Ozone in Water Treatment Processes.pdf

3/26/2017
Chemist/Ahmed Hasham
1
Ozone in Water Treatment Processes
By/ Ahmed Mohamed Hasham

Ozone in Water Treatment Processes
3/26/2017
2
https://eg.linkedin.com/in/ahmed-hasham-mmba-01024b27
Chemist / Ahmed Hasham (Hesham) ahmedhasham83@gmail.com

About the presenter
 Member of the Board scientists Egypt.
 Member of Scientific Professions Syndicate.
 Member of the Arab Society for experts and Safety Professionals.
 Member of the International Association of Engineers.
 Expert in water and waste water treatment technologies.
 Certified trainer in water treatment field .
 Certified trainer in Quality Management Systems field.
 https://eg.linkedin.com/in/ahmed-hasham-mmba-01024b27
3/26/2017
3

3/26/2017
4
Contents
1. Introduction
2. Advances in Ozone Generation Techniques
3. The Ozone Contacting System
4. Drinking Water Treatment With Ozone.
5. Pre-ozonation
6. Points of application of ozone in a general water treatment scheme
7. Disinfection
8. Application of Ozone in Water treatment

Introduction
 So far, ozone has been mainly used in disinfection, in the
inactivation of viruses, decoloration , improvement of taste
and odor of drinking water and in waste-water treatment.
 Under today' s conditions, additional treatment steps are
necessary.
 Ozonation is introduced in the oxidation of organics ; This
does not involve complete oxidation but yields products
which can be removed by a subsequent treatment step.
3/26/2017
5

 However, it has been shown that ozone is capable of doing more.
 It is used as an oxidant in controlling biological contamination and in
removing iron, manganese and other heavy metals by precipitation.
 The latest findings indicate that preozonation enhances micro-
flocculation and increases the filtration rate of rapid sand filters.
 In all cases the application of ozone helps to decrease reliance on
chlorine, which is thought to form by-products harmful to human
health.
3/26/2017
6

 Although the commonly used method of ozone
generation by silent electrical discharge has been
known for more than 130 years, there have recently
been some very important advances in this technology
which have made ozonation in water treatment more
efficient and economic.
3/26/2017
7

What is ozone?
It is a molecule comprising of three oxygen atoms
having the chemical symbol O3.
ozone does exist naturally, it is a relatively unstable
and reactive gas.
As well as being a powerful disinfectant.
 Today ozone is the strongest commercially available
oxidant.
Most commonly these have been water treatment for
many different industries, and effluent treatment.
3/26/2017
8

Ozone Generation
 Electrical energy flowing across a narrow gap that is filled
with oxygen splits the oxygen molecules into oxygen atoms
(O). These atoms combine with other oxygen molecules (O2)
to form ozone (O3).
 Specific energy requirement = 0.820 kWh/kg O3
 The actual specific energy requirement is much higher (10X
to20X) due to generation inefficiencies
3/26/2017
9

3/26/2017
10

 Economics has favored LOX-fed ozone systems since the late 1980s,
when medium-frequency ozone generators, which produce ozone
efficiently at high concentrations, were commercialized.
 Oxygen containing feed gas can also be produced using pressure
swing adsorption or vacuum-pressure swing adsorption (also called
vacuum swing adsorption) technology to increase the oxygen
concentration in the feed gas from ambient air levels (21 %vol) to
greater than 90 %vol.
3/26/2017
11

3/26/2017
12

Recognized methods FOR O3 generation
There are four recognized methods:
 Corona Discharge
 Ultraviolet Radiation
 Electrolysis
Radiochemical
3/26/2017
13

Corona Discharge
 A high voltage passes through an air gap. In the case of
ozone production, this high voltage transfers energy for
the breaking of the O2 molecule, allowing the formation
of a 3-atom oxygen molecule - ozone. This method is
today the most widely used for commercial ozone
production
3/26/2017
14

3/26/2017
15

Ultraviolet Radiation
 the formation of ozone from oxygen is endothermic, that is it requires
energy. When exposed to light an oxygen molecule in a ground state
will absorb the light energy and dissociate to a degree dependent on
the energy and the particular wavelength of the absorbed light. The
oxygen atoms then react with other oxygen molecules to form ozone.
 For effective ozone production it is therefore necessary to utilize a short
wavelength ~185nm. In theory, the yield of O3 from 185nm UV light is
130g/kWh of light. As lamp efficiencies are so low, ~1%, the production
per kWh from the power source is greatly reduced.
3/26/2017
16

