Part Three Softening

Which 5 items should an operator check when troubleshooting the operation of the backwash stage of an ion exchange softener?

1. Is there sufficient time to complete the backwash stage. 2. Are the flow rates high enough to remove trapped turbidity particles. 3. Make sure the flow rates are not excessive to prevent washing resin from the unit. 4. Check the condition of the resin by visually inspecting the top layer of the bed. 5. Watch the timer to make sure the unit is washed for the required length of time.

How many gallons of water with a hardness of 8 grains per gallon may be treated with an ion exchange softener with an exchange capacity of 8,000 kilograins?

1.00 M Gal

Some textbooks define hard water as a water with a hardness of more than?

100 mg/L as calcium carbonate

How many hours will an ion exchange softening unit operate when treating an average flow of 300 GPM? The unit is capable of softening 400,000 gallons of water before requiring regeneration.

22.2 hours

How many hours will an ion exchange softening unit operate when treating an average flow of 250 GPM? The unit is capable of softening 400,000 gallons of water before requiring regeneration.

26.7 hours

Alkalinity is a measure of how much acid must be added to a liquid to lower the pH to?

4.5

Which items are limitations of the lime-soda softening process?

A high degree of operator control must be exercised for maximum efficiency. Color removal may be complicated by the softening process due to high pH levels. Inability to remove all hardness. Large quantities of sludge are created that must be handled and disposed of in an acceptable manner.

The way an operator can prevent a full scale problem is to recognize what?

A minor problem and fix it

What can solve many treatment plant problems or avoid them to begin with?

Adequate recordkeeping systems

An operator can find the optimum dosages that give the desired softened water results by running which tests?

Alkalinity, Hardness, pH

When using the lime-soda process to soften water, which items are considerations in treated highly colored waters?

Alum is a good coagulant to treat highly colored waters. Ozone, permanganate, and chlorine may be tried to oxidize color. These waters must be coagulated for color removal at low pH values.

Most of the ion exchange water softening equipment on the market today is manual or automatic in operation?

Automatic

What are the common stages of operation for an ion exchange softener? 4 stages

Backwash, Brine, Rinse, Service

Noncarbonate hardness is remove by what two things?

Both Lime and Soda

Which factors influence the procedures used to operate an ion exchange unit and the efficiency of the softening process? 5 factors

Brine contact time, Characteristics of the ion exchange resin, Quality of the source water, Rate of flow applied to the softener, Salt dosage during regeneration

How can an operator prevent scale formation on the filter sand, distribution mains, and household plumbing?

By converting the excess caustic and unprecipitated carbonate to soluble forms

During the brine stage of an ion exchange softener, how is full contact between the brine solution and the resin provided?

By displacing all water from the resin

How can an operator determine if an ion exchange softener is operating properly during the service stage?

By running hardness tests on the softener effluent to ensure the water has a hardness of zero

Alkalinity is the?

Capacity of water or waste-water to neutralize acids. It is not the same as pH.

The application of Lime for the removal of carbonate hardness also removes what?

Carbon Dioxide

When pH is above 8.3 there is not what present?

Carbon Dioxide

When the alkalinity (expressed as calcium carbonate equivalent) is greater than the total hardness, all the hardness is in the what?

Carbonate form

In addition to the removal of hardness from water, some of the benefits of softening include which items? Name five.

Control of corrosion when proper stabilization of the water is achieved. Disinfection due to high pH values when using lime. Removal of iron and manganese. Removal of radioactivity. Sometimes a reduction in tastes and odors.

Addition of polyphosphate to softened water can prevent the formation of scale on filter media and in distribution system mains but it does not prevent what?

Corrosion

A negative Langelier index indicates the water is?

Corrosive

What are the two undesirable characteristics of the by-products of the waste discharge from softeners?

Corrosive to material they contact and possess varying toxic levels in relationship to the environment.

Why is excessive hardness in water undesirable? Name five problems it causes

Damage in some industrial processes. Deposition of scale in boilers. Formation of soap curds. Increased use of soap. Objectionable tastes.

