Biomass-based porous activated carbon is a carbon-based material with well-developed pore structure, good adsorption, and capacitive properties. To achieve the goals of peak carbon dioxide emission and carbon neutrality, biomass-based porous activated carbon is widely used in the fields of electrochemical energy storage, capacitive deionization, and wastewater treatment owing to its low cost, environmental friendliness, and cleanness. Biomass-based porous activated carbon is one of the commonly used electrode materials for supercapacitors, whose electrochemical performance is mainly influenced by its physicochemical structure. To address the problems of high energy consumption and difficult regulation of the performance of porous activated carbon electrode materials, some research has proposed the activation and oxidation gradient heat treatment technology. This technology adopts a chemical-physical co-activation synergistic control process and utilizes the waste heat of pyrolysis activation, which can reduce the consumption of chemical activator and reaction energy and alleviate environmental pollution. This technology can attain the dual objectives of efficient and clean conversion of agricultural and forestry waste and high-value utilization of porous activated carbon. In this study, porous activated carbon was prepared by using waste bamboo as the carbon source and KHCO₃ as the activator for medium- to high-temperature (500-800 ℃) activation and low-temperature (200-350 ℃) air oxidation using air for synergistic regulation. The study also investigated the physicochemical structure and electrochemical properties of porous activated carbon under the synergistic effect of different activation and oxidation temperatures. The results showed that porous activated carbon activated at 600 ℃ was oxidized by low-temperature air at 350 ℃ (PAC-600-350), and the specific surface area was increased from 154.361 to 264.235 m²/g, indicating that O₂ in the air activates the expansion of pores. An increase of oxidation temperature from 200 ℃ to 350 ℃ elevated the elemental oxygen content in the porous activated carbon and the content of surface oxygen-containing groups (such as -C=O-O and -C-OH), enhanced the wettability, and improved the defect structure and pore structure. Moreover, the porous activated carbon after activation at medium to low temperatures (600 ℃ and 700 ℃) is more sensitive and susceptible to oxidation by low temperature air. Among different activation temperatures from 500 to 800 ℃, the PAC-600-350 porous activated carbon had the highest oxygen content (25.54%) and degree of defects (2.53) at the activation temperature of 600 ℃; while the pore structure of PAC-800-350 is the most developed at the activation temperature of 800 ℃, with a specific surface area as high as 1096.18 m²/g. In addition, PAC-800-350 is less affected by the oxidation of low temperature air and its surface oxygen-containing groups change to a lesser extent. In the three-electrode test, the specific capacitance of PAC-600-350 at a current density of 1 A/g was 215.29 F/g, which is 1.47 times that of non-air oxidized porous activated carbon. At the current density of 5 A/g, PAC-600-350 exhibited higher cycling stability with a capacitance retention rate of 93.51% after 5000 cycles of charging and discharging. In the two-electrode test, the symmetrical supercapacitor with PAC-600-350 as the working electrode showed good electrochemical performance, with an energy density of 9.06 Wh/kg at a power density of 215 W/kg. Overall, PAC-600-350 porous activated carbon is considered to have potential for practical application, this study can provide a reference for high value utilization of agroforestry wastes.

In order to solve problems such as low pollutant concentrations, large treatment volumes and high purification costs in tailwater treatment of recirculating aquaculture systems, a new renewable biomass ash filter material was developed to remove nitrogen and phosphorus from tailwater, which is environment-friendly, economical and highly effective. Properties of biomass ash filter materials produced under different conditions were studied through orthogonal experiments with sintering temperature, keeping time and material trapped time as factors and the main control factors affecting the properties of filter materials were obtained. The pore evolution and forming principle of the filter material during the sintering process can be inferred by characterizing and analyzing the structural characteristics and microscopic morphology of biomass ash filter materials produced at different sintering temperatures. This helps to clarify the performance control mechanism of these filter materials via their different structures. Based on this, the biomass ash filter material that has the best performance could be selected as a test group. And commercial filter materials including biochar, ceramic granules and natural zeolite were used as control groups to conduct phosphate and nitrite adsorption tests to evaluate the adsorption performance of the biomass ash filter material. The results show that sintering temperature is the main control factor affecting the properties of biomass ash filter materials. As the sintering temperature increases, wollastonite, melilite and anorthite phases are generated sequentially in the filter materials, which leads to a series of microstructure transformations, such as crystallization, vitrification and precipitation. This is the reason for the formation of the different pore structures. In this process, water pores in the filter materials are gradually converted into closed pores. This causes positive effects of high sintering temperature on stomatal porosity, total porosity, and compressive strength. It also brings negative effects of high sintering temperature on permeable porosity, water pore rate, water absorption and permeability, pH and EC values. The performance control mechanism of these filter materials exists because of the two contrary effects. Without aging, the biomass ash filter material produced by sintering at 1170 ℃ for 40 minutes has better performance. This kind of filter material has a high saturation water absorption and average permeability rate, short water holding time, good formability and pore structure with a compressive strength of 0.74 MPa and total porosity of 65.49%. Its pH and EC values meet the demands of water purification. The unit adsorption capacity and removal rate of this filter material on phosphate can reach 0.996 mg/g and 2.767%, respectively. The phosphate adsorption effect is significantly better than that of biochar, ceramic granules and natural zeolite. The unit adsorption capacity and removal rate of this filter material on nitrite are 0.317 mg/g and 0.881%, respectively, which is equivalent to that of ceramic granules, significantly higher than natural zeolite and slightly inferior to biochar. The new renewable biomass ash filter material improves the defects of current mainstream filter materials for water purification. It is expected to meet the demand for nitrogen and phosphorus removal from circulating aquaculture tail water and can be used widely.

The discrete element method (DEM) was used in this study to numerically simulate the mixing process and motion law of particles in brown rice germination device. And the reliability of simulation experiments was verified through physical experiments. In the discrete element simulation experiment, there were three mixing stages in the mixing process of the particles. The particle motion conditions at different rotational speeds were rolling, cascading, cataracting and centrifuging. The lower the filling degree, the higher the particle mixing efficiency. The radial trajectory of the particles was approximated as an elliptical helix that continuously shrank towards the axis. The research results indicated that under the same speed and filling conditions, the motion of brown rice particles in both the simulated and physical test environments is rolling and the drop height is the same.