The rationale for alternative fertilization: Equilibrium isotherm, kinetics and mass transfer analysis for urea-nitrogen adsorption from cow urine

• Simultaneous minimization of ammonia losses and urea recovery from cow urine.
• Activated carbon recovers 90% urea from urine during adsorption-regeneration cycle.
• Sorption has Langmuir monolayer uptake (146 mg.g−1) with second-order kinetic fit.
• Thermodynamics demonstrates sorption's spontaneity, reversibility and favorability.
• Mechanistic modeling indicated film diffusion governs overall urea recovery.

In an effort to minimize the loss of urea-N through volatilization and concurrently recover urea in a usable form from cow urine, adsorption experiments using bamboo-based activated carbon were performed. Batch studies were undertaken to evaluate the effect of initial concentration, sorption time and temperature on the variation in urea uptake capacity of the prepared carbon. Equilibrium data were tested against various isotherms, kinetics and mass transfer models. The Langmuir monolayer sorption was found to be 146.12 mg.g−1 with nearly 90% urea recovery attained. The process was found to be reversible as seen through regeneration experiments. Thermodynamic parameters indicated that urea sorption was physical, spontaneous and exothermic in nature. Kinetic studies revealed that the rate of urea uptake was limited by both surface adsorption and intra-particle diffusion. It was concluded that the mass transfer of urea molecules over the activated carbon was governed by film diffusion at all concentrations examined.

Graphical AbstractFigure optionsDownload as PowerPoint slide