When the water becomes supersaturate with calcium carbonate and magnesium hydroxide what occurs?

Deposition of precipitates in filters and pipelines

Aluminum and iron salts are acidic and react with the alkalinity in water to cause a demand the same way that what will?

Free Carbon Dioxide

Name three factors that influence the consumers' attitudes toward the hardness of their water?

Hardness levels in source waters. Local conditions. Local usage.

When ion exchange softeners remove iron in the ferrous (soluble) form, what problems could result?

If the resin becomes iron coated, the efficiency of the softener will be reduced greatly. The resin bed will become plugged or clogged. The resin bed will develop an orange or rusty appearance.

What is stable water? A water

In chemical balance

How is Alkalinity expressed?

In milligrams per liter of equivalent calcium carbonate.

Which items are limitations of the ion exchange softening process?

Increase in the sodium content of softened water. Ultimate disposal of rinse waters. Ultimate disposal of spent brine.

Which items should be checked when an ion exchange unit is shut down?

Inspect the brine inlet distributors. Inspect the underdrain structures. Make a complete visual inspection. Make sure the pipe work is level.

What can happen if water high in iron and manganese is applied to the ion exchange resin for very long?

Iron fouling or the loss of exchange capacity will result

Carbonate Hardness which is also called temporary hardness can be removed by the use of what only?

Lime

Calcium carbonate hardness is removed at a higher or lower pH than magnesium carbonate hardness?

Lower

Feeding of excess carbon dioxide may result in?

No lowering of hardness

Why must care be exercised when using recarbonation? Feeding of excess carbon dioxide may result in?

No lowering of hardness

What if the total hardness is greater than the alkalinity? Given that all carbonate hardness is alkalinity how is the noncarbonate hardness calculated? What is the formula?

Noncarbonate hardnes- mg/L as CaCO3 is equal to Total Hardness-mg/L as CaCO3 minus Alkalinity mg/L as CaCO3

What type of hardness requires both lime and soda for removal?

Noncarbonate hardness also called permanent hardness.

There is no Carbon Dioxide in the water when what is present?

P alkalinity

When pH is below 8.3 there is no what present?

P alkalinity

The addition of carbon dioxide to treated water is called?

Recarbonation

What is the addition of carbon dioxide to water treated with excess lime called?

Recarbonation

The addition of acid to prevent calcium carbonate scale will not accomplish the same things as?

Recarbonation and the addition of polyphosphate.

A positive Langelier index indicates the water is?

Scale forming

Excessively hard water can cause what in regards to pipes?

Scaling on the inside of pipes and thereby restrict flow.

How is an ion exchange resin regenerated?

Sodium cations are exchanged for calcium and magnesium cations

The feed rates determined by jar tests do not always produce what in the actual plant?

The exact same results

Water hardness is a measure of which item?

The soap or detergent consuming power of water.

How does the resin in an ion exchange softerner work?

The sodium ions on the resin are exchanged for calcium and magnesium ions in the water

Total Hardness can be described as? Two ways?

The sum of the hardness caused by both calcium and magnesium ions and can be described as the sum of carbonate (temporary) and noncarbonate (permanent) hardness.

What happens during the backwash stage of an ion exchange softener?

The unit is taken out of service and the flow pattern through the unit is reversed

Why must water with zero hardness not be sent into the distribution system?

The water will be very corrosive

What is the purpose of the backwash stage of an ion exchange softener?

To expand and clean the resin particles

What is the best way for an operator to ensure that an ion exchange softener will continue to operate properly?

To occasionally test the unit during various stages of operation

The neutralizing capacity measured as Alkalinity is caused by?

Water's content of carbonate, bicarbonate, hydroxide, and occasionally borate, silicate, and phosphate.

Following the lime-soda softening process, under what conditions will the deposition of precipitates occur in filters and pipelines?

When water is supersaturated with calcium carbonate and magnesium hydroxide.

The effluent from an ion exchange unit usually will have a hardness of what level until the unit needs regeneration?

Zero

Calcium and Magnesium can be removed from water as insoluble precipitates at high what?

pH levels