ÇMB 730 PHYSICAL AND CHEMICAL PROCESSES OF WATER POLLUTION CONTROL

ÇMB 730ÇMB 730PHYSICAL AND CHEMICAL PROCESSES PHYSICAL AND CHEMICAL PROCESSES

OF WATER POLLUTION CONTROLOF WATER POLLUTION CONTROL

Prof. Dr. Mirat Gürol

DISINFECTIONDISINFECTION

ÇMB 730 - PHYSICAL AND CHEMICAL PROCESSES OF WATER POLLUTION CONTROL


DISINFECTION Purpose: Destruction of pathogenic microorganisms. The organisms of interest causing water-borne diseases: 1. Bacteria (Affect mostly gastrointestinal tract) Salmonella typhosa : Typhoid fever S. paratyphii : Paratyphoid Shigella : Bacillary dysentery Vibrio comma : Cholera Legionella : Legionnaires’ disease 2. Virus (Affect nervous system) Poliovirus : Polio Echo virus : Meningitis Coxsackie virus : Hepatitis, meningitis, paralysis Hepatitis : Infectious hepatitis



3. Protozoa (Generally milder gastrointestinal disorders) Endamoeba histolytica : Amebiasis (dysentery) Giardia lamblia : Giardiasis Cryptosporidium : Diarrhea 4. Parasitic Worms Schictosomiasis, Ascaris (round worm), Taenia saginata (tape worm) Outbreaks of water-born diseases due to

insufficient treatment

accidents

insufficient training of operators



Indicator organisms: Used to estimate the probability of the presence of pathogenic organisms in water. Desirable characteristics of indicator organisms:

1. Present in large numbers (1011-1012 coliforms per gallon of domestic sewage)

2. Associated with pathogens (coliform and pathogens both live in the intestines of warm-blooded animals)

3. Easy to identify and count

4. More resistant than pathogenic organisms to environmental conditions outside the animal body

Example:

Coliform : Ferment lactose with gas production within 48 hours at 35˚C.

E. Coli : Intestinal origin (Repeate test at 44˚C to differentiate).

Aerobacter : Soil origin.



USEPA Primary Drinking Water Regulations for Microbiological Parameters

MCLG (noneforceable goal)

MCL* (enforceable regulation)

Total coliform zero P/A test **

Turbidity none Filtration & disinfaction

Giardia zero Filtration & disinfection (99.9%)

Viruses zero Filtration & disinfection (99.99%)

Legionella zero Filtration & disinfaction

* 1984 Surface Water Treatment Rule ** P/A Test: Small systems cannot have more than 1 coliform-positive sample per month; for large systems, not more than 5% of total samples per month may be coliform-positive

Water Pollution Control Act

E. Coli in effluents (1972-1976): Mandatory National Discharge Standard of 200 per 100 ml.

Since 1976, states free to establish requirements: Generally < 200 per 100 mL of E. Coli < 400 per 100 mL over any 7 day period



Modes of Disinfection 1. Chemical means:

- Halogens (chlorine, bromine, iodine) - Ozone, ClO2, H2O2, KMnO4 - Heavy metals (e.g. silver, copper)

Halogens and ozone are believed to inhibit the enzyme activity by reacting with enzymes. Heavy metals destroy the cell walls, ClO2 causes specific poisoning. 2. Physical means: - Heat - Light (UV, γ) These usually change the nature of the protoplasm. - Coagulation, sediment, filtration (not designed primarily for disinfection) Disinfection Kinetics

Kinetics expressions are empirical. They are different for different situations. Chick’s Law (1908) – most widely used.

kNdt

dN N: number of organisms k: susceptibility coefficient



Disinfection Kinetics Kinetics expressions are empirical. They are different for different situations. Chick’s Law (1908) – most widely used.

kNdt

dN N: number of organisms k: susceptibility coefficient

The expression holds for ideal conditions:

- All the cells of a single species are equally susceptible to the disinfectant. - Cells and the disinfectant are uniformly dispersed in water - Concentration of disinfectant and the water matrix remain constant throughout the

period of contact

k 0N

dN

t



The rate of kill way increase or decrease with time.

t

0N

dNIf rate increases: a) Competition reactions might be slowing down the

disinfection rate during early stages, or b) Disinfection might be a two-step process:

- diffuses of disinfectant thru the cell membrane of the organisms, and

- specific reaction inside the cells (poisoning). Diffusion step might be slower than poisoning step, or a certain amount of a accumulation of disinfectant inside the cell might be needed for killing. (Ex. UV irradiation)

Decrease in rate due to;

- variation in resistance of different cells within the same culture

- a decline in the conc. of disinfactant

t

0N

dN



Other rate expressions:

mktN

N

0

ln

mktN

N

0

(m<1; retardation; m>1 autocatalytic)