3/26/2017
17

Electrolysis
 Electrolysis is the process in which an electric current
is passed through a liquid, causing a chemical
reaction, resulting in the evolution of gases.
 In relation to ozone production, water can be used
as the electrolyte leading to direct diffusion, or
special electrolytes such as H2SO4 can be used and
ozone gas drawn off and diffused and contacted
by the usual methods.
3/26/2017
18

Radiochemical
 High energy irradiation of oxygen by radioactive rays
can promote the formation of ozone. Whilst high yields
have been achieved under specific conditions using
oxygen, the best results from an air flow through system
at atmospheric pressure, has been ~ 3-4 mg/m3 . The
process is fraught with complications in filtering harmful
isotopes and it is not viewed with potential use in
commercial applications.
3/26/2017
19

Key Factors affected amount of ozone
 The amount of ozone produced together with the efficiency and reliability
of that production are directly related to a number of key factors the main
ones being: -
 Feed gas quality.
 Power input.
 Generation module construction.
 Temperature.
3/26/2017
20

3/26/2017
21

3/26/2017
22

Advantage of Ozone application
1. That ozone can be produced from oxygen at higher ozone
concentrations.
2. While consuming low to moderate specific energy (kWh/lbo,).
3. Has lowered operating costs.
4. Also, the number and size of ozone system equipment components
have been reduced, lowering capital and maintenance costs.
3/26/2017
23

Personal Exposure Effects and limits for Ozone
 OSHA Permissible Exposure Limit: 8 hour 0.1 ppm
 Short Term Exposure Limit 0.3 ppm
 light; 0.08 ppm
 moderate; 0.05 ppm
 2 ppm Immediately Dangerous to Life or Health
 5 ppm Respiratory Protection: Use full face self-contained breathing
apparatus for entering areas with high concentration of ozone.
 Lethal to small animals within 2 hours 15-20 ppm.
 Engineering controls: use ozone destruct units (thermal and/or catalytic) for
off gassing ozone.
 Lethal in a few minutes >1,700 ppm.
3/26/2017
24

3/26/2017
25

Leaks detection
 These leaks can be located in one of the following three ways and should
be repaired as soon as practical.
 Leaks can be located using:
1. A portable ozone detector
2. A weak soap solution sprayed onto the potential leak area (bubbles will
form as the gas escapes)
3. Chemical detection, whereby potassium iodide (2% KI) solution soaked on
a white rag or white paper towel turns a brownish color in the presence of
ozone
3/26/2017
26

Applications in Drinking Water Treatment
 All ozone applications involve oxidative reactions, whether ozone is used
for disinfection or oxidation of specific Contaminants.
DISINFECTION TREATMENT
The primary purpose of ozonation at many water treatment plants is to
achieve disinfection log-inactivation credit for viruses, Giardia, and
Cyptosporidium at regulated or above-regulated levels.
3/26/2017
27

 The value of 1-log inactivation is the same as 90% inactivation, 2 log is 99%, 3
log is 99.9%) etc.
 The term log removal or log inactivation, instead of percent removal, is used in
regulations for ease in disinfection reporting.
 Bubble-diffuser contactors that are used for disinfection applications typically have 6, 8,
10, or 12 chambers.
 Fewer chambers and shorter detention times (e.g., 6 to 10 min) are commonly used to
meet Giardia and virus disinfection objectives, since required CT values are fairly low.
 Extra chambers and additional detention time (e.g., 20 to 60 min) are used for
enhanced disinfection applications.
3/26/2017
28

3/26/2017
29

OZONE OXIDATION TREATMENT
 Pre-ozonation
1. Improved particulate removal from filtration, as evidenced by lower
turbidity and lower particle count of the filtered water.
2. Reduced coagulant dosage (e.g., alum or ferric).
Also can used for :
 Improved aesthetic quality through elimination of undesirable tastes, odors,
and color.
 Oxidized synthetic compounds including pesticides and solvents.
3/26/2017
30

Iron and Manganese Oxidation
 Iron and manganese are oxidized easily by ozone.
 Soluble ferrous iron Fe(I1) is oxidized to ferric iron (FeIII), which slowly
hydrolyzes to form particulate Fe(OH)3. The reaction consumes 0.43 mg of
ozone per mg of Fe(I1)
 Manganese oxidation by ozone and subsequent manganese removal is
quite complex. Ozone oxidizes soluble manganese [Mn(II)] to form
particulate removable) manganese dioxide [MnOz - Mn(IV)]. The reaction
consumes 0.88 mg of ozone per mg of Mn(I1)
3/26/2017
31

