An innovative way to determine on-site ozone delivery ... · An innovative way to determine on-site ozone delivery efficiency Aikaterini Spiliotopoulou1,2, Richard Martin3, Henrik

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An innovative way to determine on-site ozone delivery efficiency

Spiliotopoulou, Aikaterini; Martin, Richard; Andersen, Henrik Rasmus

Publication date:2016

Document VersionPeer reviewed version

Link back to DTU Orbit

Citation (APA):Spiliotopoulou, A., Martin, R., & Andersen, H. R. (2016). An innovative way to determine on-site ozone deliveryefficiency. Abstract from 11th International Conference on Recirculating Aquaculture (ICRA) and 2016Aquaculture Innovation Workshop (AIW), Virginia, United States.

An innovative way to determine on-site ozone

delivery efficiency

Aikaterini Spiliotopoulou1,2

, Richard Martin3, Henrik R. Andersen

1

1Department of Environmental Engineering, Technical University of Denmark, Miljøvej 113, 2800 Kongens Lyngby,

Denmark

2 OxyGuard International A/S, Farum Gydevej 64, 3520 Farum, Denmark

3 Water ApS, Farum Gydevej 64, 3520 Farum, Denmark

Abstract In recirculating aquaculture systems (RAS), the water quality changes continuously due to fish feed,

excretions and makeup water or piping system, affecting system’s equilibrium. Accumulation of

organic and inorganic compounds, where proteins, ammonia and heavy metals are the most

pronounced; creates toxic conditions for aquatic organisms, leading to system failure. The dissolved

organic matter (DOM) varies among the different water sources, affecting the reaction rate of ozone

and consequently its lifetime.

Ozone is a strong oxidizing agent, reacting rapid and in low concentrations, first with the easily

degradable DOC (Eq.1) and inorganic pollutants, and then with the decreasingly reductive

pollutants. If more ozone is dosed than the immediate demand by reducing pollutants, it will be

decomposed to hydroxyl radicals (Eq.2), which are non-selective, highly reactive species oxidizing

a range of recalcitrant dissolved pollutants (Eq.3).

DOC + O3 → DOCselectively oxidized Eq. 1

H2O + O3 → O2 + 2 HO• Eq. 2

DOC + HO• → DOCradical oxidized Eq. 3

When ozone is introduced into water, bacteria load and dissolved organic matter (DOM) are

diminished while redox level, water clarity and UV transparency are increased. Protein degradation

is accelerated and coagulation, filtration and nitrification processes are improved. However, in a

non-meticulously designed system, residual ozone (due to overdose) with longer lifetime will reach

the culture tanks causing significant harm to cultured specie. Ozone has been reported to be toxic to

a wide range of marine and freshwater organisms at residual concentrations between 0.01 mg/L and

0.1 mg/L. The risk to lose fish and the high ozonation cost are limiting parameters and contribute to

a reluctance by the aquaculture industry to use ozone. Therefore, ozone should be properly

delivered, efficiently dissolved and accurately controlled to ensure that it is completely consumed

before returning to culture tanks.

The present study investigates the optimal technology to transfer ozone into water based on

physicochemical model applied to different established delivery methods e.g. gas cone, gravitation

bubble column or venturi injector. Depending on the water quality (DOC, salinity, pH, temperature,

etc.), which will be analysed in advance in the laboratory, the three dissolving alternatives will be

tested in site. Based on the water flow and the disinfection needs of the facility, it will be suggested

which is the optimal gas transfer method. The transfer efficiency will be monitored with oxidation

reduction potential (ORP) sensors in site and by a colorimetric assay which will be developed in the

laboratory.

Water samples were collected and transferred to the laboratory for further analysis. Ozone

measurement in water is usually achieved by a spectrophotometer utilizing a colorimetric assay,

since ORP sensors do not determine it successfully. Therefore, the possibility to determine the

delivered ozone dose by utilizing the natural fluorescence caused by certain proteins, which are

contained into RAS is investigated. Preliminary experiments to test this hypothesis have been

conducted in wastewater effluent providing satisfactory results. Since the aquaculture water is

enriched with proteins it is expected that the fluorescence effect will be greater leading to an

innovative ozone determination technology. The method is evaluated by comparing it with a

colorimetric assay.

