alkalinity 101 · 2018. 1. 31. · alkalinity facts the main sources for natural alkalinity are...

ALKALINITY 101A Basic Non-Chemistry approach to

understanding how Alkalinity can

affect your plant operations

By Mary Evans

WHAT IS ALKALINITY?

The alkalinity of water is a measure of its

capacity to neutralize acids. It also refers to the

buffering capacity, or the capacity to resist

changes in pH upon the addition of acids or

bases

ALKALINITY IS NOT pH !

pH is NOT the same as Alkalinity. pH can be

affected by alkalinity, but it is not the same thing.

Alkalinity is a measure of the buffering capacity

of water - its ability to resist sudden changes in

pH.

pH is a measure of how acidic or basic water is. It

measures the degree of alkalinity but not its

quantity. (It is like the relationship between

temperature and heat).

pH AND ALKALINITY ARE NOT THE

SAME THING?

THREE FORMS OF ALKALINITY

Carbonate

Bicarbonate

Total (Sum of Carbonate and Bicarbonate)

WHERE DOES ALKALINITY COME FROM?

Alkalinity is present in liquids as dissolved minerals

like calcium and magnesium.

These alkali metals are found everywhere in nature,

especially in the earth’s crust. One source of alkalinity

is calcium carbonate (CaCO3), which is dissolved in

water flowing through geology that has limestone

and/or marble formations. Limestone is a sedimentary

rock formed by the compaction of fossilized coral,

shells and bones. Limestone is composed of the

minerals calcium carbonate (CaCO3) and/or

dolomite (CaMg(CO3)2), along with small amounts of

other minerals.

ALKALINITY FACTS

The main sources for natural alkalinity are rocks which contain carbonate, bicarbonate, and hydroxide compounds. Borates, silicates, and phosphates also may contribute to alkalinity. Limestone is rich in carbonates, so waters flowing through limestone regions or bedrock containing carbonates generally have high alkalinity - hence good buffering capacity Bicarbonates represent the major form of alkalinity in natural waters; its source being the partitioning of CO2 (Carbon Dioxide)from the atmosphere and the weathering of carbonate minerals in rocks and soil.

Alkalinity can increase the pH (make water more basic), when the alkalinity comes from a mineral source such as calcium carbonate (CaCO3)

ADDITIONAL ALKALINITY INFORMATION

Potable water treatment plants sometimes use

groundwater as a source for drinking water, and

this water may contain many milligrams per liter

(mg/L) of dissolved calcium and magnesium and

have higher alkalinity values.

Conversely, areas rich in granites and some

conglomerates and sandstones may have low

alkalinity and therefore poor buffering capacity.

SURFACE WATER AND ALKALINITY

Surface water (especially in many areas of Texas)

tends to have low alkalinity values.

If your source of drinking water is a lake, river or

reservoir, the levels of alkalinity are usually lower than

that of groundwater

Surface water is greatly impacted by acid rainfall in

certain regions of the state

Geographic location within the state impacts the

levels of alkalinity in water

SOURCES OF DRINKING WATER CAN

INFLUENCE THE AVAILABILITY OF

ALKALINITY IN WASTEWATER

OPERATIONS Once drinking water reaches a sink or shower drain, it

becomes wastewater. Thus, the amount of alkalinity

in wastewater treatment plant influent is usually close

to the alkalinity in the potable water supply.

There are exceptions, especially considering the

source and type of drinking water treatment,

industrial contributions to the sewer system and

rainwater inflow and infiltration.

Raw wastewater contains some alkalinity. How much

depends on a few factors, including the source of the

water. Water from a deep aquifer, reservoir, river, or

lake contains different amounts of alkalinity

HOW NITRIFICATION AFFECTS

ALKALINITY

Biological processes like nitrification and anaerobic

digestion rely on alkalinity. Without alkalinity, organic acids

formed during these processes would drive the pH down to

a point where the bacteria would be inhibited or could no

longer survive

THE NITRIFICATION PROCESS

Certain classes of aerobic bacteria, called nitrifiers,

use ammonia [NH3] for food instead of carbon-based

organic compounds. This type of aerobic metabolism,

which uses dissolved oxygen to convert ammonia to

nitrate, is referred to as nitrification.

To fully convert one pound of ammonia/ammonium to

nitrate, it takes about 7.14 pounds of alkalinity to

support the nitrifiers. The higher the ammonia value,

the more alkalinity that is needed.

WASTEWATER TREATMENT PLANTS ARE NET

ACID PRODUCING SYSTEMS

Wastewater treatment operations are net acid producing. Processes that biologically produce acids or acidic chemicals include:

Biological nitrification (the conversion of ammonium to nitrite then nitrate)

Anaerobic conditions in sewer systems

Anaerobic conditions in primary clarifiers

Anaerobic sludge digestion processes

Anaerobic fermentation basins in biological phosphorus removal systems

Chemical coagulant addition (aluminum sulfate, ferric sulfate, ferric chloride)

Pure gaseous chlorine for disinfection

WASTEWATER OPERATIONS RESULT

IN LOSS OF ALKALINITY

0

20

40

60

80

100

120

1 2 3 4 5 6 7 8 9 10 11 12 13

Ammonia Concentration vs Alkalinity Depletion

Ammonia mg/L Alkalinity mg/L

WHAT HAPPENS WHEN A

TREATMENT PLANT DOES NOT

HAVE ENOUGH ALKALINITY?

Lack of carbonate alkalinity will stop nitrification.

Nitrification is pH-sensitive, and rates of

nitrification will decline significantly at pH values

below 6.8.

At pH values near 5.8 to 6.0, the rates of

nitrification may be 10 - 20 percent of the rate of

a pH of 7.0 std/units (U.S. EPA, 1993)

pH VS. NITRIFICATION RATES

From EPA-625/4-73-004a Revised

Nitrification and Denitrification Facilities

Wastewater Treatment

EPA Technology Transfer Seminar

NITRIFICATION RATES ARE pH

DEPENDENT

pH Activity

7.2 1.00

7.0 0.83

6.8 0.67

6.6 0.50

6.4 0.34

6.2 0.17

Nitrification Activities at pH 7.2 and below

THE RELATIONSHIP BETWEEN pH

AND NITRIFICATION RATES

A pH of 7.0 to 7.2 is an optimum

range to maintain typical

nitrification rates.

However, for various reasons,

some plants are operated at pH

values as low as 6.0 or as high as

8.5 std/units.

OPERATING OUTSIDE THE ZONE

When a facility operates outside of

the ideal conventional pH zone of

7.0 - 7.4, either by choice or

accident, there could be

unintended consequences which

should not be overlooked by the

operators of a facility.

pH 6 – PLANT OPERATING EFFICIENCY OF 12%

Potential for a greater differential in the Food/Microorganisms (Ratio of Food/greater biomass/microorganisms)

Lower nitrification rates – takes longer for complete nitrification resulting in longer detention times

Higher biomass (MLSS) - more bio-solids processing and disposal costs

Higher oxygen input – especially if air is used as the mixing mechanism

Higher mixing energy needed – More weight carried in plant, harder to mix

No buffering potential to counter pH swings – sudden changes in pH possible. No buffering available

Higher chlorine costs

Different operating conditions exist for treatment at a lower pH than a higher pH. Typical operating parameters may need to be evaluated and adjusted to accommodate the differences in pH – Just as a plant changes operating conditions for a change from seasonal cold weather to warm weather operating conditions.

Potential for permit violations associated with incomplete nitrification or low pH

Lower chemical costs for alkalinity supplementation


Normal (typical) plant operations occur at pH ranges of 7.0 – 7.4.