Hydrogen Sulfide
Hydrogen sulfide is oxidized easily by ozone to form (ultimately) sulfate.
 Oxidation proceeds in stages:
1. first forming insoluble elemental sulfur, which is evidenced by a light-colored
colloidal suspension.
2. Further oxidation dissolves the elemental sulfur, forming soluble sulfite, and
continued oxidation produces sulfate.
3. More ozone is required to completely oxidize sulfide to sulfate than is required to
produce the insoluble, colloidal elemental sulfur.
3/26/2017
32

 The theoretical O3 to H2S ratio is 3:l mg/L .
 The operating O3 to H2S ratio is 4:1 mg/L.
a. The selected operating ratio is higher so that a moderate ozone residual (0.2
mg/L to 0.3 mg/L in chamber 2) can be maintained.
b. The ozone residual in the downstream chamber is used for process control.
3/26/2017
33

Color Removal
 Color in water is removed for at least two reasons:
1. Color is unattractive and is responsible for customer complaints.
2. Color is linked to the presence of fulvic or humic acids, which consume
large amounts of chlorine and form halogenated organics.
 Color can be removed sufficiently with coagulation in conventional and
direct filtration water treatment plants, but color is removed very effectively
by ozone oxidation.
3/26/2017
34

Turbidity Removal
Benefits of using Ozone before coagulation / filtration process :
1. Increased filtration rate by 33%.
2. lowered coagulant dose by 50%
3. Reduced filtered water turbidity by 50%
3/26/2017
35

Ozone-based advanced oxidation treatment
 Oxidation during ozonation also occurs via hydroxyl
radicals(HO'), which are secondary oxidants that are formed by
ozone decomposition via a complex mechanism.
 processes in which 03 is purposefully decomposed into HO') are
important in drinking water treatment because of reactions with
organic molecules such as some solvents
3/26/2017
36

Bromate Formation
 Bromate formation and control has been the focus of intensive research
efforts since the early 1990s when bromate (BrO3-) was implicated as a
potential carcinogen.
 BrO3- MCL value at 10 µg/L (USEPA, 1998).
 Ozone plants can be subdivided into the following three categories, which
relate to their relationship to bromate issues and considerations:
1. Bromide is absent in the source water or is present at low concentration.
2. Bromide is present in the source water at moderate concentration
3. Bromide is present in the source water at a relatively high concentration
3/26/2017
37

1. Bromide is absent in the source water
 Bromide is absent in the source water or is present at low concentration.
Bromate formation is proportional to bromide concentration for given water
quality and ozone dose operating conditions. Low bromide concentration
means low bromate formation potential.
3/26/2017
38

2. Bromide is present in the source water at moderate
concentration
 Bromide is present in the source water at moderate
concentration (e.g., 50 to 100 µg/L), but ozone dose
requirements are such that bromate formation is below the MCL
value of 10 µg/L.
 Bromate formation is minimized when:
a. Ozone dose is low as a result of plant operation at low CT value that is still
sufficient to meet the disinfection treatment objective, such as 2-log virus or
0.5-log Giurdia inactivation credit.
b. Ozone dose is low even to meet elevated disinfection requirements (e.g.,
0.5-log Cryptosporidium inactivation credit), because water quality
characteristics are such that the ozone demand is low and ozone decay is
slow (i.e., long ozone half-life).
3/26/2017
39

3. Bromide is present in the source water at
a relatively high concentration
 Bromide is present in the source water at a relatively high
concentration such that bromate formation would exceed
the 10 µg/L MCL value unless bromate mitigation measures
are implemented.
 Bromate mitigation options are described here and include
lowering pH, adding ammonia, adding chlorine and
ammonia, or using chlorine dioxide.
3/26/2017
40

References
 Kerwin Rakness-Ozone in Drinking Water Treatment_ Process Design,
Operation, and Optimization-American Waterworks Association .
3/26/2017
41

 ahmedhasham83@gmail.com
 Isct.Egypt@gmail.com
 https://www.facebook.com/isct.site/
 00201159465989
 00201146139692
3/26/2017
42
https://eg.linkedin.com/in/ahmed-hasham-mmba-01024b27

Ozone in Water Treatment Processes.pdf

Recomendados

Recomendados

Mais conteúdo relacionado

Semelhante a Ozone in Water Treatment Processes.pdf

Semelhante a Ozone in Water Treatment Processes.pdf (20)

Último

Último (20)

Ozone in Water Treatment Processes.pdf