The biosorption of Co(II) by Homalothecium sericeum from aqueous solutions under batch conditions: response surface methodology optimization and Daphnia magna bioassay

In the present work, Homalothecium sericeum biomass was used for removal of Co(II) from aqueous solution. The effects of process parameters (contact time, biosorbent amount, and initial Co(II) con-centration) on the response (Co(II) % removal) were investigated using a batch adsorption system optimized with response surface methodology/central composite design method. Under optimized conditions the maximum Co(II) removal efficiency achieved is 94.07% at an initial Co(II) concentration of 2.05 mg/L, a H. sericeum amount of 0.34 g/50 mL, and a process time of 36.09 min. In this study, the toxicity of the medium after biosorption carried out under optimized conditions was also tested with Daphnia magna bioassay. When mortality results with D. magna were evaluated, although a removal efficiency of 94.07% was obtained after biosorption, this was not sufficient to reduce mortality of D. magna.