Chapter 11: Water Treatment

_____ is commonly used in the improvement of water quality.

aeration

Municipalities aerate drinking water that is drawn from underground aquifers to remove the ____________, volatile organic compounds.

foul-smelling H2S and organosulfur compounds,

Aeration of drinking water also results in reactions that produce _____ from the most easily oxidized organic material.

CO2

If necessary for reasons of odor, taste, or health, most of the remaining organics can be removed by subsequently ___________, although this process is relatively expensive

passing the water over activated carbon

What is aeration?

the process of circulating, mixing, or dissolving air into a liquid or substance.

What are 4 advantages of Aeration of water?

1) removes foul-smelling H2S and organosulfur compounds

2) produces CO2

3) remaining organics can be removed

4) increases oxygen content which oxidizes water-soluble Fe²⁺ to Fe³⁺

After aeration, ______ in the water are removed.

colloidal particles

in water purification, if the water is excessively hard, ____ and ____ are removed.

calcium, magnesium

what are the 4 key steps in water purification?

1) Aeration

2) Settling and precipitation (use Al or Fe salt to precipitate colloids)

3) Hardness removal

4) Disinfection

If the water comes from wells in areas having limestone bedrock, it will _____.

contain significant levels of Ca2+ and Mg2+ ions

Calcium can be removed from water by?

the addition of phosphate ions

How are calcium ions removed form hard water?

Ca2+ is removed by precipitation and filtering of the insoluble salt CaCO3. The carbonate ion is either added asCaCO3 or if sufficient HCO3^- is naturally present in the water. The hydroxide ion is added in order to convert dissolved bicarbonate ions to carbonate

How are magnesium ions removed from hard water?

After removal by filtration of CaCO3 and Mg(OH)₂, the pH of the water is readjusted to near-neutrality by bubbling carbon dioxide into it.

Magnesium ions precipitate as insoluble _____, when the water is made sufficiently alkaline when the OH ion content is increased.

Magnesium hydroxide, Mg(OH)₂

In terms of causing sickness and death, ____ contaminants of water are almost always much more important than ____ ones.

biological, chemical

What is disinfection?

the elimination of microorganisms that can cause illness.

Many microorganisms in raw water are present as a result of contamination by human and animal ____.

feces

What are the three key microorganisms eliminated from water?

1) bacteria like salmonella and E. coli

2) viruses

3) protozoans

When filtering raw water that is obtained from rivers, likes, or streams contains a multitude of ____, some of which consist of or contain microorganisms.

tiny particles

When filtering water, any of the small suspended particles are composed of ___, and resulted from the erosion of ___ and ___, whether by _____ or due to plowing of land for ____, ___, or _____.

clay, soil, rock, natural forces, agriculture mining, commercial housing development

The suspended particles increase the water’s ____, and thereby reduce the ability of light to penetrate deeply enough to support photosynthesis.

turbidity

the suspended particles increase the water’s turbidity and thereby reduces the ability of light to ____.

penetrate deeply enough to support photosynthesis

The larger of the particles suspended in water are often removed from the water by simply filtering it by?

passing it through a bed of sand

The sand retains suspended solids of all types, including microorganisms, down to about ___ micrometers in size.

10

In the removal of colloidal particles by precipitation, most municipalities allow raw water to settle, since this permits large particles to ____ or to be ____.

settle out, readily separated

during the removal of colloidal particles by precipitation, much of the insoluble matter, which originates from rocks and soil, and from the ____ and ____ of water-based plants and animals, will not precipitate spontaneously since it is suspended in the water in the form of ____.

disintegration, decomposition, colloidal particles.

colloidal particles must be removed from drinking water for both ____ and ___ reasons.

aesthetic, health-safety

What are colloidal particles?

particles that have diameters ranging from 0.001 to 1 micrometer and consist of groups of molecules or ions that are weakly bound together.

How are colloidal particles removed?

- a small amount of either Fe₂(SO₄)₂, or Al₂(SO₄)₂ is dissolved in the water.

- The water is made neutral or alkaline in pH 7 and up.

Both the Fe³⁺ and Al³⁺ ions produced from the salts form gelatinous hydroxides that physically incorporate the colloidal particles and form a removable precipitate.

water can be purified of most contaminant ions, molecules, and small particles including viruses and bacteria by ?

passing or forcing it through a membrane in which the individual holes, called pores, are of uniform and microscopic size.

Explain the reverse osmosis process.

- Water is forced under high pressure to pass through a semipermeable membrane.

- that membrane is composed of an organic polymeric material such as cellulose acetate or triacetate or a polyamide.

- Since only water can pass efficiently through the pores, the liquid on the other side of the membrane is purified water.

Water aeration removes what type od dissolved gases?

a) H₂S

b) CO₂

c) VOC

d) CH₄

a,c

How do you remove odor and improve the taste of water?

a) producing CO₂

b) passing over activated carbon

c) removing iron

d) removing VOC

b

How are calcium ions be removed from wastewater?

a) adding phosphate

b) adding carbonate

c) adding OH-

d) aeration

a,b,c

How are magnesium ions removed from wastewater?

a) adding phosphate

b) adding carbonate

c) adding OH-

d) aeration

c

what are the main microorganisms in wastewater

a) viruses

b) protozoans

c) bacteria

d) fungus

a,b,c

what substances are removed by filtering wastewater?

a) suspended particles

b) Ca²⁺ ions

c) bacteria

d) colloidal particles

a

What is the range of size of colloidal particles?

a) 2-10 micrometers

b) 5-15 micrometers

c) 0.001-1 micrometer(s)

d) 10-20 micrometers

c

Colloidal particles are removed by..

a) adding phosphate

b) adding iron (III) sulfate

c) adding alum

d) aeration

b,c

reverse osmosis is used to removed?

a) salts

b) Ca and Mg

c) bacteria

d) viruses

a

The most common water purification agent used in North America is
_____.

hypochlorous acid, HOCl

HOCl is a neutral, covalent compound that kills_______

microorganisms as it passes through their cell membranes

at the molecular level, HOCl is used to ______

deactivate essential enzymes by oxidizing some of their side chains that involve sulfur

is disinfection by chlorinate relatively expensive or inexpensive?

inexpensive

chlorinate is more common that ozonation in North America because generally _____.

the raw water is less polluted.

HOCl is not stable in _____ so it cannot be stored.

concentrated form

For large-scale installations, HOCl is generated by dissolving ______ in water. Then, a very dilute aqueous solution of chlorine in water contains very little aqueous Cl₂ itself. What does this reaction look like?

molecular chlorine gas in water

in small-scale applications of chlorination, as in swimming pools, handling cylinders of Cl₂ is _____ and ____.

inconvenient, dangerous

HOCl is generated from _____, or is supplied as an aqueous solution of _____.

the salt calcium hypochlorite, Ca(OCl)₂, sodium hypochlorite, NaOCl.

in water, an ____ reaction occurs to convert most of the OCl^- in the substances above to HOCl.

acid-base