Key-words: Ozone, gas solubility, fluorescence, ozone dose control

I would like the present abstract to be taken under consideration as an oral presentation. My

submission is intended for the session: Waste Management and Water Quality

An innovative way to determine on-site ozone delivery efficiency

Aikaterini Spiliotopoulou1, 2, Richard Martin3, Henrik R. Andersen1

1Department of Environmental Engineering, Technical University of Denmark 2 OxyGuard International A/S 3 Water ApS

Recirculating Aquaculture System (RAS)

1

Sludge

(N and P removal)

Biologi

-cal

filter

NH3

Make up water

Air

O3PSA

Air blower

Monitor of:

O2

Salinity

Temperature

pH etc.

CO2 Foam

Skimmer

Drum

filter

Ozone

DissolverBiologi

-cal

filter

Pump

Ozone

Sensor

16% of animal derived protein is from fish

More than 2,6 billion people get more than 20% of their protein intake from fish

A few years ago: more than 60% of the fish consumed around the world is farmed

RAS implications Low exchange RAS (90% or more of water is

recycled)

Accumulation of:

Dissolved organic mater (DOM)

Micro-particles

Dissolved N-compounds (e.g ammonia)

Heavy metals

Microbial abundancies

Potentially leading to:

Suboptimal conditions

Cu2+

Pb2+ As3+

Hg

Cd2+

2

Dual Functions of Ozone

3

Disinfection

Efficient against

Bacteria

Viruses

Parasite

Oxidation

Strong oxidizing agent

Rapid reactions

Removal of natural DOM

Acceleration of protein degradation

Increased water clarity and UV transparency

Improve

• coagulation

• filtration and

• nitrification processes.

Challenges

4

Ozone overdose

Never present in culture tank

Significant harm to cultured species

> 0.01 mg/L

In case of saltwater system:

Hypobromous acid formation

toxic

Reluctance to use ozone due to:

Risk of losing fish

Cost

Need for an operational method to monitor the ozone demand in the

water phase!!!

Low Dosage High Dosage

Oxidation Disinfection

(Need of free

concentration)

Traditional residual ozone determination

5

Dissolved (actual) ozone into water

Off-line colorimetric method (e.g. DPD, indigo trisulfonate)

Spectrophotometer

• complicated method

Test kits

• expensive

Online measurement

Potentiometric principle probe

• quite expensive

Oxidation potential reduction (OPR)

• cheap

• do not measure ozone

• non specific (cannot distinguish e.g. O3 from Cl2)

• risk of failure when exposed to high ozone concentration

Delivered Ozone determination

6

We propose a new method to determine how much ozone

dosage is added into water

Fluorescence

Based on natural fluorescence of DOM

rapid detection

precise characterization of DOM composition

Tested in wastewater, river water, seawater, etc.

Never used to control ozone in aquaculture until now

Fluorescence

7

Lightsource

Excitation nm

Emission nm

Samplecuvette

DetectorOutput

(Fluorescence principle)

DOM contains:

Chromophores (absorb light)

Fluorophores (re-emit light)

Humic substaces (plant origin)

• Refered as humic-like

Amino acids (proteins)

• Refered as protein-like

Low wavelength

High energy

High wavelength

Low energy

Excited state

Energy loss

Photon

Fluorescence transitions

8

Fluorophore type Excitation/Emission wavelength (nm)

Protein-like (Tyrosine-like) 231/315

Protein-like (Tryptophan-like) 231/360

Humic-like 249/450

Protein-like (Tyrosine-like) 275/310

Protein-like (Tryptophan-like) 275/340

Humic-like 335/450

Based on fluorescence transitions published in an wastewater overview paper (Hudson et al., 2007)

To characterized micro-pollutants in waste water

We use the same wavelength pairs

Our Aim

9

Does naturally fluorescent DOM exist in RAS?

Is the natural fluorescence in RAS reacting

with ozone?

How could this knowledge be implemented in

real life applications?

Sampling sites

10

Model trout farm

Tivoli

The Blue Planet

Eel fish farm

Pilot scale RAS

Experimental setup-lab scale

11

Stock solution of ozone

1 h

Fluorescence analysis

Ozone doses

0 to 20 mg O3/L

Water characterization

1 mL 15 mL 2 mL 5 mL

Water characterization based on fluorescence

12

Humic-like

Protein-like

0 5 10 150

10

20

30

40

50

Model trout farm

Ozone dosage (ppm)

Flu

ore

sce

nce

In

ten

sity

Fluorescence profile in different water samples

13

Fish-farms: humic-like fluorescence dominates

Aquariums: more diverse fluorescence

High ozone sensitivity in low concentrations

0 5 10 150

1

2

3

4

The Blue Planet

Ozone dosage (ppm)

