Enhancement of heavy metal removal by sulfate-reducing bacteria: the role of graphene and zero-valence iron

The contamination of industrial wastewater by heavy metals (HMs) is an increasing concern due to its potential threats to both human health and the environment. One promising method for addressing this issue involves using sulfate-reducing bacteria (SRB) to precipitate HMs as metal sulfides. However, the efficacy of this approach is often hindered by the toxic effects of high HM concentrations on SRB. On one hand, zero-valent iron (ZVI) has been shown to enhance microbial activity by generating molecular hydrogen through its oxidation, which acts as an electron donor to support bacterial growth. ZVI can also stabilize pH levels and lower redox potential, creating a more favorable environment for microbial growth. On the other hand, graphene oxide (GO) enhances bacterial activity by serving as an electron shuttle to facilitate redox reactions and by providing a large surface area for bacterial attachment, thereby promoting microbial growth. Various studies have demonstrated that adding GO and ZVI significantly enhances the precipitation of HMs by SRB, overcoming limitations associated with elevated HM levels and extreme culture conditions. This review provides a systematic assessment of the published work regarding the roles of GO and ZVI in enhancing SRB activity. It explores the properties of ZVI and GO that make them effective tools for improving SRB efficacy and discusses. Strategies that increase the efficacy of these particles are also presented.