Food/Microorganisms (Ratio of Food/biomass/microorganisms) slightly higher than normal

Detention times longer for complete nitrification

Bio-solids processing and disposal costs higher

Oxygen exchange lower

Energy costs higher

Minimum pH Buffering available

Chlorine Costs vulnerable to sudden changes


Less differential in F/M Ratio – Food is divided by less biomass

Higher nitrification rates resulting in lower costs for:

▪ Solids processing

▪ Dewatering

▪ Chemical usage (polymers, etc)

▪ Disposal costs

▪ Electrical costs

Better oxygen utilization

higher BOD solubility

Lower biomass

Lower oxygen input – Especially if air is used as a mixing mechanism

Lower mixing energy needed because less solids are in the plant

Sufficient buffering to counter pH swings

Higher chemical cost associated with alkalinity supplementation

THE IMPORTANCE OF STEADY

STATE OPERATIONS

Biological processes like nitrification and anaerobic

digestion rely on alkalinity. Without alkalinity, organic acids

formed during these processes would drive the pH down to

a point where the bacteria would be inhibited or could no

longer survive

Effective and efficient operation of a biological process

depends on steady state conditions.

The best operations will be carried on without sudden

changes in any of the operating variables.

STEADY STATE VS. VARIABLE

OPERATING CONDITIONS

0

2

4

6

8

10

12

14

16

1 2 3 4 5 6 7 8 9

Steady State Operations vs Variable

Conditions

Variable Conditions Steady State Conditions

STEADY STATE OPERATIONS =

GOOD FLOCK

If kept in a steady state, good flocculating types

of microorganisms will be more numerous

ALKALINITY = STEADY STATE

OPERATIONS

Alkalinity is the key to steady state operations. The

more stable the environment for the

microorganisms, the more effectively they will be

able to work.

In other words, a sufficient amount of alkalinity can

provide for improved performance and expanded

treatment capacity.

HOW DO I KNOW HOW MUCH

ALKALINITY I NEED FOR MY SYSTEM

TO OPERATE PROPERLY?

The theoretical reaction shows that approximately 7.14 mg of alkalinity as Calcium Carbonate (CaCO3) is consumed for every mg of ammonia oxidized.

To nitrify, alkalinity levels should be roughly eight times the concentration of ammonia present in the raw wastewater influent.

This value may be higher for raw wastewaters with higher influent ammonia concentrations than "normal." (recycle or side streams operations)

In addition, you should provide enough residual alkalinity to maintain pH for downstream operations

WHY RESIDUAL ALKALINITY?

After complete nitrification, a residual alkalinity of 70 to 80

mg/L as Calcium Carbonate (CaCO3) in the aeration tank is

desirable (M&E).

If this alkalinity is not present, then alkalinity should be

introduced in the form of a chemical treatment to the

aeration tank to provide additional alkalinity.

This chemical adjustment will provide additional buffering

downstream of the aeration process.

WHAT HAPPENS IF I DON’T HAVE

ENOUGH ALKALINITY?

If alkalinity is inadequate there could be incomplete

nitrification and depressed pH values in the plant.

These conditions can result in:

▪ Elevated effluent ammonia

▪ Poor flock formation

▪ Increased BOD and TSS effluent values

▪ Lower pH values in effluent

DEPRESSED ALKALINITY VALUES CAN

CONTRIBUTE TO LOWER PH

OPERATING CONDITIONS





NOW THAT I KNOW THE EFFECTS A LOW

ALKALINITY CAN HAVE ON MY TREATMENT

PLANT, HOW CAN I DETERMINE IF MY

TREATMENT FACILITY HAS SUFFICIENT

ALKALINITY?

To determine alkalinity requirements for plant operations, it is

critical to know these three things:

influent ammonia in mg/L (36)

influent total alkalinity in mg/L (124)

effluent total alkalinity in mg/L

STEP ONE

DETERMINE HOW MUCH ALKALINITY

I NEED TO NITRIFY

To calculate theoretical ammonia removal:

_____ mg/L raw ammonia X 7.14 = _______ mg/L alkalinity

Needed for complete nitrification

Example

36 mg/L raw ammonia X 7.14 = 257 mg/L alkalinity

EXAMPLE

CALCULATIONS FOR

DETERMINING ALKALINITY NEEDS

Plant Influent Ammonia = 36 mg/L

36 mg/L ammonia X 7.14 mg/L alkalinity =

257 mg/L alkalinity requirements

257 mg/L is the minimum amount of alkalinity needed

to nitrify 36 mg/L influent ammonia.

CALCULATED ALKALINITY VS

ACTUAL ALKALINITY

Once you have calculated the minimum amount of

alkalinity needed to nitrify the ammonia present in the

wastewater

it is then critical to compare this value against your

measured available influent alkalinity to determine if you

have enough for complete ammonia removal and how

much (if any) additional alkalinity is needed to complete

the nitrification process.

STEP TWO

DETERMINE INFLUENT ALKALINITY AND

CALCULATE TO DETERMINE IF THERE IS

ENOUGH ALKALINITY TO NITRIFY

257 Calculated alkalinity – 124 = 133 alk needed

EXAMPLE

Influent Ammonia Alkalinity needed for nitrification = 257 mg/L

Actual Influent Alkalinity = 124 mg/L

Influent Ammonia Alkalinity needs = (257 mg/L)

– Influent Alkalinity (124 mg/L)

= (257-124)

= 133 mg/L alkalinity deficiency.

I GET IT !!

In this example, sufficient alkalinity is not available

to completely nitrify the influent ammonia and,

supplementation through denitrification and/or

chemical addition will be required.

Remember that this is a minimum. You still need

some for acid buffering in downstream processes

like disinfection.

ALKALINITY 101, OR: BIO-AVAILABLE

ALKALINITY

Most experts recommend an alkalinity residual (effluent

residual) to be between 70 – 80 mg/L as CaC03 (M&E).

As previously identified, total alkalinity is measured to a pH

endpoint of 4.5 standard units (su). For typical wastewater

treatment applications, operational pH levels never go that

low.

WHAT IS BIO-AVAILABLE

ALKALINITY?

When measuring for total alkalinity, the endpoint reflects

how much alkalinity would be available at a pH of 4.5.

At higher pH values of 7.0-7.4 su, where wastewater

operations are typically conducted, not all of a total

alkalinity measured to a pH of 4.5 su is available for use. This

is a critical distinction for available alkalinity or the Bio-

availability of alkalinity.

THE EXPERTS SPEAK

in addition to the alkalinity required for nitrification, additional

alkalinity must be available to maintain the pH in the range

from 7.0 to 7.4 standard units.

Typically the amount of residual alkalinity required to

maintain pH near a neutral point is between 70 and 80 mg/L

as CaCO3 (M&E).

A REMINDER – PH AND

ALKALINITY





WHY DO I NEED ALKALINITY, AND

THE TREATMENT PLANT DOWN THE

ROAD DOESN’T?

Ok, You’ve done the math. Your calculations show that your

plant needs alkalinity. One of the questions you might have is:

What makes my plant different? Why do I need alkalinity?

▪ The answer can be related to sources of drinking water

(ground versus surface) and/or seasonal changes to the

water including rainfall and potential I/I (dilution) in the

influent water.

NOW WHAT DO I DO?

If you have determined that you

need alkalinity, then your next step is

to identify which source of alkalinity

supplementation is best for your

facility, and the rate of application

that you will need to achieve

adequate alkalinity residual.

STAY CALM, AND

SUMMARY OF NEUTRALIZATION

REAGENT OPERATING ISSUES SOURCE: CHARLES RIVER ASSOCIATES, 1993

MAGNESIUM HYDROXIDE LIME CAUSTIC SODA SODA ASH

SAFETY

Primary compound (or derivatives) in “Milk of

Magnesia”, antacids, foodstuffs, etc..

Comparatively safe to handle. Contact with

eyes may cause temporary injury to cornea.

Contact with skin rarely causes irritation.

Hazardous to handle. Contact with eyes can

cause permanent loss of vision. Repeated and

prolonged contact with skin may cause severe

irritation, mild burns and, in extreme cases,

systemic injuries due to absorption. Breathing

dust or mist may cause intolerable discomfort

to nose and throat

Extremely hazardous to handle. Contact with

eyes can cause permanent loss of vision.

Contact with skin may cause severe burns.

Breathing vapor may cause damage to the

upper respiratory tract and the lungs.