Flu

ore

sce

nce

Inte

nsity

0 5 10 15 200

10

20

30

40

50

60

70 Pilot scale RAS

Ozone dosage (ppm)

Flu

ore

scence I

nte

nsity

0 5 10 150

10

20

30

40

50

Eel fish farm

Ozone dosage (ppm)

Flu

ore

scence I

nte

nsity

0 5 10 150

1

2

3

Tivoli

Ozone dosage (ppm)

Flu

ore

scence I

nte

nsity

Humic-like fluorescence calibration curve

14

Slopes among samples varied

0 1 2 3 4 50

10

20

30

40

50

Ex335Em450

R2=0.9734

Model trout farm

Slope: -5,124

Ozone dosage (ppm)

Flu

ore

scence Inte

nsity

0 5 10 150

10

20

30

40

50

Ex335Em450

Model trout farm

Ozone dosage (ppm)

Flu

ore

scence Inte

nsity

0 5 10 150

10

20

30

40

50

Ex335Em450

Eel fish farm

Ozone dosage (ppm)

Flu

ore

sce

nce

In

ten

sity

0 1 2 3 4 5 60

10

20

30

40

50

Ex335Em450

R2=0.9844

Slope: -6,991

Eel fish farm

Ozone dosage (ppm)

Flu

ore

scence Inte

nsity

Protein-like fluorescence calibration curve

15

0 5 10 150

1

2

3

4

5

6

7

Ex275Em310

Model trout farm

first

second

Ozone dosage (ppm)

Flu

ore

sce

nce

In

ten

sity

0 1 2 3 4 50

1

2

3

4

5

6

7

Ex275Em310

R2=0,9587

Model trout farm

Slope:-0.7428

Ozone dosage (ppm)

Flu

ore

sce

nce

In

ten

sity

0 5 10 15

0

2

4

6

8

10

Ex275Em310

Eel fish farm

first

second

Ozone dosage (ppm)

Flu

ore

scence Inte

nsity

0 1 2 3 4 5

0

2

4

6

8

10

Ex275Em310

R2=0,9638

Slope: -0.467

Eel fish farm

Ozone dosage (ppm)

Flu

ore

scence Inte

nsity

Slopes among samples varied

Other OM contained in water are competing fluorescence

Unlike to have a universal sensor controlling ozone into water

Application #1: Determination of delivered ozone dose

16

Sludge

(N and P removal)

Biologi

-cal

filter

NH3

Make up water

Air

O3PSA

Air blower

Monitor of:

O2

Salinity

Temperature

pH etc.

CO2 Foam

Skimmer

Drum

filter

O3

DissolverBiologi

-cal

filter

Pump

Validation of ozone generator

Without sensor installation

Calibration curve in the lab based on fluorescence

Grab samples before and after

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 150

10

20

30

40

50RAS Fish farm

Ozone dose (ppm)

Flu

ore

sce

nce

In

ten

sity

Does the generator deliver the ozone dose that the specifications promise?

How does it work?

In

Out

In

Out

Delivered ozone dose=3,7 g/m3

17

Online Fluorescence sensor

Removal of

O3 demand

Remaining O3 demand

Control point

(ensuring remaining O3 demand)

Sludge

(N and P removal)

Biologi

-cal

filter

NH3

Make up water

Air

O3PSA

Air blower

Monitor of:

O2

Salinity

Temperature

pH etc.

CO2 Foam

Skimmer

Drum

filter

O3

DissolverBiologi

-cal

filter

Pump

0 1 2 3 4 5 60

10

20

30

40

50

Ex335Em450

R2=0.9844

Slope: -6,991

Fish farm 2

Ozone dosage (ppm)

Ozone d

em

and

Aim:

Ozone demand is defined

Low disinfection but high transparency

Financially robust

Application #2: On-line control

How does it work?

Choose a fluorescence intensity within a calibration curve and add as much ozone as needed to achieve this intensity

Take-home message

18

Fluorescent DOM does exist in aquaculture water

Fluorescence is highly sensitive to ozone mostly in low ranges

(0-5 mg O3/L)

Fluorescence can be used as:

Off-line control verifying ozone dosage and evaluating

ozone generator leading to a more robust operation

On-line sensor controlling ozone dosage by keeping

fluorescence signal within predetermined ranges

Acknowledgements

19

Thank you for the attention !!!