Application of Some Domestic Wastes as New Low-Cost Biosorbents for Removal of Methylene Blue: Kinetic and Equilibrium Studies

In this study, parsley stalks (PS), cucumber peels (CP), and watermelon seed hulls (WSH) were used as novel low-cost adsorbents to remove methylene blue (MB) from aqueous solutions. The biosorption of MB onto PS, CP, and WSH was investigated as a function of pH (2-10), initial dye concentration (25-450mg/L), temperature (293-333K), ionic strength (0.0-1.0mol/L NaCl), and biosorbent dose (0.1-1.0g/50mL). While the biosorption of MB on PS followed the Freundlich isotherm, biosorption on CP and WSH followed the Langmuir isotherm at all the temperatures studied. The monolayer biosorption capacities of PS, CP, and WSH were found to be 400, 111.11, and 57.14mg/g, respectively. The biosorption of MB onto PS followed pseudo-second-order kinetics, and the biosorption onto CP and WSH followed pseudo-first-order kinetics. Thermodynamic studies showed that the biosorption of MB onto PS, CP, and WSH was spontaneous and feasible. The pH(zpc) values (of) PS, CP, and WSH were found to be 6.26, 6.42, and 6.83, respectively. Desorption studies were also carried out with various desorbing agents. HCl and H3PO4 were more effective desorbents than other desorbents used.