Lin S.D. Water and Wastewater Calculations Manual

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Step 2. Calculate log inactivation for Giardia (X ) and viruses (Y )

X ⫽ 3(CT

cal

/CT

99.9

) ⫽ 3 ⫻ 0.45 log

⫽ 1.35 log

Y ⫽ 4 (CT

cal

/CT

) ⫽ 4 ⫻ 0.45 log

⫽ 1.8 log

Example 4: A water system pumps its raw water from a remote lake. No ﬁl-

tration is required due to good water quality. Chlorine is dosed at the pump-

ing station near the lake. The peak pumping rate is 320 gpm (0.02 m

/s). The

distance from the pumps to the storage reservoir (tank) is 3300 ft (1000 m);

the transmission pipe is 10 in in diameter. The chlorine residual at the outlet

of the tank is 1.0 mg /L (C for the tank). The T

for the tank is 88 min at the

peak ﬂow rate determined by a tracer study. Assuming the inactivation for

the service connection to the ﬁrst customer is negligible, determine the min-

imum chlorine residue required at the inlet of the tank (C at the pipe) to meet

Giardia 3-log removal at 5°C and pH 7.0.

solution:

Step 1. Calculate CT

cal

for the pipe

Q ⫽ 320 gpm ⫽ 320 gal/min ⫻ 0.1337 ft

/gal

⫽ 42.8 ft

/min

T ⫽ ␲ r

L/Q ⫽ 3.14 (0.417 ft)

⫻ 3300 ft/(42.8 ft

/min)

⫽ 42 min

cal

(pipe) ⫽ 42 C

(mg/L)min

where C

is chlorine residual at the end of the pipe.

Step 2. Calculate CT

cal

for the tank, CT

cal

(tank)

cal

(tank) ⫽ 1.0 mg/L ⫻ 88 min ⫽ 88 (mg/L) min

Step 3. Find CT

99.9

for Giardia removal

At water temperature of 5°C, pH 7.0, and residual chlorine of 1.0 mg/L, from

Table 5.7:

99.9

⫽ 149 (mg/L) min

Step 4. Calculate chlorine residue required at the end of the pipe (tank

inlet), C

cal

(pipe) ⫹ CT

cal

(tank) ⫽ CT

99.9

From Steps 1 to 3, we obtain

42 min ⫻ C

(mg/L) ⫹ 88(mg/L)min ⫽ 149(mg/L)min

⫽ 1.45 mg/L (minimum required)

Public Water Supply 485

Example 5: In a 1-MGD water plant (1 MGD ⫽ 694 gpm ⫽ 0.0438 m

/s),

water is pumped from a lake and prechlorinated with chlorine dioxide at the

lake site. The source water is pretreated with chlorine at the intake near the

plant. The peak ﬂow is 600 gpm. The worst conditions to be evaluated are at

5°C and pH 8.0. Gaseous chlorine is added at the plant after ﬁltration (clear-

well inlet). The service connection to the ﬁrst customer is located immediately

next to the clearwell outlet. The following conditions also are given:

Treatment unit Volume, gal Outlet residual Cl

, mg/L Bafﬂing conditions

Rapid mixer 240 0.4 Bafﬂed at inlet and outlet

Flocculators 18,000 0.3 Bafﬂed at inlet and outlet

and with horizontal paddles

Clariﬁers 150,000 0.2 Only bafﬂed at outlet

Filters 6600 0.1

Clearwell 480,000 0.3 (free)

1.6 (combined)

Chlorine and ammonia are added at the clearwell inlet. Residual free and

combined chlorine measured at the outlet of the clearwell are 0.3 and 1.6

mg/L, respectively. Estimate the inactivation level of Giardia and viruses

at each treatment unit.

soution:

Step 1. Calculate CT

cal

for the rapid mixer

Assuming average bafﬂing condition and using Table 5.6, we obtain the cor-

rection factor (T

/T) ⫽ 0.5 for average bafﬂing.

