DISINFECTION

Dr. Eng. Joni Aldilla Fajri

 Disinfection
• Selective destruction of disease-causing organisms in water
supply or wastewater effluent.
• Necessary for safe potable water supplies and for healthy rivers
and streams
Method of disinfection
• Physical methods: heat (pasteurization) and ultraviolet
radiation (function of penetration depth, contact time, and
turbidity or SS)
• Radiation: gamma ray emitted from a radioactive source such
as cobalt 60 – effective to disinfect or sterilize water,
wastewater, and sludge – unsafe
• Chemical methods: oxidizing agents - chlorine, bromine, iodine,
O3, H2O2, KMnO4; alcohols; phenol and phenolic compounds;
heavy metals, quaternary ammonium compounds (positively
charged polyatomic ions of the structure NR4+ with R being
alkyl groups); soaps and synthetic detergents; and alkalies and
acids.
 Chlorinatio
n
• Effective in destroying a variety of bacteria,
viruses and protozoa, including Salmonella,
Shigella and Vibrio cholera.
• Wastewater chlorination was initially applied in
1910 in Philadelphia, PA, and was soon
implemented in many other cities in the United
States based on this early success.
• Benefits: Disinfection, controlling odor and
preventing septicity, aiding scum and grease
removal, controlling activated sludge bulking,
controlling foaming and filter flies, stabilizing
waste activated sludge prior to disposal, foul
air scrubbing, destroying cyanides and phenols,
ammonia removal
 Chlorine
 Cl2 gas, Ca(OCl)2, NaOCl, and ClO2
 Used for disinfection, taste and odor control, color
removal, oxidation of ammonia, and iron,
manganese, sulfide, and BOD removal.
 Advantages: cheap, effective, available in large
quantities, nontoxic in low concentrations to higher
forms of life, and residual.
 Disadvantages: acid generation (HCl), buildup of
total dissolved salts, and formation of potentially
carcinogenic, halogenated organic compounds
 Selection based on the size of the treatment facility,
objectives, economics, and safety considerations
 Chlorine
Chemistry
• Efficiency: contact time, chlorine dosage, temp.,
pH, nature of liquid and suspended matter, and
type and number of organisms
• Free Chlorine Residual
Cl2 + H2O  HOCl + H+ + Cl-
HOCl  H+ + OCl-
Ca(OCl)2 + 2H2O  2HOCl + Ca(OH)2
NaOCl + H2O  HOCl + NaOH
• Combined Chlorine Residual
NH3 + HOCl  NH2Cl + H2O
NH2Cl + HOCl  NHCl2 + H2O
NHCl2 + HOCl  NCl3 + H2O
 Breakpoint
Chlorination
NH2Cl + NHCl 2 + HOCl  N2O + 4HCl
4NH2Cl + 3Cl2 + H2O  N2 + N2O + 10HCl
2NH2Cl + HOCl  N2 + H2O + 3HCl
NH2Cl + NHCl2  N2 + 3HCl
8
Chlorine Residual
mg Cl2/mg NH4-N

6
NHCl2
4
HOCl + OCl-
2
NH2Cl NCl3
0
0 2 4 6 8 10 12 14 16
Chlorine Dose, mg Cl2/mg NH4-N
 Chlorine Dosages for Proper
Disinfection
of Wastewater Effluents
Effluent Dosage range
mg/L
Untreated wastewater 6~25
Primary sedimentation 5~20
Chemical precipitation 3~10
Trickling filter 3~10
Activated sludge 2~8
Multimedia filter following activated 1~5
sludge plant

For disinfection of wastewater, a chlorine residual of 0.5

mg/L after 20~30 min. of contact time is required.
 Total Coliform Remaining in the
Effluent
Total chlorine Total chloroform (#/100 mL)
residual (mg/L) Primary eff. Secondary effl.
0.5~1.5 24,000~400,000 1,000~12,000
1.5~2.5 6,000~24,000 200~1,000
2.5~3.5 2,000~6,000 60~200
3.5~4.5 1,000~2,000 30~60

