Emerging Trends in

Wastewater UV Disinfection

Michael J. Watts, PhD, PE

Senior Process Engineer

Garver

TACWA – Garland

May 30, 2014

Germicidal UV for Disinfection

Important UV Milestones

1903 – Sensitivity of microbes to 250 nm light

observed

. . . now known as germicidal Action Spectra

Germicidal Absorbance Spectra

Critical Difference Between UV and Cl2

Photo-dimerization

Chemical change in pathogenic DNA caused by

photon absorption

Inhibits normal cell replication (Pathogen Inactivation)

Pathogen remains viable but not infectious

Germicidal UV for Disinfection

Important UV Milestones

1904 – First water-tight, UV lamp in a quartz

sleeve developed

Unreliable ignition, coinciding with advancements

in industrial chlorine production, meant limited

application

Germicidal UV for Disinfection

Important UV Milestones

1938 – 1st Fluorescent, (Hg) gas vapor lamp

demonstrated

Modern concept of ballasted lamp matured –

1940’s

Reliable ignition, predominantly monochromatic

emission

(253.7 nm)

Germicidal UV for Disinfection

Important UV Milestones

1970’s – EPA invests in UV disinfection research and

reactor construction grants

1978 – Full-scale wastewater UV disinfection

demonstrated

(Bergen, NJ)

1982 – Submerged UV lamp, open-channel wastewater

disinfection concept developed.

Factors Driving UV Growth

By 2019, UV expected to replace Chlorine as predominant

disinfectant used in municipal water/wastewater (Frost & Sullivan,

2013)

Pressures to Switch

1. Safety – No off-gas monitoring, no emergency-response plans for gas

release

2. Cost – No gas scrubbers needed, no dechlorination chemicals needed,

smaller disinfection facilities

3. Regulatory –

1. Chlorine-, and Ozone-resistant pathogens (protozoa)

2. Water Reuse

So how do we still end up here?

Critical Concepts for Effective UV

UV Dose (or Fluence, H’)

UV DOSE = Iavg. x t(s)

(mW-s/cm2 or mJ/cm2)

0

20

40

60

80

100

120

140

160

180

UV

Do

se, m

J/cm

2

Pathogen Inactivation 1-log 2-log 4-log

Critical Concepts for Effective UV

UV Dose (or Fluence, H’)

UV DOSE = Iavg. x t(s)

(mW-s/cm2 or mJ/cm2)

solid-state radiometer • Iavg. Light

Attenuation

Critical Concepts for Effective UV

UV Dose (or Fluence, H’)

UV DOSE = Iavg. x t(s)

(mW-s/cm2 or mJ/cm2)

• Iavg.

Rate of Attenuation is a Function of. . .

1. Germicidal Output

(W per lamp x number of lamps)

2. UV Absorbance (UV254, cm-1)

(%UVT = 100 x 10-UV254)

3. TSS/Turbidity (mg/L or NTU)

-light reflection, scattering

Optimizing Germicidal Output

First Decision: Lamp Selection

Low-Pressure-Hg, standard-output UV lamps (LP)

Flow-path is parallel, or perpendicular to lamps

Power per

Lamp

40 - 250 W

Emissions

Spectrum

Monochromatic

(254 nm)

Lamp Life 4,000 – 9,000

hrs

Surface Temp. 90 -120 C

Optimizing Germicidal Output

First Decision: Lamp Selection

Low-Pressure-Hg, high-output UV lamps (LPHO)

Flow-path is parallel, or perpendicular to lamps

Power per

Lamp

500 W

Emissions

Spectrum

Monochromatic

(254 nm)

Lamp Life 8,000- 12,000

hrs

Surface Temp. 90 – 120 C

Optimizing Germicidal Output

First Decision: Lamp Selection

Medium-Pressure-Hg UV lamps (MP)

Flow-path is perpendicular to lamps, fewer lamps than with LP UV

Power per

Lamp

>1 kW

Emissions

Spectrum

Polychromatic

Lamp Life <5,000 hrs

Surface Temp. 500 – 950 C

TRA UV Disinfection Pilot – Dec 2013

• 4, 1.5 to 20-MGD Pilot Reactors

• Closed-Vessel

• Open-Channel

• Energy-Efficient Lamp Technologies

Lamp selection impacts kWh($) per log-removal

MP UV

LP UV

More UV

energy in

Germicidal

Absorbance

Band

However. . . some pathogens can be more

sensitive to MP UV spectrum

Linden et al. (2007) AEM

Shorter-wave light has greatest germicidal potency

Adenovirus

However. . . some pathogens can be more

sensitive to MP UV spectrum

MP UV achieved 5-log

inactivation at lower UV Dose

Linden et al. (2009) Journal-AWWA

Regulations can impact UV design and lamp

selection

New focus on relatively UV-resistant pathogens of

concern?

