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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 !!!