Moderately hazardous to handle. Contact with

eyes may cause temporary injury to the

cornea. Contact with skin may cause slight

irritation. Breathing dust may cause painful

irritation to the nose and throat and prolonged

exposure may cause systemic injury.

ENVIROMENTAL EFFECTS

As noted above, is the base of “Milk of

Magnesia” and, as such, is relatively

harmless. Magnesium hydroxide is a natural

mineral that poses no unusual threat to the

environment. In fact, it is beneficial.

Limestone (CaCO3) is a naturally occurring

mineral that poses no threat to the

environment. Lime (CaO) and hydrated lime

(Ca(OH)2), however, are highly caustic and

can cause immediate damage to the

environment.

Because caustic soda is highly corrosive, it can

cause severe physical injury to plant and

animal life if it escapes.

A by-product of neutralization is a sodium salt

which, in high concentrations, may harm

animals and vegetation.

EASE OF HANDLING

Supplied as a ready-to-use slurry or powder.

Requires no special equipment except

possibly an agitator in the slurry storage

tank to prevent settling. Low temperatures

create no special problems, because the

slurry freezes at the same temperature as

the water being treated, i.e. 32oF.

Expensive solids handling equipment is

required. To maximize effectiveness, lime is

often slaked into a hydrated slurry. A large

storage hopper is needed. A slurry with the

maximum 30% solids content will contain grit

that causes rapid wear to costly valves and

pumps.

Requires elaborate safety equipment and

rigorous, time-consuming safety procedures.

Workers must be trained in safety and wear

special clothing and goggles. Low

temperatures can create major problems

because a 50% solution freezes at 57oF. Often

requires temperature sensors and heaters

throughout the distribution system.

Very difficult to handle. Requires special solids-

handling equipment. If used in solution, usually

requires heated valves and pipes because it

freezes at 80oF. Generates carbon dioxide,

which may cause foaming and various process

problems.

SLUDGE

With a wide range of acids and metals,

creates a sludge that is very dense, fast-

settling and easily filtered and dewatered.

Less sludge, less cost.

With heavy metals and sulfuric acid, lime

creates large quantities of calcium sulfate

dehydrate, a sludge that settles very slowly

and is difficult to filter and dewater.

If effluent contains heavy metals, creates large

quantities of gel-like, slow settling sludge that is

difficult to filter and dewater.

If effluent contains heavy metals, creates large

quantities of gel-like, slow settling sludge that is

difficult to filter and dewater.

EQUIPMENT COSTS

Less than for caustic soda, lime, and soda

ash, even with an agitator to prevent slurry

settling in storage. May be used in

powdered form (MgO, Mg(OH)2) with minor

modifications to installed feed systems.

Equipment costs higher than for magnesium

hydroxide. Equipment maintenance is also

higher because lime is abrasive.

Greater than for magnesium hydroxide

because of need for heated system and safety

equipment. Corrosive.

Greater than for magnesium hydroxide

because it requires either expensive solids

handling equipment or heaters for handling a

solution that freezes at 80oF.

RESIDENCE TIME

(REACTION RATE)

Moderately fast acting to 95% of neutral.

Slower above pH 6, resulting in more

controllable process conditions and

enhancing flocculant performance in solids

settling.

Fast acting to full neutralization, but can

become coated with, for instance, calcium

sulfate, leading to high usage rates.

Extremely fast acting with most acids. Difficult

process control conditions and inefficient solids

removal frequently occur when neutralization

takes place very rapidly.

Fast acting to full neutralization with most acids.

Difficult process control conditions and

inefficient solids removal frequently occur when

neutralization takes place very rapidly.

DISSOLVED SOLIDS

EFFLUENT*

(Based on stoichiometric

ratios)

1.31 tons per ton of HCl. 1.23 tons per ton

H2SO4. Generates only soluble salts.

1.52 tons per ton of HCl. 1.74 tons of insoluble

salt per ton of sulfuric acid. (CaSO4-2H2O)

1.60 tons per ton HCl. 1.45 tons per ton of

sulfuric acid.

1.61 tons per ton of HCl. 1.45 tons per ton of

sulfuric acid.

MAXIMUM pH IF

OVERTREATED

Usually no higher than pH 9, the limit set for

most countries (i.e. the U.S. Clean Water

Act).

Can reach pH of 12. Can reach pH of 14. Can reach pH of 11.

AVAILABILITY

Available throughout the world in powder or

slurry form (growing demand could limit

supply in some countries).

Readily available throughout the world. Readily available, but because caustic soda is

co-produced with chlorine, the supply varies

widely from surplus to shortage. Prices vary

accordingly.

Readily available throughout the world, but

produced in only a few localities in a limited

number of countries.

.

IF YOU ARE INTERESTED IN USING LIME FOR

THIS APPLICATION, IT WOULD BE GOOD

FOR YOUR TO BE FAMILIAR WITH THIS

REFERENCED EPA DOCUMENT

NEUTRALIZATION OF SULFURIC ACID (H2SO4)

For one mole (98 lbs) of 100% (H2SO4 – Sulfuric Acid) to be neutralized, the following

chemical reactions occur:

Magnesium Hydroxide Mg(OH)2 + H2SO4 MgSO4 + 2H2O (58.3 lbs) (98 lbs) (120.3 lbs) (36 lbs)

Hydrated Lime Ca(OH)2 + H2SO4 CaSO4-2H2O (74 lbs) (98 lbs) (172 lbs)

Caustic Soda 2NaOH + H2SO4 Na2SO4 + 2H2O (80 lbs) (98 lbs) (142 lbs) (36 lbs)

Soda Ash Na2CO3 + H2SO4 Na2SO4 + CO2 + H2O (106 lbs) (98 lbs) (142 lbs) (44 lbs) (18 lbs)

Caustic Potash 2KOH + H2SO4 K2SO4 + 2H2O (112 lbs) (98 lbs) (174 lbs) (36 lbs)

These equations can be used to calculate the amount of alkali needed to neutralize one

ton of sulfuric acid and the resultant amount of salt formed:

Neutralizing

Agent

Lbs Required

To

Neutralize

1 Ton H2SO4

Ratio To

Mg(OH)2

Total Dissolved Solids

In Effluent (100%

Basis)

Per Ton of Acid

Magnesium

Hydroxide Mg(OH)2 1190 1.00 2460

Hydrated Lime Ca(OH)2 1510 1.27 3510**

Caustic Soda NaOH 1630 1.37 2900

Soda Ash Na2CO3 2160 1.82 2900

Caustic Potash KOH 2290 1.92 3550

** The CaSO4-2H2O will precipitate as a sludge.

SOURCES OF ALKALINITY AND

LBS/ALKALINITY PER GALLON

HOW TO EVALUATE THE DATA

➢ When reviewing the lbs. alkalinity per gallon in the

previous chart, each of the products identified have

specific chemical properties which determine the

amount of alkalinity present in the different products.

➢ It is important to be aware that these values are based

on specific concentrations of product and that different

concentrations provide different volumes of alkalinity.

WHAT YOU NEED TO KNOWTo evaluate the best option for your facility,

it is important to determine the following

facts:

How much alkalinity is present in each

product under consideration (lbs alkalinity

per gallon)

Rate of application

Cost/Budget

Safety

Site specific considerations for your facility

HOW MUCH ALKALINITY DO I

NEED PER MGD?

Plant Influent

Alkalinity in

mg/L

Plant Influent

NH3-N

in mg/L

What is the

Calculated

Amount of

Alkalinity

needed for

nitrification in

mg/L?

(33 X 7.14)

What is amount

of available

Alkalinity in

mg/L?

(235.6 – 212)

Is there sufficient

alkalinity present

to nitrify?

If not, how

much

additional

alkalinity is

needed to

nitrify?

If yes, is there

sufficient

alkalinity to

provide an

effluent residual

of 80 mg/L?

How much additional

alkalinity (if any) is

needed to achieve

80 mg/L effluent

residual?

