4/27/2020

Disinfection: Microbiology and Chemistry

J(Hans) van Leeuwen Disinfection 1

Introduction



Need for disinfection

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Alternative disinfectants

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Disinfection kinetics



Disinfectant chemistry

Disinfection 2

Topics of Discussion



Diseases borne by water



Comparison of disinfectants



The Ct concept

Disinfection 3

Some common water-borne diseases prevented by disinfection Bacterial Viral Protozoan

Typhoid fever Para-typhoid Bacterial diarrhea Cholera Legionnaires’ disease Hepatitis Rotavirus diarrhea Amoebiasis Giardiasis Crypto sporidiasis

Disinfection 4

The rate of disinfection

Like most biological processes, disinfection follows a first-order reaction with respect to the number of microbes of a certain species surviving as a function of time at a constant level of a disinfectant - dN/dt = kN, which is also known as Chick’s Law dN/N = - kdt (separating variables) ln N/N o = - kt or N = N o e -kt (from integration) Disinfection 5

The Ct Concept

In disinfection, the ability to inactivate microorganisms is a function of both disinfectant concentration and time.

Fractional removal, N/N o = C n t m This is generally simplified to N/N o = Ct Ct values have been determined for 99.99% virus and 99.9% Giardia removal Disinfection 6

Disinfection 7

Ozone Ct values

Microorganism Ct (mg min l -1 ) T ( o C) pH log reduction

E.coli

Legionella pneumophila Rotavirus

0,009 1,05 0,006-0,06 Giardia lamblia (cysts) 0,17 Giardia muris (cysts)

Cryptosporidium

parvum (oocysts) 0,27 5,39** 12 12 5 25 25 20 * * 6-7 7.2 7 * 4 log 2 log 2 log 2 log 2 log 2 log

Disinfection 8

Chlorination

Disinfection 9

Chlorinator Disinfection 10

Chlorine gas flow control Disinfection 11

Chlorine contact tank with baffles Disinfection 12

Gravity fed chlorine solution feeder Disinfection 13

Gravity fed chlorine solution feeder Disinfection 14

Disinfection 15

Disinfection 16

Disinfection 17

Ultraviolet Irradiation

Disinfection 18

Disinfection 19

Disinfection 20

Simple Solar Disinfection Disinfection 21

Solar Disinfection Disinfection 22

Ozonation

Disinfection 23

Disinfection 24

Disinfection 25

Disinfection 26

Disinfection 27

Disinfection 28

Biomass bulking control Disinfection 29

Disinfection 30

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Disinfection 32

Disinfection 33

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Disinfection Effect of ozonation on sludge settling 35

Disinfection 36

Disinfection 37

Selective oxidation

Disinfection 38

MeBl oxidation

Disinfection 39

Effect on protozoa

Disinfection 40

Ships’ Ballast Water Disinfection

41

Alien Invaders in our Coastal Waters - weirder and risky

Disinfection 42

Disinfection 43

Zebra Mussel Distribution

Disinfection 44

San Francisco Bay:

212 exotic species and 140 more suspected

Disinfection 45

Disinfection 46

Propeller exposed under

Disinfection

unballasted conditions

47

Into the Tonsina’s ballast tanks

Disinfection 48

View of ballast tanks from below

Disinfection 49

Disinfection

Interconnectivity of ballast tanks in sideview

50

INSIDE THE OZONE GENERATOR ON THE TONSINA Disinfection 51

Disinfection

Side-stream ozone injection

52

Ozone Reactions in Seawater

1.

2.

3.

4.

O 3 + Br OBr + O 3 OBr BrO 2 + O 3 + O 3

   

OBr + O 2 2O 2 BrO 2 BrO 3 + Br + O 2 5.

H + + OBr -



HOBr HOBr main contribution to total residual oxidant (TRO)

Disinfection 53

TRO Decay with time

Unfiltered Puget Sound TRO Decrease

0.00

-0.40

-0.80

-1.20

TRO 4.0

TRO 3.0

TRO 2.0

-1.60

-2.00

0 50 100

Time (h)

150 200

Decrease in TRO (mg/L Br 2 ) in unfiltered Puget Sound seawater over time, starting at 2.0, 3.0 and 4.0 mg/L Br 2 . Data are the mean + SD of four replicates.

Disinfection 55

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Flowdiagram with Cyclones & UV .

UV Contro l Panel

11.06.99

Halvor Nilsen To/from ballast tanks.

Disinfection 1 60

Disinfection 61