Water and Wastewater Engineering

Подождите немного. Документ загружается.

18-18 WATER AND WASTEWATER ENGINEERING

Class B:

The requirements in one of the three alternatives below must be met in addition to Class B site restrictions

for the application of biosolids to land.

Alternative 1 Monitoring of indicator organisms: test for fecal coliform density as an indicator

for all pathogens at the time of biosolids use or disposal

Alternative 2 Use of PSRP: biosolids are treated in one of the processes to signifi

cantly

reduce pathogens (PSRP)

Alternative 3 Use of processes equivalent to PSRP: biosolids are treated in a process

equivalent to one of the PSRPs, as determined by the permitting authority

TABLE 18-13 (continued)

Pathogen reduction alternatives

Source: U.S. EPA (1992).

TABLE 18-14

Processes to further reduce pathogens (PFRPs) listed in Appendix B of 40 CFR Part 503

1. Composting

Using either the within-vessel composting method or the static aerated pile composting method, the

temperature of the sewage sludge is maintained at 55C (131F) or higher for 3 days.

Using the windrow composting method, the temperature of the sewage sludge is maintained at

55C

(131F) or higher for 15 days or longer. During the period when the compost is maintained at

55C (131F) or higher, there shall be a minimum of five turnings of the windrow.

2. Heat drying

Sewage sludge is dried by direct or indirect contact with hot gases to reduce the moisture content of the

sewage slu

dge to 10% or lower.

Either the temperature of the sewage sludge particles exceeds 80C (176F) or the wet bulk temperature of

the gas in contact with the sewage sludge as the sewage sludge leaves the dryer exceeds 80C (176F).

3. Heat treatment

Liquid sewage sludge is heated to a temperature of 180C (356F

) or higher for 30 minutes.

4. Thermophilic aerobic digestion

Liquid sewage sludge is agitated with air or oxygen to maintain aerobic conditions and the mean cell

residence time (i.e., the solids retention time) of the sewage sludge is 10 days at 55C (131F) to 60C (140F).

5. Beta ray irradiation

Sewage sludge is irradiated with beta rays fro

m an electron accelerator at dosages of at least 1.0 megarad

at room temperature (ca. 20C [68F]).

6. Gamma ray irradiation

Sewage sludge is irradiated with gamma rays from certain isotopes, such as Cobalt 60 and Cesium 137, at

dosages of at least 1.0 megarad at room temperature (ca. 20C [68F]).

7. Pasteurization

The temperat

ure of the sewage sludge is maintained at 70C (158F) or higher for 30 minutes or longer.

Source: U.S. EPA (1992).

GENERAL WASTEWATER COLLECTION AND TREATMENT DESIGN CONSIDERATIONS 18-19

Sludges meeting the Class A pathogen densities may be land -disposed immediately. Time

restrictions are placed on harvesting crops, grazing of animals, and public access to sites on

which Class B sludge is applied. These are summarized in Table 18-16 .

TABLE 18-15

Processes to significantly reduce pathogens (PSRPs) listed in Appendix B of 40 CFR Part 503

1. Aerobic digestion

Sewage sludge is agitated with air or oxygen to maintain aerobic conditions for a specific mean cell

residence time (i.e., solids retention time) at a specific temperature. Values for the mean cell residence

time and temperature shall be between 40 days at 20C (68F) and 60 days at 15

C (59F).

2. Air drying

Sewage sludge is dried on sand beds or on paved or unpaved basins. The sewage sludge dries for a minimum

of 3 months. During 2 of the 3 months, the ambient average daily temperature is above 0C (32F).

3. Anaerobic digestion

Sewage sludge is treated in the ab

sence of air for a specific mean cell residence time (i.e., solids retention

time) at a specific temperature. Values for the mean cell residence time and temperature shall be between

15 days at 35C (95F) to 55C (131F) and 60 days at 20C (68F).

4. Composting

sing either the within-vessel, static aerated pile, or windrow composting methods, the temperature of the

sewage sludge is raised to 40C (104F) or higher and remains at 40C (104F) or higher for 5 days. For

4 hours during the 5-day period, the temperature in the compost pile exceeds 55C (131F).

5. Lime stabilization

Sufficient lime is added to the sewage sludge to raise the pH of the sewage sludge to 12 after 2 hours

of contact.

