Determination of Applied Ozone Dose and the Use of Ozone Controllers

1
(No Transcript)
2
Safe and Effective Application of Ozone Via
Applied Dose, Redox, and Husbandry
TechniquesANDREW AIKEN 1, 2 and MARK SMITH
3

• National Aquarium In Baltimore.
• Aqua-Brio.
• cosestudi.

3
Presentation outline

• Redox
• Oxidative Redox Potential (ORP)
• Ozone
• Oxidants (TRO)
• Dosing strategy
• Applied Ozone Dose (AOD)
• ORP controllers
• Monitoring
• Conclusions

4
Redox
Reduction-Oxidation or Redox is a paired
reaction involving the exchange of electrons.
Oxidizing agents remove electrons and in the
process become reduced. An example of an
oxidizing agent is Ozone
Reducing agents supply electrons and in the
process become oxidised. An example of a
reducing agent is Nitrite (NO2-)

5
Oxidative Redox Potential

• Redox reactions generate a measurable electical
  potential called ORP (Oxidative Redox Potential).
• 2. ORP is measured in mV (millivolts) and is the
  sum of all reactions, or half-reactions,
  involving the transfer of electrons.

ORP S of all half-reactions
6
Oxidative Redox Potential
Hydrogen cell (standard) Oxygen Sulphate Ozone
2H 2e- ? H2 Eo 0000 mV O2 2H2O 4e- ?
4OH- Eo 401 mV SO42- H2O 2e- ? SO32-
2OH- Eo - 936 mV O3 2H2O 2e- ? O2 2OH-
Eo 1240 mV
ORP S of all half-reactions
7
Oxidative Redox Potential

• 3. ORP ä with ã organic carbon.
• ORP ã with ã oxidizing agents.
• 4. ORP indicates water quality by quantifying the
  relative concentrations of oxidizing and reducing
  compounds.

8
Ozone

• 1. Ozone (O3) is a strong oxidizing agent.
• 2. When applied carefully ozone can remove
  organic pollutants and disinfect aquarium water
  through two processes
• (a) Flocculation in a foam fractionator.
• (b) Oxidation in a contact chamber.
• 3. Ozone and some of its by-products are toxic to
  aquatic life!

9
Oxidants N

• When ozone reacts with seawater oxidizing agents
  are produced. These oxidizing agents take part in
  the water treatment process.
• It is very important to match ozone dosing rate
  to biological demand! If oxidizing agents are not
  consumed by reducing compounds, or excessive
  ozone is used, persistent and dangerous oxidants
  may result and ultimately enter an exhibit!
• Aquatic life exposed to high concentrations of
  oxidants will ultimately perish!

10
Oxidants N
4. Chronic exposure to low concentrations of
oxidants may promote long-term maladies - e.g.,
hypermetaplasia and susceptability to other
diseases.
11
Oxidants N
4. Chronic exposure to low concentrations of
oxidants may promote long-term maladies - e.g.,
hypermetaplasia and susceptability to other
diseases.
Gill lamellae of teleost fish suffering from
hypermetaplasia
12
Oxidants N

• Typical persistent oxidants include
• bromine (Br-), bromite (OBr-), bromate (BrO3-),
  and hypobromous acid (HOBr).

• 5. Principal among persistent oxidants produced
  when applying ozone to seawater are the Halide
  derivatives.

13
Oxidants N

• 8. Maximum allowable TRO concentrations

• Persistent oxidants produced during ozonation are
  collectively referred to as the TRO (total
  residual oxidants). It is TRO that presents a
  risk to aquatic life, not ORP!

14
Oxidants N
9. TRO, predominantly bromine derivatives, may be
measured using a DPD (N,N-diethyl-p-phenylenediami
ne) total chlorine colorimetric test (APHA) or an
Indigo trisulfonate Accu Vac analysis
(Hach). 10. If ORP exceeds 400 mV within an
exhibit toxic oxidants are probably present! This
is an indicator only! There is no direct
correlation between ORP and TRO. It is TRO that
should be your final control not ORP!
15
Oxidants N
16
Oxidants N
Example Amount of sodium thiosulphate
required to neutralise 0.5 mg. / litre TRO in a
25,500 litre exhibit?
11. In the event of an ozone overdose 2.81 grams
of sodium thiosulfate may be used to neutralize
1.00 gram of TRO.
17
Oxidants N
Example Amount of sodium thiosulphate
required to neutralise 0.5 mg. / litre TRO in a
25,500 litre exhibit?
11. In the event of an ozone overdose 2.81 grams
of sodium thiosulfate may be used to neutralize
1.00 gram of TRO.
25,500 litres
0.5 mg. / litre
x
Required Sodium thiosulphate
2.81
x

