Detoxification of Wastewater by Paw–Paw (Carica papaya L.) Seeds Adsorbents

The present work reports the biosorption studies of metal ions viz., Pb(II) and Cu(II) from aqueous solution onto paw-paw seeds (PPS), acid treated paw-paw seeds (ATPPS) and base treated paw-paw seeds (BTPPS) adsorbents by batch method. A series of tests were carried to evaluate the effect of the system parameters, i.e. adsorbent dosage, initial concentration, temperature and contact time. The obtained kinetic data showed that the pseudo first order model best fitted the biosorption of both metal ions with (r2) values of 0.9918, 0.9674 and 0.9463 for Cu(II) onto PPS, ATPPS and BTPPS, respectively and for Pb(II) 0.8513, 0.8686 and 0.9434 onto PPS, ATPPS and BTPPS respectively. Estimated surface adsorption of intra-particle diffusion estimated that surface sorption dominated. Thermodynamic parameter (ΔGo) gave negative values indicating that the biosoption processes were spontaneous and feasible. ΔHo gave positive and negative values indicating that some biosorption processes were endothermic and some exothermic. Isotherm data indicated that Langmuir best described the biosorption. The reusability of PPS, ATPPS and BTPPS adsorbents was evaluated up to five cycles without showing significant drop in sorption efficiency.