Source: U.S. EPA (1992).

Restrictions for the harvesting of crops and turf

1. Food crops with harvested parts that touch the biosolids/soil mixture and are totally above ground shall

not be harvested for 14 months after application of biosolids.

2. Food crops with harvested parts below the land surface where biosolids remains on the land surface

for 4 months or longer prior to inc

orporation into the soil shall not be harvested for 20 months after

biosolids application.

3. Food crops with harvested parts below the land surface where biosolids remains on the land surface for

less than 4 months prior to incorporation shall not be harvested for 38 months after biosolids application.

4. Food crops, feed crops, an

d fiber crops whose edible parts do not touch the surface of the soil shall not

be harvested for 30 d after biosolids application.

5. Turf grown on land where biosolids are applied shall not be harvested for 1 year after application of

the biosolids when the harvested turf is placed on either land with a high potential for public exposure

or a lawn, unless otherwise spec

ified by the permitting authority.

TABLE 18-16

Site restrictions for Class B biosolids

(continued)

18-20 WATER AND WASTEWATER ENGINEERING

Restriction for the grazing of animals

1. Animals shall not be grazed on land for 30 d after application of biosolids to the land.

Restrictions for public contact

1. Access to land with a high potential for public exposure, such as a park or ball field, is restricted for

1 year after biosolids application. Examples of restricted access include posting with no trespassing

signs or fencing.

2. Access to land with a low potential for public exposure (e.g., private farmland) is restricted for

30 d after biosolids application. An example of restricted access is remoteness.

Source: U.S. EPA, 1992.

TABLE 18-16 (continued)

Site restrictions for Class B biosolids

Vector Attraction Reduction

Vectors are insects (or other animals) that transmit disease. The organic nature of sludge often

attracts vectors after the sludge is land-applied. The 503 regulations provide 11 alternatives to

reduce vector attraction. These are described in Table 18-17 .

18-5 PLANT SIZING AND LAYOUT

Once the preliminary selection of the wastewater treatment unit operations and processes has

been made (the screening process discussed in Chapter 1), rough calculations are mad e to

determine sizes to be used in examining feasibility of site locations and cost. The elements to be

con

sidered in plant sizing include: (1) number and size of process units and (2) number and size

of ancillary structures. The layout should include: (1) provision for expansion, (2) connection to

the transportation net, (3) connection to the wastewater collection system, (4) effluent discharge

location, and (5) residuals handling system.

Number and Size of Process Units

To ensure the provision of wastewater treatment, in general, a minimum of two units is provided

for redundancy. When only two units are provided, each shall be c apable of meeting the plant

design capacity. There are actually two design capacities. The first is the design process flow

capacity that is use

d to design processes such as ac tivated sludge. The second is the hydraulic

flow capacity that is used to size pumping facilities and physical facilities such as bar racks and

screens. The EPA’s design guidanc

e is summarized in Table 1-4 in Chapter 1. Consideration

should also be given to the efficiency/effectiveness of the process units with the low flows at

start-up of the facility and other low flow periods. Nighttime flows and loss of a major contribu-

tor because of relocation or failure of a business are other examples of low flow conditions that

frequently occur.

Number and Size of Ancillary Units

The ancillary units include: administration building, laboratory space, storage tanks, mechanical

building for pumping facilities, roads, and parking. The size of these facilities is a function of the

18-21

Requirement What is required?Most appropriate for:

Option 1

503.33(b)(1)

At least 38% reduction in volatile solids

during sewage sludge treatment

Sewage sludge processed by:

• Anaerobic biological treatment

• Aerobic biological treatment

• Chemical oxidation

Option 2

503.33(b)(2)

Less than 17% additional volatile solids

loss

during bench-scale anaerobic batch

digestion of the sewage sludge for

40 additional days at 30C to 37C

(86F to 99F)

Only for anaerobically digested sewage sludge

that cannot meet the requirements of Option 1

Option 3

503.33(b)(3)

Less than 15% additional volatile solids

redu

ction during bench-scale aerobic

batch digestion for 30 additional days

at 20C (68F)

Only for aerobically digested sewage sludge with

2% or less solids that cannot meet the requirements

of Option 1—e.g., sewage sludges treated

in extended aeration plants

Option 4

503.33(b)(4)

