The toxicity of graphene and its impacting on bioleaching of metal ions from sewages sludge by Acidithiobacillus sp.

The increasing production of graphene raised concerns about their releasing into sewage sludge, however, there is little information about graphene impacting on the growth of bacteria and hence their bioleaching of metal ions from sewages sludge. In this study, we reported that Acidithiobacillus sp., isolated from sewages, were used to bioleach Cu2+ and Zn2+ from sewages sludge in the presence of graphene. The negative effect on the growth of Acidithiobacillus sp. and dose-dependent were observed in presence of graphene, where the optical density (OD420) of the culture decreased from 0.163 to 0.045, while the bioleaching efficiency of Cu2+ (70%-16%) and Zn2+ (80%-48%) were also reduced when the graphene dose decreased from 50 mg L−1 to 1 mg L−1. Furthermore, scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirmed that the direct contacts between graphene and cell at 1 mg L−1 graphene caused cell membrane disruption, while Acidithiobacillus sp. grew better by forming dense biofilms around the suspended graphene at a 50 mg L−1. LIVE/DEAD staining further demonstrated that almost no live cells were detected at 1 mg L−1 graphene. The toxicity of graphene could generally be explained by depending on the concentration of graphene. The new findings provide an insight into dose dependence, which impacted on the growth of Acidithiobacillus sp. and their bioleaching of metal ion from sludge.