Combining high electron transfer efficiency and reductibility in nZVI with coatings of EPS to enhance nitrate removal

Nanomaterials have the potential to enhance the nitrate bio-removal. In particular, nano zero-valent iron (nZVI) can serve as an electron donor to improve microbial nitrate reduction. However, the rate of electron supply from nZVI does not match the rate of electron utilisation by microorganisms. Competitive effects of coexisting substances on nZVI electrons, and low efficiency of nZVI electron utilization. Moreover, toxicity of nZVI to microorganisms and inhibition of metabolic activities. The extracellular polymer (EPS), a polymer mixture secreted by microorganisms, is a key interfacial substance for wastewater treatment microorganisms. Based on the electron transfer mediator property of EPS, EPS@nZVI was developed and its morphology and surface functional groups were characterised. EPS@nZVI showed great nitrate removal efficiency even under low C/N ratios on account of that EPS could coordinate and complex with nZVI and mitigate the toxicity of nZVI. Coated EPS promoted electron transfer and reducibility of nZVI. Besides nZVI, functional groups and redox substances on EPS were responsible for nitrate removal. EPS@nZVI promoted the gene expression of C-cyts and denitrification in the activated sludge system. The development of bio-adaptable EPS@nZVI was considered from the point of view of reducing the toxic effect of nZVI and improving the electron transfer efficiency.