Thus

ERT ⫽ HRT (T

/T ) ⫽ 0.4 min ⫻ 0.5

⫽ 0.2 min

Use this ERT as T for CT calculation

cal

⫽ 0.4 mg/L ⫻ 0.2 min

⫽ 0.08 (mg/L) min

Step 2. Determine CT

cal

/CT

for the rapid mixer

Under the following conditions:

pH ⫽ 8.0

T ⫽ 5°C

5 0.4 min

HRT 5

240 gal

600 gal/min

486 Chapter 5

residual chlorine ⫽ 0.4 mg/L

log inactivation ⫽ 3

From Table 5.7, we obtain:

99.9

⫽ 198 (mg/L) min

cal

/CT

⫽ (0.08 (mg/L) min)/(198 (mg/L) min)

⫽ 0.0004

Step 3. Calculate the log inactivation of Giardia for the rapid mixer

log removal ⫽ 3 (CT

cal

/CT

99.9

)

⫽ 0.0012

Step 4. Similar to Steps 1 to 3, determine log inactivation of Giardia for the

ﬂocculators

with a superior bafﬂing condition from Table 5.6, the correction T

/T ⫽ 0.7

ERT ⫽ HRT (T

/T) ⫽ 30 min ⫻ 0.7

⫽ 21 min

then

cal

⫽ 0.3 mg/L ⫻ 21 min

⫽ 6.3 (mg/L) min

log removal ⫽ 3 [6.3 (mg/L) min]/[198 (mg/L) min]

⫽ 0.095

Step 5. Similarly, for the clariﬁers

Bafﬂing condition is considered as poor, thus

/T ⫽ 0.3

ERT ⫽ 250 min ⫻ 0.3 ⫽ 75 min

cal

⫽ 0.2 mg/L ⫻ 75 min ⫽ 15 (mg/L) min

HRT 5

150,000 gal

600 gpm

5 250 min

5 30 min

HRT 5

18,000 gal

600 gpm

Public Water Supply 487

log removal ⫽ 3 ⫻ 15/198

⫽ 0.227

Step 6. Determine Giardia removal in the ﬁlters

/T ⫽ 0.5

(Teefy and Singer, 1990. The volume of the ﬁlter

media is subtracted from the volume of ﬁlters with

good-to-superior bafﬂing factors.)

ERT ⫽ 11 min ⫻ 0.5 ⫽ 5.5 min

cal

⫽ 0.1 mg/L ⫻ 5.5 min

⫽ 0.55 (mg/L) min

log removal ⫽ 3 ⫻ 0.55/198

⫽ 0.008

Step 7. Determine Giardia removal in the clearwell

There are two types of disinfectant; therefore, similar calculations should be

performed for each disinfectant.

(a) Free chlorine inactivation.

In practice, the minimum volume available in the clearwell during the

peak demand period is approximately one-half of the working volume

(Illinois EPA, 1992). Thus, one-half of the clearwell volume (240,000 gal)

will be used to calculate the HRT:

HRT ⫽ 240,000 gal/600 gpm

⫽ 400 min

The clearwell is considered a poor bafﬂing condition, because it has no inlet,

interior, or outlet bafﬂing.

/T ⫽ 0.3 (Table 5.6), calculate ERT

ERT ⫽ HRT ⫻ 0.3 ⫽ 400 min ⫻ 0.3

⫽ 120 min

The level of inactivation associated with free chlorine is

cal

⫽ 0.3 mg/L ⫻ 120 min

⫽ 36 (mg/L) min

From Table 5.7, CT

99.9

⫽ 198 (mg/L) min

HRT 5

6600 gal

600 gpm

5 11 min

488 Chapter 5

The log inactivation is

log removal ⫽ 3 ⫻ CT

cal

/CT

99.9

⫽ 3 ⫻ 36/198

⫽ 0.545

(b) Chloramines inactivation

cal

⫽ 1.6 mg/L ⫻ 120 min

⫽ 192 (mg/L) min

For chloramines, at pH ⫽ 8, T ⫽ 5°C, and 3-log inactivation

99.9

⫽ 2200 (mg/L) min (from Table 5.7)

Log inactivation associated with chloramines is

log removal ⫽ 3 ⫻ 192/2200

⫽ 0.262

The log removal at the clearwell is

log removal ⫽ 0.545 ⫹ 0.262

⫽ 0.807

Step 8. Summarize the log Giardia inactivation of each unit in the water

treatment plant

Unit Log inactivation

Rapid mixing 0.0012 (Step 3)

Flocculators 0.095 (Step 4)

Clariﬁers 0.227 (Step 5)

Filters 0.008 (Step 6)

Clearwell 0.807 (Step 7)

Total 1.138

The sum of log removal is equal to 1.138, which is greater than 1. Therefore,

the water system meets the requirements of providing a 3-log inactivation of

Giardia cysts. The viruses inactivation is estimated as follows.