30 min. of contact time

Initial primary effluent: 3.5  107 total coliform/100 mL
Initial secondary effluent: 1  106 total coliform/100 mL
 Design of Chlorination
System
Chlorine Supply
• Chlorine: gaseous or liquid supplied in 45.4~68 kg
(100~150 lb) cylinders, 907-kg (1 ton) containers, and in
tank cars
Design and Safety Consideration
• Chlorine room must be near the point of application.
• Chlorine storage and chlorinator equipment must be
housed in a separate building.
• Adequate exhaust ventilation at floor level should be
provided because chlorine gas is heavier than air.
• Chlorine storage should be separate from the chlorine
feeders and accessories.
 Design of Chlorination System
- continued
Design and Safety Consideration - continued
 The chlorinator room should have temperature control. Min. temp.
= 21°C The chlorine supply area (> 10°C) should be kept cooler
than the chlorinator.
 The sun should not be permitted to shine directly on the cylinders
and heat should never be applied directly to the cylinders.
 The chlorine storage and feed system should be protected from fire
hazards.
 A clear viewing window should be provided for viewing the
chlorination equipment. Blower control and gas masks should be
located at the room entrance.
 Wrought iron piping should be provided for liquid chlorine and
chlorine gas. Tough plastic piping should be provided for chlorine
solutions. Liquid chlorine has a very high volume expansion
coefficient, therefore, sufficient air cushion or expansion chambers
should be provided in liquid chlorine lines.
 Design of Chlorination System
- continued
Design and Safety Consideration - continued
 Chlorine cylinders in use should be set on platform scale and loss
of weight should be used for record keeping of chlorine dosages.
Hypochlorite
 More expensive, loss of strength in storage, difficult to feed, safer
than chlorine gas or liquid.
 Many large plants in urban areas use hypochlorite.
 Sodium hypochlorite solution is available in 1.5~15% strength in
4.9~7.6 m3 tanks and tank cars.
 Stronger solutions decompose readily by exposure to light and heat.
 High-test calcium hypochlorite contains at least 70% available
chlorine. It is available in 45- to 360-kg drums as power, granules,
or compressed tablets or pellets.
 Hypochlorites and solutions must be stored at cool and dry places
for a better shelf life.
 Chlorine
Feed
• The chlorine feed or injector system is essential because it
provides the required dosage at the point of application.
Chlorine feed system
• Pressure injection: may pose risks of gas escaping; normally
used in small plants or in large facilities where safety
precautions are rigidly followed.
• Vacuum feed: apply a specified vacuum to evaporate and
move chlorine gas from the supply source to the chlorinator
where it is mixed with water and carried to the point of
application; must have enough amount of water to (1)
maintain chlorine concentration in the solution below a
given concentration (3,500 mg/L) and (2) create required
amount of vacuum in the line to the chlorinator and in all of
the components of the chlorinator system.
 Mixing and
•
Contact
Rapid mixing of chlorine solution into wastewater followed by a
quiescent contact period is essential for effective disinfection.
The chlorine solution is provided through a diffuser system. It is
then mixed rapidly by (1) mechanical means, baffle arrangement,
and (3) hydraulic jump.
• Chlorine contact chamber: to provide the contact time necessary
for the disinfecting compound to reduce the number of
organisms to acceptable levels; 15~30 min. contact time; 15 min.
at peak flow
• Design: minimize short circuiting and dead spaces, maximize
mixing for better disinfection, and reduce settling of solids in the
basin.
• Chlorination  solids settling   deposited sludge chlorine
demand  and anaerobic organism growth  gas   solids rise
and thus solids in the effluent 
 Chlorine
•
Dose
Chlorine Demand = Applied Chlorine Dose – Chlorine
Residual
• Typically 5~20 mg/L
Example
• Assume that a chlorinator is set to feed 834 lbs/day, flow
rate is 10 MGD, and the chlorine as measured after 15
minutes contact is 0.5 mg/L.