SOUR at 20C (68F) is

1.5mg oxygen/

hr/g total sewage sludge solids

Sewage sludges from aerobic processes (should

not be used for composted sludges)

Option 5

503.33(b)(5)

Aerobic treatment of the sewage sludge for

at least 14 days at over 40C (104F) with

an average temperat

ure of over

45C (113F)

Composted sewage sludge (Options 3 and 4 are likely

to be easier to meet for sludges from other aerobic

processes)

Option 6

503.33(b)(6)

Addition of sufficient alkali to raise the pH

to at least 12 at 25C (77F) and maintain

a pH  12 for 2 hours and a pH  11.5

for 22 more hour

Alkali-treated sewage sludge (alkalies include lime,

fly ash, kiln dust, and wood ash)

Option 7

503.33(b)(7)

Percent solids  75% prior to mixing with

other materials

Sewage sludges treated by an aerobic or anaerobic

process (i.e., sewage sludges that do not contain

unstabilized

solids generated in primary wastewater

treatment)

Option 8

503.33(b)(8)

Percent solids  90% prior to mixing with

other materials

Sewage sludges that contain unstabilized solids

generated in primary wastewater treatment

(e.g., any heat-dried sewage sludges)

Option 9

503.33(b)(9)

Sewage sludge i

s injected into soil so that

no significant amount of sewage sludge

is present on the land surface 1 hour after

injection, except Class A sewage sludge,

which must be injected within 8 hours

after the pathogen reduction process.

Sewage sludge applied to the land or placed on

a surface dis

posal site. Domestic septage applied

to agricultural land, a forest, or a reclamation

site, or placed on a surface disposal site

Option 10

503.33(b)(10)

Sewage sludge is incorporated into the soil

within 6 hours after application to land

or placement on a surface disposal site,

except Class A sewage sludge, which

must be applied to or placed on the land

surface within 8 hours after the pathogen

reduction process.

Sewage sludge applied to the land or placed on

a surface disposal site. Domestic septage applied

to agricultural land, a forest, or a reclamation site,

or placed on a surface disposal site

Option 11

503.33(b)(11)

Sewage sludge placed on a surface disposal

site must be covered with soil or other

material at the end of each operating day.

Sewage sludge or domestic septage placed on a surface

disposal site

TABLE 18-17

Summary of requirements for vector attraction reduction under Part 503

Source: U.S. EPA, 1992.

18-22 WATER AND WASTEWATER ENGINEERING

size of the plant. In small- to medium-sized facilities, particularly in cold climates and when land

is expensive, administration, laboratory, pumping and storage are housed in one building.

The storage tanks include those for chemicals and, in some instances, fuel. Space for storage

of chemical residuals must also be provided.

Plant Layout

When space is not a constraint, a linear layout generally allows the maximum flexibility for

expansion. Redundancy is enhanced if the units are interconnected in such a way that the flow

through the plant can be diverted from one treatment train to another. Because chemicals must be

delivered to the plant, conne

ction to the transportation net becomes an integral part of the layout.

Likewise, because residuals are generally transported offsite, the residuals handling system is an

integral part of the plant layout. The plant layout should minimize in-plant pumping.

18-6 PLANT LOCATION

I deally a site comparison study will be performed after alternatives have been screened and rough

sizing of the processes is complete. Many factors may preclude the ideal situation. For example,

in highly urbanized areas the availability of land may preclude all but one site. In so

me cases the

availability of land may force the selection of processes that fit into the available space.

Given that more than one site is available, there are several major issues to be considered.

As noted in Chapter 1, cost is a major element in the selection process. The site should allow

for expansion. The location of the plant relative to the receiving water for dispo

sal of the treated

wastewater, the service area, and the transportation net should be weighed carefully. The physi-

cal characteristics of the site alternatives that must be evaluated inclu de the potential for flood-

ing, foundation stability, groundwater intrusion, and the difficulty in preparing the site. Because

the hydraulics of the colle

ction system is primarily governed by the ground slope, the treatment

facility is often placed at the lowest possible elevation. The soils and groundwater table at these

sites should be examined carefully for foundation stability. Other issues to be considered include

wetland

infringement, the availability of alternate, independent sources of power, waste disposal

options, public acceptance (particular attention must be paid to odor control), and security.

