DSD Research & Development Forum 2018 1. Introduction 1.1 - - PowerPoint PPT Presentation

Hong Kong University of Science and Technology

Novel Photocatalytic Disinfection of Sewage with Visible-light-driven Magnetic Photocatalysts

Irene M. C. Lo, PhD, JP

F.HKIE, F.ASCE, F.HKIQEP, M.EASA Chair Professor of Civil and Environmental Engineering Director of Environmental Engineering Program Academician, European Academy of Sciences and Arts

Smart City · Innovative Wastewater Management

5 December 2018

DSD Research & Development Forum 2018

Hong Kong University of Science and Technology

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• 1. Introduction

1.1 Pathogens in sewage

• Bacteria and virus
• Waterborne disease
• E.coli as indicator organisms

1.2 Sewage disinfection

• Remove and inactivate/kill

pathogenic microorganisms to the level in compliance with the discharge standards

• Prevent diseases from spreading and

safeguard human health

Source:

http://www.freedrinkingwater.com/images

• new/education-page/image/water-

contaminants.jpg

Microorganisms in water causing disease

Hong Kong University of Science and Technology

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1.3 Conventional disinfection technologies

• Chemical-intensive process
• Disinfection byproducts (DBPs):

cancer causing compounds

 Chlorination  UV disinfection

• UV lamps: expensive; aging; fouling
• Energy-intensive process
• Bacteria regrowth

Ref.: UV Disinfection Fact Sheet, Environmental Technology Initiative (1998) Ref: Chlorination Disinfection Fact Sheet, Environmental Technology Initiative (1998) UV disinfection system Picture from Xylem https://www.xylem.com/

Hong Kong University of Science and Technology

1.4 Photocatalytic disinfection

Photocatalyst

e- h+

e- O2 h+

.O2-

H2O

.OH

bacteria

Excitation

hv>Eg

Inactivation Damage to cell structure Solar light： abundant, free and renewable energy on earth

Hong Kong University of Science and Technology

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2.1 TiO2 photocatalyst  TiO2

Advantages: Low cost, nontoxicity, and good chemical stability Drawbacks: Large bandgap of 3.2 eV and limited absorption of visible light; Separation difficulty of fine size of photocatalyst from water; Recombination of photo-electrons and holes

• 2. Modified Titanium Dioxide (TiO2)-based

Magnetic Photocatalyst

 Engineering methods to modify TiO2

Magnetic Fe3O4@SiO2 TiO2 @ Fe3O4@SiO2 Co-doping with ions Visible light-driven TiO2- based magnetic photocatalyst

Hong Kong University of Science and Technology

• 3. Advantages of our magnetic photocatalysts

(I) No toxic DBP formation and bacteria regrowth/reactivate (II) Economical and environmental friendly process

• No extra treatment process (i.e., replacing chlorination or UV

disinfection by photocatalysis)

• Solar energy driven (i.e., visible light driven)
• Reusable photocatalysts with magnetic property

(III) Photocatalytic disinfection with additional degradation of EDs/PPCPs

Hong Kong University of Science and Technology

7 Visible-light-emitting compact fluorescent lamps

Batch reactor with visible-light CFL

• 4. Methodology

Hong Kong University of Science and Technology

(1) Ag/Fe,N-TiO2/Fe3O4@SiO2 Magnetic Photocatalyst

• photocatalytic performance using synthetic

wastewater and visible-light lamp

• bacteria regrowth
• magnetic separation efficiency
• reusability of magnetic photocatalytic
• photocatalytic performance in real sewage

(2) rGO-Fe/N-TiO2/Fe3O4@SiO2 Magnetic Photocatalyst

• photocatalytic disinfection using solar simulator and real

sewage

• Prototype photocatalytic reactor with magnetic separator

system

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• 5. Results

Hong Kong University of Science and Technology

9  Simultaneous photocatalytic degradation of bisphenol A (BPA) and disinfection of E. coli  Photocatalytic disinfection of E. coli

Photocatalyst 1 g/L

• E. coli

106 CFU/mL Visible light 330 W/m2 Water matrix 0.9 wt% NaCl solution Photocatalyst 1 g/L

• E. coli

106 CFU/mL BPA 2 mg/L Visible light 330 W/m2 Water matrix 0.9 wt% NaCl solution

Complete disinfection in 120 min and 90% degradation of BPA in 120 min Complete disinfection in 120 min.

