Disinfection

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Disinfection

MK Satuan Proses

Environmental Engineering

Materi

1. Purpose of disinfection2. Disinfection methods 3. Mechanisms of Disinfectant4. Disinfection kinetics


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Purpose of disinfection

• The killing of pathogenic organisms with the objective of preventing the spread of water-borne diseases.

• This process is function– Type and concentration microorganism– Type and concentration disinfectant– Presence of oxidant-consuming compounds– Temperature– Dose of chemical– Contact time– pH


Disinfection Method

Physical methods• Heat treatment• Exposure to UV-rays• Exposure to metal ions

(silver, copper)

Chemical Methods• Chlorine gas• Chlorinated compounds

(chlorine dioxide)• Phenol• Phenolic compounds• Various alkalies and

acids• Ozone


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Desinfection: Clorine, UV, and Ozone

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Disinfection with Chlorine

Golongan Senyawa Klorine

1. Chlorine, Cl22. Sodium hypochlorite, NaOCl3. Calcium Hypochlorite, Ca(Ocl)24. Chlorine dioxide, ClO2

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Mechanisms of Disinfectant

1. Damage to the cell wall– Inhibit the synthesis of the bacterial cell wall– Agent : penicillin

2. Alteration of cell permeability– Allow vital nutrients, such as nitrogen and

phosphorus, to escape– Agent: phenolic compounds and detergents


Mechanisms of Disinfectant

3. Alteration of the colloidal nature of the protoplasm.– Heat will coagulate the cell protein and acids or bases

will denature proteins, producing a lethal effect.– Agent : Heat, radiation, and highly acidic or alkaline

agent4. Inhibition of enzyme activity

– Alter the chemical arrangement of enzymes and deactivate the enzymes.

– Agents: Oxidizing agents, such as chlorine


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Chlorine Chemistry

• When chlorine is added to wastewater (NH3 & Organic compounds) , part of it reacts to produce

• First Parts– Hypochlorous acid (HOCl) (free chlorine residual)

• Cl2 + H2O ⇌ HOCl + HCl

• Second Parts– Hypochlorite ion (OCl-) (free chlorine residual)

• HOCl⇌ OCl- + H+

– Disinfection power of HOCl is about 40-80 times greater than that of OCl-


Chlorine Chemistry

• Third Part– reaction with ammonia to form chloroamines (mono-, di-

, and trichloroamines) (combined chlorine residual)• NH3 + HOCl NH2Cl (monochloroamines) + H2O• NH2Cl + HOCl NHCl2 (dichloroamine) + H2O• NHCl2 + HOCl NCl3 (trichloroamine) + H2O

– Comparing with free chlorine residual, combined chlorine residual, due to chloroamines, has a lower disinfecting property


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Chlorine Chemistry

• Fourth part– oxidizing inorganic matter (e.g hydrogen

sulfide, iron, manganase)

• Fifth part– Reaction with organic compounds to form trihalomethanes

(THMs) and other chlorinated organics


Breakpoint Chlorination

• When chlorine is added to water– It is consumed in oxidizing wide variety

compounds present in water.• No chlorine residual can be measured until the chlorine

demand is satisfied.

– Then chlorine reacts with ammonia producing combined chlorine residual.

• Combined chlorine residual increases with additional dosage until a maximum combined chlorine residual is reached


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Breakpoint Chlorination

– Further addition of chlorine causes a decrease in combined chlorine residual.

• At this point the chloroamines are oxidized to oxides of nitrogen or other gases.

– After breakpoint chlorination is reached, free chlorine residual develops at the same rate as applied dosage



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KINETIKA DESINFEKSI


Chick’s Law

• In 1908 Ms. Harriet Chick found that her disinfection experiments could best be described by a first-order reaction:


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Chick’s LawEnvironmental Engineering

• Relationship between disinfectant concentration and contact time

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


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• ExampleDetermine 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

• SolutionGiven 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



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 konstantapersamaan Chick-Watson model jika kematianbakteri 99%!

klor tersediabebas mg/l

waktu kontak, menit

1 3 5 10 200.05 96 81 62 20 0.3

0.1 91 58 27 0.5 -0.18 64 10 0.7 - -

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Chick-Watson model

• Bentuk Integral

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

• Bentuk Liniear


Chick-Watson model

• Bentuk Liniear (Concentration vs time)

n = 1 konsentrasi dan waktu adalah pentingn > 1 konsentrasi lebih pentingn < 1 waktu lebih penting


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• Plotting grafik -Ln(Nt/N0) vs waktu

klortersediabebasmg/l

- Ln (Nt/N0)

waktu kontak, menit

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 - -


0.000

1.000

2.000

3.000

4.000

5.000

6.000

7.000

0 2 4 6 8 10 12 14 16 18 20

-ln(N

t/N

o)

time, min

0.05

0.1

0.18

99% mati


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• Waktu kematian bakteri 99% untuk tiapkonsentrasi (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


y = -0.964x - 0.266

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

00 1 2 3

ln C

ln t

Series1 Linear (Series1)


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• Persamaan garis y = -0.964x - 0.266

• Menetukan nilai n

- 1/n = -0.964n = 1.03

• Menentukan nilai k’

= -0.266

0.964 ln[1/k’(-ln 1/100)] = -0.266ln[1/k’(-ln 1/100)] = -0.276

ln[1/k’ (4.61)] = -0.2761/k’(4.61) = exp (-0.276)

1/k’ = exp(-0.276)/4.611/k’ = 0.164

k’= 6.097


t

0

Nln

N

Jadi persamaan Chick-Watson Model

= -6.097 C1.03t


• Mencari nilai a dan b untuk persamaan garisY = bX + a

Disinfection

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