Step 9. Estimate viruses inactivation in the rapid mixer

Using CT

cal

obtained in Step 1

cal

⫽ 0.08 (mg/L) min

Referring to Table 5.9 (T ⫽ 5°C, 4 log),

99.99

⫽ 8 (mg/L) min

Public Water Supply 489

The level of viruses inaction in the rapid mixer is

log removal ⫽ 4 ⫻ CT

cal

/CT

99.99

⫽ 4 ⫻ 0.08/8

⫽ 0.04

Step 10. Estimate viruses inactivation in the ﬁocculators

cal

⫽ 6.3 (mg/L) min (Step 4)

log removal ⫽ 4 ⫻ 6.3/8

⫽ 3.15

Step 11. Estimate viruses inactivation in the clariﬁers

cal

⫽ 15 (mg/L) min (Step 5)

log removal ⫽ 4 ⫻ 15/8

⫽ 7.5

Step 12. Estimate viruses inactivation in the ﬁlters

cal

⫽ 0.55 (mg/L) min (Step 6)

log removal ⫽ 4 ⫻ 0.55/8

⫽ 0.275

Step 13. Estimate viruses inactivation in the clearwell

For free chlorine

cal

⫽ 36 (mg/L) min (Step 6(a))

log removal ⫽ 4 ⫻ 36/8

⫽ 18

For chloramines

cal

⫽ 192 (mg/L) min (Step 6(b))

99.99

⫽ 1988 (mg/L) min (Table 5.9)

log removal ⫽ 4 ⫻ 192/1988

⫽ 0.39

Total log removal ⫽ 18 ⫹ 0.39 ⫽ 18.39

Step 14. Sum of log inactivation for viruses in the plant is

Plant log removal ⫽ sum of Steps 9 to 13

⫽ 0.04 ⫹ 3.15 ⫹ 7.5 ⫹ 0.275 ⫹ 18.39

⫽ 29.35

Note: Total viruses inactivation is well above 1.

The water system meets the viruses inactivation requirement.

490 Chapter 5

In summary, a brief description of regulations in the United States and

determination of CT values are presented. Under the SWTR, all surface

water supplies and groundwater supplies that are under the inﬂuence

of surface water must calculate CT values daily during peak hourly

ﬂow. A minimum of 3-log Giardia lamblia and 4-log virus removal and/or

inactivation performance must be achieved at all times to comply with

the existing SWTR. The CT values are used to evaluate the achievement

of disinfection and to determine compliance with the SWTR. They also

are used to compute the log inactivation of Giardia and viruses during

water treatment and to construct a disinfection proﬁle.

To calculate the CT value, operation data, e.g. disinfectant concen-

tration, water pH, and water temperature, should be measured daily

during the peak hourly ﬂow. Contact time (T

), actual calculated CT

value (CT

cal

), 3-log Giardia inactivation (CT

99.9

from Table 5.7), and/or

4-log virus inactivation (from Table 5.9), CT

cal

/CT

99.9

, and CT

cal

/CT

99.99

should be calculated for the estimated segment log inactivations. The

total plant log inactivation is the sum of all segment log inactivations.

The daily log inactivation values can be used to develop a disinfection

proﬁle for the treatment system.

18.5 Disinfection by-products

Water disinfection and its by-products. Chlorine has been widely used as

a disinfectant in water treatment process to kill or inactivate waterborne

pathogens. Chlorine disinfection of public drinking water had dramati-

cally reduced outbreaks of illness. In 1974, chloroform (trichloromethane)

was discovered as a disinfection by-product (DBP) resulting from the

interaction of chlorine with natural organic matter in water. This ﬁnd-

ing raised a serious dilemma that water chlorination clearly reduced the

risk of infectious diseases and might also result in the formation of poten-

tially harmful DBP with this exposure in drinking water. DBP problem

is currently most concerned by water supply professionals.

