Holmes, Andrew

Dr. Andrew Holmes is a process engineer with Geosyntec Consultants in Toronto, Ontario, Canada, who specializes in selenium (Se) treatment of industrially impacted water. Developing passive water treatment techniques and source control methods has been a recent focus for chemical manufacturing, power and mining clients. Dr. Holmes has recent experience designing water treatment systems to remove Se from mine impacted water (MIW) and flue gas desulphurization water (FGDW) for the power industry. Dr. Holmes specializes in designing and operating laboratory studies which elucidate key design parameters required to build pilot and full-scale water treatment plants designed to remove Se, nitrate, sulphate, organics, heavy metals, etc.

Titles from this speaker

Description: Enhancing Product Selectivity During Selenium Reduction Using Noble Metal-TiO2...

Enhancing Product Selectivity During Selenium Reduction Using Noble Metal-TiO2 Heterogeneous Photocatalysts

Abstract

Selenium (Se) is a naturally occurring non-metal, which is essential for all living organisms including humans in trace amounts. Of all essential elements, Se has one of the narrowest therapeutic windows between dietary deficiency (< 40 µg/day) and toxicity (> 400 µg/day) (Fordyce, 2013), which makes it important to carefully control Se exposures to humans and aquatic life. Se can enter surface waterways through a variety of sources, including agricultural runoff, mining, industrial production, coal-powered thermal electric generation, and other anthropogenic activities (Holmes and Gu, 2016; Santos et al., 2015). The World Health Organization (WHO) and the U.S. Environmental Protection Agency (U.S. EPA) recognize the dangers of Se and have mandated maximum acceptable levels for Se in water of 10 µg/L and 1.5 µg/L, respectively (World Health Organization, 2011; U.S. EPA Office of Water, 2016). Se exists in many forms, both organic and inorganic, but the high solubility and bioavailability of inorganic species such as selenite (SeO32-) and selenate (SeO42-) makes these oxyanions the primary focus of Se removal from water. Many methods of removal have been attempted for selenate impacted water including biological reduction (Lai et al., 2014; Mal et al., 2017) and wetland remediation (Mooney and Murray-Gulde, 2008), but the advanced operating complexity, high start-up costs and large footprint requirement have limited the practical application of these techniques. Alternatively, Se adsorptive techniques have been explored which rely on the affinity of selenite and selenate to the surface of designed adsorbents such as ferrihydrite (iron (III) oxyhydroxide), hematite, goethite, activated alumina or various ion exchange resins (Ippolito et al., 2009; Rovira et al., 2008). However, the weak complexation between selenate and mineral surfaces through an outer-sphere adsorption complex makes adsorptive techniques much less effective (Jordan et al., 2013). Photocatalytic techniques have been shown to remove both selenite and selenate with great efficiency (Nakajima et al., 2013; Nguyen et al., 2005; T.T.Y. Tan et al., 2003a). Herein, we synthesize a variety of noble metal (Au, Ag, Pt and Pd) deposited TiO2 photocatalysts for the reduction of selenate from water. By modifying TiO2 with different metallic co-catalysts that have controllable electron affinities, we are able to tune the Se product selectivity towards favourable Se products. The final fate of Se during treatment is a key factor in determining the successful adaptation of a water treatment approach.

Selenium (Se) impacted water resulting from anthropogenic activity (i.e. power generation, mining, and oil & gas refining) is a global concern due to the associated aquatic toxicity concerns. Herein, heterogenous photocatalysts were produced by depositing noble metal nanoparticles (gold, silver, platinum, and palladium) onto titanium dioxide, which demonstrated work-function dependent selectivity of final reduction by-products during the photocatalytic reduction of selenate to elemental Se or hydrogen selenide gas. Finally, tunability of the Se reduction product is key to designing a sustainable treatment approach with a potential for Se capture and reuse.

SpeakerHolmes, Andrew

Presentation time

14:36:00

14:58:00

Session time

13:30:00

15:00:00

SessionUnique Approaches for Removal of Selenium and Other Constituents from Wastewater and Groundwater

Session number503

TopicIndustrial Issues and Treatment Technologies

Author(s)

Andrew Holmes

Author(s)A. Holmes1; F. Gu2;

Author affiliation(s)Geosyntec Consultants, Toronto, ON, CA1Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON, CA2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2021

DOI10.2175/193864718825158163

Volume / Issue

Content sourceWEFTEC

Word count12

Description: Utilization of Recyclable Photocatalysts for Selenium Removal from Industrial...

Utilization of Recyclable Photocatalysts for Selenium Removal from Industrial Wastewater

Abstract

Herein, we demonstrate excellent selenium (Se) removal efficacy through photocatalytic reduction of selenate (SeO42-) as a treatment method for selenium (Se) removal from flue gas desulphurization wastewater (FGDW). The simultaneous generation of elemental selenium (Se0) and hydrogen selenide (H2Se) through two consecutive first-order reductions is reported over a photocatalyst (P25 Aeroxide TiO2). In this work, we demonstrate the ability to reduce selenate in FGDW with concentrations of many co-existing ions >2,500x that of selenate. Through a robust understanding of the reaction mechanisms the complete removal (2,500x that of selenate. Through a robust understanding of the reaction mechanisms the complete removal (< 1 µg L-1) of selenate through photocatalytic reduction over TiO2 in FGDW was shown, for the first time. In addition, we demonstrate a new approach to nanoparticle catalyst recovery, combining the advantages of flocculation with magnetic separation to enable simple collection of non-magnetic nanoparticles.

SpeakerHolmes, Andrew

Presentation time

09:10:00

09:30:00

Session time

08:30:00

09:30:00

SessionSelenium and Metals in Electric Power Generation Wastewater and Non-contact Cooling Water

Session number501

TopicIndustrial Issues and Treatment Technologies, Microconstituents, Research and Innovation

Author(s)

A. HolmesF. Gu