Advanced Oxidation of Drinking Water using Ultraviolet Light and Alternative Solid Forms of
OXIDATION PROCESSES IN DRINKING WATER TREATMENT (EXAMPLES)
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Transcript of OXIDATION PROCESSES IN DRINKING WATER TREATMENT (EXAMPLES)
OXIDATION PROCESSES IN DRINKING WATER TREATMENT
(EXAMPLES)
What processes can we use?
1. oxidation-reduction
2. pH and buffering capacity adjustment (pH optimum of processes)3. chemical precipitation (dissolved particulate)
4. adsorption (bind to surface)
5. phase separation (removal of different phases: solid/liquid and gas/liquid phase separation)
6. other (e.g. reverse osmosis)
2. pH and buffering capacity adjustment (pH optimum of processes)
What processes can we use?
1. oxidation-reduction
3. chemical precipitation (dissolved particulate)
4. adsorption (bind to surface)
5. phase separation (removal of different phases: solid/liquid and gas/liquid phase separation)
6. other (e.g. reverse osmosis)
Oxidation and Oxidation and reductionreduction
The processes are parallel with each other, The processes are parallel with each other, they take place atthey take place at the same time the same time
The oxidation agent will be reducedThe oxidation agent will be reduced (it gets (it gets electron)electron), while the reduction agent will be , while the reduction agent will be oxidized oxidized (it loses electron)(it loses electron)
In drinking water treatment chemicals are In drinking water treatment chemicals are oxidized in order to make them non-soluble, oxidized in order to make them non-soluble, in order to make them less toxic or in order in order to make them less toxic or in order to kill bacteria (disinfection)to kill bacteria (disinfection)
Oxidizing agents are: oxygen, ozone, chlorineOxidizing agents are: oxygen, ozone, chlorine, , potassium permanganate, chlorine, chlorine-potassium permanganate, chlorine, chlorine-dioxide, chloraminesdioxide, chloramines……
To convert the soluble compounds into non-soluble compounds:
Fe(II) Fe(III)Mn(II) Mn(IV)
Oxidation is also used to oxidize some compounds to make them non-soluble
(oxidation of iron, oxidation of manganese)
THE APPLICATION OF AIR/OXYGEN AS OXIDIZING
AGENT
Reaction of oxygen with dissolved iron:
Fe2+ + 2H2O Fe(OH)2 + 2H+
Fe(II)Soluble form
4Fe(OH)2 + 2 H2O + O2 4Fe(OH)3
Fe(II) Fe(III)Non-soluble form
Oxidation by air/oxygen
Reaction of oxygen with dissolved manganese:
Mn2+ + 2H2O Mn(OH)2 + 2H+
Mn(II)Soluble form
2Mn(OH)2 + O2 2MnO(OH)2
Non-soluble form Mn(II) Mn(IV) MnO(OH)2 MnO2 + H2O
Oxidation by air/oxygen
Oxidation of hydrogen-sulfide:
2H2S + O2 2S + 2H2O
H2S: rotten-egg odour
Oxidation by air/oxygen
THE APPLICATION OF OZONE
Oxidation of:
iron Fe(II) Fe(III)manganese Mn(II) Mn(IV)arsenic As(III) As(V)organic compoundscompouds causing colourcompounds causing tastecertain micropollutants (cyanide pollution in 2000)microorganisms
Oxidation by ozone
O3
Generation:
from
3 O2 + energy 2 O3
the preparation of feed-gas is needed before ozonation
airoxygen
water water isis a common medium for a common medium for microorganisms microorganisms the spread of the spread of infectious diseaseinfectious diseases (pollution from waste s (pollution from waste water)water)
The most important aspect of water The most important aspect of water treatment is treatment is the removal of pathogenic the removal of pathogenic microorganisms!microorganisms!
This process is called is disinfection and it is usuallyThis process is called is disinfection and it is usuallyan oxidation process (expect the UV radiation)an oxidation process (expect the UV radiation)
Another purpose of oxidation...the disinfection
DisinfectantsDisinfectants::
ChlorineChlorine ClCl22
ChloraminesChloramines NHNH22-Cl-Cl
Chlorine dioxideChlorine dioxide ClOClO22
OzoneOzone OO33
SilverSilver AgAg
UV radiationUV radiation
Disinfection
to decrease the number of pathogenic microorganisms in water: bacteria, viruses, protozoa
evaluation of other disinfectants
from the 1910s: the application of chlorine (cheap, efficient)
1970s: harmful by-products of chlorine were discovered
Aim of disinfection
THE APPLICATION OF CHLORINE
Chlorine Cl2it reacts with the water:
hypochlorous acid
Cl2 + H2O HOCl + H+ + Cl-
hypochlorite ion
HOCl H+ + OCl-
HOCl is more efficient than OCl-
the best pH values: between 2 and 6, but this is too low (corrosive water)!!
pH is between 7 and 7.5 !!