Chlorine, chlorine dioxide, chloramines, ozone, and potassium per-

manganate are used in US water treatment plants as a disinfectant.

Table 5.11 lists some of the microorganisms targeted by disinfection

practice and some of more appropriate disinfectants for each microor-

ganism. Based on the types of disinfectants used, the numbers of water

supplies are roughly (keep changing) 22,000 (91.6%), 360 (1.5%), 140

(0.6%), 300 (1.3%), and 1200 (5.0%), respectively. The disinfectants are

often so powerful that they nonselectively react with other substances

in the water. There are actually thousands of DBPs. When natural

waters are disinfected, more than 100 potentially toxic halogenated

compounds can be created (Gray et al., 2001). The compounds of concern

are halogenated methanes, haloacetic acids, and nitrosamines.

Public Water Supply 491

Two classes of DBPs that dominate the identiﬁable organic matter;

trihalomethanes (THMs) and haloacetic acids (haloacetates, HAAs) are

of regulatory interest. THMs are a group of compounds with three halo-

gen atoms. Only chlorinated and brominated ones are routinely found

in potable water. Chloroform (CHCl

) is one of a class of compounds of

THMs. In the United States, since 1974, additional DBPs have been

identiﬁed in potable water and concerns have intensiﬁed about health

risks resulting from exposures to them. Along with chloroform, three

species that are of most concern are bromodichloromethane (CHBrCl

dibromochloromethane (CHBr

Cl), and tribromomethane (bromoform,

CHBr

). The above four species are called trihalomethanes. The sum of

these four species is expressed as total trihalomethanes (TTHMs). THMs

are regulated under the Stage 2 DBP rule (Table 5.11).

HAAs (Table 5.12) are also formed during chlorination of water. Like

THMs, HAAs are also linked with increased incidence of cancer in lab-

oratory animals (Herren-Freund et al., 1987; Xu et al., 1995). Unlike

THMs, HAAs are capable of dissociating in water. HAAs are >99% ion-

ized (deprotonated) to the haloacetate anions under drinking water con-

ditions. However, they are regulated and usually reported in terms of

the parent acids rather than the carboxylate anions (US EPA, 2001).

HAAs account for about 13% of the halogenated organic matter after dis-

infection (Weinberg, 1999).

Bromate is formed from the ozonation of source waters that contain

bromide. In ozonated water supplies, a variety of aldehydes and ketones

abound as well as some carboxylic acids. In addition to these organic

products, inorganic species are also found. These include oxyanions of

halogens, such as chlorite, chlorate, and bromate, which can be formed

by a variety of oxidizing disinfectants. Bromate is of particular interest

since it is suspected of posing one of the highest cancer risks of any DBP

(US EPA, 2001).

492 Chapter 5

TABLE 5.11 Effects of Disinfectants on Waterborne Pathogens

Bacteria, such as Giardia Cryptosporidium

coliform (E. coli), lamblia parvum

Disinfectants Legionella cysts oocysts Viruses

(Health effects) Legionnaire’s

disease, GI,* death GI, death GI, death GI, death

Chlorine X X X

Chlorine dioxide X X X X

Ozone X X X X

Chloramine X

*astroenteric disease

Due to concern about these DBPs for more than 3 decades, some DBPs

have been regulated and/or subjected to monitoring rules aimed to meet

the simultaneous goal of disinfecting water and controlling DBPs. Table

5.13 presents regulated compounds along with their important infor-

mation. It should be noted that only a very small subset of the much

larger list of substances have been identiﬁed as DBPs.

The Stage 2 DBP rule issued in January 2006, had (1) lowered the

TTHMs MCL 0.10 to 0.08 mg/L; (2) established an MCL of 0.06 mg/L

for ﬁve haloacetic acids (HAA5), including, monochloroacetic acid,

dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibro-

moacetic acid; (3) added an MCLG of 0.07 mg/L for (mono)chloroacetic

acid; (4) established an MCL of 0.010 mg/L for bromate; and (5) established

an MCL of 1.0 mg/L for chlorite.

