Samuel Mbugua Nyambura

Recent advances in nickel-based catalysts for plastic pyrolysis, emphasizing reaction mechanisms, catalyst design, and emerging innovations that enhance product selectivity, yield efficiency, and sustainable polymer recycling.

An optimized tumbling process can significantly improve the oxygen dissolving capacity of composting and fertilizer quality: by increasing the fluffiness of the lower layer of the pile, localized anaerobic fermentation can be avoided, thereby enhancing compost quality. This paper presents a method for improving the oxygen dissolving capacity of rotary drum food waste composting through a combination of simulation optimization and experimental validation. First, the discrete element method was used to optimize the key parameters of the tumbling process. The response surface method was then employed to analyze the composting test results and determine the optimal conditions. To ensure the reliability of the equipment under this method, failure risk analysis was conducted using the finite element method. The simulation optimization results showed that with a rotary drum reactor speed of 3.5 r/min, a horizontal angle of inclination of 2.5°, a mixing blade angle of inclination of 43°, and a blade pitch of 580 mm, the fluffiness of the lower layer of the pile increased by 8.515%, achieving the best tumbling and indirectly enhancing oxygen dissolving capacity. The maximum deformation of the load-bearing components was only 0.0548 mm, and the minimum safety factor was 4.408 (≥1 is considered safe). A 14-day composting experiment was conducted to validate the optimized parameters. The results showed that the maximum temperature of the compost pile reached 68.34 °C (lasting 7 days), with the pH, moisture content, C/N ratio, humus substances, humic acid, and fulvic acid contents of the fertilizer all meeting or exceeding the levels recommended by Chinese national standards. These findings indicate that the optimized tumbling device effectively improved the stability and dissolved oxygen efficiency of food waste composting, providing valuable practical insights and a research foundation for enhancing oxygen efficiency in the composting of other organic wastes.

Ni–Co–P alloy coatings were successfully fabricated by jet electrodeposition with varying pulse frequencies and duty cycles in order to prolong the longevity of steel C1045 substrates. The results showed that the microstructures and properties of samples were significantly affected by pulse frequencies and duty cycles. All the samples with varying pulse frequencies and duty cycles exhibited a face-centered cubic (FCC) structure. Additionally, the average grain size of the samples reached 20.6 nm. The microhardness of the coatings was observed to first increase, and then decrease, with a rise in pulse frequencies and duty cycles. The microhardness reached 656.2 HV_0.1, and the wear scar width of the coatings reached 414.4 µm at 4 kHz pulse frequency and 80% duty cycle. Additionally, the corrosion current densities (I_corr) of samples reached a minimum value of 0.74 µA·cm⁻², the corrosion rates (R_corr) reached a minimum value of 8.9 µm·year⁻¹, and the charge transfer resistance (R_ct) reached a maximum value of 8.36 × 10⁴ Ω·cm⁻², which indicated the optimal seawater corrosion resistance of the deposited coatings.

Optimized design of the pneumatic precision seed-metering device for carrots

Co-pyrolysis of food waste with coconut fiber to produce hydrogen is considered an effective strategy for clean waste disposal and high value-added product synthesis. This study investigated the co-pyrolysis mechanism and hydrogen yields of food waste and coconut fiber at different blending ratios by thermogravimetric analysis and regression optimization. A heating rate of 10 ℃/min ranging from 30 ℃ to 900 ℃ coupled with the Svante August Arrhenius kinetic equations were utilized to derive the activation energies of the samples. Thermogravimetric analysis presented positive synergistic effects between coconut fiber and food waste to accelerate weight loss rate, and the main pyrolysis peak (200 ~ 450 ℃) moved to low temperature areas as the coconut fiber proportion increased. Additionally, kinetics showed that the lowest activation energy was 29.28 kJ at 1:3 blending ratio of coconut fiber to food waste. Based on this, response surface methodology (RSM) by Design-Expert.V8.0.6 ((Box-Behnken Design) (BBD)) was applied to optimize the microwave co-pyrolysis parameters (1600 W microwave power, 5 mm feedstock size, and 74% food waste proportion), thus the predicted maximum hydrogen yield was 46.20 vol.%. This study contributes to ameliorating the potential for solid waste microwave co-pyrolysis for value-added products production, therefore providing a reference for the further development of clean disposal technology and waste resource utilization. GRAPHICAL ABSTRACT

To improve the problem of low seeding efficiency facing the single-row planting mode traditionally used in China, this study aimed to design a novel three-row pneumatic precision metering device. The working principle and main structure were introduced in the paper. The three main factors affecting the seeding performance comprised of vacuum pressure, angular velocity of the metering tray, and taper angle of the sucking hole. A Box-Behnken experiment design having the qualified index and missed seeding index as the experimental index was used, and the results indicated that optimal performance of the metering device was achieved when the vacuum pressure was 2.16 kPa, the angular velocity of the metering tray was 29.43 rpm, and the taper angle of the sucking hole was 61.51°. The qualified index of the inner, middle, and outer ring was 95.12%, 94.68% and 94.24% respectively, while the missed seeding index of the inner, middle, and outer ring was 3.67%, 3.12% and 2.58% respectively under the optimal combination of parameters. The bench test results were basically consistent with the optimized results. This paper can provide support for the design of a three-row pneumatic precision metering device for Brassica chinensis.

In this study, Ni–Co–P–BN(h)–Al₂O₃ binary nanocomposite coatings were fabricated on steel C1045 substrates by jet electrodeposition. The samples were then processed using self-made laser processing equipment to investigate the influence of long-pulse laser processing parameters variation on samples’ surface morphology, roughness and wettability. Additionally, the properties of samples before and after laser processing were analyzed and characterized. The results showed that the surface morphologies, surface roughness and wettability of samples were affected by laser output power, pulse width and spot-to-spot distance variation. A convex dome was formed on the samples’ surface at a low laser output power and a suitable pulse width, while a dimple was formed on the samples’ surface at a high laser output power. The surface roughness and water contact angle of samples increased with the rise in laser output power or pulse width. The water contact angle decreased with the rise in the spot-to-spot distance, and the water contact angle reached a maximum value of 139.8° with a laser output power of 50 W, a pulse width of 100 µs and a spot-to-spot distance of 150 µm. The samples after laser processing exhibited a higher wettability, microhardness and wear resistance compared to those of the normal samples. The microhardness of the heat-affected zone reached a maximum value of 812.1 HV_0.1, and the wear scar width of the samples reached a minimum value of 360.5 µm. However, after laser processing, the samples’ seawater corrosion resistance decreased slightly.