834 lbs/day  mg/L

 10 mg/L
10 MGD  8.34 lbs/Mgal
Chlorine dose: 10.0 mg/L
Chlorine residual: 0.5 mg/L
Chlorine demand: 9.5 mg/L
 Dechlorinatio
n
• It is necessary to dechlorinate, or remove chlorine
from a wastewater by the addition of
dechlorinating agents.
• The most common chemicals used for
dechlorination are sulfur dioxide, sodium bisulfate,
sodium sulfite, sodium thiosulfate and activated
carbon.
• The chemical equivalents required for
dechlorination can be calculated; however,
laboratory experiments should be used to help to
define the required dose.
 A Compound-Loop Control System
for Chlorination with Liquid Chlorine
and Dechlorination with Sulfur
Dioxide
 UV
Disinfection
• Transfers electromagnetic energy from a mercury
arc lamp to an organism’s genetic material (DNA
and RNA)  destroys the cell’s ability to reproduce
400 nm 40 nm
Radio IR Visible UV X-Rays
Light


UV-A UV-B UV-C Vacuum
UV

300 nm 200 nm

Germicidal Range (250~270 nm)

 Prevention of Cell Reproduction
by UV

Thymine Dimerization...,
O O O O
CH3 H3C
C C C C
CH3 H3C
HN C C NH h HN C C NH
+
C CH HC C C C C C
O O O N N O
N N
H H
H H H H
thymine thymine thymine dimer
 UV
Usage
Over 20% of U.S. Wastewater Treatment
Plants now use UV Disinfection
 UV Installations in the
U.S.
Over 4300 Installations:
Very Small Plants (< 1 MGD)
- 2300 installations treating 580 MGD
Small Plants (1 ~ 5 MGD)
- 1160 installations treating 2.6 BGD
Medium Plants (5 ~ 25 MGD)
- 750 installations treating 8 BGD
Large Plants (> 25 MGD)
- 125 installations treating 5.5 BGD
Very Large Plants (> 100 MGD)
- 22 installations treating 3.8 BGD
 Advantage
s
• UV disinfection is effective at inactivating most viruses,
spores, and cysts.
• UV disinfection is a physical process rather than a chemical
disinfectant, which eliminates the need to generate,
handle, transport, or store toxic/hazardous or corrosive
chemicals.
• There is no residual effect that can be harmful to humans
or aquatic life.
• UV disinfection is user-friendly for operators.
• UV disinfection has a shorter contact time when compared
with other disinfectants (approximately 20 to 30 seconds
with low-pressure lamps).
• UV disinfection equipment requires less space than other
methods.
 Disadvantage
s
• Low dosage may not effectively inactivate some viruses,
spores, and cysts.
• Organisms can sometimes repair and reverse the
destructive effects of UV through a "repair mechanism,"
known as photo reactivation, or in the absence of light
known as "dark repair."
• A preventive maintenance program is necessary to control
fouling of tubes.
• Turbidity and total suspended solids (TSS) in the
wastewater can render UV disinfection ineffective. UV
disinfection with low-pressure lamps is not as effective for
secondary effluent with TSS levels above 30 mg/L.
• UV disinfection is not as cost-effective as chlorination, but
costs are competitive when chlorination/dechlorination is
used and fire codes are met.
 UV
Disinfection
• Goal: Meet disinfection target
– Absolute (e.g., 200 FC/100 mL)
– Relative (e.g., 4 log virus)
• Step 1: How much UV dose to meet target?
– Collimated beam dose-response
• Step 2: How much UV equipment?
– Function (Flow, UVT, Power of Lamps)
– Function (UV Reactor Design)
• Ultra-violet Transmittance (UVT)
A measurement of the ability of UV radiation to pass
through a fluid of a fixed path length (i.e., 1 cm)
Typically reported as: %T at 254 nm
UV in Normal Wastewater - Step 1
UV Dose (Collimated Beam)

UV Lamp

Sample
Stirrer
 UV in Normal Wastewater - Step 1
UV Dose (Dose-Response Curve)

0.0
Log Survival Microbes

-1.0

-2.0

-3.0

-4.0

-5.0

-6.0
0 20 40 60 80 100

UV Dose (I x t, C x t, mJ/cm2)
 UV in Normal Wastewater - Step 1
UV Dose (Absolute Target)
7.0 Fecal Coliform
6.0 200 FC Limit
5.0
Log N

4.0

3.0

2.0

1.0

0.0
0 10 20 30 40 50 60

UV Dose (mJ/cm 2)
 UV in Normal Wastewater - Step 1
UV Dose (Relative Target)
0.0 Rotavirus

