Optimization of Fluidized-Bed Process Parameters for Coating Uniformity and Nutrient-Release Characteristics of Controlled-Release Urea Produced by Modified Lignocellulosic Coating Material

Controlled-release fertilizers are employed in precision agriculture to optimize technology-enabled farming without environmental deterioration. In this study, almond-shell lignocellulosic waste particles are chemically processed to synthesize a coating suspension for the production of controlled-release urea (CRU) in a Wurster fluidized-bed reactor. The interactive effect of process parameters such as atomizing air pressure (P-air), fluidized-bed temperature (T-fb), spray rate (R-spray), and fluidizing-air flow rate (Q(air)) on the (i) coating-film uniformity of CRU particles and (ii) longevity of nutrient-release from CRU is reported. CCRD is used with RSM to design the experiments for the optimization of nutrient-release performance and coating-film uniformity in terms of a coefficient-of-variance (CoV) of film thickness. The regression models indicate a good prediction of coating-film uniformity and nutrient-release time, with R-2 = 0.971 and R-2 = 0.98, respectively. The optimum conditions for coating-film uniformity are determined to be P-air = 3.5 bar, T-fb = 80 degrees C, R-spray = 0.15 mL/s, and Q(air) = 72 m(3)/h, with a predicted CoV film thickness of 11.5%. Similarly, P-air = 3.2 bar, T-fb = 78 degrees C, R-spray = 0.125 mL/s, and Q(air) = 75 m(3)/h are the optimum conditions for nutrient-release performance, with a prediction nutrient-release time = 56 h. The experimental validation yields a CoV of film thickness = 12.6% and a nutrient-release time = 49.5 h, indicating good agreement between predicted and experimental values. In addition, T-fb appears to be the most significant parameter.