1,000
18
Oxidants N
Example Amount of sodium thiosulphate
required to neutralise 0.5 mg. / litre TRO in a
25,500 litre exhibit?
11. In the event of an ozone overdose 2.81 grams
of sodium thiosulfate may be used to neutralize
1.00 gram of TRO.
12,750 mg.
Required Sodium thiosulphate
2.81
x

1,000
19
Oxidants N
Example Amount of sodium thiosulphate
required to neutralise 0.5 mg. / litre TRO in a
25,500 litre exhibit?
11. In the event of an ozone overdose 2.81 grams
of sodium thiosulfate may be used to neutralize
1.00 gram of TRO.
Required Sodium thiosulphate
2.81
12.75 grams
x

20
Oxidants N
Example Amount of sodium thiosulphate
required to neutralise 0.5 mg. / litre TRO in a
25,500 litre exhibit?
11. In the event of an ozone overdose 2.81 grams
of sodium thiosulfate may be used to neutralize
1.00 gram of TRO.
Required Sodium thiosulphate
35.83 grams

21
Dosing strategy
To correctly dose ozone it is important to
monitor each of the following
(1) Applied Ozone Dose (AOD) (2) Oxidative
Redox Potential (ORP) (3) Total Residual Oxidants
(TRO) (4) Turbidity (NTU) (5) Husbandry (Feeding
Cleaning) (6) Animal behaviour
22
Applied ozone dose

• 1. AOD (Applied Ozone Dose) is the weight of
  ozone added to a known volume of water entering a
  reactor vessel i.e., foam fractionator or ozone
  contact chamber.
• A high AOD may result in residual oxidants
  entering the exhibit. This is indicated by a high
  ORP in the exhibit.
• A low AOD may result in little or no benefit to
  water quality. This is indicated by a low ORP in
  the exhibit.

23
Applied ozone dose

• 5. For exhibits with a normal bio-load AOD
  should be in the approximate ranges

• An appropriate AOD will improve water quality and
  is indicated by favorable and stable ORP values
  (300 380 mV) within the exhibit.

Flocculation 0.01 - 0.05 mg. /
litre (Typical for Foam Fractionators)
Oxidation / Disinfection 0.10 - 1.00 mg. /
litre (Typical for Contact Chambers)
24
Applied ozone dose
6. AOD is calculated using the following formula
25
Applied ozone dose
x
Applied Ozone Dose

26
Applied ozone dose
Water flow is determined by a gauge measuring the
total volume of water entering a reactor vessel.
1
6.70 m3 / hour or 111.7 litres / min.
27
Applied ozone dose
3
litres of gas
mg. of ozone
2
x
minute
litres of gas
Applied Ozone Dose

111.7 litres of water
minute
28
Applied ozone dose
Ozone gas flow is determined by a gauge measuring
the total volume of ozone gas entering a reactor
vessel.
2
125 litres / hour or 2.08 litres / min.
29
Applied ozone dose
3
2.08 litres of gas
mg. of ozone
x
minute
litres of gas
Applied Ozone Dose

111.7 litres of water
minute
30
Applied ozone dose
Ozone mass is determined by a high concentration
ozone monitor.
1.1 g / m3 or 1.1 mg. / litre
3
31
Applied ozone dose
2.08 litres of gas
1.1 mg. of ozone
x
minute
litres of gas
Applied Ozone Dose

111.7 litres of water
minute
32
Applied ozone dose
2.08 litres x 1.1 mg. of ozone
2.288 mg. of ozone
minute
Applied Ozone Dose

111.7 litres of water
minute
33
Applied ozone dose
2.288 mg. of ozone
Applied Ozone Dose

111.7 litres of water
34
Applied ozone dose
This AOD is typical for a foam fractionator.
0.020 mg. / litre
Applied Ozone Dose

If AOD is out of the expected range verify and
adjust each parameter.
35
Applied ozone dose

• Once an operator has established AOD this setting
  can be fine-tuned to maintain a steady flow of
  ozone and stable ORP.
• Factors affecting AOD include
• Water flow rate.
• Ozone gas flow rate.
• Ozone generator settings.
• Ozone generator status (e.g., maintenance of
  dielectrics, air dryers, etc.).

