Novel bionanotechnological approaches for the remediation of contaminated land

Abstract

It is widely known that bacteria posses the capacity to degrade organic and transform inorganic contaminants to less hazardous products, either through direct enzymatic processes or mediated by the production of reactive biogenic nanoparticles. The harnessing of this ability for the treatment of "real world" contaminant issues is a key area of research for the effective application of these techniques. The significant challenge of remediating high pH Cr(VI) contamination, related to chromite ore processing residue (COPR), in Glasgow, UK, was used to test the effective application of novel bioremediation and bionanoremediation methods. Initially, the alkaline Cr(VI) contaminated COPR leachate was treated using a haloalkaliphilic bacterium, of the Halomonas genus. This isolate was able to reduce toxic and soluble Cr(VI) to the less toxic and poorly soluble Cr(III) (confirmed by XPS), up to a starting pH of 11. Interestingly, this bacterium also exhibited growth concomitant to Cr(VI) reduction at pH 10. Solid COPR material and Cr(VI)-contaminated groundwaters were further tested using a biogenic reactive nano-magnetite (BnM), biosynthesized using Geobacter sulfurreducens. The BnM and a commercially available nano zero valent iron (nZVI) were able to effectively reduce Cr(VI) from COPR groundwater and stabilize solid COPR, bringing bulk Cr(VI) from 26% (of total Cr) to 4-7%, by addition of greater than or equal to5% w/w BnM or greater than or equal to2% w/w nZVI (Cr oxidation state determined by XANES). In aqueous experiments, increased passivation of the nanoparticle surface was linked to the presence of groundwater components (Ca, Si and S), identified by XPS and TEM-EDX analysis. To extend the reactivity of the BnM, it was used as a support for a Pd(0) catalyst (Pd-BnM), which was again tested with COPR leachates and model pH 12 Cr(VI) solutions. In model solutions, using H2 and formate as electron donors for catalysis, maximum Cr(VI) removal was far greater than has previously been reported for magnetite or nZVI, with eventual catalyst inactivation noted by the formation of a Cr(III)OOH surface phase (determined by TEM-EDX, XPS and EXAFS). The formate was found to be a poor electron donor in the COPR leachate, while the H2 observed an increase in reaction rates, but a decrease in maximum Cr(VI) removal, inferred to be due to greater passivation from increased abundance of Ca and Si on the catalyst surface. The ability of BnM and Pd-BnM to reduce nitrobenzene (ArNO2) and tetrachloroethylene (PCE) was also assessed. The BnM and Pd-BnM/H2 were able to effectively reduce ArNO2 quantitatively to aniline (ArNH2), with the Pd-BnM/H2 reducing 5 mM of substrate without loss in activity. The PCE proved recalcitrant to reaction with BnM, however, the Pd-BnM rapidly dechlorinated the PCE to ethane in the presence of H2, achieving reaction kinetics comparable to the most reactive synthetic alternatives. These findings therefore demonstrate the clear potential of bionanocatalysts for the effective treatment of land and water contaminated with a wide range of toxic metals and organics.

Date of Award	1 Aug 2015
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Jonathan Lloyd (Supervisor) & Royston Goodacre (Supervisor)