The Remediation of Wastewater by Adsorption on an Agro-based Waste

Foods and oil industries, including laboratories of traditional medicines, generate a considerable amount of waste, such as spent/used cumin seeds (binomially named Cuminum cyminum). The idea of using this waste for the removal of toxic metals serves a dual purpose of waste valorization as well as remediation of waste water. The preliminary work includes the optimization of the experimental parameters, namely, pH, contact time, adsorbent and metal concentrations and temperature. Fourier transform infra-red spectroscopy was employed for examining the probable sites, available on the adsorbent, for interacting with the metal ions. The studied isothermal models, namely the Langmuir, Freundlich and Dubinin-Radushkevich models, collectively suggest physio-chemical sorption as the primary mode of retention of metal ions. The spontaneous nature of adsorption is indicated by the calculated thermodynamic parameters. The adsorption process was found to follow the pseudo-first order kinetic model and also followed the intraparticle diffusion up to 50 minutes of contact time. The recovered adsorbent was then subjected to several cycles of loading and elution and was found to retain 97% of the sorption capacity up to 3 cycles.