Biosorption of cadmium from aqueous solution by combination of microorganisms and chitosan: response surface methodology for optimization of removal conditions.

The food-grade adsorbents of (10 CFU/mL), (10 CFU/mL) and chitosan (1%w/v) alone or in combination were used for biosorption of cadmium (Cd) from aqueous solution. Among the tested adsorbents, combination of and chitosan had the highest efficiency. Therefore, biosorption process with /chitosan as the most efficient biosorbent was optimized by variables of pH (3-6), temperature (4-37 °C), contact time (5-180 min) and Cd concentrations (0.01-5 mg/L) using RSM. Twenty-seven tests were carried out and the data fitted to the second-order polynomial models. Results revealed that 99.11% of Cd was reduced within 180 min at concentration of 2.5 mg/L, pH 6 and temperature of 20.5 °C that were considered as the optimal conditions for Cd removal. The trend of isotherm was more fitted to the Langmuir model and maximum biosorption capacity was obtained about 3.61 mg/g. The pseudo-second-order fitted the biosorption kinetics for Cd ions. The /chitosan biosorbent exhibited the high affinity to Cd ion in the presence of coexisting metal ions. It could remove 81.18% of Cd from simulated gastrointestinal tract. Thus, /chitosan can have good potential as an effective adsorbent for Cd biosorption from aqueous solutions and human body.