DISINFECTION

THE ENEMY:• BACTERIA

– Cholera, typhoid

• VIRUSES– Polio, Hepatitis A

• PROTOZOA– Giardia– Cryptosporidium

BATTLE TACTICS

• Clint Eastwood approach:“Kill ‘em all and let God sort

them out”

STERILIZATION:

KILLS ALL LIVING ORGANISMS IN THE WATER, HARMFUL AND HARMLESS

• Guided Missile approach

Selective targeting of the most dangerous

DISINFECTION:

KILLS ALL PATHOGENS IN THE WATER; SOME HARMLESS BACTERIA MAY SURVIVE

MOST COMMON RESULT OF AN ATTACK BY ENEMY FORCES

GASTROINTESTINAL ILLNESS:

AKA VOMITING, DIARRHEA, ‘STOMACH FLU’……

SOME HISTORY

• In the mid 1800’s, an epidemic of cholera in London killed 90% of the citizens it infected.Oddly enough, they all drank water from the same well.

No one believed the doctor who said the water was causing the illness – so he took the pump handle off at the well. There were no further cases of cholera in the area – other scientists began to take notice.

SOME HISTORY

• In 1854 when the Louisville Water Company was incorporated, Louisville was known as “The Graveyard of the West” because of the terrible yearly epidemics of cholera in the area.

By the 1870’s, continuous chlorination of Louisville’s drinking water had eliminated cholera in the area, and the US Dept of the Army pronounced Louisville the most healthful place to build a new Army post, Camp Zachary Taylor.

So, what modern-day weapons do we have to fight this battle?

• Emerging high-tech weaponry:– OZONE , ULTRAVIOLET

• The old reliable stand-by:– CHLORINE (bleach, gas, HTH, chloramine, ClO2)

• Primitive, last-resort defense:– BOIL WATER NOTICE

(aka “do it yourself” disinfection)

Survey says…..

• How many of you are working in water systems that use:

• Liquid Bleach (Sodium Hypochlorite)• Chlorine Gas• Calcium Hypochlorite (liquid solution)• Chloramines (chlorine + ammonia)• Chlorine Dioxide

?

CHLORINE GAS

ADVANTAGES

• Most effective form of chlorine, 100% pure Cl

• Cheaper than other forms of chlorine

DISADVANTAGES

• Wants to escape out of pressurized cylinders

• Can be lethal in high concentrations

• Corrosive when combined with moisture

Properties of Chlorine Gas

Liquid &Gas in Cylinder: Liquid on the bottom*

* Why is that important?

A small amount of liquid chlorineWill expand to a vapor cloud 460 times its original size

How to find a chlorine leak…

• WRONG WAY • RIGHT WAY

Ammoniasolution

WhiteSmoke ifChlorine isPresent !

Chlorine Cylinders

• Like the more common propane cylinders, a chlorine cylinder will ‘freeze up’ on a hot day if gas is withdrawn too rapidly.

• Cylinders are manufactured with a fusible metal plug that melts at a lower temperature than the metal the cylinder is made of – creating a vent / small leak when the cylinder gets too hot (instead of a cylinder explosion).

Hypochlorites

Calcium Hypochlorite

• 65-70% strength

• Powder/tablet/granules

Sodium Hypochlorite

• 5 – 15% strength

• Raises pH of water

Gas Chlorine vs HypochloritesGas chlorine:

• 100% pure chlorine 95 % water

5% chlorine

Sodium hypochlorite:

Calcium hypochlorite:

35% filler

65% chlorine

100%

So, how much are we feeding?

• Feed 10 pounds of chlorine gas……..

Get 10 pounds of chlorine!

• Feed 10 pounds of 10% bleach……

Get 1 pound (10% of it) of chlorine…..

And 9 pounds of water!

All of these are compounds that release chlorine

• Chlorine Gas• Sodium Hypochlorite• Calcium Hypochlorite

The germ-killing power of these disinfectants comes from CHLORINE

Chlorine Fights Pathogens

Lots of chlorine (100%) in chlorine gas

Less chlorine (65-70%)

in calcium hypochlorite (HTH)

Very little chlorine (5 -15%)

in sodium hypochlorite (bleach)

When some of chlorine’s power is tied up through bonding with other chemicals we call that “Combined Chlorine”

• For example, some systems use CHLORAMINES: Chlorine bonded with ammonia

NOW CHLORINE HAS TO FIGHT GERMS ONE-HANDED!

So when is chlorine a stronger disinfectant:When it is by itself (FREE CHLORINE)?

Or when it is COMBINED with another chemical?

• COMBINED CHLORINE RESIDUAL

• Chlorine is fighting germs “with one hand tied behind his back”!

So remember:

• FREE CHLORINE RESIDUAL

• Two-fisted germ fighting power!

CHLORINE HAS HISTORICALLY BEEN OUR MOST EFFECTIVE WEAPON AGAINST PATHOGENS

HOW EFFECTIVE IS IT?

Appropriate doses of chlorine with properly operated conventional treatment will kill

99.9% of all bacteria and protozoa

99.99% of all viruses

3 LOG removal = 99.9% = 3 ‘nines’

4 LOG removal = 99.99% = 4 ‘nines’

How do I know what the appropriate dose should be?

C T CALCULATION

C O

NC

EN

TR

AT

IO

N

T IM

E

Other important factors:

Temperature

pH

Point of Application

Dose and Demand

• To understand the impact of each of these factors, we have to understand HOW DISINFECTION WORKS.

So stay tuned for the next presentation!

Temperature

pH

Point of Application

Dose and Demand