Valorisation of Cocoa (Theobroma cacao) pod husk as precursors for the production of adsorbents for water treatment

ABSTRACT Cocoa pod husk (CPH) has been valorised as adsorbents for the removal of a variety of chemical species from aqueous media. This review was conducted to catalogue the empirical findings, discuss the current state of knowledge, observe the research trend, identify research gaps and predict future perspectives in the research area. CPH has been processed into unmodified biosorbent, chemically modified biosorbent and bio-based-activated carbon. Much of the research interest in CPH adsorption has been majorly focused on heavy metals and dyes. The removal efficiency of the CPH adsorbent for most of the pollutants was above 90% but for a few exceptions. The effect of temperature, solution pH, adsorbent dosage, agitation time and initial concentration of the pollutants were considered in the review. Furthermore, the equilibrium data were always best fit to either Langmuir or Freundlich isotherm models. It was also observed that the pseudo-second order kinetic model was the best fit for the adsorption of pollutants onto CPH adsorbents. Thermodynamic calculations revealed that CPH adsorption was mainly spontaneous and exothermic. Future perspectives were suggested in the domain of desorption studies, reusability studies, continuous flow experiments and adsorbent immobilisation, pilot and semi-pilot scale-up systems and financial and techno-economic investigations. GRAPHICAL ABSTRACT