerobic digestion

The combination of hydrothermal humification and biological fermentation converts straw lignocellulose into artificial fulvic acid

In order to solve the problem of difficult efficient utilization and production of lignocellulosic macromolecules in crop straw, as well as the high pollution production of fulvic acid (FA). We developed an efficient biomass conversion technology that combines hydrothermal humification and biological fermentation in a low alkaline environment. Discussed material conversion and FA structural composition. FA was produced through five steps, namely, enzymatic hydrolysis, hydrothermal treatment, concentration, fermentation and spraying, with a maximum yield of 39 %. The optimal enzymatic hydrolysis conditions were 0.2 % hemicellulase, 50 °C and 6 h. The optimal hydrothermal conditions were 5 % KOH, 160 °C and 2 h. The optimal distillation conditions were 50 °C for 25 min. The optimal conditions for microbial fermentation were 0.02 % Bacillus subtilis/Bacillus licheniformis, 35 °C and of 48 h. Finally, high-temperature spraying was performed at 240 °C. Under these conditions, benzofuran, 2,3-dihydro, and 2-methyl-4-vinylphenol provided precursors for FA and increased the total acidic groups to 14.06 mmol/g. In practical applications, artificial FA has also demonstrated its ability to regulate the absorption of cadmium by plants. In addition, the prepared artificial FA has a relatively high content of hydroxyl and carboxyl groups, which may have strong electron transfer and metal binding abilities. Suitable for various applications in sustainable agriculture and biomass directed conversion.

Artificial Humic Substances as Biomimetics of Natural Analogues: Production, Characteristics and Preferences Regarding Their Use

Various processes designed for the humification (HF) of animal husbandry wastes, primarily bird droppings, reduce their volumes, solve environmental problems, and make it possible to obtain products with artificially formed humic substances (HSs) as analogues of natural HSs, usually extracted from fossil sources (coal and peat). This review studies the main characteristics of various biological and physicochemical methods of the HF of animal wastes (composting, anaerobic digestion, pyrolysis, hydrothermal carbonation, acid or alkaline hydrolysis, and subcritical water extraction). A comparative analysis of the HF rates and HS yields in these processes, the characteristics of the resulting artificial HSs (humification index, polymerization index, degree of aromaticity, etc.) was carried out. The main factors (additives, process conditions, waste pretreatment, etc.) that can increase the efficiency of HF and affect the properties of HSs are highlighted. Based on the results of chemical composition analysis, the main trends and preferences with regard to the use of HF products as complex biomimetics are discussed.

Comparative advantages analysis of oxidative torrefaction for solid biofuel production and property upgrading

This study performs the comparative advantage analysis of oxidative torrefaction of corn stalks to investigate the advantages of oxidative torrefaction for biochar fuel property upgrading. The obtained results indicate that oxidative torrefaction is more efficient in realizing mass loss and energy density improvement, as well as elemental carbon accumulation and surface functional groups removal, and thus leads to a better fuel property. The maximum values of relative mass loss, higher heating value, enhancement factor, and energy yield are 3.00, 1.10, 1.03, and 0.87, respectively. The relative elemental carbon, hydrogen, and oxygen content ranges are 1.30-3.10, 1.50-3.30, and 2.00-6.80, respectively. In addition, an excellent linear distribution is obtained between the comprehensive pyrolysis index and torrefaction severity index, with elemental carbon and oxygen component variation stemming from pyrolysis performance correlating to the elemental component and valance.