Optimization of process and properties of biochar from cabbage waste by response surface methodology

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.