Ywann Penru1, Andrea R. Guastalli1,2, Santiago Esplugas1, Sylvie Baig2

 1Department of Chemical Engineering, University of Barcelona, Spain. (penru@angel.qui.ub.es , Tel: (+34) 934 021 293, Fax: +34 934 021 291)

2Degrémont SA, France.

Disinfection of seawater:

Application of UV and Ozone

Paris, May 25, 2011, IOA-IUVA World Congress

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Overview

I. Introduction

• Seawater disinfection, why?

• UV, Ozone and seawater chemistry

II. Materials and Methods

• UV254 irradiation: 2 devices for 2 objectives

• Ozone: a 2-step process

• Analytical tools

III. Results and Discussions

• UV254 irradiation

• Ozone

IV. Conclusions

Paris, May 25, 2011, IOA-IUVA World Congress

Introduction: Seawater disinfection, why?

Paris, May 25, 2011, IOA-IUVA World Congress

Nowadays, seawater disinfection is an issue in several areas:

• Ballast water: Prevention from the spread of harmful aquatic organisms carried by

ships' ballast water (International Maritime Organization, 2004).

• Marine recirculation aquaculture systems and seawater aquaria:

Prevention from microorganisms and viruses accumulation,

Prevention from organic and inorganic by-products accumulation.

Application of new technologies for seawater disinfection:

Ozone

UV254 irradiation

Membrane filtration

Acoustics or electric pulses

2 / 13

• Seawater, a peculiar chemistry:

High salt content Scaling formation on Quartz sleeves.

High Bromide and Chloride concentration: ≈ 64 mg/L and 19 g/L

• Bromide and Chloride reactivity:

Catalytic consumption of Ozone by Bromide

Hypobromous acid and bromate formation

Analogous reaction with chloride but kinetic constants much lower

• Seawater reactivity:

Seawater Bromide/Chloride ratio: 1.5 10-3

Chloride catalyser of Bromide oxidation:

Introduction: UV254, Ozone and seawater chemistry

BrOOBrO k23

1

BrOBrOO k23

2

323 22 3 BrOOBrOO k

4

2 3

kH O HOBr H O BrO

8kHOCl Br HOBr Cl

Seawater ozonation leads to Bromide oxidation

Toxic and carcinogenic compounds!

Paris, May 25, 2011, IOA-IUVA World Congress 3 / 13

Material and methods: UV254 irradiation, 2 devices for 2 objectives

• 1st Objective: Minimum UV254 dose requirement for total disinfection. Laboratory batch reactor.

2 L cylindrical glass reactor recovered by aluminium foil

3 submerged Hg-low pressure lamps

Photon flow = 9.0 µEinstein.s-1

UV doses applied: 0 – 500 J.L -1

• 2nd Objective: Impact of UV254 disinfection on organic matter.

Pilot reactor in continuous operation.

1.1 L tubular UV705 Trojan reactor

One central Hg-low pressure lamp

Photon flow = 34.2 µEinstein.s-1

Continuous feeding at 200 L.h-1

UV dose applied: 320 J.L-1

Seawater tank

UV reactor

Paris, May 25, 2011, IOA-IUVA World Congress 4 / 13

Material and methods: Ozone, a 2-step process

• Method:

1st Step: Ozone dose production

Reach Henry’s law equilibrium:

2nd Step: the disinfection reaction

Addition to seawater of the solution saturated with ozone.

• Materials:

Ozone generator unit: Ozat CFS, Ozonia

Ozone gaseous-phase analyser: BMT 693

Ozone dissolved sensor: ATI Q45H/64

• Experimental conditions:

ge3O2H

O2H*l3 O

He

TR

M

ρ][O

[O3]ge g O3/Nm3 13 26 40 88 136 170

[O3]l* mg O3/L 4.1 8.0 12.5 27.4 42.2 53.8

Ozone dose applied

mg O3/L 0.38 0.73 1.14 2.49 3.84 4.89

Paris, May 25, 2011, IOA-IUVA World Congress 5 / 13

N2

O2

O3 Generator

O3 Gas Analyzer

KI

Vent

O3 dissolvedsensor

P

• Disinfection quantification: Adenosine Tri-Phosphate (ATP) liberation

ATP: Bio-molecule present in all microorganisms involved in the energy generation

process.

Calculation:

Cellular ATP = Total ATP – Free ATP

Material and methods: Analytical tools

Direct sample analysis:

Total ATP measurement

Analysis after filtration (0.22µm):

Measurement of Free ATP

Complete disinfection = Cellular ATP elimination

Paris, May 25, 2011, IOA-IUVA World Congress 6 / 13

Material and methods: Analytical tools

• Oxidant / Oxidation potential

Oxidation Reduction Potential (ORP):

Total Residual Oxidant (TRO):

Quantification of total BrOH / BrO- (in mg Br2.L-1)

DPD colorimetric method

Bromate and Chlorate

Ionic chromatography

Dilution 1/10

Detection limit:

BrO3- = 10 µg.L-1

ClO3- = 200 µg.L-1

Paris, May 25, 2011, IOA-IUVA World Congress 7 / 13

Material and methods: Analytical tools

• Organic matter parameters

Total Organic Carbon (TOC)