-1.0 4 Log Limit

Log Reductions

-2.0 Dose Per Log Reduction

-3.0 1/Slope = 10 mJ/cm2/log

-4.0

-5.0

-6.0
0 10 20 30 40 50 60
UV Dose (mJ/cm2)
 UV in Normal Wastewater - Step 2
Amount of UV Equipment
100 100
75 Flow 75 Power

RED
RED

50 50
25 25
0 0
0 25 50 75 100 0 25 50 75 100
Operating Variable Operating Variable

100 100
Headloss UVT
Rel. HL

75 75

RED
50 50
25 25
0 0
0 25 50 75 100 0 25 50 75 100
Operating Variable Operating Variable

100 Lamp &

ost

75 Power Costs
 UV in Normal Wastewater - Step 2
Amount of UV Equipment

60% UVT
120
80% Power
100
UV Dose (mJ/cm2)

80

60

40

20

0
0 10 20 30 40
Flow (gpm/Lamp)
 UV in Low Quality Wastewater
What is the Impact on Disinfection?

• High Solids: How much dose?

• Low UVT: How much equipment?

• Fouling Potential: Cleaning system?

 Impact 2: Low UVT

100 100

60 60

36

1 cm 2 cm
 Impact 2: Low UVT

100 100

40 40

16

1 cm 2 cm
 Impact 2: Low UVT
Dark Zones Between Lamps

High UVT Low UVT

 UV for Low Quality Wastewater
Eliminate Dark Zones

• Use narrow lamp spacing (headloss

constraints)

• Use brighter lamps

• Mix flow between lamps

 Eliminate Dark Zones - Option 1
Narrow Spacing (Headloss)

Low UVT Low UVT

Wide Spacing Narrow Spacing
 Eliminate Dark Zones - Option 2
Use Brighter Lamps
• Low Pressure / Amalgam
– Relatively low intensity

• Medium Pressure
– Relatively high intensity
 Eliminate Dark Zones - Option 2
Use Brighter Lamps

Low UVT Low UVT

Normal Lamps High Power Lamps
Eliminate Dark Zones - Option 3
Mix Flow Between Lamps
Eliminate Dark Zones - Option 3
Mix Flow Between Lamps
Eliminate Dark Zones - Option 3
Mix Flow Between Lamps
Impact 3: Fouling and Cleaning
 Impact 3: Fouling and Cleaning

100
Relative Sleeve UVT (%)

Physical-Chemical
80

60

40

Physical
20
No Wipe
0
0 1000 2000 3000 4000 5000
Time (h)
 Section
Criteria
• Hydraulic properties of the reactor: Ideally, a UV
disinfection system should have a uniform flow
with enough axial motion (radial mixing) to
maximize exposure to UV radiation. The path that
an organism takes in the reactor determines the
amount of UV radiation it will be exposed to
before inactivation. A reactor must be designed to
eliminate short-circuiting and/or dead zones,
which can result in inefficient use of power and
reduced contact time.
 Selection Criteria - continued
• Intensity of the UV radiation: Factors affecting
the intensity are the age of the lamps, lamp
fouling, and the configuration and placement
of lamps in the reactor.
• Wastewater characteristics: These include the
flow rate, suspended and colloidal solids, initial
bacterial density, and other physical and
chemical parameters. Both the concentration
of TSS and the concentration of particle-
associated microorganisms determine how
much UV radiation ultimately reaches the
target organism. The higher these
concentrations, the lower the UV radiation
absorbed by the organisms.
 Factors Affecting UV Performance
Characteristics Effects on UV disinfection
Ammonia Minor effect, if any
Nitrite & nitrate Minor effect, if any
BOD Minor effect, if any. Humic and./or
unsaturated compounds
Hardness Affects solubility of metals that can
absorb UV lights
Humic materials, iron High absorbency of UV
pH Affects solubility of metals and
carbonates
TSS Absorbs UV radiation and shields
embedded bacteria
 Basic
Components
• UV dose (Fluence) (mJ/cm2) = UV intensity
(Watts/cm2) × Exposure duration (seconds);
between 15 and 50 mW-sec/cm2
• Type of lamp: Low Pressure (LP) ( ≤ 0.5 MGD);
LP High Output (LPHO) (most flow rates);
Medium Pressure (MP) (less lamps than LPHO);
determined based on life cycle analysis (LCA)
• Type of sensor: Primary means to monitor the
performance; lamps 6~16 months
 Basic Components -
continued
• UV transmittance: Secondary effluent – 50~65%; tertiary
effluent – 65~80%
• System configuration: Based on ease of lamp replacement
and cleaning, # of treatment trains, level of redundancy
required, hydraulic head loss, and available space