Performance of TiO2-based photocatalyst (AgFeNTFS)

Photocatalyst (Ag/Fe,N-TiO2/Fe3O4@SiO2)

Ag/Fe,N-TiO2/Fe3O4@SiO2 Magnetic Photocatalyst

Hong Kong University of Science and Technology

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4',6-diamidino-2-phenylindole (DAPI) and propidium iodide (PI) dyes were employed to stain the DNA of bacteria.

DAPI Live cells Dead cells PI Dead cells Penetrate into the integrated and damaged cell membrane (blue fluorescence) Penetrate only into the damaged cell membrane (red fluorescence)

Investigation of the changes of bacterial membrane structure

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• Cell membranes were damaged in photocatalytic process indicating

bacteria inactivation. No regrowth of bacteria after 2 days.

0 min. 120 min.

Fluorescence microscope images of bacteria

Blue fluorescence Red fluorescence

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2.4 Magnetic property of AgFeNTFS photocatalyst

Saturation magnetization = 5.82 emu/g 12

• Vibrating sample

magnetometer (VSM) analysis

TiO2-based magnetic photocatalyst in water

• Separation from

treated water

• Magnetic separation

efficiency of photocatalyst by a magnet

99% magnetic separation efficiency in 5 min

Magnetic Separation of Photocatalyst

Hong Kong University of Science and Technology

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2.5 Reusability for photocatalytic disinfection

 In 3 cycles, the photocatalytic disinfection performance of recycled photocatalyst remained the same as that of the initial one.  Good reusability for photocatalytic disinfection Reusability of photocatalyst for photocatalytic disinfection after magnetic separation from treated synthetic water AgFeNTFS

Hong Kong University of Science and Technology

Photocatalytic degradation of BPA in sewage Photocatalytic disinfection in sewage

• 100% photocatalytic disinfection (3.7 log of bacteria disinfected) in 210 min.
• Only 1.5 log of disinfection in 60 min.
• 100% of BPA was photocatalytic degraded from sewage in 300 min.

Simultaneously photocatalaytic disinfection and degradation in sewage obtained from Sai Kung STW

(AgFeNTFS) (AgFeNTFS)

Hong Kong University of Science and Technology

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The FeNTFS photocatalyst can only inactivate 1.5-log E.coli reduction in 60 min. The new rGO-FeNTFS can effectively inactivate E. coli cells, achieving about 3.0-log of reduction in 60 min in synthetic saline solution under CFL reactor.

Redesign the photocatalysts: rGO-FeNTFS

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Photocatalytic disinfection in real sewage

Setup for the photocatalytic disinfection by rGO-FeNTSF under solar simulator

Irradiance spectrum of authentic sunlight (1pm, 11th July 2018 at HKUST) and light irradiance spectrum of the reaction flask position under solar simulator Integrated irradiance=8×104 W/m2

Batch reactor using solar simulator

Solar simulator Reaction flask Stirrer Fan

Hong Kong University of Science and Technology

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Sewage samples collected from Sai Kung STW before disinfection

Sai Kung STW

(secondary treatment, low-saline sewage) Source: https://www.dsd.gov.hk E.coli =80000 CFU/100 mL

Hong Kong University of Science and Technology

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Ngong Ping STW

(tertiary treatment, low-saline sewage) Source: https://www.dsd.gov.hk

Sewage samples collected from Ngong Ping STW before disinfection

E.coli = 51000 CFU/100 mL

Hong Kong University of Science and Technology

Light source Sai Kung (3 g/L of dosage) Ngong Ping (1 g/L dosage) (90 min) E. coli reduction Time to meet discharge standard (90 min)E. coli reduction Time to meet discharge standard Solar simulator with filter (only visible-light) 1.9-log 90 min 1.2-log 60 min Solar simulator without filter (full spectrum) 3.1-log 60 min 2.0-log 30 min

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Photocatalytic performance in Sai Kung and Ngong Ping sewage

Hong Kong University of Science and Technology

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Magnetic separation Unit: patent in HK & China in 2015

Prototype photocatalytic reactor integrated with a magnetic separation unit Electromagnetic system Magnetic separation unit Photocatalytic reactor

Hong Kong University of Science and Technology

Research group on photocatalysis study

BiOX-based photocatalytic removal of PPCPs TiO2-based photocatalytic disinfection and photocatalytic removal of EDs Simultaneous photocatalytic removal of PPCPs and hydrogen evolution g-C3N4/La-based photocatalytic removal of phosphate g-C3N4/based photocatalytic disinfection Piezophotocatalysis for removal of PPCPs

Hong Kong University of Science and Technology

Acknowledgement The financial support from General Research Fund, HKSAR and the upcoming financial support for this R&D project from DSD, HKSAR are appreciated.

HKUST