High-temperature catalytic oxidation

UV absorbance at different wavelength (Aʎ)

Biochemical Oxygen Demand at seven days (BOD7)

Closed Bottle Method: BOD7 = [O2]day 0 - [O2]day 7

Autochthonous microorganisms

Residual oxidant quenching by sulphite

Modified BOD7:

No quenching of residual oxidant

A254 Aromatic organic matterA272 Aromatic organic matter without sulphide interferenceA330 BrO- absorption peak (ɛ = 340 L mol-1 cm-1)

Paris, May 25, 2011, IOA-IUVA World Congress 8 / 13

Results and discussions: UV254 irradiation

• Disinfection: Minimum UV254 dose required

UV254 irradiation decreases the cellular/total ATP ratio:

Elimination of cellular ATP Seawater disinfected

Minimum UV dose for complete disinfection = 320 J.L-1

0

20

40

60

80

100

0 80 160 240 320 400

rati

o of

Cel

lula

l ATP

/ to

tal A

TP (

%)

UV Dose applied per litre of seawater (J/L)

Exp n°1

Exp n°2

Exp n°3

Exp n°4

Exp n°5

Initial cellular/total ATP ratio:

Ratio variation with sampling day

Mainly > 50% high content of living cells

Paris, May 25, 2011, IOA-IUVA World Congress 9 / 13

Results and discussions: UV254 irradiation

• Organic matter parameters: UV254 dose applied = 320 J.L-1

UV254 irradiation interacts with seawater organic matter:

Low reduction of UV absorbance, TOC and BOD7

Low reduction of seawater aromaticity and biodegradability

Low interaction with organic matter

Radiation is mainly used for disinfection.

A254 TOC BOD7 SUVA254 BOD7/TOC

m-1 mg C.L-1 mg O2.L-1 L.mg C-1.m-1 mg O2.mg C-1

Seawater 0.64 0.97 0.71 0.66 0.73

UV treated 0.57 0.93 0.66 0.61 0.71

Removal (%) 11.7 4.2 7.0 7.8 3.0

Paris, May 25, 2011, IOA-IUVA World Congress 10 / 13

Results and Discussions: Ozone application• Disinfection: Minimum ozone dose required

• Oxidant formation

Complete disinfection by ozone

Minimum O3 dose:

Cellular ATP removal: 0.4 mg O3.L-1.

Total ATP removal: 1.1 mg O3.L-1.

Very fast dissolved O3 consumption

High ORP increases (> 700 mV)

Highly oxidative water

No proportional relation with O3 dose.

Formation of residual oxidant:

Proportional to O3 dose.

No bromate nor chlorate formation

Paris, May 25, 2011, IOA-IUVA World Congress 11 / 13

0 1 2 3 4 50

2,000

4,000

6,000

8,000

10,000

ATP Total

ATP cell

Ozone dose applied (mg O3.L-1)

AT

P (

RL

U)

0 1 2 3 4 50

200

400

600

800

0

4

8

12

16

20

ORP TRO measured TRO maximum

Ozone dose applied (mg O3.L-1)

OR

P (

mV

)

TR

O (

mg

Br2

.L-1

)

Results and Discussions: Ozone application• Organic matter:

Organic matter oxidation by ozone

UV absorbance removal up to 50%

Low mineralization, max: 10%.

BOD7 increases

Residual oxidants modify the activity of autochthonous microorganisms.

Modified BOD7 < conventional BOD7

Negative values for Modified BOD7

Potential use for microorganism inhibition in seawater.

Microorganism endogenic respiration

Modified BOD7 =

Respiration sample with

residual oxidant-

Paris, May 25, 2011, IOA-IUVA World Congress 12 / 13

0 1 2 3 4 50

10

20

30

40

50

60A 254 A 272 TOC

Ozone dose applied (mg O3.L-1)

Rem

oval

of a

bsor

banc

e an

d TO

C (%

)

0 1 2 3 4 5

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

BOD7BOD7 modified

Ozone dose applied (mg O3.L-1)

BOD7

(mg

O2.

L-1)

13 / 13

Conclusions• Complete seawater disinfection obtained for both processes

Minimum dose: UV254 = 320 J.L-1, O3 = 0.4 mg O3.L-1

Ozonation leads to the formation of secondary oxidant :

Long term inhibition of autochthonous microorganisms.

No bromate formation (for the applied doses).

Interesting properties for ballast water treatment.

Post-treatment required after ozone application for aquaculture purposes (protection from toxic residual oxidant).

• Partial degradation of seawater organic matter by UV254 and ozone

Higher removals by ozone (up to 50% vs. 10% for A254).

Low mineralization in both cases (3 vs. 10%).

Opposite effect on biodegradability:

UV Reduction ≠ Ozone Increase.

Paris, May 25, 2011, IOA-IUVA World Congress

Ywann Penru1, Andrea R. Guastalli1,2, Santiago Esplugas1, Sylvie Baig2

 1Department of Chemical Engineering, University of Barcelona, Spain. (penru@angel.qui.ub.es , Tel: (+34) 934 021 293, Fax: +34 934 021 291)

2Degrémont SA, France.

Disinfection of seawater:

Application of UV and ozone

THANKS FOR YOUR ATTENTION

Paris, May 25, 2011, IOA-IUVA World Congress