( 23.6 + 80)

212 33 235.6 212 No 23.6 no 104

MATH REVIEW

Here is a worksheet which further explains and/or shows how these

numbers were determined:

Plant influent ammonia in mg/L (33) X 7.14 alkalinity needed to

remove 1 mg/L ammonia

= 235.62 mg/L alkalinity required

235.62 mg/L alkalinity required – 212 mg/L influent (available)

alkalinity

= 23.62 mg/L alkalinity needed (deficit)

MATH REVIEW

(CONTINUATION)

We have identified that you need at least 23.62

mg/L additional alkalinity to be able to nitrify

“remove” plant influent of 33 mg/L ammonia. The

23.62 mg/L additional alkalinity will bring me to zero

(0).

ADDITIONAL ALKALINITY NEEDED

Now you will need additional residual alkalinity to insure that

you can handle any additional pH changes – in other words,

you need additional “buffering”.

You have determined that Metcalf & Eddy says that you

need to have a residual alkalinity of 80 mg/L.

Therefore:

23.62 mg/L additional alkalinity is needed for ammonia

removal + 80 mg/L alkalinity for effluent

= 104 total mg/L total additional alkalinity needed per mgd

MATH AND MORE MATH!!

If the plant needs an additional 104 mg/L of alkalinity per MGD

per day, we then calculate the different options in this

manner:

Alkalinity Deficiency in mg/L X 8.34 X plant mgd/ lbs of

alkalinity per product chosen

= gpd feed of alkalinity supplement.

EXAMPLE

Product

Alkalinity

Deficiency

in mg/L

X 8.34

Pounds

Per gallon

X (times)

mgd of

plant flow

(1 mgd)

/ (divided by)

pounds of

alkalinity per

gallon for selected

product

Calculated

GPD of

Product per

MGD

Lime Slurry 104 867.36 867.36 3.6 241

Caustic

Soda104 867.36 867.36 7.43 117

Magnesium

Hydroxide104 867.36 867.36 13.38 65

ANSWERS

In the above chart, you identify the mg/L alkalinity

deficiency X pounds of alkalinity per gallon of product =

Calculated Gallons per Day of product needed per 1 MGD.

From there, you need to calculate total number of product

gallons to match your plant MGD flow.

For instance, if you decide on Lime slurry at 241 gallons per day per

MGD and your daily plant MGD flow is 12 MGD……

➢ you multiply your results times 12 for a total product volume per

day.

For example:

241 Gallons per Day (GPD) per Million Gallons per Day (MGD) 12

= 241 X 12 = 2892 gallons per day of lime slurry for 12 MGD flow

Once you know what your alkalinity needs are, you can then calculate your costs per gallon or

ton for alkalinity supplements based on quotes you receive from

your vendor or supplier.

PRODUCT QUALITY IS CRITICAL

It is important to recognize that there are superior

and inferior products on the market.

It is critical for you to be knowledgeable about

your product and specify products that meet both

your standards as well as stringent industry

standards.

You should maintain a strict quality control check

on any product you receive.

Cost should be a consideration, but not your only

criteria

WITH PROPER ALKALINITY…..

A treatment plant experiences optimum microscopic organisms whose primary function is to reduce waste.

(Alkalinity = Capacity)

When not provided with adequate alkalinity, the ability of these micro-organisms to settle is greatly impaired.

ADDITIONAL BENEFITS OF GOOD

ALKALINITY

In activated sludge, the good microorganisms are the type of

floc forming organisms that have the capability, under the

right conditions, to clump together and form a gelatinous floc

which is heavy enough to settle. The formed floc or sludge

can be then characterized as having a SVI.

SVI (Sludge Volume Indexes) are at their optimum with an

adequate level of alkalinity.

ALKALINITY = CAPACITY

The optimum pH range for good plant

operations is between 7.0-7.4. Although growth

can and does occur at pH values of 6-9, it does

so at much reduced rates (See above charts). It

is also quite likely that undesirable forms of

organisms will form at these outside ranges and

cause bulking problems.

The optimal pH for nitrification is 8.0; with

nitrification limited below pH 6.0.

OPTIMUM OXYGEN UPTAKE AND BOD

REMOVAL

Oxygen uptake is optimum at pH’s

between 7.0 and 7.4 and shows a

reduction as pH goes outside this

range.

BOD removal efficiency also

decreases as the pH moves outside

the optimum range.

DENITRIFICATION CAN ADD

ALKALINITY

Plants with the ability to denitrify are able to

add back valuable alkalinity to the process.

Those values should be taken into

consideration when doing mass balancing.

On average, experts state that well operated

facilities should recover approximately 4.2

mg/L alkalinity.

CONCLUSION

In conclusion, Alkalinity is a major

chemical requirement for nitrification,

and testing can be an important and

beneficial tool for use in process control

and plant operations.

References and Sources of Additional Information

1. Metcalf & Eddy, Wastewater Engineering Treatment and Reuse, 4th Edition Revised;

McGraw-Hill Companies, Inc, 2003

2. USEPA Advanced Waste Treatment, A Field Study Training Program, California State

University Department of Civil Engineering and the California Water Pollution Control

Association, 1989

3. USEPA Process Control Manual for Aerobic Biological Wastewater Treatment Facilities,

March 1977

4. Water Environment Federation Operation of Municipal Wastewater Treatment Plants

Manual of Practice 11, 1990

5. USEPA Nitrification and Denitrification Facilities, Wastewater Treatment, EPA

Technology Transfer Seminar Publication EPA-625/4-73-004a Revised

6. Hartley, K.J., Operating the Activated Sludge Process, Gutteridge Haskins & Davey, 1985

7. USEPA Manual of Nitrogen Control, Office of Research and Development Center for

Environmental Research Information Risk Reduction Engineering Laboratory, Cincinnati,

OH, September 1993 EPA/625/R-93/010

8. USEPA Process Design Manual for Nitrogen Control, USEPA Technology Transfer,

October 1975

1

Alkalinity Profiling in Wastewater Operations By: Mary Evans for Operation Challenge Laboratory Event

The purpose of this paper is to familiarize operators with the concept of alkalinity, and the influences on plant operations related to proper alkalinity levels.

Alkalinity Defined The alkalinity of water is a measure of its capacity to neutralize acids. It also refers to the buffering capacity, or the capacity to resist a change in pH. For wastewater opera�ons, alkalinity is measured and reported in terms of equivalent calcium carbonate (CaCO3). It is common prac�ce to express alkalinity measured to a certain pH. For wastewater, the measurement is total alkalinity which is measured to a pH of 4.5 Standard Units (su). Even though pH and alkalinity ARE related, there are dis�nct differences between these two parameters, and how they can affect your plant opera�ons

Alkalinity and pH

Alkalinity is often used as an indicator of biological activity. In wastewater operations, there are three forms of oxygen available to bacteria: dissolved oxygen (O2), nitrate ions (NO3- ), and sulfate ions (SO42-). Aerobic metabolisms use dissolved oxygen to convert food to energy. Certain classes of aerobic bacteria, called nitrifiers, use ammonia (NH3) for food instead of carbon-based organic compounds. This type of aerobic metabolism, which uses dissolved oxygen to convert ammonia to nitrate, is referred to as nitrification.

Nitrifiers are the dominant bacteria when organic food supplies have been consumed. Further processes include denitrification, or anoxic metabolism, which occurs when bacteria utilize nitrate as the source of oxygen and the bacteria use nitrate as the oxygen source. In an anoxic environment, the nitrate ion is converted to nitrogen gas while the bacteria converts the food to energy.

Finally, anaerobic conditions will occur when dissolved oxygen and nitrate are no longer present and the bacteria will obtain oxygen from sulfate. The sulfate is converted to hydrogen sulfide and other sulfur related compounds.

2

Alkalinity is lost in an ac�vated sludge process during nitrifica�on. During nitrifica�on, 7.14 mg of alkalinity as CaCO3 is destroyed for every 1 mg of ammonium ions oxidized.

Lack of carbonate alkalinity will stop nitrification. In addition, nitrification is pH-sensitive and rates of nitrification will decline significantly at pH values below 6.8. Therefore, it is important to maintain an adequate alkalinity in the aera�on tank to provide pH stability and also to provide inorganic carbon for nitrifiers.