36
ORP controllers

• 1. ORP controllers are used primarily as safety
  mechanisms to prevent overdosing within reactor
  vessels and exhibits.
• Using a negative-feedback logic control process
  an ORP controller will trigger specific actions
  and alarm systems.
• Two ORP sensors should be employed for a given
  controller one directly after the reactor vessel
  to modulate dosing and another within the exhibit
  to prevent overdosing.

37
ORP controllers - operation
38
ORP controllers - operation
39
ORP controllers - operation
40
ORP controllers - operation
41
ORP controllers - operation
42
ORP controllers - operation
43
ORP controllers - strategy
High level set point for exhibit
Low level set point for exhibit
44
ORP controllers - strategy
ORP reaches high level set point and ozone supply
closes
45
ORP controllers - strategy
ORP reaches low level set point and ozone supply
opens
46
ORP controllers - strategy
47
ORP controllers - strategy
AOD setting too High!
48
ORP controllers - strategy
ORP never reaches High or Low alarm!
On
49
ORP controllers - strategy
AOD setting too Low!
On
50
ORP controllers - strategy
On
ORP never reaches High or Low alarm!
51
ORP controllers - strategy
On
52
ORP controllers - strategy
On
Good AOD setting!
53
Monitoring - ORP
54
Monitoring - ORP

• In general ORP sensors are unreliable. They tend
  to drift out of calibration and require frequent
  cross-checking.
• Also remember that ORP gives an indirect measure
  of TRO only.
• 3. ORP sensors are therefore convenient
  controllers and useful for monitoring trends but
  they must be used in conjunction with other
  parameters - i.e., AOD, TRO, turbidity, animal
  husbandry, and animal behavior.

55
Monitoring - Turbidity
56
Monitoring - Turbidity

• Typical values include

• Turbidity is the result of particles - e.g.,
  organic carbon, microorganisms and inorganic
  precipitates - causing light to be scattered and
  absorbed.
• It is measured in NTU (Nephelometric Turbidity
  Units).

57
Monitoring - Turbidity

• Turbidity can be used to understand changing
  concentrations of organics and therefore the
  effectiveness of ozone treatments (e.g.,
  turbidity may increase with an increased
  bio-loading associated with the addition of new
  specimens).
• Great care must be excercised when interpreting
  the cause of increased turbidity as it may be the
  result of increased inorganic particles (e.g.,
  turbidity resulting from the addition of new
  substrate).

58
Monitoring - Interpretation
59
Monitoring - Interpretation
60
Monitoring - Interpretation
61
Monitoring - Interpretation
62
Monitoring - Husbandry
63
Monitoring - Husbandry

• ORP, TRO and Turbidity should always be
  interpreted within the context of husbandry
  activities (e.g., the addition or removal of
  specimens, cleaning of exhibits, etc.).

64
Monitoring - Behaviour
65
Monitoring - Behaviour

• ORP, TRO and Turbidity should always be
  interpreted within the context of animal
  behaviour (e.g., rapid swimming near the surface
  by some elasmobranch species can indicate
  elevated TRO concentrations).

66
Conclusions

• 1. ORP is the sum of all Redox (Reduction-Oxidatio
  n) reactions and is measured in mV (millivolts).
• Oxidants increase ORP and reductants decrease
  ORP.
• When ozone reacts with seawater it produces
  oxidants. If these oxidants are not consumed by
  reducing compounds they may persist and become
  toxic to aquatic life.

67
Conclusions

• Applied Ozone Dose (AOD) should be used as the
  starting point for an ozone dosing strategy (AOD
  mg. ozone / liters of water).
• Total Residual Oxidants (TRO) should be used as
  the final control for an ozone dosing strategy.
• Water flow meters, ozone flow meters, and high
  concentration ozone monitors are essential to
  calculate AOD and correctly apply ozone to a
  system.

68
Conclusions

• 7. ORP controllers should be used to control
  ozone dosing but should not be relied upon to
  protect aquatic life from TRO.
• 8. AOD should be set to a point where ORP remains
  within ORP controller safe limits and yet
  allows effective ozone dosing to continue
  throughout the day.
• 9. Only through analysis of AOD, TRO, ORP,
  Turbidity, Husbandry and Behaviour can an
  appropriate ozone dosage strategy result.

69
(No Transcript)