Preparation and characterisation of chitosan/bacterial Escherichia coli biocomposite for malachite green dye removal: modeling and optimisation of the adsorption process

Herein, a new biocomposite was obtained by loading a bacterial suspension of Escherichia coli onto a chitosan matrix to produce a unique biocomposite (chitosan - E. coli) with effective properties for biosorption of malachite green dye from water. The physicochemical characteristics of the chitosan - E. coli biocomposite were studied by employing XRD, FTIR, FESEM-EDX and pHpzc. The optimisation of biosorption conditions was achieved using a Box-Behnken Design (RSM-BBD) to assess the effect of variables on the dye removal: biocomposite dose (0.02-0.1 g/100 mL), pH (4-8) and contact time (10-300 min). The optimal conditions for dye removal (84.3%) were achieved with a chitosan - E. coli dose of 0.1 g/100 mL, and a contact time of 160 minutes with a pH of 8. The equilibrium and kinetic experimental findings show the biosorption of malachite green dye by chitosan - E. coli follows the Langmuir and pseudo-second-order models, respectively. The maximum dye adsorption capacity (qmax) of malachite green for the chitosan - E. coli biocomposite was 164.7 mg/g, where the dye adsorption mechanism was attributed to several effects such as hydrogen bonding, n-pi interactions, and electrostatic attraction. Thermodynamic analysis indicated that the biosorption process was spontaneous and endothermic, with a positive enthalpy change (Delta H degrees = 40.9 kJ/mol) and a negative Gibbs free energy (Delta G degrees) at all tested temperatures. The biocomposite chitosan - E. coli adsorbent exhibits favourable cationic dye adsorption that is anticipated to have utility for remediation of dye effluent in industrial wastewater.