At pH values near 5.8 to 6.0, the rates may be 10 to 20 percent of the rate at pH 7.0 (U.S. EPA, 1993). A pH of 7.0 to 7.2 is normally used to maintain reasonable nitrification rates, and for locations with low-alkalinity waters, alkalinity is added at the wastewater treatment plant to maintain acceptable pH values. The amount of alkalinity added depends on the initial alkalinity concentration and amount of NH4-N to be oxidized (Metcalf & Eddy).

A�er complete nitrifica�on, a residual alkalinity of 70 to 80 mg/L as CaCO3 in the aera�on tank is desirable (M&E). If this alkalinity is not present, then alkalinity should be added to the aera�on tank.

0

20

40

60

80

100

120

1 2 3 4 5 6 7 8 9 10 11 12 13

Ammonia Concentration vs Alkalinity Depletion

Ammonia mg/L Alkalinity mg/L

3

From EPA-625/4-73-004a Revised Nitrification and Denitrification Facilities

Wastewater Treatment EPA Technology Transfer Seminar

4


Nitrification and Denitrification Facilities Wastewater Treatment


pH Activity

7.2 1.00

7.0 0.83

6.8 0.67

6.6 0.50

6.4 0.34

6.2 0.17

Nitrification Activities at pH 7.2 and below

5

Why is Alkalinity or Buffering Important?

Or: Alkalinity = Capacity Aerobic wastewater operations are net acid producing. Processes influencing acid formation include, but are not limited to:

• Biological nitrification in aeration tanks, trickling filters and RBC’s • The acid formation stage on anaerobic digestions • Biological nitrification in aerobic digesters • Gas chlorination for effluent disinfection • Chemical addition of aluminum or iron salts

In wastewater treatment, it is critical to maintain pH in a range that is favorable for biological activity. As seen in the charts above, the optimum conditions include a near neutral pH value between 7.0-7.4. Effective and efficient operation of a biological process depends on steady state conditions. The best operations will be carried on without sudden changes in any of the operating variables. If kept in a steady state, good flocculating types of microorganisms will be more numerous. Alkalinity is the key to steady state operations. The more stable the environment for the microorganisms, the more effectively they will be able to work. In other words, a sufficient amount of alkalinity can provide for improved performance and expanded treatment capacity.

How do I know how much alkalinity I need for my system to operate properly? To nitrify, alkalinity levels should be at least eight �mes the concentra�on of ammonia present in the wastewater. This value may be higher for raw wastewaters with higher influent ammonia concentra�ons than the "normal." The theore�cal reac�on shows that approximately 7.14 mg of alkalinity (as CaCO3) is consumed for every mg of ammonia oxidized.

If adequate alkalinity is not present, this could result in incomplete nitrifica�on and depressed pH values in the plant. Plants with the ability to denitrify are able to add back valuable alkalinity to the process, and those values should be taken into considera�on when doing mass balancing. If denitrifica�on is a factor, facili�es should analyze the amount of alkalinity recovered during their facility process to add to the mass balance.

6

The Math To determine alkalinity requirements for plant operations, it is critical to know:

• influent ammonia in mg/L • influent total alkalinity in mg/L • effluent total alkalinity in mg/L

For every mg/L of converted ammonia, alkalinity will decrease by 7.14 mg/L. Therefore, to calculate theoretical ammonia removal, multiply the influent (or raw) ammonia mg/L X 7.14 mg/L alkalinity to determine a minimum amount of alkalinity needed for ammonia removal through nitrification.

EXAMPLE

Influent Ammonia = 36 mg/L

36 mg/L ammonia X 7.14 mg/L alkalinity to nitrify = 257 mg/L alkalinity requirements

257 mg/L is the minimum amount of alkalinity needed to nitrify 36 mg/L influent ammonia.

Once you have calculated the minimum amount of alkalinity needed to nitrify the ammonia present in the wastewater, it is then critical to compare this value against your actual measured available influent alkalinity to determine if you have enough for complete ammonia removal, and how much (if any) additional alkalinity is needed to complete the nitrification process.

Example

Influent Ammonia Alkalinity needs for nitrification = 257 mg/L

Actual Influent Alkalinity = 124 mg/L

Influent Ammonia Alkalinity needs (257 mg/L) – Influent Alkalinity (124 mg/L) = 133 mg/L alkalinity deficiency.

In other words, in this example, sufficient alkalinity is not available to completely nitrify the influent ammonia, and supplementation through denitrification and/or chemical addition will be required. Remember that this is a minimum — you still need some for acid buffering in downstream processes, like disinfection.

7

Alkalinity 101, or: Bio-Available Alkalinity

Most experts recommend an alkalinity residual (effluent residual) to be between 75-150 mg/L alkalinity. [NOTE: For information related to this paper, we will be referencing Metcalf & Eddy who recommend 70 to 80 mg/L as CaC03 for residual alkalinity].

As previously identified, total alkalinity is measured to a pH endpoint of 4.5 standard units (su). For typical wastewater treatment applications, operational pH never goes that low. When measuring total alkalinity, the endpoint reflects how much alkalinity would be available at a pH of 4.5.

At higher pH values of 7.0 - 7.4 su, where wastewater operations are typically conducted, not all of a total alkalinity measured to a pH of 4.5 su is available for use.

This is a critical distinction for available alkalinity or the “Bio-availability” of alkalinity. Therefore, in addition to the alkalinity required for nitrification, additional alkalinity must be available to maintain the pH in the range from 7.0 to 7.4 standard units. Typically the amount of residual alkalinity required to maintain pH near a neutral point is between 70 and 80 mg/L as CaCO3 (M&E).

Proper levels of alkalinity in treatment processes:

• Provides for optimum microscopic organisms whose primary function is to reduce waste. When not provided with adequate alkalinity, the ability of these microorganisms to settle is greatly impaired.

• In activated sludge, the good microorganisms are the type of floc forming organisms that have the capability, under the right conditions, to clump together and form a gelatinous floc which is heavy enough to settle. The formed floc or sludge can be then characterized as having a SVI

• The optimum pH range for good plant operations is between 7.0-7.4. Although growth can and does occur at pH values of 6-9, it does so at much reduced rates (See above charts). It is also quite likely that undesirable forms of organisms will form at these outside ranges and cause bulking problems. The op�mal pH for nitrifica�on is 8.0; with nitrifica�on limited below pH 6.0.

• Oxygen uptake is optimum a pH’s between 7.0 and 7.4 and shows a reduction as pH goes outside this range. BOD removal efficiency also decreases as the pH moves outside the optimum range.

8

Why Do I Need Alkalinity, and the Treatment Plant Down the Road Doesn’t?

Plant operations and alkalinity values are dependent upon several basic fundamental criteria:

• Source of drinking water (ground or surface) • Geological factors related to source of water (soils/lithology) • Industrial discharges (high ammonia loading) • Weather patterns

Typically, ground water used as a source of drinking water provides a higher rate of alkalinity than surface water. This is of course dependent on soil from which the water is drawn. Lake and/or reservoir water can, and most often are, lower in available alkalinity. Additional factors can be seasonal and related to changes in sources of drinking waters. At one time of the year, your drinking plants may be dependent on surface water, at others groundwater only, and at different times some combination of both. These varying amounts can and do contribute to changes taking place in your plant. Finally, the impact from industrial discharges can affect your facility, especially those that are associated with high ammonia loadings.

Now What Do I Do?

If you have determined that you need alkalinity, then your next step is to identify which source of alkalinity supplementation is best for your facility, and the rate of application that you will need to achieve adequate alkalinity residual.

The chart below provides a summary of the common neutralization chemicals, and operating issues related to each. A review of this information can help you become familiar with the different types of supplementation available, as well as handling procedures.

9

Summary of Neutralization Reagent Operating Issues

Source: Charles River Associates, 1993

MAGNESIUM HYDROXIDE LIME CAUSTIC SODA SODA ASH

SAFETY

Primary compound (or derivatives) in “Milk of Magnesia”, antacids, foodstuffs, etc.. Comparatively safe to handle. Contact with eyes may cause temporary injury to cornea. Contact with skin rarely causes irritation.