Oxidation by chlorine
Cl2 + H2O HOCl + H+ + Cl-Reaction of chlorine with water
Reaction of calcium-hypochlorite with water
Ca(OCl)2 + 2H2O 2HOCl + Ca(OH)2
Reaction of sodium-hypochlorite with water
NaOCl + H2O HOCl + NaOH
formation of hypochlorous-acid (HOCl) !!Addition of Cl2, Ca(OCl)2, NaOCl
Oxidation by chlorine
Breakpoint chlorination
Chlorine reacts with ammonia to form chloramines:
monochloramine
NH3 + HOCl NH2Cl + H2O
dichloramine
NH2Cl + HOCl NHCl2 + H2O
trichloramine
NHCl2 + HOCl NHCl3 + H2O
Oxidation by chlorine
Disadvantage of chlorination
Formation of trihalo-methane compounds andhalogenated organic compounds
chloroform
chlorinated phenol
Examples:
Oxidation by chlorine
Summary of advantages & disadvantages of chlorination
Advantages
easy to prepare (from NaCl)
strong oxidant
cheap
safe
sufficient residual can be maintained
Disadvantages
reaction with ammonium
formation of harmful by-products
Oxidation by chlorine
THE APPLICATION OF CHLORINE-DIOXIDE
Chlorine-dioxide
no reaction with ammonium
no THM formation
By-products:
formation of aromatic chlorinated compounds
it has to be produced on-site because of the risk of explosure
Advantages
Disadvantages
ClO2
formation of chloritheClO2-
formation of chlorathe (harmful)ClO3-
Oxidation by chlorine-dioxide
THE APPLICATION OF OZONE
Decomposition of ozone - Milli-Q water
0
0,05
0,1
0,15
0,2
0,25
0 50 100 150 200
time (min)
ozone c
oncentr
ati
on (
mg/l) T = 20 ˚C
pH = 6-7
Decomposition of ozone – ion-free water
time (min)
con
cen
trati
on
of
ozo
ne
(mg
/l)
Decomposition of ozone - Tap water
0
0,05
0,1
0,15
0,2
0,25
0 20 40 60 80 100 120 140time (min)
ozo
ne c
once
ntr
ati
on (
mg/l) T = 10 ˚C
pH = 8,6
Decomposition of ozone – tap water
time (min)
con
cen
trati
on
of
ozo
ne
(mg
/l)
Advantages Disadvantages
Efficient disinfectant
THMs are not formed
It decompoeses easily; There is no residual disinfectant
o o oo o oo o o
O3
Secondary disinfectant
By-product formation;
easily biodegradable organic compounds
Oxidation by ozonation
o o oo o oo o o
O3
Secondary disinfectantBAC
Advantages
Efficient disinfectant
THMs are not formed
Disadvantages
It decompoeses easily; There is no residual disinfectant
By-product formation;
easily biodegradable organic compounds
Expensive
bromate formation
Oxidation by ozonation
0 1 2 3 4 5 6 7 8 9 10 11
5
4
3
2
1
0
time (day)
logC
FU/m
L
Regrowth of microorganisms after disinfection
after treated by chlorine
after treated by ozone
(Miettinen et al.)
APPLICATION OF UV LIGHT FOR DISINFECTION
(THIS IS NOT AN OXIDATION PROCESS)
UV light – It inactivates the microorganisms by physical way
TG
A A C
T T G T
A
G
C
C
A
TG
C
G
CA
AC
GT
UV253,7 nm
Formation of double bond
inhibits replication
DNA
Disinfection by UV radiation
Incomplete penetration
UV light scatterParticle
shading
Region of limited cellular
damage
Complete penetration
UV light scatter
Region of limited cellular
damage
UVlamp
Particle shading
Incomplete penetration
Complete penetration
UVlamp
Disinfection by UV radiation
UV light – advantages and disadvantages
Advantages
It inactivates the microorganisms by physical way
Harmful by-products are not formed
Short contact time
Disadvantages
There is no residual disinfectant
The impact of water quality on the efficiency of disinfection
Buildup of Ca, Mg, Fe scales on the sleeve
Biofilm formation on the sleeve
Absorption of UV in water; particle interactions
Disinfection by UV radiation
PROBLEMS WITH THE WATER QUALITY AFTER DISINFECTION
g/m
2 in
ner
pip
e s
urf
ace
Biofilm formation
(Lund et al.)
Without any disinfection
Treated by chlorine
Treated by UV radiation
Treated by ozone
Summary, conclusions
The importance of the evaluation of water quality parameters
The efficiency of disinfection
The evaluation of other oxidation processes
Formation of by-products
Problems with the water quality after disinfection