Control of DBPs and pathogens. US EPA’s current drinking water research

program (in-house/contracted) is more sophisticated than it was in the

1980s. For example, when the treatment technology manual was pub-

lished in 1981, it reported primarily on treatment-oriented research.

Twenty-ﬁve years later, the technology research program includes source

water protection, treatment technology, and distribution system studies.

The research also reﬂects a concern over balancing the risks of potential

carcinogenic exposure against the risks from microbial infection.

Techniques for controlling DBPs and waterborne pathogens below have

mostly followed the US EPA (2001) report. The controlling techniques

include source protection, treatment process modiﬁcation (enhanced

coagulation), alternative disinfectants, activated carbon, other granu-

lar ﬁltration, membrane ﬁltration process, control in drinking water

distribution system, etc.

Public Water Supply 493

TABLE 5.12 Haloacetic Acids Found in Potable Water

Haloacetic acids Chemical formula Grouping*

Chloroacetic acid ClCH

COOH HAA5, 6, 9

Dichloroacetic acid Cl

CHCOOH HAA5, 6, 9

Trichloroacetic acid Cl

CCOOH HAA5, 6, 9

Bromoacetic acid BrCH

COOH HAA5, 6, 9

Dibromoacetic acid Br

CHCOOH HAA5, 6, 9

Tribromoacetic acid Br

CCOOH HAA9

Bromochloroacetic acid BrClCHCOOH HAA6, 9

Bromodichloroacetic acid BrCl

CCOOH HAA9

Dibromochloroacetic acid BrClCCOOH HAA9

NOTES: *HAA5 is the sum of the concentrations of mono-, di-, and trichloroacetic acids and

mono- and dibromoacetic acids. HAA5 concentrations (as the sum) are regulated under the

Stage 2 DBP Rule. HAA6 data must be obtained and reported under the Information

Collection Rule (ICR). HAA9 data are encouraged to obtain and report under the ICR, but

not required.

494 Chapter 5

Compound

Total trihalomethanes

(TTHMs)

Chloroform

Bromodichloromethane

Bromoform

Dibromochloromethane

Haloacetic acids (HAA5)

(Mono)chloroacetic acid

Dichloroacetic acid

Trichloroacetic acid

Bromate

Chlorite

Residual disinfectant

Chlorine

Chloramines

Chlorine dioxide

MCLG,

mg/L

0.07

0.06

0.07

0.02

0.8

MRDLG,

mg/L

4.0

0.8

MCL,

mg/L

0.080

LRAA

0.060

LRAA

0.010

1.0

MRDL,

mg/L

0.8

By-products of

Chlorination

and

chloramination

Chlorination

and

chloramination

Chlorination

and

chloramination

Ozonation,

chlorination,

and

chloramination

Chlorination

and

chloramination

Chlorination,

and

chloramination

Chlorination

and

chloramination

Chlorination

and

chloramination

Chlorination

and

chloramination

Ozonation

Chlorine

dioxide

Potential health effect

Cancer and other

effects

Cancer, liver, kidney,

and reproductive

effects

Cancer, liver, kidney,

and reproductive

effects

Cancer, nervous

system, liver, and

kidney effects

Nervous system,

kidney, liver, and

reproductive effects

Cancer and other

effects

Cancer and other

effects

Cancer and other

effects

Possible cancer and

other effects

Cancer

Hemolytic anemia

TABLE 5.13 National Primary Drinking Water Regulations Regulated Levels for DBP

and Residual Disinfectants

NOTE: MCLG ⫽ maximum contaminant level goal, MCL ⫽ maximum contaminant level,

TTHMs ⫽ the sum of the concentrations of chloroform, bromodichloromethane,

dibromochloromethane, and bromoform, LRAA ⫽ a locational running

annual average,

HAA5 ⫽ the sum of the concentrations of mono-, di-, and trichloroacetic acids and

mono- and dibromoacetic acids,

MRDLG ⫽ maximum residual disinfectant level goal, MRDL ⫽ maximum residual

disinfectant level.

SOURCE: US EPS, 2001; www.epa.gov/OGWDW/regs.html, 2007