Hazardous to handle. Contact with eyes can cause permanent loss of vision. Repeated and prolonged contact with skin may cause severe irritation, mild burns and, in extreme cases, systemic injuries due to absorption. Breathing dust or mist may cause intolerable discomfort to nose and throat

Extremely hazardous to handle. Contact with eyes can cause permanent loss of vision. Contact with skin may cause severe burns. Breathing vapor may cause damage to the upper respiratory tract and the lungs.

Moderately hazardous to handle. Contact with eyes may cause temporary injury to the cornea. Contact with skin may cause slight irritation. Breathing dust may cause painful irritation to the nose and throat and prolonged exposure may cause systemic injury.

ENVIROMENTAL EFFECTS

As noted above, is the base of “Milk of Magnesia” and, as such, is relatively harmless. Magnesium hydroxide is a natural mineral that poses no unusual threat to the environment. In fact, it is beneficial.

Limestone (CaCO 3 ) is a naturally occurring mineral that poses no threat to the environment. Lime (CaO) and hydrated lime (Ca(OH) 2 ), however, are highly caustic and can cause immediate damage to the environment.

Because caustic soda is highly corrosive, it can cause severe physical injury to plant and animal life if it escapes.

A by-product of neutralization is a sodium salt which, in high concentrations, may harm animals and vegetation.

EASE OF HANDLING

Supplied as a ready-to-use slurry or powder. Requires no special equipment except possibly an agitator in the slurry storage tank to prevent settling. Low temperatures create no special problems, because the slurry freezes at the same temperature as the water being treated, i.e. 32

oF.

Expensive solids handling equipment is required. To maximize effectiveness, lime is often slaked into a hydrated slurry. A large storage hopper is needed. A slurry with the maximum 30% solids content will contain grit that causes rapid wear to costly valves and pumps.

Requires elaborate safety equipment and rigorous, time-consuming safety procedures. Workers must be trained in safety and wear special clothing and goggles. Low temperatures can create major problems because a 50% solution freezes at 57

oF. Often requires

temperature sensors and heaters throughout the distribution system.

Very difficult to handle. Requires special solids-handling equipment. If used in solution, usually requires heated valves and pipes because it freezes at 80

oF. Generates

carbon dioxide, which may cause foaming and various process problems.

SLUDGE With a wide range of acids and metals, creates a sludge that is very dense, fast-settling and easily filtered and dewatered. Less sludge, less cost.

With heavy metals and sulfuric acid, lime creates large quantities of calcium sulfate dehydrate, a sludge that settles very slowly and is difficult to filter and dewater.

If effluent contains heavy metals, creates large quantities of gel-like, slow settling sludge that is difficult to filter and dewater.

If effluent contains heavy metals, creates large quantities of gel-like, slow settling sludge that is difficult to filter and dewater.

EQUIPMENT COSTS

Less than for caustic soda, lime, and soda ash, even with an agitator to prevent slurry settling in storage. May be used in powdered form (MgO, Mg(OH) 2 ) with minor modifications to installed feed systems.

Equipment costs higher than for magnesium hydroxide. Equipment maintenance is also higher because lime is abrasive.

Greater than for magnesium hydroxide because of need for heated system and safety equipment. Corrosive.

Greater than for magnesium hydroxide because it requires either expensive solids handling equipment or heaters for handling a solution that freezes at 80

oF.

RESIDENCE TIME (REACTION RATE)

Moderately fast acting to 95% of neutral. Slower above pH 6, resulting in more controllable process conditions and enhancing flocculant performance in solids settling.

Fast acting to full neutralization, but can become coated with, for instance, calcium sulfate, leading to high usage rates.

Extremely fast acting with most acids. Difficult process control conditions and inefficient solids removal frequently occur when neutralization takes place very rapidly.

Fast acting to full neutralization with most acids. Difficult process control conditions and inefficient solids removal frequently occur when neutralization takes place very rapidly.

DISSOLVED SOLIDS EFFLUENT

* (Based on stoichiometric

ratios)

1.31 tons per ton of HCl. 1.23 tons per ton H 2 SO 4. Generates only soluble salts.

1.52 tons per ton of HCl. 1.74 tons of insoluble salt per ton of sulfuric acid. (CaSO 4 -2H 2 O)

1.60 tons per ton HCl. 1.45 tons per ton of sulfuric acid. 1.61 tons per ton of HCl. 1.45 tons per ton of sulfuric acid.

MAXIMUM pH IF OVERTREATED

Usually no higher than pH 9, the limit set for most countries (i.e. the U.S. Clean Water Act).

Can reach pH of 12. Can reach pH of 14. Can reach pH of 11.

AVAILABILITY Available throughout the world in powder or slurry form (growing demand could limit supply in some countries).

Readily available throughout the world. Readily available, but because caustic soda is co-produced with chlorine, the supply varies widely from surplus to shortage. Prices vary accordingly.

Readily available throughout the world, but produced in only a few localities in a limited number of countries.

10

In addition to learning about the basics of each chemical, you should also be aware of the neutralization capabilities of the different products, and have a rudimentary understanding of the chemistry related to each product. The chart below shows how to calculate the results if you would like to make the exercise.

NEUTRALIZATION OF SULFURIC ACID (H2SO4)

For one mole (98 lbs) of 100% (H2SO4 – Sulfuric Acid) to be neutralized, the following chemical reactions occur:

Magnesium Hydroxide Mg(OH)2 + H2SO4 MgSO4 + 2H2O (58.3 lbs) (98 lbs) (120.3 lbs) (36 lbs)

Hydrated Lime Ca(OH)2 + H2SO4 CaSO4-2H2O (74 lbs) (98 lbs) (172 lbs) Caustic Soda 2NaOH + H2SO4 Na2SO4 + 2H2O (80 lbs) (98 lbs) (142 lbs) (36 lbs) Soda Ash Na2CO3 + H2SO4 Na2SO4 + CO2 + H2O (106 lbs) (98 lbs) (142 lbs) (44 lbs) (18 lbs) Caustic Potash 2KOH + H2SO4 K2SO4 + 2H2O (112 lbs) (98 lbs) (174 lbs) (36 lbs)

These equations can be used to calculate the amount of alkali needed to neutralize one ton of sulfuric acid and the resultant amount of salt formed:

Neutralizing Agent

Lbs Required To

Neutralize 1 Ton H2SO4

Ratio To Mg(OH)2

Total Dissolved Solids In Effluent (100%

Basis) Per Ton of Acid

Magnesium Hydroxide Mg(OH)2 1190 1.00 2460

Hydrated Lime Ca(OH)2 1510 1.27 3510** Caustic Soda NaOH 1630 1.37 2900

Soda Ash Na2CO3 2160 1.82 2900 Caustic Potash KOH 2290 1.92 3550

** The CaSO4-2H2O will precipitate as a sludge.

11

For those not interested in doing the mathematical and chemistry equations, the chart below is a quick guide to determining the pounds of alkalinity per gallon of the most common chemicals used for alkalinity addition in our geographic area.

How to Evaluate the Data

When reviewing the pounds of alkalinity per gallon in the above chart, each of the products identified have specific chemical properties which determine the amount of alkalinity present.

It is important to be aware that the alkalinity values are based on specific concentrations and quality of products, and that different concentrations provide different volumes of alkalinity (and consequently, different pricing).

12

What You Need to Know

To evaluate the best option for your facility, it is important to determine the following facts:

• How much alkalinity is present in each product under consideration ( pounds of alkalinity per gallon)

• Rate of application – How much alkalinity per MGD • Cost/Budget

Calculating How Much Alkalinity per MGD

Plant Influent Alkalinity

mg/L

Plant Influent NH3-N in mg/L

What is the Calculated Amount of

Alkalinity needed for nitrification

in mg/L?

What is amount of available Alkalinity

in mg/L?

Is there sufficient alkalinity

present to nitrify?

