Exam 2 ~ Drinking Water

Where does our drinking water come from (US)?

Public (84%) and Private (16%) systems

Which system for drinking water is more safe

public because it is monitored

2 key things to avoid waterborne disease

Protecting water source from fecal contamination + treating water

4 main types of pathogens

Viruses, Bacteria, Protozoa, and Helminths

Untreated water is a

primary vector for disease

Waterborne disease can cause

1. Pneumonia and 2. Diarrhea

5 main objectives of Water Treatment

1. Remove/kill pathogens 2. Remove solids (piping issues) 3. Remove taste/odor 4. Adjust hardness and pH 5. Add beneficial substances (fluoride)

Hardness is

the sum of calcium and magnesium ions in water

Why do we want to remove hardness in water

High calcium build-up destroys longevity of pipes

Why is protecting a clean water source important (3 things)

1. Increases quality of water 2. Protection of health 3. Lowers treatment costs

Preliminary Treatment consists of

removing large particles via bar screens and primary settling

Coagulation

neutralizing particle charges

Flocculation

sticking particles together

Softening is the act of

removing Ca and Mg hardness

Sedimentation is

removing flocculated particles

Filtration is

removing smaller particles

Disinfection’s primary goal is the

killing of harmful microbes

Common flocculation agents

Al₂(SO₄)₃ ~ “Alum”

What does “Alum” do

positively charged Al³⁺ neutralize particles negative surface charge

What law does Flocculation follow

Stokes Law ~ particles grow and settle faster due to gravity

Filtration agents, smallest filtration to biggest

Charcoal, sand, gravel

Disinfection’s secondary goal is to

maintain a disinfectant residual in the distribution system

Common disinfectants

Chlorine, Ozone, UV light

Chlorine dissolved in water will form

Hypochlorous acid (HOCl)

Depending on the pH, hypochlorous acid dissociates into what

H and OCl

Viscosity

Thickness of water

viscosity rules

cold water is more thick, warm water is less thick

Settling velocity increases if

Viscosity decreases and diameter of particle increases

most important factor in determining settling velocity (stokes law)

diameter of particle

Two types of softening

Lime Softening and Ion exchange softening

Lime Softening

Bind with calcium of carbonate and settle particles at treatment plant rather than in homes

Lime Softening Purposes

1. Lessen scale formation 2. Reduce detergent needed 3. Reduce soap scum

Ion Exchange Softening

Used in homes rather than industrial purposes

What does Ion Exchange Softening consist of?

exchanges 2 sodium for every calcium (adds Na to water)

Chlorination Byproducts

Trihalomethanes (CHCl₃)

What are Trihalomethanes (THMs)

Byproducts formed when chlorine reacts with organic matter in water

Trihalomethanes are a

carcinogen

Disinfection key rule is

Chlorine Concentration x Contact Time

The Distribution System is

the very last step in drinking water treatment

A disadvantage of UV disinfection that can make it ineffective is when

water has high turbidity

Safe Drinking Water Act (1974) outlines

1. How you have to sample 2. What you have to sample for 3. MCL (maximum contaminant level) 4. MCGL (maximum contaminant level goal)

After treatment, the distribution system pumps water to a

water tower

Gravity Flow

can carry water to customers