UV Transmission Scale:
20% - 50% 50% - 70% > 70%
• Primary Effluent • Secondary Effluent • Post-membrane
• Blended Effluent • Filtered Effluent • High-level reuse
• Lagoons • WW Reuse • Contaminant
• CSO, SSO • Fixed Film Effluent destruction
 UV
Dose
• US wastewater industry standard: 30 mW-sec/cm2
• US reuse standard: 50~100 mW-sec/cm2
• German drinking water standard: 40 mW-sec/cm2
 General
Relationships
• Intensity: Distance from the source ↑ 
intensity ↓
• Flow rate ↑  detention time ↓  dose
acquired by water ↓
• Turbidity inhibits ultraviolet disinfection only
when organisms are lodged within the particles
or when the particles themselves are UV-
absorbers. Otherwise turbidity is not a
hindrance to disinfection.
• Water depth ↑  water thickness ↑ 
attenuation of light ↑  dose reaching water
at bottom tube (negative quality) ↓
 Bulb
Types
LP/Low MP/Medium
Characteristic
Intensity intensity
Typical energy use 60 W 5,000W
% output at 253.7 nm 88% 44%
Ozone production None Possibly
Susceptibility to cooling Yes No
Benefits Efficiency Smaller, less
(lower energy maintenance, use
requirements) with poor quality
water
 Comparison of Disinfection
Processes
On-site
Chlora-
UV Cl2 gas NaOCl HOCl Ozone ClO2
mines
generation
Giadia Excel. Fair Fair Fair Excel. Excel. Poor
Crypto Excel. Poor Poor Poor Good Excel. Poor
Virus Excel. Good Good Good Excel. Very good Fair
Residual None Good Good Good None Fair Excel.
Organic DBPs None High High High Low Low Low
Brominated DBPs None High High High High None None
Safety risk Low High Low Low Medium Medium Low
Complexity Low Medium Medium Medium High High Medium
Capital cost Medium Medium Medium Medium High Medium Medium
O&M cost Medium Low Low Low High Medium Low
 System
Configuration
• Contact types: A series of mercury lamps, enclosed in
quart sleeves to decrease cooling effects of wastewater,
submerged in water
Contact
Type
 System Configuration - continued
• Non-contact type: UV lamps suspended outside a
transparent conduit, which carries wastewater to
be treated. Rare
• A ballast, or control box, engenders starting
voltage for the lamps and maintains continuous
current
• Flap gates, or weirs, control level of water being
treated
• Water runs perpendicular or parallel to lamps
• Mechanical cleaners, ultrasonic cleaners, other
self-cleaners
• Alarm systems that indicate minor and major
failures
 General
O&M
• Lamp changes: once every year or if light
transmission efficiency has decreased to 70%
• All surfaces between UV radiation and water
should be clean; chemical treatment – use of
citric acid or mild vinegar solutions.
• Quarts sleeves should be wiped down every 6
months with soapy solution; replace every 5 to
8 years
• No finger print left on glass
• Use of UV system and a pump on same
electrical line can mar the life of UV lamp and
ballast
JEFFERSON COUNTY, AL (200 FC/100 ml)
Valley Creek WWTP: 600 MGD, 65% UVT secondary effluent
Village Creek WWTP: 360 MGD, 50% UVT SSO effluent
 UV for Low Quality
Water
• Determine proper UV dose requirement (impact of
high solids)
– Collimated beam dose-response
• Ensure proper reactor design (impact of low UVT,
fouling)
– Technology & designs available
– Test/pilot reactor designs (disinfection,
headloss, cleaning)
• UV is working on low quality wastewater today:
The Future is Now
 Environmental Engineering

KINETIKA DESINFEKSI
 Environmental Engineering

Chick’s Law
• In 1908 Ms. Harriet Chick found that her disinfection
experiments could best be described by a first-order reaction,
for calculating contact time
 Environmental Engineering

Chick-Watson Low
• Relationship between disinfectant
concentration and contact time
 Environmental Engineering

Chick-Watson model
• Bentuk Integral

• Where
k’ = die-off constant
C =konsentrasi disinfektan
n = coeeficient of dillution

• Bentuk Liniear
 Environmental Engineering

Chick-Watson model
• Bentuk Liniear (Concentration vs time)

n = 1  konsentrasi dan waktu adalah penting

n > 1  konsentrasi lebih penting
n < 1  waktu lebih penting
 Environmental Engineering

The Van‘t Hoff-Arhenius Eq.