If not, how much

additional alkalinity is needed to

nitrify?

If yes, is there

sufficient alkalinity to provide an

effluent residual of 80 mg/L?

How much additional alkalinity (if any) is needed to

achieve 80 mg/L effluent residual?

212 33 235.6 212 no 23.6 no 104

Here is a worksheet which further explains and/or shows how these numbers were determined:

Plant influent ammonia mg/L (33) X 7.14 alkalinity needed to remove 1 mg/L ammonia

= 235.62 mg/L alkalinity required

235.62 mg/L alkalinity required – 212 mg/L influent (available) alkalinity

= 23.62 mg/L alkalinity needed

Now, I know that I need at least 23.62 mg/L additional alkalinity to be able to nitrify “remove” my plant influent of 33 mg/L ammonia. The 23.62 mg/L additional alkalinity will bring me to net zero (0). Now I will need additional residual alkalinity to insure that I can handle any additional pH changes – in other words, I need additional “buffering”. We have already determined that Metcalf & Eddy says that we need to have a residual alkalinity of 80 mg/L. Therefore:

23.62 mg/L additional alkalinity needed for ammonia removal + 80 mg/L alkalinity for effluent

= 104 total mg/L total additional alkalinity needed

13

If the plant has an alkalinity deficit of 104 mg/L alkalinity, then we calculate the different options in the outlined in the chart below (information taken from charts above):

Product Alkalinity

Deficiency mg/L

Pounds of Alkalinity per

Gallon of Product

Flow in MGD

Daily Product Feed Rate in GPD for 12.5 MGD Flow

(mg/L alkalinity needed * 8.34) =

lbs/alkalinity needed

(lbs alkalinity needed / lbs of alkalinity per gallon per chemical) = GPD product needed

Lime Slurry 104 3.6 12.5 3012

Caustic Soda 104 7.43 12.5 1459

Magnesium Hydroxide 104 13.38 12.5 810

In the above chart, you identify the mg/L alkalinity deficiency X pounds of alkalinity per gallon of product = Calculated Gallons per Day of product needed. From there, you need to calculate total number of gallons for your MGD plant flow.

For instance, if you decide on Lime slurry to provide the alkalinity, and your daily plant flow is 12 MGD, then you will need to calculate your total daily GPD of Product

Alkalinity Deficiency in mg/L X 8.34 X Flow 0f 12.5 mgd

= 104 X 8.34 X 12 = 10,842 / 3.6 lbs of alkalinity per gallon

= 3012 Gallons per day of lime slurry for 12.5 MGD flow

Once you have determined what your alkalinity needs are, then you can calculate your costs per gallon or ton based on quotes you receive from a supplier.

14

Product Quality is Critical – Or, A Word to the Wise!

When you are making your final considerations for determining which product you will use, it is important to recognize that there are superior and inferior sources of product on the market, as well as a wide variance in prices.

It is critical for you to be knowledgeable about your product, and specify products that meet stringent industry standards. If you are not sure, consult with individuals in the industry that you trust. As a good practice, if you will go out to bid, think about incorporating some of these basic items into your bid specifications:

• Minimum product quality specifications (concentration/impurities/etc..) • References from at least three (3) municipalities utilizing this vendor and product in

your state/region (And, check the references!!) • Source of the product (where is it made? Imported or Domestic? Alternate supplies of

product?

Finally, you should maintain a strict quality control check on product that you receive.

Just remember, cheap is not always best if the quality of product is inferior.

Remember, With Proper Alkalinity…….

• A treatment plant experiences optimum microscopic organisms whose primary function is to reduce waste

• When not provided with adequate alkalinity, the ability of these microorganisms to settle is greatly impaired

• Good microorganisms provide good sludge settling • Good alkalinity provides for optimum BOD removal efficiency and Optimum Oxygen

Uptake • Good alkalinity = Capacity

In conclusion, Alkalinity is a major chemical requirement for nitrification, and can be a useful and beneficial tool for use in process control.

References and Sources of Additional Information

1. Metcalf & Eddy, Wastewater Engineering Treatment and Reuse, 4th Edition Revised; McGraw-Hill Companies, Inc, 2003

2. USEPA Advanced Waste Treatment, A Field Study Training Program, California State University Department of Civil Engineering and the California Water Pollution Control Association, 1989

15

3. USEPA Process Control Manual for Aerobic Biological Wastewater Treatment Facilities, March 1977

4. Water Environment Federation Operation of Municipal Wastewater Treatment Plants Manual of Practice 11, 1990

5. USEPA Nitrification and Denitrification Facilities, Wastewater Treatment, EPA Technology Transfer Seminar Publication EPA-625/4-73-004a Revised

6. Hartley, K.J., Operating the Activated Sludge Process, Gutteridge Haskins & Davey, 1985 7. USEPA Manual of Nitrogen Control, Office of Research and Development Center for

Environmental Research Information Risk Reduction Engineering Laboratory, Cincinnati, OH, September 1993 EPA/625/R-93/010

8. USEPA Process Design Manual for Nitrogen Control, USEPA Technology Transfer, October 1975

WHAT COLOR IS YOUR SYSTEM?

Using Surface pH to Map, Assess and Evaluate Wastewater Collection

System CorrosionMary Evans

Premier Magnesia, LLC

South Central Regional Account Manager

Challenges in U.S. Wastewater Infrastructure

*American Society Of Civil Engineers“U.S. Water Infrastructure Needs” 3/28/01

American wastewater systems currently require $12 billion* a year more than available funds to replace

and failing infrastructure.

And the shortfall is increasing every year…

aging

The American Society of Civil Engineers (ASCE) has reported to

Congress and the Senate…

Compared with roads and bridges, aging is not the underlying problem in

this case.

However…

In 1977 the clean water act* increased treatment requirements

for municipal wastewater.

*Recommended by ASCE

This legislation has contributed to subtle changes in wastewater

chemistry which increased sulfide production across the country.

The result has quietly cost U.S. taxpayers billions of dollars.

Mandated Heavy Metals Discharge Requirements

Since 1987, the amount of heavy metals being discharged by regulated businesses fell as much as

90% or more

1972, The Federal Government Passed The Clean Water Act (CWA)

Amendments in 1977 and 1987

H2S

Acid AttacksConcrete

H2S H2S

SO42- HS- H2SX H2S

Wastewater has changed.It’s become more corrosive.

Data provided by the City of Los Angeles

1980 1985 1990 19950

5

10

15

DI

SSO

LVED

SUL

FIDE

CO

NCEN

TRAT

ION

(mg/

l)

Corrosion Threshold

Sulfide

s

Data courtesy of the City of L.A., CA

Today, wastewater infrastructure is subject to much more corrosion than before 1980.

1980 1985 1990 19950

10

20

0

5

10

15

D

ISSO

LVED

SU

LFID

E C

ON

CEN

TRA

TIO

N (m

g/l)

TOTA

L M

ETA

LSC

ON

CEN

TRA

TIO

N (m

g/l)

DISSOLVED SULFIDE VS. TOTAL METALS HYPERION WWTP

Corrosion Threshold

Metals Sulfide

s

DISSOLVED SULFIDE VS. TOTAL METALS

Negligible Corrosion

Mandated Heavy Metals Discharge Requirements

Sulfide gas is converted to corrosive sulfuric acid on surfaces inside sewers. This acid dissolves concrete and metal.

That’s why, in 2000 the EPA estimated municipal sewers subject to corrosion

were failing six times faster than the rate they’re being repaired.

By 2020, the EPA now expects more than 40% of the country’s 600,000 miles of major sewer lines will be in poor, very

poor or inoperable condition.

Tucson, Arizona

EPA Gap Analysis

5

Collapsed or collapse imminent Collapse likely in foreseeable future Collapse unlikely in near futureMinimal collapse risk Acceptable structural condition

10%

EPA Gap Analysis


23%

EPA Gap Analysis

9


42%

As a result, debt service in many of America’s cities is becoming an ever-increasing percentage of annual revenue, driving rate increases

Here’s how it happens…

Acid corrosion is the problem.