Oklahoma Administrative Code (2013)

Category 2 (Urban unrestricted reuse)

(A) 5-log removal or inactivation of Adenovirus-15

(B) 5-log removal or inactivation of Salmonella typhimurium

(C) 3-log Giardia lamblia removal or inactivation

If regulatory focus turns to both chlorine-resistant and LP-UV-

resistant pathogens like Adenovirus, will we see a shift from LP UV to

MP UV for high-level reuse water disinfection?

Beyond urban unrestricted reuse. . .

CDPH: 12/10/10

12-log virus inactivation

10-log Giardia

10-log Crypto

Public Health Goals for DPR

Cryptosporidium Giardia Virus

Activated Sludge 1.3 1.6 1.2

MF/UF

Membranes

4.5 4.0 3.0

RO 2.0 2.0 2.0

UV/H2O2 AOP 6.0 6.0 6.0

Chlorine 0 0.5-1.0 4.0

Total Log-Removal 13.8 14.6 16.2

Source: CDPH/WateReuse Foundation 2013

H2O2 Action Spectra (for AOP)

0

50

100

150

200

250

200 220 240 260 280 300

Wavelength (nm)

e (

M-1

cm

-1) H2O2

·OH

MP UV

LP UV

UV

Critical Concepts for Effective UV

UV Dose (or Fluence, H’)

UV DOSE = Iavg. x t(s)

(mW-s/cm2 or mJ/cm2)

• Iavg.

Rate of Attenuation is a Function of. . .

1. Germicidal Output

(W per lamp x number of lamps)

2. UV Absorbance (UV254, cm-1)

(%UVT = 100 x 10-UV254)

3. TSS/Turbidity (mg/L or NTU)

-light reflection, scattering Critical to

UV AOP Success

0

10

20

30

40

50

60

78% UVT 99% UVT

% o

f L

igh

t A

bs

orb

ed

by O

xid

an

t H2O2 Dose of 5 mg/L in a UV AOP reactor

Tertiary Filtered

Effluent

NF/RO Membrane

Permeate

HOCl: A better photon absorber

Tertiary Filtered

Effluent

NF/RO Membrane

Permeate

H2O2 Cl2

Cl2

H2O2 OCl-

HOCl

LP UV, 254 nm

UV254 Absorbance higher with free chlorine

0

10

20

30

40

50

60

70

80

90

100

78% UVT 99% UVT

% o

f L

igh

t A

bs

orb

ed

by O

xid

an

t

Oxidant Dose of 5 mg/L in a UV AOP reactor

Tertiary Filtered

Effluent

NF/RO Membrane

Permeate

H2O2 Cl2

Cl2

H2O2

UV

• Theoretical yield = 2 ·OH

• Actual yield limited by water

caging and recombination

UV

• Theoretical yield = 1 ·OH

• Actual yield can be 40% greater

than from H2O2*

*Watts and Linden (2007). Water Research.

Future AOP for reuse?

4-10 mg/L Cl2

• 1o Disinfection

• Cl2 reduced 25-50%

Residual Cl2 for

2o Disinfection

What if we could custom design UV reactors for

specific wavelengths?

Energy-efficient

UV LEDs

Select an array of

LEDs that emit

wavelengths specific to treatment objectives

260 nm for bacteria and protozoa

277 nm for adenovirus

227 nm for NDMA 1st Commercial UV LED

reactor for flows < 5 gpm

(Aquionics, USA)

Returning to the present. . .

1. Selecting the right lamp, and number of lamps for the job.

2. Selecting UV equipment with on-line UVT monitoring.

3. Record keeping that allows for correlation of influent and effluent

microbial testing(e.g., coliform) to influent water quality (UVT, TSS).

4. Regular mechanical checks on automatic cleaning systems.

Questions? More info?

MJWatts@GarverUSA.com