• The Van’t Hoff-Arrhenius equation can be used to
relate the effects of temperature on the disinfection
process
Ln (t1/t2)=[E(T2-T1)]/R.T2.T1
• Where
– t1,t2 = time required for the given kills, s
– E = activation energy, cal
– T1,T2 = temperature corresponding to t1 and t2, K
– R = gas constant
 Environmental Engineering

• Example
Determine the contact time needed for a disinfectant
to achieve a 99.99% kill for a pathogenic
microorganism that has a rate constant of 0.1 s-1
• Solution
Given rate of kill = 99.99%, k = 0.1 s-1
Find the contact time from Chick’s Law
t = -(1/k)*ln(N/No)
t = -(1/0.1 s-1)*ln(100-99.99/100)
t = 92.103 s
 Environmental Engineering

Menentukan konstanta Chick-Watson Model

• Data berikut adalah hasil tes pada reaktor batch

untuk kemampuan hidup E.coli (dalam persen)
setelah dikontakkan dengan klor. Tentukan konstanta
persamaan Chick-Watson model jika kematian
bakteri 99%!
waktu kontak, menit
klor tersedia
bebas mg/l
1 3 5 10 20
0.05 96 81 62 20 0.3
0.1 91 58 27 0.5 -
0.18 64 10 0.7 - -
 Environmental Engineering

• Plotting grafik -Ln(Nt/N0) vs waktu

klor - Ln (Nt/N0)
tersedia
waktu kontak, menit
bebas
mg/l
1 3 5 10 20
0.05 0.041 0.211 0.478 1.609 5.809
0.1 0.094 0.545 1.309 5.298 -
0.18 0.446 2.303 4.962 - -
 Environmental Engineering

7.000

6.000

5.000

4.000
-ln(Nt/No)

0.05
0.1
3.000 0.18
99% mati

2.000

1.000

0.000
0 2 4 6 8 10 12 14 16 18 20
time, min
 Environmental Engineering

• Waktu kematian bakteri 99% untuk tiap

konsentrasi (dari grafik)  - ln(Nt/N0)=4.61
• Mengubah C vs t dalam bentuk ln C vs ln t 
persamaan garis y=bx+a
C t ln C ln t
0.05 16.6 -2.99573 2.809403
0.1 8.6 -2.30259 2.151762
0.18 4.4 -1.7148 1.481605
 Environmental Engineering

ln t
0
0 1 2 3
-0.5

-1

-1.5
ln C -2

-2.5
y = -0.9644x - 0.2665
-3

-3.5
Series1 Linear (Series1)
 Environmental Engineering
• Persamaan garis y = -0.964x - 0.266

• Menetukan nilai n

- 1/n = -0.964
n = 1.03
• Menentukan nilai k’
Jadi persamaan
= -0.266
Chick-Watson Model
0.964 ln[1/k’(-ln 1/100)] = -0.266
ln[1/k’(-ln 1/100)] = -0.276
ln[1/k’ (4.61)] = -0.276 ln
Nt
1/k’(4.61) = exp (-0.276) N0

1/k’ = exp(-0.276)/4.61
1/k’ = 0.164
k’= 6.097 = -6.097 C1.03t
 Environmental Engineering

• Mencari nilai a dan b untuk persamaan garis

Y = bX + a
 Tugas.#4
•Tabel dibawah ini menunjukkan hasil tes pada reaktor batch
untuk kemampuan hidup bakteri Escherichia Coli (dalam
persen) setelah dikontakkan dengan klor. Tentukan konstanta
persamaan Chick-Watson model jika kematian bakteri 98%!

Waktu kontak, menit

Klor tersedia
bebas mg/l 1 3 5 10 20

0.06 95 80 61 19 0.2
0.10 90 57 26 0.4 -
0.18 63 9 0.6 - -