2

0

ln ktN

N (chlorination)

3

0

)23.01( CtN

N (chloramines for primary effluent, coliform)

Disinfectant Concentration

Cn ∙ t = constant = K (for a specified percent kill)

C = concentration of disinfectant

t = contact time

n = a constant (coefficient of dilution)



n = 1 ; C and t are equally effective

n > 1 ; C is more effective

n < 1 ; t is more effective

K = 0.24 for E. Coli with chlorine

K = 1.20 for poliovirus with chlorine

In Chick’s Law, ktN

N

0

ln (concentration dependent)

Chick-Watson Law, tCkN

N n0

0

ln

If n = 1, Ct

N

N

k 00

ln

k

: extent of destruction of microorganisms per unit conc. of the disinfectant per unit time



For 99% kill at 5˚C, Carell Morris reported the following for k0 (L/mg∙min):

Disinfectant E. Coli Anaerobic Cyst Viruses Spores

O3 500 0.5 5 2

HOCl as Cl2 20 0.05 1.0 < 0.05

OCl- as Cl2 0.2 0.005 < 0.02 < 0.0005

NH2Cl as Cl2 0.1 0.02 0.005 0.001

Ref: Disinfection Ed. By J.D: Jhonson, 1975, Ann Arbor Scteuce. Effect of Temperature

21

12

2

1 )(ln

TRT

TTE

k

k a Arrhenius Eqn.

or, 2)10( Qk

k

T

CT rate doubles for every 10˚C increase

Effect of pH

Bacteria have surface charges similar to inorganic colloids due to the hydrolysis of amino acids. Therefore OCl- is less effective than HOCl, i.e., low pH in better. For O3, low pH, for ClO2 high pH is better.







Table 1 Comparison of virus inactivation by free residual chlorine at pH 6.0 and 10.0 and 5.0˚C ± 0.2˚C *

Time elapsed for 99% inactivation (min)

Virus Strain pH 6.0 pH 10.0 Ratio **

Coxsakie A9 (Griggs) 0.3 1.5 5

Echo 1 (Farouk) 0.5 96.0 192

Polio 2 (Lansing) 1.2 64.0 53

Echo 5 (Noyce) 1.3 27.0 21

Polio 1 (Mahoney) 2.1 21.0 10

Coxsakie B5 (Faulkner) 3.4 66.0 19

* After Engelbrecht et.al. ** Time required at pH 10.0 / Time required at pH 6.0 Table 2 Summary of disinfectant characteristics relating to biological efficiency

Rating *

Disinfectant Biological Efficiency

Stability

pH Effects on Efficiency

(pH range 6-9)

Ozone 1 4 little effect

Chlorine dioxide ** 2 3 pH increase is beneficial

Free chlorine ** 3 2 pH increase is detrimental

Chloramines 4 1 little effect

* Best, 4 and worst 1 ** Rating influenced by pH





1

10

0.1C

lO2

– m

g/L

10 100 1000







Free Chlorine Species

Cl2 (aq) + 2e- = Cl- E0 = 1.36 V

HOCl + 2e- = Cl- E0 = 1.49 V

OCl- + 2e- = Cl- E0 = 0.90 V

Complete Reactions

Cl2 (aq) + 2e- Cl-

HOCl + 2e- + H+ Cl- + ½ H2O

OCl- + 2e- + 2H+ Cl- + ½ H2O

- oxidation of water -

2H2O O2 + 4H+ + 4e-

- reduction of water -

2H2O + 4e- H2 + 2OH-





Decomposition of ozone in water:

2 / O3 + H2O + 2e- → O2 + OH-

2H2O → 4H+ + O2 + 4e-

2O3 + 2H2O + 4e- → 2O2 + 4OH-

2H2O → 4H+ + O2 + 4e-

4OH- + 4H+ 4H2O

Net Reaction: 2O3 3O2

HO2-, O3

-, HO2∙, OH∙

























Breakpoint Chlorination

Chlorination to satisfy all the chlorine demand in order to obtain free chlorine.

1) inorganic chlorine demand

2) organic chlorine demand

3) ammonia reaction to form chloramines (combined chlorine)

4) oxidation of chloramines to N2, NO, NO3-





Free chlorine = HOCl, OCl-, Cl2

Combined chlorine = Chloramines























2ClO2 + H2O ClO3- + ClO2

- + 2H+ - No THM formation but some TOX when organics,

e.g., phenols → chlorophenol, chloroquinones

olefins → epoxide

disprop.



Distribution of species of chlorine, bromine and iodine vs. pH

ÇMB 730 PHYSICAL AND CHEMICAL PROCESSES OF WATER POLLUTION CONTROL

Documents

chemical means

physical means

surface water treatment

pathogens coliform

meningitiscoxsackie

polioecho virus

coliformpositive sample

large systems