Visit the text website at www.mhprofessional.com/wwe for supplementary materials

and a gallery of photos.

18-7 CHAPTER REVIEW

When you have completed studying this chapter, you should be able to do the following without

the aid of your textbook or notes:

1 . Explain why wastewater flow estimates for the components of wastewater flow should

be made separately.

2. Explain the difference between infiltration and inflow to a citizen’s group.

3. Explain why infiltration rates for new sewers are expected to be lower than for old

existing sewers.

GENERAL WASTEWATER COLLECTION AND TREATMENT DESIGN CONSIDERATIONS 18-23

4. Compare the physical characteristics of fresh sewage and septic sewage.

5. Distinguish between conventional and nonconventional pollutants.

6. State the BOD

, suspended solids, and fecal coliform concentrations that are often cited

as a definition of secondary treatment.

7. Explain why industries are required to pretreat wastewater before discharging to

municipal sewers.

8. Discuss a design strategy to address the issue of low flow at the s

tart-up of a new

wastewater treatment plant.

9. Discuss the conflicting desirability of locating the wastewater treatment plant at a low

elevation and the potential soil and groundwater problems in construction at such a site.

W ith the aid of this text, you should be able to do the following:

10. Estimate the wastewater flow from commercial, institutional, and recreational facilities

based on

characteristic units such as occupancy, seats, guests, beds, and so on.

11. Estimate the wastewater flow reduction that may be obtained by requiring the use of

water saving devices.

12. Estimate the average daily, maximum day, peak hour, and

minimum flow for domestic

wastewater production.

13. Estimate the infiltration flow rate for a given area with old or new sewers.

14. Estimate the infiltration flow rate for a given length of pipe.

15. Using topographic maps, select likely locations for a wastewater treatment plant.

18-8 PROBLEMS

18-1. Estimate the average and peak hour wastewater flow rate for Camp Swampy. State

all assumptions. The facility composition is shown below.

a . Camp with central toilet and bath facilities—350 campers

b. Staff cottages with private bath, two people per cottage—40 staff members

c. Dining hall serves three meals per day to campers and s

taff

18-2. A proposal to build Hotel California is being evaluated to estimate wastewater flow

rates. Two proposals are being considered. Estimate the average and peak hour

wastewater flow rate for each proposal. State all assumptions. The owner has asked

two questions:

(1) What is the impact on wastewater flow rate of having a bar with the restaurant?

(2) With respect to wastewater flow, are there an

y economies of scale?

The proposals are outlined in the table below. Assume an average occupancy of 80%, 1.5

people per room, and a maximum occupancy of 100%, 2 people per room.

18-24 WATER AND WASTEWATER ENGINEERING

Unit Proposal A Proposal B

Guest rooms 120 240

Number of employees 12 17

Self-service laundry machines 24

Restaurant, no bar, seats 80 120

Restaurant, with bar, seats 100 160

18-3. Repeat Problem 18-1 assuming the following water saving features are introduced:

a . Low-flush toilets that reduce flow from 73 to 35 L/capita · d.

b. Limiting flow shower head that reduces flow from 50 to 42 L/capita · d.

c. Energy-saver dishwasher that saves 10 L/meal.

18-4. Repeat Problem 18-2 assuming the following water saving features are intro

duced:

a . Low-flush toilets that reduce flow from 73 to 35 L/capita · d.

b. Limiting flow shower head that reduces flow from 50 to 42 L/capita · d.

18-5. Analyze Xenia’s wastewater flow rate data to estimate the following: average daily

flow rate, estimated maximum day, estimated peak hour, minimum

day, and dry

weather flow. Assume the dry season occurs from the beginning of May to the end of

September. (Data from Metcalf & Eddy, 2003.)

Xenia’s flow data, m

Year 2006 2007

Population 8,690 9,400

Month

January 8,800 13,900

February 6,200 9,900

March 6,800 8,100

April 4,000 4,200

May 4,000 5,700

June 3,600 3,600

July 2,400 2,600

August 2,000 1,500

September 2,800 2,000

October 3,200 4,800

November 4,800 3,200

December 5,200 6,700

18-6. Analyze Eau Gaullie’s wastewater flow rate data to estimate the following: average

daily flow rate, estimated maximum day, estimated peak hour, minimum day, and

GENERAL WASTEWATER COLLECTION AND TREATMENT DESIGN CONSIDERATIONS 18-25

dry weather flow. Assume the dry season occurs from the beginning of May to the

end of September. (Data from Metcalf & Eddy, 2003.)

