title: Influence of zero-valent iron nanoparticles on nitrate removal by Paracoccus sp.
abstract: Nitrate contamination in drinking water is a major threat to public health. This study investigated the efficiency of denitrification of aqueous solutions in the co-presence of synthesized nanoscale zero-valent iron (nZVI; diameter: 20-80 nm) and a previously isolated Paracoccus sp. strain YF1. Various influencing factors were studied, such as oxygen, pH, temperature, and anaerobic corrosion products (Fe(2+), Fe(3+) and Fe3O4). With slight toxicity to the strain, nZVI promoted denitrification efficiency by providing additional electron sources under aerobic conditions. For example, 50 mg L(-1) nZVI increased the nitrate removal efficiency from 66.9% to 85.2%. However, a high concentration of nZVI could lead to increased production of Fe(2+), a toxic ion which could compromise the removal efficiency. Kinetic studies suggest that denitrification by both free cells, and nZVI-amended cells fitted well to the zero-order model. Temperature and pH are the major factors affecting nitrate removal and cell growth, with or without the presence of nZVI. In this study, nitrate removal and cell growth increased in the pH range of 6.5-8.0, and temperature range of 25-35 °C. These conditions favor the growth of the strain, which dominated denitrification in all scenarios involved. As for anaerobic corrosion products, compared with Fe(2+) and Fe(3+), Fe3O4 promoted denitrification by serving as an electron donor. Finally, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) confirmed attachments of nZVI on the surface of the cell, and the formation of iron oxides. This study indicated that, as an electron donor source with minimal cellular toxicity, nZVI could be used to promote denitrification efficiency under biotic conditions.
authors.affiliation: School of Environmental Science and Engineering, Fujian Normal University, Fuzhou 350007, Fujian Province, China; Fuzhou Research Academy of Environmental Sciences, Fuzhou 350011, Fujian Province, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Environmental Toxicology, The Institute of Environmental and Human Health (TIEHH), Texas Tech University, Lubbock, TX 79409-1163, USA.
authors.forename: Shibin
authors.initials: S
authors.lastname: Li
authors.affiliation: School of Environmental Science and Engineering, Fujian Normal University, Fuzhou 350007, Fujian Province, China; Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia. Electronic address: Zuliang.chen@unisa.edu.au.
authors.forename: Zuliang
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia.
authors.forename: Mallavarapu
authors.initials: M
authors.lastname: Megharaj
authors.affiliation: Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia.
authors.forename: Ravi
authors.initials: R
authors.lastname: Naidu
mesh_terms: D058440:Denitrification / Q000187:drug effects*; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D053758:Nanoparticles / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D009566:Nitrates / Q000302:isolation & purification* / Q000378:metabolism; D010230:Paracoccus / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism*; D013696:Temperature; D014874:Water Pollutants, Chemical / Q000302:isolation & purification* / Q000378:metabolism; D018508:Water Purification / Q000379:methods*; D014961:X-Ray Diffraction
chemical_list: D009566:Nitrates; D014874:Water Pollutants, Chemical; D007501:Iron
keywords: Biological denitrification; Nanotoxicology; Paracoccus sp.; nZVI