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Generating value from wastes via pyrolysis has been increasingly researched in recent times. Biochar is a versatile pyrolysis product with yields based on many process parameters, including feedstock type and particle size, and operating conditions such as pyrolysis reactor, heating rate, residence time, and reaction temperature. The heterogeneous nature of waste biomass creates challenges in controlling the pyrolysis' product selectivity. Intensive and time-consuming experimental studies are often required to determine product distribution for the pyrolysis of each unique feedstock. Alternatively, prediction models that learn from a wide range of existing experimental data may provide insight into potential yields for different biomass sources. Several advanced models exist in the literature which can predict the yield of biochar and subsequent products based on operating temperature. However, these models do not consider the combined effect of biomass characteristics and operating conditions on biochar yield, which is considered a decisive factor for biochar formation. As such, the objective of this study is to develop a prediction model based on the biomass' fixed carbon content (14–22%), reaction temperature (350–750 °C), and heating rate (5–10 °C/min) using the response surface methodology. Biomasses, date stones, spent coffee grounds, and cow manure have been used to design a Box-Behnken experiment based on the three factors for the biochar yield response. An empirical equation is developed based on a statistically significant quadratic model to produce optimized biochar yield with high prediction accuracy. The study discussed the 3D response and diagnostic plots and conducted validation experiments to confirm the applicability of the developed model. The biochar yields are significantly affected by the fixed carbon content of the feedstock and the reaction temperature, and the experimental validation confirms the accuracy of biochar yield quantification. The model can be easily applied for further process flow modeling of biomass pyrolysis, only relying on proximate feed analysis, operating temperature, and heating rate. [ABSTRACT FROM AUTHOR]

The properties of biochar produced by pyrolysis are strongly influenced by various factors such as feedstock. Cabbage makes up around 6.5% of global vegetable production with around 30% wasted from the farm to plate, making it a considerable and widely available biochar feedstock. This study investigates the optimization of three design factors, namely, pyrolysis temperature, feed particle size, and quantity of waste cabbage biomass to produce biochar. Feed particle size was selected due to its relevance to solar or other drying pretreatment, necessary for moisture reduction. To evaluate the influence of these parameters and find their optimum conditions, response surface methodology (RSM) with a central composite design of experiments was used. Optimum response for cabbage biochar was observed at lower temperature (360 °C) with particle size of 0.90 mm and a relatively low quantity, though this latter parameter had minimal influence on most response parameters. Temperature was the most influential parameter on all response variables, although particle size was important for nitrogen content, cation exchange capacity (CEC), and electrical conductivity. Biochar produced at an optimum pyrolysis temperature of 360 °C and nearest practical size of 1 mm was tested with Ipomoea purpurea in sandy soil. Two percent biochar loading provided an increase in water retention from 6.5% in the control to 10% in the biochar amended soil (p = 0.016). Increases were also observed in plant height and leaf production but were not statistically significant at α = 0.05. [ABSTRACT FROM AUTHOR]

The application of biochar in agriculture is a developing means to improve soil water retention, fertility, and crop yield. The present work focuses on biochar preparation from mixed vegetable and fruit wastes, using cauliflower, cabbage, banana peels, corn leaves, and corn cobs. The biochar produced at 400 °C was applied to the soil as an amendment to observe the qualitative changes of soil quality, plant growth, and water retention capacity of the soil based on screening in a previous study. Pot experiments were conducted at a laboratory scale having 0%, 2%, and 6% biochar mixed with sand. Each pot was sown with seeds of chickpeas (Cicer arietinum L.) and monitored over 60 days. Two biochar application rates improved soil quality by increasing soil porosity from 49.3 to ≥ 53.4%, more than doubling cation exchange capacity to ≥ 21.1 cmolc.kg−1, providing a small reduction in bulk density of approximately 10% and decreasing electrical conductivity of the extract by at least 40% in comparison to control condition. The biochar application also increased key soil nutrients K, Mn, S, and P by a factor of 2–9 times. Application of biochar at 2% and 6% improved water retention from 55 to 77 and 91 mL respectively over the study and, more importantly, more than doubled the biomass yield for the same water application. The lower biochar application rate of 2% led to more germinated seeds (p = 0.0001), leaves (p = 0.0001), flowers, and fruiting chickpeas than the control condition. The 6% biochar application rate slightly improved plant height (p = 0.01) and provided a small reduction in water loss compared with the 2% biochar. Both biochar loadings increased the root and shoot biomass (p = 0.005) and nutrient content of the shoot and root biomass, particularly K, P, and S (p = 0.0001). This study demonstrates that biochar application at 2–6% is an effective means to increase chickpea yield and reduce water stress. Given small differences in performance within this application range, 2% application is recommended. The study establishes valorization of cellulose rich food waste in the form of biochar as a potential method for positive soil management and increased agricultural productivity in arid environments. [ABSTRACT FROM AUTHOR]