Eau Gaullie’s flow data, m

Year 2008 2009

Population 11,030 12,280

Month

January 8,300 10,000

February 11,800 18,400

March 9,400 13,000

April 6,500 5,000

May5,300 7,600

June 4,800 4,600

July 3,300 3,800

August 3,800 3,100

September 2,800 2,200

October 4,400 4,400

November 6,000 6,500

December 7,300 8,600

18-7. Use Figure 2-1 to estimate the peak hour flow rate for the data from Problem 18-5 .

18-8. Use Figure 2-1 to estimate the peak hour flow rate for the data from Problem 18-6 .

18-9. The town of Aulwaze has asked your firm to begin preliminary planning for a new

wastewater treatment plant. Based on current records, the following data have been

provided to you. The population density ha

s been and is expected to continue to be

16 people/ha. For the purpose of infiltration estimates, the sewer system after 1978

is considered to be new. Estimate the average daily and peak flow rates at the begin-

ning of the design life in 2011 and at the design life of 15 years after start-up. Use

a spreadsheet program you have written to graph the data, fit trend lines, and d

erive

curve fitting equations for population and for wastewater flow.

Village of Aulwaze population estimates and wastewater flow rates

Year 1978 1999 2009

Population 10,400 14,600 16,800

Wastewater flow rate, Lpcd 401 464 494

18-10. The Village of Royalflush has asked your firm to begin preliminary planning for a

new wastewater treatment plant. Based on current records, the following data have

been provided to you. The population density has been and is expected to continue

to be 16 people/ha. For the purpose of infiltration estimates, the sewer system after

18-26 WATER AND WASTEWATER ENGINEERING

1980 is considered to be new. Estimate the average daily and peak flow rates at the

beginning of the design life in 2011 and at build out in 2030. The build-out popula-

tion is estimated to be about 1,700. Use a spreadsheet program you have written to

graph the data, fit trend lines, and derive curve fitting equations for population and

for wastewater flow.

Village of Royalflush population estimates and wastewater flow rates

Year 1973 1980 1990 2000 2009

Population 1,400 1,380 1,420 1,510 1,630

Wastewater flow

rate, Lpcd

380 385 475580 680

18-11. On a copy of the map for LaNeige Fondue and vicinity, identify potential sites for a

new WWTP. The WWTP will treat wastewater from the village, the biofuel plant,

and the retirement center.The 100-year flood elevation is along the 480 m contour.

M - 65

PDQ

485 m

Moselle

River

Mt Blank Rd

480 m

Cre

Two Lake

485 m

Biofuel

Plant

500 m

La Neige

Fondue

Mud Lake Drain

Pine Lake Drain

M.L.D

11 JAN 2008

M - 65

485 m

La Neige Fondue and

Vicinity

Scale :

100 m

Contour interval = 5 m

Bastogne

Center

480 m

Retirement

FIGURE P-18-11

GENERAL WASTEWATER COLLECTION AND TREATMENT DESIGN CONSIDERATIONS 18-27

18-12. On a copy of the map for Waffle and vicinity, identify potential sites for a new

WWTP. The WWTP will treat wastewater from the village and the brewery. The

100-year flood elevation is along the 120 m contour.

136

Brewery

120

112

109

112

120

128

120

104

196

120

Waffle

128

136

120

Scale

200 m

Contour interval = 8 m

Waffle and Vicinity

MLD

1 MAR 2008

p River

eberr

Creek

104

Coffee Creek

FIGURE P-18-12

18-9 DISCUSSION QUESTIONS

18-1. A local service organization has asked you to make a presentation about a city

proposal to address the issue of combined sewer overflow. Prepare one or two

PowerPoint graphics that you will use to show the difference between infiltration

and inflow.

18-2. In the following list of pollutants mark those that are conventional with a “C” and

those that are nonconventional with “NC.”

a . Chromium VI

b. pH

c. TSS

d. Phenol

Oil and grease