Biosorption performance of powdered waste sludge for removal of Congo Red: Equilibrium and kinetic modeling

Dyes are important water pollutants generally present in the effluents of textile industries. a high level of worldwide production and extensive use of dyes generate substantial volumes of colour ed wastewaters. industrial effluents treatment is becoming an obligation in tunisia both environmentally and for water re-use. another important waste produced by contemporary society in abundant quantity is industrial and municipal sewage sludge,which calls out for efficient and environmentally friendly approaches to its valorisation. the aim of the present work was to develop an effective and inexpensive technology for removing dyes from aqueous solution using powdered waste sludge (pws). congo red (cr) was chosen as a dye model. the effects of operation variables,such as ph of the solution,adsorbent amount,initial cr concentration and agitation speed were investigated using batch adsorption technique. sorption kinetics,isotherms and thermodynamic parameters were conducted. the results showed that the retention capacity of the mud increases with the increase of the sorbent quantity,the temperature,the cr concentration,as well as the agitation speed. the best sorption amounts were obtained at ph 6. the parameters of both kinetic and equilibrium modelling showed that the kinetic data were accurately described by the pseudo-second-order model. the equilibrium data were analyzed using five isotherms models,langmuir,freundlich,redlich-peterson,temkin,and elovich models. results showed a good fit with redlich-peterson and langmuir models suggesting monolayer coverage of dye molecules onto the biosorbent surface and adsorption active sites of quite similar affinities toward the experimental textile pollutant. the thermodynamic parameters such as gibbs free energy change δg0,standard enthalpy δh0,and standard entropy δs0 indicated that congo red adsorption onto powdered sludge was endothermic,spontaneous,involving a chemical bonding. this study indicates then that the sewage sludge has the potential to be used as a biomaterial for dye removal process from contaminated waters.