Other bacteria present in the water convert sulfates to sulfides. This causes the rotten egg smell, hydrogen sulfide gas (H2S).

When the dissolved oxygen concentration falls below 0.1 mg/l, the water becomes septic.

H2S Gas H2S GasH2S Gas H2S Gas

pH ~ 7D.O.

SO42- HS- H2S

H2S Gas H2S Gas

H2S Gas

H2S H2SH2S

In water at pH 7, about 50% of the dissolved sulfide converts to H2S gas.

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0

200

400

600

800

1000

1200

3 4 5 6 7 8 9 10

H2S

(aq)

and

HS-

in s

olut

ion

(mg/

L)

H2 S

(g) in air (ppm)

pH

H2S(g)

H2S(aq)

HS-

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0

200

400

600

800

1000

1200

3

4

5

6

7

8

9

10

H

2

S

(aq)

and HS

-

in solution (mg/L)

H

2

S

(g)

in air (ppm)

pH

H

2

S

(g)

H

2

S

(aq)

HS

-

On the surfaces above the water, H2S gas is converted to strong sulfuric acid by Thiobacillus bacteria.

This acid corrosion, not “aging”, then dissolves the infrastructure. Acid returned to the water releases more H2S.

SO42- HS- H2S

H2S

Thiobacillus

+ O2 = H2SO4

Acid AttacksConcreteAnd virtually

nothing is being done to stop it from happening.

Moreover, the traditional tools and models lack the ability to provide real-time feedback on current corrosion rates.

Collapses routinely occur when preventable corrosion

is allowed to continue unchecked.

SO42- HS- H2S

H2S + O2 = H2SO4

Acid AttacksConcrete

Once rebar is exposed, the sewer is structurally

compromised.

• Widespread corrosion is “relatively” new and although much faster today, it still happens gradually. Structural problems and collapses take years to develop. (But they are happening regularly now.)

• Many wastewater professionals underestimate the extent of the problem.

How could this happen?

• Liquid phase control of sulfides and mitigation of sulfide gas release• Air phase control and ventilation of sulfide gas•CCTV, Sonar Inspection, Physical Inspection•Rehabilitation/Replacement with Corrosion Resistant Materials

However, these technologies are not able to quickly and simply assess current conditions and rates of corrosion within a system.

What’s being done to evaluate and combat the corrosion?

Corrosive conditions are the problem and that can easily be detected using a simple,

inexpensive surface pH test.

Although the rate of corrosion can be assessed with a simple surface pH test,

…many utilities have yet to hear about or implement this testing as a

regular field parameter

But it’s not that complicated…

Dissolved sulfide concentration and H2S gas are unreliable predictors of local corrosion.

High dissolved sulfide or headspace H2S do not always predict areas of corrosion.

Section 4 - LACSD Pub CCr.pdf

Surface pHtells the whole story…

100 YearsSurface pH Identifies Hotspots

Surface pH of Manhole

Manhole < 7 years old showing

severe corrosion. Installed 2003

L.A.County San Districts

0.001 0.01 0.1 1.0

Corrosion Rate (in./year)

7

6

5

1

0

pH

Cor

rosi

on R

ange

4

3

2

0.25

20

Years of Life

(2” of sacrificial concrete)

100

Surf

ace

8

Section 4 - LACSD Pub CCr.pdf

When surface pH falls below four, life cycle cost assumptions are no longer valid.

The impact to CAPEX and OPEX is shocking.

Equipment• Multi-range pH Paper• Electrical Tape• Long pole (Extension

pole recommended)• Simple “L” shaped

supporting bracket

pH paper “A”

pH paper “B”

pH paper “C”

Optional cotton ball backing dampened with distilled water for dry surfaces.

Sample the Surface pH• On maintenance hole covers and near the upper region of

maintenance holes, the pH paper may be applied directly to the surface without a pole.

• For sidewall readings, lower the pole through the man-hole and touch pH paper “A” to the surface. Take three representative readings.

• pH paper “B” can be used for benches and “C” for crowns. Three readings are suggested for each area.

• Use light pressure, and make contact with the surface, so as to expose the pH paper to moisture found on the surface or from the optional wetted cotton backing.

• Any part of the pH paper that “changes” color, indicates the pH of that surface.

Measure & Map The System437

Hydrogen Sulfide can be measured and quantified using Odalogs or similar

technologies

Hydrogen Sulfide Can be measured and quantified

REMEMBER……Many technologies claim that they reduce or eliminate odor and corrosion. Odor, or H2S reduction, can be measured and quantified through the use of Odalogs or similar technologies.

However, up until recently, there has been no method that could confirm corrosion control in a

system. The assumption that controlling H2S odors eliminates corrosion is flawed. The ONLY

definitive method for determining the effectiveness of corrosion control is surface pH measurement.

Evaluate if current treatmenttechnologies improve surface pH

pH Pinellas Co Inlet Manhole LS 16

0

1

2

3

4

5

6

7

8

Dec

-05

Jan-

06

Feb-

06

Mar

-06

Apr

-06

May

-06

Jun-

06

Jul-0

6

Aug

-06

Sep

-06

Oc t

-06

Nov

-06

Dec

-06

Date

Surf

ace

pH

Chart1

38699

38753

38831

38947

39066

Date

Surface pH


2

5

6

7

7

Sheet1

12/13/052

2/5/065

4/24/066

8/18/067

12/15/067

Sheet1

Date

Surface pH


Sheet2

Sheet3

Red is bad, green is good.

7= NeutralAbove 7 = BasicBelow 7 = Acidic

WHAT COLOR IS YOUR SYSTEM?

Red? Green? In Between?

WEF Fellows 2 - TEEX Release FormWEF Fellows 3 - Alkalinity 101 WEAT PresentationWEF Fellows 4 - Alkalinity Profiling in Wastewater Operations White PaperAlkalinity Profiling in Wastewater OperationsBy: Mary Evans for Operation Challenge Laboratory EventAlkalinity DefinedThe alkalinity of water is a measure of its capacity to neutralize acids. It also refers to the buffering capacity, or the capacity to resist a change in pH. For wastewater operations, alkalinity is measured and reported in terms of equivalent calcium...From EPA-625/4-73-004a RevisedNitrification and Denitrification FacilitiesWastewater TreatmentEPA Technology Transfer SeminarFrom EPA-625/4-73-004a RevisedNitrification and Denitrification FacilitiesWastewater TreatmentEPA Technology Transfer SeminarWhy is Alkalinity or Buffering Important?Or: Alkalinity = CapacityHow do I know how much alkalinity I need for my system to operate properly?To nitrify, alkalinity levels should be at least eight times the concentration of ammonia present in the wastewater. This value may be higher for raw wastewaters with higher influent ammonia concentrations than the "normal." The theoretical reaction ...If adequate alkalinity is not present, this could result in incomplete nitrification and depressed pH values in the plant. Plants with the ability to denitrify are able to add back valuable alkalinity to the process, and those values should be taken i...The MathTo determine alkalinity requirements for plant operations, it is critical to know:

WEF Fellows - 6 PPTWHAT COLOR IS YOUR SYSTEM?Slide Number 2Slide Number 3Slide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Surface pH of Manhole Manhole < 7 years old showing severe corrosion. Installed 2003Slide Number 32Slide Number 33EquipmentSlide Number 35Slide Number 36Sample the Surface pHSlide Number 38Slide Number 39Slide Number 40REMEMBER……Many technologies claim that they reduce or eliminate odor and corrosion. Odor, or H2S reduction, can be measured and quantified through the use of Odalogs or similar technologies. However, up until recently, there has been no method that could confirm corrosion control in a system. The assumption that controlling H2S odors eliminates corrosion is flawed. The ONLY definitive method for determining the effectiveness of corrosion control is surface pH measurement.Evaluate if current treatment�technologies improve surface pHRed is bad, green is good.WHAT COLOR IS YOUR SYSTEM?

alkalinity 101 · 2018. 1. 31. · alkalinity facts the main sources for natural alkalinity are...

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